Subject: [MMUSIC] ICE Issue #11: ICE Pacing

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 12 Sep 2006 11:30:46 -0400

Currently, ICE specifies that connectivity checks are paced at one every 
  50ms. Per previous open issues, I've made the proposal to re-split the 
checks out into a separate check list for each media stream. That would 
open the possibility that we can pace the connectivity checks for each 
media stream at a rate on par with the media stream bandwidth itself.

Currently, the limit of a check every 50ms is there to meet two objectives:

1. rate control, so as not to flood the network
2. limiting the rate of new binding allocations in a nat, to avoid 'nat 
overload'

It makes sense to set the pacing such that checks generate traffic equal 
to the media bandwidth, since clearly this is no more or less load on 
the network than the media will later create. THis would allow checks 
for video to go very fast, for example. To deal with the second 
constraint, my idea was to back off on new checks when a check produces 
a peer derived candidate. This allows the checks to go fast when no 
bindings are being created, but slow down when they are.

Its non-trivial to work out all of the math here, since STUN checks are 
not constant rate. They are variable rate, and the total bandwidth 
depends on whether they succeed or fail.

So, the tradeoff here is complexity vs. performance. We can make ICE 
faster by allowing checks to go at the rate of the media, but at the 
cost of increased spec and implementation complexity.

Preferences?

-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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