SIP Overload Control Problem Statement

This document reviews the SIP server overload problem statement. SIP servers can become overloaded when they receive more SIP messages than they have resources to handle. This reduces server performance and can cause complete service failure. The current 503 Service Unavailable response in SIP is unable to prevent overload collapse or spread of overload throughout the network. Causes of SIP server overload include poor capacity planning, capacity reductions, avalanche restarts from failures, flash crowds, disasters, and denial of service attacks. Overload impacts user behavior, server resources like CPU and memory, and can affect other servers. Existing overload control mechanisms have limitations. Open issues remain to be addressed.