I know that this topic was originally started late last year but as a Telecom tech, I would like to advise the readers of my own recent experience with 2 wire vs 4 wire T1 circuits for voice traffic.
One week ago, I had to de & re a phone system for a customer that relocated to another city. At their old location they had 2 T1 circuits that were 4 wire and we never had any problems with them for almost 5 yrs that they were in that location. At their new location, the T1 circuits were 2 wire circuits.
About 3 days before the move, I brought out a test system to the new location for the turn up and test. No, I don't have a T-bird for testing. At first, I kept getting "Out of Frame" errors on my system on both T1s, which the CLEC was able to stabilize after making adjustments somewhere and then the turn up and test went smoothly. On the day of the move, after re-installing the system, sporadically, I would get Yellow Alarms, which sometimes would last anywhere from 10 seconds to about 2 minutes.
Opening a trouble ticket with the CLEC, they looped and tested to both the smart jack and to the system's CSU for about 30 minutes each on both T1s. After the testing and unlooping, again we started getting hits on both T1s. The local Telco, which is AT&T, came out and moved both T1s to new pairs and they then appeared to be working properly. I asked the AT&T tech how far it was from the CO and he said it was less than 4000 ft.
The next business day, which was the customer's first work day, the sh*t hit the fan, both T1s kept going down all day. Again they tested them and they ran clean but the customer still had problems with the circuits. The tester for the CLEC tried to claim it must have been a problem with the customer's equipment but I explained to them that this equipment had been in and working for over 4 years with out any problems. By the way, this customer has had this same type of equipment at other locations without any problems either.
I wasn't involved in any other conversations over this problem but finally, just yesterday, the CLEC sent out a tech with a T-Bird for another vendor meet. He tested the first T1 for 20 minutes with only 2 errors, tested the second T1, which he said was clean. Then he tested the first one again and almost immediately he got over a million errors and at first he wanted to put the blame on the cabling for the extended T1s from the Smart Jacks at the NIUs, which are on the first floor to the customer's suite on the fourth floor. He went downstairs and tested it directly at the NIU and got similar results.
The CLEC opened a new trouble ticket with the local telco, why it was only put in for the first T1, I don't know but last night they reconfigured it as a 4 wire circuit and it has been up all day with out any problems, the second T1 though, which is still a 2 wire circuit, went down 6 times today. They called the CLEC to have AT&T to convert the 2nd T1 to a 4 wire circuit too.
I'm convinced that 2 wire T1s just aren't as stable as 4 wire circuits. At least not T1s for voice channels. Maybe data only circuits have the same problem but it isn't apparent because they only think their network is slow when it's down. Of course with VOIP being used more and more, they will realise the problem if they any VOIP connections over those T1s, like remote extensions, networked systems or use SIP trunks.
Now they are going to have to figure out who is going to be responsible for all my extra time I've spent on this, which will cost them somewhere between $800 and $1000 more than the original estimate for the de & re!
