cjroehrig@poppy.uwaterloo.ca (Chris J. Roehrig) (06/30/90)
We have a new NeXT that we want to connect to the campus Ethernet
backbone. We have a 25 meter Ethernet drop in our lab which would
do fine except that it has a DB15 (thick Ethernet) connector on the
end.
So we need an adapter to go from the DB15 connector to a
BNC connector -- should be pretty straight-forward, right?
Well, all the Ethernet users I have talked to say that there's
a box that does just that for around $300, but nobody has any
definite information. When I talk to the network people, they
all say that the only way to do what I want is to buy a single-
port repeater, which they'd be happy to sell me for $1637 (CDN).
This is apparently a box with a DB15 connector and a single
BNC port.
So what's the deal? Surely someone else out there has
tried to connect a NeXT to a thick ethernet line. I find it
hard to believe that this requires $1600 worth of electronics.
Chris Roehrig
Audio Research Group
University of Waterloo, Canadahempling@quorum.com (07/02/90)
cjroehrig@poppy.uwaterloo.ca (Chris J. Roehrig) writes: >We have a new NeXT that we want to connect to the campus Ethernet >backbone. We have a 25 meter Ethernet drop in our lab which would >do fine except that it has a DB15 (thick Ethernet) connector on the >end. > So we need an adapter to go from the DB15 connector to a >BNC connector -- should be pretty straight-forward, right? Right. Cabletron sells one for ~ $250. It's a very small box with the DB15 connector on one end and a BNC on the other. The official name on the box is TMS-3 Ethernet/IEEE 802.3 Transceiver Unit (MAU). The main Cabletron office is in Rochester, NH. (P.O Box 6257, Rochester, NH 03867). The number is 603-332-9400. They do have regional offices elsewhere that can ship the box to you within a couple of days if they have them in stock. The San Jose office is at 2170 Paragon Drive, San Jose, CA 95131. The number there is 408-441-9900. A fellow there, David Vaiasicca, helped me out. Good Luck, dave hempling@quorum.com
chambers@pine.uh.edu (Charles Chambers) (07/03/90)
In article <1990Jul1.194133.2889@quorum.com> hempling@quorum.com writes: > cjroehrig@poppy.uwaterloo.ca (Chris J. Roehrig) writes: >>We have a new NeXT that we want to connect to the campus Ethernet >>backbone. We have a 25 meter Ethernet drop in our lab which would >>do fine except that it has a DB15 (thick Ethernet) connector on the >>end. >> So we need an adapter to go from the DB15 connector to a >>BNC connector -- should be pretty straight-forward, right? >Right. Cabletron sells one for ~ $250. It's a very small box with the >DB15 connector on one end and a BNC on the other. The official >name on the box is TMS-3 Ethernet/IEEE 802.3 Transceiver Unit (MAU). > The main Cabletron office is in Rochester, NH. (P.O Box 6257, >Rochester, NH 03867). The number is 603-332-9400. They do have >regional offices elsewhere that can ship the box to you within a >couple of days if they have them in stock. The San Jose office is >at 2170 Paragon Drive, San Jose, CA 95131. The number there is >at408-441-9900. A fellow there, David Vaiasicca, helped me out. >Good Luck, >dave >hempling@quorum.com Wrong, That part is for going from Thin-Wire Ethernet to AUI (i.e. the DB15) Not from a transeiver cable to Thin-Wire. You do in fact need a single port repeater, or a ip-router. The singe port repeater can be found from a number of vendors, but it should be pointed out that repeaters should only be connected to the Ethernet backbone segment, and not daisy chained from one segment to another. A cheap IP-router can be put together using an PC with two ethernet controllers. I do not have the details about doing this, but it has been discussed here in the past. (maybe is the future NeXT will have an AUI connection option). Charles Chambers (713)-749-2531 University of Houston chambers@uh.edu College of Engineering chambers@uhou.bitnet
madler@piglet.caltech.edu (Mark Adler) (07/03/90)
Chris J. Roehrig (cjroehrig@poppy.uwaterloo.ca) writes: >> Well, all the Ethernet users I have talked to say that there's >> a box that does just that for around $300, but nobody has any >> definite information. When I talk to the network people, they >> all say that the only way to do what I want is to buy a single- >> port repeater, which they'd be happy to sell me for $1637 (CDN). And Dave (hempling@quorum.com) writes: >> Right. Cabletron sells one for ~ $250. It's a very small box with the Wrong. You have to be a little careful here. Just because a box has the right connectors doesn't mean it does the right thing. A bit of explanation is in order, but the summary is that Chris's network people are right---you need a repeater to do the job, and the $200 to $300 transceivers have an entirely different function. I agree that you shouldn't need a $1637 box to do it, but that is all that's commercially available. (I believe there are $1000 thick-to-thin