Subject: RE: Duration

From: Jerry Perser <[email-masked]>
Date: Mon, 21 Jun 1999 15:07:01 -0700

John,

You started the discussion talking about "physical errors".  My response was
referring to CRC, Alignment errors, and other physical media errors.  I did
not mean to imply the quality of the test setup.

I have had my share of bad cables, bad switch blades, bad power supplies,
bad configuration, and (gulp) bad SmartCards.  As Michael pointed out, he
has had problems with bad cables.  But these problems were from
manufacturing defects, not a BER.  If you grab 200 Random SmartCards off our
production floor you will get two different BER.  About 0.06% will have a
BER of 0 (will call these cards DOA), and the rest will have a BER better
than 10E-13.

If you have a bad test setup, then your test results are invalid.  Correct
the setup and rerun the test.  Nobody intentional runs a test knowing that
their cables are bad.  I run a series of test on my SmartBits and cables to
verify that they are Known Good Devices.

The example I gave about running "604,800 seconds with *ZERO* physical
errors" was an extra requirement from a customer.  It was not my idea.  I
would of love to say that one error frame in a million is acceptable, and
saved me the week of running an 80 ports systems to prove the BER.  It was
meant to illustrate at what level one company is testing to.  What kind of
BER are End Users demanding from the DUT/SUT?

In my Lab, when I have a test fail, the reason can be trace to one of the
following listed in order of occurrence:

     1. Wrong Configuration (IP address, VLAN setting).
     2. Insufficient buffer space (line rate on all ports for 60 seconds).
     3. Bad cables (plug/unplug cycling).
     4. Design bug in the DUT/SUT (running Alpha or Beta code).
     5. Bad SmartCard (MTBF).

I have yet to trace a failed test due to a CRC error, Alignment error, or
other physical media error that was not induced by one of the reasons above.
If it is happening, it's at such a low rate that I am missing them.

___________________________________________________________ 
Jerry Perser               Phone: 818.676.2320 
SmartLab Manager           Lab:   818.676.2336 
Netcom Systems Inc.        Fax:   818.880.9165     
26750 Agoura Road          Corp:  818.676.2300 
Calabasas, CA, 91302       Pager: [email-masked]