Special Feature

Multilayer Traffic Engineering (TE)
Based on IP Optical TE Server
Eiji Oki†, Daisaku Shimazaki, Ryuichi Matsuzaki,
Ichiro Inoue, and Kohei Shiomoto
Abstract
This article presents an IP (Internet protocol) optical traffic engineering server, which performs traffic
control in cooperation with IP routers and optical cross-connects (OXCs) in IP optical networks. This
server utilizes network resources, responds flexibly to unexpected changes in traffic demand, andrestores network connectivity quickly in the event of a system failure or natural disaster.

1. Introduction
The network is required to be both flexible and reliable. It should have sufficient flexibility to cope with
unexpected traffic fluctuations and should provide
highly reliable services while utilizing network
resources efficiently. Therefore, it is expected that thenetwork topology will be controlled by integrated
management of both IP (Internet protocol) routersand optical cross connects (OXCs).
NTT Network Service Systems Laboratories has
researched and developed an IP optical backbone network that can achieve integrated management of both
IP routers and OXCs [1]. As a result, NTT has developed an IP optical TE server for linking the IP routers
and OXCs in an IP optical backbone network andcontrolling traffic. It has conducted successful testbed trials of dynamic network control in an IP opticalbackbone network configured with IP routers andOXCs.
2. Multilayer traffic engineering
Multilayer traffic engineering can optimize network resource utilization considering all layers,rather than performing optimization independently
for each layer. As shown in Fig. 1, IP routers and† NTT Network Service Systems Laboratories
Musashino-shi, 180-8585 Japan
Email: oki.eiji@lab.ntt.co.jp

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OXCs are managed and operated by the optical TEserver considering the network resources of both layers. The IP optical server computes path routes acrossdifferent layers and controls them upon request fromusers and operators. The optical TE server dynamically reconfigures an IP network topology that consists of several optical paths, known as a virtual network topology (VNT), in response to traffic demand
fluctuations and network failures. The detailed functions of the IP optical TE server are described below.
(1) Multilayer path computation and several constraints
Let us consider computing a route between a source
router and a destination router in an IP optical network. There are two possible ways to do this: by asingle-layer or multilayer path computation. In thesingle-layer path computation, only IP links that havealready been established are considered. They may beoptical paths. On the other hand, in the multilayer
path computation, the possibility of new IP links,
which are optical paths that will be established later,
are considered as well as IP links that have alreadybeen established. For example, if the source router is
not connected to the destination router in the current
IP topology, the IP optical TE server may decide toestablish a new optical path for the requested end-toend packet path based on both IP and optical network
resources. In the calculation, constraints such as
bandwidth, delay, link attributes, inclusive/exclusive
routes, and protection class are taken into account.
Which multilayer route is selected also depends on aNTT Technical Review

Special Feature

IP optical TE server
Carriers’ policy implemented(multilayer, quality of service, reliability, etc.).
The policies can be customized.
IP/MPLS network

Multilayer routes

IP layer
Optical layer
VNT #1VNT reconfiguration

VNT #2

Optical network

Fig. 1. Multilayer traffic engineering based on IP optical TE server.

carrier’s policy. For example, one policy might try tofind available existing optical paths as much as possible, while another might try to establish a new optical
path in order to minimize the number of hops
between source and destination routers.
(2) VNT reconfiguration
The optical TE server can reconfigure the VNT in
response to a change in traffic demand change, a network failure, or a change in topology or under thecontrol of an operator. These trigger cases areexplained below.
(a) Traffic demand change: A traffic matrix isdefined as the traffic volume between borderrouters, which are located at the edges of optical networks. The traffic information is periodically collected from networks, the optimal
VNT is computed, and the VNT is changed
by setting up and releasing optical paths.
(b) Network failure: If a network failure occurs,
the optical TE server detects it by means of a
trap or advertisements of a routing protocol
such as OSPF (open shortest path first).
Based on new network resources and the traffic matrix, VNT reconfiguration is performed.
(c) Topology change: When a new link is added
or some existing links are deleted, the optical
TE server detects the topology change throughthe advertisement of a routing protocol. If aVol. 5 No. 3 Mar. 2007

network failure occurs, then based on new
network resources and the traffic matrix,
VNT reconfiguration is performed.
(d) Operator initiation: An operator can also initiate the VNT reconfiguration using the IP
optical TE server.
When the VNT is reconfigured, the concept ofshared risk link group (SRLG) should be considered.
As shown in Fig. 2, separate logical links that areaccommodated in the same fiber, fiber cable, or conduit may all be simultaneously affected by a singlefailure. Consider two different IP links, which are
optical paths. If these links belong to the same SRLG,
such as the same fiber, then a single failure in the network will cause multiple link failure. Therefore, ourVNT design algorithm considers SRLG constraints.
(3) Traffic matrix estimation
The VNT design algorithm uses a traffic matrix as
input information. Each element of the traffic matrix
is the traffic volume between a pair of border routers.
When the network becomes large, the number of border routers increases and it becomes difficult to measure all the traffic volumes between border routers. Inaddition, in the case of IP packet networks, it also
becomes difficult to analyze the IP headers of all theIP packets to determine their destination borderroutes. Therefore, the traffic matrix derivation
method must be scalable in terms of network size.
Our approach is to estimate the traffic matrix based61Special FeatureIP network topology(VNT)

Physical layer topology
VNT design framework

Input:
Traffic matrix
Physical network topology

Physical network topology
VNT designalgorithm

IP router
Optical cross connect
Optical path

IP layer topology

Constraints:
Shared risk link group
Distance/delay
Number of hops, etc.

