On Sat, 9 Sep 2000, Alex Lee wrote:
> Hello Jay,
>
> Two stupid questions :
> (a) Why is that a 56 K crossover pin-out (is this the correct term ?)
> differs from a T1 ?
Different telco standards. No real reason, they just chose to use
different pairs. T-1 is an RJ-48 standard, and 56K is an RJ-45. Note
that many people mistakenly refer to any 8-pin modular connector as an
"RJ-45". This is not technically accurate. The manner in which the
connector is used determines its RJ-number. "RJ-nn" is an FCC standard
for "Registered Jack", describing interfaces to the telephone network in
Part 68 of FCC Rules. An 8-pin modular connector by itself isn't an
RJ-anything until it is wired to a network.
> (b) What is the purpose of using a 56K or T1 crossover cable ?
Anywhere you have a physical protocol that uses one physical wire or pair
for transmitting and another for receiving there may be the need to connect
two devices directly without an intermediate medium. A 56K or T1 crossover
would be used to connect two CSUs for a lab or short-haul connection. It's
the same principle as an ethernet crossover or a null-modem for RS-232.
The signal originating outbound on one side is connected to the input
expecting a signal on the other side, and vice-versa.
> Can you give me links so that I can get some more details info ? Thanks.
http://www.cisco.com/univercd/cc/td/doc/product/access/acs_mod/cis3600/marcabl.htm
More Cisco pinouts than you'll ever want to know about. The docs for each
router series have a section on cables used with that particular box. The
URL above is for a 3600 which should cover most of them.
--
Jay Hennigan - Network Administration - [EMAIL PROTECTED]
NetLojix Communications, Inc. NASDAQ: NETX - http://www.netlojix.com/
WestNet: Connecting you to the planet. 805 884-6323
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