QoS-Aware Path QoS-Aware Path ProtectionProtectionin MPLS Networksin MPLS Networks

Ashish GuptaAshish GuptaAshish GuptaAshish GuptaBijendra JainBijendra Jain

Indian Institute of Technology Indian Institute of Technology DelhiDelhi

Satish TripathiSatish Tripathi

University of California University of California at Riversideat Riverside

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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

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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

47.1

47.247.3

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BACKUP PATH

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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

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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

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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

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Segment Based Protection

The Main Idea

Look at the path as a sequence of segments and protect each segment separately

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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

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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)

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Fault Detection , Location and Notification

• Faults detected using live-ness messages with periodicity Ttest

• Notification messages to segment switching routers (SSR)

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Analysis

Bound on time during which packets are lost

RTT( Ri , Rj ) + Ttest

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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, Ttest = 10 ms

R4R3R2R0 R1 R11R10R9R8R7R6R5

19 1113141110 8 3 10 15 10

Segment 1

RTT + Ttest = 58

Segment 2

RTT + Ttest = 51Segment 3

RTT + Ttest = 45

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Another algorithm to identify segments

• Example: consider network with link RTT = 10 ms, Ttest = 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

10 ms10 ms

10 ms10 ms

10 + 10 + 10 + 5 = 35 < 40

10 + 10 + 5 = 25 < 40

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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

10 ms10 ms

10 ms10 ms

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End to End Delay

In this analysis, we need to consider backup paths also.

Max (T + ( T2 – T1 ) ) <

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End to End Delay

d1 d2 d3

d1 + d2 + d3

d3

0

d2 + d3

Dummy node

Finding the backup path

- Can use shortest-path approach to find the backup path

- Backup path can land at multiple nodes

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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 10000 units

• Periodicity of liveness messages = 2 ms

• BW: 50 to 100

• Results indicate advantages of segment based approach

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Description of Simulation Setup

• Topology used

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Simulation Results

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

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Simulation Results

• Reserved BW vs. switch-over time

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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