cabling question

[drhixson]

in a recent technicial interview one of the guys kept insisting you really only need 1 pair (2 wires) to run ethernet, tr, or whatever. I disagreed with him. Can anyone agree or disagree and explain?

thanks

 

[mradmin]

Hi, the short answer is that not 1 but 2 pair are used for ethernet, if you mean 10Base-T or 100Base-TX. One pair is used for receive and one for transmit. To be completely accurate to the standard, the other two pairs must be terminated correctly, but aren't used for data. Check the first FAQ in this forum for details! By the way, I believe that in Gigabit Ethernet, all four pairs are used.

 

[daronwilson]

Yes indeed, you need two pairs of wires for ethernet or token ring, one transmit pair and one receive pair.

I guess...in those situations, I like to hand the person a single pair wire and some modular plugs and say "please show me".

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[drhixson]

I'm going to challange him tomorrow... we'll see what he says...

 

[Bobg1]

You go back to the old 10base-2 and in theory it was 1 pair
but then again it was also coax. Maybe thats what he's thinking.

 

[daronwilson]

I don't think there is any twisted pair in 10base-2 is there? I thought that was just unbalanced coax, perhaps AUI, but I don't think there was any balanced twisted pair.

Anyway, if he's that far behind in data, better watch out

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[Bobg1]

Daron, that is correct, that's why I stated in "theory"
(You know inside conductor and outside conductor> thats 2> thats a pair) You never can tell what might be going through some peoples heads.
Yes if they are that far behind, where have they been hiding...

 

[smah]

Could he be referring to DSL type transmission? This usually comes in over 1 pair that's not even twisted. I'm not exactly sure how it works, but I would expect that it could be used to connect computers in a LAN type configuration with the right equipment (which is probably cost prohibitive in a LAN configuration).

 

[daronwilson]

XDSL generally is on twisted pair. You may find a patch cord from the jack to the 'modem' but it normally comes in on telephone cabling which are twisted pairs. It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[InnoTech]

i've seen DSL installed with cat5 from outside box to modem in a few places(friends and family). i do know that cat5 is not needed, though. i was also under the impression that it used two pairs. it is "power over ethernet" so i think it IS two pairs. i have supported DSL but didn't stay long with that company so i didn't get the chance to learn the enter-workings of DSL. "Jack of all trades. Master of none."

 

[daronwilson]

XDSL and ethernet are completely different types of circuits.

DSL is available in many flavors and is often just referred to as XDSL where you replace X with whatever flavor you want (ADSL, HDSL, etc). Generally the ISP has a device called a DSLAM (Digital Subscruber Line Access Multiplexer) at the Telco Central Office and the provides you a DSL 'modem' (not really a modem, modems convert digital data to analog data MODulatorDEModulator, the DSL equivelant is actually an ATU-R but often referred to a modem). Additionally, depending on the type of service, you may get a filter that filters out the high pitched digital noise after your 'modem' gets it, allowing you to use the lower frequencies of the single pair circuit for normal voice use.

POE (power over ethernet) refers to using a spare pair (ore more) in the 4 pair cat5 ethernet circuit to provide power to a piece of remote equipment. Generally this is used to power small switches, wireless access points, etc. All that is done here is an unused pair gets a voltage dropped on it, and we pick it up at the other end and power a device with it.

Hope that explains it, I'm honestly trying not to get too complicated with it.

Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[Bobg1]

drhixon
Have you found out what method he was going to use yet?

There are multiple ways to connect computers and terminals using only 1 pair, but thats not the current
"common practice"
for setting up a network.

 

[AdmanOK]

Cisco have what they call Long Range Ethernet (LRE) which runs up to 5000' over a single copper pair (even runs over barbed wire). Maybe this is what he is talking about.

 

[daronwilson]

Cisco's LRE is actually very much like a DSL circuit, check the throughput, I think you will find it is nowhere near 10 or 100 mbs. But hmm, now I'm curious, I saw the dog and pony show about this gear and remember the barbed wire comment...but...at what speed?

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[drhixson]

He stated he has saw it but when I asked him to explain it in technicial terms or "show me" he couldnt...

 

[InnoTech]

just re-read my last post....... I meant "PPP over Ethernet" i always get those terms confused. sorry. "Jack of all trades. Master of none."

 

[AdmanOK]

The LRE docs that I have say "The Cisco LRE technology dramatically extends the reach of Ethernet up to 5,000 feet over existing Category 1/2/3 wiring at speeds from 2 to 15 Mbps symmetric". I've order some of this stuff but haven't got it in yet to do any testing... will let you all know the results when I have.

 

[xmar]

I think I would have asked him "In what situation would you only want to run one pair" My school of thinking is that if you have 8 wires, wire all of them correctly. Who knows what new technology may come out to use the rest of the wires! It don't think it's any faster to do 2 or 4 than 8. I've worked in alot of environments where there are only 4 of the 8 terminated, but never just 2.

I was curious whether the difference between half and full duplex was in the number of wires. All need to know to do my job is the wiring schemes for straight through and for crossover, carry a crimping tool and some mod plugs.

 

[dschartung]

Yes LRE is over pair of plain copper wires.
It is basically xDSL with proprietary compression. Works great. I can get 8MBit across 1000' run. We have a guardshack about 1000' from the nearest ethernet switch. Plenty fast enough to run Terminal Services there.