My email's way behind and coming in all jumbled, so apologies if better
explanations have already been provided.
I think it really needs a detailed mathematical derivation, which I
certainly can't provide, but off the top of my head...
If your interface claims to be transmitting at 1.50 Mbps, that is just an
average over some period of time. When you shrink the granularity right
down, either the interface is transmitting a packet (100% utilised) or it's
not (0% utilised).
And, if packets arrived at precisely the right intervals, then the queue
depth would sit at 1 even at a very high average utilisation.
But packets don't arrive at precisely the right intervals - and I think
that the queue depth formula given by Priscilla is a statistical one - in
other words, as the *average* utilisation increases, the *average* queue
depth also increases. A burst of packets (which is more likely as
utilisation increases) increases the queue depth, while a quiet period
(less likely as utilisation increases) decreases the queue depth.
And of course, the increased (average) queue depth increases the time a
packet is sitting in a buffer, and so increases the ping time.
Of course, as utilisation gets higher, the chance of packet drops also
increases, but you're obviously aware of that.
If I'm spouting rubbish, I'm sure somebody (probably Howard) will correct
me...
JMcL
---------------------- Forwarded by Jenny Mcleod/NSO/CSDA on 31/07/2001
04:30 pm ---------------------------
"Priscilla Oppenheimer" @groupstudy.com on 31/07/2001
04:58:42 am
Please respond to "Priscilla Oppenheimer"
Sent by: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
cc:
Subject: Re: Doubt... [7:14233]
The number of packets in a queue on a packet-switching device increases
exponentially as utilization on the output port increases.
Queue depth = utilization/(1 - utilization)
So, do the math. If utilization is 90%, there will be more packets in the
queue than if utilization if 50%.
That's how I learned it, but it's probably more complex than this....
Comments, anyone else?
Thanks
Priscilla
At 10:41 AM 7/30/01, anil.philip wrote:
>Dear Priscilla,
>
>I have a small doubt. I think you are the best person to ask about. May be
>you think this as a stupid question. but this is making me crazy.
>
>If there is a serial link b/w two sites, at what point of % utilisation
>the response start degrading???
>
>Ideally if I have a T1 link, i shud get the same ping response time
>till the load on that link is 100%???
>
>When I say a T1, it is 1.55 M packets /s. So if the link is utilised for
>99% (say 1.50Mb..) still I have
>0.05 Mb left on that link and I shud be able to get a ping (32byte)
>response time, equivalent to 0% utilisation. Why the response time start
>degrading at some point of % utilisation??
>Let us assume there is no packet drop, memmory prob, enough buffer space
>etc....
>
>Request to do a REPLY ALL this email.
>
>
>Regds,
>Anil Philip
>AT&T Solutions.
>anil.philip
>e-mail: [EMAIL PROTECTED]
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=14332&t=14233
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