Subject: Re: [Tsvwg] Re: comments on draft-baker-mlef-concerns-00.txt (3) MLEF Thres...

From: [email-masked]
Date: Thu, 11 Dec 2003 08:49:46 EST

In a message dated 12/10/2003 1:49:49 PM Eastern Standard Time, 
[email-masked] writes:

> Nobody has yet responded to the math, or the fundamental system effects. 
> All I have heard is handwaving about how it couldn't be that bad, because 
> EF seems to work, but ignoring the fundamental reason why the military is 
> concerned about call preemption. 
> 
> 

[MAP] I'm not sure what the math is here that needs to be responded to. There 
were comments before (included some from me and in the MLEF draft) that used 
rather crude math for the situation that talked about 20 routine calls being 
100% utilization and adding 1 priority call causing 5% packet loss. However, I 
realize that the real math is a little more complex, and is probably rather 
meaningless without actual traffic studies (or a very complex model). As you 
pointed out in your e-mail, "congestion" != "100% utilization" and " In the 
Internet, congestion is related to the probability of a significant queuing delay 
or the occurrence of packet loss, which is something that queuing theory tells 
me happens at a utilization rather lower than 100%."

I believe that an actual simulation would show that, in order to meet a 
desired performance (lost packets, etc) that the traffic needs to be limited to 
maybe 70%. Adding 1 Priority call then brings it to 73.5%. Real simulations (or 
real live traffic) would be needed to determine what impact this has on packet 
loss rate. The 5% above is the layman's (mine) answer, but I suspect it is in 
the ballpark. In any case, going from 0% to 5% packet loss results in a drop 
in the MOS score from about 4.1 to 3.9 (for random loss) and to 3.3 (for bursty 
loss), according to your reference [18]. Certainly something DoD should 
accept as the price for getting a high priority call through.

The point is that adjustment of the parameters (queue thresholds for MLEF) as 
well as the CAC limits will be done in real live networks with real traffic. 
Before that, if one decides what result they can tolerate (MOS degradation, 
length of impairment, blocked calls, etc.) one can also do simulations to 
approximate these limits.

Mike Pierce