Serial Forking and 605
Microsoft Corporation
The session initiation protocol (SIP) [2] allows users' end systems to decline calls for many reasons. 6xx response codes communicate global failures generated by callee's end system. It defines 6xx class response codes in the spirit of parallel forking scenarios only. There're scenarios where, authoritative server performs parallel forking of the call to callee's own set of endpoints, and then serially move on to fork call to alternate set of endpoints (callee's voice mail and/or team call). This draft clarifies behavior for existing 603 response code and proposes new 605 response code to handle complete rejection of the call, which halts any further processing of the call.