hd@philtis.UUCP (Henk D. Davids @ PMSN) (01/13/89)
For some time now there are several companies that offer so-called Ethernet Line Extenders: a pair of boxes that extend the length of a transceiver cable from the standard 15 meters to up to 250 meters; the boxes communicate with each other over 4-wire cable. I was just wondering: does anyone have experiences with these devices? Is there anything to be said against them, like a possible violation of some standard? Any information will be appreciated, be it positive or negative ... Henk -- Henk D. Davids @ PHILIPS Medical Systems Nederland BV, Dept. SWE-CF Building QA-II PO Box 10000 NL-5860 DA Best The Netherlands UUCP: ...!mcvax!philmds!philtis!hd Voice: +31 40 762255
smb@ulysses.homer.nj.att.com (Steven M. Bellovin) (01/15/89)
The problem with Ethernet line extenders is that you have to be careful of your delay budget. That is, in an Ethernet configured according to the letter of the spec, each component -- coax, repeaters, drop cables, etc. -- has been assigned a delay time. The sum of the maximum possible end-to-end delays must be less than a certain amount, to wit the round trip time for a minimum length packet. If you increase the length of a drop cable, you must decrease the maximum coax length that you use. You must also allow for propagation delay through the extenders. Let me give some numbers. The signal speed in thick (or for that matter, thin) coax is given in the spec as .6667 c, whereas the signal speed in the transceiver cable is .5 c. Thus, an increase in drop cable length from 50 to 250 meters must be compensated for by a decrease in the maximum diameter of the net by 267 meters, thus *decreasing* the maximum extent. If you're careful, and if you know what you're doing -- for example, only putting long drop cables in the middle of the net, or restricting other components -- you can get away with it. The vendor may be able to help you as well. Bottom line -- you can sometimes use such boxes.
norm@cfctech.UUCP (Norm Meluch) (01/17/89)
In article <582@philtis.UUCP> hd@philtis.UUCP (Henk D. Davids @ PMSN) writes: >For some time now there are several companies that offer >so-called Ethernet Line Extenders: a pair of boxes that >extend the length of a transceiver cable from the standard >15 meters to up to 250 meters; the boxes communicate with >each other over 4-wire cable. > >I was just wondering: does anyone have experiences with these >devices? >Henk Our new STARLAN 10 here runs on 10 Mbit ethernet hardware and most of the cards for the machines (3B2/600, PS/2 Microchannel) need this "thing" called an AUI adapter. It seems to have the properties described above. It takes the 15 pin AUI output of an ethernet card and "translates" it into the 8 wire twisted pair for the STARLAN hub, building and PC card wiring. The 15 pin tranceiver cable goes about 15 meters and the AUI adapter will allow a twisted pair wire to go about 100 meters beyond that. The AUI is about $200 a crack. However no problems with them so far. |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Norman J. Meluch ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| | Mail:uunet!umix!cfctech!norm Voice: (313) 244-1809 | |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| | Note: The opinions expressed here are in no way to be confused with valid | |_______ideas or corporate policy._____________________________________________|
smb@ulysses.homer.nj.att.com (Steven M. Bellovin) (01/17/89)
In article <2214@cfctech.UUCP>, norm@cfctech.UUCP (Norm Meluch) writes: } } Our new STARLAN 10 here runs on 10 Mbit ethernet hardware and } most of the cards for the machines (3B2/600, PS/2 Microchannel) need } this "thing" called an AUI adapter. It seems to have the properties } described above. It takes the 15 pin AUI output of an ethernet card } and "translates" it into the 8 wire twisted pair for the STARLAN hub, } building and PC card wiring. In essence, the AUI is a transceiver; it just goes to STARLAN 10 wire instead of coax. It does nothing to extend the distance between a host and the coax, though the flexibility of star-wiring may make it seem that way. STARLAN 10 has its own set of wiring guidelines and restrictions; these are derived from the same basic principles and constraints as conventional coax wiring plans.