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PS.ThA2

Performance Evaluation of Optical Label Switched Path Routing

Algorithms in Photonic Networks

MasaruKATAYAMA, E･iji OXI, Eohei SHIOMOTO, Naoaki YAMANAKA, WatartL IMAJtrEU

NTT Network IrLnOVation IJaboratories

319-ll Midori-cho Musashino-shi, Tokyo 180-8585 JAPAN

Absiraci- We describe and evaluate 0-LSP (Op-

ticalLabel Switched Path) routingalgorithms in

photonic networks･ We extend the OSPF (OpenShortest Path First) protocol so tllat the wave-

length statllS Of each荘nk is advertised for 0_ESP

setting･

I. INTRODUCTION

The explosion of lntemet tra爪c has led to a greater

need for high-speed backbone networks. In order to

copewith the tra爪C) new technology nodes, which are

opticaleross-connectsl1]and photonic GMPI.S (Gen-

eralized Multi-Protocol IJabel Switching) routersl2],

【3日4】, are going to be introduced in backbone net-

works.

In opticalbackbone networks, 0-I.Spa (OpticalI,a-

bel Switched Paths) are provisioned l'Singlmg trafRcdemand cycles? that isl the photonic network doesn't

change dynamically. However, the opticalnetwork re-

sources, such as the wavelengths and the wavelength

converters mllSt be used e鮎iently because lnternet

tra用c is increaslng raPidly･ Dynamic 0-IJSP setting

tllat responds to tTa琉c demand is needed.

A key problemwith Dense Wavelength Division Mul-

tiplexing (DWDM) networks is the Routing and Wavel

1engthAssignment (RWA) problemlS]. This problem

prevents us from setting the 0-I･SPs even if the short-

est path doesnlt belong to the same wavelength plane

because path setting considers only fiber topology In-

formation The RWA problem basically consists of

the network structure problem and the node structure

problem･ The network structllre Problem is whether

the network has Wavelength converters or not. In a

network that doesn)I have wavelength converters, the

OIIJSP must be calculated on each waveleTLgth plme.

There are many calctllationalgorithms on one wave-

length planelS]. h a network that has wavelength

converters, each 0-I.SP must be determined for the

network topology ln Which wavelength planes are con-

PS 2002, 21-25 July 2002. Cheju. Korea

nected by wavelength converters･ Thus, the Calcula-

tion time is w2 times the calctllation time on the五ber

topology information, where w is number of wave-

length planes.

The node structllre Problem is how to connect wave-

length converters･ One approach is the trunk-type

wavelength converterl the other is the port-type waNe-

length converterl aB Shown in Figllre l･

The trunk-type wavelength converter is phced be-

tween the ingress portand the egress port on the op-

ticalcross-connect (0XC) like as五gllre 1 (a). The

wavelmgth converter is shared byall ports･ The ad-vantage of this structtLre is that the wavelength con-

ve-ter is used simply by setting the OXC･ However,

the OXC becomes too big because leach port of wave-

length converter must be specifically assigned to the

ports of the OXC.

The port-type wavelength converter is connected to

the ingress port of the OXC shownin Figure 1 (b).

It is problem that we mustknOw which ports of the

OXC have the wavelength converter becatISe Wave-

length converter depends on the port of the OXC. In

addition, the network has a directionaltopology be-

cause of the convertersI ThenI the network topology

size becomes very big.

However, ifall ports have this type wavelength con-

verters, the RWA problem vanishes becallSe a Wave-

(a) Trunk-type　　　　　(b) Port-type

Waverength converter Wavelength converter

Fig･ ll Node Architecturewith Wavelength Converter

C ap ab ility

217

length canalways be corLVerted into any of the other B. LL ALgorilhm

wavelengths･　　　　　　　　　　　　　Link cost is the recIPrOCalof the number of the un-

In this paper, we consider the trunk-type wave-　qsed wavelengths in the link･

length converter, and describe evaluation results for

the combination of 0-LSP routingalgorithms and the

trunk-type wavelength converter.

II. 0-LSP RoUTING ALGORITFMS

In order to evJaluate the routingalgorithms, We must

decide what we make a cost to calculate the 0_LSP

route･ Therefore, We consider the routing policies.

h the photonic IP network, there is a requirement

of emcient use of the network resources. The network

resources are link resources (wavelengths) and wave-

length conversion resources (wavelength converters)･

The network has better be a.s many untlSed network

resources a5 POSSible in order to llSe network resotlrCeS

e爪ciently･ We can accommodate many 0-LSPs in the

network if manyuntlSed resources are remained in the

network･ An additionaldemand is to avoid congestion

as mllCh aS possible･ The usage for each link may as

well batten even if the detollr Path is llSed.

We evaluate two conventionalalgorithms to meet

these requirementsl One is SPF (Shortest Path First)

algorithm and the other is I,I･ (Least I.oad)algorithm.

