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ASAP: an AS-Aware Peer-Relay Protocol for High Quality VoIP

ASAP: an AS-Aware Peer-Relay Protocol for High Quality VoIP. Shansi Ren, Lei Guo, and Xiaodong Zhang Ohio State University. VoIP Packets Traveling in Internet. Long router queuing delay!. Alice, I am Bob~~. Bob, What did you say?!!. Internet. Alice. Bob. Bob -> Alice voice pkts.

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ASAP: an AS-Aware Peer-Relay Protocol for High Quality VoIP

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  1. ASAP: an AS-Aware Peer-Relay Protocol for High Quality VoIP Shansi Ren, Lei Guo, and Xiaodong Zhang Ohio State University

  2. VoIP Packets Traveling in Internet Long router queuing delay! Alice, I am Bob~~ Bob, What did you say?!! Internet Alice Bob Bob -> Alice voice pkts. Internet routing is Critical for VoIP Quality! Alice -> Bob voice pkts.

  3. VoIP Quality Requirements • Mean Opinion Score (MOS) metric • MOS > 3.5 is acceptable. • Network factors • E2E one-way latency < 150 ms • E2E loss rate < 0.5%

  4. Some Facts of VoIP in Internet • Two end hosts communicate through their direct IP routing path by default. • Direct routing path may not always meet the VoIP quality requirements. • Overlay routing sometimes may have better routing performance.

  5. direct, 1-hop, and 2-hop overlay routing host B host C host A direct IP routing path 1-hop overlay routing path Internet host D 2-hop overlay routing path host E host A communicates with host C

  6. Internet Routing • Internet consists of Autonomous Systems (ASes), and hosts are administered in the unit of AS. • ASes are connected by core routers, and routing between ASes relies on the Border Gateway Protocol (BGP). • Connected ASes has customer-provider and peer-peer relationship. • An customer AS connecting to multiple upstream ASes is called a multihoming AS. (or multiple providers) • Valley-free: a direct Internet routing path has the form (customer-provider)*(peer-peer)?(provider-customer)*.

  7. Targeted Research Questions • How insufficient is Internet direct routing for VoIP? • Under what condition, can overlay routing(relay) improve VoIP quality? • What kind of quality does Skype provide, and what are the limits in its routing? • How to design efficient routing methods for high quality VoIP with low overhead?

  8. Outline of Talk • VoIP application introduction • Internet e2e latency measurements • Skype measurement and observations • ASAP protocol design and evaluation • Conclusion

  9. E2E Latency Measurement Procedures Gnutella IP probing online Gnutella IP addresses Limewire software modification Gnutella IP crawler BGP tables and updates IP prefix and origin AS extraction IP prefix table AS-level cluster Identification and delegate IP selection cluster delegate IP addresses pairwise IP DNS server latency measurement pairwise delegate IP latency King tool based prober development King prober

  10. Sessions and their RTTs • A session consists a pair of end host. • We randomly generate 105 sessions among cluster delegates. • We measure session direct RTTs using king facility. • For delegates a, b, c, relay path a-b-c RTTa-b-c = RTTa-b + RTTb-c + relay delay.

  11. Internet e2e RTT Measurement DNS server of host c DNS server of host b IP of host c? host b IP of host c Internet IP of host c host c IP of host c? host a host a measures RTTb-c via recursive DNS queries

  12. Direct vs 1-Hop RTT 50% sessions have optimal 1-hop RTT < direct IP RTT 25% sessions whose opt. 1-hop relay can reduce direct IP RTT by more than 50%

  13. Overlay Routing Reduces RTT Sessions whose direct IP RTTs > 300 ms Sessions opt. 1-hop RTTs are always < 300 ms

  14. Relay Improves VoIP Quality • There are 2% and 10% of sessions with direct RTTs above 300 ms and 250 ms, respectively. • We can always find one-hop relay paths whose RTTs are below the threshold for these sessions. • Peer relay plays an important and critical role in improving the quality for VoIP applications.

  15. Direct Path Is Congested direct path between AS A and AS C AS H is congested AS G AS H AS D AS E AS F 1-hop relay path betweenAS AandAS C via AS B AS A AS B AS C direct path betweenAS BandAS C direct path between AS A and AS B provider-to-customer edge peer-to-peer edge

  16. Multi-homed AS B As 1-hop Relay direct path between AS A and AS C AS H AS I AS F AS G AS D AS E AS B AS C AS A direct path between AS A and AS B direct path betweenAS BandAS C AS B ismulti-homed, connects to AS A and AS C 1-hop relay path betweenAS AandAS C viaAS B provider-to-customer edge peer-to-peer edge

  17. Outline of Talk • VoIP application introduction • Internet e2e latency measurements • Skype measurement and observations • ASAP protocol design and evaluation

  18. Skype Experimental Sites and Sessions Vancouver, Canada Dalian, China Jersey City, NJ Bozeman, MT Beijing, China Baltimore, MD Reston, VA Shanghai, China Williamsburg, VA Jingzhou, China Austin, TX We have chosen 14 representative Skype sessions

  19. Skype Relay Selection Limits Limit 1: Long latency due to improper relay node selections. Session 4 300 ms Session 10 300 ms

  20. Limit 2: Probing multiple latent nodes in the same AS. two probed relay nodes in session 8 relay node DNS zone name relay path RTT 85.64.x.x barak-online.net 360 ms 85.65.x.x barak-online.net 359 ms Limit 3: Taking a long time to find major relays.

