2. A General approach to MPLS Path Protection using Segments Ashish Gupta Ashish Gupta

3. 1 Overview Intro to MPLS —Difference from IP Why Path Protection ? —Existing Schemes Segment Based Approach —Its Mechanisms —Algorithm for segment setup —Simulation Results —Detection, Notification and Path Switching

4. 2 MPLS BUILT ON STANDARD IP 47.1 47.2 47.3 1 2 3 1 2 3 1 2 3 Destination based forwarding tables as built by OSPF, IS-IS, RIP, etc.

5. 3 IP FORWARDING USED BY HOP- BY-HOP CONTROL 47.1 47.2 47.3 IP 47.1.1.1 1 2 3 1 2 1 2 3

6. 4 MPLS Label Distribution 47.1 47.2 47.3 1 2 3 1 2 1 2 3 3 Mapping: 0.40 Request: 47.1 Mapping: 0.50 Request: 47.1

7. 5 Label Switched Path (LSP) 47.1 47.2 47.3 1 2 3 1 2 1 2 3 3 IP 47.1.1.1

8. 6 MPLS : ROUTE AT EDGE, SWITCH IN CORE IP Forwarding LABEL SWITCHING IP Forwarding IP #L1IP#L2IP#L3 IP  Applies concept of VC routing  Packet forwarding is done based on Label Switching  FEC: Destination address prefix, Traffic Engineering tunnel, Class of Service.

9. 7 WHY MPLS ? Ultra fast forwarding IP Traffic Engineering —Constraint-based Routing Virtual Private Networks —Controllable tunneling mechanism Voice/Video on IP —Delay variation + QoS constraints

10. 8 BEST OF BOTH WORLDS PACKET ROUTING CIRCUIT SWITCHING MPLS + IP form a middle ground that combines the best of IP and the best of circuit switching technologies. MPLS +IP IPATM HYBRID

11. 9 Path Protection and its Purpose What happens if fault occurs in a network element ? For traffic with critical QOS requirements, fast rerouting is required IP rerouting can take order of seconds Solution : Protect the path with another backup path

12. 10 Existing Schemes Global Path Protection Local Path Protection Link Failure Node Failure 1+1 Path Protection Sharing Modes - 1 : 1, 1 : N, M : N r Original LSP Backup LSP No flexibility in providing path protection for a MPLS network Segment Based Approach : A General Scheme for Path Protection

13. 11 Example  Global Path Protection : Large Notification Delay  Local Path Protection : Small delay but large number of backup paths  These solutions lie at two extremes.  Segment Based Approach : A General Scheme for Path Protection

14. 12 Segment Based Approach Protect each segment separately : Each segment seen as a single unit of failure SSR – Segment Switching router Flexibility in creating segments -> flexibility in Path Protection ( delay and backup paths ) SBPP – Segment Based Path Protection

15. 13 Steps in SBPP Creation of LSP Creation of segments - Greedy Algorithm Reservation of Backup Paths —Backup paths as tunnels A new combined Algorithm —Advantages Label Management in SBPP Label Distribution Mechanisms Signaling mechanisms Buffering to avoid packet loss and reordering Steps in recovery : —Fault Detection and Location —Fault Notification– How does it work in MPLS ? —Switching the path —Backup Path recovery Experimental Results

16. 14 Steps in SBPP For setting up a path request - Local Computation Information needed —Topology —Link Delays and congestion information —Bandwidth of each link – primary, backup, free After computation – Label information disseminated

17. 15

18. 16 Fault Detection, Location and Notification Fault can be detected by periodically sending liveness messages – Absence of response indicates link/node failure For faster detection, each node sends periodic messages to its neighbors Timing Analysis for Detection and Notification

19. 17 Fault Detection, Localization and Notification

20. 18 Creation of Segments Created according to QOS criteria —Delay or Reliability or a combination Ensure each segment individually meets the criteria Example - Bounded Delay on switching —Greedy Algorithm Some Problems - Experiments

21. 19

22. 20 Reservation of Backup Paths Advantage of SBPP – Flexibility in reservation of backup paths, not rigid Issues —Avoiding Loops Sharing of backup paths important —Cases : –1. Multiple LSPs, Multiple Segments –2. Multiple LSPs, Same Segment —Assumptions : Only one failure at a time Problem with the previous approach – see figure

23. 21 Loops in Backup Paths

24. 22 Problem with Greedy Algorithm

25. 23 A New Combined Algorithm Possible approaches —Exhaustive search for a suitable path – computationally exhaustive – need a heuristic The Combined Path Setup Algorithm —1. Setup a primary path ( based on a constraint e.g. min delay) —2. Start from egress node and find the largest possible segment which satisfies bounded delay switching time constraint ( call the SSR of this segment S1 ) —3. Find a backup path for this segment starting from S1 —4. If no backup path can be found, shrink the segment and try to find the backup path from the new SSR. If no further shrinking is possible then Reject request( or try another primary path - see below) —5. Repeat Step 4 until a segment with a backup path is found. —6. Repeat from step 2 for creating the next segment —7. Do this until the complete LSP is segmented.

26. 24 Advantages of this algorithm Ensures that if segmentation is possible on the primary path, then it will be performed. Here we have multiple starting nodes possible for finding the backup paths, so possibility of finding backup paths is more Can add more flexibility for the choice of SSR in forming segments e.g. case of overloaded LSR – won’t be made a SSR

27. 25 Description of Simulation Setup An MPLS network with —100 Nodes —200 Edges RTT of each link = 10 ms Periodicity of Liveness messages = 2 ms BW – 50 to 100 Generated large number of random LSP requests and observed various parameters Results indicate advantages of SBPP

28. 26 Segment Size vs BW reserved

29. 27 Segment Size vs BW reserved

30. 28 Segment Size vs Rejection Rate ( for 250 LSPs )

31. 29 No. of Requested LSPs vs Rejection Rate

32. Effect of Backup Path Sharing

33. 31 Bandwidth reserved vs No. of LSPs setup

34. 32 Crossover - Effects of backup path sharing

35. 33 Further Analysis – Improvement to Algorithm Delay over Backup Path also affects jitter ! Long backup paths : Higher end-to-end delay : Higher Switching time so have to constrain backup path construction also New expression for switching time —T p + RTT + (t2-t1) < max. switching delay Improvements to our Algorithm due to this

36. Steps in Rerouting

37. 35 A Mechanism for Notification After a fault is detected, notification needs to be sent to the SSR for switching the traffic Some nodes will participate in notification and the SSR will switch the route What information will be passed after a fault occurs ? What changes do we need in the LSR tables for switching? Case of Multiple LSPs : All LSPs using that segment may not pass through the faulty node/link – Only concerned LSPs should be switched

38. 36 A Mechanism for Notification

39. 37 Other work Creating Backup paths using tunnels Analysis of Liveness message periodicity

40. 38 Future Work Label Management and Distribution Issues Formal Definition of Protocol and Signaling Mechanisms required for detection, notification and other parts of our scheme Use of buffering to reduce packet loss during switchover Recovery Issues Implementation of our scheme in MPLS emulator.

41. 39 Targets specified in Mid-sem December 1 st 2001 —Error detection and notification issues in Segment based protection (SBP) —Work out example scenarios using SBP —An algorithm for SBP —Label management issues in SBP May 1 st 2002 —Simulations to test performance and resource usage vs. other schemes —Explore other issues like Buffering —Documenting our work

42. Thank You