Subject: [MMUSIC] ICE-10 Issue #5: Removing a peer derived candidate

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 05 Sep 2006 17:10:47 -0400

In ICE-10, you can do a reinvite at any time, and add or remove 
candidates you offered previously. We don't have any really solid use 
cases for removing candidates but the feature is there.

One thing which is missing in ICE-10 is that there is no way to remove a 
peer derived candidate. So, if one is discovered by ICE and then the 
agent who owns it decides, for some reason, that it can't be used, there 
is no way to get rid of it. In ice-09, you could get rid of them, but 
only by also removing its generating candidate. In ice-10, even that 
will not work.

I see a few options:

1. this is a don't care. No one needs this feature anyway.
2. I can add a mechanism for removing them, but it will require a timer 
and has a race condition. Here is the race. Consider agents A and B. 
There is a symmetric NAT between A and B so that a check from A to B 
informs A of a peer derived candidate. It would like to remove it. So, A 
sends a re-invite to B, and omits that peer derived candidate from the 
list of candidates. Note that this peer derived candidate wasn't in the 
previous offer from A. Thus, B cannot tell whether: (1) A has gotten the 
response to the binding request, learned this peer derived candidate, 
and is now removing it, or (2) A generated a reinvite prior to learning 
this new peer derived candidate.
3. the race can be eliminated by also including some kind of check 
sequence number, so that the answerer can know whether the offerer got 
the binding response prior to the reinvite or not. This adds more 
complexity.

I am inclined towards (1).

Comments?

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
Cisco Fellow                                   Parsippany, NJ 07054-2711
Cisco Systems
[email-masked]                              FAX:   (973) 952-5050
http://www.jdrosen.net                         PHONE: (973) 952-5000
http://www.cisco.com

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