KDM101@psuvm.psu.edu (Kevin Maher) (06/14/90)
We have several labs here on campus that we would like to interconnect. One problem is that the combined length of cable for the 3 labs exceeds 600 feet (which I have heard to be the limit of ethernet when using coax). We estimate the length to be just over 700 feet. What I would like to know is if this would cause any problems, or if the 600 foot limit is just a recommended suggestion. If it would be a problem, what can we do to get the 3 networks connected without having to purchase expensive repeater boxes? (we're working on a very limited budget here) Thanks in advance --------------------------------------------------------------------------- | OOO | | | O O SSS | Why do today what's due tomorrow? | | O O PPP U U S | | | O O P P U U SSS | Hey...sounds good to me! =-) | | O O PPP U U S | | | OOO P UUU SSSS | KDM101@PSUVM O04@PSUVM | | P | KXM@PSUARCH kmaher@psusun01 | --------------------------------------------------------------------------- Why should I want to disclaim anything??? It only makes me look guilty!
ssw@cica.cica.indiana.edu (Steve Wallace) (06/14/90)
I have see some working ethernet segments over 2000 feet. 1000- 1500 foot segments are very common. I wouldn't sweat 700 feet. Steven Wallace Indiana University wallaces@ucs.indiana.edu
spurgeon@ut-emx.UUCP (Charles Spurgeon) (06/14/90)
In article <90164.140927KDM101@psuvm.psu.edu> KDM101@psuvm.psu.edu (Kevin Maher) writes: >We have several labs here on campus that we would like to interconnect. >One problem is that the combined length of cable for the 3 labs exceeds >600 feet (which I have heard to be the limit of ethernet when using coax). >We estimate the length to be just over 700 feet. What I would like to know >is if this would cause any problems, or if the 600 foot limit is just a >recommended suggestion. If it would be a problem, what can we do to get >the 3 networks connected without having to purchase expensive repeater >boxes? (we're working on a very limited budget here) 10BASE5 thick Ethernet, using Belden 9880 (PVC) or 89880 (FEP) or equivalent coax, has a maximum segment length of 500 meters or about 1,640 feet. Up to 100 stations can be attached, spaced 2.5 meters (8.2 feet) apart. 10BASE2 thin Ethernet, using RG58A/U or RG58C/U cable or Belden 9907 coax, has a maximum segment length of 185 meters or about 600 feet. Up to 30 stations can be attached, spaced .5 meters (1.7 feet) apart. To go beyond these lengths requires a repeater or bridge. So if you're using thick Ethernet you're ok. I'll assume you're using thin Ethernet (from the evidence of the length you cite above) and go on to mention some problems you could encounter. Overlong segments can result in excessive round trip times for packet propagation, which could lead to the failure of the Ethernet collision detect mechanism. On a sufficiently busy network, the result can be so many packet failures that users report a "slow" network. Overlong segments can also have too high a signal loss, resulting in "ghost hosts" that appear and disappear on the network. In other words, the signal level gets so marginal that, depending on the number of active hosts, packet traffic, and phase of the moon, some hosts can be reached some times and not other times. I've seen this happen on several overlong 10BASE2 thin Ethernet systems in the past. Back in the dark ages the original 3COM EtherSeries thin Ethernet system (the precursor to the IEEE 802.3 10BASE2 thin Ethernet system) allowed up to 300 meter segments, and when people started using 10BASE2 equipment on those networks the performance could get real strange. If you're using thin Ethernet, the least expensive repeater I know of off hand (and have the pricing info on) is the Cabletron MR2000, list price $865.00. It comes with one thin Ethernet port and one thick Ethernet port. You can attach the thick Ethernet port to another thin Ethernet cable with a Cabletron ST500-03 BNC equipped transceiver, list $275.00. That means you've used up all the ports to link the thin Ethernets together, and do not have an attachment to the building network, if there is one. There's also the MR5000, a 4 port thin Ethernet repeater with a thick Ethernet port for attachment to the backbone network. This lets you interconnect up to four thin Ethernet segments. At a list of $2195, that works out to $439 per Ethernet attachment. Educational sites can often get good discounts on these prices. Cabletron's phone number is (603) 332-9400.
oberman@rogue.llnl.gov (06/14/90)
In article <90164.140927KDM101@psuvm.psu.edu>, KDM101@psuvm.psu.edu (Kevin Maher) writes: > We have several labs here on campus that we would like to interconnect. > One problem is that the combined length of cable for the 3 labs exceeds > 600 feet (which I have heard to be the limit of ethernet when using coax). > We estimate the length to be just over 700 feet. What I would like to know > is if this would cause any problems, or if the 600 foot limit is just a > recommended suggestion. If it would be a problem, what can we do to get > the 3 networks connected without having to purchase expensive repeater > boxes? (we're working on a very limited budget here) Thanks in advance Please read a pamphlet on Ethernet configuration before you put this together! The limit on "standard" Ethernet cable is 500 Meters or something about 1600 feet. If you are using RG-58 or an equivalant "thin" cable, the length is 600 feet. While the thick cable is quite a bit more expensive as are taps and other related hardware, it may prove cheaper in the long run to use thick cable. Cheating on the length works as long as the cable is not too busy, but cheating is still a very bad idea because networks tend to grow and get busy. A couple of new NFS servers, just a little more cable for the new workstation across the room... All of a sudden users are mad about poor performance. R. Kevin Oberman Lawrence Livermore National Laboratory Internet: oberman@icdc.llnl.gov (415) 422-6955 Disclaimer: Don't take this too seriously. I just like to improve my typing and probably don't really know anything useful about anything.
marke@ultra.com (Marke Clinger - NorthWest District SE - Ultra Networks) (06/15/90)
I have seen some conflicting lengths which I would like to make sure get cleared up. I have the DEC/Intel/XEROX Ethernet Specification sitting on my lap...an excerpt..... This is talking about the Thick Ethernet that has been mentioned. I believe all of the numbers for thin have been right and without conflicts: 1) A coaxial cable, termincated in its specified characteric impedance at each, can be a maximum of 500 Meters of coaxial cable. 2) A maximum of 2 repeaters in the path between any two stations. Each Repeater counts to the maximum number of nodes/stations on a network. Use to extend the length of the channel and to extend the topology from 1 to 3 dimensional. 3) A maximum of 50 meters of transceiver cable between any station and its associated transceiver. (ie the station can be at most 50m from the coax cable as the drop cable goes) 4) A maximum aggregate of 1000 meters of point-to-point links between any two stations in the system. 5) A maximum of 100 stations per segment. If you are going to be implementing Ethernet, I recommend getting a copy of the Ethernet specification. DEC bookstores sell it. The one I have says: The Ethernet, Version 2.0, November 1982, AA-K759B-TK The Pamphlet recommended in a previous posting is also very good and I think DEC has this also. Marke Clinger Systems Engineer Ultra Network Technologies (The Gigabit Network) marke@ultra.com