rg@gandp (Dick Gill) (09/27/90)
Hello
I hope I won't wear out my welcome with a few more questions.
I have decided to use standard thin ethernet (cheapernet) for
the lan based on the strong recommendation of net
correspondents, the confirmation by others that the unshielded
twisted pair technology is still new and delicate and, most of
all, the substantial additional cost in the interface cards and
the hub for twisted pair.
I am now into another new world (aka "learning experience" !-). I
am familiar with the mechanics of coax from my years as a TV
broadcast technician but need a little help in the physical
aspects of building a cheapernet LAN.
1. Where (aside from friends on the net) should I look for
information about physically setting up a cheapernet lan? Any
practical publications to recommend?
2. At the most basic level it appears that RG-58 (50 ohm) coax
is used with BNC connectors; are there any traps or potential
problems here? What should I look out for in buying the pieces?
3. In terms of design, I understand that this is a bus topology
characterized by a single spine to which individual nodes are
attached. I guess the simplest model is a coax connecting a
group of PC-NIC's via a "T" in the bus.
T-----------//---------T--------//---------T------->>--<50ohm
| | |
----I---- ----I---- ----I----
PC A PC F PC W
--------- --------- ---------
Within the distance restrictions, is this model correct?
4. How long can a line to a node be from the bus? Can, for example,
PC-D below be 30 feet from the bus? How about 100 feet?
T---------T-//---------T--------//---------T------->>--<50ohm
| | | |
----I---- | ----I---- ----I----
PC A | PC F PC W
--------- | --------- ---------
|
|
----I----
PC D
---------
5. If the answer to 4 above is yes, can I further split that line
to create nodes PC-D(1) and PC-D(2)?
T---------T-//---------T--------//---------T------->>--<50ohm
| | | |
----I---- | ----I---- ----I----
PC A | PC F PC W
--------- / \ --------- ---------
/ \
/ \
----I---- ----I----
PC D(1) PC D(2)
--------- ---------
6. Because I will not be able to test the wiring before the job is
completed, I would appreciate any other tips on how to do it right
the first time.
Please E-Mail; I will post or mail results as requested.
Thanks for your help.
Regards,
Dick Gill
--
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Dick Gill Gill & Piette, Inc. "I can be a humble guy when I need to."
(703)761-1163 ..uunet!gandp!rg Donald Trump
normt@cbnewsc.att.com (Norman R Tiedemann) (10/01/90)
In article <313@gandp>, rg@gandp (Dick Gill) writes: > I am now into another new world (aka "learning experience" !-). I > am familiar with the mechanics of coax from my years as a TV > broadcast technician but need a little help in the physical > aspects of building a cheapernet LAN. > 1. Where (aside from friends on the net) should I look for > information about physically setting up a cheapernet lan? Any > practical publications to recommend? There are some Tech notes that come with Cheapernet <-> Ethernet transceivers which help. Also if you are buying cheapernet PC cards, they should have a decent description of the physical aspects. > 2. At the most basic level it appears that RG-58 (50 ohm) coax > is used with BNC connectors; are there any traps or potential > problems here? What should I look out for in buying the pieces? No, as long as you get good quality connectors. The T's must be sturdy and good connections must be made with the cable. > 3. In terms of design, I understand that this is a bus topology > characterized by a single spine to which individual nodes are > attached. I guess the simplest model is a coax connecting a > group of PC-NIC's via a "T" in the bus. > T-----------//---------T--------//---------T------->>--<50ohm > | | | > ----I---- ----I---- ----I---- > PC A PC F PC W > --------- --------- --------- Almost. You will also need a 50ohm terminator on the end of a piece of cable on the left side of PC A. Each transceiver must see a 25ohm load (i.e. 50ohms at each end.) > 4. How long can a line to a node be from the bus? Can, for example, > PC-D below be 30 feet from the bus? How about 100 feet? > Here is where I'm going to break your heart. The length that this drop cable can be is on the order of Centimeters not Meters. Since the transceiver must identify collision on the bus within the 64 bit preamble time, this is very different from Ethernet. Normally you connect the T directly to the PC board connector and run both cables to this. You should not think of putting another piece of cable between the T and the actual termination device. > 5. If the answer to 4 above is yes, can I further split that line > to create nodes PC-D(1) and PC-D(2)? > > T---------T-//---------T--------//---------T------->>--<50ohm > | | | | > ----I---- | ----I---- ----I---- > PC A | PC F PC W > --------- / \ --------- --------- > / \ > / \ > ----I---- ----I---- > PC D(1) PC D(2) > --------- --------- Sorry, this obviously won't work either, for reasons given above. Hope this helps. Norm Tiedemann AT&T Bell Labs IH 2G-419 att!ihlpy!normt 2000 Naperville Rd. normt@ihlpy.att.com Naperville, IL 60566 -- Norm Tiedemann AT&T Bell Labs IH 2G-419 att!ihlpy!normt 2000 Naperville Rd. normt@ihlpy.att.com Naperville, IL 60566