Subject: Latency and load step tests

From: Jim McQuaid <[email-masked]>
Date: Fri, 20 Aug 1999 13:03:41 -0400

So what this kind of looks like as a method is something like this:

a)	step tests on forwarding rate to determine thruput_rate as per
	2544 today

b)	step tests on latency from thruput_rate down to ??? to determine
	the "breaks" or "knees" in the latency 'curve.' The result is a
table.

How do we bound the "down to ??"?  I suppose the test steps down until the
latency no longer changes. 

Jim McQuaid
Ganymede Software

---

From: Steve Bell <[email-masked]>
Date: Fri, 20 Aug 1999 11:20:27 -0700

Jim, that's pretty close but actually we'd prefer to see equipment that can
accurately measure what's happening to average latency (computing it on the
packets that aren't being dropped) between the throughput rate and 100% as
well, for devices with throughput <100% (there are still plenty of those).

For down to ??? -- the latency tends to flatten out at lighter loads, so
stopping at 10 or 15% load makes sense.  The entropy is such that
measurement can be coarser below throughput rate, that's why the suggestion
of 15%, 50% as useful latency benchmarking levels, elimininating a lot of
"stepped" measurements which are time-consuming and of questionable value.

The interesting data is typically just below throughput level to wire speed,
but you then you need a baseline from the fairly flat area 15-50% loading to
compare it to.  In addition to latency being an absolute measurement, this
adds a relative relative measurement which speaks volumes about what's going
on inside the switch.

-Steve Bell
 SVNL

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of Jim McQuaid
Sent: Friday, August 20, 1999 10:04 AM
To: 'David Newman'; bmwg
Cc: Jim McQuaid
Subject: Latency and load step tests

Jim McQuaid
Ganymede Software