NTT Technical Review
January 2014 Vol. 12 No. 1
View from the Top
Yasuyoshi Katayama, Senior Executive Vice President, NTT

Front-line Researchers
Masayuki Abe, Senior Distinguished Researcher,
Research Group Leader, NTT Secure Platform Laboratories

Feature Articles: Software Development Technologies
Software Development Technology Initiatives at
NTT Laboratories
Improving the Planning andRequirements Definition Process
Test Automation Technology to Reduce Development Costs
And Maintain Software Quality
R&D Software Development Standards
and their Operation

Feature Articles: Optical Node and Switch Technologies
for Implementing Flexible and Economical Networks
Optical Node and Switch Technologies for
Flexible and Economical Networks
Next-generation Optical Switch Technologies for
Realizing ROADM with More Flexible Functions
WSS Module Technology for Advanced ROADM
Multicast Switch Technologythat Enhances ROADM Operability

Regular Articles
Statistical Grammar Induction for Natural Language Parsing

Global Standardization Activities
G.epon and Current Status of Related Standardization

Papers Published in Technical Journals andConference Proceedings
Papers Published in Technical Journals andConference Proceedings

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Innovation and Collaboration:
Ride a Big Wave, Create a Big Wave
—Towards the Next Stage in 2014
Yasuyoshi Katayama
Senior Executive Vice President, NTT
Overview

Technical innovation in the world of information and communications
technology has certainly been amazing, especially in cloud computing,big data, and security. Today, the telecommunications industry is looking
for even more technological leaps, and the NTT Group is playing a hublike role in this endeavor. We asked Yasuyoshi Katayama, NTT Senior
Executive Vice President, about the company’s objectives for 2014
“towards the next stage.”
Keywords: innovation, collaboration, telecommunication industry

Towards the next stage:a revolutionary era for all of society—Mr. Katayama, what was last year like for the telecommunications industry?
It’s been no more than a year or so since the NTT
Group announced its Medium-Term Management
Strategy “Towards the Next Stage” in the fall of 2012,
but I can already see that a variety of technical andsocial trends have taken root, which makes me feelthat the move “towards the next stage” has truly
begun.
Beginning with advances in individual technicalfields such as the cloud and big data, information andcommunications technology (ICT) has grown to apoint where it is now beginning to generate new value
overall.
In the field of smart grids, for example, electric
power companies have begun to introduce smart
meters in earnest, and in the field of cloud computing,orders from our customers to have their internal systems moved to our cloud have been accelerating.
Furthermore, in the field of big data, the Internet and
ICT are coming to generate new value by applying
big data in a common-sense manner to the analysis of
Twitter posts, to data analysis in elections, etc.
The use of ICT in a wide variety of fields is coming
under the spotlight even as a matter of national policy—I believe that society on the whole is looking forchange in this direction.
—Amid these changes, what has the NTT Group
achieved and how does it plan to face the challengesof 2014?
Since last year, we have been focusing our attention
on the global cloud business, and one achievement
here is that NTT Group companies that have been
expanding overseas through M&A (merger andacquisition) activities have begun to generate a synergetic effect with each other and enter new markets.
Furthermore, the great potential of the NTT
Innovation Institute, Inc. (NTT I3) established in May
2013 in Silicon Valley is materializing, and concrete
results even in business terms are beginning to take
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shape. The feeling is that NTT I3 has already establisheda strong foundation and that the seeds of new business are beginning to sprout in many areas.
Cloud, big data, and security:
today’s growth fields
We can expect the field of cloud computing to continue growing into the future. At present, we are providing individual companies with means of entrusting their systems to us and making full use of theadvantages of cloud computing through cost controls
and flexible mechanisms tailored to the scale of theirbusinesses. But looking to the future, we see ourcloud as playing the role of an intermediary that connects information between company A and company
B that have so far had no point of contact. In this way,
we think that we can create new services and industries as a new movement in cloud computing.
Our aim is to provide a place where such businessactivities can blossom and to support the businessesof individual customers and the businesses born out
of customer tie-ups. Of course, we are just one player
among many in the field of cloud computing, but webelieve we can help our customers in various industries and fields to manifest their full abilities by providing them with an extensive ICT infrastructure. For
example, we created a group called “Japan Connectedfree Wi-Fi” that interconnects operators that provide
open Wi-Fi at airports, train stations, and other locations. Up to now, the word “connect” in our business
implied the provision of communications such as byconnecting two telephones. As we go forward, I
would like the NTT Group to expand upon this roleby helping companies, businesses, and services toconnect with each other, that is, to collaborate.
Meanwhile, big data technology is making it possible to deal with data that up until recently was notvery manageable. For example, smartphones areequipped with a variety of sensors such as those forhandling GPS data, and the network connection provided by smartphones has made it easy to collect andstore data at low cost. In addition, the detailed analysis of information has become possible thanks togreater computer processing power and advanced
software techniques. As a result, information that had
previously been treated as obscure and out of reach is
now being targeted for creating real value.
This capability is being applied in the field of marketing too. While the answer to the question “Whatdo I need right now?” can be inferred from that person’s purchase history, we might be entering an era inVol. 12 No. 1 Jan. 2014

which big data analysis techniques will be able todetermine what those needs are more accurately thanthe person in question (smiles).
As for network security, this is a major issue ofconcern. In addition to requesting individual customers to change their passwords frequently to prevent
malicious behavior such as spoofing (impersonation),
we still must provide a solid guarantee of safety on
the network above and beyond such safe practices.
From the beginning, it has been difficult to predictsecurity threats, and while threats have traditionallybeen of the mischievous type, they have recently beenmorphing into those associated with crime, terrorism,
and other heinous activities. We must therefore construct systems that can stand up to attackers, but giventhat new technologies are constantly being developed
and promptly incorporated into attacking schemes, itwould be hard to say that any set of security measures
could cover all threats completely. It is said that wehave entered an era in which attacks on users must be
prevented through the collaboration of multiple players since no single operator can deal with all threats
to its users.
With this in mind, my plan is to promote researchand development efforts in security while listening toour customers’ comments and opinions, and in addition to developing world-leading security technologies, I would like to see a higher level of interaction
among our global operations in regards to security.
Furthermore, when talking about security, attention
must be paid to the value of the information in question. For example, a terrorist attack on a country’s
smart grid can halt the supply of power and simply
paralyze the social functions of that country, and an
attack on a hospital’s computer system can corrupt
information related to medical care and put patients’
lives at risk. Research and development (R&D) must

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proceed taking into account the abilities of attackers,
the vulnerabilities of systems, and the value of target
information.
Creating an ICT environment forstress-free sharing by customers—Can you give us some uplifting words as 2014
begins?
We expect 2014 to mark a full-scale recovery of theJapanese economy while being a year of much activity including the launch of preparations for the big
event in 2020.
At NTT too, we see 2014 as being an auspicious
year. We aim to provide new technologies and tocreate an environment in which customers can accessthe information they need in a stress-free manner andjointly experience a deeper level of feelings and emotion through ICT.
Let me give an example in relation to high-definition television (TV), which is a technology familiar to
all of us. At the current level of resolution, the true
worth of high-definition TV comes out in scenes
involving movement, as in a program broadcasting asports event. But at 4K or 8K levels of ultrahigh definition, such scenes invoke feelings or emotions completely new to us. In fact, even in a program having

little movement, as in the broadcast of a Japanesechess match (shogi), ultrahigh-definition images canconvey even the tension felt by the players. Similarly,
in videoconferencing, it has not been possible up to
now to observe fine points in the other party’s facial
expressions such as detailed eye movements, butultrahigh-definition technology makes that possible.
When the era of ultrahigh-definition video truly
arrives, telecommunication operators will be obliged
to support the transmission of such video over the
network. According to forecasts made by IDC, themarket research company, the global amount of information will increase by more than 30 times the present level by 2020. How will we deal with this explosive growth in traffic? This is not simply a matter ofincreasing and enhancing our telecommunication
facilities.
Up to now, we have been able to handle increases in
the amount of network traffic as content expandedfrom email to images and video by developing technology from a hardware perspective. Our problem
here was how to increase the capacity of a single optical fiber to carry more information. Going forward,
however, we must work to enhance network capabilities from both hardware and software points of view.
We must implement without delay such mechanisms
as efficient data transmission using the HEVC (High
Efficiency Video Coding) format and proactive, predictive type of network control using SDN (Software
Defined Networking), which enables flexible control
by converting network processes to software. This iswhat I believe is our mission in 2014.
It has been said that locations such as Singaporeand Hong Kong have served as Asian hubs, but I canenvision Japan becoming a world hub using advanced
ICT such as the 4K/8K ultrahigh-definition technology that I just mentioned. It has also been said thatJapan is a country at the frontier of emerging social
issues, and in this sense, I would like to see Japansolve its agricultural and medical-care problems
through ICT originating in Japan and thereby fulfill
its role as a member of the global community. I truly
believe that ICT has the power to solve such keysocial problems that affect many developed nations.
Taking the lead with a sense of balance andan acceptance of collaboration—What are your hopes for R&D?
The network control and security measures that I
just talked about are the conditions that must be met

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for ICT to be an enabler, to perform its functions correctly. Though we take great pride in being one of the
top companies in the telecommunications industry
even on a global basis, getting these technologies to alevel where they can actually be used to provide services to our customers will require that we first
implement the results of R&D in our business operations and create a rock-solid network.
In this regard, we are not yet at the point where weare confident enough to introduce, for example, thisadvanced network control technology on a global
level, so I don’t think that we have to be alone at thehead of the pack as long as we maintain our standing
as a top-level player.
NTT personnel involved in R&D have neverworked with a catch-up frame of mind. They havealways set their goals high with the aim of developingworld-leading technologies. For this reason, I would
like to see our researchers feel their way forward andundertake their work with a firm sense of direction. I
want them to make NTT a global driver of technology.
Even if we were to be “running in the lead,” wecould never do everything on our own. For example,
when requesting a vendor to manufacture certain
equipment, costs could escalate and create havoc if
we did not procure that equipment under the condition that many other parties must be able to use it andnot just ourselves. To prevent such havoc, I think thatit’s very important that we disseminate our R&D
results widely and provide equipment and technologies that everyone can use while collaborating withother operators in the world. On the other hand, I
would like NTT to be number one in the advanced
research of translation technology. However, it won’t
work to adopt a self-centered attitude here. In the end,
it all comes down to having a sense of balance in our
R&D endeavors.
The Japanese economy is now regaining its healthand spirit. With the big event in 2020 as a target, I feelthat a big wave is coming, in which Japan’s presencein the world will reach new heights through the powerof ICT.
Accordingly, to help invigorate society even more,
I ask our researchers to work with the aim of riding
this wave, and if possible, to even create a wave of
their own.
By all means, let’s use ICT to create a movement ina positive direction. Let’s bring about change—wecan’t just stay still.

Vol. 12 No. 1 Jan. 2014

“My best work is my next movie!”—Charlie Chaplin—Mr. Katayama, can you say a few things to everyone in the NTT Group?
Of course. It’s not just a matter of providing services on our own. There are a variety of players in theindustry, and we must find out what they are doing
and what they are thinking, and we must pursue tieups with them.
Charlie Chaplin famously said “My best work is
my next movie!” It’s important that we think about
what we will do next. Let’s take up the challenge of
doing something new. Instead of going deeper intothings that we already know about, let’s undertakenew things going forward.
To grow as a group that is recognized by society for
its innovation, collaboration is essential. For example,
NTT and Dwango formed a business alliance in July
2013. I would also like to promote collaboration withpeople in genres new to the NTT Group to stimulate
ideas and create new value.
Customer needs play a big role here, and there aremany things that can be created to satisfy those needs.
Since we don’t know in advance what value can befound where, we should attach great importance tointeracting with people in fields that are new to us.

View from the Top

Interviewee profile
Career highlights
Yasuyoshi Katayama joined Nippon Telegraphand Telephone Public Corporation (now NTT) in
1976. He became Senior Vice President andExecutive Manager of the Fundamental Services
Department and Executive Manager of the Plant
Planning Department of NTT WEST in 2004,
Senior Vice President and General Manager of
Networks of NTT WEST in 2006, and NTT
Senior Vice President and Director of theTechnology Planning Department in 2008. After
serving as NTT Director and Executive Vice
President and as Director of NTT’s Technology
Planning Department from 2009, he took up his
present position in June 2012.

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NTT Technical Review

Front-line Researchers

Taking on Pioneering Research witha Worldview as a Specialist
in Cryptographic Theory
Masayuki Abe
Senior Distinguished Researcher,
Research Group Leader, NTT Secure Platform Laboratories
Masayuki Abe, an NTT Senior Distinguished Researcher, hasbeen researching cryptography for over 20 years. He has played
an important role in this special field even at an international level
having written a number of papers on cryptographic theory andhaving served as executive committee chairman and programcommittee member for various international conferences. The
origin of this active life is no doubt the personal relationships that
he formed during his stays at prominent research laboratories in
Switzerland and the United States. We last spoke with him in2006. We sat down with him again recently to find out more about
his research career and current issues, and we asked him to leavea message for young researchers.
Keywords: cryptographic theory, digital signature, structure-preserving

Engaged in overseas research activities
while pursuing electronic money protocol
and other projects—Dr. Abe, please tell us about the path your research
has taken to date.
Well, during my university years, I studied subjects
such as radar-screen image processing and speakerrecognition, which, needless to say, are unrelated to
my current research. Then, in 1992, I began working
at NTT Network Information Systems Laboratories
in Yokosuka, and it was there that I first took up
research in cryptography. That research group was
researching both symmetric-key cryptography andpublic-key cryptography, but I became involved in
the latter, and after being taught the basic concepts ofpublic-key cryptography by NTT Fellow Tatsuaki
Okamoto, who, by the way, received Japan’s Medalwith Purple Ribbon in 2012, I became firmly
entrenched in this research field.
For the first two years, I was engaged in the designand development of cipher-and-authentication LSIs
(large-scale integrated circuits) in cooperation withNTT Communication Science Laboratories. I next
took up the research of cryptographic protocols, andthinking that such a protocol should not only be used
to conceal a cipher but also to create something interesting, I undertook the development of electronicmoney. As a form of digital information, electronic
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Front-line Researchers

money can be easily copied, and preventing its duplicate use is a major issue. In 1995 and 1996, I was incharge of protocol design for electronic money aswell as its software implementation. Then, afteralmost completing my work on the electronic money
protocol, I was given the opportunity to study abroadat the Swiss Federal Institute of Technology (ETH
Zurich) as a guest researcher in 1996.
Upon returning to Japan in 1997, I entered the cryptographic theory research group and continued mywork on multi-party theory that I had first taken up in
Switzerland. It was during this time that I first produced results that were good enough to be acceptedby a highly competitive international conference. The
words “Do your work with the world in mind” spoken
by my group leader soon after entering NTT kept running through my head, and I realized that I wanted tosubmit work that would be well received by the world
at large. From then on, one of my objectives was tosubmit results worthy of presenting at a leading international conference. Although the risk is great indoing so, a successful paper can generate considerable response, and I have been fortunate in receiving
good feedback over the years. I am still following thisresearch style, but I sometimes feel that I’ve been
neglecting involvement with the local research community in Japan.
Next, I became interested in cryptography components in applications such as electronic voting andbecame involved in the research of advanced digital
signatures and advanced ciphers. It was during thistime that I became a Distinguished Researcher, a title
bestowed by the NTT Distinguished Researcher system. Then, in 2004, I travelled to North America with
the idea of enriching my knowledge and working inan environment in which I could concentrate on asingle research problem. I spent a year and eightmonths doing research at the IBM Watson ResearchCenter, a major hub of cryptography research. I continued researching a variety of cryptography components after returning to Japan, and in recent years, I
have been researching topics within a single field thatI developed called structure-preserving cryptographic
systems.

a wonderful teacher had a big influence on my later
research activities, but so did the interaction andexchanges I had with the students around me. The
people in that research group are today very active inthe front lines of cryptography research. I was able to
make invaluable friendships with many of them, suchas Ronald Cramer of the Netherlands, a very wellknown researcher in this field.
For my second overseas research trip, I thought thatsince I had already studied at a European university,
it would be advantageous to spend time at a company
in North America. Therefore, I chose the IBM Watson
Research Center, which had a formidable cryptography research team. Here as well, the connections I
was able to make with the people around me were ofgreat benefit. I was able to live in direct contact witha number of prominent researchers, and from them I
learned how to approach my research with a sense ofurgency and also how to cope with problems. These
researchers at the front line of cryptography wereindeed larger-than-life people overflowing withenergy. They were capable of tackling problems byharnessing their knowledge and applying various
techniques in a short period of time. I came away with
the impression that research is a very physical activity. The connections I made there had a beneficial
effect in various ways on my later activities.
Since 2001, I have served as program committee
member and chairman of many international conferences. The program committee is a forum where
members discuss which papers submitted to the conference are to be included in the proceedings. Since
space is limited, there are times when even good
papers cannot be included, and disputes in this regard
occur not infrequently. This committee is an important gathering where one can listen to the true feelingsof other committee members on a variety of research
results. However, unless you are well connected, youare almost never invited in, and it was even difficult
for me when serving as conference chairman to get aseat. On the other hand, once you do get into a program committee, your connections widen, and I havebeen called upon to give invited lectures and participate in other activities as a result.

—What did you bring back from your two overseas
experiences?

Answering the question “What is safe?” toformulate a fundamental theory of cryptography

At ETH Zurich, my supervisor was Ueli Maurer, ayoung, up-and-coming professor at the time but a top
authority in the field of cryptography today. He was avery exacting mentor. Of course, learning a lot from

—Can you tell us about your current research?

Vol. 12 No. 1 Jan. 2014

My research concerns basic cryptographic theory,
and while this may be a bit difficult to understand, myFront-line Researchers

Public key for signature verification
Documents chosen by adversary
A

B

New

C

SignerAdversary
N
A

B

C
Correct signature for new
document not previously signed

Correct signatures for each document

A signer attaches correct signatures to documents arbitrarily chosen by an adversary who
has obtained a public key; the adversary is unable to create a correct signature for any
other document.

Fig. 1. Existential unforgeability against adaptive chosen message attacks.

aim is to create a foundation for safety in the provision of various types of products and services.
For example, I think about the question “What issafe?” in my research. This is what I would call cryptographic theory—defining the concept of safety
from a theoretical and mathematical perspective.
Let’s imagine that person A sends the message“Tomorrow’s plans are cancelled.” to person B in
encrypted form. Now, if an eavesdropper happens toview that ciphertext but cannot restore it to the original message, I wonder whether or not we can call thatencryption safe. If a high degree of safety is desired,
it is essential that no part of that message, such as“tomorrow’s plans” or “are cancelled,” be leaked.
Partial information of this type such as what kind ofplans were made for tomorrow or what has been cancelled could be very valuable to an eavesdropper. It isalso necessary to deal with even more aggressive
attacks such as those that send out ciphertexts thatgenerate decryption errors and then analyze the typeof error message returned to get hold of internal information.
This view of “safety” also holds true for digital
signatures, one of my research themes. For example,
if someone would like to forge an IOU with a digital
signature saying “Mr. Abe borrowed 1 million yen”
but there’s nothing to forge such a document from,then can we say that we have a “safe” system? Moreover, if an IOU with a signature stating “Mr. Abeborrowed 100,000 yen” were to exist beforehand, andif “100,000 yen” could be rewritten as “1 million
yen,” we would certainly have a problem. In short, ifan adversary can get hold of signatures for arbitrarily
chosen messages but cannot create a signature for any
other message, we can call this situation “safe”. Thiskind of safety is referred to as “existential unforgeability against adaptive chosen message attacks,”
which, with the exception of physical attacks, is considered to be a standard of safety that must be satisfied by a digital signature system (Fig. 1). There arealso schemes such as blind signatures and group signatures with more advanced functions, but the usage
scenario differs for each, and as the usage environment becomes more complicated as the functions
become more advanced, it becomes increasingly difficult to accurately express what is “safe” about eachsystem.
You cannot expect to construct a safe system without clearly defining what “safe” is, and without sufficiently investigating whether that is truly a valid
definition. The result of creating such a theoreticalfoundation is not something that is quickly manifested, but I believe that such foundations contributeto the safety of systems and methods used in society.
—Can you tell us about any specific achievements?
Well, I have published theoretical results as journal
papers, but I have also developed various encryption
schemes on top of those theoretical foundations. One
example is the ECAO (Elliptic Curve Abe-Okamoto)signature, which is a message-recovery type of digital
signature scheme in which existential unforgeability
comes down to the discrete logarithm problem on an
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Front-line Researchers

elliptic curve. This scheme has been adopted by ISO(International Organization for Standardization).
To give a more concrete example, I independently
developed a mix-net anonymous communication
scheme. This scheme can be used as the core component of an electronic voting system and has alreadybeen introduced to regional voting systems in Japan(Fig. 2). In this regard, anonymous communication
software called Tor has recently appeared as one
example of a mix-net application. Tor is a system that
protects the privacy of users by preventing their communication paths from being traced. It can be used forwhistle-blowing purposes, for example, and its use in
the Arab Spring pro-democracy movement in the
Middle East was recently in the news. Technology of
the Tor kind has both a good and bad side to it, andwhile it was not a product of my own, this use of
research results specifically for such activities
reminded me of how socially significant my research
field is, as a researcher pursuing safety in terms ofprivacy.

AC

MIX servers

T

Z

Partial decryption by each server
in a random order

Inputs a sequence ofencrypted plaintexts

Outputs plaintexts
in random order

Encrypted plaintexts from multiple users are received by aset of servers in a multiplex manner. Each server performs
some decryption before passing on results to the nextserver in a random order. A random sequence of plaintexts
is eventually output, and anonymity is protected since
which user input which plaintext is unknown.

