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Enhancing BGP for Multi-QoS Support

This document discusses QoS enhancements to BGP for diverse QoS paths, including multiple metrics and path selection algorithms. It addresses limitations and proposes changes for exposing varied network paths to applications with different QoS needs.

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Enhancing BGP for Multi-QoS Support

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  1. QoS Enhancements to BGP in Support of Multiple Classes of Service Andreas Terzis Computer Science Department Johns Hopkins University ID: draft-liang-bgp-qos-00.txt 66th IETF

  2. Motivation • Applications of emerging IP networks require network paths with diverse QoS characteristics • Global Information Grid (GIG) • Large-scale internet for the US government • Diverse link characteristics • OC-192 backbone, satellite links, tactical wireless networks, etc. • Diverse applications • VoIP, bulk data transfer, etc. 66th IETF

  3. Current Limitations • Current BGP design limits ability to provide multiple QoS paths • Reachability under policy constraints is BGP’s focus. • Single route advertised  Limited route visibility • Path selection logic does not consider QoS characteristics • Number of AS hops is the only rough indication of path quality 66th IETF

  4. Goal • Expose multiple network paths to applications with different QoS requirements • Paths can have multiple QoS attributes (bandwidth, delay, loss, etc.) • Paths span multiple administrative domains 66th IETF

  5. Proposed BGP Changes • Maintain multiple QoS metrics for each path • Exchange multiple paths per destination • Prune the set of known paths to a dominant set while maintaining optimality • Choose a particular path from this dominant set for the unique QoS requirements of a traffic class 66th IETF

  6. Maintaining QoS metrics • Need to accumulate QoS parameters across E2E path • Different accumulation rules for different QoS metrics. • Additive metrics: e.g. latency • Multiplicative metrics: e.g. packet loss rate • “Min” metrics: e.g. bandwidth. 66th IETF

  7. Dominant Path Selection Algorithm (DPSA) • BGP routers are allowed to advertise multiple paths for a given destination prefix to neighbor routers • DPSA reduces the number of paths exchanged while maintaining path optimality • A path P dominates a set S of paths if it can provide better QoS than any path in S for all QoS metrics of interest • If more than one dominant paths have identical QoS metric values, the path with lower AS_PATH hop count and lower next-hop IP is preferred. 66th IETF

  8. AS1 AS2 AS3 AS4 AS5 AS6 DPSA Example Delay: 1 BW: 1 Delay: 0 BW: 4 Delay: 1 BW: 4 Delay: 1 BW: 4 Delay: 1 BW: 2 Delay: 1 BW: 4 Delay: 3 BW: 4 Delay: 1 BW: 3 66th IETF

  9. Route Pinning • Routers have multiple paths to a destination prefix, packets should follow QoS compliant path • A set of network-wide traffic classes with different QoS requirements is predefined • We opt Multi-Protocol Label Switching (MPLS) with Class-assignment algorithm 66th IETF

  10. Route Pinning – Our Approach • Under each destination prefix in routing table, every traffic class is assigned to at most one path. • Class-assignment information at each border router is also injected into IGP routers • Forwarding decision is based on packet destination address and class identifier stored in fields, such as IPv4 TOS or IPv6 Priority 66th IETF

  11. Class Assignment Algorithm • Class-assignment algorithm matches at most one path to each traffic class under each destination prefix in routing table. • From the set of paths satisfying a traffic class’ QoS requirement, the algorithm chooses the path offering the best QoS service. • In case of two QoS metrics, the chosen path would be the “furthest” path. 66th IETF

  12. Class Assignment Algorithm R will usepath P1 66th IETF

  13. Changes to BGP route decision process • Effective QoS routing needs routes from all neighbors to ideally be enabled. This requires manipulating Local_Pref and AS_Path attributes. • All enabled routes in Loc-RIB undergo DPSA before Output Policy Engine. • All enabled routes in Loc-RIB undergo DPSA and class-assignment algorithm before FIB. 66th IETF

  14. Changes to BGP packet • Need to extend AS_PATH attribute to store QoS attributes • Modeled after TLV (Type-Length-Value) model 66th IETF

  15. Simulation Results • ns-2 simulations of GIG-like topology • Vary network size • Link in dominant path is removed/added • Metrics • Convergence time • Number of updates 66th IETF

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