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
3
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
4
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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