ArcNet and the Pursuit of Multiple Topologies

On Oct 12, 13:46, Eric J. Korpela wrote: it's That's true, you can run all sorts of things over Cat5 "structured wiring", in fact that's the point of structured wiring. 10baseT uses two pairs (pins 1+2, 3+6), the phone uses the centre pair (pins 4+5). ISDN uses all four pairs. Serial lines use either the middle pairs (for Tx/Rx) or all four (DTR/DSR, Tx, Rx, RTS/CTS) if they follow the DEC (and other) system. Some use the same pairs as Ethernet (which means a crossover cable for Ethernet also works as a null-modem for Tx/Rx on serial lines). 100baseTX uses the same pairs as 10baseT. You're not supposed to run a phone line (pins 4+5) on the same cable as an Ethernet (pins 1+2, 3+6); it breaks the spec. However, you'll normally get away with it with 10baseT, and it *may* work for 100baseTX over short distances. It certainly won't work for 100baseT4 (does anybody still have any of that?) or 1000baseTX (Gigabit) because they use all four pairs. Nevertheless, you can buy little boxes which are essentially a Y-piece for phone+10baseT -- you need one at each end of the cable. They consist of a small box with two RJ45 sockets and a short Cat 5 lead ending in an RJ45 plug. You can also get similar boxes to combine/separate two 10baseT signals (they move the second signal from pins 1+2 and 3+6 onto 4+5 and 7+8) and ones to simply double up the sockets (pin 1 to pin 1 to pin 1; ... ; pin 8 to pin 8 to pin 8) which are sometimes used for ISDN. For some reason they tend to be different prices, and all overpriced (over here they cost ?8 - ?15, though you can make one for about ?3 including the cost of the box to put the PCB in). I'd be wary of running Localtalk over a cable carying a phone or Ethernet signal. Again, it might work, but it will probably generate interference which might be hard to track down -- I write from experience[1]. Better to use one cable for one service at a time. The real reason for using different pairs for different services is partly serendipity, and partly to avoid damage if you plug the wrong device into a cable which is already connected to something incompatible at the other end. In my workshop and study I have quite a lot of Cat5 (actually Cat5e, the Cat5 standard is officially obsolete) which I use for 10baseT, 100baseTX, serial lines, ISDN, a phone line, and even the audio to the speakers. I'm about to add a couple of Econet adapters, and I'll probably use it for some LocalTalk (PhoneTalk) when I get round to sorting out the non-Ethernet Macs. [1] More than one bad experience, but exemplified by the occasion when I had to make a trip to Northern Ireland with a couple of technical staff staff insisted everything was done to the standard, but it turned out that their erratic network problems were due to putting LocalTalk down the existing network cables. It had worked for a while, but when they extended the networks, both suffered. -- Pete Peter Turnbull Network Manager University of York