R&D Spirits
The GE-PON System as a Means to Achieve
Competitive Superiority in the World FTTH MarketYukihiro Fujimoto
Senior Research Engineer, Supervisor
Innovative Access Systems Group
Optical Access Systems ProjectNTT Access Network Service Systems Laboratories†

NTT Access Network Service Systems Laboratories has developed a GE-PON (gigabit Ethernet-passive optical network) that conforms to the IEEE 802.3ah standard approved in June
2004. This technology will reduce the expense of the FTTH (fiber to the home) access systemand encourage its widespread adoption. We asked Yukihiro Fujimoto, a Senior Research Engineer in NTT who is involved in GE-PON development and standardization activities, about
future use of this technology and about international development and technological applications.

Using LAN Ethernet technology
for a more economical access system—Could you tell us about the research that is currently in progress?
The access network is my current research topic. As
a research topic, the access network covers a very
wide variety of things, ranging from equipment suchas metallic and optical telephone lines and optical
network units (ONUs) to access system construction
methods and network design (Fig. 1). Of those, myresearch mainly concerns the application of the Ethernet technology that is generally used in local area
network (LAN) systems to optical fiber access systems.
—What are the objectives of this research? What canbe implemented with it?

hardware of Ethernet systems is dramatically lower incost than that of conventional telecom carrier systemequipment. Thus, cost was the first motivation for thisresearch into applying Ethernet technology to theaccess system.
Another objective is to replace so-called legacy systems. In this context, a legacy system is an old systemfrom the era in which a carrier’s only business wastelephony. Equipment from 20–30 years ago is still inuse, though spare parts may no longer be available.
Of course, future replacement with a FTTH (fiber tothe home) access system is likely, but customer decisions are also involved, so total replacement within
the next 10 years is unlikely. Therefore, replacing
failing legacy systems by Ethernet technology is one
path toward effective future use of facilities. Thisaffects all carriers, not just NTT, so it is a simple but
important mission.
—What are the main technical points of the research?

Ethernet is currently used in the LAN interface ofall personal computers. It is capable of data transfer
speeds ranging from 10 Mbit/s to 10 Gbit/s and the† Present address: NTT West R&D Center
Konohana-ku, 554-0024 Japan

6The key technical problem is how Ethernet, which
is a LAN technology, can best be incorporated into a
carrier-grade network system. What makes this difficult is that Ethernet was originally an enterprise-centric technology and used mostly within a company, soNTT Technical Review

R&D Spirits

ONU

Aerial cable section(distribution section)
ONU

NTT central office
ONUOLTONUFTM

SNOLT

SN

ONU

ONU

Underground section(feeder section)
OLT: optical line terminal
FTM: fiber termination module
SN: service node

Metallic cable
Optical fiber cable
System for telephony services
System for broadband accessFig. 1. Fiber optic access network system.

many of the functions are inadequate for use in a carrier’s network. The most obvious examples are thelack of operation, administration, and maintenance(OAM) functions. To use this technology in a public
network without supplementing such functions
would be a fatal mistake. However, to make the system economical, we must decide between simplicity
on the one hand and the functionality required for apublic network on the other. Making the best choicesin that respect so as to achieve a well-balanced system is the biggest issue for this research.

ture from work on the FTTH access system, fromnow on, I will continue with a serious study of legacy
systems. I am pursuing the application of Ethernet
technology to these systems and the development of
economical telephony services, while keeping thecurrent service level.

Attraction of GE-PON to carriersin Asian countries—Could you tell us about international trends related to this research?

