Fiber Ethernet problem


Terry Slattery (tcs@USNA.ARPA)
Sun, 21 Sep 86 14:17:56 EDT


We have a fiber optic based Ethernet product installed here and are
having a problem with a Gould 9050 being attached to the net.

DESCRIPTION:

We have the Codenoll ethernet on fiber optic product with the following
configuration:

----------- ~325M -------------- ~800M ---------------
|usna.arpa|-----------|Star Coupler|----------------|usna-gus.arpa|
----------- -------------- ---------------
                            |
                            | ~75M
                            |
                      ---------------
                      |usna-cs1.arpa|
                      ---------------
M = meters

Both usna.arpa and usna-cs1.arpa can communicate. Usna-gus.arpa can hear
some (most?) rwho packets from usna and cs1. Gus cannot send anything
out without error. A Gould 6050 which is co-located with usna can
communicate over the 325 meter segment without problems.

ANALYSIS:

Optical power measurements show -15db at usna and -12db at gus (better
polished connectors and lower loss cable are the difference). The
flux budget is 21db, so we are well within spec there.

A recent note to these lists leads me to believe that there is a timing
problem. Codenoll supplied the following timing info:

Device Delay (ns)
Controller encoder 100
Xcvr xmit 300
Fiber cable (1600 Fiber cable (1600 meters@4.33ns/m) 6928
Xcvr rcv 650
Xcvr cable (60 Xcvr cable (60 meters@5.13ns/m) 308
                                        -----
TOTAL 8386

I have connected the Gould and a Tektronix 6130 to a TCL MP station
and they communicate without problems, thus proving that the interface
is working correctly.

MISC. INFO:

The Gould Ethernet Controller Model 8561 Tech. Manual (May 85)
says that it tries 16 retransmits before giving up completely.
It also mentions a control bit described as:
  "Transmit even if no arrrier sense signal is detected."
The driver doesn't include any code to modify this bit; it
is automatically reset upon board power-up.

QUESTIONS:

Is the timing out of spec with respect to what the Gould ethernet
interface is capable of handling?

What time delay does most equipment expect?

Does anyone else have experience with this or Siecor's product over
the distances involved here?

Are there more details available on what Gould did w.r.t. the problem
reported at Perdue?

Please respond directly and I will summarize the responses. Thanks,
        -tcs
        Terry Slattery U.S. Naval Academy 301-267-4413
        ARPA: tcs@usna.arpa
        UUCP: decvax!brl-smoke!usna!tcs



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