Subject: Re: I-D ACTION:draft-ietf-bmwg-mswitch-01.txt

From: Kevin Dubray <[email-masked]>
Date: Fri, 04 Jun 1999 09:08:40 -0400

Forwarded from [email-masked]:

I have a concern with respect to offered load.  I realize that I may be 
nit picking, but I feel that their is a very important concept that is 
not being properly communicated.  The concept deals with intended versus
offered load.

The draft document uses some boiler plate material in a number of
sections.

   Forwarding rate (FR) of the DUT/SUT ... MUST be reported as the
number
   of frames per second that the device is observed to successfully
transmit
   to the correct destination interface in response to a specified
offered 
   load. The offered load MUST also be cited.

My concern relates the usage of the phrase, specified offered load.  An 
offered load can not be specified, it can only be measured.  An intended 
load can be specified, but it does not guarantee a specific offered
load.

So if offered load is measured, what is the measurement period and how
are
large bursts of half-duplex traffic to be considered?  This is a sticky 
issue as bursty traffic will have very non-uniform transmission rates
due 
to capture effects on the wire.  The offered load will not be a
constant, 
but can be averaged over the course of the entire test.  This is further
complicated by the fact that even though all ports will start
transmitting
at the same time, the test will finish transmitting differently on every 
port (i.e. ports that capture the wire early in the test process will 
transmit a fixed number of packets before other ports that mostly defer 
in early parts of the test process).

Any ideas?  Is this as serious as I think, or am I nit picking
unnecessarily.
John

---

From: "Robert Mandeville" <[email-masked]>
Date: Tue, 8 Jun 1999 11:09:26 +0200

I agree that some nitpicking is in order on the point of deciding how
offered load is to be apprehended. Indeed offered load cannot be specified
but only measured. Intended load is specified, as you also rightly point
out. I don't want to cause a revolution here but let's look at what we all
do in practise. We report intended load and then the measured forwarding
rate. We may see that offered load is less than intended load, as for
example when we deliberately oversubscribe a given output port, but we still
want to characterize such a test as a congestion test, in which case we have
to refer to intended load and not offered load. I conclude that we MUST
report intended load and not offered load. We simply need be aware that in
half duplex mode offered may differ significantly from intended load. I am
aware that this does not concord with 2285. I am not sure how changes are
made if the group agrees with what we, I think, are both saying here.