[Sip-implementors] RE: Significance of Route, Record-Route and Path Header Field

[Chris Boulton]

Hemant,   Record route and route headers are tightly linked.  A session could be initiated through a SIP proxy server but subsequent transactions will travel directly between User Agents.  This will result in the SIP proxy server not seeing requests such as BYE or Re-INVITE.  This makes it impossible for entities that maybe want to bill calls or keep call state for the entire call duration.  Record route is used a ‘stamping’ mechanism so that SIP proxies that see a request can view all related (subsequent) requests.  The record route header is then used by the endpoints to construct a route set.  This route set is then constructed at endpoints and followed for subsequent requests, rather than sending direct.  Record-route and route header fields are separated as they are constructed independently at UAS/UAC – they have to be separated.   If any of these header fields are missing, the proxy will not be traversed by subsequent requests.   Path has a very similar function to Record route and was designed for use with 3GPP implementations.  It’s purpose is solely to allow requests to be routed to an endpoint once a lookup has been done on a registration, ensuring correct proxies are visited on the way (Forcing them to visit and not got directly to client).  The two are needed as Record route can not be used with the Register request due to backward compatibility issues.        Regards,   Chris.   -----Original Message----- From: Hemant Pandey [mailto:[EMAIL PROTECTED]] Sent: 04 March 2003 10:18 To: Chris Boulton; [EMAIL PROTECTED] Subject: Significance of Route, Record-Route and Path Header Field   Hi All         I am confused between Route, Record-Route and path Header fields.I am not able to understand their significance and their need in different SIP messages. It seems the these header fields contain duplicate copy of same information.   Could any one help me out to understand significance of these Header fields?       Why and when these different Header fields required? Can't a single Header field (Route or Record-Route or Path) solve the purpose of all three header fields? what problems will arise if any one of these header field is missing?   I need ur cooperation to understand these points.   Regards   Hemant