Subject: RE: [Sip] SIP session without SDP

From: "Christer Holmberg (JO/LMF)" <[email-masked]>
Date: Fri, 7 Oct 2005 09:19:36 +0200

Hi,

>There are dialogs, and there are things that use dialogs: invites and 
>subscriptions. The dialog itself has a certain amount of state 
>associated with it. Then each usage has some added state. So, 
>a dialog has: route set, target address, callid, local and remote CSeq, ...

True. But, all of this is "maintained" using SIP headers/parameters. You don't need SDP for that.

>An invite dialog usage has very little state of its own. I think you can 
>probably consider offer/answer state to be part of this, maybe the most 
>recent offered and answered sdp.

True. But, offer/answer state is needed only when you DO use SDP.

Regards,

Christer

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From: Paul Kyzivat <[email-masked]>
Date: Fri, 07 Oct 2005 09:10:26 -0400

> True. But, offer/answer state is needed only when you DO use SDP.

No. offer/answer state is needed when you exchange offers and answers, 
whether you use SDP, SDPng, or something else yet to be invented.

The primary *purpose* of the INVITE is to initiate the exchange of 
offers and answers. I believe it is required to do so.

If you don't need the state of the invite dialog usage, then you don't 
need the INVITE. That was my point in bringing up dialog usages. If all 
you want to do is exchange MESSAGEs within a dialog, then you should 
create some new way to establish a message-dialog-usage.

	Paul