tcs@USNA.ARPA (Terry Slattery) (09/21/86)
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 meters@4.33ns/m) 6928 Xcvr rcv 650 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