This is one of the reasons we are working on session-mode IM. Use of the MESSAGE message is page-mode IM. In page mode, there is no session, so in general the proxy will be involved in routing each message. And if the target has multiple UASs then each message may be forked. Responses are a bit of an issue as well - in general the best you can do is address a response to the From address in the request.
Technically you can send MESSAGE messages within a dialog and so guarantee a consistent pair of endpoints are interacting, and generally cut the proxy out as well. (I believe this is what MS does.) But that is not recommended behavior. And because MESSAGE is not dialog establishing you need to do something else to establish the dialog, such as send a media-less invite.
While not yet complete, the direction we are pursuing for session oriented IM is to send an invite with an offer for a message-session media stream. And then send the IMs via that stream rather than via MESSAGE messages. The protocol for this is still in progress, with the working name of MSRP. (Message Session Relay Protocol.)
Paul
Upaya wrote:
Thank you and Smith for the reply on my previous message.
I have a question regarding an IM conversation. Similar to MSN Messenger and Yahoo Messenger, users can exchange messages in one session/window.
For example: A Short Conversation
John wrote: Hi Mary! Mary wrote: Hello John John wrote: How are you?
Based on RFC3428, John sends the first message to the proxy server, then the proxy server forwards the message to Mary.
What about the second and the third message? Does it still need the proxy server to perform lookup and forward? Also, all three messages above should be in the same session, right?
Thanks,
Wendy
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