On 11/3/06, Giancarlo Murino <[EMAIL PROTECTED]> wrote: > > So, if I have understood, if there are parallel dialogs (as in forking case) > I have to use the same Call-Id , but different to tag and from tag, >
Yes, exactly. So far, so good. > > because such dialogs are part of the same call. > Whether those two dialogs end up becoming part of the same call is a matter of application policy. For example, the UAC sends an INVITE and it gets forked to two UASs, which I'll call UASa, and UASb. Both UASa and UASb send a 200 OK response. The UAC receives both responses and establishes two dialogs. Note, however, that SIP doesn't define what the UAC should do with the media. One possibility is that the UAC implements a "three-way call" type of feature. In that case, it would be reasonable to say the two dialogs are part of the same call/session. Or, the UAC could implement a "call hold" type of feature and let the user switch back and forth between the two dialogs. In this case, the two dialogs wouldn't really be considered part of the same call/session. Or, the UAC could accept the one of the dialogs and send a BYE to the other dialog. I'm not sure whether you'd consider the two dialogs part of the same call/session or not. > > But if I have two sequencial dialogs > like in the following flow: > ------------->INVITE (start first dialog) > <------------- OK > --------------> BYE (end first dialog) > ------------->INVITE (start second dialog) > <------------- OK > --------------> BYE (end second dialog) > Are they a part of the same call, or they belong to two different calls? > According to > the definition of call (a call is a group of one or more dialogs), I think > they are a part > of the same call. So, must they share the same Call-ID? If they aren't a > part of > the same call, why? Giancarlo > They are two different calls. One completes before the other starts. And the UAC would have to generate a new Call-ID for the second INVITE request. So I think you're confused by the relationship between call/session, dialog, and Call-ID. In very rough terms, the call/session is a user-centric term. If users are speaking to each other (or more generally exchanging media) then they consider themselves to be part of the same call. The dialog is a formal entity in the SIP protocol. It contains state information that user agents use to exchange SIP messages. The Call-ID is a unique identifier the UAC generates whenever it sends an initial INVITE request. Hope that helps -- Gary Cote www.awardsolutions.com _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
