Traffic Grooming in WDM Networks

Traffic Grooming in WDM NetworksTraffic Grooming in WDM Networks

Wang Yao

WDM TechnologyWDM Technology

increases the transmission capacityof optical fibers

allows simultaneously transmissionof multiple wavelengths within asingle fiber

SONETSONET

SONET ring network is currently the mostwidely deployed optical networkinfrastructure

SONET Add/Drop Multiplexer (SADM) canbe used to aggregate lower rate streamfrom different end-users into a singlehigh-rate SONET stream in Time DivisionMultiplexing (TDM) fashion.

In SADM, traffic needs to be processed inelectronic domain.

SONET over WDMSONET over WDM

With WDM technology, multiple SONETrings can be supported on a single fiberpair by using multiple wavelengths.

Requires more electronic multiplexingequipments .

The cost of electronics, instead of thecost of optics, dominates the cost ofoptical network

Optical Bypass using WADMOptical Bypass using WADM

WDM add/drop multiplexers (WADMs) provide theability to drop (or add) only the wavelength that carriesthe traffic destined to (or originated from) the node.

On the other hand, WADMs bypass other wavelengthsoptically.

Traffic GroomingTraffic Grooming

Every wavelength needs a SADMonly at every node where it is ended

Using the optical bypassing capacityprovided by WADMs, the traffic canbe groomed in such a way that thetotal number of SADMs needed isminimized.

Traffic Grooming Illustrated (I)Traffic Grooming Illustrated (I)

Unidirectional ring network with fournodes

each wavelength supports an OC-48ring

between each pair of nodes there areeight OC-3 circuits

Traffic Grooming Illustrated (II)Traffic Grooming Illustrated (II)

Trafficassignment:

1: 1↔2, 3↔4

2: 1↔3, 2↔4

3: 1↔4, 2↔3

Traffic Grooming Illustrated (III)Traffic Grooming Illustrated (III)

Trafficassignment:

1: 1↔2, 1↔3

2: 2↔3, 2↔4

3: 1↔4, 3↔4

Traffic Grooming & RWA (I)Traffic Grooming & RWA (I)

without considering sharing ofSADMs, each lightpath requires twoSADMs

Proper routing and wavelengthassignment (RWA) allows moresharing of SADMs among lightpaths

Traffic Grooming & RWA (II)Traffic Grooming & RWA (II)

RWA#1

1: 1↔2, 2↔3, 4↔5, 5↔6, 7↔8, 8↔9 (9 SADMs)

2: 1↔3, 4↔6, 7↔9 (6 SADMs)

Total = 15 SADMs

RWA#2

1: 1↔2, 2↔3, 3↔1 (3 SADMs)

2: 4↔5, 5↔6, 6↔4 (3 SADMs)

2: 7↔8, 8↔9, 9↔7 (3 SADMs)

Total = 9 SADMs

Traffic Grooming & RWA (III)Traffic Grooming & RWA (III)

Two-step approach to design network

–low level grooming of tributaries traffic ontolightpaths

–executing RWA algorithm on the resultinglightpaths

An improvement of 20% can be achieved ifthe two steps are considered jointly.

Traffic Grooming & RWA (IV)Traffic Grooming & RWA (IV)

Two goals to design network

–Minimum number of wavelengths

–Minimum number of electronicequipments (SADMs)

The two goals may not be achievedsimutaneously

Modeling Traffic GroomingModeling Traffic Grooming

Integer Linear Programming (ILP) approach

Single-hop bidirectional ring

Modeling Traffic GroomingModeling Traffic Grooming

Nomenclature

Modeling Traffic GroomingModeling Traffic Grooming

Computational Complexity

–NP-complete

–Needs heuristic algorithm

Special Cases

–Static traffic

–Uniform traffic

–Hub traffic

Grooming BenefitGrooming Benefit

unidirectional ring with uniform traffic

A Heuristic Two-Step ApproachA Heuristic Two-Step Approach

Pack traffic demands (e.g., OC-3s) intocircles

–Capacity of each circle equals to basictributary rate (OC-3)

–Contains nonoverlapping traffic

All the circles are grouped intowavelengths

–As many end nodes as possible must bematched

Grooming Dynamic TrafficGrooming Dynamic Traffic

Most earlier works focus on statictraffic, which is applicable in networkdesign with well-estimated steadytraffic demands

Traffic demands may change over along period, it is important toaccommodate traffic changes.

Grooming with Cross-ConnectsGrooming with Cross-Connects

Another approach to reduce SADMs is touse cross-connects at several nodes.

Cross-connects is capable of switch trafficfrom one wavelength to another wavelength

Various network architectures with differentamounts of cross-connect capabilities havebeen studied.

Usually less electronics can be achieved atthe expense of more wavelengths.

Grooming in IP/WDM NetworksGrooming in IP/WDM Networks

In future IP over WDM networks,SADMs may not be needed.

The function of multiplexing trafficonto wavelengths falls on IP routers.

Optical bypass ability may beprovided by WDM cross-connect.

Grooming in IP/WDM NetworksGrooming in IP/WDM Networks

Without optical bypass, routers would be burdenedwith processing information on all wavelengths.

The goal is to minimized the number of ports innetworks.

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Grooming in Mesh NetworksGrooming in Mesh Networks

Due to the increase of Internet traffic,more WDM networks would bedeployed in general mesh topologyto meet this demands. Thus morework needs to be done in the meshnetworks grooming problem.

AcknowledgementAcknowledgement

1.Eytan Modiano and Phil Lin, "Traffic Grooming in WDM networks," IEEE Communications Magazine, July, 2001.

2.J. Wang, W. Cho, V. R. Vemuri, and B. Mukherjee, “Improved Approaches for Cost-Effective Traffic Grooming in WDM Ring Networks: ILP Formulations, Single-Hop and Multihop Connections,” IEEE/OSA Journal of Lightwave Technology,vol. 19, no. 11, pp. 1645-1653, Nov. 2001.

3.X. Zhang and C. Qiao, “An Effective and ComprehensiveApproach to Traffic Grooming and Wavelength Assignment inSONET/WDM Rings,” IEEE/ACM Transactions onNetworking, VOL. 8, No. 5, October 2000.

This presentation document is based onthe following papers.

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