Traffic Grooming in WDM Networks

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Traffic Grooming in WDM Networks

• Wang Yao

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WDM Technology

• increases the transmission capacity of optical
  fibers
• allows simultaneously transmission of multiple
  wavelengths within a single fiber

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SONET

• SONET ring network is currently the most widely
  deployed optical network infrastructure
• SONET Add/Drop Multiplexer (SADM) can be used to
  aggregate lower rate stream from different
  end-users into a single high-rate SONET stream in
  Time Division Multiplexing (TDM) fashion.
• In SADM, traffic needs to be processed in
  electronic domain.

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SONET over WDM

• With WDM technology, multiple SONET rings can be
  supported on a single fiber pair by using
  multiple wavelengths.
• Requires more electronic multiplexing equipments
  .
• The cost of electronics, instead of the cost of
  optics, dominates the cost of optical network

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Optical Bypass using WADM

• WDM add/drop multiplexers (WADMs) provide the
  ability to drop (or add) only the wavelength that
  carries the traffic destined to (or originated
  from) the node.
• On the other hand, WADMs bypass other wavelengths
  optically.

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Traffic Grooming

• Every wavelength needs a SADM only at every node
  where it is ended
• Using the optical bypassing capacity provided by
  WADMs, the traffic can be groomed in such a way
  that the total number of SADMs needed is
  minimized.

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Traffic Grooming Illustrated (I)

• Unidirectional ring network with four nodes
• each wavelength supports an OC-48 ring
• between each pair of nodes there are eight OC-3
  circuits

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Traffic Grooming Illustrated (II)

• Traffic assignment
• ?1 1?2, 3?4
• ?2 1?3, 2?4
• ?3 1?4, 2?3

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Traffic Grooming Illustrated (III)

• Traffic assignment
• ?1 1?2, 1?3
• ?2 2?3, 2?4
• ?3 1?4, 3?4

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Traffic Grooming RWA (I)

• without considering sharing of SADMs, each
  lightpath requires two SADMs
• Proper routing and wavelength assignment (RWA)
  allows more sharing of SADMs among lightpaths

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Traffic Grooming RWA (II)

• RWA1
• ?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
• RWA2
• ?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

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Traffic Grooming RWA (III)

• Two-step approach to design network
• low level grooming of tributaries traffic onto
  lightpaths
• executing RWA algorithm on the resulting
  lightpaths
• An improvement of 20 can be achieved if the two
  steps are considered jointly.

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Traffic Grooming RWA (IV)

• Two goals to design network
• Minimum number of wavelengths
• Minimum number of electronic equipments (SADMs)
• The two goals may not be achieved simutaneously

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Modeling Traffic Grooming

• Integer Linear Programming (ILP) approach

Single-hop bidirectional ring
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Modeling Traffic Grooming

• Nomenclature

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Modeling Traffic Grooming

• Computational Complexity
• NP-complete
• Needs heuristic algorithm
• Special Cases
• Static traffic
• Uniform traffic
• Hub traffic

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Grooming Benefit

• unidirectional ring with uniform traffic

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A Heuristic Two-Step Approach

• Pack traffic demands (e.g., OC-3s) into circles
• Capacity of each circle equals to basic tributary
  rate (OC-3)
• Contains nonoverlapping traffic
• All the circles are grouped into wavelengths
• As many end nodes as possible must be matched

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Grooming Dynamic Traffic

• Most earlier works focus on static traffic, which
  is applicable in network design with
  well-estimated steady traffic demands
• Traffic demands may change over a long period, it
  is important to accommodate traffic changes.

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Grooming with Cross-Connects

• Another approach to reduce SADMs is to use
  cross-connects at several nodes.
• Cross-connects is capable of switch traffic from
  one wavelength to another wavelength
• Various network architectures with different
  amounts of cross-connect capabilities have been
  studied.
• Usually less electronics can be achieved at the
  expense of more wavelengths.

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Grooming in IP/WDM Networks

• In future IP over WDM networks, SADMs may not be
  needed.
• The function of multiplexing traffic onto
  wavelengths falls on IP routers.
• Optical bypass ability may be provided by WDM
  cross-connect.

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Grooming in IP/WDM Networks

• Without optical bypass, routers would be burdened
  with processing information on all wavelengths.
• The goal is to minimized the number of ports in
  networks.

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Grooming in Mesh Networks

• Due to the increase of Internet traffic, more WDM
  networks would be deployed in general mesh
  topology to meet this demands. Thus more work
  needs to be done in the mesh networks grooming
  problem.

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Acknowledgement

• This presentation document is based on the
  following papers.

• Eytan Modiano and Phil Lin, "Traffic Grooming in
  WDM networks," IEEE Communications Magazine,
  July, 2001.
• 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.
• X. Zhang and C. Qiao, An Effective and
  Comprehensive Approach to Traffic Grooming and
  Wavelength Assignment in SONET/WDM Rings,
  IEEE/ACM Transactions on Networking, VOL. 8, No.
  5, October 2000.

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Thanks!