Fig. 2. Achieving transmission anonymity by mix-net.

Structure-preserving signatures that efficiently
combine cryptographic components
successfully developed in 2010!
—Can you tell us something about structure-preserving cryptographic systems that you are now working
on?
There was a time when fears were growing about
Vol. 12 No. 1 Jan. 2014privacy infringements by companies. In 1999, there
was talk that the Pentium III was equipped with a
CPU (central processing unit) serial-number notification function, and that mounting that chip on a personal computer would enable that user to be identified and all user activity, for example, websites visited, to be determined. Then, in 2003, Benetton, theclothing retailer, decided to tag its products withsmall radio frequency identification (RFID) radio
chips to improve product management. This kind of
product/customer management raises fears that, inthe extreme case, such chips could be scanned atsome location to determine who is wearing what itemand other types of personal information. Such corporate actions have given rise to boycotts and otherforms of protest. Walmart in partnership with Gillettealso conducted an RFID-based tag-management
experiment and likewise created an uproar among
consumers.
As a result of these experiences, the idea that
“ignoring customer privacy issues is wrong” began topermeate corporate consciousness. For example, acryptographic protocol was proposed that would prevent any serial number incorporated in a chip frombeing disseminated to the outside world and thatwould only make it possible to verify whether “agenuine chip is mounted.” This protocol is currently
in the process of being standardized. In other words,
the need was felt for a technology that could indicatethat something holds true while hiding other details.
My research objective is to construct an efficient
cryptographic protocol that can prove the correctnessof something while preserving privacy in this manner.
As part of this effort, I have been working on the
micro-problem of how to combine cryptographic
components to achieve “safety.” First, in 2008, I
attempted to achieve an advanced type of digital signature called a “blind signature” that would combine
a digital signature with a tool for convincing anotherparty of something, which is called a non-interactive
zero-knowledge proof. However, the interfaces ofthese two components were completely different,
which created a problem. Specifically, an efficient
digital signature has a mathematical structure
expressed by group elements, while a non-interactive
zero-knowledge proof accepts input expressed by alogic circuit to maintain maximum versatility. I therefore saw the need for middleware that could make theinput and output of these two components compatible. Theoretically speaking, middleware could combine these components well, but it could also be asource of program bugs while delaying development
Front-line Researchers

work. With this in mind, I arrived at the idea of creating cryptographic components having compatible
input/output to maintain a “group structure.”
At first, I ran into problems, as I was not able tocreate a digital signature having structure-preserving
characteristics. One aspect of cryptography is guaranteeing safety by outputting input information in aform different from its original form in such a waythat the original form cannot be restored. As a result,it was very difficult to satisfy the constraint that the
input and output have the same form while alsoachieving safety. Nevertheless, by applying a trialand-error process and building up empirical rules
much like solving a puzzle, I at long last made thefirst step in achieving a structure-preserving scheme
in 2010 (Fig. 3).

Signature verification (A, B, Gz, Gr, Hz, Hu, Gi, Hi) ∈keys
Documents to be Mi ∈signed

n

2
T ×

2n+4

(i = 1, …, n)(i = 1, …, n)Signatures (Z, R, S, T, U, V, W ) ∈7

Signature verification A = e (Gz, Z ) e (Gr, R) e (S, T )e (Gi, Mi)
equations
B = e (Hz, Z ) e (Hu, U ) e (V, W )e (Hi, Mi)
By treating public keys, documents, and signatures asgroup elements on an elliptic curve, only group operations
and pairing operations need to be performed to verify
signature correctness. These characteristics make for
efficient non-interactive zero-knowledge proofs.

Fig. 3. Structure-preserving signature scheme.

—What are your future ambitions?
When new worldviews or methodologies are proposed, many problems arise that need solving. There
are also many things that cannot be accomplished bysuch methodologies that need to be pursued. At present, I am working on various new problems that seemto be arising one after another in that way. I often findmyself thinking, “I want to enhance this paradigm,”
and that generally takes two to three years. Additionally, I would like to continue my research in efficiently creating cryptographic protocols that canprotect privacy.

Playing with his children and listening to jazz
piano as his great pleasures—What do you do for rest and relaxation?
When I am engrossed in my work, I cannot get the
research out of my head. However, once my concentration is broken, it’s difficult to return to a zone ofdeep thinking. Thus, during times of concentration, it
would be a shame to stop while commuting. For me,
thinking is not a stressful activity. Stress for me is notgetting a good reception for a paper that I have written to convey a scheme’s benefits and safety. At mostmajor international conferences related to cryptography, the paper selection rate is about 20%. I myself
have lost out two times. I get especially stressed when
my paper is not understood even after submitting it
repeatedly. Of course, I am very pleased when a paperof mine is accepted, and I’m in a great mood for awhile after that. For twenty years, I have advocatedthe approach of working with the world in mind, andwhile I have experienced some very trying times, I
have colleagues that have persevered through toughtimes in the same way.
My greatest pleasure is taking my children to a poolin a neighborhood park and spending time with themon weekends. Since I will not be able to do this once
they get older, I want to play with them as much as
possible at this time.
In addition, during my stay in the United States, I
wanted to do something that I could not do in Japan,
so I bought a vacuum-tube audio system at an auction
and listened to jazz piano to my heart’s content in myroom. Later, I found that I could not do without thisaudio system even on returning to Japan and mysmall apartment, and now I often listen to music
using headphones. I especially like the pianist Marian
McPartland.
Don’t shut yourself off from the outside world—
current technology may last only 10 years but
personal relationships can last a lifetime—Dr. Abe, please leave us with a message for young
researchers.
When I look at young researchers, there is much to
be admired and to be amazed at—they are truly
industrious and serious about their work.
So I can’t say that I have any advice in particular,
but based on personal experience, I would like topoint out that new technology comes around about
NTT Technical Review

Front-line Researchers

every five years and that a certain type of technology
may last for only five to ten years before becoming
obsolete. That is a natural cycle. Personal relationships, however, can be maintained for 20 years andlonger, and the benefits they provide can change withthe passage of time. I would therefore encourage
young researchers to create opportunities for themselves to talk with all kinds of people all the time. In
other words, do not close yourself off in your researchlaboratory and limit your relationships to the same setof colleagues. If you talk about your ideas to ten
people, some of them may become quite captivatedabout your work, which will more than make up foryour efforts. And if you get an opportunity to doresearch overseas, by all means take it!

Interviewee profile
Career highlights
Masayuki Abe received the B.E. and M.E.
degrees in electrical engineering from the Science
University of Tokyo and the Ph.D. degree fromthe University of Tokyo in 1990, 1992, and 2002,
respectively. He joined NTT Network Information
Systems Laboratories in 1992 and engaged in thedevelopment of fast algorithms for cryptographic
functions and their software/hardware implementation and the development of a software cryptographic library. From 1996 to 1997 he was a guest
researcher at ETH Zurich, where he studied cryptography, especially multi-party computation,
supervised by Professor Ueli Maurer. From 1997
to 2004 he was in NTT Information Sharing
Platform Laboratories (now NTT Secure Platform
Laboratories), where he worked on the design
and analysis of cryptographic primitives and protocols, including electronic voting, a key escrowsystem, blinding signatures for digital cash systems, message recovery, and publicly variable
encryption schemes. He also engaged in efficient
multi-party computation based on cryptographic
assumptions and zero-knowledge proofs in multiparty computation. From 2004 to 2006 he was avisiting researcher at IBM T. J. Watson ResearchCenter, NY, USA, working with the Crypto
Group, where he researched hybrid encryption,
zero-knowledge proofs, and universally composable protocols. He has been a Senior Distinguished
Researcher and Research Group Leader of NTT
Secure Platform Laboratories since July 2013.

Vol. 12 No. 1 Jan. 2014



Feature Articles: Software Development Technologies

Software Development Technology
Initiatives at NTT Laboratories
Takashi Hoshino, Kazuhito Suguri,
Katsuyuki Natsukawa, and Yasuharu Yamada
Abstract

A large amount of software is used within the NTT Group of companies. Development is in progresson much of this software, but this development does not always run smoothly. Because of this, the NTT
Software Innovation Center conducts research and development of software development technology inorder to increase the stability and efficiency of software development. This article reports on some of theresearch and development underway.
Keywords: software development, software engineering, development processes

1. Introduction
A survey conducted by the Information-technology
Promotion Agency (IPA) indicated that only about
15% of software projects exhibit no problems after
release, and more than 10% of projects have morethan ten trouble issues. The three key aspects of software development are quality, cost, and delivery(QCD); from a developer’s perspective, delivery
dates are met in about 85% of cases, but quality andcost targets are achieved in less than 80% of cases.
From a user’s perspective, cost objectives are met inapproximately 80% of cases, but quality and delivery
objectives are only met in approximately 70 to 75%
of cases. There has been some gradual improvement
when looking at changes year-to-year, but the current
state is still inadequate [1].
Much software is also developed and used within
the NTT Group companies. We are continually making improvements in these development projects, andefficiency is increasing, but this does not mean thatall software development proceeds smoothly andsteadily. In order to provide services quickly, development of the software supporting those services
must proceed even more efficiently.
The NTT Software Innovation Center (SIC) is conducting research and development to create softwaredevelopment technologies that will bring greater stability and efficiency to all software development at
the NTT Group companies.
2. Software development technology
Software engineering includes studying how to
improve software development efficiency. The IEEE
(Institute of Electrical and Electronics Engineers)
Computer Society defines software engineering as:“(a) The application of a systematic, disciplined,
quantifiable approach to the development, operation,and maintenance of software; that is, the applicationof engineering to software. (b) The study of approaches, as in (a)”. This definition suggests an academic
approach such as in establishing systematic methods.
In contrast, our project is called the Software Development Technology Project and does not use the term
software engineering. While the term software development technology certainly includes the systematicand quantitative initiatives of software engineering, italso implies the active pursuit of initiatives related topractical technologies commonly in use in the development workplace, which are not necessarily coveredby this definition, for example, knowledge and knowhow tools and other work-place aids [2].

NTT Technical Review

Feature Articles

Software development technology for providing services more quickly, inexpensively, and with higher quality- Initiatives to create software development technology to quickly provide high quality services including
maintenance, and to reduce TCO

Changes of external conditions and requirements
Planning and requirements
definition processes, techniques

Planning andrequirements definition

Planning andrequirements definition

DesignCodingTesting

Businessanalysis

DesignBusinessanalysis

Coding

Systemanalysis

Testing

CodingTest automation
technology

Service operation
Rationalization of softwaredevelopment for NTT laboratories
Management technology for software development
Human resources development

Fig. 1. Initiatives of Software Development Technology Project.

3. Research and development towards
rationalized QCD
Our goal at SIC is to create software development
technologies for providing services quickly, inexpensively, and with good quality. To achieve rapid service provision and to contribute to reducing the total
cost of ownership (TCO), we are working on creating
software development technology for application
software in particular.
The typical software development process flow andactivities supporting it are shown in Fig. 1. Before
software is introduced for a service, it is developed ina series of processes, which are: planning andrequirements definition, in which the functionality
and performance required by users is decided basedon objectives, return on investment, and analysis of
the current system; design, in which the functionality
and performance of the system to be provided to users
is decided based on the requirements, along with how
it will specifically be implemented; coding, in which
the program is coded according to the design; andtesting, in which the implemented program is checkedVol. 12 No. 1 Jan. 2014

to make sure it operates correctly according to thedesign and requirements and that it satisfies theoriginal user requirements. When additional development is done to improve functionality or for otherreasons, this process is repeated.
These processes must be performed reliably inorder to achieve appropriate levels of QCD in software development. The planning and requirements
definition is the most fundamental process; it is an
important elemental step in which developers ask
what needs to be done or what needs to be created,
and it has a significant influence on later processes. If
this definition is ambiguous, a lot of work may haveto be repeated, which affects all aspects of QCD: cost
increases (C), delayed completion (D), and lower
than expected functionality or quality (Q). Thus, it isextremely important to conduct the planning andrequirements definition accurately. At SIC, we areconducting research and development (R&D) on processes for performing the planning and requirements
definition, and on notation practices for documenting
requirements.
The testing process involves checking the operationFeature Articlesof the software and increasing functional quality, so
this work really focuses on ensuring quality (Q) andis the last measure to prevent poor quality. Testingalso accounts for a large share of the software development work and cost, so improving testing efficiency can reduce the cost and shorten the development time, two factors that are directly related tocosts (C) and delivery (D).
SIC is also developing technologies to support testplanning and execution, with the goal of performing
this test work more accurately and efficiently. The
work done in all the steps of the planning and requirements definition and testing processes discussed here
can have a significant effect on QCD. Further, each of
the aspects of QCD is intimately related to each other.
For example, pursuing a higher level of quality (Q)than required can incur more work, higher costs, anda longer time to ensure the higher quality level, which
will have undesired effects on C and D. It is therefore
important to proceed with an appropriate QCD balance, so it is necessary to manage QCD appropriately.
SIC is conducting R&D on management of softwaredevelopment, with a view toward providing such
QCD management. This includes issues such as
establishing methods to evaluate quality and productivity, gathering development data needed for such
evaluations, and establishing and operating softwaredevelopment standards that will formalize and enable
the entire development process to proceed efficiently.
Addressing the management of development quantitatively in this way will bring stability to each process
and contribute to the overall stability of softwaredevelopment.
In these Feature Articles, we introduce some of
SIC’s initiatives related to important technologies
and activities for increasing the stability and efficiency of software development, as discussed here.
SIC has not performed this technical developmentfrom scratch on its own, but has used technologies
that NTT Group companies already possess, as well
as open source software and commercial technologies, with the aim of advancing open innovation and

producing results quickly.
4. Linking practical needs and
NTT Group companies
For software development technology, it is important to produce technologies that are immediately
useful in the development workplace. In order tounderstand the needs of the software development
workplace accurately, we are strengthening our ties
with NTT Group companies.
Within the NTT Group, there are companies onboth sides of software development: those that placeorders requesting software development and then use
the completed software, and those that take suchorders and develop the software. We are striving for
optimal technology development that will substantially increase development efficiency by listening toboth sides, understanding, analyzing, and optimizing
the real issues and needs in both workplaces, andadvancing our work while increasing collaboration
with companies that handle a lot of software development—even those just within the NTT Group such as
NTT DATA and NTT Comware.
5. Towards the future
SIC has pursued these initiatives while maintaining
a strong awareness of, and cooperating more deeply
with, the development workplace. We will continue
to work on creating technologies that are immediately
useful in the development workplace and will selectresearch themes suited to the needs of this workplace
while striving to increase the stability and efficiency
of software development within the NTT Group.
References[1][2]

The Information-technology Promotion Agency, Japan, “2012 Surveyof the State of the Software Industry,” Apr. 2013 (in Japanese).
H. Ogawa, “Software Development and Software Engineering inIndustry,” Computer Software, Vol. 28, No. 3, pp. 2–11, 2011 (inJapanese).

NTT Technical Review

Feature Articles

Takashi Hoshino

Katsuyuki Natsukawa

Kazuhito Suguri

Yasuharu Yamada

Project Manager, Software Engineering Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees fromthe University of Electro-Communications,Tokyo, in 1989 and 1991, respectively. He joined
NTT in 1991. His current research interests
include software engineering.

Senior Research Engineer, Supervisor, Software Engineering Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees from
Toyohashi University of Technology, Aichi, in
1990 and 1992, respectively. Since joining NTT
in 1992, he has contributed to the development ofvideo-codecs, communication equipment, andcontent delivery platforms. His current researchinterests include software development processes, model-driven-development, and software
metrics. He is a member of the Information Processing Society of Japan and IEEE.

Vol. 12 No. 1 Jan. 2014

Senior Research Engineer, Supervisor, Group
Leader, Software Engineering Project, NTT
Software Innovation Center.
He received the M.E. degree in engineeringfrom NARA Institute of Science and Technology
in 1996. He joined NTT in 1996. During 2009–2012, he worked for NTT DATA. His current
research interests include software engineering.

Senior Research Engineer, Software Engineering Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees in electronic-mechanical engineering from Nagoya
University, Aichi, in 1992 and 1994, respectively.
He joined NTT in 1994. His current researchinterests include software engineering.

Feature Articles: Software Development Technologies

Improving the Planning andRequirements Definition Process
Yukako Iimura, Setsuo Yamada, and Nobuyuki Kobayashi
Abstract

The first process in software development is the planning and requirements definition. In this process,the stakeholder requirements must be organized, and the requirements for implementing the softwaremust be clarified. However, many issues arise with this process in practice, and improvement is therefore
needed. In this article, we introduce our activities related to improving the planning and requirements
definition process, including studying trends in research and practice.
Keywords: software development, requirements definition, planning

1. Introduction
A survey by the Information-technology Promotion
Agency (IPA) [1] found that although achievementlevels for quality, cost, and delivery (QCD) targets forsoftware development projects are gradually improving, a number of problems still remain.
To solve these problems, we have been focusing on
improving the planning and requirements definition
process of software development projects. This is thephase in which it is determined what is to be achievedby the software and what return on investment can beobtained.
The IPA survey also investigated the causes when
QCD objectives were not met. It found that, from thedeveloper perspective, 35% or more of the projects
had problems at or before requirements definition,and from the user perspective, this figure was approximately 90%. In other words, many developers andusers recognized problems in the planning andrequirements definition process.
Generally, problems that occur in this process are
due to differences between what the users really need
and what the developers think they are supposed tobuild. If developers develop software based on a misunderstood view of what users need, the developed
software will not meet user needs. As a result, all of
the work up to the point where the difference was
detected must be reworked. Several researchers havepointed out that the cost of this rework increases rapidly as the time it takes to discover the error increases.
A recent survey [2] reported that the cost of fixing arequirement error discovered in the system operation
phase costs 68 to 110 times more than what it would
cost if discovered during the planning and requirements definition process (see Table 1).

Table 1. R elative cost to correct a requirement defectdepending on when it is discovered.
Development phase

Relative cost to correct a defectRequirements

Base value of 1

Design2 to 3 times higher (than base value)

Coding5 to 10 times higher

Testing

8 to 20 times higher

Operation

68 to 110 times higher

2. Challenges of the planning and requirements
definition process
Here, we discuss the various challenges that arise in
the planning and requirements definition process.

NTT Technical Review

Feature Articles(1) Diversity of stakeholders
The term stakeholders refers to the group of people
who are involved in a software development projector are affected by the project. Generally, the stakeholders in such a project can be divided into users anddevelopers. Users include end-users who will beusing the software, and others such as the information
technology department and management, for example, the chief information officer. Similarly, developers include software engineers, vendor project managers, and management, for example, the chief technology officer. The perspectives of each of thesestakeholders are different, and they often have conflicting interests. Because of this, stakeholders sometimes have contradictory requirements, and thesemust be adjusted in order to reach agreement on what
will be achieved with the software. Thus, as the number of stakeholders increases, dealing with the contradictory requirements in this way becomes more difficult.
(2) Changing requirements
In the planning and requirements definition process, requirements from stakeholders are adjusted,
and agreement is reached on the function and performance of the software. However, these functions
and/or performance may need to change in therequirements process due to omissions in the requirements or later changes in the environment. Handlingsuch changes often results in scheduling delays ordegraded quality. Also, adding requirements causes
wide-ranging effects if they conflict with other existing requirements, as the existing requirements thenneed to be re-examined, and adjustments need to bemade with the relevant stakeholders.
(3) Ambiguity in requirements documentation
Because the purpose of planning and requirements
definition is to reach agreement among stakeholders,documentation of these requirements is extremely
important. However, if requirements definition is
ambiguous, multiple readers of a requirement may
have a different understanding of what it means, orthey may be confused as a result of interpreting arequirements statement in different ways.
If the stakeholders have differing expectations
regarding the function that the software will have due
to such ambiguity in the documentation, reworking
will be necessary. For example, even if the developers
follow the requirements definition, they may understand them in a way that is different from the users’
intentions because of the ambiguous specifications,Vol. 12 No. 1 Jan. 2014

and all of the work starting from the design phase willneed to be reworked.
3. Standards and guidelines related tothe planning and requirements
definition process
Interest in the planning and requirements definition
process has increased recently, and consequently,
there has been an increase in the number of related
standards and guidelines being published. This section describes the Requirements Engineering Body ofKnowledge (REBOK) [3]*1—a requirements engineering knowledge system, ISO/IEC/IEEE*2 29148[4]—a standard related to requirements engineering,and the Software Life Cycle Process Japan Common
Frame (SLCP-JCF) [5].
3.1 REBOKThe first edition of REBOK was released by theJapan Information Technology Services Industry
Association (JISA) in 2011. It provides a set of common knowledge shared and used by stakeholders
consisting of both users and developers, and for both
enterprise/business software systems and embedded
software systems, except for domain specific knowledge. The requirements engineering process is shownin Fig. 1. It configures the four key knowledge areasof (1) elicitation, (2) analysis, (3) specification, and(4) verification, validation, and evaluation in an
incremental and iterative way. It aims to provide
appropriate knowledge to all the stakeholders
involved in the requirements engineering process at
appropriate levels of expertise; the stakeholders
include corporate management, end-users, project
managers, and software developers.
3.2 ISO/IEC/IEEE 29148: 2011
ISO/IEC/IEEE 29148: 2011 covers processes andproducts related to the engineering of requirements
for systems and software products and services
throughout their life cycle. It provides additional
guidance in the application of requirements engineering and management processes for requirementsrelated activities in ISO/IEC 12207 and ISO/IEC
15288. It includes perspectives from areas beyond
software such as the business or project that is the*1	 REBOK is a registered trademark of JISA (Registered trademark
classification 9, registration no. 5458370).
*2 ISO: International Organization for Standardization; IEC: International Electrotechnical Commission; IEEE: Institute of Electrical and Electronics Engineers.

