atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's 2 Wire T1 vs. 4 Wire T1

Digital is magic. That's why you see the south end of the north bound horse us old phone guys are riding.

Ed -

When I was with GTE we always ran T-Screened cable. General Cable had a type that had a foil shield on each pair and an overall braid. We never had a problem. Transmits and receives under the same sheath, but it was enormous - an eight pair cable was the size of a standard 50 pr!

When I did carrier work for my current employer, we ran either 2 @ 6p 22AWG shielded for small installs, or 2 @ 25 pr 22AWg for larger installs, or 2 @ 30/32 pr 22 AWG ABAM cables.

All the cable was shielded and we ran the transmits in one cable and the receives in the other. If you tried to run them in the same cable it would fail the stress tests every time.

The only exception was short (<50') runs of Cat 5 that some customers spec'd and we tried to keep away from that.

I always felt that the Transmit & Receive pairs of a carrier circuit were like Boys and Girls at a High School dance. Always trying to get together and make trouble. You had to keep them apart and when they did come together, get that shield on!

Sam

Ed,
As always I appreciate your post and even the soap-box rant… There’s more to it than a “psychological issue” with binder group separation… Though you correct that the overall proximity of say cable: A pr:23 and cable: A pr:32 are very close together when looking at a cross-sectioned cable with your eye or even a physical measuring device for the proximity of pairs. The biggest concerns that binder separation accomplishes is really eliminating capacitance between pairs.

Now I’ll admit the theory get’s to be a bit more complex than I ever cared to ponder on, but the rather miniscule amount of separation is pretty large when applied it how a capacitor works with distance between insulator plates (for cable pair that’s the paper or plastic insulators.) I have a feeling this is WAY too simplified of an explanation but it’s how I try to understand it myself … The less amount of capacitance between pairs there is, the less the pair will know the other even exists. (That could be so over simplified to the point of not even being accurate but that’s how I get by.)

Bryan:

I didn't think it could make it that far either. I'm sure that the Verizon technician who told me this didn't know what he was talking about.

As for the load coils, about three miles of the 2,700 and 2,400 pair cables are brand-new (less than two years old). So are the load coils. I'm sure that only certain binders are actually loaded for the POTS services. :rolleyes:

Our ADC HDSL shelves provide separate amphenol connectors at the rear of each chasis; 1 for the transmit, and 1 for the receive. The two 25 pair cables are terminated to a horizontal block at the MDF, by combining both cables to form each HDSL pair on the block.

Wow... great information guys. I came here today to see if I could find answers to the same questions. Our CLEC just moved a T1 for one of our customers and this time they installed a single pair T1. I was worried because we've had other issues with this CLEC and I figured this would just be something else to figure out.

I understand the concept of separating the transmit and receive for a T1, but sometimes I see it come in on separate binders, but go to the customer's RJ21X on 2 pairs together, such as 24 and 25. Is this a bad thing?

Jeff -

It's not the best practice. The big thing is to keep the transmits and recieves apart. The longer they're running side by side, the more likely that there will be problems. If the circuit comes in on different binders and just goes to the demarc with a x-connect then there probably won't be any trouble - as long as the customer separates it again from that point on.

But it's still not the best practice.

Sam

How bad is it for the T1 to be in a single cable from the smartjack to the equipment, about 10 feet long?

Rob, it's not bad at all. In general, if it's under 166 feet, the circuit is relatively tolerant. Now if that cable is wrapped around a fluorescent light fixture, then you might have issues.