Simulation Study on the Effect of the trTCM ParametersHakyong KIM

R&D Center, Corecess Inc.Tel : +82-2-2056-5264PCS : +82-505-254-1434Mail : hykim@ieee.orgFeb. 27, 2002

Table of ContentsIntroduction to Rate Limiting/PolicingTraffic Conditioning/Traffic ConditionertrTCM AlgorithmSimulation ResultsSummarySimple and Flexible**Contents

*Simple and Flexible*

Rate Limiting / PolicingDefinitionPolicing is the packet-by-packet monitoring function at a network border (ingress point) that ensures a host does not violate its promised traffic characteristics. from Routing and Switching by Rita Pumanov

231Suitable for Real-Time Applications due to No Queueing Delay !!NOT Suitable for Loss-Sensitive Application !!

*Simple and Flexible*

Rate Limiting / PolicingOperation of Traffic Shaping

*Simple and Flexible*

Needs for PolicingWithout Rate Limiting

*Simple and Flexible*

Problems of PolicingInaccuracy in TCP environment20~30% accuracy (i.e., 70~80% inaccuracy)Due to flow control feature of TCPSettled by queueing traffic shapingCause additional queueing delayNot suitable for real-time applicationInaccuracy in Policer implementation~3% of inaccuracy due to the processing granularityPhysical limitation of processing chipPractically impossible to resolve.Inaccuracy due to improper settings of policing parametersNetwork operator are not familiar with policing parameter settingResolvable with a guideline

*Simple and Flexible*

Traffic ConditioningWhat is Traffic Conditioning?Policing/Rate Limiting in terms of DiffServ Configuration of the Traffic ConditionerClassifier (Classification)Meter (Metering) and Marker (Marking)Dropper (Dropping) / Shaper (Shaping)Traffic Conditioning Action (in DiffServ)RFC 2597 - Assured Forwarding PHB Group Shaping, Discarding, Mark-down / Mark-up of Drop PrecedenceReassigning of packets to other AF classes Must NOT cause reordering of packets of the same flow.Traffic Conditioners in RFCs RFC2697 A single rate three color marker (srTCM)RFC2698 A two rate three color marker (trTCM)RFC2859 A time sliding window three colour marker (TSWTCM)RFC2963 A rate adaptive shaper for differentiated servicesRFC2698 A two rate three color marker (trTCM)

*Simple and Flexible*

ClassifierMarkerMarkerMarkerMeterMeterMeterShaper/DropperShaper/DropperShaper/DropperPackets entering the networkMarked packets passed to the forwarderflow 1flow 2flow n

*Simple and Flexible*

Two-Rate Three-Color MarkerRFC2698Marking is based on CIR, PIR and CBS, PBS.tr-TCM AlgorithmSee next slide.Similar to the policing mechanism of ATM.Useful for ingress policing The bit rate, not burst length, determines service eligibility.A peak rate needs to be enforced separately from a committed rate.Operation ModesColor-Blind ModeColor-Aware Mode

*Simple and Flexible*

tr-TCM AlgorithmThe tr-TCM uses two Token Bucket Counters Tc and Tp.Initial values: Tc(0) = CBS, Te(0) = PBSPBS CBS maximum possible packet sizeTc is increased by one CIR times per second up to CBS.Tp is increased by one PIR times per second up to PBS.Size of the arrived packet : BColor-Blind ModeIf Tp(t) B < 0, then mark red. Else,If Tc(t) B < 0, then mark yellow and Tp = Tp B. Else,Mark green. Tp = Tp B. Tc = Tc B. Color-Aware ModeIf the arrived packet is precolored as red or Tp(t) B < 0, then mark red. Else,If the arrived packet is precolored as yellow or Tc(t) B < 0, then mark yellow and Tp = Tp B. Else,Mark green, Tp = Tp B. Tc = Tc B.

*Simple and Flexible*

tr-TCM Algorithm Mark RedYesYesNoNo Mark Yellow Mark Green Increase token counts

*Simple and Flexible*

Simulation Environments & AssumptionsObjective of SimulationTo look into the effect of the tr-TCM parameters on policing accuracyTo find out parameter sets guaranteeing 97% policing accuracySimulation EnvironmentsBC++ 6.0Pentium IV 1.5 GHzTraffic FlowA single traffic flow at the rate of 50 Mbps or 100 MbpsComposed of either fixed-length packets or variable-length packetsRunning Time20 seconds to get a result for a situation.1 sec is composed of 6x106 time slots or ticks.One time slot (tick) is 1.67x10-7-sec long.A full set of the trTCM operations occurs during a time slot.Industrial criteria :more than 95% or 97% accuracy

*Simple and Flexible*

Effect of CBS and PIRSimulation Environments & AssumptionsThe incoming traffic flow is composed of fixed-length packets.Packet length is fixed to 1500 bytes.The incoming traffic of 50 Mbps is policed to 10 Mbps.That is, CIR = 10 MbpsCBS is increased by 200 bytes from 2300 bytes to 3500 bytesPBS is set to equal to CBS.PIR is increased by 0.1 Mbps from 10.0 Mbps to 14.9 Mbps.

*Simple and Flexible*

A larger CBS yields the more accurate policing result.When CBS is greater than twice the average packet size, the tr-TCM guarantees 97% or more policing accuracy.When PIR is equal to CIR, we can get maximum accuracy.Result 1

*Simple and Flexible*

Effect of PBS and PIRSimulation Environments & AssumptionsThe incoming traffic flow is composed of fixed-length packets.Packet length is fixed to 1500 bytes.The incoming traffic of 50 Mbps is policed to 10 Mbps.That is, CIR = 10 MbpsCBS is set to either 2300 or 3500 bytesPBS is increased by 200 bytes from 2300 bytes to 3500 bytes.PIR is increased by 0.1 Mbps from 10.0 Mbps to 14.9 Mbps.

*Simple and Flexible*

PBS has no effect on the policing accuracy.When PIR is equal to CIR, we can get maximum accuracy.Result 2

*Simple and Flexible*

Effect of the Packet Size Distribution Simulation Environments & AssumptionsThe incoming traffic flow is composed of variable-length packets.Packet length distribution is based on the table below.Average packet length is fixed to 900 bytes in every cases.The incoming traffic of 100 Mbps is policed to 10 Mbps.That is, CIR = 10 MbpsCBS and PBS are set to 1200.PIR/CIR is increased by 0.05 from 1.0 to 1.95.

*Simple and Flexible*

The trTCM algorithm provides better policing accuracyfor the traffic with larger standard deviationResult 3

Curve 1Curve 2Curve 3Curve 4Curve 5Possible packet lengthFixed to900Random between 600 and 1200Random among 600, 900, and 1200Random among 300, 600, 900, 1200, and 1500Random among 300, 900, and 1500Standard deviation0173.2245424.3490

*Simple and Flexible*

SummaryPolicing/Rate Limiting Concept and its NeedsA procedure to ensure a host does not violate its promised traffic characteristics.Needed to prevent possible congestion by excessive traffic.Two-Rate Three-Color MarkerUse 4 parameters of CIR, PIR, CBS, and PBSWhen PIR is equal to CIR, policing result is most accurate.In this case, trTCM becomes srTCM.When CBS is greater than twice of the maximum packet size, we can get 97%+ policing accuracy.PBS has no effect on policing accuracy.

Thank You!YOUR SUCCESS IS CORECESSwww.CORECESS.comHakyong KIMwww.hakyongkim.net