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Home > Archive > CCNP > May 2002 > 2 wire/4 wire Leased line
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2 wire/4 wire Leased line
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| ss2001 2002-05-14, 1:13 am |
| Hi all!!
Can someone explain me the difference between a 2wire & a 4wire leased line?I suppose that 2wire supports upto T1 & 4wire supports anything above T1.Is it right?
Also in ISDN does this 2wire or 4wire hv any significance?
Thanx in advance
ss | |
| peterd 2002-05-14, 3:19 am |
| hello,
the main difference between 2 wire and 4 wire is that the 4 wire circuit can be balanced and amplified as required to give a higher grade circuit.
A 2 wire can be amplified but not balanced so is limited in bandwidth.
I know that the limits are always being extended but I would have said that a T1 line would need 4 wires...but I could be wrong on this point.
I recall, not so long ago, that as a British Telecom data tech, I was installing 'fast' modems running at 2400 baud and that was all that a standard 2 wire could take! The 'standard' data speed was 1200 then and if you wanted anything like a 4800 baud then you had to have a 4 wire circuit...
ISDN BRI is a 2 wire circuit (on the local line side). A PRI should, I presume, be 4 wires (or co-ax, or fibre) but as I mentioned above, they may have managed to get a T1 working over 2 wires by now...
We have four PRI's on this site and they come in over co-ax from the local exchange, but that could be because BT wanted to push all four down the same wire to save money.
Regards
Peter | |
| wirechild 2002-05-14, 10:09 am |
| T1 does normally require 4 wire or 2 pair. However many Telcos are now using HDSL and SDSL to deliver your T1 and this only requires 2 wires. PRI's have the same physical requirements as a T1.
Here is some examples:
BRI - 2 wires middle 2 pins
T1/FT1 - 4 wires pins 1,2 & 4,5
PRI - 4 wires pins 1,2 & 4,5
xDSL - 2 wires middle 2 pins
56K - 4 wires pins 1,2 & 7,8
by the way if your PRI's are coming from Telco via COAX then they are part of a DS3. | |
| ss2001 2002-05-15, 12:13 am |
| Thanx peter & wirechild for ur clarifications.To an extent Iam clear.
I hv one more query.Assuming I hv a 4wire leased line,are all the 4wires used at a time?
Also I understand from ur post that compared to 2wire ,more bandwidth is supported by 4wire since it can be balanced.Is it right?
Thanx once again for ur valuable inputs
ss | |
| peterd 2002-05-15, 2:51 am |
| Hi Guys,
Wirechild, thanks for the update.
SS2001, basically on a 4 wire circuit you'd have one pair for transmit and one pair for receive.
The telco can add amplifiers, inductors and capacitors as required (balancing) to make the line look like it only connects directly from one piece of equipment to another, ie, no losses on the line. This is what allows the increase in bandwidth.
With the cables that we use getting better all the time, it's now possible to get higher bandwidth down 2 wires which makes the circuits much cheaper to install.
How far will this trend go? Where will it end? I'd hesitate to say what we'll be using in 20 years time...wet string, probably!
Regards
Peter | |
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| 4wire vs 2 wire:
Wirechild was right on with the pinouts for the various types of circuits. I just want to make sure you're not confusing analog and digital. The ones he was describing were digital. Both analog and digital can be called four wire leased lines.
There are still a lot of analog circuits out there carrying low speed data great distances. I've worked on some that go from Alaska to France -- all four wire -- all analog.
I'm not sure what kind you are talking about for India. Just in case they are analog, the pin out is usually TX on 4,5 and RX on 3,6. (That's TX to the telco and RX from the telco)
Plus, regarding the HDSL circuits. They are two wire on the telco side but they change back to standard T-1 four wire on the customer side.
Speaking of T-1. Does India use a T-1 or E-1 platform? | |
| wirechild 2002-05-16, 5:18 pm |
| I wasn't taking that into consideration. Almost everything new is digital, but there are still lot's of analog circuits in use and being installed for various reasons.
We recently replaced an analog circuit that went form Houston, TX to Mexico City. |
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