! Naive n-way unicast does not scale. ! IP multicast to the rescue. ! Extends IP architecture for efficient multi-point delivery. !

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1 Bayeux: An Architecture for Scalable and Fault-tolerant Wide-area Data Dissemination ACM NOSSDAV 001 Shelley Q. Zhuang, Ben Y. Zhao, Anthony D. Joseph, Randy H. Katz, John D. Kubiatowicz {shelleyz, ravenben, adj, randy, IP! Naive n-way unicast does not scale! IP multicast to the rescue! Extends IP architecture for efficient multi-point delivery! Packets travel on common parts of the network only once to reach receivers -> reducing bandwidth! Sender transmits packets only once for any number of receivers -> reducing server load! Problems! Absence of a good inter-domain multicast routing protocol! Only best-effort packet delivery! root, core, RP discovery remains difficult The Problem! Internet broadcast applications! E.g. Mars Polar Lander mission! Application demands! One-to-many communication! Fault-resilient delivery despite common faults! Large scale issues:! Efficient routing: minimize delivery delay! Packet duplication: minimize unnecessary b/w usage! Ease of management as a Higher-Level Service?! Application-level multicast! Offers multi-point delivery as an application-level service! Removes many of IP multicast deployment barriers! Maintains the simplicity of the underlying IP layer! Allows for application-specific adaptation to deal with heterogeneity! Delay and bandwidth penalty are low! Limitations! Do not address fault-resilient packet delivery! -way tradeoff: scalability, delay, bandwidth efficiency! Do not solve root discovery problem 1

2 Our Approach! View multicast as an application-level infrastructure service! How to construct efficient and robust spanning tree?! Tapestry (Zhao, Kubiatowicz, Joseph U.C. Berkeley)! Overlay location and unicast routing infrastructure! Locates nearest copy of replicated objects! Efficient and fault-resilient routing! Bayeux! group addressing! E.g. <MarsPolarLander, NASA>! root discovery via object location! forwarding algorithm! Tree maintenance algorithm Basic Tapestry Mesh Incremental suffix-based routing 05E FE 555E 09E 9FE FE E 7FE 1FE FE 9E 1 0FE 99E F990 Outline Use of Tapestry Mesh Randomization and Locality Location

3 Outline Tree Maintenance 05E FE 555E 09E 9FE TREE FE E 7FE 1FE TREE FE 9E 0FE TREE JOIN 99E 9990 F990 ing with Bayeux 05E FE 555E 09E 9FE FE E 7FE 1FE FE 9E 0FE 99E 9990 F990 Outline

4 Simulation Setup! Implemented Tapestry routing and Bayeux tree protocol as a packet-level simulator! Focus on delay and bandwidth metrics! Delay is measured in terms of network hops! Do not model the effects of cross traffic or queuing delays! Four topologies: AS, MBone, GT-ITM, TIERS Performance Analysis - PLS! Physical Link Stress: measure of effectiveness in distributing network load across physical links PLS = # of identical copies of a packet carried by a physical link! With Unicast, two links carry 09 copies! With Bayeux, worse link carry 8 copies Performance Analysis - RDP! Relative Delay Penalty: measure of overlay routing overhead # physical hops traveled via overlay RDP = # physical hops traveled via shortest IP route 90% < Outline

5 Scalability Enhancements Tree Partitioning JOIN FE 05E 555E 09E 9FE JOIN FE E 7FE 1FE FE 9E JOIN 0FE 99E 9990 F990 Outline Scalability Enhancements Tree Partitioning! Eliminates JOIN/LEAVE implosion at root (R)! s will join a nearby multicast root via the Tapestry location service Can We Use Tapestry s Redundancy for Adaptive Fault-Resilience?! Yes!! IP routes via Border Gateway Protocol (BGP)! Convergence time ~ O(minutes)! Fault-detection/reroute occur on macro timescale! Routing decisions do not consider path performance! Tapestry fault-resilient packet delivery! Explicit redundant paths! History window of UDP beacons gauges link quality! Reroute to alternate paths when appropriate 5

6 Path Redundancy! Each entry in the Tapestry neighbor map maintains secondary neighbors in addition to the closest primary neighbor A D C B E Shows maximum connectivity compared to IP routing as link failures increase A B C D E IP Tapestry No path exists to dest. First Reachable Link Selection (FRLS) A D C B E Shows reachability using FRLS versus IP routing as link failures increase! Fault-resiliency approaches the maximum resiliency provided by Tapestry s routing redundancy First Reachable Link Selection (FRLS) 9FE 1FE 9E " Periodic UDP packets to gauge link condition " Packets routed to shortest good link " Relevant membership state forwarded to backup routes 0FE Related Work! IP! EXPRESS/SSM, REUNITE! Application-Level! Narada, Yallcast, Scattercast, Overcast! Wide-area Location Services! Content-Addressable Networks (CAN), ACIRI/UCB! Chord, MIT/UCB! Pastry, Microsoft Research! Tapestry: explicit correlation between overlay distance and underlying network distance 6

7 Conclusion! Advantages of Bayeux! Resilient to failures in routers and network links! Efficient support for large-scale data dissemination! Transparent discovery of multicast roots! Service model simple to implement and manage! Future work! Study the performance and tradeoffs in alternative fault-resilient delivery protocols! Deployment on real networks and applications Tapestry Neighbor Map Example: Hexadecimal base, 16 namespace F90 Neighbor map for node x090 x190 x90 x90 x590 x690 xf90 xx00 xx10 xx0 xx0 xx0 xx50 xx60 xxf0 xxx1 xxx xxx xxx xxx5 xxx6 xxxf 1 Routing levels Performance Analysis - PLS Backup slides! Physical Link Stress, measure of effectiveness in distributing network load across physical links PLS = # of identical copies of a packet carried by a physical link 7

8 Fault-Resilient Packet Delivery Protocols Hierarchical Path Convergence 1. First Reachable Link Selection. Explicit Knowledge Path Selection. Proactive Duplication. Application-specific Duplication 5. Prediction-based Selective Duplication! Alternate path converge quickly to primary path! Packet duplication protocols can have low b/w overhead with duplicate suppression Hierarchical Path Convergence Duplicate Suppression 9FE 1FE! Protocols,, 5 actively duplicate packets! Will duplicates converge & allow duplicate suppression?! Alternate path convergence! # of candidates for next hop decreases quickly! Primary route of an alternate path is on the original primary path with high probability! Will not flood network with duplicate packets 9E 8