—What is the current state of development?
At present, an FTTH access system that applies
GE-PON (gigabit Ethernet-passive optical network),a media converter (ONU), and other Ethernet technology is being used in NTT’s B FLET’S service(Fig. 2). In particular, GE-PON, which allows theEthernet frames generally used in LAN systems to besent and received without any modification, isexpanding by millions of lines per year. Concerning
the standardization activities that we have participated in from the beginning, the IEEE 802.3ah standard
was approved in June 2004. While that was a deparVol. 3 No. 11 Nov. 2005

To date, NTT is alone in having introduced GEPON to the extent of several million lines. However,seeing the expansion of economical FTTH in Japan,
carriers in other Asian countries are following thislead. The approach in Europe and North America, on
the other hand, is somewhat different. While ourFTTH service provides all types of data on the same
platform, different protocols are used for telephony,video, and the Internet in Europe and North America,
in a scheme known as “triple-play”. Consequently,
the specifications for systems based on ATM (asynchronous transfer mode) such as B-PON (broadband7

R&D Spirits

NTTCustomer premises

1.49 µm
1.31 µm

GE-PON
Ethernet(1000BASE-X/100BASE-X)

WDM

ONU

WDM

1.55 µm

GE-PON
OLT

SwitchInternet

Contents
serverSplitter(1:32)
Video provider
Broadband routerRF
OLT: optical line terminal

Video
OLT

VideoONU

RF: radio frequency

Videohead end

WDM: wavelength division multiplexing

Fig. 2. GE-PON system with multi-channel video overlay.

PON) and G-PON (gigabit-PON), which is a fasterversion of B-PON, are being formulated by ITU-T(International Telecommunication Union Telecommunication Sector). However, the economical advantages of GE-PON are being recognized in Europe andNorth America, too, so I think the development ofNTT’s FTTH is attracting attention there as well.
Although IEEE 802.3ah is now finished, there arestill areas that it does not cover. In particular, there isa question of whether it would be good to have specifications for the maintenance and administration
functions that are unified to some extent. There is a
growing movement to transfer these activities fromIEEE to ITU-T. NTT is also participating in that, eventhough we are a different group.
—Are any international collaboration efforts inprogress?
No formal collaborative research has begun yet, but
we are already engaged in loose cooperative activities
with carriers in Taiwan and Korea that include
exchanging visits and information several times a8year. GE-PON is attracting the attention of carriers in
Taiwan, Korea, and other countries in Asia. Sincemany countries in Asia have the technology to build
systems on their own, we would like to actively support to those carriers.
—How do you feel NTT is regarded in international
standardization activities?
At the onset of standardization efforts, the participants were mostly LAN system vendors and venturebusinesses. We were the only company with experience in actual development of PON and FTTH. It wastherefore inevitable that we took on a leadership rolein identifying the requirements for applying Ethernet
technology in the access network. However, the LANvendors, as might be expected, wanted to avoid theexcessively high system cost associated with implementing sophisticated requirements. There was thus
some conflict between our posture regarding investigating service provisioning and their posture regarding investigating greater economy. We had rather
intense discussions in weekly teleconferences, but
NTT Technical Review

R&D Spirits

Ops interface
DBA/QoS
Encryption
security
OAM

Systemcontrol

Specifications not covered by standards.
For interoperability between ONU and OLT from different
vendors, these specifications should be categorized into two:
1) Standardized or de facto standardized
2) System differentiation

MAC/MPMC
Specifications covered by standards

PHY

DBA: dynamic bandwidth allocation
QoS: quality of service

MAC: media access control
MPCP: multipoint MAC control
PHY: physical layer

Fig. 3. GE-PON system function layer.

basically our view was held in high regard.

R&D efforts under the major theme of FTTH

—What problems might there be in future for international expansion?

—What is your scholastic background?

One reason we have for actively supporting the carriers of other countries with GE-PON is the economy
of scale and technological progress that come withmass implementation. The Japanese market scale isabout 50 million, which is not at all small. Nevertheless, if we limit our market to Japan, then that iswhere development of this system will probably end.
We believe that GE-PON is an excellent technology,
so we want to avoid limiting its use to NTT alone. We
think that, for systems such as GE-PON, the old way
in which the system is constructed by system vendors
selected only on the basis of the carrier’s technology
will not work. Actually, Ethernet is a technology forwhich openness is very advanced, and there are many
companies throughout the world that manufacturecomponents and equipment for it. It therefore is not
something that we could control even if we had amind to. In such a situation, the support for carriers inother countries is accompanied by an important risk.
Accordingly, even if the technology is driven by standard specifications, I believe that in the future product differentiation in which control is achieved
through proprietary technology will be important(Fig. 3).

