QoS-Aware Path Protection in MPLS Networks Ashish Gupta Ashish Gupta Bijendra Jain Indian Institute of Technology Delhi Satish Tripathi University of California at Riverside

1 Overview MPLS networks —Special need for path protection Approaches to path protection in MPLS networks —Link, node based —LSP based Segment Based Approach —Mechanisms (detection, notification and path switching) —Algorithm for segment identification —Some simulation results

2 Path protection Routing algorithms for IP networks take seconds to re- compute routes Voice & video are sensitive to “switch-over” time —require switch over in less than 50 to 100 ms Identify and set-up back-up paths a-priori BACKUP PATH

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4 Path protection in MPLS networks Protection against link and node failure —We consider both types of failures Single vs. multiple failures —We largely consider single failures, but… Centralized vs. distributed computation and setup —We permit centralized computation

5 Major considerations —Bound switch-over time (and consequent loss of data) –Of the order of 50 ms to 150 ms —Meet SLA commitments –viz. QoS constraints – Path availability – End-to-end delay – Jitter – Packet drop rate —Use resources for path protection efficiently

6 Path protection in MPLS networks Complete LSP by-pass —allocation of resources along back-up path is efficient —time to detect failure and switch over is large —difficult to identify a node-disjoint path that also meets the specified QoS constraints

7 Path protection in MPLS networks Link by-pass —allocation of resources for back-up paths is unlikely to be efficient —fault detection and switch over can be fast —cannot be sure about QoS resulting from any failure —does not address node failure

8 Path protection in MPLS networks Node by-pass —allocation of resources for back-up paths is unlikely to be efficient —fault detection and switch over can be very fast —cannot be sure about QoS resulting from any failure

9 Segment Based Protection The Main Idea Look at the path as a sequence of segments and protect each segment separately

10 Segment based protection: a proposal —flexibility in identifying segments –schemes to protect LSP, links, or nodes are special cases —efficient allocation of resources for back-up paths —bounds on fault detection and switch over time —ability to identify back-up paths that meet specified QoS constraints

11 Focus of our paper develop algorithms to identify segments, and back-up paths, such that —switch over time (time for which packets are lost between failure and recovery) is bounded —path resulting from any single failure continues to satisfy given QoS constraints —resources are used efficiently (or more precisely, the number of segments is minimized)

12 Algorithm for Bounded Switch over time Switch over time The time for which packets are lost between failure and recovery

13 Fault Detection, Location and Notification Faults detected using live-ness messages with periodicity T test Notification messages to segment switching routers (SSR)

14 Analysis R 5 fails at time t After t - OWD(R 2,R 5 ), packets uncertain R 2 gets notified at t + t test + OWD(R 5,R 2 )

15 Analysis Bound on time during which packets are lost RTT( R i, R j ) + T test

16 Identifying Segments: A greedy algorithm Identify segments such that —switch-over delay is bounded (for instance, 60 ms) —Fewest no of segments Example computation: 11 hop LSP, T test = 10 ms R4R3R2R0R1 R11R10R9 R8R7R6R Segment 1 RTT + T test = 58 Segment 2 RTT + T test = 51 Segment 3 RTT + T test = 45

17 Another algorithm to identify segments Example: consider network with link RTT = 10 ms, T test = 5 ms —bounded switch-over delay of 40 ms —with as few segments as possible —disjoint, loop-free back-up paths exist Segment switch router Ingress router 10 ms = 35 < = 25 < 40

18 Other algorithms to Identify Segments Algorithms to identify segments such that: —Switch-over time is bounded —Fewest no. of segments —disjoint, loop-free back-up paths exist —QoS constraints are satisfied in case of ONE failure –End-to-end delay, Jitter, Drop rate Ingress router 10 ms

19 Identifying Back-up paths An individual back-up path: —is node- and link-disjoint from the segment it protects —may terminate at any node beyond the last node on the segment –Gives greater flexibility The back-up paths taken as a whole: —Must not form loops (equivalently, individual segments must be node- and link-disjoint from all nodes, links in earlier segments) Together with the original path, the back-up paths must satisfy QoS constraints assuming at most one link/node failure Segment 1Segment 2

20 End to End Delay In this analysis, we need to consider backup paths also. Max (T + ( T 2 – T 1 ) ) < 

21 End to End Delay d1d1 d2d2 d3d3 d 1 + d 2 + d 3 d3d3 0 d 2 + d 3 Dummy node Finding the backup path - Can use shortest-path approach to find the backup path - Backup path can land at multiple nodes

22 Other work in the paper

23 Description of Simulation Setup An MPLS network with —50 Nodes —82 Edges Random LSP that require 20 to 70 units of BW RTT of each link = 8 to 12 ms BW between 3000 and units Periodicity of liveness messages = 2 ms BW: 50 to 100 Results indicate advantages of segment based approach

24 Description of Simulation Setup Topology used

25 Simulation Results BW reserved for back up vs. number of LSP for different bound on switch-over time

26 Simulation Results Reserved BW vs. switch-over time

27 Summary Segment based approach offers a range of schemes for path protection —From link or nodes to segments, to paths The approach permits one to insist that back-up paths continue to provide committed QoS even when there is a failure The approach ensures that resources are reserved only to the extent necessary Many of our algorithms are good, and provably correct, but may not be optimal