Feature Articles

Requirements planning and management

Requirements
elicitation

RD (Req. development)

Req. elements

Requirements
analysis

Structured req.

Requirements
specification
REBOK
extension

Enterprise analysis
Requirements verification,
validation, & evaluation

Product analysis

Foundation

Req. specifications

Software construction

Requirements source (stakeholders, documents, etc.)

REBOK coreRequirements engineering process

Practical
considerations

Practice

Requirements engineering fundamentals

Fig. 1. REBOK process.

External environment· Market trends· Laws & regulations· Legal liabilities· Social responsibilities· Technology base
· Labor pool
· Competing products· Standards & specifications· Public culture· Physical/natural environment

Organization environment· Policies & procedures· Standards & specifications· Guidelines· Domain technologies· Local culture

Business operation
Business operation· Processes· Constraints· Policies & rules· Modes· Quality· Business structure

Stakeholders(Business managementlevel)

System operation
SystemSystem elements
Softwarerequirements

Stakeholders(Business operationlevel)

Systemrequirements

Software

System elements

Fig. 2. Areas covered by ISO 29148.

basis for the system and the operation of the system,
as shown in Fig. 2.
3.3 S
 oftware Life Cycle Process Japan Common
Frame (SLCP-JCF)
The Software Life Cycle Process Japan Common
Frame (SLCP-JCF) was created in 1994 in Japan with


the goal of eliminating misunderstandings among
stakeholders involved in software development. It
provides comprehensive regulation of tasks and roles
needed in the areas of business analysis, businessdesign and software-related planning, requirements
definition, development, operation, and maintenanceas well as various other related activities. SLCP-JCF
NTT Technical Review

Feature Articles

(%)
60

0%

−40
−60

Integration test

System test

6

Unit test

Coding

10
Architecture design

−20

18

Requirements
Specification0−9 −12−9 −12−9 −12

Time

25

−10%
−15%

Time
−27%

−30%
−35%
−40%

−46 −45

Cost

−20%
−25%

Software design

23

−5%

Cost

37

40
20

Average total change incost and time

Changes in cost and time per phase

−36%
(b)

(a)

Fig. 3. Cost and time changes of software development in (a) individual development phases and (b) overall.

2007 was published in 2007 and incorporates the ideathat there are fundamental issues to be addressed in
the process from business and project planning
through to requirements definition and enhancing theoperation and user processes. SLCP-JCF 2013 waspublished in 2013, with improvements made to therequirements definition, operations, and service processes.
4. Initiatives related to planning andrequirements definition
The NTT Software Innovation Center is studying
the following areas related to planning and requirements definition.
4.1 P
 lanning and requirements definition process
As stated previously, there are many stakeholders in
the planning and requirements definition process. To
achieve smooth communication among them, theymust have a common understanding of what sorts ofprocedures need to be implemented, what steps need
to be taken, what inputs and outputs are necessary,and what they each must accomplish with respect tothe software development project.
Accordingly, we have been studying planning andrequirements definition processes that clarify andstandardize the procedures that must be implemented
for planning and requirements definition, for defining
the styles of deliverables, and for clarifying the diviVol. 12 No. 1 Jan. 2014sion of roles.
Also, as discussed earlier, requirements change
during the planning and requirements definition process due to changes in the environment or adjustments made between stakeholders. These changes inrequirements also require changes in the schedule orfunctions to be realized, which have already been
agreed upon by stakeholders. Consequently, we arealso studying requirements management processes
that enable effective management of any changes
made to requirements and analysis of the effects ofadopting the changes.
We believe that application of these processes wehave been studying will help to advance softwaredevelopment projects by achieving mutual understanding among multiple stakeholders.
4.2 S
 tudy of methods and techniques used in theplanning and requirements definition process
Although procedures and outcomes are decided
during this process, the work could proceed moresmoothly if certain know-how or skills were appliedsuch as knowledge of writing requirements documents in ways that reduce ambiguity. We are therefore also creating and organizing examples of suchknow-how and skills.
4.3 P articipation in REBOK Working Group(WG)
REBOK has been presented at internationalFeature Articles

conferences related to requirements engineering [6].
The English edition of REBOK is under constructionin order to meet the expectations of many people inresearch and industry. Initiatives to support the use of
REBOK are also being undertaken. We are participating in planning for the REBOK WG and are contributing to activities that promote REBOK.
5. Study of the state of development
The improvements achieved at a German company
as a result of initiatives they introduced are shown in
Fig. 3. By performing requirements definition andother upstream processes soundly, they were successful in reducing the cost and time required for later
processes, and were able to reduce the overall development cost by 27% and the development time by
36% [7].
We hope to achieve the same kinds of improvements by studying the planning and requirements
definition processes and the techniques used in those
processes.

Yukako Iimura

Researcher, Software Engineering Project,
NTT Software Innovation Center.
She received the M.S. degree in engineeringfrom Kumamoto University in 2001 and joined
NTT the same year. Her research interests
include requirements engineering and knowledge engineering. She is a member of REBOKWG and the Information Processing Society ofJapan (IPSJ).

In this study, it will be necessary to understand theissues involved in the early process through surveys
and other means, and to incorporate input from those
involved in actual development.
References
[1]
[2]
[3]
[4]
[5]
[6]

[7]

The Information-technology Promotion Agency, Japan, “2012 Surveyof the State of the Software Industry,” Apr. 2013 (in Japanese).
K. Wiegers, “More About Software Requirements: Thorny Issues andPractical Advice,” Microsoft Press, 2006.
JISA REBOK WG (ed.), Requirements Engineering Body of Knowledge, Version 1.0, Kindaikagakusha, 2011 (in Japanese).
ISO/IEC JTC1/SC7, “IEEE Std. 29148: 2011, IEEE Systems andsoftware engineering—Life cycle processes—Requirements engineering,” 2011.
The Information-technology Promotion Agency, Japan, “Common
Framework 2013,” (in Japanese).
M. Aoyama, T. Nakatani, and S. Saito, “REBOK Manifest: Towards a
Requirements Engineering Body of Knowledge,” Proc. of the 18th
IEEE International Requirements Engineering Conference (RE2010), IEEE Computer Society, pp. 383–384, Sydney, Australia.
M. Broy, “Opportunities and Challenges in Software Engineering for
the Next Generation Automotive,” Proc of the IEEE 35th Annual
Computer Software and Applications Conference (COMPSAC 2011),
Munich, Germany.

Nobuyuki Kobayashi

Senior Research Engineer, Supervisor, Software Engineering Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees inapplied mathematics and physics from Kyoto
University in 1987 and 1989, respectively. He
joined NTT in 1989. His research interests
include database engineering and software engineering. He is a member of IPSJ, the Institute ofElectronics, Information and Communication
Engineers, and the Database Society of Japan.

Setsuo Yamada

Research Engineer, Software Engineering
Project, NTT Software Innovation Center.
He received the M.S. degree in information
science from Tokyo Denki University in 1992
and the Ph.D. degree in engineering from Tottori
University in 2006. He joined NTT in 1992.
From 1997 to 2000, he was with ATR Spoken
Language Translation Research Laboratories. He
moved to NTT in 2000. His research interests
include natural language processing and software
engineering, especially requirements engineering. He is a member of IPSJ and the Association
for Natural Language Processing.



NTT Technical Review

Feature Articles: Software Development Technologies

Test Automation Technology to
Reduce Development Costs andMaintain Software Quality
Haruto Tanno, Xiaojing Zhang, Keiichi Tabata,Morihide Oinuma, and Kazuhito Suguri
Abstract

As companies increasingly strive to reduce the cost of software while maintaining its quality, interestin technology supporting software testing is also increasing since testing is vital to maintaining quality,
and it accounts for a large share of the total development cost. Currently a large part of testing is done
manually, which is expensive and prone to mistakes and oversights. In this article, we introduce technologies that automatically generate comprehensive test cases and test data from software design documents, as a way to resolve these types of problems.
Keywords: software testing, integration testing, test design

1. Introduction

2. Current state of software testing support

Software development is divided into processes, as
shown in Fig. 1. Of these processes, testing is estimated to account for 50% of the total cost. However,most of this work is done manually, so it is an area
where there is room for cost reductions. Further,faults that do not get exposed in the testing process
will be released to market unresolved, so testing isreally the last defense against poor quality. The factthat it is done manually, which results in errors andomissions, presents another problem in ensuring
quality.
These issues could be resolved by raising the skill
level of testing staff, by increasing the number ofpeople involved, or by delaying delivery to provide
additional testing time. As long as the work is done
manually, though, errors and omissions cannot be
entirely eliminated. In addition, these measures could
lead to an increase in costs.
Given these circumstances, the NTT Software
Innovation Center is working on a test automation
approach that will use computers to replace work
being done manually.

The objectives of software testing are to verify thatsoftware has been implemented according to thedesign and specifications, and to reduce the numberof defects. The testing process mainly consists of thefive tasks shown in Fig. 2: test planning, test design,
test execution, test reporting, and test management.
In test planning, issues such as the time frame andallocation of resources for testing are decided basedon the overall development plan. Test design involves
clarifying the various tests that must be done anddesigning test cases comprehensively. In test execution, the test data are input for each of the test cases,
and the software is run to check that it behavesaccording to design. In test management, real-time
management of the state of test execution is carriedout, and the test plan is revised if necessary. When all
tests have been executed, the results are summarized
in test reporting, completing the process.
We are working to support testing in the design andexecution tasks, which are the main tasks in the testing process. Automation of these tasks can be very
effective in reducing costs and ensuring quality.



NTT Technical Review

Feature Articles

Requirements
definition

DesignCodingTesting

Fig. 1. Overall development process.

Test management
Test planning
Test design

Test execution

Test reporting

Fig. 2. Testing process.

Currently, a degree of automation has been achievedin test design and execution for unit testing of source
code, with tools such as Parasoft Jtest*1 and JUnit*2.
However, automation is still inadequate in integration
testing, which checks the operation of software combining multiple modules, and in system testing,which tests entire systems.
Various tools are available to support the design ofsome functionality tests. For example, PictMaster(Microsoft) generates combinations of input values
based on a combinatorial method called All-Pair, andEnterprise Architect (Sparx Systems) can generate
test cases from module descriptions written in the
UML (Unified Modeling Language) specification
language. However, there are major barriers to introducing these tools in the development workplace.
These barriers include the need for testing staff tohave specialized knowledge of the tools and the testing technique which the tools use, and the need towrite descriptions in an unfamiliar language.
There are also test execution tools such as Open2­
Test, which automates testing of Web applications
based on test scripts. However, even when using suchtools, the test scripts and test data must still be prepared manually, and thus, there is still much room forfurther automation.
3. Research vision
Our vision is to reduce the cost and maintain softVol. 12 No. 1 Jan. 2014

ware quality in the testing process by achieving automation of test design and test execution, as shown in
Fig. 3. One feature of our approach is that it requires
only the software design documents, which is theartifact of processes preceding testing, and no othernew input needs to be specially created. The software
design documents are input, comprehensive test cases
are extracted, and test procedures, data, and scripts
are generated automatically. This removes the needfor testers to have specialized knowledge or to learn a
new notation, so it should be possible to introduce itsmoothly into the development workplace. Also, byusing the test data and scripts generated during thetest design, we can link tests with existing test execution tools to implement fully automated testing in one
button click, from test design through to test execution.
4. Scope: Integration testing ofenterprise applications
Our scope is integration testing of enterprise applications, which involves testing a system to check
whether it operates correctly when a web browser,
server-side processing, and database are integrated,
as shown in Fig. 4. For example, when a search is
performed using a search screen, the operations to be*1	 Parasoft Jtest: An automated testing tool from TechMatrix Corp.
*2	 JUnit: A framework for automating unit testing.

Feature Articles

Software design

Test design

Test execution
Output (1)Test design artifact

Input
Software design artifacts

http://www.xxxx.com/

Login ID

Click!

Password

Click!

SubmitItem

1
2

Designdocuments…

Test design
automation
technology

N

Procedure…
…
…
…

Test data

Test case list

NTTtechnology

Click!

Test script

Automatic
test
execution
tool

Execution
results, logs,
and otherrecording tools

Existing
technologies

Existing
technologies

Output (2)Test execution results
Item

1
2
…
N

Detail…
…
…
…

Pass/fail…
…

Test results report

Fig. 3. Research vision.

Screen after operation
Search result list screen

10

Ota

Search condition
Age

to
Lower

Web browser

Server

Omori

Section 3

Section 3

Next page

Upper
SearchDepartment

119

Department…

Training candidate
employee search

…

ID

…

Screen before operation

Employee
nameError screen“Invalid age range”

Back

Error screen“Unauthorized access”

Back

Business
logic

Database

Fig. 4. Integration testing of enterprise applications.



NTT Technical Review

Feature Articles

OutputInput
Software design
documents

TesMa

Item

Procedure

1

…

2

…

…

Test case list

…

N

…

E.g.,:

Test data

E.g.,:

Screen design document

Process flow diagram

Screen transition diagram

Test case list

Fig. 5. Integration testing design support tool: TesMa.

checked include the search function to determine if
the search occurred normally, as well as the transitions to the search results screen and to error screens.
Therefore, in test design, test cases for all variationsin operation and inputs, such as login IDs, must becovered without missing any test case which should
be done. Test data include values to input on web
browser screens and data to be inserted in the database beforehand for each test case, and these data
must be created in the test design stage.
5. Integration testing design
support tool: TesMa
We propose here an integration testing design support tool called TesMa, which automatically generates test cases and test data required for integration
testing of enterprise applications from software
design documents, as shown in Fig. 5. This capability
can reduce the effort required for creating test cases
and test data, which was previously done manually by
testing staff, to the scope covered by TesMa. This tool
extracts a comprehensive set of test cases, so it also
avoids omissions that can occur when doing this work
manually.
The tool has the following features:-	The input for the tool is a set of design documents written according to some set descriptive
Vol. 12 No. 1 Jan. 2014

rules. These documents are the results of thedesign process, which is part of the existingdevelopment process. Thus, it has the advantage
of being easy to introduce into the development
workplace.
-	The tool generates a comprehensive set of test
cases [1] and test data [2], [3] based on processing patterns and input data variations. This helps
to prevent omissions from occurring in manually
generated test designs and also generates the test
data required to execute each test case, so test
execution is much easier.
These features enable the test tool to reduce the costof integration testing, while maintaining software
quality through a comprehensive test design.
6. Achievements and future prospects
TesMa technology is already being introduced in
NTT Group companies, and its effectiveness in
reducing costs while maintaining quality in comprehensive test design is becoming apparent. There arestill some issues to be addressed involving the introduction of automatic test-data-generating technology
into the development workplace, so some further
improvements are needed. This will be a task carriedout through consultation with the relevant companies.
In the future, we will work on integrating our testFeature Articles

design automation technologies with automated test
execution tools, and on achieving testing that is fully
automated, from test design to execution. We intend
to continue to advance our research and development
step-by-step toward our goal of reducing costs while
maintaining quality.

References
[1]

[2]
[3]

Haruto Tanno

X. Zhang, H. Tanno, and T. Hoshino, “Introducing Test Case Derivation Techniques into Traditional Software Development: Obstacles
and Potentialities,” Proc. of the 6th Testing: Academic and Industrial
Conference––Practice and Research Techniques (TAIC PART), Berlin, Germany, 2011.
X. Zhang and T. Hoshino, “Test Case Extraction and Test Data Generation from Design Models,” Proc. of the 5th World Congress for
Software Quality (5WCSQ 2011), Shanghai, China.
H. Tanno, X. Zhang, and T. Hoshino, “Design-Model-Based Test Data
Generation for Database Applications,” Proc. of the 4th Workshop on
Model-based Testing in Practice (MoTiP 2012), pp. 201–206, Dallas,
TX, USA.

Morihide Oinuma

Researcher, Software Engineering Project,
NTT Software Innovation Center.
He received the B.E. and M.E. degrees in computer science from the University of ElectroCommunications, Tokyo, in 2007 and 2009,
respectively. He joined NTT in 2009. His interests include programming language and software
testing. He received the Super Creator Award
from the Information-technology Promotion
Agency, Japan, in 2008 and the Distinguished
Paper Awards from the Information Processing
Society of Japan (IPSJ) in 2009 and 2013. He isa member of IPSJ.

Senior Research Engineer, Software Engineering Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees in electrical engineering from Keio University, Kanagawa, in 1984 and 1986, respectively. He joined
NTT in 1986. His current research interests
include software engineering. He is a member of
IPSJ.

Xiaojing Zhang

Kazuhito Suguri

Researcher, Software Engineering Project,
NTT Software Innovation Center.
She received the B.E. and M.E. degrees incomputer science from Kyushu University,
Fukuoka, in 2005 and 2007, respectively. She
joined NTT in 2007. Her main interest is software engineering, especially model based development. She is a member of the Institute ofElectronics, Information and Communication
Engineers.

Senior Research Engineer, Supervisor, Software Engineering Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees from
Toyohashi University of Technology, Aichi, in
1990 and 1992, respectively. Since joining NTT
in 1992, he has contributed to the development ofvideo-codecs, communication equipment, andcontent delivery platforms. His current researchinterests include software development processes, model-driven development, and software
metrics. He is a member of IPSJ and IEEE.

Keiichi Tabata

Researcher, Software Engineering Project,
NTT Software Innovation Center.
He received the B.E. and M.E. degrees in computer science from Waseda University, Tokyo, in2010 and 2012, respectively. He joined NTT in
2012. His interests include software engineering.



NTT Technical Review

Feature Articles: Software Development Technologies

R&D Software Development
Standards and their Operation
Kumi Jinzenji, Naoki Kasahara, and Takahiro Muraki
Abstract

The NTT Service Innovation Laboratories has created original software development standards forvarious quality levels from product incubation through to finished commercial products. These standards
have been in operation for about four years and have been applied to approximately 200 software products, most of which were provided to business companies of the NTT Group. The developers andresearchers in our laboratories have secured the quality and identified the risk of the products before
releasing them under the responsibility of the authorized organization. This article describes our latest
R&D (research and development) software development standards, including their features, operation,effects, and future developments.
Keywords: software development process, quality, risk

1. Introduction
NTT laboratories develop a variety of software
products such as business applications, middleware,and information processing engines. The range of
quality levels is diverse, from commercial-level highquality to low-level quality that is sufficient for product incubation. The skill levels of developers are also
diverse. Moreover, these products are used in various
departments of the business companies, which havedifferent requirements and demands for software
quality depending on their business objectives. These
differences in our products and how they are usedhave sometimes resulted in problems after theirrelease to business companies. Defects have beenfound when products were used in ways not anticipated by the developers, and delays have occurred indealing with such defects. To solve these issues, it
was necessary to establish rules for the organizations
developing the software so that they could secure thesoftware quality and identify the associated risk ofthe products and could take responsibility for implementing the rules. Accordingly, in July 2009, theNTT Software Innovation Center started addressingthese issues by creating standards for software development and clarifying the rules for operation of these

standards. Generally, software development standards define processes and activities necessary tocontinually improve product quality or productivity.
Our software development standards have additionalfeatures over typical standards, with added processes
that enable the software product developing organization to take responsibility for product quality and risk.
The standards have undergone a few revisions inrecent years, but NTT Service Innovation Laboratories settled on the new R&D (Research and Development) Software Development Standards in April
2013.
2. Features of the R&D softwaredevelopment standards
The document describing the R&D software development standards has four parts: the main text of thestandards, the forms and samples section, operationalguidelines, and additional documents that help readers understand the development standards. All of theprocesses and activities described in the main text do
not necessarily always have to be performed. The
processes and activities that are particularly important are marked and selected as a mandatory process
checklist. Achieving these mandatory processes can
NTT Technical Review

Feature Articles

Table 1. Definitions of software quality classes.
Quality class

Definition with respect to suitability for introduction in a business

Example of use

Main expected users

A

Companies can introduce the software product to their businesses
Infrastructure or network
largely as-is, and it will be used under a very strict SLA, as withservice in a company.
infrastructure or network services for which the service must not stop.

Individual consumer
and cooperate
customer

B

Companies can introduce the product to their businesses as-is, but
it will be used in conditions where the application can be restarted
to some extent, as with a software package or solution.

Package or solution in acompany, disclosure oftechnology to a relatedcompany.

Individual consumer
and cooperate
customerC

The product is used in a somewhat limited manner, as with a trial,and is introduced to companies with conditions on its functionality.
Some of the architecture will require further improvement or
additional testing.

Service trial conductedby company orlaboratory.

Individual consumer,
cooperate customer
and company
employees

D

Usage is extremely limited, as with a demonstration of functionality;
for installation, there are conditions on functionality andarchitecture, and testing may require drastic revision.

Demonstration at acompany

Company employeesE

No quality evaluation has been done, so it cannot be introduced ina business.