Fig. 2. Reliable IP network topology (VNT) design.

(1) Retrieve traffic information using
SNMP from interface MIB.

IP optical
TE server

SNMP
GMPLS router(2) Estimate traffic matrix
IP router

IP link (optical path)

Input
Traffic volumepassing throughIP link (optical path)

OutputTraffic matrix
Traffic matrix
estimation
algorithm

Routing information
MIB: management information baseFig. 3. Traffic matrix estimation.

on the traffic volume passing through IP links (whichare optical paths) and on IP/MPLS routing information, instead of directly measuring each traffic volume between border routers. We implemented ourtraffic matrix estimation function in the IP optical TE
server. The traffic matrix estimation procedure isshown in Fig. 3. In step 1, the traffic volume passing
through IP links is retrieved using SNMP (simple network management protocol)*1 from the interface
management information base. In step 2, the trafficmatrix is estimated using the retrieved traffic volume
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and the IP/MPLS routing information. This estimation reduces the complexity of the traffic measurement, making it proportional to the number of IPlinks, whereas in the conventional approach it is proportional to the number of border router pairs. As aresult, VNT reconfiguration is possible even when
network size is large.
*1 SNMP is used by network management systems to monitor network-attached devices for conditions that warrant administrativeattention.

NTT Technical Review

Special FeatureTable 1. Functions of IP optical TE server.
Functions
MPLS/GMPLS
path computation

Interfaces

Single layer
Multiple layer

Route control
Path state management
IP network topology (VNT) control
Traffic matrix estimation
PCEP(working in progress)

Multivendor interfaces
Customization of path computation/control algorithms
Topology
RetrievalSingle layer

OSPF

Multiple layer

OSPF

Traffic volume

SNMP

Established path states

SNMP

3. Separation of traffic control algorithm fromnode equipment
Implementing this IP optical traffic control algorithm for the IP optical backbone network in the IP
optical TE server separately from node equipment
enables a carrier to apply traffic control policies considering quality of service, reliability, and efficiency.
This allows the carrier to differentiate its network
operations from those of other carriers. As a result,
NTT can provide stable, reliable, and flexible services using its own policies and algorithms. The control interface between the server and node equipment
is currently being standardized in the Path Computation Element (PCE) Working Group of the Internet
Engineering Task Force (IETF) based on the participation of NTT, several overseas telecommunication
carriers, and various communications equipmentvendors.
4. Functions of IP optical TE server
The functions of the IP optical TE server are shownin Table 1. To perform multilayer traffic engineering,
it requires several types of information, including theIP and optical topologies, traffic volume, and path
attributes. In addition, requests and replies for pathcomputation and path setup/release require interfaces
between the IP optical TE server and router. As muchas possible, the IP optical TE server uses standardized
interfaces between the server and routers, such as
OSPF, SNMP, and PCEP (PCE communication protocol)*2.

Vol. 5 No. 3 Mar. 2007

5. Experiments
The functions of multilayer traffic engineering,
including path computation across multiple layers
and dynamic VNT reconfiguration in response totraffic fluctuation, were tested in an IP optical backbone network consisting of an IP optical interlinking
server, IP routers, and OXCs. The experimental network configuration is shown in Fig. 4. The network
consisted of four GMPLS routers, two MPLS routers,
a distributed traffic generation tool, and a VNT viewer. The distributed traffic generation tool generated
traffic from multiple terminals and consists of a traffic controller and traffic generators. It could emulate
the traffic fluctuation that occurs in a real network
environment. The VNT viewer is a tool for displaying
the topology of each layer and the network status. A
schematic screen image is shown in Fig. 5. The viewer provided a realtime display of the physical network
topology, IP network topology (VNT), traffic volume
passing through optical paths and MPLS paths, andlists of MPLS and optical paths including their routesand attributes.
NTT demonstrated multilayer traffic engineering
based on the IP optical TE server in the iPOP2006
Interoperability Showcase using multivendor equipment at this international conference held on June
22–23 in Tokyo.
*2 PCEP is a protocol for communication between a path computation client (PCC) and a path computation element (PCE), orbetween two PCEs. The communication consists mainly of pathcomputation requests and path computation replies as well as notifications and error messages.

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Special Feature

IP optical TE server
IP/MPLS network

VNT
viewer

GMPLS network

IP/MPLS
network

IP/MPLS
network

GMPLS router

Distributed traffic
generation tool

MPLS router
OXC

IP/MPLS networktraffic generator

Fig. 4. Configuration of experimental network.

