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Building Differentiated Services Using the Assured Forwarding PHB Group

Building Differentiated Services Using the Assured Forwarding PHB Group. Juha Heinänen Telia Finland Inc. jh@telia.fi. AF PHB Group (RFC 2597). Provides forwarding of IP packets in four independent service classes at each hop, each class has its own, configurable forwarding resources

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Building Differentiated Services Using the Assured Forwarding PHB Group

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  1. Building Differentiated Services Using the AssuredForwarding PHB Group Juha HeinänenTelia Finland Inc.jh@telia.fi

  2. AF PHB Group (RFC 2597) • Provides forwarding of IP packets in four independent service classes • at each hop, each class has its own, configurable forwarding resources • within each class, an IP packet is assigned one of three levels of drop precedence • lower drop precedence means higher probability of forwarding

  3. AF PHB Group Implementation • forwarding resources (buffer space and bandwidth) can be allocated using • FBA, CBQ, WFQ, priorities, etc. • dropping of packets is based on the Random Early Drop (RED) algorithm • each level of drop precedence (green, yellow, red) has its own RED threshold

  4. Example of Output Behavior RED thresholdfor “Red” packets R R R R R R Each AF class hasits own queue and forwarding resources RED thresholdfor “Yellow” packets

  5. RED with Multiple Thresholds Discard Probability “Red” Packets “Yellow” Packets “Green” Packets 1 AverageQueue Length 0 0 “Red” Threshold Full “Yellow” Threshold “Green” Threshold

  6. AF Based Services • service characteristics of an AF class depend on • traffic conditioning actions at the edge • relative traffic load and scheduling policy of the class in the core • different combinations result in relative or quantitative bandwidth and/or delay assurances

  7. R R Metering, Marking and Policing May classifypackets to service classes Host May select outgoing packets and drop excess ISP May meter hostbehavior and shape packets Enterprise Network R May police hostbehavior and classify packets onbehalf of host May meter aggregate behavior, classify, (re)mark, drop, andshape packets Polices aggregatebehavior and remarks or drops excess

  8. Examples of Markers • Two Rate Three Color Marker (trTCM) • marks packets green, yellow, or red based on Peak and Committed Information Rates • useful when peak rate needs to be enforced • Single Rate Three Color Marker (srTCM) • marks packets green, yellow, or red based on a rate and two burst sizes • useful when only burst size matters

  9. A Two Rate Marker New token CIR times/sec CBS New token PIR times/sec Not enough yellow tokens PBS Enough yellow tokens, but not enough green tokens Enough yellow andgreen tokens ?

  10. A Single Rate Marker Overflow tokens from C New token CIR times/sec EBS Not enough green nor yellow tokens CBS Te Enough yellow tokens, but not enough green tokens Tc Enough greentokens ?

  11. Selection of Outgoing Traffic Guaranteed Minimum Allowed Maximum Weight Guaranteed Minimum Allowed Maximum Weight ... Service Classes Outgoing “streams” Link

  12. Assured Bandwidth (AB) Service • traffic is policed at the ingress using one of the two three color markers • green packets are delivered with high probability, yellows as best effort, and reds are discarded • resources are allocated so that the AF class is only moderately loaded with greens

  13. Assured Delay (AD) Service • traffic is policed so that only green packets are allowed into the network • green packets are delivered with high probability and low delay variation • resources are allocated so that the AF class is very lightly loaded with greens

  14. PSTN VoIP/Web Example 20 Mb AB128 Kb AD ISP 10 Mb AB 512 Kb AD Enterprise Network WebServer VoIP GW No Profiles PRI ISDN 128 Kb AD IP PBX

  15. R Service Implementation Policer keeps links only lightly loaded with green packets Assured Delay WFQ Weight: 80 % R R Best Effort service can implemented as an AB Service with CIR = 0 Assured Bandwidth WFQ Weight: 20 %

  16. Mapping AF PHBs to ATM • each service class is allocated a set of forwarding resources on every link • signaling of UBR VCs is extended by a service class indicator • hierarchical scheduling first per service class and then per VC within the class • AF drop precedence is mapped to the CLP bit

  17. ATM Backbone Example of Diff-Serv Mapping R DropPrec ATM CLP 0 1 R R UBR VC for Assured Delay Service UBR VC for Assured Bandwidth Service

  18. Summary • AF PHB group provides a flexible means to implement services for both delay sensitive and delay insensitive applications • AF support is already available at least in a limited form in popular routers • AF based services will become available from ISPs during 1999

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