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Perspective on Overlay Networks

This panel explores the challenges and implications of computing on a massive scale, including the benefits of overlay networks, infrastructure scalability, dynamic environments, extending the scope of overlays, introspective tuning, and security challenges.

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Perspective on Overlay Networks

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  1. Perspective on Overlay Networks Panel: Challenges of Computingon a Massive ScaleBen Y. ZhaoFuDiCo 2002

  2. Why Overlays • Changes to standards is hard • Possible benefits of overlays • Extensible communication models(more than best-effort point to point) • More easily deployed services / infrastructures • More adaptable, fault-tolerant … ravenben@eecs.berkeley.edu

  3. Massive Scale • It’s coming… • Driven by global scale resource sharing apps • File-sharing, data dissemination, shared computation • Viral deployment (Kazaa / alt.net) • More thin clients going online: cellphones, PDAs, fridges, toasters ravenben@eecs.berkeley.edu

  4. Implications of Scale • Pushing bounds of infrastructure scalability • Logarithmic bounds are not enough! • Worse case: massive congestion, network partitions, data / service unavailability • Scrutinize infrastructure scalability • Re-examine system level primitives • Control traffic, fault-detection, replication overhead • Dampen impact of operations on infrastructure • Localize bandwidth / storage requirements, faults ravenben@eecs.berkeley.edu

  5. Highly Dynamic • It’s here… • Small half-life for P2P apps (leeching) • Connectivity loss from congestion, flash crowds, misconfiguration, hardware faults, lower MTBF • BGP convergence 3-15 mins • Mobile clients in semi-connected mode • E.g. chatting / file-sharing on your IPAQ / Palm ravenben@eecs.berkeley.edu

  6. Implications of Change • Have to reexamine stability assumptions • Overlay maintenance under instability • Without care, worst case: sub-optimal paths, network partitions, broken invariants  loss of availability • Proactive overlay construction and maintenance • Integrate optimal routes from square 1 • Estimate global knowledge w/ distributed algorithms at node insertion • Run-time heuristics are too late • Constant fault-detection and self-repair • Use of redundancy to mask self-repair ravenben@eecs.berkeley.edu

  7. Extending Scope of Overlays • Broader utility than file storage and retrieval • General routing layer (efficiency, fault-tolerance) • Detour, RAMP, RON, Tapestry • Flexible data dissemination layer • overlay multicast, anycast, mobility • Collaborative applications • Shared annotations, mail filtering • Data transcoding • Shared workspaces, games • Distributed computation • Barter incentives • (Mojos, ads, access to resources) ravenben@eecs.berkeley.edu

  8. Introspective Tuning for Reality • Exploit knowledge of the environment • Network latency discontinuity • Order of magnitude latency jump from LAN to WAN • Generic solution:Brocade: minimize wide-area hops via 2nd overlay • Non-uniformity in node resources • PDA < laptops < desktops < servers • Segregate supernodes, infrastructure routers, pure clients, storage devices ravenben@eecs.berkeley.edu

  9. Many Security Challenges • Open P2P = Infrastructure for attacks? • Misreporting data  unfair resource allocation • DDoS attacks on infrastructure • Sybil attack  enabling scale for attacker • Detecting maliciousness made harder • Scalable defense? • Cryptographic methods for authentication, privacy, etc. • Byzantine agreement • Redundancy (ID aliasing, multiple namespaces) • Misuse leads to resource based DDoS • Access control? ravenben@eecs.berkeley.edu

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