Integrated Routing Strategies in IP over WDM Networks

Malathi Veeraraghavan Antonio Rodriguez-Moral Jon Anderson

Bell Labs - Lucent Technologies [email protected]

[email protected]

[email protected]

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Outline

    IP over WDM  Motivations  Protocol stacks  Network architectures IP/WDM integrated routing  Problem statement  Two-layer routing problem  Possible solution strategies  Integrated routing at IP and WDM layers • Interaction with the routing protocols used in IP networks  Greedy distributed solution  Network-wide centralized solution Extensions Summary April 20 2

IP over WDM - Motivations

   IP traffic volumes  Traffic volumes on the Internet double every six months  Aggregate bandwidth required by the Internet in the US by the year 2005 is expected to be in excess of 35 Terabytes/sec New high-capacity networks  To meet this anticipated need, carriers in the US are in the process of deploying high-capacity networks (OC-48~2.5 Gbps, and soon OC-192 ~10Gbps) for the sole purpose of delivering Internet data  Some new carriers are building networks customized for IP traffic (most existing “transport” networks were built primarily for voice traffic) IP-centric and IP multi-service networks: Voice over IP, Video over IP, ...

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IP over WDM - Motivations

      WDM reduces costly mux/demux function, reuses existing optical fibers.  Alternative to new fiber installation  Consolidation of legacy systems  Maximizes capacity of leased fibers  Future-proofing of new fiber routes WDM allows high flexibility in expanding bandwidth Cost Reduction - integrating optics and eliminating mux stages Operation Efficiency - elimination of redundant protocol layers Transport Efficiency - elimination of transport protocol overhead Emergent technology is evolving WDM from optical transport (point-to point line systems) to true optical networking (add-drop multiplexers and cross-connects) April 20 4

IP over WDM - Protocol stacks

1 2 3 IP AAL5 ATM SONET/SDH WDM IP PPP HDLC SONET/SDH WDM IP SDL SONET/SDH WDM April 20 IP: Internet Protocol AAL5: ATM Adaptation Layer 5 ATM: Asynchronous Transfer Mode SONET: Synchronous Optical NETwork PPP: Point-to-Point Protocol [1] W. Simpson, “PPP over SONET/SDH,”

IETF RFC

1619, May 1994.

[2] J. Manchester, J. Anderson, B. Doshi and S. Dravida, “IP over SONET,” IEEE Communications Magazine, Vol. 36, No. 5, May 1998, pp. 136-142.

HDLC: High-level Data Link Control WDM: Wavelength Division Multiplexing SDL: Simplified Data Link •provides length-based delineation instead of flag-based delineation 5

IP over WDM - Network architectures

R 1 SXC R 2 WDM NE R 3 With and without SONET/SDH multiplexing R 5 WDM NE R 6 ADM WDM NE ADM SONET/SDH ring ADM WDM NE R 4 R 7 SXC SONET/SDH Cross-Connect ADM SONET/SDH Add-Drop Multiplexer R WDM NE IP Router WDM Cross Connect or Add-Drop Multiplexer • All three protocol stacks can be used in conjunction with SONET/SDH multiplexing • Even without SONET/SDH multiplexing (for example R3 to R6 communication), since IP routers have SONET/SDH interfaces, IP over WDM could involve a SONET/SDH layer April 20 6

IP over WDM - Network architectures

Multiplex several SONET OC3, OC12, OC48 interfaces on to one fiber using WDM

R R

WDM Multiplexer WDM Multiplexer

R R

IP PPP HDLC SONET/SDH OC3/OC12/OC48 IP PPP HDLC SONET/SDH WDM IP PPP HDLC SONET/SDH OC3/OC12/OC48 * Could even multiplex some IP/AAL5/ATM streams with IP/PPP/HDLC streams April 20 7

IP/WDM integrated routing - Problem statement

 Develop algorithms for integrated management of routing data in IP over WDM networks

Problem space Solution space

IP over WDM without multiplexing capabilities in intermediate layers 2-layer problem IP over WDM with multiplexing capabilities in intermediate layers 3 or 4-layer problem Centralized Distributed   With SONET cross-connects, it becomes a three-layer problem With SONET cross-connects and ATM switches, it becomes a four layer problem April 20 8

Two-layer routing problem

R 1 R 2 R 3 R 4 R 5 R 6 R 7 R 1 R 2 R 3 R 6 OXC R 5 OXC OXC R 7 OXC R 4

Physical Topology Virtual Topology

 What are the benefits/costs (in terms of network performance and management complexity) of performing traffic/QoS management and survivability at the WDM optical layer instead of at the IP layer?

 Is there a hybrid or cooperative approach that is more optimal given a set of realistic performance and complexity constraints?

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What is particular about this (IP/WDM) 2-layer routing problem?