Research use

Researchers

be considered to be conforming to the development
standards. The main text of the standards is used as areference for these mandatory processes. These standards were written based on the assumption that awaterfall development*1 process is used, but by redefining several mandatory processes, these standards
can be applied to agile development*2 processes as
well.
Further, these development standards have four
original features not generally seen in existing standards. The first three features were introduced in thepredecessor to this research, Essentials of Software
Development for Incubation [1], and this revision
strengthens and improves the original features. The
four features are described in detail in the subsections
below.
2.1 Introduction of software quality classes
The quality classes defined in the R&D softwaredevelopment standards are listed in Table 1. There
are five quality classes, A to E. These five quality
classes can be broadly divided into three categories.
First of all, Classes A and B consist of software thatcompanies can use as-is (that is, the software can bedirectly introduced into a company’s package or service). Further, Class A software has a strict service
level agreement (SLA) to ensure the system the software is used in never stops, while Class B software
permits restarts of the certain degree.
Second, in Classes C and D the software cannot be
used as-is and/or needs further improvement. Class C
software requires some quality issues to be improved
before it can be released for business use, and Class
Vol. 12 No. 1 Jan. 2014

D software needs to be totally improved or refactored.
Finally, Class E includes products of unknown
quality, so this software cannot be introduced in abusiness in operation.
These quality classes were decided by developers,
who considered how the software would be used after
being released to business companies.
2.2 Q
 uality requirement to build in and verify
with a quality checklist
The R&D software development standards establish 105 items to be checked in a quality class checklist based on quality characteristics and sub-characteristics of ISO/IEC (International Organization forStandardization/International Electrotechnical Commission) 9126, the international standard for theevaluation of software quality. This makes it possible
to gain a concrete understanding of work required tobuild in and verify quality (Table 2). The quality
checklist provides recommended criteria for eachquality class, which is based on building in and verifying quality with business applications. The recommended criteria are general information for thedevelopers but are not mandatory because the product*1	 Waterfall development: A development method in which all functions sequentially pass through several processes to completion.
In principle, the previous process is completed before proceeding
to the next.
*2 Agile development: A development method in which the item
being developed is divided into many small functions, which areiteratively implemented one after another, minimizing the risk
due to changes in requirements.

Feature Articles

Table 2. Quality characteristics and recommended criteria.
Recommended criteria
Quality class

Quality characteristics
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28

Qualitycharacteristics
Functionality

Reliability

Usability

Efficiency
Maintainability

Portability

Sub-characteristics

A

B

Suitability
AccuracyInteroperability
Security
Functionality compliance
Maturity (validity)
Maturity (fault convergence)
Fault tolerance
Recoverability
Reliability compliance
Understandability
Learnability
Operability
Attractiveness
Usability complianceTime behaviour
Resource utilization
Efficiency compliance
Analyzability
Changeability
Stability
Testability
Maintainability compliance
Adaptability
Installability
Co-existence
Replaceability
Portability compliancequality requirement depends on the characteristics ofeach software product and on the developers’ customers. It is important that all developers share thechecked result and recognize which quality characteristics are included in the development requirements.
2.3 Documentation according to quality class
The skill levels of developers at NTT laboratories
are quite diverse, so the development standards provide sample documents with levels of descriptions
corresponding to high-quality products of Class B
and above, including a basic design document, a project planning document, and a release readiness document (the three principal documents). Some examples
of items included in a project planning document arelisted in Table 3. General-development-standard
documents typically only describe items in simple,
general, and broad terms, so it is difficult to create
concrete and usable documents for a high-qualityclass product without adequate development experience, knowledge, and skills. Thus, for the R&D soft

C

D

E

Examples of conformancepoints for recoverability(1) After a fault occurs, the software is able toreturn to the initial statebefore processing
started, and perform the processing overagain.
(2) Data can be recovered accurately using
checkpoints or another mechanism after afault occurs, and processing can resume
within the required recovery time.
(3) The affected processes can be isolated
when a fault occurs, and other processes cancontinue to operate.
(4) Traces, logging, dumps, or other records
for analyzing the fault can be used when afault occurs.

ware development standards, we make it possible toachieve the desired quality class regardless of theskill set available by including many possible activities, metrics, and evaluation methods. When a product with a lower quality class is developed, only itemsin the samples up to the target quality level need to befollowed, and the rest of the items can be deleted.
When we evaluated the description levels in documents within NTT laboratories, we found that thelevel of description seemed to correspond to the quality level better when using the Class B samples thanwhen using the Class C samples.
2.4 Mandatory processes based on quality class
These development standards define mandatory
processes according to the target quality class(Table 4). Mandatory processes can be broadly
divided into three categories: two project reviews,
creation of the three principal documents, anddevelopment management. We have made it possible
to select three levels of process sets for each of thesecategories according to the target quality level.
NTT Technical Review

Feature Articles

Table 3. Example descriptions of verification methods and metrics in a project planning document.
Process
Verification
methodMetrics

Detailed
designFunctional
designCodingUnit testing

Integration
testing

Software review

Systemtesting

Field testing

Software testing

Review

Review

Code review- White box
test- Black box
test- Black box
test- Regression
test- Recovery
test- Black box
test- Regression
test- Time andresource
efficiency test
- Recovery
test- Load test
- Stability test
- Multihardware test
- Manual test

- Black box test
- Regression
test- Operational
test- Non-functional
tests- Review
frequency
and time- Number of
errors- Number ofcomments- Review
frequency
and time- Number of
errors- Number ofcomments- Review
frequency
and time- Number of
errors- Number ofcomments- Coverage- Number oftest cases- Test density- Number ofbugs- Bug density- Number oftest cases- Test density- Number ofbugs- Bug density- Number oftest cases- Test density- Number ofbugs- Bug density- Fault
convergence- Number of testcases
- Test density- Number ofbugs- Bug density- Fault
convergence

Table 4. Mandatory processes.
Mandatory processes

Class AClass BClasses C and D

1

Project review

Mandatory

2

Create three principal documents

Mandatory (level of description according to quality class)3

Development management

Mandatory

Mandatory processes concerned with two projectreviews are common to all quality classes in order toallow the software development organization to takeresponsibility for their project risk as well as theirproduct risk and product quality. In addition, the firstproject review is done by an organization manager toconfirm project baselines and decide whether or not
to continue the project. The second project review isalso done by an organization manager to verify the
product quality and decide whether the product isready for release. Creation of the three principal
documents is also common to all quality classes, but
the description details depend on each project. Furthermore, parts of the development management
process can be omitted, depending on the quality
class. We also define mandatory processes for existing products, which refers to software products developed before our R&D software development standards were in operation. Specifically, for existingVol. 12 No. 1 Jan. 2014

Partially mandatory

Not mandatory

products, most of the mandatory processes are activities centered on the second project review (releasedecision).
3. Operation of the R&D Software
Development Standards
In order to avoid ending up with standards that are
only a mere façade and the possibility that they will
become obsolete, the R&D software development
standards are operated using a Plan-Do-Check-Act(PDCA) cycle (Fig. 1). The core activities of this
PDCA cycle are described below.
3.1 Operational rule provisions
The following two operational rules were authorized in NTT Service Innovation Laboratories whenestablishing the R&D software development standards.
Feature Articles

P
Creation of development standards
and rules for operation

A
Revision (standards rules),deployment

Objective
To secure productquality, responsibility
for risk held byorganization

D
Conformance check andfeedback

Analysis, evaluation,and disclosure
C

Fig. 1. PDCA cycle.

(1)	The R&D software development standards shallbe applied to products intended for use in thebusiness companies and products intended foruse in service trials for NTT customers, and theyshall achieve one of the four quality classes from
A to D.
(2)	The top managers of the software developing
organization shall conduct two project reviewson cases where the R&D software development
standards are being applied.
Rule (1) clarifies what is subject to the development
standards and the target quality class, and Rule (2)ensures that the organization is taking responsibility
for the quality and risk associated with products.
In the first project review, the managers holding
responsibility in the organization check the project
scope, QCD (quality/cost/delivery) baseline, as wellas the risk. In the second project review, they make adecision on release after checking the product quality,
provision conditions, and risk.
3.2 Standards compliance check and feedback
The standards compliance check involves comparing checklists submitted by developers with evidence
to see whether the mandatory processes are being
achieved. Currently, this procedure is being done by
the development standards operation group. The standards compliance check is done immediately after thetwo project reviews. The results of the check arebrought back to developers by the development standards operation group in a meeting, which is used asa setting for communication between the softwaredeveloper and the operation side that is also creating
the development standards. These activities ensurethat all projects can be monitored in the laboratories
and thus avoid having standards that are mere
façades.
3.3 Analysis and evaluation of the state of operation
Approximately once every six months, overall
trends in the state of operation are analyzed, evaluated, and disclosed. These results are brought back sothey can be used in subsequent actions of each software development project.
3.4 Revision and deployment
The development standards need to be updated
when issues arise. To maintain the quality of standards documents during the updating process,reviewers selected within each organization apply thedevelopment standards. Trials are sometimes conducted to examine the effects of new policies on R&D
activity. Reviews and trials have also been conductedwhen updating the R&D software development standards in order to check whether there are any issues
with their operation or effects. Then a formal meetingis held to authorize the development standards, andthey are deployed through presentations and by publishing the standards documents on a dedicated website.

NTT Technical Review

Feature Articles

4. Application results, effects, and future issues
The R&D software development standards havebeen in operation since April 2013, and as of the endof July 2013, they have been applied to approximately 30 cases. When the preceding development standards are included, the number of cases they havebeen applied to exceeds 200. We now have an
understanding of the quality of software products thathave been introduced into the business companies, so
the objectives of this initiative have been achieved. A
task for the future is to quantitatively evaluate theefficiency of operation and the validity of our strategies towards securing software quality and recogniz-

Kumi Jinzenji

Senior Research Engineer, Software Engineering Project, NTT Software Innovation Center.
She received the B.E. degree in electrical andelectronic engineering from Sophia University,
Tokyo, the M.E. degree in electronics and telecommunication engineering, and the Ph.D.
degree in global informatics and telecommunication from Waseda University, Tokyo, in 1989,
1991, and 2005, respectively. She joined NTT in
1991 and was a visiting researcher at Global
Informatics and Telecommunication Institute of
Waseda University during 2003–2004. She was a
project manager of software development fornational network systems at NTT Communications from 2005 to 2007. Her current researchinterests are project management, software reliability, and software development processes andquality. She received the Young Researcher’s
Encouragement Award in 1998 from the Instituteof Electronics, Information and Communication
Engineers (IEICE). She is a member of IEICE
and the Information Processing Society of Japan.
She has been certified as a Project Management
Professional (PMP) by the Project Management
Institute (PMI), USA.

Vol. 12 No. 1 Jan. 2014

ing risk.
It is important how both the creation of softwaredevelopment standards and their operation are considered. We will expand the implementation of our
R&D software development standards and our operational know-how to organizations within the NTT
Group.
Reference[1]

K. Jinzenji and T. Hoshino, “Essentials of Software Development for
Innovation,” NTT Technical Journal, Vol. 23, No. 8, pp. 52–55, 2011
(in Japanese).

Naoki Kasahara

Research Engineer, Software Engineering
Project, NTT Software Innovation Center.
He received the B.S. degree in mathematics
from Keio University, Kanagawa, in 1991. He
joined NTT in 1991. He worked at NTT Communications from 2001 to 2003 and at NTT
Resonant Inc. from 2004 to 2006. He has a PMP
certification from PMI, USA. He also has a Project Manager qualification from the Informationtechnology Promotion Agency, Japan. His interests are methodologies of project management
and project risk/quality management. He is amember of PMI and the Project Management
Association of Japan.

Takahiro Muraki

Research Engineer, Software Engineering
Project, NTT Software Innovation Center.
He received the B.E. and M.E. degrees in electrical and electronic engineering from Gifu University, in 1989 and 1991, respectively. He joined
NTT in 1991. His interests include project management and analysis of project risk and quality.
He is a member of Japan Academy of Facial
Studies.

Feature Articles: Optical Node and Switch Technologies
for Implementing Flexible and Economical Networks

Optical Node and Switch
Technologies for Flexible andEconomical Networks
Mitsunori Fukutoku, Yasuhiro Sato, and Senichi Suzuki
Abstract

Network traffic is increasing rapidly, and high-performance optical nodes are needed to build networks
that can handle it with flexibility and efficiency. This article introduces the latest technical trends in thisarea, including reconfigurable optical add/drop multiplexer (ROADM) technology, which is used to
implement advanced optical nodes, and optical switching technology, which is the basis for the primarydevices used for ROADM.
Keywords: ROADM, optical switch, optical node

1. Introduction
The Internet and various other network services
were developed based on their use via personal computers (PCs). However, with the spread of smartphones and tablet PCs, such services have become
even more common and have permeated broadly into
our lives. NTT’s research laboratories have continuously engaged in research and development (R&D)
of optical networks as a base technology for providing network services. Domestic and international
Internet traffic figures are shown in Figs. 1 and 2 [1],[2]. As network services have expanded, traffic has
increased by a factor of approximately 1.4 each year.
In the future, the use of smartphones and tablet PCs
will continue to spread, but various other items in ourdaily lives will also become networked devices, or inother words, devices that are always connected to the
network and that generate data without human intervention, and communicate machine-to-machine(M2M). When such an environment is realized, thedata traffic passing through optical networks will
surely increase further still. It has been estimated that
global traffic on the Internet will triple over the fiveyear period from 2012 to 2017 [2]. Such rapid
increases in network traffic will require optical network systems, especially long-haul and metropolitanarea systems that concentrate data traffic, to accommodate the yearly increases with flexibility, efficiency, and economy.
The latest optical transport technologies achieveultrahigh-speed communication at 100 Gbit/s on asingle channel using digital coherent technology by
combining coherent transmission, which uses wave
properties widely used in wireless networking, anddigital signal processing (DSP) technology [3]. In
addition to conventional high-density optical wavelength division multiplexing (WDM), which uses
fixed frequency intervals, research has begun on theuse of optical frequencies with higher information
density for high-capacity, ultrahigh-speed optical
network systems [4].
2. Advanced optical node technology for
optical networks
2.1 WDM technology
Similarly, optical cross-connect technology uses
high-density WDM technology to achieve flexible
and economical optical networking systems. Thechanges in optical network system architectures over
the years are shown in Fig. 3. These networks beganwith point-to-point connections, which realized highcapacity through optical signal WDM, and progressed
NTT Technical Review

Feature Articles(Gbit/s)
1800
1600

Total IP traffic

1400

Traffic

1200
1000
800
600
400
200
0

2007.5 2007.11 2008.5 2008.11 2009.5 2009.11 2010.5 2010.11 2011.5 2011.11
Source: MIC FY2012 Information and Communications White Paper
FY: fiscal year
IP: Internet protocol
MIC: Ministry of Internal Affairs and Communications

Fig. 1. Internet traffic in Japan.

(PB/mo.)80,00070,000

MetroLong haul

2012

2013

Traffic

60,00050,00040,00030,00020,00010,000
0

2014

2015

PB: petabytes
VNI: Visual Networking Index

2016
2017
Source: Cisco VNI 2013

Fig. 2. Global Internet traffic.

through single-ring configurations using reconfigurable optical add/drop multiplexers (ROADM) able to
add and drop individual optical signals, to the current
economical optical network systems in multi-ring
configurations using multi-degree ROADM.
An illustration of ROADM is shown in Fig. 4. Input
optical signals can be dropped or added, and paths
can be selected without converting optical signals toelectrical signals. This allows ring network systems
to be constructed economically. An example of abasic two-path ROADM configuration is shown in
Vol. 12 No. 1 Jan. 2014

Fig. 4(a). Optical multiplexers and demultiplexers
separate multiple wavelengths, and an optical switch
adds or drops signals according to the wavelength.
Signals can be added and dropped without convertingthem from optical to electrical, enabling high-capacity optical paths to be provided economically. The
optical switches used for ROADM use quartz planar
lightwave circuit (PLC) technology, which was firstused in components such as optical multiplexers,
demultiplexers, and splitters, and is very reliable
since there are no moving mechanical parts [5].
Feature Articles

Functionality utilizing optical characteristics

100G/T
Multidegree
ROADM

d
ee

40G/100G

sp

ROADM
ROADM

ROADM

ROADM

Multidegree
ROADM

ROADM

10G/40G

Multidegree
ROADM

Multidegree
ROADM

pa

a
rc

he

Hig

/
city

Multidegree
ROADM

Multidegree
ROADM

Multidegree
ROADM
Mesh

ROADM

ROADM

Multi-ring
ROADM

ROADM

ROADM

2.5G/10G

ROADM

ROADM

Ring

rk

o
etw

v

ad

t
en

em

c
an

N

DWDM
Point-to-point
2000

2005

2010

Time

2015

Fig. 3. Optical Network Development.

Demultiplexer

Add/drop
Multiplexer
optical switch
Optical fiber
Optical fiberPathconfiguration
function

CDC-less function(in transponder)

Transponder
Variable wavelengthtransponder(a) Two-path ROADM configuration example(b) Multi-path ROADM configuration example
CDC: colorless, directionless, and contentionlessFig. 4. ROADM configuration examples.

NTT Technical Review

Feature Articles

2.2 CDC technology
An example of a multi-port ROADM configuration
implementing a multi-ring mesh network is illustrated in Fig. 4(b). As shown in the figure, with multiport ROADM, signals carried by multi-path fibers are
not converted to electrical signals, and paths can bechanged, dropped, or added (optical cross-connect
operations) according to wavelength. Currently, in
addition to path changes, drops, and adds, even moreadvanced optical cross-connect operations using
ROADM are being studied. With ROADM thus far,
the wavelength or path has been fixed for each trans­
ponder (the optical transmit/receive interface). Colorless, directionless, and contentionless (CDC) functions are being studied that will enable implementation of flexible and economical network systems inwhich wavelengths and paths can be configured
freely, faults can be switched out by wavelength, andoptical paths can be configured remotely. ROADM
using CDC functions is called CDC-ROADM. Here,colorless refers to functionality that allows input andoutput wavelengths on ports to be allocated freely
through the addition of a variable wavelength function to the demultiplexing and multiplexing filters.
The transponder wavelengths can be changed without
having to physically switch connections. Directionless refers to functionality whereby the directions of
input and output paths can be configured freely rather
than being fixed by creating switches comprised oftransponders. Contentionless refers to functionality
in optical nodes implementing the previous two functions whereby any wavelength can be allocated toother paths with no restrictions on wavelength configuration. These functions enable signals to be configured freely. CDC-ROADM is described in detailwith configuration examples implementing this functionality in the Feature Article entitled, “Next-generation Optical Switch Technologies for Realizing
ROADM with More Flexible Functions [6].”2.3 WSS technology
Currently, the main device used in multi-degree
ROADM as a path-configurable switch is the wavelength selective switch (WSS) utilizing spatial optics
technology. Wavelength-multiplexed input signals
are demultiplexed using a diffraction grating, andadd, drop, and path selection operations are implemented without converting signals from optical toelectrical. This is done using spatial light modulatorssuch as microelectromechanical systems (MEMS)
mirrors or liquid crystal on silicon (LCOS) devices toconfigure paths by wavelength. It is now possible toVol. 12 No. 1 Jan. 2014

implement multi-path path selection using MEMS
mirrors or LCOS, and multi-ring optical networks
have been implemented with the development of this
optical switching technology. Details of WSS are
introduced in the Feature Article entitled, “WSS
Module Technology for Advanced ROADM [7].”Several methods for implementing CDC functionality have been studied. One such method uses multicast switches using PLCs; these switches have asimple structure that can be implemented in compact
form. The Feature Article entitled, “Multicast Switch
Technology that Enhances ROADM Operability [8],”introduces the functions enabled in transponders.
3. Topics covered in Feature Articles
As discussed above, advances in ROADM are necessary in order to implement networks that are able todeal with the increasing traffic flexibly and economically. Currently, NTT Network Innovation Laboratories, NTT Microsystem Integration Laboratories, and
NTT Photonics Laboratories are collaborating on
optical-switch R&D in order to realize highly
advanced ROADM. These Feature Articles introduce
the initiatives underway at these three laboratories.
First, CDC-ROADM, which is necessary for highly
operable and reliable optical networks, is describedusing practical examples. Then, WSS, which realizes
the per-wavelength path configuration function of
ROADM, is introduced. MEMS WSS is taken as an
example of WSS, and technologies required to implement it are explained, including optical design,
implementation design, and control function technologies. Finally, we describe a multicast switch
technology that uses PLC technology to implement
CDC functions.
References
[1]
[2]

[3]

[4]

[5]

FY2012 Information and Communications White Paper by Ministryof Internal Affairs and Communications (in Japanese).
http://www.soumu.go.jp/johotsusintokei/whitepaper/ja/h24/
Cisco Visual Networking Index (VNI): Forecast and Methodology:
2012–2017 (in Japanese).
http://www.cisco.com/web/JP/solution/isp/ipngn/literature/white_
paper_c11-481360.html
S. Matsuoka, “Ultrahigh-speed Ultrahigh-capacity Transport Network Technology for Cost-effective Core and Metro Networks,” NTT
Technical Review, Vol. 9, No. 8, 2011.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2011
08fa1.html
M. Jinno, H. Takara, B. Kozicki, Y. Tsukishima, Y. Sone, and S.
Matsuoka, “Spectrum-efficient and scalable elastic optical path network: architecture, benefits, and enabling technologies,” IEEE
Comm. Mag., Vol. 47, No. 11, pp. 66–73, Nov. 2009.
T. Watanabe, “Silica-based PLC optical switches designed andFeature Articles

[6]

[7]

fabricated for OADM and OXC,” Proc. of the 9th Optoelectronics andCommunications Conference/3rd Conference on Optical Internet(OECC/COIN 2004), Paper 13F2-3.
Y. Sakamaki, T. Kawai, and M. Fukutoku, “Next-generation Optical
Switch Technologies for Realizing ROADM with More Flexible
Functions,” NTT Technical Review, Vol. 12, No. 1, 2014.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2014
01fa6.html
Y. Ishii, N. Ooba, A. Sahara, and K. Hadama, “WSS Module Technol-

Mitsunori Fukutoku

Senior Research Engineer, Supervisor, Photonic Transport Network Laboratory, NTT Network Innovation Laboratories.
He received the B.S. and M.S. degrees from
Tokushima University in 1989 and 1991, respectively. In 1991, he joined NTT Transmission
Systems Laboratories, where he engaged in R&D
of optical WDM systems. In 2000, he moved to
NTT Communications, where he engaged in
WDM network planning. He jointed NTT Network Innovation Laboratories in 2009.

