When UAS gets INVITE then it tries to process it. While doing that UAS can send 100 Trying to UAC so that it does not re-transmit the INVITE message again. Processing can take some time ( more that 500ms i.e. default T1 timer ). Once call is processed ( find route etc ) and send 200 OK. Subsequently ACK will be received. That time dialog will be created ( to-tag, from-tag and call-id ). When re-INVITE is received in UAS again. Dialog is already exist. Nothing to do with the call processing at that time. You just need to send the final response. If you don't have the dialog you can send 481 response right away. As per protocol: A UAS MAY choose not to generate 180 (Ringing) responses for a re- INVITE because UACs do not typically render this information to the user. For the same reason, UASs MAY choose not to use an Alert-Info header field or a body with Content-Disposition "alert" in responses to a re-INVITE. Probably you can send 100 Trying. If you can send final response with in T1 timer then why to send 100 Trying.
Thanks, Uttam -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of sumin seo Sent: Saturday, August 05, 2006 2:33 AM To: [email protected] Subject: [Sip-implementors] 100 Trying for Re-INVITE Hi All, I have checked re-INVITE signaling flow in several RFCs, but I couldn't find 100 Trying after re-INVITE. But I have seen 100 Trying almost every times while i am doing interop with other sip servers. Could you let me know pros and cons of 100 Trying for re-INVITE and what the recommendation is? to send 100 Trying for peace of mind? Somebody said that UA can have time before it sends 200 OK when it has to negotiate media. If that is the case, why don't we use 100 Trying for Update? Thanks in advance. Regards, Sumin. _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