  Limit on the number of optical amplifiers a lightpath can traverse before requiring electronic regeneration  All wavelengths amplified equally at an optical amplifier Without wavelength changers at OXCs (Optical Cross-Connects), wavelength assignments to lightpaths need to ensure availability of selected wavelength on all fibers on the lighpath R 1 R 3 OXC R 6 Optical Amplifier R 5 OADM OXC R 7 OXC R 2 R 4 April 20 10

Solution strategies

   Integrated routing at the IP and WDM layers  Interaction between existing routing schemes at the IP layer and this new integrated solution “Greedy” distributed solution  Monitor lightpath utilization and change allocations of lightpaths between pairs or routers accordingly Centralized system-wide optimal solution 11 April 20

Generic integrated approach (not specific to IP)

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Solve four sub-problems:

 1. Determine virtual topology to meet all-pairs (source-destination) traffic  2. Route lightpaths on the physical topology  3. Assign wavelengths  4. Route packet traffic on the virtual topology Sub-problems 1 and 4 are equivalent to a data network design/optimal routing problem  Capacity assignments between routers are determined for a given traffic matrix  Flows are determined along with capacity assignments Metrics optimized:  Minimize costs  Subject to an average packet delay constraint  use M/M/1 queues and independence assumption to determine delay [3] B. Mukherjee, D. Banerjee, S. Ramamurthy, A. Mukherjee, “Some Principles for Designing a Wide Area WDM Optical Network,”

IEEE Journal on Selected Areas in Communications

, Vol. 4, No. 5, Oct. 12

Routing protocols used in IP networks

R 1 1 2 R 2 4 R 3 R 4 1 1 3 R 5 1 R 6 R 7 1 

Link state based routing protocols, e.g., Open Shortest Path First (OSPF)

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Currently OSPF Link State Advertisements (LSAs) mainly include operator-assigned link weights

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Shortest-path algorithms used to determine routing table entries based on these link weights (Dijkstra’s, Bellman-Ford)

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Example: Shortest path from R3 to R7 is via R4 and R5

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QoS extensions to OSPF

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Flow-based IP traffic

 Have LSAs include “available bandwidth”  Each flow has a required bandwidth; delete all links in graph that do not have requisite available bandwidth  Then apply shortest-path algorithm using link weights

Connectionless traffic

 Modified Bellman-Ford to determine shortest-paths using link weights  If there are multiple paths with the same minimal weight, then the path with the maximum available bandwidth is chosen [4] R. Guerin, S. Kamat, A. Orda, T. Przygienda, D. Williams, “QoS Routing Mechanisms and OSPF Extensions,” IETF Internet Draft, 30 Jan. 1998, draft-guerin-qos-routing-ospf 03.txt.

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Classification of routing schemes

Routing schemes Table-based Self-routing    Shortest-path routing (user-level optimization) Optimal routing (system-level optimization) Optimal schemes base routing decisions on all-pairs source destination traffic e.g., the integrated four sub-problem solution Shortest-path schemes make routing decisions for per-nodepair traffic e.g., OSPF [5] C. Baransel, W. Dobosiz, P. Gewicburzynski, “Routing in Multihop Packet Switching Networks: Gb/s Challenge”,

IEEE Network Magazine

, 1995, pp. 38-61.

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Interaction between OSPF and integrated solution

   No conflict:  The integrated solution changes “maximum” capacities between routers  OSPF (with QoS extensions) uses this information along with “available” capacities to make routing decisions Potential conflict:  Should the integrated solution change the forwarding table entries based on flows computed as part of the capacity assignment problem?

 If so, both OSPF and integrated solution are changing forwarding table entries Other issues:  OSPF LSAs need to exchange maximum bandwidths  Can instabilities result in forwarding data if both OSPF and integrated IP/WDM routing software make changes?

April 20  What is the time scale of operation for the integrated IP/WDM software?

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Greedy distributed solution

R 3 R 6 R 6 OXC R 1 R 1 R 3 R 5 R 5 OXC OXC R 4 R 7 R 2 R 7 R 2 OXC R 4 Virtual Topology Physical Topology   WDM network routing does not change the virtual topology It measures utilization on each lightpath (between pairs of routers)  If under-utilized, decrease number of lightpaths or data rates used on lightpaths  If over-utilized, increase number of lightpaths or data rates used on lightpaths  Using wavelength availability and optical amplifier related constraints, find shortest path for lightpath and establish crossconnections (“greedy” user-level April 20 17 optimal) Basis: optical layer routing should not change IP-layer routing data

Centralized network-wide solution

R 1 R 2 R 3 OXC OXC R 6 OXC R 5 R 7 Network Management System R 4 OXC   In greedy distributed solution, there may be instances when a lightpath could have been accommodated if routes or wavelength assignments of existing lightpaths had been adjusted All-pairs traffic demand is given; find optimal routes and wavelength assignments of lightpaths (also called the RWA problem) April 20 18

Extensions

   Consider multiple QoS metrics while finding optimal solutions  For example, in integrated solution, consider packet loss ratio, packet delay variation, improved packet delay formulations (assuming MMPP traffic) Extend solutions to allow for multiple service classes  Differentiated services in IP networks  Simple schemes for packet tagging, classification and per-hop behavior  Integration of IP service classification with routing and wavelength assignment Allow for network and service survivability  Use full capacity or have spare capacity April 20  Use protection fibers for increased throughput, but when fault occurs, throttle back best-effort traffic and accommodate all higher priority traffic 19

Summary

    Defined IP over WDM network architectures and protocol stacks Defined routing problem statement for two-layer networks  Special features of WDM networks: optical amplifier constraints, wavelength continuity constraints Proposed three solution strategies:  Integrated IP/WDM optimal routing to operate in parallel with OSPF shortest-path routing  Greedy distributed solution - monitors traffic offered to WDM network and determines shortest-paths meeting certain constraints (user-level optimal)  Centralized system-wide optimal solution - adjusts existing lightpaths if needed to accommodate newly requested lightpath Identified possible extensions 20 April 20