Yasuhiro Sato

Senior Manager, Network Hardware Integration Laboratory, NTT Microsystem Integration
Laboratories.
He received the B.S., M.S., and Dr.Sci. degrees
in chemistry from the University of Tokyo in
1987, 1989, and 2004, respectively. In 1989, hejoined NTT LSI Laboratories, Atsugi. He
engaged in research on LSI interconnection technology, ultrathin-film CMOS/SOI process integration for low power applications, low-power
communication appliances for ubiquitous services, ultra-high speed millimeter wave wirelesscommunication technology, and MEMS technology for telecommunication applications. He iscurrently conducting research on wavelength
selective switches, silicon photonics, and wearable sensor technology. He is a member of theJapan Society of Applied Physics (JSAP), theInstitute of Electronics, Information and Communication Engineers (IEICE), and IEEE.

[8]

ogy for Advanced ROADM,” NTT Technical Review, Vol. 12, No. 1,
2014.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2014
01fa7.html
T. Watanabe, K. Suzuki, and T. Takahashi, “Multicast Switch Technology that Enhances ROADM Operability,” NTT Technical Review,Vol. 12, No. 1, 2014.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2014
01fa8.html

Senichi Suzuki

Vice President of NTT Photonics Laboratories.
He received the B.E., M.S., and Ph.D. degrees
in electrical engineering from Yokohama National University, Kanagawa, in 1984, 1986, and1995, respectively. In 1986, he joined NTT Electrical Communication Laboratories, Musashino,
Tokyo, where he engaged in research on photonic components and guided wave opticalresearch. He subsequently investigated silicabased planar lightwave circuits and their applications to functional and dynamic photonic components and modules. He received the Electronics
Society Award in 2010 and the Achievement
Award in 2013 from IEICE. He is an IEEE Fellow, a senior member of IEICE and a member of
JSAP.

NTT Technical Review

Feature Articles: Optical Node and Switch Technologies
for Implementing Flexible and Economical Networks

Next-generation Optical Switch
Technologies for Realizing ROADM
with More Flexible Functions
Yohei Sakamaki, Takeshi Kawai, and Mitsunori Fukutoku
Abstract

Colorless, directionless, and contentionless reconfigurable optical add/drop multiplexing (CDCROADM) has been attracting considerable attention recently for its potential use in constructing costeffective photonics transport networks in long-haul and metro area transmission systems and improving
their operational flexibility. This article describes the latest trends in the research and development of
optical switch technologies for realizing CDC-ROADM.
Keywords: ROADM, optical switch, WSS

1. Overview of multi-degree ROADM
Reconfigurable optical add/drop multiplexing(ROADM) has brought new flexibility and scalability
to conventional static photonic transport networks.
Multi-degree ROADM was developed after the introduction of basic 2-degree ROADM in order to realize
mesh-based network topologies [1].
We first describe here the multi-degree ROADM
node configuration. A 4-degree ROADM node configuration connecting two ring networks is shown in
Fig. 1 as an example. The incoming wavelength-division-multiplexing (WDM) signals from the degree-1
input fiber are delivered to the drop-side opticalswitch. If these signals are to be transferred to other
ROADM nodes, the optical switch selects the optical
path to degree 2 (red line), degree 3 (orange line), or
degree 4 (green line) for each wavelength signal.
When the transponders at this node receive these signals, the optical switch selects the drop path (purpleline) to deliver the signals to another optical switch,
namely a transponder aggregator (TPA). Then, the
TPA allocates the input signals to each desired transponder for each wavelength channel. On the addside, the output signal from the transponder is routed
to an add-side optical switch by way of an add-side
TPA. The add-side optical switch collects add signals
and signals that pass through this node and thenlaunches them into the output fiber.
Today, in addition to the multi-degree function,colorless, directionless, and contentionless (CDC)
functions are expected to play important roles inachieving more flexibility in terms of wavelength
routing and wavelength assignment [2].
2. Optical switch technologies for realizing
CDC-ROADM
Next, we describe in detail the optical switch technologies required for constructing a CDC-ROADM
node.
2.1 Colorless function
The freedom provided by the colorless function isthat the optical signal wavelength is not fixed by thephysical input/output port of the TPA and can be set
using software control. The colorless function isshown in Fig. 2 in more detail. Note that the figure
shows the optical switches of degrees 1 and 3 extracted from Fig. 1(b).
The switch structure of the TPA without the colorless function is shown in Fig. 2(a). To connect the
optical paths of the WDM signals between the input/
output fibers of each degree and the transponders at
NTT Technical Review

Feature Articles(a)Ring A

4-deg. ROADM
Deg. 2

Ring B
Deg. 32-deg. ROADM
Deg. 4Deg.1(b)Deg. 2Rx
SW Drop-side switch

Tx

…

Tx
Tx

…

SW SW

Tx
…
Tx
Tx

Rx
Rx

…

Rx
Rx

Rx

Drop path

SW SW

Deg. 1SW SW

Drop-side TPA
Deg. 3Rx

ReceiverSW Add-side switch

Tx

…

…
Rx

Rx
Rx

Tx
Tx

…

Tx
Tx

Tx

Rx
Rx

Rx

Add-side TPA
…

SW SW

Transmitter

Tx

Deg. 4

Fig. 1. (a) Example of multi-ring network and (b) 4-degree node configuration.

Rx

…

Rx
Rx

Tx

…

Tx
Tx

Rx

…

Rx
Rx

Tx

…

Tx
Tx

Rx
Rx

Rx

…

Receiver 1
AWG

λ1

AWG

SW

λ1

SW

SW
Transmitter 1

Rx
Rx

Rx

…

(b)

Tx
Tx

Tx

…

Receiver 1

SW

WSS

λ1

WSS

SW

λ1

SW

SW
Transmitter 1
…

Tx
Tx

Tx

Vol. 12 No. 1 Jan. 2014

(a)

SW

the ROADM nodes, the TPA must select the signal
path to the desired transponder for each wavelength
channel. Since a conventional TPA consists of anarrayed-waveguide grating (AWG) where the output
port assignment is determined by the wavelength ofthe optical signal, the signal wavelength of the transponder is also determined by the port connected to
the TPA. This switch structure causes certain problems with respect to operation. For example, if thesignal wavelength of the transponder needs to bechanged from λ1 to λ2 to deal with a traffic change,
the connection port of the TPA must also be changed.
This connection port change involves tasks that mustbe performed manually in the field at the site where
the node equipment is located, and this reduces theflexibility of the network operation.
This restriction can be lifted by using a wavelengthselective switch (WSS) instead of an AWG at the
TPA. The switch structure of the colorless TPA isshown in Fig. 2(b). The WSS can deliver the input
WDM signals to any output port for each wavelength
channel. Moreover, these output port assignments canbe changed under software control. Therefore, byFig. 2. (a) Colored TPA and (b) colorless TPA.



Feature Articles

…

Rx
Rx

…

Rx
Rx

Rx

Rx
Rx

Rx

…

Rx

(a)

(a)

Receiver 1

Receiver 1

Receiver 2
WSS1
WSS2
SW
SW

SW

SW

SW

SW

SW
WSS

SW

WSS

Transmitter 1

WSS2
WSS1

Transmitter 1
Tx

…

Tx
Tx

Transmitter 2

Rx

…

Rx
Rx

Receiver 2

Rx
Rx

Rx

…

…

Tx
Tx

(b)

Tx

Tx
Tx

Tx

…

Receiver 1

(b)

WSS1
WSS2

Receiver 1

SW

SW

SW

SW

SW

WSS2

SW

SW

SW

N × M-WSS

WSS1

Transmitter 1
Tx
Tx

Tx

…

N × M-WSS

Transmitter 1
Tx
Tx

Tx

…

Transmitter 2

Fig. 3. (a) Directed TPA and (b) directionless TPA.
Fig. 4. (a) Contention TPA and (b) contentionless TPA.

using the WSS, we can change the wavelength pathsetting without having to do any work in the field.
This added function is called colorless because thepath between the transponders and the input/output
fiber is not fixed by the wavelength (= color) of the
optical signal.
2.2 Directionless function
A directionless function provides the freedom toconnect the signal path from the transponder to any
input/output fiber by connecting the TPA to every
degree of the ROADM node. The switch structure of
the directed TPA is shown in Fig. 3(a). Since commercially available WSSs have a 1 × N switch structure, the signal path from the transponder can beconnected to only one input/output degree. This
restriction presents no problem for a conventional 2degree ROADM, but it imposes an operational limitation on a multi-degree ROADM.
As shown in Fig. 3(b), the opposite WSSs provide
a way to overcome this restriction. WSS1 aggregatesthe signals from the transmitters (or to the receivers),
and then WSS2 connects them to the desired input/
output fiber for each wavelength channel. This addedfunction is referred to as directionless. The directionless function provides numerous benefits. For example, a colorless and directionless ROADM allows
spare transponders to be shared among all the wavelength channels and degrees in the node.
2.3 Contentionless function
A contentionless function removes the wavelength
restriction from the TPA. This function allows multiple wavelength channels of the same wavelength at asingle TPA. Thus, a transponder can be assigned to
any wavelength as long as the number of wavelength
channels with the same wavelength does not exceed
the number of degrees.
The switch structure of a TPA with colorless anddirectionless functions and CDC functions are shownin Figs. 4(a) and (b), respectively. In Fig. 4(a), multiple wavelength channels with the same wavelength
cannot be input because a single fiber connects two
WSSs (WSS1 and WSS2). This TPA structure imposes a restriction; that is, when the path of an opticalsignal with a wavelength of λ1 is connected between
transponder 1 and the input/output 1-degree fiber, thepath of the signal with a wavelength of λ1 cannot be
connected between transponder 2 and any input/output fibers, even those other than the 1-degree fiber.
The contentionless function removes thisNTT Technical Review

Feature Articles

wavelength restriction from the TPA. A TPA with thecontentionless function is shown in Fig. 4(b). To realize this function, we expect to see the development of
an M × N WSS, where one of the M input ports canbe connected to any of the N output ports. However,
M × N WSSs are not yet commercially available
because of the high level of difficulty involved inachieving them. Thus, multi-cast switches have been
attracting considerable attention as an alternative.
3. Recent trends in WSS development
Next, we provide a brief introduction to recent
R&D activities related to the development of the
WSS, which is essential if we are to realize CDCROADM.
(1)	High port count: We must increase the numberof output ports of the WSS if we are to increase
the number of degrees and transponders in the
ROADM node. The 1 × 2 and 1 × 4 WSSs weredeveloped at an early stage, and the 1 × 9 WSS
is now commercially available. To realize alarge-scale node such as that required for 8degree ROADM, a target of 20 or more output
ports is expected.
(2)	Downsizing: The equipment size increases as
the number of optical switches in the ROADM
nodes increases. Thus, downsizing the WSS
module is an important issue in terms of realizing more functional nodes within a limited
equipment size. Now, the realization of a twoin-one concept whereby a single module has thesame functionality as two separate WSSs has
become the development goal.
(3)	Performance improvement (wider bandwidthand lower insertion loss): Successive opticalfiltering as a result of cascading ROADM nodes
with the WSS has led to a reduction in the available bandwidth and an increase in optical signal
loss. This performance degradation becomes
more significant with increases in the number of
WSSs that an optical signal passes through.
Therefore, to suppress the degradation effectcaused by introducing CDC functions into
ROADM nodes, it is important to improve such
optical characteristics as the bandwidth and theinsertion loss of a single WSS. For example, wemust achieve a wider bandwidth so that the performance degradation caused by filtering can bealmost halved compared with that of a conventional WSS.
(4)	Flex grid: The elastic optical network has beenVol. 12 No. 1 Jan. 2014

attracting considerable attention regarding theconstruction of next-generation optical communication systems with higher spectral efficiencies [3], and there has been extensive researchand development activity with a view to achieving this concept. In such networks, it is essential
to realize a flex grid where the frequency bandwidth occupied by a single wavelength channel
can be flexibly adjusted. Thus, it is also necessary for the WSS to be able to adjust the channel
bandwidth during operation.
4. Activities of NTT laboratories
Finally, we describe the recent activities of NTT
laboratories in relation to CDC-ROADM. We proposed a CDC-ROADM node configuration composedof a 1 × 43 WSS and an 8 × 12 MCS based on silicabased planar lightwave circuit (PLC) technology.
These optical switches were first developed in ourlaboratories. Our proposed approach will contributeto a substantial reduction in the size and cost of the
CDC-ROADM node equipment. In addition, we
reported the results of a transmission experimentshowing that the introduction of these optical switches imposed no significant penalty on 100G PDMQPSK (polarization-division-multiplexing quadrature phase-shift keying) signal transmission systems[4].
5. Future development
The traffic generated by the expanding use ofvarious new services continues to increase. To deal
with the larger amounts of traffic while maintaining
or lowering network costs, we need to ensure that
ROADM nodes to achieve greater flexibility, forexample, by providing a CDC function. Meanwhile,
to satisfy the various demands caused by the extension of the ROADM application range, it is importantto achieve the optimal balance between node scaleand cost. Thus, optical switches with more input/output ports and flexible connections will play importantroles in achieving such optical nodes. In the future,
we believe that the sophistication and miniaturization
realized by integrating additional functions such as
optical channel monitoring into optical switches will
steadily progress once a WSS with a higher port
count or an M × N WSS becomes commercially available.

Feature Articles

References
[1]

[2]

E. B. Basch, R. Egorov, S. Gringeri, and S. Elby, “Architectural trade­
offs for reconfigurable dense wavelength-division multiplexing systems,” IEEE J. Sel. Topics Quantum Electron, Vol. 12, No. 4, pp.
615–626, July/August 2006.
S. Gringeri, B. Basch, V. Shukla, R. Egorov, and T. J. Xia, “Flexible
architectures for optical transport nodes and networks,” IEEE Commun. Mag., Vol. 48, No. 7, pp. 40–50, 2010.

Yohei Sakamaki

Research Engineer, Photonics Integration
Laboratory, NTT Photonics Laboratories.
He received the B.E. and M.E. degrees in material science and engineering from Kyoto University in 2002 and 2004, respectively and the Ph.D.
degree in electrical and electronic engineeringfrom Tokyo Institute of Technology in 2010. In
2004, he joined NTT Photonics Laboratories,
where he engaged in research on optical waveguide design using the wavefront matching
method. He then participated in a project related
to the development of optical receiver modules
such as silica-waveguide DQPSK demodulatorsand dual-polarization optical hybrids for digital
coherent detection. From 2010 to 2012, he was a
researcher at NTT Network Innovation Laboratories, where he studied the architecture of multidegree CDC-ROADM and arrayed optical amplifiers in ROADM nodes. He is currently engaged
in the development of optical components fornext-generation optical fiber communication
systems.



[3]

[4]

M. Jinno, H. Takara, B. Kozicki, Y. Tsukishima, Y. Sone, and S. Matsuoka, “Spectrum-efficient and scalable elastic optical path network:
Architecture, benefits, and enabling technologies,” IEEE Comm.
Mag., Vol. 47, No. 11, pp. 66–73, 2009.
Y. Sakamaki, T. Kawai, T. Komukai, M. Fukutoku, T. Kataoka, T.
Watanabe, and Y. Ishii, “Experimental demonstration of multi-degreecolorless, directionless, contentionless ROADM for 127-Gbit/s PDMQPSK transmission system,” Optics Express, Vol. 19, No. 26, pp.
B1–B11, 2011.

Takeshi Kawai

Research engineer, Photonic Transport Network Laboratory, NTT Network Innovation
Laboratories.
He received the B.E., M.E., and Dr.Eng.
degrees in electronics information engineeringfrom Nagoya University, Aichi, in 1990, 1992,
and 1995, respectively. In 1995, he joined NTT
Optical Network Systems Laboratories, where heengaged in research on optical network systems.
He is currently working on R&D of next-generation optical fiber communication systems. He isa member of the Institute of Electronics, Information and Communication Engineers andIEEE.

Mitsunori Fukutoku

Senior Research Engineer, Supervisor, Photonic Transport Network Laboratory, NTT Network Innovation Laboratories.
He received the B.S. and M.S. degrees from
Tokushima University in 1989 and 1991, respectively. In 1991, he joined NTT Transmission
Systems Laboratories, where he engaged in R&D
of optical WDM systems. In 2000, he moved to
NTT Communications, where he engaged in
WDM network planning. He jointed NTT Network Innovation Laboratories in 2009.

NTT Technical Review

Feature Articles: Optical Node and Switch Technologies
for Implementing Flexible and Economical Networks

WSS Module Technology for
Advanced ROADM
Yuzo Ishii, Naoki Ooba, Akio Sahara,
and Koichi Hadama
Abstract

Wavelength selective switches (WSSs) are the key to implementing advanced reconfigurable optical
add/drop multiplexing (ROADM) with colorless- directionless-contentionless (CDC) functionality, but
a complex module (subsystem) requires a skillful balance combining optical, mechanical, and control
design technologies. This article discusses technical issues in implementing WSS from optical, mechanical, and control perspectives.
Keywords: WSS, MEMS, LCOS

1. Introduction
Wavelength selective switches (WSSs) are components used in wavelength division multiplexing(WDM) optical networks to route signals between
optical fibers according to wavelength. The basic
functions of WSSs are shown in Fig. 1. The mainfunctions are switching by port switches, which areconnected to output ports for each wavelength in the
input WDM signal, and attenuation, in which thepower level of transmitted light is adjusted for eachwavelength. The hardware is divided into an optics
module and a control module. A WSS has many input
and output ports, so a bulk diffraction grating is used,which is able to multiplex and demultiplex signals at
the same time in a single port. Active elements
include a spatial light modulator device, for example,
a microelectromechanical systems (MEMS) mirror[1], or a liquid crystal on silicon (LCOS) device,
which can change the reflected direction of the input
light beam. Beam pathways are different for eachcombination of wavelength and port, so beams crosseach other within the WSS optical module. All ofthese pathways must be stable and have low losses, so
the design of beam paths and spatial light modulator
drivers and controls is very important in implementing appropriate attenuation. In addition to driving andcontrolling the switching element (spatial light mod

ulator), the control module must detect module faults
and errors, perform monitoring and control for coordination with higher-level systems, and provide auser interface.
Technical issues in implementing WSSs are discussed below from the perspectives of optical,
mechanical, and control (electronic monitoring andcontrol) design.
2. WSS technical issues
2.1 Optical design
The optical system for a WSS can be broadly
divided into two sections: the wavelength section,
which separates the input wavelengths using a diffraction grating, and the switch section, with its arrayof ports. The wavelength section design is basically aconfocal optical system with the beam waists of thefiber end and MEMS mirror (or LCOS device) end.
Wavelengths are separated spatially, so the configuration is similar to a high-resolution spectrometer. To
achieve a wide transmission bandwidth, the beam
diameter must be small at the MEMS mirror. However, this also reduces the depth of focus, so a meniscus lens or prism can be added for image correction.
The switch section design differs depending on thetype of switch element used. A comparison between
MEMS mirrors and an LCOS device is shown in
NTT Technical Review

Feature Articles

Optics module

Output port #1

Common port
Output port #2

Switch element

Output port #N

Control module- Switch element control (port switch, attenuation, etc.)- Monitoring control

Fig. 1. Basic functionality of WSS.

Fig. 2. With MEMS mirrors, it is more difficult toincrease the size of the MEMS mirrors than to achievea larger rotation angle, so the optical system for theswitch section is divided into a front end and a backend. The front end generates a beam diameter thatsuits the size of the MEMS mirror. A confocal opticalsystem, symmetric on either side of the diffraction
grating, is generally used for the back end. For attenuation, optical axes are intentionally offset by rotating the MEMS mirror perpendicular to the switch
face (wavelength face).
By contrast, with an LCOS device, instead of theadvantage of providing a large reflection surface on
the order of millimeters, the device generates diffraction losses (excessive losses) using a large diffraction
angle. Thus, when an LCOS device is used, theswitch section can be implemented with just a 2-f
optical system* for the front end. This configuration
may seem simple, but it is inseparable from the wavelength section, so there are many design constraints.
LCOS devices are also polarization dependent, which
presents other difficulties such as the need for a polarization diversity configuration.
With these forms used as a base, an optimal design
must satisfy WSS performance specifications (number of ports, bandwidth, losses, cross-talk, size, etc.),
while considering switch element characteristics(rotation angle, size, losses, etc.). Lens and opticalsystem aberrations are related to the dependence ofVol. 12 No. 1 Jan. 2014

losses and bandwidth on wavelength and port, andresidual stray light causes degradation due to transmission ripple and cross-talk. Aberration and straylight are therefore significant problems. When thenumber of ports is increased in the future, there will
be room to work with the arrangement of the ports,
and configurations such as 2D port arrangements
have been proposed. There are also other devices
besides the MEMS mirrors and LCOS devices discussed above that can be used as switch elements, forexample, digital micro-mirror devices and transmission-type LCDs (liquid crystal displays). LCOS andDMD devices are composed of small pixel elements,
so they are suitable for FlexGrid applications.
2.2 Optical module design
The optical module is composed of optical components such as lenses and switch elements, as well asmechanical components for maintaining highly accurate positioning of the optical components.
The shape and position of the optical components
were determined through simulation in order toachieve the desired optical design characteristics. To
implement these characteristics at the module level,*	2-f optical system: An optical system with the front focal point of
the lens at the object, and the back focal point at the image plane.
If the fiber array is aligned parallel to the optical axis on the object plane so it intersects the image plane, then it is also an optical system that converts between position and angle.

