Performance & QoS CongestionControl · Congestion avoidance Packet marking Traffic shaping Traffic...
Transcript of Performance & QoS CongestionControl · Congestion avoidance Packet marking Traffic shaping Traffic...
Performance&QoSCongestion Control
ETSF05/ETSF10– InternetProtocols
QualityofService(QoS)
• Maintainingafunctioningnetwork–Meetingapplications’demands
• User’sdemands=QoE (QualityofExperience)
– Dealingwithflowcharacteristics
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Jitter = Packet Delay Variations
Figure 22.1 Architectural Framework for QoS Support
Queuemanagement
Congestionavoidance
Packetmarking
Trafficshaping
Trafficpolicing
Trafficclassification
Queueing &scheduling
Data Plane
Admissioncontrol
QoSrouting
Resourcereservation
Control Plane
Servicelevel
agreement
Trafficrestoration
Policy
Trafficmetering
andrecording
Manag
emen
t
Plane
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DataPlane• Includesthosemechanismsthatoperatedirectlyonflowsofdata– Queuemanagementalgorithms
• TaildropvsRED(RandomEarlyDetection)– Queueingandscheduling– Congestionavoidance– Packetmarking– Trafficclassification– Trafficpolicing– Trafficshaping
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ControlPlane
• Concernedwithcreatingandmanagingthepathwaysthroughwhichuserdataflows– Admissioncontrol– QoS routing– Resourcereservation
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ManagementPlane
• Containsmechanismsthataffectbothcontrolplaneanddataplanemechanisms– Servicelevelagreement(SLA)– Trafficmeteringandrecording– Trafficrestoration– Policy
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Networkperformance• Datarate(Bandwidth)– Bitspersecond
• Throughput– Efficiency,alwayslessthancapacity(<1)– Alternatively:availabledatarate
• Latency(Delay)– Transmission,propagation,processing,queueing– OnewayorRTT(RoundTriptime)
• PDV=PacketDelay Variation(Jitter)– Real-time applications!
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Otherparameters
• BitErrorRate– L1parameterthatheavilyimpactsonL3– Frame/PacketLossonhigherlayers
• InterPacketGapvariations– “Jitter”– Couldbenon-zeroalreadyatsender
• Ratioofpacketsoutoforder– ImpactondelayinTCP
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Packetloss• Due to– Biterror inpacket
• Routersdiscard erronous packet• LinkorPhysical Layer?
– Queue overflow• Discard packets• Node problems
• Inreal-timemultimedialatepacketsconsidered lost• Packetlossratio (%)• NoteTCP’s sensitivity to packetloss
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Circuit Switching Datagram Packet Switching Virtual Circuit Packet Switching
Dedicated transmission path No dedicated path No dedicated path
Continuous transmission of data
Transmission of packets Transmission of packets
Fast enough for interactive Fast enough for interactive Fast enough for interactive Messages are not stored Packets may be stored until
delivered Packets stored until delivered
The path is established for entire conversation
Route established for each packet
Route established for entire conversation
Call setup delay; negligible transmission delay
Packet transmission delay Call setup delay; packet transmission delay
Busy signal if called party busy
Sender may be notified if packet not delivered
Sender notified of connection denial
Overload may block call setup; no delay for established calls
Overload increases packet delay
Overload may block call setup; increases packet delay
Electromechanical or computerized switching nodes
Small switching nodes Small switching nodes
User responsible for message loss protection
Network may be responsible for individual packets
Network may be responsible for packet sequences
Usually no speed or code conversion
