cyrus@hi.UUCP (Tait Cyrus) (08/29/87)
We all know that there are well defined specifications for an
ethernet cable and the placement of transceivers on that cable,
but I can't find anything which talks about the specifications
(if any exist) for the transceiver cable.
Some transceiver cables that you can get come in 5, 10, 20 and
40 meter lengths. Are these the ONLY lengths possible? If not,
can I make one that is 0 meters long, 2 meters long or 2.1 meters
long? Now I say 0 meters because here at the University of New
Mexico we are using thin wire and in quite a few cases have a
DEC DESTA directly attached to the back of a computer (no transceiver
cable).
I have looked through the "Blue Book" and did not see anything
on the subject.
Thanks in advance for any and all help, suggestions, advice, etc..
--
@__________@ W. Tait Cyrus (505) 277-0806
/| /| University of New Mexico
/ | / | Dept of EECE - Hypercube Project
@__|_______@ | Albuquerque, New Mexico 87131
| | | |
| | hc | | e-mail:
| @.......|..@ cyrus@hc.dspo.gov or
| / | / seismo!unmvax!hi!cyrus
@/_________@/phil@amdcad.AMD.COM (Phil Ngai) (08/29/87)
In article <14301@hi.UUCP> cyrus@hi.UUCP (Tait Cyrus) writes: > > We all know that there are well defined specifications for an >ethernet cable and the placement of transceivers on that cable, >but I can't find anything which talks about the specifications >(if any exist) for the transceiver cable. > Some transceiver cables that you can get come in 5, 10, 20 and >40 meter lengths. Are these the ONLY lengths possible? If not, >can I make one that is 0 meters long, 2 meters long or 2.1 meters The nominal maximum transceiver cable length is 50 meters, based on a loss/meter spec and a maximum loss spec. This includes everything, like the cable from the interface board to the computer's backpanel. Cables are sometimes rated in terms of equivalent cable length which is different from physical cable length; this reflects a higher loss/meter than the spec calls for. The Interlan NI1010A board cable, for example, falls in this category (although I don't think Interlan actually specifies its equivalent cable length), as do DEC's office transceiver cables. Most people don't sell 50 meter cables to allow for the loss in the board cable. DEC's office transceiver cables are rated at 4X, that is, a 5 meter cable has the loss of 20 meters. As you can see, they are not useful for long runs, what you can't see without holding one in your hands is that they are very convenient, nice solid shells with flexible wire. We love to use them in our racks, going from DELNIs to internet routers, for example. There is no integer multiple of anything restriction on transceiver cable lengths as there is on the trunk cable. Although it can be viewed as a transmission line, there are no stubs to worry about and thus no problems with reflections reinforcement. This kind of stuff is in the blue book, although it helps to know what they're trying to tell you already. If you're making your own cables, be aware that the Ethernet 2.0 spec and the 802.3 spec is different. I also recommend you look in the Belden catalog for the wire; they make the best stuff, bare none. (I own no stock in Belden, I just want the best wire possible for my company.) -- I speak for myself, not the company. Phil Ngai, {ucbvax,decwrl,allegra}!amdcad!phil or amdcad!phil@decwrl.dec.com