Does the TA900 support 4 Wire T1s?

[bama]

Does the TA900e (3rd Gen) support 4 wire T1s facing the customer's PBX?    We have a customer with an old PBX that requires a 4 wire T1 for their voice and I can't find any documentation that says anything about 4 Wire T1s.

[Anonymous]

Doesn't a T1 normally have only 4 wires connected, as two twisted pairs?

Keep in mind that a modern "2-wire" T1 is really a DSL signal, and there is almost always a conversion back to "four-wire" at the demarc. It sounds like your PBX is pretty standard, and this is what the TA900 is designed for.

https://www.dasblinkenlichten.com/how-to-t1-circuits-and-wiring/

[jayh]

All T-1 circuits are four-wire. Two pairs, one for transmit and one for receive. Some older T-1 connectors use a DB-15 connector instead of an 8-pin modular jack. It should be compatible but you may have to make a custom cable.

[bama]

I've been doing this with TA900s since the 1st Gen routers were out.  I've never run into a telecom switch guy who made as big of a deal over 4 wire vs 2 wire as this guy has made.   I just assumed the Adtran supported both but I couldn't find any documentation on the Adtran site to defiantly say one way or another. 

This T1 interface is facing the customer's PBX not our network.   I don't really know what PBX they are using but I do know it was installed in the early 90s and they can't really tell much of anything about their side other than they stress the 4 wire over 2 wire T1s.   

[Anonymous]

In your position, I would find out the make/model/whatever of the PBX and to some digging to confirm that it's a normal T1 interface just to assuage the customer's concerns. You might luck out and find some document with the PBX pinout, so you can show how that will match the TA with the proper cable and connectors.

If you ever find out what the big deal is, please share

[jayh]

The telecom switch guy is probably referring to the outside plant HTU-C to HTU-R setup from the central office to the smartjack. For shorter loops these can be 2-wire but the handoff to the customer on the smartjack will always be 4-wire for T-1.

You never want to connect customer equipment directly to the pair(s) coming from the CO, only to the customer handoff jack. The wires from the CO will have 130 volts on them to power the smartjack. Customer handoff on T-1 is always four wire (two pairs).

[Anonymous]

As Jay pointed out - T1 circuits/interfaces are 4-wire. Page 30 of the installation guide (Total Access 900e Series Hardware Installation Guide) shows the pin-out for the NETWORK T1 0/1 through 0/4. Pins 1 & 2 are receive data, and pins 4 & 5 are transmit data.

When connecting to a PBX, you may need a T1 cross-over cable (https://supportforums.adtran.com/docs/DOC-4103) in order for the circuit to come up.

Hope this helps,

Patrick