repeaters that don't have the full functionality of a general repeater, but that still seems like a lot.) Now for the explanation for those who would like to know ... Ethernet uses a single medium to send one message at a time from one station to another. If a station is sending a message, the other stations have to wait. If two (or more) stations try to send a message at the same time, then all stations will detect this, and then back off from trying again for a random period of time. Ethernet uses a coaxial cable to carry the messages. Each station connects to the cable using an "MAU", or medium attachment unit---better known as a transceiver. The other end of the transceiver impements the AUI, or attachment unit interface which carries transmit, receive, and collision signals, and power for the transceiver. The station takes these signals and then implements the last part of the physical layer, which is to encode and decode the bits and extract the clock. For thick ethernet, the coaxial cable is quite thick (about 1/2" in diameter), not very bendable, and an ugly yellow to boot. Because of all of this, these cables are usually kept behind closet (not a typo) doors and run in relatively straight lines. You then need a way to connect the cable to the station, without requiring the station to be very nearby. This is why the whole MAU/AUI thing was needed---the AUI specifies how signals are sent to the station from the cable, and the MAU is the electrical interface to buffer the signal, and clamps directly on the thick cable. The AUI standard specifies the DB-15 connector signals. The station then has a DB-15 jack to connect the AUI cable to, and that goes to the station's encoder and decoder. This was all kind of awkward for small networks, so they came up with thin ethernet. This has a shorter range and fewer stations than thick ethernet, but uses nice black bendable coax, that you can reasonably run behind every station. Each station then has the transceiver built into it, and even though the AUI signals are still there, there are no DB-15's between the MAU and the rest of the station's electronics. This further decreases the cost of a thin-net network. The NeXT assumes that you want to connect a thin net to it, and only brings out the coaxial connector for direct connection to the thin-net. Even though the AUI signals are in the machine, they did not bring them out to a DB-15, like most sensible manuafacturer (Sun being an example). There is another thing people like to do, which is to go beyond the limits of both thick and thin net. This is done by connecting separate thick and/or thin nets using a "repeater". What a repeater does is watch both coaxial cables it is hooked up to and watch for signals on both of them. If it detects bits on one of them, it repeats those bits to the other. If it sees bits on both sides or a collision on either side, it will send a jam signal to both sides for a specified time to ensure detection of the collision. A repeater necessarily includes two transceivers, one for each net it is connected to. All of this is complicated and (apparently) expensive. What you need to connect a NeXT to a thick net is either a repeater to link the thin net (albeit a net with only one station) of the NeXT to the thick net, or you need to bring out the AUI signals buried in the NeXT. I previously posted to this newsgroup an untested way to do the latter. The former requires one of those terribly expensive repeaters. So what happens if you just naively use one of those boxes with the right connectors and just wire them together? Well, first you'd have to use a little intelligence to connect in to out and out to in (just connecting pin to pin would not do anything at all interesting, except perhaps eventual destroy the line drivers). When doing this, you'll connect the transmit pair to the receive pair, the receive pair to the transmit pair, and then be leftover with a few things. One is collision pairs coming out of each transceiver. Being naive, you would just leave those open and hope the collision infomation isn't important. You would also be left with power going into both transceiver, and you would then connect a power supply to those lines. Now what you have should do something anyway. So what happens? Well even if only one station transmits (no collisions), this gets repeated to the other side (so far, so good), but then is received by the other transceiver, and sent back to the first side with a little delay, and then this is repeated ad inifnitum, completely destroying the ability of either net working properly by itself. Hence, you need a little more electronics between the two transceivers, and that is precisely what a repeater provides. It should be possible to simplify the repeater somewhat for the case of a one-station network on one side, but I'd guess even that wouldn't reduce the cost much. Mark Adler madler@tybalt.caltech.edu