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

Christer Holmberg <christer.holmberg@ericsson.com> Sat, 06 October 2012 18:38 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Martin Thomson <martin.thomson@gmail.com>
Date: Sat, 6 Oct 2012 20:38:49 +0200
Thread-Topic: [rtcweb] JSEP: Relaxing SDP O/A rules?
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References: <7F2072F1E0DE894DA4B517B93C6A0585340A1E3AB1@ESESSCMS0356.eemea.ericsson.se> <CABkgnnUFvw_J2+tvVBoHrzR9ZRkPT-6LhXvbaz_U1P7gqtJ4xw@mail.gmail.com> <7F2072F1E0DE894DA4B517B93C6A0585340A7BC848@ESESSCMS0356.eemea.ericsson.se> <CABkgnnV6NcTeh=L_fpkpLv5UpkUSuacmQUtYwNKKwAfcb5+JQA@mail.gmail.com> <506D4F7A.5020109@alvestrand.no> <CABkgnnUgHRw4dtihk2fZppmzVWuV4hpvWtXt70N1HWQpJ+KsZw@mail.gmail.com> <7F2072F1E0DE894DA4B517B93C6A05853409FF2FDF@ESESSCMS0356.eemea.ericsson.se> <CABkgnnV+jHWF3t8s3t37pbQyXJEP9N_MyHWd3SsfoNrhMU=NXw@mail.gmail.com> <7F2072F1E0DE894DA4B517B93C6A0585340A7BD0C5@ESESSCMS0356.eemea.ericsson.se> <CABkgnnVFWDroiTWVOm6F3FRQ6dDkRjKdyV8apRK=0Y_ReYtmPA@mail.gmail.com> <7F2072F1E0DE894DA4B517B93C6A05853409FF2FE5@ESESSCMS0356.eemea.ericsson.se>, <CABkgnnUR6XL4QLmZAUVqnB5S+UFh7sfmzkDzfjK52+e9_FFkJg@mail.gmail.com>
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Subject: Re: [rtcweb] JSEP: Relaxing SDP O/A rules?
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Hi,

>>>> 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.

Correct.

> 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).

Regards,

Christer