Vol. 3 No. 11 Nov. 2005

As a graduate student, my major study was urban
planning in the graduate course on construction in theDepartment of Environmental Science. My specificresearch area was the simulation of urban fires after
earthquakes. I created evaluation simulators fordetermining where to focus firefighting efforts whenfires break out and how to construct cities so as toreduce the likelihood of disastrous fires as much aspossible. My current direction has changed a gooddeal, and you probably wonder why I joined NTT
Laboratories. There is some overlap in the study ofnetwork wiring methods and urban planning, so I personally don’t feel that research on the NTT accessnetwork is so great a departure from my background.
—What research have you been involved in at NTT
Laboratories so far?
From 1990 to 1993, right after joining NTT’s Communication Network Technology Division, I workedon the transition to an optical subscriber network,
investigating mainly the viewpoint and order for an
economical transition from existing metallic lines toFTTH. In 1994, I was transferred to the User System
Division and worked on the development of opticalfiber laying methods and the development of practical optical fiber cable and other wiring products.
9R&D Spirits

Then, in 1997-98, I spent a year as a guest researcher
at Lucent Technologies Bell Labs in the Netherlands.
At that time, Lucent was one of the system hardware
vendors for the STM-PDS (synchronous transfermode-passive double star) system that was referred toas the “π system” in NTT. I was doing development
work such as attending specification meetings andconducting factory inspections. After returning from
Lucent, I joined NTT Access Service System Laboratories and helped to develop the π-system-based
STM-shared system to a practical stage. The STMshared system was an FTTH system that provided adata transfer speed of 10 Mbit/s. It became the precursor to NTT’s commercial FTTH system. From2001 until last year, I was involved in GE-PON standardization activities at IEEE.
—What are your thoughts looking back on the R&D
accomplished so far?
The major R&D theme has been FTTH, but at thetime I began R&D work, we had the slogan “provide
10 Mbit/s for 10,000 yen per month”. Incidentally,
although the current GE-PON provides customers
with a transfer rate of 100 Mbit/s, it actually has atransmission capacity of 1 Gbit/s, and the monthly
charge for today’s typical FTTH access service is lessthan 5000 yen. This means that we are now offering
100 times the speed at half the cost relative to that ‘90
target, so looking back I would have to say that I am
again struck by the truly remarkable technologicalprogress and at the same time feel deeply moved.
—What about the future direction of R&D?
Today, there is a demand for R&D to be rapid.
Because many researchers have their own research
inclinations, they are often not satisfied unless they
can work on their own research topics from start tofinish. However, the real world does not afford us thetime to do as we would like, so it is important to positively tackle technology that is peripheral to us, even
if it means putting less emphasis on the technology
where our own strength lies. GE-PON involves LSI(large-scale integration) chips and other componentsthat are made by suppliers outside Japan. While they
are assembled as a system in another country, thefunctions implemented in those chips must of course
be designed by us. Unless we do this in an open system with complete division of labor, we will lose outto our competitors in development.
On the other hand, it is difficult to make appealing
10products without independence in research. Forexample, when our competitors first begin to use GEPON for FTTH, it would have been embarrassing if
the system had been exactly the same as that used byNTT. One must incorporate functions that other companies cannot implement. That means we must identify differentiating functions, determine their targets,develop functions that other companies cannot imitate, and incorporate them into our systems.