Feature Articles

MEMS mirrors
Port
Port lens

MEMS mirror

Front end

VOA

LCOS

Ap
pr
ox
.2
00
–5
00

Features:- Beam diameter suited to the size of MEMS mirrors can begenerated in the front end, so the switch section (front end) andwavelength section (back end) can be designed separately.
- Module height is determined by the diffraction grating (back end).

µm

Port switch

LCOS
Port lens

0–
.1
ox
pr
Ap

Features:- Can be configured with only a position/angle varying
system (2-f); many design constraints because design
cannot be separated from the wavelength section

20

m

m

Fiber
Polarization separation
collimator

Fig. 2. Comparison of optical systems used for switch section.

the production variances and accuracy of alignment
in assembly are verified and are taken into consideration while designing the configuration and assembly
procedures. Also, in order to achieve the high wavelength accuracy and stable transmission characteristics needed for the WSS, a final process had to beplanned. This process involved aligning the element
positions and checking the characteristics while actually passing light through the system, and then fixing
the positions.
In theory, a WSS is a three-dimensional (3D) optical system that must be of sufficient size and that has
light paths expanding in both the wavelength andswitch axis directions. However, in actual devices,reflective mirrors are used to fold up the light paths
and achieve a compact design configuration. Reducing the size of the optical system not only reduces thesize and weight of the module, it is also important forincreasing the mechanical strength, reducing dependencies on environmental factors, and maintaining
stable optical characteristics. A schematic diagram of
the 1 × 9 WSS optical module developed by NTT isshown in Fig. 3. A compact and stable module is
implemented by arranging each optical element in 3D
on an alloy block with a low thermal-expansion coefficient.
The WSS module is built as a hermetically sealed
structure for two reasons. The first is that the refractive index of air is dependent on environmental factors such as air temperature and pressure, and this cancause fluctuations in the diffraction angles of the diffraction grating, and thus, in the WSS channel wavelengths. Creating a hermetically sealed structure fixes
the air density and controls the channel wavelength
fluctuation within the level needed for current highdensity WDM systems. The second reason is thatchanges in internal humidity can reduce the reliability of MEMS mirrors or LCOS switch elements. By
maintaining low internal humidity in the structure,
the high stability and reliability required of a telecommunication device can be maintained, even whenused in high-temperature environments.
Also, when MEMS mirrors are used, the characteristics can fluctuate due to its structural resonances,
and anti-vibration structures such as rubber dampers
must be used to prevent damage. For the 1 × 9 WSS
using MEMS mirrors, hermetically sealed conditions
for the optical module were achieved by fixing it in ahermetic case with a rubber damper, fixing the coverto the hermetic case using welding techniques, andpassing input/output fibers and MEMS driver electrical terminals through a solder seal.
2.3 Electrical monitoring and control
Electrical monitoring and control drives andcontrols the active elements of the optical module
NTT Technical Review

Feature Articles

Folding mirrors

Input/output fiber
Image plane correction lensMain lens

Folding prism
Fiber collimator array

Front end
MEMS mirror

Diffraction grating
Folding mirror

Wave plate
Light path

Fig. 3. Internal structure of WSS optical module.

Electrical connector

Wavelength selective switch

Non-volatilememoryUser-IF (DPRAM)
Reset (Warm/Cold)

Power Voltage
source generator

Control section (processor) functions(1) Path configuration
Configures the connection
paths for each opticalchannel(2) Light level control
Adjusts the output level foreach optical channel(3) Shutdown
Switches the output level of
any optical channel to OFF(4) Fault/error monitoring
Detects faults or errors
within the module, andnotifies the user with alarms(5) Reset
Able to restart the control
section only, withoutchanging the state of the
optical switch (without
interrupting the opticalsignals passing through theoptical switch), and able torestart the control section,
including the states of the
optical switch(6) Firmware download
Able to upgrade the control
firmware within the module
without changing the stateof the optical switch

VolatilememoryADC

Temp.
sensorDAC

Optical switch
section

ADC: analog-to-digital conversion
DAC: digital-to-analog conversion
DPRAM: dual-ported random access memory
IF: interface

VoltagemonitorFig. 4. WSS module control structure.

(the spatial light modulator), and also detects any
faults or errors in the module, provides the monitoring and control required for linking with higher-levelsystems, and controls the user interface.
The overall control structure of the WSS module isshown in Fig. 4. This module is composed of a control process, a voltage generator/monitor section,
volatile and nonvolatile memory, temperature senVol. 12 No. 1 Jan. 2014

sors, and other components, which are used to control
the optical module described above (optical switch in
the diagram). The control processor performs control
processing for the switch device in the optical module(MEMS mirror or LCOS device) and also processes
control signals such as resets or commands sent by
the user, monitors for faults or errors in the WSS
module, and notifies the user if any such fault or errorFeature Articles

Table 1. WSS module fault/error monitoring items.
(i) Command error

Monitors whether or not commands sent by the user can be processed correctly by the module(ii) Temperature anomalies

Monitors whether the temperature has exceeded the range in which the module can operatecorrectly, whether due to external or internal causes(iii) Firmware error

Monitors whether any errors occur when new control firmware is downloaded(iv) Hardware fault

Monitors for faults in components within the module (memory, control components, sensors, power
circuits, ADC, etc.)(v) Data error

Monitors whether data values used in control section have changed from their original values due
to hardware fault, software error, or other cause

Table 2. Severity for user when faults/errors occur.
(1) Requires module to bechangedWhen a hardware fault or other issue cannot be resolved while the user isusing the module(2) Resolvable with operations by When the issue can be resolved by having the user send commands, suchthe useras when a command error occurs(3) No user operations required

When the software is able to resolve the error within the module itself, as
when there is a data abnormality due to a software error

occurs in the module. Communication with the user(commands, reset, alarms, etc.) occurs through theelectrical connectors.
Control in the WSS module is divided into six functions: (1) Path configuration, (2) Light level control,(3) Shutdown, (4) Fault/error detection, (5) Reset,and (6) Firmware download (Fig. 4).
Implementing monitoring functions as a subsystemof the WSS module is important, and the fault/error
monitoring functions are described in detail below.
The WSS control module monitors fault/error items
including: command errors, temperature anomalies,
firmware errors, hardware faults, and data errors(Table 1).
If a fault or error occurs while the WSS module isoperating, the effects on the user are categorized into
one of three levels (Table 2).
- The module must be changed-	The issue can be resolved through user operations- The issue does not require user intervention
Thus, when a fault or error occurs, it is important toconsider the effect of the problem on the user as
described here when determining what sort of alarmor notification will be sent to the user.
3. Future prospects

mented by combining a wide range of technologies.
For example, even for the thermal characteristics
alone, it was necessary to coordinate a wide range ofdesign techniques. These included optical design toconsider how the refractive index of glass depends on
temperature, mechanical design to consider the thermal deformation of parts and the effects of environmental changes, and control design to compensate fortemperature issues.
In the future, it will be necessary to further increase
the bandwidth and number of ports for the WSS, anda much greater level of coordination will be necessary. Regarding the FlexGrid, a WSS using an LCOS
device has been progressing, but while it is possible
to control an LCOS device at the pixel level, drivercontrol at that level is very complex. Manufacturingthat is able to skillfully coordinate optical, mechanical, and control design techniques is expected to drive
the development of ROADM with CDC functionality.
Reference[1]

J. Yamaguchi, T. Sakata, N. Shimoyama, H. Ishii, F. Shimokawa, andT. Yamamoto, “High-yield Fabrication Methods for MEMS Tilt Mirror Array for Optical Switches,” NTT Technical Review, Vol. 5, No.
10, 2007https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2007
10sp5.html

As discussed above, the WSS module was imple-



NTT Technical Review

Feature Articles

Yuzo Ishii

Engineering Assistant Manager, Technology
Development Center, NTT Electronics Corporation.
He received the B.S., M.S., and Ph.D. degrees
in precision machinery engineering from the
University of Tokyo in 1995, 1997, and 2005,
respectively. In 1997, he joined NTT Optoelectronics Laboratories, where he engaged inresearch on microoptics for chip-to-chip opticalinterconnection. During 2005–2006, he was avisiting researcher at Vrije University in Brussels, Belgium. In 2006, he began developing awavelength selective switch using MEMS technology. He moved to NTT Electronics Corporation in 2013. He received the Microoptics Conference Best Paper Award in 1999. He is a member of the Japan Society of Applied Physics(JSAP).

Naoki Ooba

Engineering Assistant Manager, Technology
Development Center, NTT Electronics Corporation.
He received the B.E. and M.E. degrees inchemical engineering from the University ofTokyo for work on oxide superconductors in1987 and 1989, respectively. In 1989, he joined
NTT Optoelectronics Laboratories, where he
was involved in developing nonlinear opticalmaterials and polymer waveguides. He workedon the development of optical components using
PLC and free space optics technologies at NTT
Photonics Laboratories. He moved to NTT Electronics Corporation in 2012. He is a member of
JSAP and the Institute of Electronics, Information and Communication Engineers (IEICE).

Vol. 12 No. 1 Jan. 2014

Akio Sahara

Project Leader, Optical Communication Systems Business Unit, Broadband System &Device Business Group, NTT Electronics Corporation.
He received the B.S., M.S., and Ph.D. degrees
in electrical engineering from Kyoto University
in 1992, 1994, and 2003, respectively. He joined
NTT in 1994 and engaged in research on optical
networks. He is a member of IEICE and IEEE.

Koichi Hadama

Senior Research Engineer, Optical Network
Device Research Group, Network Hardware
Integration Laboratory, NTT Microsystem Integration Laboratories.
He received the B.E. and M.S. degrees inapplied physics from the University of Tokyo in
1999 and 2001, respectively. He joined NTT
Microsystem Integration Laboratories in 2001.
He is currently engaged in the development of
free-space optical modules for fiber communication networks. He is a member of IEICE and the
Optical Society of Japan.

Feature Articles: Optical Node and Switch Technologies
for Implementing Flexible and Economical Networks

Multicast Switch Technology that
Enhances ROADM Operability
Toshio Watanabe, Kenya Suzuki, and Tetsuo Takahashi
Abstract

A multicast switch is a compact and cost-effective optical switch that realizes a colorless, directionless, and contentionless function and enhances the operability of a multi-degree reconfigurable optical
add/drop multiplexer. This article describes the circuit configuration and characteristics of the multicast
switch, which employs a silica-based planar lightwave circuit.
Keywords: ROADM, optical switch, PLC

1. Overview of CDC function
A colorless, directionless, and contentionless(CDC) function enables us to connect optical add/
drop signals at any wavelength and from/to any direction in a multi-degree reconfigurable optical add/drop
multiplexer (ROADM) to local transponders without
any signal contention. ROADM systems are advantageous in that wavelength division multiplexing(WDM) optical signals can be routed individually
without optical-electrical conversion, and they havebeen evolving from ring to multi-degree ROADM
systems. A multi-degree ROADM can select wavelength-by-wavelength whether an incoming WDM
signal from any direction will pass through the nodeand continue in any direction or will be added/
dropped at the local node. However, in a conventional
ROADM, the wavelength and direction of the optical
add/drop signals are assigned in terms of the port towhich they are connected, and this makes it necessary
to reconnect optical fibers to transponders manually.
A multi-degree ROADM with a CDC function thatmakes it possible to connect optical signals with any
wavelength in any direction to any transponder
enhances system operability and enables us to construct more flexible and reliable networks.
2. TPA using multicast switch
To realize the CDC function, an optical switch that

can assign any wavelength and any direction to eachtransponder must be employed between the add/drop
ports and the transponders. This switch is called atransponder aggregator (TPA). An N × M TPA isrequired on both the drop and add sides; here, N is thenumber of input/output routes, and M is the numberof transponders. In the TPA, WDM signals are incoming from or outgoing to the ROADM, while a single
wavelength is received from or sent to the transponders. On the drop side, the capability to connect different wavelength signals from the same direction todifferent transponders is required, while on the addside, the capability to launch different wavelength
signals from different transponders in the same direction is required.
Among TPA configurations, the multicast switch
offers a compact and cost-effective TPA. The TPA
architecture that employs a multicast switch is shownin Fig. 1. In a multicast switch on the drop side,
WDM signals from each direction are broadcast by a
1 × M splitter, and the signals from the desired
incoming fiber are selected by an N × 1 opticalswitch. A WDM signal at the desired wavelength isextracted by a tunable filter, and then the selectedsignal is received by the transponder. This architecture enables us to select an optical signal at any wavelength from any direction. The same wavelength signals from other input directions are rejected by the
optical switch, which eliminates any signal contention in the TPA.
NTT Technical Review

Feature Articles

Drop
#1

#2

Add
#N

#1

#2

#N

1 × M splitterN × 1 switch

M × 1 coupler

N
×
1

N
×
1

N
×
1

N
×
1

N
×
1

N
×
1

#1

#2

#M

#1

#2

#M

1 × N switch

Tunable filter

Rx

Tx

Fig. 1. TPA architecture employing multicast switch.

On the add side, the output signals from the transponders are routed to a desired outgoing fiber by a
1 × N switch array, combined with different wavelengths by an M × 1 coupler, and then launched into
the add ports of the ROADM. This architecture
enables us to send an optical signal at any wavelength
in any output direction.
The advantage of a TPA using a multicast switch isthat it is composed of compact optical components
including optical splitters and switches. This is unlike
a TPA, which uses a wavelength selective switch(WSS) or a large matrix switch. Although a multicast
switch has an intrinsic splitting loss because it
includes an optical splitter, we can compensate forthis loss with an optical amplifier. A multicast switch
based TPA also has the advantage that its switch scale
can be expanded by cascading optical splitters when
the number of transponders increases. Thus, it is suitable for multi-degree ROADMs that have a small
number of add/drop signals.
3. Multicast switch using PLC
3.1 Circuit configuration
An optical switch using a silica-based planar lightwave circuit (PLC) is operated by the thermo-optic
effect of silica-on-silicon waveguides. It offers good
reliability and mass producibility because it has nomoving parts, and many chips can be fabricatedVol. 12 No. 1 Jan. 2014

simultaneously in wafer processing [1]. Anotheradvantage is that many functional elements can be
integrated, thus making it suitable for constructing a
multicast switch.
As shown in Fig. 1, the TPAs on both the drop andadd sides comprise N units of 1 × M splitters (or M ×
1 couplers) and M units of 1 × N switches that areinterconnected, and they are identical except for the
tunable filters on the drop side. This architecture is
the same as that of an optical switch used for photonic transport systems [2], and an 8 × 8 switch was
fabricated using a PLC. However, the conventionalswitch comprises 8-arrayed 1 × 8 switches and 8arrayed 8 × 1 couplers, and those chips are separated
and connected via a 64-fiber circuit sheet as shown in
Fig. 2(a) to avoid having too many waveguide crossings on a PLC chip. They were packaged into a 240
mm × 95 mm × 12.5 mm module [3]. We recently
developed a new circuit configuration that integrates
the splitter and switch [4], as shown in Fig. 2(b). The
8-arrayed 1 × 8 switch comprises eight 1 × 2 switch
elements cascaded serially, with a gate switch placed
after each 1 × 2 switch element. We divided the 8 × 1
coupler into 2 × 1 elements, and placed them between
the stages of the switch elements. This new circuit
configuration reduces the maximum number of waveguide crossings by three fourths, and establishes aneven number of them between the paths. This allows
single chip integration of the 8 × 8 multicast switchFeature Articles

1 × 2 switch
8-arrayed 1 × 8 switch(a)

64-fibercircuit sheet

8-arrayed
8 x 1 coupler

Gate switch

2 × 1 splitting element(b)

Fig. 2. (a) Conventional and (b) new circuit configuration of PLC-based multicast switch.

and makes it possible to eliminate the fiber circuit
sheet, which reduces the size of the optical switch
module as described below.
3.2 Fabricated PLC
We fabricated an 8 × 8 multicast switch using a
PLC based on the architecture shown in Fig. 2(b).
The 1 × 2 and gate switch elements are based on a
Mach-Zehnder interferometer with a path differenceof half a wavelength between its arms. When we activate a thermo-optic phase shifter, optical outputs
between the two ports are switched in 2 ms [1]. The
fabricated chip and module are shown in Fig. 3. The
chip is 110 mm × 15 mm, and the fiber pig-tailed
module is 150 mm × 45 mm × 13 mm, which is one
third the size of the conventional module.
3.3 Optical performance
The measured performance of the multicast switch
is shown in Fig. 4. The average insertion loss of theswitch was 11.9 dB with a maximum value of 12.0 dB.
This is the same as that of a conventional switch usinga fiber circuit sheet. The loss includes an intrinsic
splitting loss of 9 dB and an excess loss of 3 dB. The
waveguide crossing induced loss was estimated to be
1 dB. The average and maximum polarization dependent losses (PDL) were 0.13 and 0.22 dB, respectively. The average wavelength dependent loss
(WDL) between 1530 and 1570 nm was 0.66 dB, andthe maximum value was 1.10 dB. The average andminimum off-state losses were 62.6 and 42.4 dB,
respectively. We employed heat-insulating grooves toFig. 3. Fabricated chip and module.

reduce power consumption. The average electricalswitching power was 0.2 W per path, and the total
power consumption was 1.6 W. This performance issatisfactory for practical applications.
We also fabricated an 8 × 12 multicast switch basedon the circuit configuration [5]. The average andmaximum insertion losses of the 8 × 12 multicast
switches were 14.1 and 14.5 dB, respectively, including an intrinsic splitting loss of 10.8 dB. The PDL
was less than 0.2 dB. The average WDL between
1530 and 1570 nm was only 0.1 dB, and the maximum value was 0.3 dB. The average extinction ratio
between the on and off states was 59.2 dB, and theminimum value was 45.4 dB. These results indicate
the good scalability of the PLC-based multicast
switch.
4. Conclusion
We described the circuit configuration and the performance of an N × M multicast switch that integrates
1 × M splitters and 1 × N switches into a single PLC
NTT Technical Review

Feature Articles

90
75

Loss (dB)60
Off state
45
Extinction ratio
30
On state

15
0

0

8

16

24

32

40

48

56

64

Number of paths

Fig. 4. Measured performance of multicast switch.

chip. This PLC-based multicast switch enables us torealize a multi-degree ROADM with a CDC function
cost effectively and with a small footprint. We plan toreduce the power consumption further and enhancethe optical performance of the PLC-based multicast
switch.

[2]
[3]

[4]

References[1]

H. Takahashi, T. Watanabe, T. Goh, S. Sohma, and T. Takahashi, “PLC
Optical Switch that Enhances the Optical Communication Network,”
NTT Technical Review, Vol. 3, No. 7, pp. 17–21, 2005.
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2005
07017.pdf

Vol. 12 No. 1 Jan. 2014[5]

M. Koga, T. Kawai, Y. Hamazumi, and N. Takachio, “Photonic Transport System,” NTT Review, Vol. 49, No. 1, pp. 42–49, 2000 (in Japanese).
H. Takahashi, T. Watanabe, M. Okuno, Y. Hibino, and T. Goh, “Silicawaveguide-based optical switches for photonic networks,” Technical
Report of IEICE, CS2003-9, Vol. 103, No. 68, pp. 1–6, 2003 (in Japanese).
T. Watanabe, K. Suzuki, T. Goh, K. Hattori, A. Mori, T. Takahashi, T.
Sakamoto, K. Morita, S. Sohma, and S. Kamei, “Compact PLC-basedtransponder aggregator for colorless and directionless ROADM,”
Proc. of the OFC/NFOEC 2011, Paper OTuD3, Los Angeles, CA,USA.
T. Watanabe, K. Suzuki, and T. Takahashi, “Silica-based PLC transponder aggregators for colorless, directionless, and contentionless
ROADM,” Proc. of the OFC/NFOEC 2012, Paper OTh3D.1, Los
Angeles, CA, USA.

Feature Articles

Toshio Watanabe

Senior Research Engineer, Photonics Integration Laboratory, NTT Photonics Laboratories.
He received the B.E., M.E., and Dr.Eng.
degrees in organic and polymeric materials engineering from Tokyo Institute of Technology in
1990, 1992, and 2001, respectively. In 1992, hejoined NTT Opto-electronics Laboratories,
where he engaged in research on polymericmaterials for optical waveguides. From 1997 to
1999, he was with NTT Optical Network Systems Laboratories, where he researched photonic
network systems. From 1999 to 2005, he wasinvolved in developing silica-based planar lightwave circuit (PLC) optical switches. From 2005
to 2008, he was with NTT Access Network Service Systems Laboratories, where he worked on
the development of WDM systems. Since 2008,
he has been with NTT Photonics Laboratories,
where he is researching photonic node devices.
He received the Microoptics Conference (MOC)
Paper Award in 2011. He is a member of theJapan Society of Applied Physics.

Tetsuo Takahashi

Senior Research Engineer, Supervisor, Group
Leader of Intelligent Photonic Node Device
Research Group, Photonic Integration Laboratory, NTT Photonics Laboratories.
He received the B.S. and M.S. degrees in physics from the University of Tokyo in 1989 and1991, respectively. In 1991, he joined NTT
Transmission Systems Laboratories and engaged
in R&D of high-speed SDH ring systems andwavelength division multiplexing systems. Since
the early 2000s, he has been engaged in R&D ofphotonic network systems, especially the development of ROADM systems and related subsystems. He received the NTT Presidential Award inboth 2000 and 2005. He is a member of IEICE.

