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Re: SDP <sess-version> element and Trickle Ice

From: Adam Roach <adam@nostrum.com>
Date: Mon, 17 Dec 2012 14:00:59 -0600
Message-ID: <50CF79FB.2030106@nostrum.com>
To: Harald Alvestrand <harald@alvestrand.no>
CC: public-webrtc@w3.org
On 12/17/12 13:51, Harald Alvestrand wrote:
> On 12/17/2012 03:56 PM, Adam Roach wrote:
>> On 12/17/12 06:11, Christer Holmberg wrote:
>>> I also think the sess-version value should be updated whenever the 
>>> remote description changes.
>>> I am not sure I understand the need for using the timestamp. If SDP 
>>> is not used on-the-wire, then the local JS app can update the remote 
>>> description value however it wants.
>>> If SDP is used on-the-wire, then the remote entity shall update the 
>>> sess-version value however it wants.
>> The problem is that we cannot be authoritative for the remote 
>> sess-version. And while the recommendation is to use an NTP 
>> timestamp, the only actual requirement is that it increase whenever 
>> the session description changes.
>> The degenerate case here is that we get an SDP from the remote party 
>> with a sess-version of 1. Then they send us a trickle ICE candidate. 
>> If we are changing the sess-version of localDescription because we've 
>> added that candidate, then the smallest increase possible would be to 
>> change sess-version to 2.
>> Now, imagine that the remote party, at some point in the future, sent 
>> us a new offer with a sess-version of 2.
>> Whoops.
> If we follow the logic of "the RemoteDescription is a picture of what 
> the browser's view of the state of the session is, not what the remote 
> guy sent us", the logical sess-version is 1.0001, not 1.
> Yes, that's not a value allowed by the SDP spec. And that's an advantage.

Are you proposing that we use that syntax (or one substantially similar 
to it) in order to address this situation?

Received on Monday, 17 December 2012 20:01:43 UTC

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