SIP Messages and Media Session

Discussion in 'VOIP' started by Anastacio, Aug 6, 2004.

  1. Anastacio

    Anastacio Guest

    Hi all,

    Suppose we have two 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?

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

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

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


    or......

    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.
    Anastacio, Aug 6, 2004
    #1
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  2. Anastacio wrote:
    > Hi all,
    >
    > Suppose we have two 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?


    RFC3261 section 15.1.1: "The UAC MUST consider the session terminated (and
    therefore stop sending or listening for media) as soon as the BYE request
    is passed to the client transaction."

    So first send BYE, then close the media session.

    BTW, your schema below is perhaps incorrect for the Open Media Session. UA2
    can start to send media as soon a SDP is received, generally in the INVITE.
    UA2 must be ready to receive the media as soon it send a SDP, generally in
    the 180 or in the 200.
    So in this case if the media session is opened after receiving the ACK, the
    beginning of the media can be lost. (This is also known as the "hello
    issue", because one of the two parties does not hear the other party saying
    "hello")

    >
    > UA1 UA2
    > |-----------> INVITE
    > <-----------| 100 TRYING
    > <-----------| 180 RINGING
    > <-----------| 200 OK
    > |-----------> ACK
    >
    > |-----------> Open Media Session
    > |-----------> Close Media Session
    >
    > |-----------> BYE
    > <-----------| 200 OK
    >
    >
    > or......
    >
    > UA1 UA2
    > |-----------> INVITE
    > <-----------| 100 TRYING
    > <-----------| 180 RINGING
    > <-----------| 200 OK
    > |-----------> ACK
    >
    > |-----------> Open Media Session
    > |-----------> BYE
    > |-----------> Close Media Session
    > <-----------| 200 OK
    >
    >
    Marc Petit-Huguenin, Aug 6, 2004
    #2
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