IEEE ICC 2011

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

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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 reliability yagainst message loss

Loss is detected as long delay in acknowledgmentLoss 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 delays may trigger more retransmissions and a Long delays may trigger more retransmissions and a positive feedback exacerbating server overload

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C t ib ti f Thi PContributions of This Paper

Using control-theoretic approach tog ppmodel the interaction of overloaded server and its

upstream server as a feedback control system

Proposing Round Trip Delay Control (RTDC) algorithm (a PI rate control algorithm) to mitigate the overload by regulating retransmissionsclamping round trip delay below a desirable target value

Performing OPNET simulations under two typical overload scenarios tovalidate RTDC (implicit SIP overload control) algorithm

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OutlineOutline

SIP Retransmission Mechanism Overview

Related Work on SIP Overload Control

Queuing Dynamics of Overloaded Server Queuing Dynamics of Overloaded Server

Control-Theoretic Design for Overload Control Based R d T i D lon Round-Trip Delay

Performance Evaluation to Validate RTDC SIP Overload Control Algorithm

Conclusions

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Typical SIP Procedure

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Retransmission MechanismRetransmission 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 (maximum 6 retransmissions). Default T1 = 0.5 s.

End-to EndFi t t i i ft T b t i 2 tiFirst 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). 1 Default T2 = 4.0 s.

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Related Work on Overload Control Most of 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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Overload Controller Design gUpstream Server 1 can process all arrival messages without any delay

• before the overload is propagated from its downstream Server 2• 2(t)=1(t) and r2(t)=r'2(t) (see previous slide #11) 2( ) 1( ) 2( ) 2( ) ( p )

Queuing dynamics of Server 2 )()()()()( 22212 tttrttq (3)

(4)Queuing delay of Server 2 )(/)]()()()([)( 222122 tttttrt ( )g y• Each request message corresponds to a response message [SIP RFC]• Thus request message service rate (i.e., the response message rate 1(t)) can approximate the total service rate 2(t)

Queuing delay of Server 2 (5))(/)]()()()([)( 112122 tttttrt

• Round trip delay of upstream server can approximate queuing delay of overloaded downstream server 2(t)

PI controller regulates retransmission rate r'2(t)

t

overloaded downstream server 2(t) when overload happens and queuing delay is dominant

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t

IP

tIP

KtK

eKteKtr

0 2020

02

))d(())((

)d()()(

Feedback Overload Control System 

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

Control plant P(s)=2(s)/r'2(s)= {2(t)}/ {r'2(t)}1/(1s)

PI controller C(s)=KP+KI/s( ) P I

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

Positive phase margin of G(s) can guarantee control system stabilityPositive phase margin m of G(s) can guarantee control system stabilityPI controller gains can be obtained based on phase margin m

)tan(1 mPK

1K

13

)(tan1 2m

PK )(tan1 2

mIK

SIP Overload Control Algorithm (RTDC)SIP Overload Control Algorithm (RTDC)

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k l lSIP Network Topology For OPNET Simulation

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Scenario to Validate Overload Control Algorithm

• Poisson distributed message generation rate and service rate• Two typical overload scenarios • 4 originating servers generated original messages with the same rate• 4 originating servers generated original messages with the same rate o= (1/4)1; Mean message arrive rate of Server 1 was 1=4o

• Mean service capacity of each originating server was Co=500 messages/secScenario 1 • Mean arrival rate 1=800 messages/sec (emulating aScenario 1Initial overload at Server 1 due to demand burst

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

• Mean arrival rate 1=200 messages/sec (emulating regular user demands) from time t=30s to t=90sregular user demands) from time t 30s to t 90s

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

S i   M i l t 200 /Scenario 2Initial overload at Server 2 due to server slowdown

• Mean arrival rate 1=200 messages/sec

• Mean server capacity C1=1000 messages/sec

• Mean server capacity C2=100 messages/sec (emulatingMean 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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Simulation Results of Scenario 1Simulation Results of Scenario 1

7

8x 10

4

s)

NOLC q1

12000

sage

s)

8

10

ages

)

NOLC q0

OLC q0

3

4

5

6

ze q

1 (mes

sage

s

OLC q1

6000

9000

ue si

ze q

0 (mes

4

6

e si

ze q

0 (mes

sa

0 10 20 30 40 50 60 70 80 900

1

2

3

Que

ue si

0 10 20 30 40 50 60 70 80 90

0

3000

NO

LC Q

ueu

0 10 20 30 40 50 60 70 80 90

0

2

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

• Overload control algorithm made queue size of Server 1 increase slowly taking 27s to cancel the overload at Server 1 after new user demand rate taking 27s to cancel the overload at Server 1 after new user demand rate reduced at time t=30s 11s faster than RRRC algorithm proposed by IEEE Globecom 2010 17

Simulation Results of Scenario 2

4

5x 10

4

mes

sage

s)

8

10

essa

ges)

NOLC q1

OLC q11.6

1.8

2x 104

ges)

NOLC q2

OLC

2

3

Que

ue si

ze q

1 (m

4

6

Que

ue si

ze q

1 (me

0.6

0.8

1

1.2

1.4

ue si

ze q

2 (mes

sag OLC q2

Q i ( ) f S 1

0 10 20 30 40 50 60 70 80 900

1

NO

LC Q

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

0

2

OLC

Q

0 10 20 30 40 50 60 70 80 900

0.2

0.4

Time (sec)

Que

u

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 2 t S 1 h i iti l l d h d t S 22 to Server 1 when initial overload happened at Server 2

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

• Overload control algorithm prevent overload propagation to Server 1O e oad co t o a go t p e e t o e oad p opagat o to Se e taking only 7s to cancel the overload at Server 2 2s faster than RRRC algorithm proposed by IEEE Globecom 2010

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Conclusions Employing control-theoretic approach to

model SIP overload problem as a feedback control problemp p

Developing Round Trip Delay Control (RTDC) algorithm (a PI rate control algorithm) to mitigate the overload by t lli t i i t controlling retransmission rate claiming round trip delay below desirable target value

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

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

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Remarks (1) Explicit SIP overload control algorithm requires the modification in the

SIP header and the cooperation among different carriers in different countries

Implicit SIP overload control algorithm does NOT require the modification in the SIP header and the cooperation among different carriers in different countries. Any carrier can freely implement implicitcarriers in different countries. Any carrier can freely implement implicit SIP overload control algorithm in its SIP servers to avoid potential widespread server crash

OPNET i l ti d f 3 i li it SIP l d t l l ith 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

RTDC algorithm (proposed by this IEEE ICC 2011 paper) has been recommended as White paper by TechRepublic (an online trade publication and social community for IT professionals, part of the CBS Interactive)

http://www.techrepublic.com/whitepapers/design-of-a-pi-rate-controller-for-mitigating-sip-overload/25142469

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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

Discussions 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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