Kenya Suzuki

Senior Research Engineer, Photonics Integration Laboratory, NTT Photonics Laboratories.
He received the B.E. and M.E. degrees in electrical engineering and the Dr.Eng. degree inelectronic engineering from the University ofTokyo in 1995, 1997, and 2000, respectively. He
joined NTT in 2000. From September 2004 to
September 2005, he was a Visiting Scientist at
the Research Laboratory of Electronics (RLE) of
Massachusetts Institute of Technology, USA.
From 2008 to 2010, he was with NTT Electronics
Corporation, where he engaged in the development and commercialization of silica-based
waveguide devices. His current research interests
are optical circuit design and optical signal processing. He received the Young Engineer Award
from the Institute of Electronics, Information andCommunication Engineers (IEICE) in 2003. He
is a member of IEICE.

NTT Technical Review

Regular Articles

Statistical Grammar Induction for
Natural Language Parsing
Hiroyuki Shindo
Abstract

Parsing, or syntactic analysis, is a fundamental problem in natural language processing. A natural
language parser begins with words of input and builds up a syntactic tree, applying grammar rules
acquired from language corpora beforehand. This article focuses primarily on the acquisition of grammar
rules from language corpora, which is called grammar induction, and describes recent advances instatistical grammar induction for statistical parsing.
Keywords: natural language processing, parsing, grammar induction

1. Introduction
Parsing, or syntactic analysis, is a fundamental
problem in the field of natural language processing(NLP). The resulting analyses are useful for developing high-quality NLP applications such as machinetranslation, automatic summarization, and information extraction. Consider the English-Japanese translation as an example. English follows the S-V-O word
order; that is, the subject comes first, the verb second,
and the object third. By contrast, Japanese follows the
S-O-V word order. Thus, when translating from one
language to another, syntactic information such as
subject, verb, and object is necessary for correct word
reordering.
It is known that the syntactic information of a sentence can be encoded in tree-structured forms such asphrase structure trees and dependency structure trees.
Many human-annotated corpora of syntax trees such
as Penn Treebank [1] have been developed. An example of a syntax tree is shown in Fig. 1. The tree contains the syntactic categories PRP, NP, VBP, VP, andS, which respectively indicate pronoun, noun phrase,verb, verb phrase, and sentence. A natural language
parser begins with words of input, for example, Sheloves me, and builds up the syntactic tree as shown in
Fig. 1, applying grammar rules such as S → NP, VP
and VP → VBP, NP.
Statistical parsing essentially involves three steps:


S
NP

VP

PRP

VBP

NP

She

loves

PRP
me

Fig. 1. Example of syntax tree.

modeling, learning, and decoding. An illustration ofthese steps used in building a statistical parser isshown in Fig. 2. Modeling syntax trees is formalized
as a probabilistic grammar. Probabilistic grammars
consist of a set of structural rules (tree fragments) thatgovern the composition of sentences, clauses, phrases, and words. Each rule, called an elementary tree, isassigned a probability.
With a probabilistic grammar and a collection ofsyntax trees, the learning process finds the optimal
parameters that fit the training data based on somecriteria such as maximum-likelihood estimation. For
decoding, the statistical parser searches over a spaceof all candidate syntactic analyses according to thegrammar rules. It then computes each candidate’s
probability and determines the most probable parse
NTT Technical Review

Regular Articles

NP
Decoding
the blue sky

DTNPParser

the

JJ

N

blue

sky

Modeling
Pr (trees Θ)

Resources

Grammar rules
N

VP

S

S
Learning
N

I

N

VP
V

NP

want

a car

DT: determiner
JJ: adjective

VP

V

NP

I

want
Pr: 0.01

Pr: 0.03

Pr: 0.005

Pr: probability

Fig. 2. Illustration of modeling, learning, and decoding for natural language parsing.

tree.
Some well-known probabilistic grammars for modeling syntax trees, which underlie the state-of-the-art
statistical parsers, are reviewed in this article. Additionally, grammar induction algorithms for learning
grammar rules based on the probabilistic grammars
are introduced.
2. Probabilistic grammars

S
NP

VP
VBP

NP
PRP
She

NP

loves
NP
PRP
me

This section briefly reviews probabilistic tree substitution grammars (TSGs) and probabilistic symbolrefined tree substitution grammars (SR-TSGs) for
statistical modeling of syntax trees.
2.1 TSGs
Formally, a TSG is defined by a 4-tuple: G = (T, N,
S, R) where- N is a finite set of nonterminal symbols,- T is a finite set of terminal symbols,- S ∈ N is the distinguished start symbol, and- R is a finite set of productions (a.k.a. (also knownas) rules).
The productions take the form of elementary trees,that is, tree fragments of height ≥ 1. The root andinternal nodes of the elementary trees are labeledwith nonterminal symbols, and leaf nodes are labeledwith either terminal or nonterminal symbols. Nonterminal leaves are referred to as frontier nonterminals
Vol. 12 No. 1 Jan. 2014

Fig. 3. Example of TSG derivation.

and form the substitution sites to be combined withother elementary trees.
A derivation is a process of forming a parse tree. It
starts with a root symbol and rewrites (substitutes)
nonterminal symbols with elementary trees until
there are no remaining frontier nonterminals. An
example of TSG derivation is shown in Fig. 3. Different derivations may produce the same parse tree.
Therefore, recent studies on TSG induction [2], [3]have employed a probabilistic model of TSG andhave predicted derivations from observed parse trees
in an unsupervised way.
A probabilistic TSG assigns a probability to eachrule in the grammar. The probability of a derivation isRegular Articles

simply defined as the product of the probabilities of
its component elementary trees as follows:

S-1
NP-0

p({e}) =where {e} = (e1, e2, …) is a sequence of elementary
trees used for the derivation, X = root(e) is the root
symbol of e, and p(e|X) is the probability of generating e given its root symbol X. It should be noted thatprobabilistic TSG assumes a sort of context-freegrammars, which means that e is generated conditionally independent of all others given X. Since thederivation of a syntax tree is usually unobserved, ourgrammar induction task turns out to be inferring themost probable TSG derivation for each syntax tree inan unsupervised fashion. The extracted TSG rules
and their probabilities are used to parse raw sentences.
2.2 SR-TSGs
The symbol-refined tree substitution grammar (SRTSG) proposed previously [4] is an extension of the
TSG model where every symbol of the elementary
trees can be refined (subcategorized) to fit the training data. An example of SR-TSG derivation is shownin Fig. 4. In the figure, syntactic categories such as
S-1 and NP-0 are refined in order to model syntax
trees more accurately. For example, grammar rules
are likely to generate pronouns such as I and you as
subject noun phrases, while generating other objects
such as pen and box as object noun phrases. We
expect symbol refinement to automatically cluster
subject noun phrases as NP-0 and object noun phrases
as NP-1. For SR-TSG, it is necessary to infer both
TSG derivation and symbol subcategories of every
node from a training corpus of syntax trees. In thestandard TSG, the extracted SR-TSG rules and theirprobabilities are used to parse raw sentences.
One major issue regarding modeling an SR-TSG isthat the space of the grammar rules will be very
sparse since SR-TSG allows for arbitrarily large tree
fragments and also an arbitrarily large set of symbol
subcategories. The authors of the previous study [4]addressed this data sparseness problem by employing
a three-level hierarchy to encode a backoff schemefrom a set of complex SR-TSG rules to a set of simpler grammar rules. An illustration of a three-level
hierarchy for the SR-TSG model is shown in Fig. 5.
In the figure, the first level allows every SR-TSG rule.
However, the second level only allows tree fragmentsof height = 1, and the third level only allows tree fragVBP-0

p(e|X)
X→e∈{e}

VP-2

NP-0
PRP-1
She

NP-1

loves
NP-1
PRP-3
me

Fig. 4. Example of SR-TSG derivation.

ments of height = 1 and unrefined child nodes. To
address the data sparseness problem, the probabilityof the SR-TSG rule (the first level) is interpolated by
the probability of simpler tree fragments (second andthird levels).
Specifically, the probability distribution of SR-TSG
is defined as follows:p(ei|{e}−i, X, dX, θX) = αei,X + βX × P0(ei|X)θ X + dX·∑ete,Xnei,X − dX·tei,X.
and βei,X =θ X + ∑enei,Xθ X + ∑enei,X{e}−i = e1, e2, … ei−1 are
where αei,X =previously generated trees, and nei,X is the number oftimes ei has been generated in {e}−i. Here, tei,X is thevalue of an internal variable called table, P0 is calleda base distribution over e, and dX and θX are parameters of the model. This probability model is based on
the Pitman-Yor process [5]. (See [4] for details.)
Roughly speaking, the first term αei‚X is the probability of e based on the number of times the tree fragment has been generated so far. The second term βX ×
P0 is the smoothing probability of e, which is computed using the simpler grammar rules as shown in
Fig. 5. Even if some grammar rule e does not appear
in the training corpus, that is, αei,X = 0 the probabilityof e becomes higher than zero due to the smoothing
probability β × P0(e|X).

NTT Technical Review

Regular Articles

Level 1

Level 2

Level 3

S-1

S-1

S-1

NP-0

VP-2
VBP-0

NP-0

NP-1

loves

VP-2

VP-2
VBP-0

NP

VBP-0

NP-1

loves

VP

VP-2
VBP

VBP-0
NP

loves

Fig. 5. Three-level hierarchy for SR-TSG model.

Iteration 1

Iteration 2

Iteration 3

S

S

S

NP

VP

PRP
PRP
She

NP
VBP

VP
VBP
VBP
loves

VP

⇒

NP
VBP

NP
⇒

NP

NP

PRP

VBP

PRP

She

loves

me

NP
PRP

VP

NP

loves

PRP
She

me

NP

NP
PRP
me

Fig. 6. Gibbs sampling for TSG induction.

3. Inference
Once we define the probabilistic grammar modelsuch as TSG or SR-TSG, we can infer the most probable grammar rules (derivation) from a training corpus of syntax trees. For the inference of grammar
rules, Gibbs sampling [6] is one of the most common
techniques applied to obtain derivation samples fromthe posterior distribution.
The basic procedure of Gibbs sampling for inferring TSG rules is explained here as an example. The
inference of TSG derivation corresponds to inducing
substitution nodes. A substitution node is a node of aparse tree that forms the root node of some elementary tree. For example, in Fig. 3, two NP nodes aresubstitution nodes, while all the other nodes are nonsubstitution nodes.
An illustration of Gibbs sampling for TSG induction is shown in Fig. 6. For each iteration, the Gibbs
sampling algorithm works by sampling the value ofeach binary variable (1 for substitution node and 0 for
non-substitution node) according to the posterior disVol. 12 No. 1 Jan. 2014

tribution in random order. When it reaches convergence, we can obtain the most probable derivationaccording to the posterior distribution over grammar
rules. For the inference of the SR-TSG model, it isnecessary to induce substitution nodes plus latent
subcategories for every node.
4. Experiment
4.1 Setting
Some experimental results of statistical parsing
using TSG and SR-TSG are introduced in this section. The standard data set for evaluating parsing
performance is the Wall Street Journal (WSJ) portionof the English Penn Treebank [1]. The Penn Treebank
data set consists of 24 sections; we used sections 2–21
for the training corpus and 23 for testing.
For training, the grammar rules are extracted by
Gibbs sampling from a collection of syntax trees inthe training data. For testing, the algorithm begins
with words of input, rather than a syntax tree, andthen predicts the syntax tree. The parsing results areRegular Articles

obtained with the MAX-RULE-PRODUCT algorithm [7] by using the extracted grammar rules. The
accuracy of the predicted syntax trees is evaluated bybracketing the parsing accuracy (F1 score) of thepredicted parse trees.
4.2 Results and discussion
The F1 scores of context-free grammar (CFG),
TSG, and SR-TSG models [4] are listed in Table 1.
The parsing accuracy of the SR-TSG model withthree backoff hierarchy settings is also listed in the
Table in order to show the effects of backoff smoothing on parsing accuracy. In Table 1, F1 (small) indicates that we used only section 2 (small training data)
for training, whereas F1 (full) indicates that we usedsections 2–21 (full training data) for training. Moreover, SR-TSG (level 1) denotes that we used only the
topmost level of the hierarchy. Similarly, SR-TSG(level 1 + 2) denotes that we used only levels 1 and 2
for backoff smoothing.

Table. 1. Comparison of parsing accuracy.
Model
CFG
TSG
SR-TSG (level 1)
SR-TSG (levels 1 + 2)
SR-TSG (levels 1 + 2 + 3)

F1 (small)
61.9
77.1
73.0
79.4
81.7

F1 (full)
63.6
85.0
86.4
89.7
91.1

essential for the SR-TSG parser.
5. Summary
This article reported on recent progress in statisticalgrammar induction for natural language parsing andpresented probabilistic TSG and SR-TSG for modeling syntax trees and a Gibbs sampling algorithm forextracting grammar rules. SR-TSG successfully outperformed the TSG model in a standard English parsing task by using a symbol refinement technique andthree-level backoff smoothing.
References
[1]
[2]
[3]

[4]

[5]
[6]

[7]

The results obtained in the previous study [4] indicate that the best model, SR-TSG (level 1 + 2 + 3),
performed the best on both training sets. This suggests that the conventional CFG and TSG models
trained naively from the treebank are insufficient to
fit the training data due to the context-free assumption and coarse symbol annotations. SR-TSG also
assumes context-freeness; however, as we expected,
symbol refinement can be helpful with the TSG
model for further fitting of the training data and for
improving the parsing accuracy.
The performance of the SR-TSG parser was strongly affected by its backoff models. SR-TSG (level 1)
performed poorly compared with the best model.
This result suggests that the SR-TSG rules extracted
from the training set are very sparse and cannot cover
the space of unknown syntax patterns in the testing
set. Therefore, well-designed backoff modeling is

M. P. Marcus, B. Santorini, and M. A. Marcinkiewicz, “Building alarge annotated corpus of English: The Penn Treebank,” Journal ofComputational Linguistics, Vol. 19, No. 2, pp. 313–330, 1993.
M. Post and D. Gildea, “Bayesian learning of a tree substitution grammar,” Proc. of the ACL-IJCNLP 2009 Conference Short Papers, pp.
45–48, Suntec, Singapore.
T. Cohn, S. Goldwater, and P. Blunsom, “Inducing compact but accurate tree-substitution grammars,” Proc. of Human Language Technologies: The 2009 Annual Conference of the North American Chapter of the Association for Computational Linguistics (NAACL ’09),
pp. 548–556.
H. Shindo, Y. Miyao, A. Fujino, and M. Nagata, “Bayesian symbolrefined tree substitution grammars for syntactic parsing,” Proc. of the50th Annual Meeting of the Association for Computational Linguistics, pp. 440–448, Jeju, Republic of Korea, 2012.
J. Pitman and M. Yor, “The two-parameter Poisson-Dirichlet distribution derived from a stable subordinator,” The Annals of Probability,
Vol. 25, No. 2, pp. 855–900, 1997.
S. Geman and D. Geman, “Stochastic relaxation, Gibbs distributions,and the Bayesian restoration of images,” IEEE Trans. on PatternAnalysis and Machine Intelligence, Vol. PAMI-6, No. 6, pp. 721–741,
1984.
S. Petrov, L. Barrett, R. Thibaux, and D. Klein, “Learning accurate,compact, and interpretable tree annotation,” Proc. of the 21st International Conference on Computational Linguistics and the 44th Annual
Meeting of the Association for Computational Linguistics (ICCLACL), pp. 433–440, Australia, 2006.

Hiroyuki Shindo

Researcher, NTT Communication Science
Laboratories.
He received the B.S. and M.S. degrees fromWaseda University, Tokyo, in 2007 and 2009,
respectively, and the Ph.D. degree in engineeringfrom Nara Institute of Science and Technology in2013. Since 2009, he has been engaged inresearch on natural language processing at NTT
Communication Science Laboratories. He
received the Best Paper Award from the annual
meeting of the Association for Computational
Linguistics (ACL) in 2012. He is a member of
ACL and the Information Processing Society ofJapan.

NTT Technical Review

Global Standardization Activities

G.epon and Current Status ofRelated Standardization
Ken-Ichi Suzuki
Abstract

G.epon is an ITU-T (International Telecommunication Union, Telecommunication Standardization
Sector) version of the system-level EPON (Ethernet passive optical network) standard that uses generic
OMCI (ONT (optical network terminal) management and control interface) in SIEPON (Service
Interoperability in EPON) package B. It was given consent in July 2013 and approved in September
2013. This article reports on G.epon, which is expected to be deployed in emerging nations and developing countries, and explains the current status of related standardization.
Keywords: EPON, SIEPON, OMCI

1. Introduction
The use of optical access systems based on passive
optical networks (PONs) has increased along with the
expansion of broadband services. GE-PON*1, a typeof EPON (Ethernet based PON), has been widely
deployed in Japan. However, the scope of IEEE
(Institute of Electrical and Electronics Engineers)
EPON standardization has been limited to the PHY(physical) and MAC (media access control) layers
and other system specifications that depended on
implementations by system vendors or telecommunication carriers to provide their services. The scope ofIEEE 802.3 [1] standardization using the layer modelof the EPON system is shown in Fig. 1. There is no
specification of higher layers in IEEE 802.3 standardization, as shown in the figure, so telecommunication
carriers desiring system deployment in multivendor
environments require additional development or
modification of firmware and hardware. Moreover,system vendors have had difficulty doing businessglobally because they could not ensure that their systems would be interoperable with other systems even
if they had been developed in compliance with IEEE
standards. In view of these situations, IEEE initiatedsystem-level EPON standardization in order to ensure
the interoperability between optical line terminals(OLTs) and optical network units (ONUs). That stan

dardization was approved in June 2013 [2]. By contrast, the trend to introduce de jure standards in developing countries and emerging nations has become anissue that must be addressed in the global promotionof EPON. In view of the fact that future networks
were expected to be packet-oriented, we began proposing that the International Telecommunication
Union, Telecommunication Standardization Sector(ITU-T) create EPON standards through the Full Service Access Network (FSAN) [3] in 2001, whenIEEE started work on EPON standardization. However, this proposal was not realized. Consequently, avariety of EPON systems with different specifications were developed. We have continued to seek away to create EPON standardization in ITU-T eversince then. By contrast, IEEE started SIEPON*2 standardization, which is a system-level EPON standard,in 2010. We decided to grab this SIEPON standardization opportunity to work on G.epon standardization in order to incorporate a full set of specificationsof widely used EPON systems into ITU-T standardization. To make a breakthrough in EPON
*1	 GE-PON: Gigabit Ethernet PON; the term GE-PON is used inthis article since it is widely used in Japan. However, the term
1G-EPON is recommended for use in the standard.
*2 SIEPON: Service Interoperability in EPON specified in IEEE
1904.1 WG (Working Group); a corporate project sponsored by
the IEEE Communication Society.

NTT Technical Review

Global Standardization Activities

Client management- SNMP, IGMP, MLD, IEEE 802.1x
Higherlayer

MAC client- Forwarding- QoS- Priority control

OAM

Client management- SNMP, IGMP, MLD, IEEE 802.1x

MAC control client- ONU registration- GATE generation- REPORT handling

OAM client- Alarm- Surveillance…

OAM

MAC client- Forwarding- QoS- Priority control

OAM

MPCP
…

MAC

OAM client- Alarm- Surveillance

OAM

MPCP
MAC

MAC control client- ONU registration- GATE handling- REPORT generation

MAC

MAC

RS

RS

Scope ofstandardization

Scope ofIEEE 802.3

PCS

PCS

PMA

PMA

PMD

PMD

OLT

ONU

IGMP: Internet group management protocol
MLD: multicast listener discovery
MPCP: multipoint control protocol
OAM: operations, administration, and maintenance

OLT: optical line terminal
ONU: optical network unit
PCS: physical coding sublayer
PMA: physical medium attachment

PMD: physical medium department
QoS: quality of service
RS: reconciliation sublayer
SNMP: simple network management protocol

Fig. 1. Scope of IEEE 802.3 standardization.

standardization in ITU-T, we focused on SIEPON
package B for G.epon standardization in the Japanesemarket and aimed for early completion of G.epon
standardization. We took into consideration the future
replacement (or coexistence) with G-PON and decided to apply OMCI (ONT (optical network terminal)
management and control interface), which is widelyused in ITU-T standards, to G.epon. The G.epon standard was given consent in July 2013 and approved in
September 2013. This article reports on ITU-T G.
epon and the current status of related standardization.
2. Overview of ITU-T Recommendation
G.epon (G.9801)
2.1 SIEPON standardization and G.epon
I briefly introduce SIEPON standardization as areference document of G.epon. SIEPON is intended
to realize service interoperability among 1G-EPONor 10G-EPON equipment. In order to achieve this, theVol. 12 No. 1 Jan. 2014

SIEPON standard specifies a system-level EPON
standard that consists of three specification packages
according to the market (Package A: North American
MSOs (multiple system operators); Package B:
Japan; Package C: China). The difference between
G.epon and SIEPON in terms of constituent standards and principal functions is shown in Fig. 2.
G.epon is an ITU-T version of the EPON standard
specified by applying OMCI, which is widely used in
ITU-T standards, to SIEPON package B. That standardization is being done under a Japanese initiative
as a part of the Telecommunication Technology Committee (TTC)’s [4] upstream activity. On the contrary,
SIEPON uses extended operations, administration,and maintenance (eOAM). However, hardware commonalization between G.epon and SIEPON compliant systems is anticipated because OAM functions
can be realized with firmware. The principal functions newly specified in G.epon/SIEPON standards
are listed in Table 1. Because the existing EPON
standards did not specify these functions, it wasGlobal Standardization Activities

Common Ethernet services
HN management BBF TR-142 (TR-069 for PON)

SIEPON

Service model BBF TR-156, 200 (TR-101 for PON)
G.988 (Generic OMCI)eOAM
System levelspecifications

G.986(1G-P2P)

G.987(XG-PON)
G.984(G-PON)

802.3av(10G-EPON)
802.3ah(GE-PON)

ITU-T Recommendations

PON management(e.g., OAM)
Higher layer specifications(e.g., QoS )MAC layer specifications(e.g., frame structure)
Physical layer specifications(e.g., transmission bandwidth)IEEE standards

G.epon

BBF: Broadband forum
HN: home networking
TR: technical report

Fig. 2. Differences between G.epon and SIEPON.

