On Survivable Routing of Mesh Topologies in IP-over-WDM Networks

1. Infocom 2005, March 13-17, Miami On Survivable Routing of Mesh Topologies in IP-over-WDM Networks Maciej Kurant, Patrick Thiran EPFL, Switzerland

2. Logical topology Mapping GΦ Physical topology Mapping • Logical topology GL - mesh of IP links • Physical topology GΦ - mesh of physical links (fibers) • Each logical link is mapped on the physical topology as a physical path called a lightpath. • We assume infinite capacities of fibers • Mapping M - a set of lightpaths associated with a set of logical links GL M

3. Logical topology Mapping GΦ Physical topology Survivability How to deal with failures? There are several methods • Protection vs restoration • WDM layer vs IP layer GL M We use only the IP restoration approach: (The failures are detected at the IP layer, and a new route is found dynamically.)

4. Logical topology Mapping GΦ GΦ Physical topology GΦ Link-survivability example GL GL GL The logical topology remains conneceted after any single physical link failure The mapping is link-survivable

5. Connected Not connected!! Connected Logical topology Mapping GΦ GΦ Physical topology GΦ Node-survivability example v* GL GL GL v* The failure of node v* disconnects the remaining logical topology GL\{v*} The mapping is notnode-survivable

6. The problem of finding a survivable mapping is not new… J. Armitage, O. Crochat, and J. Y. Le Boudec, Design of a Survivable WDM Photonic Network, Proceedings of IEEE INFOCOM 97, April 1997. E. Modiano and A. Narula-Tam, Survivable lightpath routing: a new approach to the design of WDM-based networks, IEEE Journal on Selected Areas in Communications, vol. 20, no. 4, 2002 F. Giroire, A. Nucci, T. Taft, and C. Diot, Increasing the Robustness of IP Backbones in the Absence of Optical Level Protection, Proc. of IEEE INFOCOM 2003. L-W. Chen and E. Modiano, Efficient Routing and Wavelength Assignment for Recongurable WDM Networks with Wavelength Converters, Proc. of IEEE INFOCOM’03. …

7. Our solution

8. g e e g b f f c h a d h d Contraction GC=G C G Contraction of C={a, b, c}

9. e e e e g g g g g b b b b f f f f f c c c c d a a a a d d d h h h h h Logical topology Mapping GΦ GΦ Physical topology GΦ Iteration 1 Iteration 2 Iteration 3 The SMART algorithm (link-survivability example) Contracted topology GC GC GC e e d A single node! d GL GL GL Theorem 1: If the contracted logical topology GCconverges to a single node, then the mapping is (link/node)-survivable.

10. e e e e g g g g g b b b b f f f f f c c c c d a a a a d d d h h h h h Logical topology Mapping GΦ GΦ Physical topology GΦ Iteration 1 Iteration 2 Iteration 3 Verification of mapping existence Contracted topology GC GC GC e e d d GL GL GL A node-survivable mapping of the contracted topology GC={e,d} doesnot exist. A node-survivable mapping of the logical topology GLon GΦdoes not exist. Sequence of cycles does not matter! Theorem 2: A (link/node)-survivable mapping of GL on GΦ exists iff any contracted topology GC can be mapped on GΦin a (link/node)-survivable way.

11. SMART applied to the verification of the existence of a link/node-survivable mapping Application 1

12. Verification of mapping existence (2)

13. Random graph on NSFNET

14. SMART applied to the fixing a vulnerable topology (enabling link/node-survivable mapping) Application 2

15. e e g b f i d a d h i i i GΦ Where to introduce a new link? A new logical link which is a self-loop in the contracted topology GC will never help. GC GL Only a new logical link between two different nodes in GC might help. • In simulations (up to 64 nodes): • New logical link introduced at random rarely helped (<10%) • New logical link between two different nodes in GC helped in more than 80% of cases.

16. Applications of SMART (summary) • The formal verification of the existence of a link/node-survivable mapping, • a tool tracing and repairing the vulnerable areas in network, • a fast heuristic.

17. Thank you!