From: Daniel Ginsburg (dginsburg@mail.ru)
Date: Fri Jul 30 2004 - 10:29:37 GMT-3
On Thu, Jul 29, 2004 at 10:50:38AM -0400, ccie2be wrote:
> Hey Richard,
>
> I don't dispute or disagree with what you're saying but how do know that 4
> simultaneous pings with a packet size of 1500 will load the channel to over
> 80%? How do you know what load exactly that will put on the channel? If
> you don't know exactly what load that puts on the channel, how do you know
> that that is NOT, for example, a 65% load or 75 % load?
>
Unlike many other ping implementations which send 1 echo request per
interval cisco's one sends next echo request as soon it receives echo
reply or waits for timeout if request or reply is lost. So average
bandwidth utilization in one direction with one 'ping a.b.c.d size X'
will never exceed 50%.
Let me illustrate this with the diagram
---
^ BW
|
| (1) (3) (5)
|----- ----- -----
|
| (2) (4)
----------------------------------------->
Time
(1) router transmits ping request
(2) router waits for ping reply
(3) router transmits next ping request
(4) router waits for next ping reply
etc.
So router uses the link almost[1] exactly half of the time. Please note
that this 50% figure almost[1] doesn't depend on size of echo
request/reply.
[1] I'm saying almost because router needs to ponder a very short period
of time before replying to echo request. This period of time may be
negligible or not depending on speed of the link.
Two simultaneous pings will theoreticaly saturate the link. Run four to
make sure ;)
--
dg
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