North American Network Operators Group
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Re: T1 short-haul vs. long-haul

  • From: Robert Boyle
  • Date: Wed Jul 21 09:24:11 2004 
At 08:25 AM 7/21/2004, you wrote:
Normally in Europe when you order an E1 (G.703) connection the Telco delivers a
NTU (Network termination Unit) which normally is a (S)HDSL modem converting from
two-wire DSL to four-wire E1 electrical. The cable between the NTU and the Router
is normally very short, a few feet/meters.
You can travel up to 655 ft. with a T1 cable from the NTU which the phone company will drop at your site. According to the letter of the specs, you are supposed to use "T1 cable" two 22AWG pairs individually shielded to prevent cross-talk. In practice, we have extended DMarcs up to 200-300 feet with regular Cat 3/4/5/6 cable and have never had any problems or out of spec. cross-talk as a result.

o How is this normally done in the US by the Telcos for T1 lines?
Same basic procedure, the telco will drop off a T1 smartjack (NTU) and you will plug your equipment into this box.

o I assume the difference between T1 short-haul and long-haul is the cable length.
But what is it used for? Is it still common to have long-haul T1 connections
either within buildings or towards the central office of the Telco? Would I be
fine with buying short-haul-only interfaces in any common scenario?
Most modern equipment allows you to set the tx/rx gain on the DSU. We use mostly Cisco WIC-1DSU-T1 cards which fit into any 1600/1700/2600/3600/3700 router and provide better diagnostic capabilities than older standalone DSUs. It is also nice to have a single box rather than two power cables and a serial cable to worry about at a remote site.

o What is "Wet T1 Capable"?  What is it used for and who needs this?
This is one of the "features" of the new WIC-1DSU-T1-V2. It seems that some DSUs can be powered by the telco remotely. In 15 years of working in communications, I've never seen this, but that doesn't mean it isn't used by some remote telco using old style T1 without HDSL or HDSL2 running over the line.

In almost all cases today, the T1 spam itself will be powered from the CO and the smartjack will convert 2 HDSL pairs or one HDSL2 pair to a T1 signal with distinct TX/RX pairs.

Does anyone else have more/better info?

o What else is important in dealings with US Telcos when ordering and using T1
  leased-line services?
If the service is available in your office areas, make sure to specify ESF framing and B8ZS encoding when you order the line. AMI is robbed bit signaling and will give you 24 56k channels instead of the 24 64k channels of B8ZS. The biggest problem is keeping after the carrier to actually install the circuit.

-Robert


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