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

From: Adam Roach <adam@nostrum.com>
Date: Mon, 17 Dec 2012 08:56:57 -0600
Message-ID: <50CF32B9.7030709@nostrum.com>
To: Christer Holmberg <christer.holmberg@ericsson.com>
CC: "public-webrtc@w3.org" <public-webrtc@w3.org>
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.

/a
Received on Monday, 17 December 2012 14:57:43 GMT

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