From: SungWoo Lee <[EMAIL PROTECTED]> It is straight forward to answer whichever I want. However, there is still one issue remaind. Let's say I am to send fax. After establishing voice session, the receiver side sends re-INVITE whose SDP contains both audio and image in order to switch over to T.38 mode. Obviously, from the context, I am supposed to take image in this case.
My question is how I can decide to take image in this case or decide to take audio in other case. I guess I have to check the context to decide which one to take, which is still confusing. The problem is the question of "mode". If the intention is that the connection will never use audio and image at the same time, then the initial connection should be with SDP for one medium, and then later a re-INVITE would eliminate that medium and add the other one. However, with SIP it is more common to assume that multiple media streams may be transmitted at one time, each side sending what media it desires to send at any moment, and each side receiving whatever media are sent to it at the time. If you do not have bandwidth and processing limitations, this is *simpler* than trying to negotiate and maintain a mode. If you have a situation where you can send audio or image, but only one at a thime, and the caller wants to offer to the callee using either initially, then the caller must offer both in the SDP, then wait until the callee chooses one or the other (either in the answer SDP, or if both are in the answer SDP, by which media are actually sent), and then re-INVITE to limit the media to the chosen medium. Either side then can use re-INVITE to attempt to change to the other medium. Dale _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
