Jian Pu Department of Computer Science University of Victoria November, 2002

1. Reliable MPLS(R-MPLS ) Jian Pu Department of Computer Science University of Victoria November, 2002

2. Outline • Introduction • MultiProtocol Label Switching Architecture (MPLS) • Path Restoration Schemes • R-MPLS • Overview • Path Overlapping • Alternate Path Calculation • Simulations • Summary

3. MPLS • MPLS is a label substitution protocol • MPLS is known for its label-driven routing. • Every packet has an assigned label in its header. • The labelis used as an index of the forwarding table, which specifies the next hop. • MPLS supports QoS services by explicit routing • two label signaling protocols: CR-LDP and RSVP-TE • bandwidth reservation is supported.

4. Example of an MPLS route (LSP)

5. Path Restoration Schemes • When to calculate alternate paths • Pre-calculation • pre-calculate and pre-establish alternate paths • pre-calculate alternate paths, but no pre-installation. (e.g. no resource reservation before hand, and trying to set up an alternative after a failure occurs) • On-demand calculation • when a working path is affected by a network failure, a new path will be calculated and then installed from s to t.

6. Path Restoration Schemes • How to use alternate paths Link restoration Partial path restoration Path restoration

7. R-MPLS Overview (1) • Improve reliability • multiple paths with limited shared edges for a given node pair • fast response time in case of failures by path switching • pre-calculate alternate paths and pre-establish them • use the “path restoration” scheme • the ingress node just writes new label to packet headers • Guarantee QoS requirements • Each alternate path satisfies the end-to-end delay constraint. • Each alternate path has enough bandwidth reservation. • => after path switching, the alternate path meets QoS demands.

8. R-MPLS Overview (2) • R-MPLS = MPLS + path restoration • Based on QoSOSPF • Latest bandwidth usage of each link and global network topology are known at runtime • Such information is stored in the link-state database, and maintain by the QoSOSPF • Acceptable alternate paths are calculated from the link-state database subject to the desired constraints.

9. R-MPLS -Alternate Path Calculation (1) • Problem definition • For a given node pair (s, t), calculate k paths (P0 , P1… Pk-1 , k = 2, 3) such that these k paths satisfy the following constraints: • available bandwidth >= BWrequired • include the shortest path, say P0 , from s to t • Pi(length) <= MaxLen (i = 0 , 1… k-1) • double-shared edges among P0 , P1… Pk-1 <= MaxSEdbl • triple-shared edges among P0 , P1 … Pk-1 <= MaxSEtri

10. Overlapping of three paths

11. R-MPLS -Alternate Path Calculation (2) • Three heuristic algorithms • the Modified Bak’s algorithm (MBAK) • is proposed in this conference paper • calculates an acceptable alternate path by path concatenation (i.e. Pst = Psv || Pvt) • the Extended MPS K shortest paths algorithm (EMPS) • the Edge-weight Increasing alternate path-finding algorithm (EWI)

12. R-MPLS -Alternate Path Calculation (3) • Algorithm comparisons • EWI calculates paths with minimum shared edges but longer path lengths. • EMPS calculates paths with shortest path lengths but more shared edges. • The alternate paths calculated by MBAK will have moderate paths lengths and shared edges. It stands somewhere between EWI and EMPS.

13. Network for simulations

14. R-MPLS Simulations (1) The paths calculated by EWI, MBAK and EMPS

15. R-MPLS Simulations (2) • Response time to failures • let t1represent time interval to receive the failure notice. • path switching in R-MPLS (alternate path routing) • tswitch = 0.14 millisecond (for choosing an alternative) • no time cost for establishing a chosen alternate path • the total time to respond a failure is tR-MPLS = t1 + tswitch • path re-calculation in conventional MPLS (single-path routing) • tre-cal = 5.2 millisecond (for re-calculating new paths by the Dijkstra’s algorithm) • let t2 represent the time cost to establish a new path • the total time to respond a failure is tMPLS = t1 + tre-cal + t2

16. R-MPLS Simulations (3) The ratios of path re-calculations between R-MPLS and MPLS under same injected random failure events. • Edge weight changes - a path is considered as failed when its length increases more than 50%

17. Summary • Reliability can be significantly improved by using alternate path routing in MPLS • The propose R-MPLS meets the needs. • Time for path switching is quite small. • Path re-calculations are notably reduced. • Three alternate path-finding algorithms • Enough alternate paths can be found. • All calculated paths satisfy the constraints.

18. References [1]. J. Pu, E. G. Manning, and G. C. Shoja , Reliable Routing in MPLS Networks, Proc. IASTED CCN 2002, Boston, USA, Nov. 2002 [2]. J. Pu, E. G. Manning, G. C. Shoja, and A. Srinivasan, A New Algorithm to Compute Alternate Paths in Reliable OSPF (ROSPF), Proc. PDPTA'2001, Vol. 1, pp. 299-304, June 2001, Las Vegas, Nevada, USA [3]. B. Jamoussi and et. al., RFC3212, Constraint-Based LSP Setup using LDP, Jan. 2002 [4]. D. Awduche, and et. al., RFC3209, RSVP-TE: Extensions to RSVP for LSP Tunnels, Dec. 2001 [5]. G. Apostolopoulos, RFC 2676, QoS Routing Mechanisms and OSPF Extensions, August 1999 [6]. D. Haskin and R. Krishnan, A Method for Setting an Alternative Label Switched Paths to Handle Fast Reroute, draft-haskin-mpls-fast-reroute-04.txt, Internet Draft, May 2000 [7]. E.Q.V. Martins, M.M.B. Pascoal, and J.L.E. Santos, Deviation Algorithms for Ranking Shortest Paths, International Journal of Foundations of Computer Science, Vol. 10, No. 3 (1999), pp247-261 [8]. S. Bak, J. A. Cobb and E. L. Leiss, Load-Balanced Routing via Randomization, CLEI’99, Asuncion, Paraguay, Sep. 1999 [9]. E. Rosen, A. Viswanathan, R. Callon, RFC3031, Multiprotocol Label Switching Architecture, Jan. 2001