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Overload in SIP

Overload in SIP. Jonathan Rosenberg Cisco Systems. Problem Definition. Proxy 1. Element Overloaded. INVITE. 503. Proxy A. Proxy 2. INVITE. INVITE. Proxy 3.

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Overload in SIP

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  1. Overload in SIP Jonathan Rosenberg Cisco Systems

  2. Problem Definition Proxy 1 Element Overloaded INVITE 503 Proxy A Proxy 2 INVITE INVITE Proxy 3 SIP allows request to be retriedat another server upon receipt of 503Can include Retry-After header sayingthat this server should be left alonefor some period of time SIP Client

  3. Problem Definition Proxy 1 Element Overloaded INVITE 503 Proxy A Proxy 2 INVITE Proxy 3 When all elements are overloaded, 503 creates MORE trafficAmplified further by retransmits ofINVITE since 503 is delayed or lost SIP Client

  4. Oscillation Problem 1 Proxy 1 Element Overloaded INVITE 503 Retry After 20 Proxy A Proxy 2 INVITE Proxy 1 is overloaded, rejects requestwith 503 and Retry After of 20 seconds,moving ALL work to proxy 2 SIP Client

  5. Oscillation Problem 2 Proxy 1 Proxy A INVITE Proxy 2 Element Overloaded 503 INVITE Proxy 2 is now overloaded, and rejectsall work, even though proxy 1 is nowfreed up SIP Client

  6. Solution Requirements • Keep throughput at a good level when elements are overloaded • Failures should be isolated and not cause widespread outages • Minimize configuration to work • Deal with malicious elements • Inform upstream elements of overload • Throttle upstream traffic in granular fashions • Fairness across upstream elements

  7. Sounds Familiar? • Many of these are traditional congestion control issues, applied to the SIP application plane • Input from TSV community is much desired!

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