p2p-sippeertopeerinternettelephonyusingsip(編輯修改稿)
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【文章內(nèi)容簡介】 uplicates ? Security: How to avoid spies? ? How to recover if all responsible nodes leave? 28 Conferencing (further study) ? One member bees mixer ? Centralized conferencing ? What if mixer leaves? ? Fully distributed ? Many to many signaling and media ? Application level multicast ? Small number of senders 29 Evaluation scalability ? messages depends on ? Keepalive and finger table refresh rate ? Call arrival distribution ? User registration refresh interval ? Node join, leave, failure rates M={rs+ rf(log(N))2} + (N) + (k/t)log(N) + ?(log(N))2/N ? nodes = f(capacity,rates) ? CPU, memory, bandwidth ? Verify by measurement and profiling 30 Evaluation reliability and call setup latency ? User availability depends on ? Supernode failure distribution ? Node keepalive and finger refresh rate ? User registration refresh rate ? Replicate user registration ? Measure effect of each ? Call setup latency ? Same as DHT lookup latency: O(log(N)) ? Calls to known locations (“buddies”) is direct ? DHT optimization can further reduce latency ? User availability and retransmission timers ? Measure effect of each 31 Explosive growth (further study) ? Cache replacement at supernodes ? Last seen many days ago ? Cap on local disk usage (automatic) ? Forcing a node to bee super node ? Graceful denial of service if overloaded ? Switching between flooding, CAN, Chord, … ? . . . 32 More open issues (further study) ? Security ? Anonymity, encryption, ? Attack/DOSresistant, SPAMresistant ? Malicious node ? Protecting voics from storage nodes ? Optimization ? Locality, proximity, media routing ? Deployment ? SIPP2P vs P2PSIP, Intra, ISP servers ? Motivation ? Why should I run as supernode? 33 Conclusions ? P2P useful for VoIP ? Scalable, reliable ? No configuration ? Not as fast as client/server ? P2PSIP ? Basic operations easy ? Implementation ? sippeer: C++, Linux ? Interoperates ? Some potential issues ? Security ? Performance C C C C C S P P P P P 427 763 135 365 123 324 564 364 65a1fc d13da3 d4213f d462ba d467c4 d471f1 d46a1c Route(d46a1c) Backup slides 35 Napster ? Centralized index ? File names = active holder machines ? Sophisticated search ? Easy to implement ? Ensure correct search ? Centralized index ? Lawsuits ? Denial of service ? Can use server farms P1 P2 P3 P5 P4 S Where is “quit playing games” ? P2 FTP 36 Gnutella ? Flooding ? Overlay work ? Decentralized ? Robust ? Not scalable. ? Use TTL. Query can fail ? Can not ensure correctness P P P P P P P P P 37 KaZaA (FastTrack) ? Supernodes ? Election: ? capacity ? bandwidth, storage, CPU ? and availability ? connection time ? public address ? Use heterogeneity of peers ? Inherently nonscalable ? If flooding is used P P P P P P P P P P P P 38 FreeNet ? File is cached on reverse search path ? Anonymity ? Replication, cache ? Similar keys on same node ? Empirical log(N) lookup ? TTL limits search ? Only probabilistic guarantee ? Transaction state ? No remove( ) ? Use cache replacement P P P P P P P 1 12 2 3 4 5 6 7 8 9 10 11 39 Distributed Hash Tables ? Types of search ? Central index (Napster) ? Distributed index with flooding (Gnutella) ? Distributed index with hashing (Chord) ? Basic operations find(key), insert(key, value), delete(key), no search(*) Properties/types Every peer has plete table Every peer has one key/value Search time or messages O(1) O(n) Join/leave messages O(n) O(1) 40 CAN Content Addressable Network ? Each key maps to one point in the ddimensional space ? Each node responsib
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