SIP Messages and Media Session

[Guest]

Archived from groups: comp.dcom.voice-over-ip (More info?)

Hi all,

Suppose we have two SIP UAs that one invites the other, then they
start a media session and then the connection is terminated. How
exactly the media session is being terminated? I mean, one of the UA
terminates the Media Session and then sends a BYE SIP message to the
other party; or once the media session is opened and the UA decide to
close it will send first a BYE message and then will close the media
session?

Option 1.

UA1 UA2
|-----------> INVITE
<-----------| 100 TRYING
<-----------| 180 RINGING
<-----------| 200 OK
|-----------> ACK

|-----------> Open Media Session
|-----------> Close Media Session

|-----------> BYE
<-----------| 200 OK


or......
Option 2.

UA1 UA2
|-----------> INVITE
<-----------| 100 TRYING
<-----------| 180 RINGING
<-----------| 200 OK
|-----------> ACK

|-----------> Open Media Session
|-----------> BYE
|-----------> Close Media Session
<-----------| 200 OK


Thank you very much in advance.

 

[Guest]

Archived from groups: comp.dcom.voice-over-ip (More info?)

In article <a993bdfe.0408051513.bf96604@posting.google.com>,
Anast <anastasiosm@hotmail.com> wrote:
>Hi all,
>
>Suppose we have two SIP UAs that one invites the other, then they
>start a media session and then the connection is terminated. How
>exactly the media session is being terminated? I mean, one of the UA
>terminates the Media Session and then sends a BYE SIP message to the
>other party; or once the media session is opened and the UA decide to
>close it will send first a BYE message and then will close the media
>session?


Media sessions are RTP streams over UDP, so they don't really "close"
in the way TCP sockets do. You just stop sending or stop listening.

But yes, in a typical flow, the phone that hangs up sends BYE and
stops sending (and possibly stops listening to) the RTP media stream.

The other phone gets the BYE, and similarly stops, and sends an OK.

(The first phone probably should also wait for the OK before it stops
listening, and possibly even sending.)

UDP packets don't have connections. If nobody is listening they just
vanish in a poof like a Jaffa against the Iris. Nobody knows they
didn't get received.
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