Speed and code conversion Speed and code conversion
Fixed bandwidth Dynamic use of bandwidth Dynamic use of bandwidth No overhead bits after call setup
Overhead bits in each packet Overhead bits in each packet
Table9.1
ComparisonofCommunication
SwitchingTechniques
(Tablecanbefoundonpage315in
textbook)
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(a) Circuit switching
Callrequestsignal
Callacceptsignal
propagationdelay
processingdelay
(b) Virtual circuit packet switching
Callrequestpacket
Callacceptpacket
link link link
1 2 3 4Nodes: 1 2 3 4
Acknowledge-ment signal
Acknowledge-ment packet
(c) Datagram packet switching
1 2 3 4
Userdata
Pkt1
Pkt2
Pkt3Pkt1
Pkt2
Pkt3Pkt1
Pkt2
Pkt3
Pkt1
Pkt2
Pkt3Pkt1
Pkt2
Pkt3Pkt1
Pkt2
Pkt3
Figure 9.15 Event Timing for Circuit Switching and Packet SwitchingETSF05/ETSF10- InternetProtocols 12
VirtualCircuitsvs.Datagram• Virtualcircuits– Networkcanprovidesequencinganderrorcontrol– Packetsareforwardedmorequickly– Lessreliable(compareCircuitSwitching)
• Datagram(BestEffort)– Nocallsetupphase– Individualpackethandling–Moreflexible–Morereliable
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IPPerformanceMetrics(IPPMwg)• CharteredbyIETFtodevelopstandardmetricsthatrelatetothequality,performance,andreliabilityofInternetdatadelivery
• Measurementtechniques– Active:Transmitpacketsovernetworkformeasurementpurposes
– Passive:Useexistingtrafficformeasurements
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Table22.3IPPerformanceMetrics
Metric Name Singleton Definition Statistical Definitions One-Way Delay Delay = dT, where Src transmits first bit of
packet at T and Dst received last bit of packet at T + dT
Percentile, median, minimum, inverse percentile
Round-Trip Delay Delay = dT, where Src transmits first bit of packet at T and Src received last bit of packet immediately returned by Dst at T + dT
Percentile, median, minimum, inverse percentile
One-Way Loss Packet loss = 0 (signifying successful transmission and reception of packet); = 1 (signifying packet loss)
Average
One-Way Loss Pattern
Loss distance: Pattern showing the distance between successive packet losses in terms of the sequence of packets Loss period: Pattern showing the number of bursty losses (losses involving consecutive packets)
Number or rate of loss distances below a defined threshold, number of loss periods, pattern of period lengths, pattern of inter-loss period lengths.
Packet Delay Variation
Packet delay variation (pdv) for a pair of packets with a stream of packets = difference between the one-way-delay of the selected packets
Percentile, inverse percentile, jitter, peak-to-peak pdv
Src=IPaddressofahostDst =IPaddressofahost
(a)SampledmetricsETSF05/ETSF10- InternetProtocols 15
Table22.3IPPerformanceMetrics
Metric Name General Definition Metrics Connectivity Ability to deliver a packet
over a transport connection.
One-way instantaneous connectivity, Two-way instantaneous connectivity, one-way interval connectivity, two-way interval connectivity, two-way temporal connectivity
Bulk Transfer Capacity
Long-term average data rate (bps) over a single congestion-aware transport connection.
BTC = (data sent)/(elapsed time)
(b)Othermetrics
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P(i) P(j)
P(j)
P(k)
P(k)P(i)
dTi
I1MP1
MP2
Figure 22.12 Model for Defining Packet Delay Variation
I1
I2
I2dTj dTk
I1, I2 = times that mark that beginning and ending of the interval in which the packet stream from which the singleton measurement is taken occurs.MP1, MP2 = source and destination measurement pointsP(i) = ith measured packet in a stream of packetsdTi = one-way delay for P(i)
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PDVi=dTi-dTi-1Alt.STD(dT)
Time synch!
