Overload in SIP Jonathan Rosenberg Cisco Systems Problem

Overload in SIP Jonathan Rosenberg Cisco Systems

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

Oscillation Problem 1 ITE INV 503 Element Overloaded Proxy 2 IN VI TE Proxy A y tr Re er t f A Proxy 1 20 SIP Client Proxy 1 is overloaded, rejects request with 503 and Retry After of 20 seconds, moving ALL work to proxy 2

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

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!