Re: [rtcweb] JSEP: Relaxing SDP O/A rules?

Christer Holmberg <> Sat, 06 October 2012 18:38 UTC

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From: Christer Holmberg <>
To: Martin Thomson <>
Date: Sat, 6 Oct 2012 20:38:49 +0200
Thread-Topic: [rtcweb] JSEP: Relaxing SDP O/A rules?
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Subject: Re: [rtcweb] JSEP: Relaxing SDP O/A rules?
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>>>> Can I use the same local descriptor for every setLocal() call?
>>> My experience suggests that you can.  However, that's not stipulated
>>> in the API specification, so it's not an ironclad guarantee.
>> If it doesn't, and a new local descripor is created, you would need to send that one to the remote 
>> endpoint.
> You don't create a new description, you just set one.


> The only problem arises when you can't set the local description because
> something broke since you last set it.  (Maybe setting the answer
> caused the browser to release something that you need to set the
> offer.)

That is the main difference between PRANSWER and ANSWER: PRANSWER does not release local resources based on the answer.

> If that happens, you are hosed.  You could try to make a new PeerConnection, but you'll have to resend your INVITE because you will
> get a new set of candidates, ufrag, pwd, etc...

Or, you could set the new local descriptor BEFORE you apply the answer to the previous one. I think that is how the cloning is currently described in JSEP: the cloning happens first (eventhough it may never be used, if no additional remote peers are contacted).