Integrated Routing Strategies in IP over WDM Networks

1. Integrated Routing Strategies in IP over WDM Networks Malathi Veeraraghavan Antonio Rodriguez-Moral Jon Anderson Bell Labs - Lucent Technologies mv@bell-labs.com arodmor@bell-labs.com jonanderson@bell-labs.com

2. 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

3. 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, ...

4. 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)

5. 3 2 1 IP IP IP AAL5 PPP SDL ATM HDLC SONET/SDH SONET/SDH SONET/SDH WDM WDM WDM IP over WDM - Protocol stacks • IP: Internet Protocol • AAL5: ATM Adaptation Layer 5 • ATM: Asynchronous Transfer Mode • SONET: Synchronous Optical NETwork • PPP: Point-to-Point Protocol • HDLC: High-level Data Link Control • WDM: Wavelength Division Multiplexing • SDL: Simplified Data Link • provides length-based delineation instead of flag-based delineation [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.

6. R5 R3 R6 R1 ADM SXC ADM WDM NE SONET/SDH ring ADM R2 R7 R4 WDM NE WDM NE WDM NE WDM NE IP over WDM - Network architectures With and without SONET/SDH multiplexing SXC SONET/SDH Cross-Connect SONET/SDH Add-Drop Multiplexer ADM R 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

7. R IP IP IP R PPP PPP PPP HDLC HDLC HDLC SONET/SDH SONET/SDH SONET/SDH WDM OC3/OC12/OC48 OC3/OC12/OC48 IP over WDM - Network architectures Multiplex several SONET OC3, OC12, OC48 interfaces on to one fiber using WDM R WDM Multiplexer WDM Multiplexer R * Could even multiplex some IP/AAL5/ATM streams with IP/PPP/HDLC streams

8. 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

9. R3 R6 R1 R6 R5 R1 R3 R2 R7 R5 R4 R7 R4 R2 OXC OXC OXC OXC Two-layer routing problem Virtual Topology Physical 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?

10. OXC OXC OXC OADM 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 R3 R6 Optical Amplifier R1 R5 R7 R4 R2

11. 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

12. Generic integrated approach (not specific to IP) • 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. 1996, pp. 684-696.

13. R6 R1 R3 R5 R4 R7 R2 Routing protocols used in IP networks • Link state based routing protocols, e.g., Open Shortest Path First (OSPF) • Currently OSPF Link State Advertisements (LSAs) mainly include operator-assigned link weights • Shortest-path algorithms used to determine routing table entries based on these link weights (Dijkstra’s, Bellman-Ford) • Example: Shortest path from R3 to R7 is via R4 and R5 4 3 1 2 1 1 1 1

14. QoS extensions to OSPF • 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.

15. Classification of routing schemes • 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. Routing schemes Table-based Self-routing Shortest-path routing (user-level optimization) Optimal routing (system-level optimization)

16. 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? • What is the time scale of operation for the integrated IP/WDM software?

17. R3 R6 R1 R6 R5 R1 R3 R2 R7 R5 R4 R7 R4 R2 Virtual Topology Physical Topology OXC OXC OXC OXC Greedy distributed solution • 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 optimal) • Basis: optical layer routing should not change IP-layer routing data

18. R3 R6 R1 R5 R2 R7 R4 OXC OXC OXC OXC Centralized network-wide solution • 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) Network Management System

19. 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 • Use protection fibers for increased throughput, but when fault occurs, throttle back best-effort traffic and accommodate all higher-priority traffic

20. 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