Table 1. Principal functions newly specified in G.epon/SIEPON standards.
Item

Main specifications

Encryption/authentication, protection, power saving, service Various functions
management, system monitoring

OAM client

OAM discovery, alarm handling, statistical information
processing (surveillance)

Surveillance and control functions

MAC client

Queue control, shaping, priority control, policing, etc.

Main signal control functions

MAC control client

Bandwidth control, report generation, discovery control

PON access control functionsdifficult to realize interoperability even with standard-compliant devices.
2.2 Architecture model for G.epon/SIEPONThe architecture model for G.epon/SIEPON isshown in Fig. 3. The architecture model defines Line
OLT/Line ONU having functions covered by theIEEE 802.3 standards, Client OLT/Client ONU having functions covered by G.epon/SIEPON standards,
and Service OLT/Service ONU having additional
functions for specific services provided by the communication carrier or system vendors. Moreover, thearchitecture model newly defines OLT_CI/ONU_CI
as logical interfaces on the core network/user network side of Client OLT/Client ONU and OLT_LI/
ONU_LI as a logical interface on the core network/
user network side of Line OLT/Line ONU.
Remarks

Client management

2.3 Logical function model for G.epon/SIEPONThe logical function model for G.epon/SIEPON isshown in Fig. 4. G.epon/SIEPON defines ESPs
(EPON service paths), which provide basic functional blocks of the MAC client model to achieve
provisioning, connection, and QoS in services. The
basic functional blocks (input/output, classifier,modifier, policer, cross-connect, packet queue, andscheduler) in ESPs provide data forwarding in OLTsand ONUs. A set of ESPs in an OLT and an ONU
represents a unidirectional connection. The example
in this figure shows ESP configurations for the bidirectional unicast connection between an OLT and an
ONU. The ESP concept is intended to be of help inunderstanding standard specifications because it simplifies and conceptualizes behaviors of MAC client
functions, thus absorbing implementation differences
NTT Technical Review

Global Standardization Activities

Service OLT
Client OLT
NNI

OLT_CILine OLT
OLT_LI

OLT_MDI

OLT
Servicespecificfunction

UNI

802.3
client

ONU_CI

802.3
layering
model

ONU_LIONU
Servicespecificfunction

802.3
client802.3
layering
model

ONU_MDI

Line ONU
Client ONU
CI: client interface
LI: line interface
MDI: medium dependent interface
NNI: network node interface
UNI: user network interface

Service ONU
Coverage of IEEE Std. 1904.1
Coverage of IEEE Std. 802.3

Fig. 3. Architecture model for G.epon/SIEPON.

such as single LLID (logical link ID) and multiple
LLID configurations.
3. Status of G.epon-related standardization
This section describes the current status of G.eponrelated standardization.
3.1 Interoperability test specifications for G.epon
A proposal to standardize a G.epon implementers’
guide was accepted in the ITU-T SG15/Q2 (Study
Group 15; Question 2) interim meeting in February
2013. The G.epon implementers’ guide is intended todevelop two kinds of test specifications for a conformance test, which is conducted by connecting an
ONU under test to an OLT emulator, and an interoperability test, which is conducted by connecting one
or multiple ONUs to an OLT in a multi-vendor environment. The IEEE 1904.1 WG is working on developing specifications for a conformance test (IEEEP1904.1 SIEPON/Conformance) that is performed byconnecting an OLT and an ONU to an ONU emulator
and OLT emulator, respectively. Although there aredifferences in each test configuration, the G.epon
Vol. 12 No. 1 Jan. 2014

implementers’ guide is being developed in reference
to SIEPON/Conformance standard documents. The
development of the implementers’ guide is expected
to be done through a Japanese initiative as part of
upstream activities in TTC in common with G.epon.
3.2 Interoperability tests in JapanThe development of the G.epon implementers’
guide and SIEPON/Conformance have accelerated
the movement to carry out EPON interoperability
tests in Japan. Various organizations are cooperatingin the interoperability tests, as shown in Fig. 5. The
Optical Access Ad-hoc WG was established in the
HATS (Harmonization of Advanced Telecommunication Systems) conference [5] of Japan in August
2012. This WG is an operating organization for conducting interoperability tests of G.epon/SIEPON
compliant equipment. Hereafter, the Optical Access
Ad-hoc WG is expected to conduct interoperability
tests in cooperation with the SIEPON certificate program and TTC.

Global Standardization Activities

Output [O]Scheduler [S]Queues [Q]

CrossConnect [X]

Policer/shaper [PS]Modifier [M]Input [I]Classifier [C]

EPON service path (ESP)

Provisioning/arms & status
Functional blocks related to connectivity
Functional blocks related to QoS
Example of ESP- Bidirectional unicast connection
OLT

ESP#1

ONU

ESP#2

[I] [C] [M] [PS] [X] [Q] [S] [O][I] [C] [M] [PS] [X] [Q] [S] [O][O] [S] [Q] [X] [PS] [M] [C] [I][O] [S] [Q] [X] [PS] [M] [C] [I]

ESP#3

DBA

ESP#4

Fig. 4. Logical function model for G.epon/SIEPON.

IEEE SIEPON Certification
Program (SIEPON CASG)- Conduct conformance test andissue certificate.

SIEPONInteroperability
test

Vendors
A

B
Test lab(Not in Japan)

CG.epon/SIEPON IOP Test
- Conduct IOP test of SIEPON equipment with
SIEPON certificate and G.epon equipment.
- Create test guideline.
- Global promotion of G.epon/SIEPON
equipment
HATS
conference
Optical Access
Ad-hoc WG

Telecommunication
carriers
A

B- Support for IOP
test- Provide test
machine.
- Use test results.

- Participate in
test.
Cooperation
G.eponInteroperability
test

Harmonization with
ITU-T/ASTAP

D

C
TTC
- Create related Japan standards.

ASTAP: Asia-Pacific Telecommunity Standardization Program
CASG: Conformity Assessment Steering GroupIOP: interoperability

Fig. 5. Cooperation between related organizations for interoperability test.



NTT Technical Review

Global Standardization Activities

4. Future perspectives
This article reported on G.epon, which was given
consent this July, and the status of related standardization. G.epon is an ITU-T version of the EPON
standard based on SIEPON package B for the Japanese market, which uses generic OMCI*3 instead of
eOAM. G.epon is expected to be deployed in emerging nations and developing countries that place
importance on de jure standards. The development of
the G.epon implementers’ guide, which is a reference
document for interoperability tests, and the corresponding movement to carry out interoperability tests
in Japan are expected to accelerate activities related
to interoperability test for G.epon and SIEPON.
Moreover, successful G.epon standardization is
expected to promote further cooperation between
ITU-T and IEEE such as IEEE’s request to issue an
ITU-T Recommendation number for the entire
SIEPON standard including all packages.
*3 Generic OMCI: ONT (optical network terminal) management
and control interface specified in ITU-T G.988, which has been
generalized for application to various PON systems.

Ken-Ichi Suzuki

Senior Research Engineer, Supervisor, Group
Leader of Full Service Access Group, NTT
Access Network Service Systems Laboratories.
He received the B.E. and M.E. degrees in electronic engineering from Utsunomiya University,
Tochigi, in 1988 and 1990, respectively, and the
Ph.D. degree in information science and technology from Hokkaido University in 2009. He
joined NTT laboratories in 1990, where he has
been working on R&D of optical communication
systems including PON based optical accesssystems. He currently leads the Full Service
Access Group, which is investigating opticalaccess related services/technologies. His current
research interests are 10G-EPON related opticalaccess systems/technologies and optical-amplifier-based long-reach PON systems/technologies. He is an IEEE 802.3 WG voter and was anactive member of the IEEE P802.3av Task Forcecreating 10G-EPON standardization. He has
been a Vice Chair of IEEE P1904.1 SIEPON WG
since 2011 and was an executive secretary ofIEEE P1904.1 SIEPON WG during 2009–2011.
He has been a Director of the Optical Access Adhoc WG in HATS conference of Japan for EPON
family interoperability tests since 2012. He is amember of IEEE, the Institute of Electronics,
Information and Communication Engineers(IEICE), and the Optical Society of America. He
has also been a member of the Technical Committee on Communication Systems in IEICE
Communication Society since 2008 and was an
associate editor of IEICE Transactions on Communications during 2007–2011. He is the TPC
Secretary of IEEE CQR2012, 2013, and 2014.

References
[1]
[2]
[3]
[4]
[5]

IEEE 802.3 Ethernet WG.
http://www.ieee802.org/3/index.html
IEEE 1904.1 SIEPON (service interoperability in EPON) WG.
http://grouper.ieee.org/groups/1904/1/index.html
FSAN (Full Service Access Network).
http://www.fsan.org/
TTC (Telecommunication Technology Committee).
http://www.ttc.or.jp/e/
HATS (Harmonization of Advanced Telecommunication Systems)
conference.
http://www.ciaj.or.jp/hats/english/about.html

Vol. 12 No. 1 Jan. 2014



Papers Published in Technical Journals andConference Proceedings
Definition, Implementation and Evaluation of GenericSearch Function for Current Sensor Status in Database for
Sensor Networks
T. Nakamura, Y. Higashijima, M. Nakamura, and M. Matsuo
IEICE Trans. on Information and Systems, Vol. J96-D, No. 5, pp.
1132–1144, 2013 (in Japanese).
We propose a search function for the current sensor status provided
by a database management system (DBMS) for sensor networks.
Previous studies have investigated two practically important searchfunctions in DBMSs specially designed for sensor networks: accumulated data history search and continuous search (immediate datadelivery). We determined the necessity of and the problems with athird search function that returns a list of current sensor statuses byimplementation of sensor network application systems. We also
developed a formal definition of this search function. This definition
clarifies the semantics of a search and can be used as a guide in
designing the input/output parameters in a new generic search API fora DBMS. We implemented the proposed search function and applied
it to the development of several application systems used in field trials.

Improving Nonlinear Degradation by Combining Opticaland Digital Compensation Techniques
K. Shibahara, Y. Sakamaki, T. Kawai, K. Mori, H. Kishikawa, andM. Fukutoku
Proc. of the 18th OptoElectronics and Communications Conference held jointly with 2013 International Conference on Photonics in
Switching (OECC/PS 2013), Vol. OECC, No. 2013, pp. WR4–6,
Kyoto, Japan.
We investigate the combined effect of optical and digital compensation techniques for nonlinear degradation by numerical simulation.
Q-factor improvement by digital compensation increases when nonlinearity is optically suppressed in a dispersion-managed system.

409-Tb/s + 409-Tb/s Crosstalk Suppressed Bidirectional
MCF Transmission over 450 km Using Propagation-direction Interleaving
A. Sano, H. Takara, T. Kobayashi, H. Kawakami, H. Kishikawa, T.
Nakagawa, Y. Miyamoto, Y. Abe, H. Ono, K. Shikama, M. Nagatani,
T. Mori, Y. Sasaki, I. Ishida, K. Takenaga, S. Matsuo, K. Saitoh, M.
Koshiba, M. Yamada, H. Masuda, and T. Morioka
Opt. Express, OSA, Vol. 21, No. 14, pp. 16777–16783, 2013.
We demonstrate bidirectional transmission over 450 km of newly
developed dual-ring structured 12-core fiber with a large effective
area and low crosstalk. Inter-core crosstalk is suppressed by employing propagation-direction interleaving, and 409-Tb/s capacities areachieved for both directions.

Dynamic Optical Transport Connection with a 100 Gbit/s
Digital Coherent Optical Transponder for Disaster-resilient
Networking
T. Hirooka, M. Nakazawa, H. Kubota, T. Komukai, and T. Sakano

Proc. of the IEEE Region 10, Humanitarian AdHoc Committee,
Vol. 1, No. 1, p. TS10, Sendai, Miyagi, Japan, 2013.
We demonstrate dynamic optical transport connectivity to various
lengths and types of fiber (SMF, DSF, GI-62.5/125 fiber) with a 100Gbit/s digital coherent optical transponder. The outage time associated with connection was only about 70 ms (potentially as fast as 20ms) in all configurations. This feature provides great simplicity andflexibility as regards immediate broadband connection to the backbone networks in case of a devastating disaster.

Impact of Transponder Architecture on the Scalability of
Optical Nodes in Elastic Optical Networks
T. Tanaka, A. Hirano, and M. Jinno
IEEE Communications Letters, Vol. 17, No. 9, pp. 1846–1848,
2013.
The elastic optical network has proven to be a promising networkarchitecture for handling the rapid growth in IP traffic in the opticallayer in a spectrum-efficient manner. This study reveals the opticalnode requirements in elastic optical networks by comparing multiple
network architectures using an integrated resource allocation schemethat considers both network and node parameters. Evaluations showthat the multiflow transponder-based elastic optical network architecture is superior to two other architectures in terms of scalability of
optical nodes and network costs.

Silica-based 100-GHz-spacing Integrated 40-λ 1×4 Wavelength Selective Switch
T. Yoshida, H. Asakura, T. Mizuno, H. Takahashi, and H. Tsuda
Proc. of the 39th European Conference and Exhibition on OpticalCommunication (ECOC 2013), Vol. We.4.B.3, No. 1, pp. 1–3, London, UK.
A densely integrated 1 × 4 wavelength selective switch was
designed and fabricated. The channel spacing is 100 GHz and thenumber of channels is 40. The transmission losses and the crosstalk
are less than 8.8 dB and -19.4 dB, respectively.

Impact of Multi-flow Transponder on Equipment Requirements in IP over Elastic Optical Networks
T. Tanaka, A. Hirano, and M. Jinno
Proc. of the 39th European Conference and Exhibition on OpticalCommunication (ECOC 2013), Vol. We.1.E.3, No. 1, pp. 1–3, London, UK.
We evaluate the elastic optical network performance from the
network to node equipment level using a multi-layer network design
scheme. Results show that the multi-flow transponder-based networkmodel reduces equipment requirements such as router IFs and transponders compared to mixed-line-rate and bandwidth-variable models.

NTT Technical Review

Papers Published in Technical Journals and Conference Proceedings

Noise Model Transfer: Novel Approach to Robustness
Against Nonstationary NoiseT. Yoshioka and T. NakataniIEEE Trans. on Audio, Speech, and Language Processing, Vol. 21,
No. 10, pp. 2182–2192, 2013.
This paper proposes an approach called a noise model transfer(NMT), for estimating the rapidly changing parameter values of afeature-domain noise model, which can be used to enhance feature
vectors corrupted by highly nonstationary noise. Unlike conventional
methods, the proposed approach can exploit both observed feature
vectors, representing spectral envelopes and other signal properties
that are usually discarded during feature extraction but that are usefulfor separating nonstationary noise from speech. Specifically, we
assume the availability of a noise power spectrum estimator that cancapture rapid changes in noise characteristics by leveraging suchsignal properties. NMT determines the optimal transformation fromthe estimated noise power spectra into the feature-domain noisemodel parameter values in the sense of maximum likelihood. NMT issuccessfully applied to meeting speech recognition, where the main
noise sources are competing talkers; and reverberant speech recognition, where the late reverberation is regarded as highly nonstationary
additive noise.

Usefulness of Acoustical Telepresence Robot for Auditory
Psychophysics
T. Iwaki, S. Aoki, H. M. Kondo, M. Kashino, and T. Hirahara
Journal of the Robotics Society of Japan, Vol. 31, No. 8, pp. 788–
796, 2013 (in Japanese).
We devised an acoustical telepresence robot, “TeleHead”, that has
a user-like dummy head and can be synchronized with the user’s head
movement. We performed several psychophysical experiments toassess sound localization, delay discrimination, and auditory perceptual grouping ability in humans. The errors of the sound localization
via TeleHead were less than 10 deg. Head posture changes during thediscriminable delay time ranged from 10 deg to 17 deg. The performance of auditory perceptual grouping did not differ between conditions with and without TeleHead. In addition, we used TeleHead to
divide head movement effects on perception into three factors: selfmovement, sound source movement, and acoustical change. The
results indicate that TeleHead can mirror the 3D motion of users withminimal latency and distortion, suggesting that it is a useful tool formeasurements of human auditory perception.

Image Context Discovery from Socially Curated Contents
A. Kimura, K. Ishiguro, M. Yamada, A. M. Alvarez, K. Kataoka,
and K. Murasaki
Proc. of the 21st ACM International Conference on Multimedia(MM’13), Vol. 1, No. 1, pp. 565–568, Barcelona, Spain, 2013.
This paper proposes a novel method of discovering a set of image
contents sharing a specific context (attributes or implicit meaning)with the help of image collections obtained from social curation
platforms. Socially curated contents are promising for analyzing
various kinds of multimedia information, since they are manuallyfiltered and organized based on specific individual preferences, interests or perspectives. Our proposed method fully exploits the processof social curation: (1) How image contents are manually grouped
together by users, and (2) how image contents are distributed in theplatform. Our method reveals the fact that image contents with a
specific context are naturally grouped together and every image content item includes various contexts that cannot necessarily be verbal-

Vol. 12 No. 1 Jan. 2014

ized by texts.

Heat Blueprint
T. Natsume
The OpenStack Summit Hong Kong 2013
We suggest adding a retry function and the resource type of NVP
network gateway for “Heat”, which realizes orchestration in OpenStack.

Clustering-based Anomaly Detection in Multi-view Data
A. M. Alvarez, M. Yamada, A. Kimura, and T. Iwata
Proc. of the 21st International Conference on Information andKnowledge Management (CIKM 2013), Vol. 1, No. 1, pp. 1545–
1548, Burlingame, CA, USA.
This paper proposes a simple yet effective anomaly detection
method for multi-view data. The proposed approach detects anomalies by comparing the neighborhoods in different views. Specifically,clustering is performed separately in the different views and affinity
vectors are derived for each object from the clustering results. Then,the anomalies are detected by comparing affinity vectors in the multiple views. An advantage of the proposed method over existing
methods is that the tuning parameters can be determined effectively
from the given data. Through experiments on synthetic and benchmark datasets, we show that the proposed method outperforms existing methods.

Exploiting Socially Generated Side Information in Dimensionality Reduction
A. M. Alvarez, M. Yamada, and A. Kimura
Proc. of the 2nd International Workshop on Socially-aware Multimedia, Barcelona, Spain, 2013.
In this paper, we show how side information extracted fromsocially curated data can be used within a dimensionality reduction
method and to what extent this side information is beneficial to several tasks such as image classification, data visualization and image
retrieval. The key idea is to incorporate side information of an image
into a dimensionality reduction method. More specifically, we propose a dimensionality reduction method that can find an embedding
transformation so that images with similar side information are closein the embedding space. We introduce three types of side information
derived from user behavior. Through experiments on images from
Pinterest, we show that incorporating socially generated side information in a dimensionality reduction method benefits several imagerelated tasks such as image classification, data visualization andimage retrieval.

High-charge-sensitivity Radio-frequency Field-effect Transistor with Large and Tunable Readout Frequency
K. Nishiguchi, H. Yamaguchi, A. Fujiwara, H. S. J. van der Zant,
and G. A. Steele
Proc. of the 26th International Microprocesses and Nanotechnology Conference (MNC 2013), 7B-4-1, Sapporo, Hokkaido, Japan.
We introduce the RF-FET composed of double LC matching circuits. The double matching circuits provide an additional resonancecondition tuned by a variable capacitor, which allows the extensionof the readout frequency to 200 MHz.

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Papers Published in Technical Journals and Conference Proceedings

Dual-gate Silicon Single-electron Transistor Threshold
Voltage Mapping at Nanoscale with a Scanning Microwave
Microscope
N. Clément, F. Wang, K. Nishiguchi, A. Fujiwara, G. Patriarche, D.
Troadec, B. Legrand, G. Dambrine, and D. ThéronProc. of the 26th International Microprocesses and Nanotechnology Conference (MNC 2013), 7B-4-2, Sapporo, Hokkaido, Japan.
Using a scanning microwave microscope (SMM) with F sensitivity, we demonstrate spatial mapping of the threshold voltage of asilicon single-electron transistor whose conductivity is fully controlled by dual gates composed of a back gate and an SMM cantilever.
The SMM is a reliable alternative tool for electrical characterizationof emerging nanoscale devices.

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Ultimate Integration of a PDMS-based Lab-on-a-Chip with
Nanotransistor Biosensors
R. Sivakumarasamy, K. Nishiguchi, A. Fujiwara, D. Vuillaume,and N. Clément
Proc. of the 26th International Microprocesses and Nanotechnology Conference (MNC 2013), 8C-8-3, Sapporo, Hokkaido, Japan.
We address the question of the maximum integration possible forsuch PDMS-based lab-on-chips (LOCs) and show that there is a
critical distance (typically a few tens of micrometers) between thechannel and electrical contacts, below which we observed leakage.

NTT Technical Review