• How much datafills thelink• OneWayDelay• TwoWayDelay=RoundTripTime(RTT)
Timefordata+timeforACK
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Bandwidth-delayproduct
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bandwidth:5bps,delay:5sbandwidthxdelay=25bits
Bandwidth-delayproduct
Bandwidth-delayproduct
• Importantforcongestionavoidance– Don’toverfillthelink
• Importantforefficiency– Keepthelinkfilledatalltimes– FormaxefficiencyDatachunks>2*bandwidth*delay
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Bandwidth-delayproduct
• Important fortuning (TCP)• LongFatNetwork (LFN,”elephant”)BDP>>105 bits
• Very long(high delay)links:->Bandwidth =BDP/delayBut ittakes longtime before ACKarrives …
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Performance vsARQ
• Method– Stop-&-Wait– Go-Back-N– Selective-Repeate
• Utilisation =f(window size)
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t0 T RT R
t0 + 1 T RT R
t0 + a T RT R
t0 + 1 + a T RT R
t0 + 1 + 2a ACK
Frame
t0
t0 + a
t0 + 1
t0 + 1 + a
t0 + 1 + 2a T RT R
(b) a > 1(a) a < 1
Figure 16.8 Stop-and-Wait Link Utilization (transmission time = 1; propagation time = a)ETSF05/ETSF10- InternetProtocols 23
(a) W����a + 1
�a + 1
a + 1
a
�
1
t = 0
�)UDPH���a + 1)A BA�)UDPH���a) Frame (a��� Frame (a+3)
Frame (a + 1)A BA Frame a �)UDPH��
Frame aA B Frame (a – 1) Frame 1�)UDPH��
Frame 3
�)UDPH��A B Frame 1
Frame 1A B
A B
(b) W����a + 1
�a + 1
W
1
t = 0
A BA Frame (a ����
Frame WA BA Frame (W – 1) Frame (W–a+1)
Frame W
Frame (W-a���
a + 1 Frame (a + 1)A BA Frame a �)UDPH�� Frame 3
a Frame aA B Frame (a – 1) Frame 1�)UDPH��
Frame 1A B
A B
Figure 16.9 Timing of Sliding-Window Protocol
Sliding Windowsbased• a =propagationtime
• W =window size
• Compare withBandwitdh-DelayProduct
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(a) W����a + 1
�a + 1
a + 1
a
�
1
t = 0
�)UDPH���a + 1)A BA�)UDPH���a) Frame (a��� Frame (a+3)
Frame (a + 1)A BA Frame a �)UDPH��
Frame aA B Frame (a – 1) Frame 1�)UDPH��
Frame 3
�)UDPH��A B Frame 1
Frame 1A B
A B
(b) W����a + 1
�a + 1
W
1
t = 0
A BA Frame (a ����
Frame WA BA Frame (W – 1) Frame (W–a+1)
Frame W
Frame (W-a���
a + 1 Frame (a + 1)A BA Frame a �)UDPH�� Frame 3
a Frame aA B Frame (a – 1) Frame 1�)UDPH��
Frame 1A B
A B
Figure 16.9 Timing of Sliding-Window Protocol
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(a) W����a + 1
�a + 1
a + 1
a
�
1
t = 0
�)UDPH���a + 1)A BA�)UDPH���a) Frame (a��� Frame (a+3)
Frame (a + 1)A BA Frame a �)UDPH��
Frame aA B Frame (a – 1) Frame 1�)UDPH��
Frame 3
�)UDPH��A B Frame 1
Frame 1A B
A B
(b) W����a + 1
�a + 1
W
1
t = 0
A BA Frame (a ����
Frame WA BA Frame (W – 1) Frame (W–a+1)
Frame W
Frame (W-a���
a + 1 Frame (a + 1)A BA Frame a �)UDPH�� Frame 3
a Frame aA B Frame (a – 1) Frame 1�)UDPH��
Frame 1A B
A B
Figure 16.9 Timing of Sliding-Window Protocol
1.0
0.8
0.6
0.4
0.2
0.0
Util
izat
ion
0 .1 1 1 0 1 0 0 1000a
W = 7 W = 1
W = 127
Figure 16.10 Sliding-Window Utilization as a function of a
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W=1 Stop-&-Wait
1.0
0.8
0.6
0.4
0.2
0.0
Util
izat
ion
0 .1 1 1 0 1 0 0 1000a
Stop-and-wait
W =127 Go-back-N
W =7 Go-back-N
Figure 16.11 ARQ Utilization as a Function of a (P = 10–3)
ETSF05/ETSF10- InternetProtocols 28P=Propability of frame error
1
Data1Data
Header
(a) 1-packet message (b) 2-packet message (c) 5-packet message (d) 10-packet message
Data
Data
Data2
Data1
Data2
Data1
Data2
1
2
3
4
5
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1
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1
2
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5
1
2
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4
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Figure 9.13 Effect of Packet Size on Transmission Time
X a b Y
X a b Y
X a b Y
X a b Y
PacketSize vsTransmissionTime
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Nor
mal
ized
Thr
ough
put
Load
Average delayfor packets thatare delivered
Average delayfor all packets
Del
ay
Load
Figure 20.4 The Effects of Congestion
No congestion Severe congestionModeratecongestion
A
B
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Delay andthroughput:Finite buffersNocongestioncontrol
CongestionControlinPacket-SwitchingNetworks
Sendcontrolpackettosomeorallsourcenodes• Requiresadditionaltrafficduringcongestion
Relyonroutinginformation• Mayreacttooquickly
Endtoendprobepackets• Addstooverhead
Addcongestioninformationtopacketsintransit• Eitherbackwardsorforwards
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ExplicitCongestionSignaling
• Backward– Congestionavoidancenotificationinoppositedirectiontopacketrequired
• Forward– Congestionavoidancenotificationinsamedirectionaspacketrequired
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Congestion control
• Avoiding andeliminating congestion– Open-loop=proactive,prevent congestion– Closed-loop=reactive,control congestion
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Closed-loopcongestion control (1)
• Backpressure
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Closed-loopcongestion control (2)
• Chokepacket
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ImplicitCongestionSignaling
• Withnetworkcongestion:– Transmissiondelayincreases– Packetsmaybediscarded(Packetloss)
• Sourcecandetectcongestionandreduceflow• Responsibilityofendsystems• Effectiveonconnectionless(datagram)networks
• Alsousedinconnection-orientednetworks
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ExplicitSignalingCategories
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• Binary– Abitsetinapacketindicatescongestion
• Creditbased– Indicateshowmanypacketssourcemaysend– Commonforend-to-endflowcontrol
• Ratebased– Supplyexplicitdataratelimit– Nodesalongpathmayrequestratereduction
How toimprove QoS?
