Dear experts, I have some questions about "o=" line in SDP. ( I guess this topic is related also to [A doubt in offer/answer model] of the latest subject . )
>From the mail quoted below, As my understanding, when we will modify a existing session, we MUST NOT change the "o=" line in new sdp from old sdp which established a existing session. Excepting the Version number in "o=" line. I am seeing the different example in [draft-ietf-sipping-service-examples-06]. According to [2.3 Music On Hold] in [draft-ietf-sipping-service-examples-06], it is written as follows. --------------------------------------------- (Only "o=" line of SDP is quoted.) F3 (200 OK for initial INVITE) : Bob -> Alice o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com F7 (re-INVITE for hold) : Bob -> Alice o=bob 2890844527 2890844528 IN IP4 music.server.example.com F13 (INVITE for pickup) : Bob -> Alice o=bob 2890844527 2890844529 IN IP4 client.biloxi.example.com --------------------------------------------- Note that the <address> field has changed. I am concerned that a modification of the existing session couldn't work by F7. Or a new session generated by F7? Have I made the miss reading some? Regards, ------ NTT EAST RESEARCH AND DEVELOPMENT CENTER YOSHIKAWA Tomoyuki <[EMAIL PROTECTED]> TEL: +81-3-5359-5910 ; FAX: +81-3-5333-1340 <<QUOTED MAILS>> "Manish Joshi" <[EMAIL PROTECTED]> wrote in 20 Nov 2003 17:19:07 +0530, "Brett Tate" <[EMAIL PROTECTED]> replied in Fri, 21 Nov 2003 12:49:58 -0500, > > RFC 2327 specifies the origin field as : > > > > origin-field = "o=" username space > > sess-id space sess-version space > > nettype space addrtype space > > addr CRLF > > > > Isnt it must to have "sess-version" value in > > the SDP of re-invite to be different than the > > value in original invite, given the reinvite > > does change the session parameters > > ( for ex : put a call on hold etc ). ? > > No. RFC 2327 section 6 mentions the following: > "the tuple of <username>, <session id>, > <network type>, <address type> and <address> > form a globally unique identifier for the session." > > And section 6 also mentions the following: > "<version> is increased when a modification > is made to the session data." > > Thus all the contents of origin line are used > to identify a unique SDP. And when the > <username>, <session id>, <network type>, > <address type> and <address> are the same, > the <version> must be incremented to indicate > an update to the session data. > > > I am seeing a vendor implementation where > > ( in o= field ) sess-id and sess-version > > remain same but "addr" changes. > > Should this sdp offer be treated > > different than the first one ? > > Assuming by "addr" you mean <address> > of the Origin line, the answer is yes. > > > Shouldnt combination of "sess-id" and > > "sess-version" uniquely identify a session ? > > See above comments. _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