The importance of a sense of balance between
independence and cooperation in R&D—How do you think your own research will proceed
in the future?
I think I will continue work that is mainly focusedon the access network as the major theme. Amongelectronic communication systems, the access network has hardly evolved at all in basic form in the last
100 years or so. Because the services have steadily
advanced during that time, I believe that there istremendous room for improvement. In particular,when new and old systems exist side-by-side as they
do now, how the old systems can be updated andreplaced is an important issue. I would like to consider methods for applying Ethernet technology to economical system updating and future re-use. I believe
the rapid development of those methods is also
important.
—What is your dream as an R&D scientist?
I don’t have a specific plan, but I’d like to try todevelop active international cooperation in accessnetwork research. We pride ourselves on NTT’s
access network research being top class in the world.
It would be a great waste to keep the fruits of ourwork here in Japan, so I’d like to see more extensive
international collaboration. My dream is to involve
system vendors and component vendors as well ascarriers, if possible, to work towards better accessnetworks throughout the world.
—What do you think of NTT Laboratories?
The greatest feature of NTT Laboratories is theextremely wide scope of our research topics. Even
taking the area of access alone, the topics range fromthe optical fiber core to wiring methods and on toentire systems. Another merit is the ability to develop
technology to the actual business stage and thus have
NTT Technical Review

R&D Spirits

a great impact on society. Also, the integration of theprocess from basic research to system-level researchand on to practical development is unique to NTT
Laboratories. I think there are many topics that, likeour research on network access, can be done only byNTT.
Another special feature of NTT Laboratories is an
overall open atmosphere. In particular, when participating in practical development work such as theaccess network research, there is a strong attitude ofadopting good technology that was not our own. Thatis all extremely different from the image of a“research laboratory” that I had in my student days.
—Finally, what advice do you have for youngresearchers?
To begin with, I think you should develop a senseof balance in research methodology, athough recent
R&D has departed from the style of working on
something from beginning to end. This idea should
apply to fields like basic research. Moreover, when
you are getting close to practical implementation,
cooperation with external concerns has become very
important. From now on, the R&D style in which
researchers work on their own fields of strength independently, but add to it excellent technology fromoutside their laboratories to complete overall systems
will probably become the norm. That kind of environment requires us to strike a balance between independence and cooperation.
Another piece of advice is that “perseverance ispower”. No matter what topics you pursue, follow
this principle and conduct your research with determination. If you do so, then even if you are initiallyrecognized simply as being “from NTT” at academic
meetings, you will gradually gain recognition as anindividual. Once you do, you may be called on to
make a keynote speech or submit an invited paper.
Being known by name is an honor for a researcher, socontinue your research with determination and you
may go on to become known as the foremost person
in your field.

Vol. 3 No. 11 Nov. 2005

Interviewee profile■ Career highlights
Yukihiro Fujimoto received the B.A. in educationfrom Nagasaki University, Nagasaki and the M.S.
degree in environmental sciences from the Universityof Tsukuba, Ibaragi in 1988 and 1990, respectively.
He joined NTT Telecommunications Networks laboratories in 1990 and engaged in a study of evaluation
methods of fiber-optic access network design. In 1994,
he moved to NTT network systems development
department and worked on the development of fiberrich access network systems. In 1997 and 1998, he wasat Lucent Technologies Bell Labs in the Netherlands
as a guest researcher for the development of passive
optical network systems. In 1998, he moved to NTT
Access Network Systems Labs and engaged in thedevelopment of FTTH systems including STM-PON,
GE-PON, and standardization activities in IEEE802.3.
■ Publications“FTTH Textbook,” coeditor and coauthor, IDG
Japan, August 2003 (in Japanese).
M. Abrams, P. C. Becker, Y. Fujimoto, V. O’Byrne,and D. Piehler, “FTTP Deployments in the UnitedStates and Japan—Equipment choices and service
provider imperatives,” IEEE/OSA J. Lightwave Technol., Vol. 23, No. 1, pp. 236-246, Jan. 2005.

11