geoffb@nrcvax.UUCP (05/22/86)
A short followup to my article of several months ago concerning Ethernet repeaters/extenders. Many folks seem to desire an optical link for network extension, in the case where fiber is too expensive or difficult to install, such as between buildings in a campus environment. I turned up the following interesting device/company.(NO, I don't work for them -:)) Device: Optical Link, Dual IR diode/Fresnel Lens Assembly Range 250-400 meters Bandwidth 20mhz (higher with shorter ranges, can be cranked up) Aiming - Telescopic Sight Cost ~ $3000 per side. Accepts TTL signals. This thing is currently passing ProNet signals. Adapting an 802.3 transceiver to it in progress. Device: Optical Link, IR Laser/Fresnel Lens Assy Range 1km Bandwidth 100mhz (Also can be cranked up) Aiming - Telescopic Sight Cost ~ $7000 per side Accepts TTL signals. Currently is repeating T1 signals. Ethernet transceiver being adapted. Company: Meret Laser, Santa Monica, California USA Contact: John Medved 213-828-7496 As usual, at these frequencies (IR), you can expect attenuation in heavy fog , caveat user. Hope this helps some out there who need to net multiple bulildings together. -- "Book 'em Dano" Geoffrey Baehr - N6LXA USENET- ....ihnp4! -> ucbvax!calma! -> nrcvax!geoffb US SNAIL-Network Research Corp 2380 N Rose Ave. Oxnard C.A. 93030 ATT 805-485-2700 AX.25 PKT - 145.03Mhz N6LXA!N6LUC <-145.01 <-Gateway-LA
phil@amdcad.UUCP (Phil Ngai) (05/23/86)
In article <661@nrcvax.UUCP> geoffb@nrcvax.UUCP (G. Geoffrey Baehr) writes: > Device: Optical Link, IR Laser/Fresnel Lens Assy > Range 1km > Bandwidth 100mhz (Also can be cranked up) > Aiming - Telescopic Sight > Cost ~ $7000 per side > Accepts TTL signals. Currently is repeating T1 signals. > Ethernet transceiver being adapted. I'm not sure of what you mean by "Ethernet transceiver being adapted" but if it's what I'm afraid of (extending the distance between a controller and a transceiver from 50 meters to 1000 meters) I would like to go through a simple calculation. Assume light travels at 1 nS/foot and there are 3 feet per meter. Then light takes 3000 nS to travel 1000 meters, 6000 nS to make the round trip. Ethernet heartbeat is supposed to be sent after the end of the transmission. If the transceiver returned heartbeat immediately after it perceived the end of transmission, the controller would not see heartbeat until 6 uS after it ended its transmission. Unless you "adapted" the transceiver, it would actually delay before asserting heartbeat. This is well outside the spec for both Ethernet 2 and IEEE 802.3. You should also be sure the optical link does not add a lot of timing jitter. Ethernet can not accept very much before it starts having trouble decoding the signal. We're talking budgets on the order of 1 nS for the transceiver cable. (from memory, I could be off by a couple of nS) Finally, what about radiological safety hazards? Does this device require eye protection? -- Vote Yes on Proposition 51! Phil Ngai +1 408 749 5720 UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!phil ARPA: amdcad!phil@decwrl.dec.com
mike@amdcad.UUCP (Mike Parker) (05/23/86)
In article <11771@amdcad.UUCP> phil@amdcad.UUCP (Phil Ngai) writes: >nS/foot and there are 3 feet per meter. Then light takes 3000 nS to >travel 1000 meters, 6000 nS to make the round trip. Ethernet heartbeat >is supposed to be sent after the end of the transmission. If the >transceiver returned heartbeat immediately after it perceived the end >of transmission, the controller would not see heartbeat until 6 uS >after it ended its transmission. Unless you "adapted" the transceiver, >it would actually delay before asserting heartbeat. > >This is well outside the spec for both Ethernet 2 and IEEE 802.3. > This is not the only problem. The Ethernet 802.3 spec says that the transmitting controller can expect to see its own data coming back on the RD pair within 900nS of starting to send it out on the TD pair. If it does not then it can assume that the transceiver has failed and cease transmitting. I am not certain but I am told that the Intel LANCE depends on this "sidetone" to work. Mike Disclaimer: Yep, I work for AMD and we make a LANCE too, but I'm a CAD guy and really don't know anything at all about ethernet. My opinion is not that of my employer. -- ------------------------------------------------------------------------- Say NO to Spandex and chrome, say YES to silicon! UUCP: {ucbvax,decwrl,ihnp4,allegra}!amdcad!mike ARPA: amdcad!mike@decwrl.dec.com