Backup Path Allocation Based on A Link Failure Probability Model in Overlay Networks

Weidong Cui, Ion Stoica, and Randy H. KatzEECS, UC Berkeley{wdc, istoica, randy}@EECS.Berkeley.EDU

Motivation

The Internet is actually a BIG overlay network.Link failures in an overlay network usually are not independent because they may share same links/nodes in the lower level network.Having two orthogonal service/communication paths (a primary path and a backup path) can improve service availability.This project studies the problem of how to find and set up two orthogonal paths based on a correlated link failure model in overlay networks.

The Overlay Network

The Lower Level Network

A Link Failure Probability Model in Overlay Networks

The link failure probability model has Single link failure probabilities Double link failure probabilities Assumption: probabilities are SMALL!

Path failure probabilities Single path failure probability Double path failure probability

How to obtain the link failure probabilities?

)Pr()Pr(

ai PL ia LP

bj aiPL PL jiba LLPP )),Pr((),Pr(

)Pr( iL

),Pr( ji LL

Li

Lj

lwlv

lu

The Overlay Network

The Lower Level Network

)Pr()Pr()Pr( wui llL

),Pr()Pr(),Pr( wvuji lllLL

Backup Path Routing Algorithms

Probability Cost Routing Algorithm Goal: find a backup path such that it

minimizes the joint path failure probability given a shortest path as the primary path

Probability cost for link used in the backup path is:

Second Shortest Routing Algorithm Find a second shortest path as the backup

path which is disjoint from the primary path

jL

ai PL ji LL ),Pr(

bj aiPL PL jiba LLPP )),Pr((),Pr(

Backup Path Bandwidth Allocation Algorithms

Duplicate Bandwidth Allocation Same bandwidth on backup paths as on

primary paths

Single-Link-Failure Bandwidth Allocation Allocate bandwidth on backup paths such

that it can recover from a single link failure

Zero Bandwidth Allocation A baseline for comparison.

Simulation ExperimentsUse GT-ITM to generate random network topology.Assume the link failures in the lower level network are independent.Calculate the link failure probabilities in the overlay network based on the link failure probabilities in the lower level network.Simulate the link failures in the lower level networkl1

lM

l2

T

link failure time

. . . . . . . . .

Results: Robustness

Results: Efficiency

Results: Fault Tolerance

Conclusion and Future Work

Probability-cost routing algorithm and single-link-failure bandwidth allocation algorithm have good performance on robustness and efficiency.Probability-cost routing algorithm is fault tolerant to noise of overlay link failure probabilities. Future Work Test the algorithms both in NISTNet emulation

testbed and in a real overlay network Study how to obtain overlay link failure

probabilities in real networks.