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1-800-CALL-H.E.P.

1-800-CALL-H.E.P. Warren Matthews (warrenm@slac.stanford.edu) Les Cottrell (cottrell@slac.stanford.edu) Rebecca Nitzan (nitzan@es.net). Overview. Review ESnet VoIP testbed Discuss and Review Metrics Define Quality Compare to Real Internet Production VoIP Service. 3.5 Mbps carved from

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1-800-CALL-H.E.P.

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  1. 1-800-CALL-H.E.P. Warren Matthews (warrenm@slac.stanford.edu) Les Cottrell (cottrell@slac.stanford.edu)Rebecca Nitzan (nitzan@es.net)

  2. Overview • Review ESnet VoIP testbed • Discuss and Review Metrics • Define Quality • Compare to Real Internet • Production VoIP Service

  3. 3.5 Mbps carved from ESnet ATM Backbone

  4. Hardware • Regular Telephone • PBX (Nortel) • Individual E&M (Ear and Mouth) Analog Voice Trunks. • Cisco 3640 • VODEC

  5. Software • VODEC • ITU G.729 • Policing • Cisco IOS 12.0(4.4) • Weighted Fair Queuing (WFQ) • Cisco experimental IOS

  6. A Typical VoIP call • Call set up with TCP • Voice transmitted with UDP • Managed with RTP

  7. UDP Packet Header IP UDP RTP

  8. Aims • How can VoIP be used on the Internet • under what loss/RTT (B.E. and priority) • assume some kind of QoS is required to be useful • Telephone companies claim 99.999% availability • Metrics • loss, RTT, Jitter, IQR

  9. Loss • Loss of TCP packets results in call failing to initiate, but will be re-sent • Loss of UDP packets causes break in conversation • routing change can cause seconds of loss

  10. Loss • Plot RTP seq vs Time • Seq 0-255 • Time Stamp is random (RFC 1889) • Require 56 concurrent calls to fill the pipe. Time Stamp RTP Seq #

  11. Jitter • Jitter is the variation in delay. • IETF defines IPDV • Audio is particularly sensitive to jitter.

  12. On the Real Internet

  13. Differentiated Services • Packet Loss, and hence loss of voice is unacceptable • Use Weighted Fair Queuing (WFQ) • Per-Hop Behavior (PHB) and Expedited Forwarding (EF) require Bandwidth Broker and associated infrastructure • Inter-network DiffServ still in the future

  14. Production Service • ESnet • How could/should applications set PHB • Policing • Extend test bed (Italy?) • Internet 2 (vBNS/Abilene) • Qbone • May include CERN

  15. Conclusion • VoIP is capable of high quality calls. • Work in Progress. • Future Work ?

  16. Any Questions ?

  17. VoIP - uses voice component of H.323

  18. H.323 infrastructure

  19. Voice over IP protocols From “VoIP Networking Design” by tdanford.cisco.com http://www.cisco.com/networkers/presentations/voice/1086_038.ppt

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