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PRESENTED BY

Design, Implementation, andPerformance of a Load Balancer for

SIP Server Clusters

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This paper introduces several novel load-balancing algorithmsfor distributing Session Initiation Protocol SIP! re"uests to acluster of SIP servers# $ur load balancer improves boththroughput and response time versus a single node %hilee&posing a single interface to e&ternal clients# 'e present the

design( implementation( and evaluation of our s)stem using acluster of Intel &*+ machines running ,inu 'e compare ouralgorithms to several %ell-no%n approaches and presentscalabilit) results for up to ./ nodes# $ur best algorithm(Transaction ,east-'or-,eft T,',!( achieves its performanceb) integrating several features0 no%ledge of the SIP protocol(d)namic estimates of bac-end server load( distinguishingtransactions from calls( recogni1ing variabilit) in call length(and e&ploiting di2erences in processing costs for di2erent SIPtransactions#

ABSTRACT:

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SYST! ARC"ITCT#R:

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T3E SESSI$N Initiation Protocol SIP! is a general-

purpose signaling protocol used to control varioust)pes of media sessions# SIP is a protocol of gro%ingimportance( %ith uses in 4oice over IP 4oIP!( instant

messaging( IPT4( voice conferencing( and videoconferencing# 'ireless providers are standardi1ing onSIP as the basis for the IP 5ultimedia S)stem I5S!standard for the Third 6eneration Partnership Pro7ect

86PP!# Third-part) 4oIP providers use SIP e#g#(

4onage( 6i1mo!( as do digital voice o2erings frome&isting legac) telecommunications companiestelcos! e#g#( 9T:T( 4eri1on! as %ell as their cablecompetitors e#g#( ;omcast( Time-'arner!#

$ISTI%& SYS!:

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Their load balancer is content una%arebecause it does not e&amine the contents of are"uest#

DISAD'AT%A& () $ISTI%& SYST!:

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SIP is a transaction-based protocol designed toestablish and tear do%n media sessions( fre"uentl)referred to as calls#

The session-oriented nature of SIP has important

implications for load balancing#Transactions corresponding to the same call must be

routed to the same server< other%ise( the server %illnot recogni1e the call# Session-a%are re"uestassignment S9R9! is the process %here a s)stem

assigns re"uests to servers such that sessions areproperl) recogni1ed b) that server( and subse"uentre"uests corresponding to that same session areassigned to the same server#

PR(P(SD SYST!:

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Relativel) less overhead

,oad balancing can be improved b) combiningS9R9

ADA'A%TA&S () PR(P(SD SYST!:

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S)stem 0 Pentium I4 =#> 631#

3ard Dis 0 >/ 6B#

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Ram 0 @.= 5b#

"ARD*AR R+#IR!%TS:

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$perating s)stem 0 - 'indo%s AP#

;oding ,anguage 0 949

S()T*AR R+#IR!%TS:

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Session Initiation Protocol

#ser agents

TransactionLeast*or-Left

Load .alancer

!(D#LS

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SIP is a signaling protocol designed to establish(modif)( and terminate media sessions bet%een t%o ormore parties# Several inds of sessions can be used(including voice( te&t( and video( %hich are transported

over a separate data-plane protocol# SIP does notallocate and manage net%or band%idth as does anet%or resource reservation protocol# SIP messagestraverse the SIP overla) net%or( routed b) pro&ies( toCnd the eventual destinations# $nce endpoints are

found( communication is t)picall) performed directl) ina peer-to-peer fashion# This %or focuses on scaling

the server( rather than the pro&)# SIP can run overman) protocols such as DP( T;P( T,S( S;TP( IPv>#

Session Initiation Protocol

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9 SIP uni"uel) identiCes a SIP user# This la)erof indirection enables features such aslocation- independence and mobilit)# SIP usersemplo) end points no%n as user agents#

These entities initiate and receive sessions#The) can be either hard%are or soft%are# seragents are further decomposed into ser9gent ;lients 9;! and ser 9gent Servers

9S!( depending on %hether the) act as aclient in a transaction 9;! or a server 9S!#

#ser agents

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The Transaction-,east- 'or-,eft T,',!algorithm addresses load balancing issue b)assigning di2erent %eights to di2erenttransactions depending on their relative costs#;ounters are maintained b) the load balancerindicating the %eighted number oftransactions assigned to each server# Ne%calls are assigned to the server %ith thelo%est counter# T,', estimates server loadbased on the %eighted number of transactionsa server is currentl) handling#

TransactionLeast*or-Left

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The Receiver receives re"uests %hich are then

parsed b) the Parser# The Session Recognitionmodule determines if the re"uest correspondsto an alread) e&isting session b) "uer)ing the

Session State# If so( the re"uest is for%arded tothe server to %hich the session %as previousl)assigned# If not( the Server Selection moduleassigns the ne% session to a server using T,',

algorithm# ?or several of the load balancingalgorithms( this %or ma) be based on ,oadEstimates maintained for each of the servers#

Load .alancer

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3ongbo iang,9run I)engar, Erich Nahum,'olfgang Segmuller 9sser N# Tanta%i, and;harles P#'right( Design( Implementation(and Performance of a ,oad Balancer for SIPServer ;lustersF( I/AC! TRA%SACTI(%S(% %T*(R0I%&, 12314

R)R%C: