IEEE GLOBECOM 2010

Yang Hong, Changcheng Huang, and James YanDepartment of Systems and Computer Engineering, 

Carleton University, Ottawa, Canada

Wh t i SIP?What is SIP? Session Initiation Protocol protocol that establishes,

manages (multimedia) sessions [RFC 3261]

used for VoIP presence &

Internet

Proxy Proxy used for VoIP, presence & video conference

SIP consists of two basic l t

Proxy Server

Proxy Server

elements UA (User Agent) and P-Server

(Proxy Server)

UA UA

About 1000 companies produce SIP products Microsoft’s Windows

M (≥4 7) i l d SIP

Simplified SIP Network Configuration

Messenger (≥4.7) includes SIP

2

Instant MessagingInstant Messaging

ipcall comSIP Redirect ipcall.com server

SIP proxy Location2 5

sipvoice.comvoip.com

Location

service3

4

6

10

proxy17

8

1011

12

SIP UA SIP UA sip.voip.com

913

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IMS SIP Server Overload – A f h llPerformance Management Challenge

3GPP has adopted SIP as the basis of IMS architecture

Problem: Server(s) cannot complete the processing of requests underthe processing of requests under overload conditions

Multiple causes: Insufficient pcapacity, Component Failures, Unexpected traffic surges, DOS attacks [RFC 5390]

Impact: Performance degradation, drop in throughput, revenue loss, network collapse

Si lifi d IMS C t l L O iSimplified IMS Control Layer Overview

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Why Worry About SIP Message Retransmission?Why Worry About SIP Message Retransmission?

Retransmission built-in to maintain SIP reliabilityRetransmission built in to maintain SIP reliability against message loss

Loss is detected as long delay in acknowledgment Loss is detected as long delay in acknowledgment

Surge in user demand can cause SIP server overload and long delay to acknowledge SIPoverload and long delay to acknowledge SIP messages

Long dela s ma trigger more retransmissions and a Long delays may trigger more retransmissions and a positive feedback exacerbating server overload

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Contributions of This Paper

Using control-theoretic approach tomodel an overloaded downstream server and itsmodel an overloaded downstream server and its

upstream server as a feedback control system

Proposing Redundant Retransmission Ratio Control Proposing Redundant Retransmission Ratio Control (RRRC) algorithm (a PI rate control algorithm) to mitigate the overload achieve satisfactory target redundant message ratio

by controlling retransmission rate

Performing OPNET simulations under two typical overload scenarios toValidate RRRC (implicit SIP overload control) algorithm

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OutlineOutline

SIP Retransmission Mechanism OverviewSIP Retransmission Mechanism Overview

Related Work on SIP Overload Control

Queuing Dynamics of Overloaded Server

Control-Theoretic Design for Overload Control Based gon Redundant Retransmission Ratio

Performance Evaluation to Validate RRRC SIPPerformance Evaluation to Validate RRRC SIP Overload Control Algorithm

ConclusionsConclusions

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Typical SIP Procedure

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Retransmission Mechanism

Purpose: Confirmation of successful transmission between UA and UA via P-serversbetween UA and UA via P-servers

Two Types: Hop by HopHop by HopFirst retransmission after T1 , subsequent one is 2

times previous interval. Total intervals up to 64 x T1 ( ) f(maximum 6 retransmissions). Default T1 = 0.5 s.

End-to EndFirst retransmission after T subsequent one is 2 timesFirst retransmission after T1 , subsequent one is 2 times

previous interval up to a maximum of T2 . Total intervals up to 64 x T1 (maximum 11 retransmissions). Default T2 = 4.0 s.

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Related Work on Overload Control All the existing overload control solutions adopt

push-back mechanism cancel the overload effectively by introducing overhead to advertise upstream servers to

d di t reduce message sending rate

produce overload propagation from sever to server until end-users

block a large amount of calls unnecessarily cause revenue loss of service providers

• Our Proposal: Reduce retransmission rate only to mitigate overloadby maintaining original message rate toby maintaining original message rate to keep the revenue of service providers

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SIP Overload Control Mechanism Classification

Figure 3. The classification for the existing SIP overload control schemes

Y. Hong, C. Huang, and J. Yan, “A Comparative Study of SIP Overload Control Algorithms,”N k d T ffi E i i i E i Di ib d C i A li i Edi d bNetwork and Traffic Engineering in Emerging Distributed Computing Applications, Edited byJ. Abawajy, M. Pathan, M. Rahman, A.K. Pathan, and M.M. Deris, IGI Global, 2012, pp. 1‐20.

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Queuing Dynamics of Overloaded ServerQ g y  100Trying response

Invite requestInvite request Server 2 Message buffer

2(t)1(t)1  

)('2 tr  

Invite request2  

100Trying response

Server 1

TiReset timer Timer fires

q2(t) 2(t) 1(t) q1(t)

r2(t) r1(t) 2(t) 1(t)

Queuing dynamics of Server 2

Timer buffer

Timer starts Timer expires

qr1(t)

)()()()()( 22222 tttrttq (1)

Notation: 1(t) original message rate, r1 (t) message retransmission rate, (t) service rate (t) response rate q (t) queue size

)()()()()()( 11'2111 tttrtrttq Queuing dynamics of Server 1 (2)

2(t) service rate, 1 (t) response rate, q1 (t) queue sizeOverload Scenario: Server slowdown at Server 2 due to routine maintenanceOverload Collapse: 2(t) 2(t) > 2(t) (see Eq. (1)) q2(t) t i ' (t) (t) i (t) i kl

0)(2 tq trigger r'2(t) r2(t) increases q2(t) more quicklyOverload Propagation: r'2(t) enter Server 1 (see Eq. (2)) q1(t) 0)(1 tq

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Feedback Overload Control System  

Figure 4.Block diagram of feedback SIP overload control systemg g y

Root Cause of Overload Collapse• Retransmission for loss recovery is non-redundant

Retransmission caused by the overload delay is redundant• Retransmission caused by the overload delay is redundantSolution• PI controller C(s) regulates retransmission rate r'2(t) to mitigate the overloadoverload

• achieve desirable target redundant message ratio 0• redundant message ratio is the ratio between redundant response message rate 1r and total response message rate 1espo se essage ate 1r a d tota espo se essage ate 1

• P(s) represents the interaction between an overloaded downstream receiving server and its upstream sending server

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Overload Controller Design gRedundant message ratio (t)=1r(t)/1(t) r'2(t)/1(t)

PI controller regulates retransmission rate r'2(t)PI controller regulates retransmission rate r 2(t)

t

IP

tIP

KtK

eKteKr

0 00

0'2

))d(())((

)d()((t)

IP KtK 0 00 ))d(())((

Control plant P(s)=(s)/r'2(s)=[r'2(s)e-s/1]/r'2(s)=e-s/1

PI controller C(s)=K +K /sPI controller C(s)=KP+KI/s

Open-loop overload control system G(s)=C(s)P(s)=(KP+KI/s)e-s/1

Positive phase margin of G(s) can guarantee control system stabilityPositive phase margin m of G(s) can guarantee control system stability

PI controller gains can be obtained based on phase margin m

1 )4/3(21PK

2)4/3(1 m

IK

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SIP Overload Control Algorithm (RRRC)SIP Overload Control Algorithm (RRRC)

Overload Control Algorithm

When each retransmission timer fires or expiresif < 1

elseRetransmit the message

Retransmit the message with a retransmission

Varying parameter:: Round trip delay

Retransmit the message with a retransmission probability corresponding to a retransmission rate r'2 calculated by a PI controller

Adaptive PI control algorithm:(1) Specify target redundant message ratio

1r : Redundant response message rate : Redundant message ratio 1r/ 1

KP : Proportional gain of PI controllerKI : Integral gain of PI controller

: Response message rate (1) Specify target redundant message ratio and phase margin m; Set the initial values for ,

and ; Obtain PI controller gains using Eq. (13).(2) Measure and calculate and

Fixed parameter:

r'2 : Message retransmission rate

T1 : First-time retransmission timer

KI : Integral gain of PI controller

: Monitoring parameter / 1

(2) Measure , r and calculate and upon response message arrivals. (3) If >1.5 or <0.5 , self-tune PI controller gains using Eq. (13) and update = ; Otherwise, PI controller remains unchanged.

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T1 : First-time retransmission timer: Target redundant message ratio

m : Phase margin

g(4) Calculate the retransmission rate r'2 using Eq. (7); Go to Step (2).

Scenario to Validate Overload Control AlgorithmScenario to Validate Overload Control Algorithm

• Poisson distributed message generation rate and service rate• Two typical overload scenarios

Scenario 1Initial overload at 

• Mean arrival rate 1=800 messages/sec (emulating a short surge of user demands) from time t=0s to t=30s

Server 1 due to demand burst • Mean arrival rate 1=200 messages/sec (emulating

regular user demands) from time t=30s to t=90s

• Mean service capacities of two proxy servers were• Mean service capacities of two proxy servers were C1=C2=1000 messages/sec

Scenario 2Initial overload at 

• Mean arrival rate 1=200 messages/secInitial overload at Server 2 due to server slowdown

• Mean server capacity C1=1000 messages/sec

• Mean server capacity C2=100 messages/sec (emulating server slowdown) from time t=0s to t=30s, and C2=1000 messages/sec from time t=30s to t=90s

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SIP Network Topology For OPNET SimulationSIP Network Topology For OPNET Simulation

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Simulation Results of Scenario 1Simulation Results of Scenario 1

7

8x 104

s)

NOLC q1

OLC q

10000

ges)

