Letters

Development of the New ADM Ring
SystemSatoshi Ikegawa†, Hirokazu Sumi, and Kei KaratoAbstract
We are developing a new add-drop multiplexer (ADM) ring system that utilizes the functions of ourexisting 2.4-/10-Gbit/s ADM ring systems. It has i) some new interfaces, so it can handle various kindsof traffic such as SDH, SONET, and GbE, ii) an extension of the offered CoS (class of service) domain
based on advanced standard technologies such as a 10-Gbit/s STM (synchronous transmission mode)interface, and iii) improved functions for control and supervision by the network element operating system. These features support flexible and economical networks. (SDH: synchronous digital hierarchy,
SONET: synchronous optical network, GbE: gigabit Ethernet)

1. Introduction
With the hardware of the DMS-10 switching system*1 becoming old, we intend to replace DMS-10
switching modules by new switching modules called
RSBMs (remote subscriber modules), ASMs (architectual STM modules), and SBMs (subscriber modules). However, if we simply replaced them, wewould need an optical fiber cable for each set of line
cross connect modules (LXMs) and RSBMs. This
would cause a shortage of optical fibers and thus
require a lot of investment for new optical cables. One
solution is to use an ADM ring system, but our existing one, which provides basic functions for transporting data at 10 or 2.4 Gbit/s, was introduced six years
ago, so it has become obsolete. For this level of performance, it is too big and too expensive. Therefore,
we are developing a new ADM ring system that canmultiplex several signals transported by multiple
optical fiber cables onto one cable. Figure 1 shows
an example of replacing a DMS-10 switching modulewith an RSBM in local branch networks.
2. Specifications of the new ADM ring system

ADM ring system. Any equipment can be connectedto the network element operating system (NE-OpS)
through a data communication network (DCN). We
control and supervise it via a human-machine interface (HMI). This ADM ring system has a capacity ofeither 2.4 or 10 Gbit/s on a single ring. Table 1 shows
the main specifications of this system, which has several superior functions compared with the existingone.
2.1 Various kinds of interfaces
The existing ADM 2.4-/10-Gbit/s ring system cantransport only SDH (synchronous digital hierarchy)
signals. We have developed some new tributary interfaces, such as ones for GbE (gigabit Ethernet) to handle various traffic signals, so we can provide variousnetwork services.
(1) SDH/SONET interface
As STM (synchronous transmission mode) interfaces, we developed SONET (synchronous opticalnetwork) interfaces, which are mainly used in North
America. We are also developing SDH interfaces,
which are used in existing transmission systems.
These SONET and SDH interfaces use the samehardware and are distinguished by software settings.

Figure 2 shows an example of constructing a new† NTT Network Service Systems Laboratories
Musashino-shi, 180-8585 Japan
E-mail: ikegawa.satoshi@lab.ntt.co.jp

70*1 The DMS-10 switching system from Northern Telecom (Nortel) isa carrier class central office switching platform offering dial tone
service. NTT first began using it in 1989, but has decided to phaseout this low-capacity digital switching system.

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A problem in replacing DMS-10 switching modules
D70

D70
Needs many
optical fibercables!

LXM

Transmission
system

To otherbuildings

Our new ADM ring system solves this problem.

D70150Mbit/s

Direct connection
from RSBM to
LXM by opticalfiber cables

DMS-10toRSBM

Transmission
system

LXM
ADM

Only needs two
optical fiber cables
for a ring

RSBM

RSBM
New ADM
ring system

ADM

ADM

DMS-10
RSBM

RSBM
D70: D70 switching module
DMS-10: DMS-10 switching module

RSBM: remote subscriber module
LXM: subscriber line cross connect module

Fig. 1. Effect of introducing the new ADM ring system.

HMI

NE-OpS

DCN

ADM

ADM

ADM

10 Gbit/s
ADM

ADM2.4 Gbit/s

ADM

ADM

ADM

Fig. 2. Example of a network configuration based on the new ADM ring system.
Table 1. Main specifications of new ADM ring system.
Functions of new ADM
Aggregate interfaces

Tributary interfaces

Path switching

Setting

NE-OpS

Existing ADM

2.4 Gbit/s, 10 Gbit/s

Yes

STM: 50 Mbit/s, 150 Mbit/s, 600 Mbit/s, 2.4 Gbit/s

Yes

SONET 150 Mbit/s, 600 Mbit/s, 2.4 Gbit/s—

GbE 1000Base-SX/LX—

Unprotected

Yes

Hitless switchingYes

Switching in 50 ms

Yes

Path

Virtual concatenation—RingMulti-ring, hairpin—Others

Add node in the ring with uninterrupted service
Upgrade capacity of the ring (from 2.4 to 10 Gbit/s) with uninterrupted service—Registration

Ring, NE, tributary interface, VC path (through some rings), section in the ringYes

Alarm supervision

NE in the ring, VC path (through some rings)