IP networktopology
(VNT)

MPLS
path list

Traffic volumepassing
through
MPLS path

Traffic volume passing
through optical path

Opticalpath list

Network status
Physical network topology

Fig. 5. VNT viewer.

6. Future development
In the future, in anticipation of unexpected trafficchanges, we plan to promote international standards
at IETF, conduct interoperability trials with vendors,
and add functions needed for operation and control
scenarios in actual networks.

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Reference[1]

K. Shiomoto, E. Oki, I. Inoue, and S. Urushidani, “A server-based
traffic engineering method in IP + Optical multi-layer networks,” Int.
Conf. on IP + Optical Network (iPOP) 2006 Session T3-4, June 2006.

NTT Technical Review

Special Feature

Eiji Oki

Ichiro Inoue

Senior Research Engineer, Broadband Network Systems Project, NTT Network Service
Systems Laboratories.
He received the B.E. and M.E. degrees in
instrumentation engineering and the Ph.D.
degree in electrical engineering from Keio University, Kanagawa, in 1991, 1993, and 1999,
respectively. He joined NTT Communication
Switching Laboratories in 1993. Since then, hehas been researching multimedia-communication network architectures based on ATM techniques, traffic-control methods, and high-speed
switching systems. From 2000 to 2001, he was a
Visiting Scholar at Polytechnic University,
Brooklyn, New York, where he was involved indesigning terabit switch/router systems. He is
now engaged in R&D of high-speed optical IP
backbone networks. He received the 1998
Switching System Research Award and the 1999
Excellent Paper Award from IEICE, and the2001 Asia-Pacific Outstanding Young ResearcherAward presented by IEEE Communications
Society for his contribution to broadband network, ATM, and optical IP technologies. He coauthored “Broadband Packet Switching Technologies,” published by John Wiley, New York,in 2001 and “GMPLS Technologies,” publishedby CRC Press, Boca Raton, in 2005. He is aSenior Member of IEEE and a member of theInstitute of Electronics, Information and Communication Engineers (IEICE) of Japan.

Senior Research Engineer, Supervisor, IP
Optical Networking Group, Broadband Network
Systems Project, NTT Network Service Systems
Laboratories.
He received the M.E. degree in electrical engineering from the University of Tokyo, Tokyo, in1990. He joined NTT in 1990. Since then, his
research interests have included telecommunication protocols such as IP and ATM. He has been
active in standardization such as ISO/ISC (as anational committee member), ITU-T, and IETF.
He was a Visiting Scholar at Columbia University, USA, in 1995.

Daisaku Shimazaki
Broadband Network Systems Project, NTT
Network Service Systems Laboratories.
He received the B.E. degree in applied chemistry and M.S. degree in material science fromKeio University, Kanagawa, in 1999 and 2001,
respectively. He joined NTT Network Service
Systems Laboratories in 2001. His research interests include IP optical networking and trafficengineering based on GMPLS techniques. He isa member of IEEE and IEICE.

Ryuichi Matsuzaki
Senior Research Engineer, IP Optical Networking Group, Broadband Network Systems
Project, NTT Network Service Systems Laboratories.
He received the B.E. and M.S. degrees fromWaseda University, Tokyo, in 1989 and 1991,
respectively. Since joining NTT in 1991, he has
been engaged in R&D of network performance
evaluation, an ATM network management system, a content tracking system, and IP opticalnetworks. He is a member of IEEE and the Operations Research Institute of Japan.

Vol. 5 No. 3 Mar. 2007

Kohei Shiomoto
Senior Research Engineer, Supervisor, GroupLeader, IP Optical Networking Group, Broadband Network Systems Project, NTT Network
Service Systems Laboratories.
He received the B.E., M.E., and Ph.D. degrees
in information and computer sciences from
Osaka University, Osaka, in 1987, 1989, and1998, respectively. He joined NTT in 1989 andengaged in R&D of ATM traffic control andATM switching system architecture design. During 1996–1997, he was engaged in research on
high-speed networking as a Visiting Scholar at
Washington University in St. Louis, MO, USA.
During 1997–2001, he was directing architecture
design for the high-speed IP/MPLS label switching router research project at NTT Network Service Systems Laboratories. Since July 2001, hehas been engaged in the research fields of photonic IP router design and routing algorithms andin GMPLS routing and signaling standardization,
first at NTT Network Innovation Laboratories
and then at NTT Network Service Systems Laboratories. He is active in GMPLS standardization
in IETF. He is a member of IEEE, IEICE, and theAssociation for Computing Machinery. He wasthe Secretary for International Relations of theCommunications Society of IEICE from June
2003 to May 2005. He was the Vice Chair ofInformation Services of the IEEE ComSoc Asia
Pacific Board from January 2004 to December
2005. He has been involved in the organizationof several international conferences including
HPSR 2002, WTC 2002, HPSR 2004, WTC2004, MPLS 2004, iPOP 2005, MPLS 2005,
iPOP 2006, and MPLS 2006. He received theYoung Engineer Award from IEICE in 1995 andthe Switching System Research Award fromIEICE in 1995 and 2000. He was one of theauthors of “GMPLS Technologies: Broadband
Backbone Networks and Systems”.

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