• Admission control• Resource reservation• Scheduling• Traffic shaping
• Routing?
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WheretoimproveQoS?
• Admissioncontrol– DIFFSERV:Serviceclasses– INTSERV:Reservationarchitectures
• Resource reservation– RSVP(Resource ResevationProtocol)
• Scheduling• Trafficshaping
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ANYWHEREYOUFINDQUEUES!
Scheduling:FIFOqueuing
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Scheduling:Priority queuing
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Scheduling:Weightedfairqueuing
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TrafficShaping/TrafficPolicing• Twoimportanttoolsinnetworkmanagement:– Trafficshaping
• Concernedwithtrafficleavingtheswitch• Reducespacketclumping• Producesanoutputpacketstreamthatislessburstandwithamoreregularflowofpackets
– Trafficpolicing• Concernedwithtrafficenteringtheswitch• Packetsthatdon’tconformmaybetreatedinoneofthefollowingways:– Givethepacketlowerprioritycomparedtopacketsinotheroutputqueues
– Labelthepacketasnonconformingbysettingtheappropriatebitsinaheader
– DiscardthepacketETSF05/ETSF10- InternetProtocols 50
TrafficManagement
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• Fairness– Provideequaltreatmentofvariousflows
• Qualityofservice– Differenttreatmentfordifferentflows
• Reservations– Trafficcontractbetweenuserandnetwork– Excesstrafficdiscardedorhandledonabest-effortbasis
Supportfromroutingprotocols?
Yes!• Optimalpath
– Singlemetric– Multiplemetrics?
• Multiple Equal Cost Paths– Loadsharing– Loadbalancing
• QoSrouting– Cross-layerapproaches– OSPFextensions (RFC2676)
Well,sortof!• Appliestoalltraffic
– Nodifferentiation betweenflowtypes
• Whataboutinter-domain?– Nocontrolovernetwork
resources• Moresophisticated
mechanismsneeded– MultiprotocolLabelSwitching
(MPLS)– Resource Reservation
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Layer 3congestion avoidance
• Congestion=dataload>networkcapacity– Arrival rate>processingrate– Processingrate>departurerate
• Asimplemethod– Randomearlydiscard(RED)– UDP?
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APP
TCP
IP
Traffic descriptors
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Traffic profiles
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Trafficshaping:Twoapproaches
Leaky bucket Tokenbucket
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Inputflow
Outputflow
Inputflow
Outputflow
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Traffic shaping:Leakybucket
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See also Figure 20.7
Traffic shaping:Tokenbucket
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See also Figure 20.6
TokenBucket• Widelyusedtrafficmanagementtool• Advantages:–Manytrafficsourcescanbedefinedeasilyandaccurately
– Providesaconcisedescriptionoftheloadtobeimposedbyaflow,enablingtheservicetodetermineeasilytheresourcerequirement
– Providestheinputparameterstoapolicingfunction
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Bonus:QoE,Quality of Experience
• Theuser’s subjective perceptionof thepresentationof thecontent
• Mean OpinionScore(MOS)• Researchforto find objective measures– Fullreference– Noreference– Hybrid
• What QoS give what QoE??
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https://goo.gl/forms/IRcUYcJCZTu8uo152
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