  21. Limit 4: Generating non-negligible overhead. before stabilization 10 10 after stabilization

  22. Skype Measurement Summary • Although we do not know the routing algorithm of Skype: • Non-optimal replay nodes are used often. • Seems to only reply on probes to find a relay node in a ad-hoc way: many probes. • The relay nodes are frequently changed even after the sessions are established. • It is an AS-unaware routing.

  23. ASAP: AS-Aware Peer-Relay Selection Method

  24. ASAP Design Rationale • In general, peer nodes with the same IP prefix are relatively close to each other. • With publicly available BGP tables and updates, an up-to-date annotated AS graph can be built. • Paths with longer AS hops are likely to have longer latencies. • An Internet AS-level direct IP routing path usually has the valley-free property.

  25. Three Types of ASAP Nodes bootstrap’s data structure bootstrap1 Internet AS graph bootstrap2 IP prefix to cluster Surrogate IP table cluster surrogate’s data structure IP prefix to ASN table cluster’s close cluster set Type 1: bootstraps Type 2: surrogates Internet AS graph cluster’s top node table surrogate SA cluster C surrogate SB end host h3 cluster A cluster B end host h1 Type 3: end hosts end host h2

  26. Close Clusters Construction Process AS 5 h6 h4 AS 4 AS 6 s5 s4 s6 good, 220 ms good, 180 ms s2 AS 2 h3 bad, 350 ms AS 3 good, 75 ms s3 s1 close cluster s1 s2 – 75 ms good, 52 ms AS 1 s5 – 180 ms ping s6, h6 – 220 ms h1 pong s3, h3 – 52 ms good: RTT < 300 ms && loss rate < 5% provider-to-customer edge peer-to-peer edge bad: RTT > 300 ms || loss rate > 5%

  27. h1-h4 Close Relays Selection Process AS 5 h6 h4 AS 4 AS 6 s5 s4 s6 s4 close cluster s2 – 50 ms s2 AS 2 h3 s5 – 170 ms AS 3 s3 s1 RTTh1-s2 + RTTh4-s2 = 125 ms < 300 ms s2 is good relay for h1-h4 VoIP session s1 close cluster AS 1 s2 – 75 ms h1 s5 – 180 ms s6, h6 – 220 ms s3, h3 – 52 ms provider-to-customer edge peer-to-peer edge

  28. ASAP Call Session Process bootstrap1 bootstrap’s data structure bootstrap2 cluster surrogate’s data structure Internet AS graph IP prefix to cluster Surrogate IP table cluster’s close cluster set surrogate? IP prefix to ASN table Internet AS graph surrogate IP cluster’s top node table surrogate? surrogate SA cluster C surrogate IP surrogate SB voice pkts voice pkts close set? voice pkts close set end host h3 voice pkts close set? close set cluster A cluster B end host h1 h2’s close set end host h2 control pkt. h2’s close set? voice pkt.

  29. Evaluation Metrics • Number of quality paths: number of relay paths satisfying the RTT and loss rate requirements • Shortest RTT and highest MOS of these quality paths • Overhead: measured by the number of generated messages to find quality path relay nodes

  30. Different Routing Methods • DEDI: uses dedicated relay nodes. (SOSP’01) • RAND: randomly selects relay nodes. (OSDI’04) • MIX: is a combination of RAND and DEDI. • ASAP: selects relay nodes using our AS-aware method. • OPT: always chooses relay nodes that give the shortest overlay routing latency. (Offline method)

  31. Number of Quality Paths For 90% sessions, ASAP can find more than 5,000 quality paths DEDI, RAND, and MIX can find no more than 500 quality paths for all sessions

  32. Shortest Path RTT 115 ms 1 s In DEDI, RAND, and MIX, more than 5% sessions have shortest RTT > 1s In ASAP and OPT, all sessions have shorest RTT < 115 ms

  33. Highest Path MOS 2.9 3.85 In DEDI, RAND, and MIX, about 3% sessions have highest MOSs < 2.9 In ASAP and OPT, all sessions have highest MOSs > 3.85

  34. ASAP Is Highly Scalable 23,366 end hosts 103,625 end hosts The number of quality paths found by ASAP remains stable under different end host population.

  35. ASAP Has Moderate Overhead In ASAP, 85% sessions generate less than 300 messages DEDI, RAND, and MIX all probe fixed number of nodes, i.e., 160, 160, and 200 nodes

  36. Conclusion • In a global overlay systems, 10% sessions of direct path cannot meet VoIP quality requirements. • For these sessions, there always exist multiple relay paths that can meet the requirements. • Existing relay selection methods, including Skype, do not always select proper relay nodes. • Optimal replay nodes can be found by AS-aware routing. • We show ASAP is scalable, light-weight, and outperforms all existing solutions.

  37. ASAP source code and results can be found at http://www.cse.ohio-state.edu/~sren/VoIP-Peer-Relay/

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