20

ges)NOLC qo

OLC q

4

5

6

ze q

1 (mes

sage

s OLC q1

4000

6000

8000

e si

ze q

o (mes

sag

10

size

qo (m

essa

gOLC qo

0

1

2

3

Que

ue si

z

0 10 20 30 40 50 60 70 80 900

2000

4000

NO

LC Q

ueue

0 10 20 30 40 50 60 70 80 90

0

OLC

Que

ue

Queue size q1 (messages) of Server 1 versus time

Queue size qo (messages) of an originating server versus time

0 10 20 30 40 50 60 70 80 90

Time (sec)0 10 20 30 40 50 60 70 80 90

Time (sec)0 10 20 30 40 50 60 70 80 90

• Without overload control algorithm applied, Server 1 became CPU overloaded overload deteriorated as time evolves, leading to eventual crash of Server 1

• RRRC algorithm made queue size of Server 1 increase slowly taking only 8s to cancel the overload at Server 1 after new user demand rate reduced at time t=30s

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Simulation Results of Scenario 2Simulation Results of Scenario 2

4

5x 104

sage

s)

20

ages

)NOLC q1

OLC q1

1.8

2x 104

s)

NOLC q2

OLC q

2

3

4

eue

size

q1 (m

ess

10

ue si

ze q

1 (mes

sa

0.8

1

1.2

1.4

1.6

size

q2 (m

essa

ges OLC q2

0 10 20 30 40 50 60 70 80 900

1

NO

LC Q

ue

Time (sec) 0 10 20 30 40 50 60 70 80 90

0

OLC

Que

u0 10 20 30 40 50 60 70 80 90

0

0.2

0.4

0.6

Time (sec)

Que

ue s

Queue size q1 (messages) of Server 1 versus time

Queue size q2 (messages) of Server 2 versus time

• Without overload control algorithm applied overload was propagated from Server

( ) Time (sec)

• Without overload control algorithm applied, overload was propagated from Server 2 to Server 1 when initial overload happened at Server 2

• Persisted overload would crash Server 1 after Server 2 resumed its normal service

• RRRC algorithm prevent overload propagation to Server 1 taking only 9s to cancel the overload at Server 2

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Conclusions Applying control-theoretic approach to model SIP

overload problem as a feedback control problemD l i R d d t R t i i R ti C t l Developing Redundant Retransmission Ratio Control (RRRC) algorithm (a PI rate control algorithm) to mitigate the overload by controlling retransmission rate achieving desirable target redundant message ratio

Simulation results demonstrate that RRRC (implicit SIP Simulation results demonstrate that RRRC (implicit SIP overload control) algorithm can prevent the overload propagation cancel the overload effectively

Our solution does NOT require modification in the SIP header and time-consuming standardization processheader and time consuming standardization process can be freely implemented in any SIP servers of different carriers

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Remarks (1) OPNET simulation code for 3 implicit SIP overload control algorithms

(RRRC, RTDC, and RTQC) published by IEEE Globecom 2010/ICC 2011 available for non-commercial research use upon request

RRRC algorithm (proposed by this IEEE Globecom 2010 paper) has been quickly adopted by The Central Weather Bureau of Taiwan for their early earthquake warning system “A Effi i t E th k E l W i M D li Al ith U i i “An Efficient Earthquake Early Warning Message Delivery Algorithm Using an in

Time Control-Theoretic Approach,” Ubiquitous Intelligence and Computing, Lecture Notes in Computer Science, 6905, Springer, Berlin, Heidelberg, 2011, pp. 161-173.

http://www.springerlink.com/content/b6252x2k613rv211/?MUD=MPhttp://www.ipv6.org.tw/docu/elearning8_2011/1010004798p_3-7.pdf

S C ( S ) Short review and comments on RRRC (implicit SIP overload control) algorithm: "Local SIP Overload Control", Proceedings of WWIC, June 2013.

http://link.springer.com/chapter/10.1007%2F978-3-642-38401-1_16#http://c3lab poliba it/images/2/2a/SipOverload WWIC13 pdfhttp://c3lab.poliba.it/images/2/2a/SipOverload_WWIC13.pdf

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Remarks (2) Journal version discusses how to apply RTDC algorithm to mitigate SIP Journal version discusses how to apply RTDC algorithm to mitigate SIP

overload for both SIP over UDP and SIP over TCP (with TLS) “Applying control theoretic approach to mitigate SIP overload,”

Telecommunication Systems, 54(4), 2013, pp. 387-404. Available aty ( )http://www.researchgate.net/publication/257667871_Applying_control_theoretic_approach_to_mitigate_SIP_overload

Survey on SIP overload control algorithms: “A Comparative Study of SIP y g p yOverload Control Algorithms,” Network and Traffic Engineering in Emerging Distributed Computing Applications, IGI Global, 2012, pp. 1-20.

http://www.igi-global.com/chapter/comparative-study-sip-overload-t l/67496control/67496

http://www.researchgate.net/publication/231609451_A_Comparative_Study_of_SIP_Overload_Control_Algorithms

Discussion on control system design can be found in the answers to the ResearchGate question “What are trends in control theory and its applications in physical systems (from a research point of view)? ”

https://www researchgate net/post/What are trends in control theory and itshttps://www.researchgate.net/post/What_are_trends_in_control_theory_and_its_applications_in_physical_systems_from_a_research_point_of_view2

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