Yes

SearchConstitution of path, path contained in a section—Others

Multi-server—

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Letters(2) GbE interface
The new ADM ring system can also transmit Ethernet traffic using 1000Base-LX and 1000Base-SX forIP network services. The 1000Base-LX/SX interface
uses one common GbE package for both long-distance and short-distance transmission to reduce theexpense of using multiple package types. The GbE
package includes an appropriate SFP (small formfactor pluggable module) for each. In the new ADM
ring system, we used “virtual concatenation”, whichmaps a GbE signal into the payloads of STM signals
and transmits their STM paths as if they were a single
path. This technology makes effective use of bandwidth without being limited by the existing hierarchy.
2.2 Small size and high density
We made packages much smaller, so adding ordropping 10 Gbit/s requires only one shelf of equipment in the new system compared with two or threecabinets in the existing system. And the new systemshelf fits popular cabinets such as DS1 or DS2. Thus,
we achieved a small size and high density. Furthermore, we achieved these functions at a more economical price than before.
2.3 Extension of the offered CoS domain
Like the existing ADM ring system, the new system
can transmit STM signal paths such as VC-3, VC-4,and VC4-4c (VC: virtual container), but it extends theoffered CoS (class of service) domain by introducing
the capability to add or drop paths for VC4-16c (2.4Gbit/s). We have three kinds of protection: hitless
switching protection, switching in 50-ms protection(called normal protection), and unprotected traffic.
For GbE paths that use virtual concatenation, we havenormal protection and unprotected traffic. Figure 3
shows the CoS domain offered by the new ADM ringsystem.
2.4 NE-OpS
We also improved the functions of the operations
system for the new ADM ring system (NE-OpS). The
main functions are described below.
(1) Improved control of NEs and HMIs
The new ADM ring system can control more NEs
per server (i.e., 256) than the existing system (60). It
can also handle more HMIs (up to 16) per server. Thiswas made possible by the improved performance ofcomputer and software architectures.
(2) Functions for single-vendor network operation
In the past, when we operated a path through somerings, we used to have to operate the path separatelyfor each ring. In the new ADM ring system, however,
we can operate the entire path through several rings
just like a single path. At each HMI, we can selectwhether or not alarms sent from NEs are displayed on
the operator’s screen and whether they are displayed
separately for each ring or in overall order of importance. So we can effectively supervise many NEs in awide area. Furthermore, we can comprehend theroute of a path by graphically displaying it, so we canimmediately resolve any trouble. In this way, weService level

CoS

HitlessswitchingprotectionHighSwitching in50 ms protection

Unprotected

Low
50 M

: CoS that the new ADM ring system can provide

150 M
600 M
Transmission rateGbE

2.4 G

10 G (bits/s): CoS that the existing ADM ring system can provide

Fig. 3. CoS domain offered by the new ADM ring system.

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improved the functions of NE-OpS, so we can supervise and control one vendor’s NEs as effectively as
when we use a network operating system (NW-OpS).

capacity of the ring from 2.4 Gbit/s to 10 Gbit/s without interrupting service. This function is useful if we
initially construct a 2.4-Gbit/s ring network and laterwant to upgrade its capacity. Even during the upgrading process, a path having hitless switching protection is available for service. This function enables us
to take immediate action in response to suddenchanges in demand.

3. Flexible network
The new ADM ring system lets us construct ADM
ring networks flexibly and economically in responseto changes in demands, using the four functions
shown below. We show network examples in Fig. 4.

3.4 Multi-server
A multi-server means an HMI connected to several
servers at the same time. It means that we do not haveto prepare an HMI for each server. We can supervise
and control NEs in several servers via one HMI. We
can set HMIs in various patterns for this function. For
example, we can supervise NEs from one centralized
HMI. Figure 5 shows the concept. Usually, eachbranch has an HMI for path setting, and servers areset for each area. When we supervise NEs in one
place, we do not have to prepare an HMI for eachserver in the new ADM NE-OpS. This reduces thecost of the HMIs.

3.1 Multi-ring network
A multi-ring network has an NE connected to several rings at the same time. We can set a path throughsome rings without passing through tributary interfaces except for a path added or dropped at our own
NE. Using this function, we can construct ring networks more effectively and economically thanbefore.
3.2 Hairpin cross-connection
A hairpin means a path from one tributary interface
to another tributary interface that does not go throughany aggregate interface. In other words, a hairpin is apath that doubles back on itself. This function also
lets us convert interfaces when the NE is connected toanother system.

4. Conclusion and future work
We believe that this new ADM ring system will be
introduced as an economical infrastructure. We arecontinuing to develop more convenient functions andmore useful interfaces, such as 10-GbE.

3.3 Upgrading the capacity of the ring with
uninterrupted service
In the new ADM ring system, we can upgrade the2.4-Gbit/s
ring

10-Gbit/sring

Upgrade from 2.4 to 10 Gbit/s(with uninterrupted service)
ADM
ADM

10-Gbit/s ring
(local trunk network)

Multi-ring

ADM
ADM

ADM

2.4-Gbit/s ring
(local branch network)

2.4-Gbit/s ring
(local branch network) ADM
ADM

ADM

Hairpincross-connection

Fig. 4. Making a flexible network.

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Area X

Area Y

Branch A

Branch B

ADM
ADM

ADM
ADM

Branch C

ADM

ADM

ADM

ADM

ADM

ADM

ADM
ADM

ADM
ADM

NE-OpS

HMI

Branch D

ADM

NE-OpS

HMI

HMI

HMI

HMI for supervising a wide area
(multi-server HMI)

Fig. 5. Concept of multi-server function.

Satoshi Ikegawa

Kei Karato

First Promotion Project, NTT Network Service
Systems Laboratories.
He received the B.E. degree in electronic engineering from Waseda University, Tokyo in 1997.
In 1997, he joined NTT and engaged in constructing infrastructures. In 2002, he joined theNTT Network Service Systems Laboratories andhas developed some OSSs.

First Promotion Project, NTT Network Service
Systems Laboratories.
He received the B.E. degree in information andcommunication engineering from Tamagawa
University, Tokyo in 1995. In 1995, he joined
NTT and has researched and developed IP-OSSand OSS for transportation such as ADM 2.4-/
10-Gbit/s ring systems.

Hirokazu Sumi
Second Promotion Project, NTT Network Service Systems Laboratories.
He graduated in electronic engineering from
Gifu National College of Technology, Motosu,Gifu in 1998. In 1998, he joined NTT andengaged in basic planning and provisioning.

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