Hi Lei, Questions like this should be posted to the SIP-Implementors list: [EMAIL PROTECTED]
The SIP list is for issues related to the ongoing development of the protocol. First, I suggest you look at: http://www.ietf.org/internet-drafts/draft-ietf-sip-rfc2543bis-04.txt This is the current revision of the SIP specification and has many changes from RFC 2543. The "tag" is really to used to identify a specific call-leg within a call. A given user should use the same URI in the From (when placing calls) regardless of which device. That same URI is used by others in the To header when they call. The bis-04 spec now requires that a tag be added to the From header by the UAC when placing a call. A UAS (called User Agent) will add a tag to the To header in its response. This is used to differentiate call legs when an INVITE request is forked to more than one UAS. This would occur when the called user has multiple devices. Typically this is done by using the REGISTER method to register the location of the devices with a registrar/proxy. The URI of the specific devices are contained in the Contact headers in a REGISTER request. When an INVITE arrives at the proxy for the user (identified by the To header), the INVITE is proxies to all of the registered Contact headers. The To will be unchanged in those INVITEs. I hope that helps. cheers, (-:bob ----- Original Message ----- From: "Lei Liang" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, October 04, 2001 7:27 AM Subject: [Sip] newbie's question of "tag" parameter > > Hello, everybody, > when I was reading RFC2543, I saw "tag" parameter may be added in > "from" and "to" general hearders. it was said that "tag" was used to > distinguish the user who has more than one instances with the same sip > addr, e.g. mobile and telephone. does it mean every instance has one > unique URI to identify itself from others? then what happens if one user > change his instance from a telephone to a mobile during a call or use both > of them for the same call-ID at the same time. can he do that or not? if > can, does the sip > message have to be send to two destinations which are distinguished by > using "tag" para? > any instruction will be really appreciated. > thx a lot. > cheers. > lei > > > > _______________________________________________ > Sip mailing list http://www1.ietf.org/mailman/listinfo/sip > This list is for NEW development of the core SIP Protocol > Use [EMAIL PROTECTED] for questions on current sip > Use [EMAIL PROTECTED] for new developments on the application of sip > _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
