What is a difference between 4-wire and 8-wire RJ-45 cables?

  • Thread starter Thread starter Dmitry Kopnichev
  • Start date Start date
In Dmitry Kopnichev <[email protected]> had this to say:

My reply is at the bottom of your sent message:
Why do they use a 8-wire cable for 100mbit ethernet usually too?
Click to expand...

I think that maybe you're thinking about it from the wrong direction. In a
more interesting order: CAT5 was made. Ethernet uses CAT5. CAT5 can be used
for all sorts of things from home entertainment speaker wire to supplying
power to small DC devices.

Ethernet usage didn't define CAT5, rather the usage of CAT5 is 'standard'
probably for future expansion needs in telephone service wiring. 4 pair
(CAT5) cable is cheap, allows for expansion, and while you could do it with
just a couple of pairs - what do you do about when the next generation of
comes (and note that it already has arrived) needing additional wiring?
Re-run the entire building? I suspect that it was from planning ahead more
than anything.

My guess for the "why" (and I couldn't find a reason) is
expansion/upgradability and, well, it was already on hand and it was already
being mass produced. Fortunately it is the 'standard' so that we can upgrade
easily. The cost to re-wire buildings would have made the technology
prohibitive, kept the cost up, and prevented it from becoming main-stream.

"Upgradability" is a word I hope???

--
Galen - MS MVP - Windows (Shell/User & IE)
http://dts-l.org/

"A man should keep his little brain attic stocked with all the
furniture that he is likely to use, and the rest he can put away in the
lumber-room of his library where he can get it if he wants it."

Sherlock Holmes
 
Also, it is a lot easier to crimp on a Rj-45 plug when using 8 wires instead
of four. The "other" four wires help to keep the "standard" 4 wires in
place.
 
I think that maybe you're thinking about it from the wrong direction. In a
more interesting order: CAT5 was made. Ethernet uses CAT5. CAT5 can be
used for all sorts of things from home entertainment speaker wire to
supplying power to small DC devices.

Ethernet usage didn't define CAT5, rather the usage of CAT5 is 'standard'
probably for future expansion needs in telephone service wiring. 4 pair
(CAT5) cable is cheap, allows for expansion, and while you could do it
with just a couple of pairs - what do you do about when the next
generation of comes (and note that it already has arrived) needing
additional wiring? Re-run the entire building? I suspect that it was from
planning ahead more than anything.

My guess for the "why" (and I couldn't find a reason) is
expansion/upgradability and, well, it was already on hand and it was
already being mass produced. Fortunately it is the 'standard' so that we
can upgrade easily. The cost to re-wire buildings would have made the
technology prohibitive, kept the cost up, and prevented it from becoming
main-stream.

"Upgradability" is a word I hope???
Click to expand...

The use of a 4 pair UTP cable does derive from telephone standards. In 1991
the '568 committee published standards for Ethernet cabling based on 4 pair
UTP cable. What you say about Cat 5 is a bit misleading. Ethernet
initially used Cat 3 wiring which supported 10Mbps networking. The Category
5 standard was developed to support the move to 100Mbps Ethernet.
 
In GTS <x> had this to say:

My reply is at the bottom of your sent message:
The use of a 4 pair UTP cable does derive from telephone standards. In
1991 the '568 committee published standards for Ethernet cabling
based on 4 pair UTP cable. What you say about Cat 5 is a bit
misleading. Ethernet initially used Cat 3 wiring which supported
10Mbps networking. The Category 5 standard was developed to support
the move to 100Mbps Ethernet.
Click to expand...

Much thanks. It makes a bit more sense that way. As I was saying it was, for
the most part, just guessing based on bits of information I'd heard or
studied. I actually have some old 3 pair cables tossed into boxes though the
home is wired with the 8 pair - fortunately. Snaking and dropping lines
wasn't the least bit of my idea of a good time and if I'd had to do it a
second time I'd have been a bit peeved.

--
Galen - MS MVP - Windows (Shell/User & IE)
http://dts-l.org/

"A man should keep his little brain attic stocked with all the
furniture that he is likely to use, and the rest he can put away in the
lumber-room of his library where he can get it if he wants it."

Sherlock Holmes
 
Note however, that if you are doing above 10Mbps i.e 100Mbps, you need
to connect the unused cables (4,5,7 & 8) as it reduces electromagnetic
interference (EMI) and susceptibility to common-mode sources.
 
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