Voice Over IP – RFC 3714 Presented By Page  Jaya Ravindran 1 st  August 2005
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Overview <ul><li>Introduction </li></ul><ul><ul><li>End to end con...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Motivation – Why ? Caller Callee Qos Employed Best Effort Qos Empl...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Which is the bottleneck ? Host Last Hop Bottleneck Access Links Ac...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Persistent packet drop rate – A problem <ul><li>Congestion collaps...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Rule of thump <ul><li>When packet loss rate > 20 %  </li></ul><ul>...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Fairness <ul><li>Consider </li></ul><ul><ul><li>Multiple VoIP sour...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Current efforts in the IETF <ul><li>An upgrade of RTP specificatio...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  RTP –  RFC 3551 <ul><li>“ If best-effort service is being used, RT...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  TFRC –  RFC 3267 - Equation based congestion control <ul><li>TFRC ...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  DCCP –  RFC 3267 - Datagram Congestion Control Protocol <ul><li>Fo...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Adaptive Rate Audio Codec <ul><li>Fixed codecs not helpful. </li><...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Adaptive Rate Audio Codecs <ul><li>Varies its encoded frame size. ...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Assessing Minimum Acceptable sending Rate <ul><li>For an AMR appli...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Recommendations <ul><li>Fixed rate codec + Ability to specify mini...
Voice Over IP – RFC 3714 Summer 2005 Presentation Page  Thank  You
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VoIP.ppt

