Subject: RE: [bmwg] I-D ACTION:draft-ietf-bmwg-dsmterm-00.txt

From: "John Dawson" <[email-masked]>
Date: Thu, 1 Mar 2001 13:08:50 -0800

Jerry,

In section 3.10, Jitter seems to be measured as the time between any two
packets egressing from a DUT interface.  I feel that it may be more
appropriate to define jitter at a flow, or code-point, or microflow level.
The time between unrelated streams or microflows would not seem to be the
primary measurement here.  In the case of queues and service priority
levels, we expect certain DSCP flows to have less delay than others.  Any
two adjacent packets are therefore bound to have wildly different delay
times if multiple code points are in use.  It would seem to me that if the
jitter measurement isn't tied back to a stream level, then the QOS
mechanisms afforded to high-priority traffic will mess up the measurement as
currently defined.

In response to the feedback from Robin Uyeshiro,

>> In section 3.12 Offered Load Vector, under the Issues heading, 
>> it seems to me that peak rate should be an issue only if variable 
>> rate or variable size packets are offered.  I was under the 
>> impression that most BMWG tests used periodic fixed size packets, 
>> as the tests were more deterministic and repeatable.  Maybe this 
>> won't be much of an issue?

I do not agree with this position.  I believe that offered load vectors are
critical due to the possible use of Pause frames or the possibility of
forward pressure in a half-duplex environment.  Unless offered load is
measured as a part of the test, then the entire measurement process tends to
become an unknown.  Measuring offered load also serves as a nice sanity
check that software processes are working correctly.  If the intended and
offered loads don't match up it is a good indicator that the test may not be
running properly.  Please keep section 3.12 in place - I feel that it is
very important.

Thank you in advance for your consideration in this matter.
John

---

From: "Perser, Jerry" <[email-masked]>
Date: Thu, 1 Mar 2001 16:23:14 -0800

John,
 
Agree with you on the jitter.  Jitter is "variation in the stream's delay."
The basic atomic measure of jitter is measured per stream.  I assumed per
stream, but forgot to say it.  Thanks for pointing it out.
 
Jerry.
 
-----Original Message-----
From: John Dawson [mailto:[email-masked]]
Sent: Thursday, March 01, 2001 1:09 PM
To: [email-masked]
Subject: RE: [bmwg] I-D ACTION:draft-ietf-bmwg-dsmterm-00.txt

Jerry,