A. SPF AZ90rilhm

The link cost is the advertised OSPF (Open Short-

est Path FirLqt)[6】 link cost. The pathwith minimum

cost is calculated usirLg Dijkstra's approach for the

network. The network topology JS equivalent to the

fiber topology･ Althoughthe path determination issimple with shortest pathI the wavelengths and the

wavelength convertersalong the new path must be re-

served by RSVP-TE (Resource Reservation Protocol

with Tra氏c Engineering extensions)[7】. This means

that if no continuous path is available, RSVPITE tries

to set the shortest pathwith the fewest wavelength

convertersalOng the path･ Path blocking can occur if

the wavelength conversion resollrCeS are insufRcient.

The featllre Of thisalgorithm is that the wavelength

resources are llSed e抗ciently because the shortest rout-

lng path is set. h addition, the calclllation time is

short because only SPF calculation time is needed.

218

Cost =1

NUW'+E'

where NUW'is the nllmber of the llnuSed wavelengths,

and e is aparameter (0 < e < 1)I Inorder touse this

cost, au nodes mllSt know the nllmber of unused wave-

lengthsI Accordingly, we extended the OSPF proto-

col to advertise the wavelength statllS. The path with

minimum cost is calculated using Dijkstra's approach.

The feature ofthisalgorithm is that if the SPF path

has fewunused wavelengths, it may set a detollr Path

with large number oL unused wavelengths. In other

words, I'Lalgorithm selects the pathwith low block-

lng ratio by assesslngall available paths. 1Iowever,

this approach does not guaranteeminimum resources.

The other hand, the path calculated by the SPFalgo-

rithn may be blocked because only the shortest path

is considered.

III. EvALUATION AND CoNSTDERATION

We compared the 0-LSP routingalgorithm to the

existingalgorithms in term of the llSage Of wavelength

resoⅦrces and scalability.

^･ Usage of the wavelength resources

The relationship between the totaltramcand the

nllmber of the 0-LSPs indicate the e抗cient utilization

of wavelength resollrCeS. The number of the 0-I.SPs

follows a step function. We assume that each 0-IJSP

offers lOGb/s per wavelength, theminimum number

of the 0-I･SPs is the totaltra氏c over lOGb/S. There-

fore, we evaluate the difference between thisminimum

number and the number of 0-IJSPs set by eachalgo-

rithm.

The network has COnSidered has 25 nodes,and the

average node degree is 3･2･ The relationship between

the totaltra爪c and the number of OIIJSPs is shown

in Figure 2.

The comparison shows that the SPF and I･I･algo-

rithms exhibit the same cllaraCteristics at low traf_

fie loadsT but I･I･algorithm tends to setup new OI

IJSPs more steadily as the tra氏c increases･ Moreover,

we got the results of the tLSage Of the wavelength re-

sources･ Spy Ⅶses 3･O wavelengths (2･O hops) per O-

I･SP, while LIL requires 3.2 per 0-I,SP.

PS 2002. 21-25 July 2002. Cheju, Korea

20　　　　　　　　40　　　　　　　　60

CaTried Load tGhIsI

Fig. 2. Trafnc versus Number of 0-LSPs

B･ ScaLabiliiy Evaluation

In order to evaluate the scalability ofthealgorithms,

the relationship between the network size (the number

of nodes) a･nd the average time for determining one OI

LSP route is shown in FigtLre 3･ The network model

has average node degree of 87 and the links among the

nodes are randomly connected.

Thisfigure shows that the SPFalgorithm if faster

thaTL LI･･ This is because the LI･algorithm calclllates

detollr Paths in addition to the shortest pa･th as shown

in the previotIS Section.

ⅠV. SuMMARY

We evaluated the resource utilization and the seal_

abihty for 0-LSP routingalgorithms (SPFan_d IJeaSt

IJOad) in photonic networks. It shows one 0-LSP cal_

Culated within 1 second for the network which has

more than 100 nodes, and that network resources are

used e用.ciently.

PS 2002, 21125 July 2002. Cheju. Korea

/

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粁顔一--#′′

20　　　　　40　　　　　60　　　　　80

N一mbq a Nod早さ

1∝1　　　120　　　　1 40

Fig･ 3･ Calculation Time for LSP(Average Node De-

gree=8)

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borns･ D IEICE Trans･Commlln･, E83-B, No･10, ppl22 10-

2215, 2000.

[3] KShiomoto etal""MPhmbdaS DemorLStration Employ-ing Photonic Router (256X256 0LSPS) To lrLtegrate Opti-

cil aLnd IP Networks,竹National Fiber Optic Engneers Conf.

2001 Tech. Proc.,p. 5.

(4】 F･Kano et all,《I)evelopment of Photonic Router (256X256

0LSPS) Realize Next Generation Networkwith MPLamb_

daS Control,カNational Fiber Optic Engneers Conf. 2001

Tech･ Proc.,p. 458.

[51 Ⅱ･Zang etal･,aA Review of Routing and Wavelength

Assignmeht Approaches for Wavelengt,h-Routed Optical

WDM Networks,乃　Optical Networks Magazine,January

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l6】 J･TI Moy, "OSPF Version2, " RFC2328, April 1998.

[7】 D･0.Awduche et al,"RSVP-TE: Extensions t｡ RSVPfo.

LSP Tunnels,"

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