Subject: Duration

From: John Dawson <[email-masked]>
Date: Mon, 21 Jun 1999 09:43:38 -0700

I would like to voice a concern regarding test duration.

At what point do people expect physical layer effects to start interfering
with test results?  

If you have 10 ports running gigabit wire rate with minimum sized packets
you are generating 15 million packets a second.  Do people expect no CRC,
Alignment errors, or other errors for an infinite duration?  As the number
of ports increase, and the number of bits per second increase, it will
become more and more difficult for the physical layer to support error-free
(zero loss) performance.

I expect people to argue that lab environments are expected to be sterile
and controlled and hence no loss.  However, I believe this arguement
becomes less defensible as the number of ports being tested increases.  If
you are testing 100+ port configurations from a number of different
development groups, with two or three different types of test equipment,
interoperability at the physical layer becomes a 'real' factor in the test
process.  Also, the test equipment manufacturers are using the same
commodity components as the equipment manufacturers, so at some point the
test equipment is just as likely as the DUT to contribute to physical layer
losses.

Although I am comfortable with a 30 second duration test sequence, I am
already seeing issues with devices having very, very, low levels of loss
(i.e. 1 packet per million) which causes a test failure in the binary
search process.  If people wish the test sequences to be longer than 30
seconds at what point do we allow for packet loss or re-testing of
sequences if the packet loss rates are within physical layer goals set by
the standard?

John

---

From: "Steve Bell" <[email-masked]>
Date: Mon, 21 Jun 1999 11:32:02 -0700

John, you bring up an interesting point.  I believe that GbE SX connections
today run at better than 10e-15 B.E.R., does
anyone have objective test data on that?  Perhaps Scott knows the answer, he
has run high port-count GbE tests.  Certainly,
mileage will vary depending upon which SERDES/GBIC is being used, board
layout, VCO design, not to mention brand/type of
connector/fiber used, etc.

We have run tests up to 64 ports of GbE at SVNL, and with a 30sec test
duration this hasn't become an issue - e.g. no observed
problems with RFC1944 binary search for throughput.   There are enough
things going on within the DUT fabric, buffering, etc. that it could go
un-noticed though.

Steve Bell
The Silicon Valley Networking Lab
www.svnl.com