Overload in SIP Jonathan Rosenberg Cisco Systems

Problem Definition SIP Client Proxy A Proxy 1 Proxy 2 Proxy 3 INVITE 503 INVITE Element Overloaded SIP allows request to be retried at another server upon receipt of 503 Can include Retry-After header saying that this server should be left alone for some period of time

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

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

Oscillation Problem 2 SIP Client Proxy A Proxy 1 Proxy 2 INVITE Element Overloaded Proxy 2 is now overloaded, and rejects all work, even though proxy 1 is now freed up INVITE 503

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

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