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VoIP.ppt

  1. 1. Voice Over IP – RFC 3714 Presented By Page Jaya Ravindran 1 st August 2005
  2. 2. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Overview <ul><li>Introduction </li></ul><ul><ul><li>End to end congestion control for best effort voice traffic In the internet </li></ul></ul><ul><li>Concerns </li></ul><ul><ul><li>Fairness </li></ul></ul><ul><ul><li>User Quality </li></ul></ul><ul><ul><li>Congestion Collapse </li></ul></ul><ul><li>Current Efforts </li></ul><ul><li>Recommendations </li></ul>
  3. 3. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Motivation – Why ? Caller Callee Qos Employed Best Effort Qos Employed
  4. 4. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Which is the bottleneck ? Host Last Hop Bottleneck Access Links Access Links Avoid congestion collapse along the entire path including the access links. Result ! - Bandwidth wasted Possible Measures Terminate ? Suspend ? } On Persistent high packet drop rate As VOIP requires a “Minimum sending rate”
  5. 5. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Persistent packet drop rate – A problem <ul><li>Congestion collapse Important In VoIP </li></ul><ul><ul><li>Congestion collapse – Occur mostly for flows that traverse multiple congested links. </li></ul></ul><ul><ul><li>For a VoIP network – Both ends of the VoIP call may be on a congested broadband connection, such as DSL, Backbone or Transoceanic link. </li></ul></ul><ul><li>User Quality </li></ul>Drop occurs randomly, so nobody gets benefited X X 1 2 . . . . . . N 1 2 . . . . . . N 128 Kbps 64 Kbps 64 Kbps (N-2) * 64 Dropped (N-2) / N For each flow
  6. 6. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Rule of thump <ul><li>When packet loss rate > 20 % </li></ul><ul><ul><li>Audio quality of VoIP is degraded beyond usefulness. </li></ul></ul><ul><ul><li>TCP can compete leading to jitter. (1500 packet size) </li></ul></ul><ul><ul><li>Better to terminate. </li></ul></ul>
  7. 7. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Fairness <ul><li>Consider </li></ul><ul><ul><li>Multiple VoIP sources. </li></ul></ul><ul><ul><li>Multiple TCP sources. </li></ul></ul><ul><li>Bottom line – VoIP crowds out TCP </li></ul>Possible Solutions <ul><li>Call Rejection – Does not exist for best effort </li></ul><ul><li>End to end congestion control </li></ul>
  8. 8. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Current efforts in the IETF <ul><li>An upgrade of RTP specification </li></ul><ul><li>TFRC </li></ul><ul><li>DCCP </li></ul><ul><li>Adaptive Rate Audio Codecs </li></ul><ul><li>Differentiated Services & Related Topics </li></ul>
  9. 9. Voice Over IP – RFC 3714 Summer 2005 Presentation Page RTP – RFC 3551 <ul><li>“ If best-effort service is being used, RTP receivers SHOULD monitor packet loss to ensure that the packet loss rate is within acceptable parameters. Packet loss is considered acceptable if a TCP flow across the same network path and experiencing the same network conditions would achieve an average throughput, measured on a reasonable timescale, that is not less than the RTP flow is achieving.” </li></ul><ul><li>“ In essence, this requirement states that it is not acceptable to deploy an application (using RTP or any other transport protocol) on the best-effort Internet which consumes bandwidth arbitrarily and does not compete fairly with TCP within an order of magnitude.” (Timescale & Throughput) </li></ul>
  10. 10. Voice Over IP – RFC 3714 Summer 2005 Presentation Page TFRC – RFC 3267 - Equation based congestion control <ul><li>TFRC has a much lower variation of throughput over time compared with TCP. </li></ul><ul><li>Suitable for applications such as telephony or streaming media where a relatively smooth sending rate is of importance. </li></ul><ul><li>TFRC works for fixed packet size and vary their sending rate in packets per second. </li></ul><ul><li>Some audio application </li></ul><ul><li>- Need fixed interval of time between packets. </li></ul><ul><li>- Can vary their packet size instead of packet rate. </li></ul><ul><li>TFRC-PS (TFRC Packet Size) </li></ul><ul><ul><li>- Meets the above requirement.( Fixed PPS,Variable </li></ul></ul><ul><ul><li>Payload Size) </li></ul></ul><ul><ul><li>- Hence, can be effective for congestion control. </li></ul></ul><ul><ul><li>- Can be used in a transport protocol such as RTP. </li></ul></ul>
  11. 11. Voice Over IP – RFC 3714 Summer 2005 Presentation Page DCCP – RFC 3267 - Datagram Congestion Control Protocol <ul><li>For unreliable Flows. </li></ul><ul><li>Applications can specify: </li></ul><ul><ul><li>TCP like </li></ul></ul><ul><ul><li>TFRC like services. </li></ul></ul><ul><li>Congestion Control Identifiers </li></ul><ul><ul><li>CCID2 – TCP like </li></ul></ul><ul><ul><li>CCID3 – TFRC like </li></ul></ul><ul><ul><li>CCID4 – TFRC-PS - ‘future’ </li></ul></ul>
  12. 12. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Adaptive Rate Audio Codec <ul><li>Fixed codecs not helpful. </li></ul><ul><li>Low/Adaptive rate preferable. </li></ul>
  13. 13. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Adaptive Rate Audio Codecs <ul><li>Varies its encoded frame size. (Between 11 & 32) </li></ul><ul><li>Each frame size is 20 ms of speech. </li></ul><ul><li>RTP payload format allows multiple AMR frames into the same packet. </li></ul><ul><li>Reduces transmission rate during silence periods. </li></ul><ul><li>Has employed FCE and frame interleaving. </li></ul><ul><li>Along with TFRC-PS, can provide effective congestion control mechanism. </li></ul><ul><li>Highly experimented. </li></ul><ul><li>Improves the scalability of VoIP or TCP sharing a congested link. </li></ul>
  14. 14. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Assessing Minimum Acceptable sending Rate <ul><li>For an AMR application with minimum rate M </li></ul><ul><ul><li>Is M acceptable ? </li></ul></ul><ul><ul><li>Is the limitation in PPS or BPS ? </li></ul></ul><ul><li>For a persistent packet drop D when should the application terminate ? </li></ul><ul><ul><li>Consider TCP having the same drop as VoIP </li></ul></ul><ul><ul><li>Sending rate of VoIP >> TCP, terminate. </li></ul></ul><ul><li>Reasons </li></ul><ul><ul><li>Avoiding Congestion Collapse. </li></ul></ul><ul><ul><li>Fairness for TCP like traffic. </li></ul></ul><ul><ul><li>Minimum service not achieved. </li></ul></ul>25% 64 Kbps 40% 4.7 Kbps Drop Rate Minimum Sending Rate
  15. 15. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Recommendations <ul><li>Fixed rate codec + Ability to specify minimum bit throughput. </li></ul><ul><li>Adaptive variable bit rate codec, supporting VoIP on shared internet. </li></ul><ul><li>ECN to detect congestion. </li></ul><ul><ul><li>Ensure receiving application is capable of getting this information from lower layer. </li></ul></ul>
  16. 16. Voice Over IP – RFC 3714 Summer 2005 Presentation Page Thank You

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