Session description

v= protocol version
o= owner/creator and session identifier
s= session name
[i= session information]
[u= URI of description]
[e= email address]
[p= phone number]
[c= connection information-not required if included in all media]
[b= bandwidth information]
<Time description>⁺
[z= time zone adjustments]
[k= encryption key]
[a= zero or more session attribute lines]*
<Media description>^*

Notation

{ [xx] ⇒ xx is optional}

{ [xx]⁺ ⇒ one or more times} }

{ [xx]^* ⇒ xx zero or more times}

Time description

t= time the session is active
[r= zero or more repeat times]*

Media description

m= media name and transport address
[i= media title]
[c= connection information-optional if included at session-level
[b= bandwidth information]
[k= encryption key]
[a= zero or more media attribute lines]^*]

Transcript

[slide194] We can add all kinds of extra things to it. We can add session information, we can add URI, email, phone numbers, connection information, bandwidth information, time zones, time zone adjustments, and we can even put an encryption key in to be used for the actual media session and we can have various attributes. Now, one of the things that's interesting here is there's nothing that binds the time announced in the SDP to the time when the SIP message is sent. That means I can send a SIP INVITE message and I'm inviting you to this session next Wednesday starting at 1400. And we negotiate that, we agree upon it, we close down the SIP session. 1400 next Wednesday, what happens? We start streaming media to each other. Which even further separates the SIP signaling from the media session because now can be separated in time. So it's not even sequential. That makes it really hard for a SIP provider to say I want to bill you by the minute that you're in the SIP session. Right? Because once we've agreed on the parameters for the SIP session, our SIP provider is not involved in it at all. Except to the extend that they stay involved via SIP. They are not involved in the media at all. And if we encrypted with S/MIME, they don't even know when we're going to exchange the media.