Subject: Re: [Ieprep] RE:MLPPoIP - (1) Preemption of low priority calls

From: [email-masked]
Date: Thu, 20 Nov 2003 16:23:11 EST

In a message dated 11/20/2003 2:42:10 PM Eastern Standard Time, 
[email-masked] writes:

> It seems to me that if bandwidth is scarce, silence suppression is a major 
> benefit. Typical users only speak for one third of the time.  But the CAC
> simply reserves enough bandwidth in each direction for continuous speech -  
> A factor of 3 in actual utilization.  Does this seem a reasonable approach 
> to anyone?
> 

I think you've identified one of the big issues in implementing an effective 
CAC at the same time that silence suppression is being used. Yes, silence 
suppresion can be used to reduce the overall bandwidth requirements, completely 
independent of there being multiple precedence levels. Without silence 
suppression, I suppose that one could say that CAC "reserves" enough bandwidth for 
continuous speech using the presumed codec. I would also presume that, if silence 
suppression is being used in a network, that CAC would know it and take that 
into consideration, only "reserving" maybe 1/3 as much bandwidth for each call. 
It can just view this as being a lower rate codec and depends on the 
aggregate of many such calls to even out any bursts of speech on one. Of course, the 
end result is a less exact limit on the total, causing more short periods 
during which a temporary overload exists and packets must be discarded. TASI 
systems used across the oceans have operated this way for decades to squeeze more 
calls onto a wire.

I believe this case is another strong argument for the need for a selective 
discard mechanism as defined in MLEF.

Mike Pierce