sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's Extending a T-1 from a 66 Block Demarc

If Telco drops off a T-1 at a 66 block how will I know which pair is Telco's transmit pair and which pair is Telco's receive pair? Is there a rule of thumb that says the top pair is one or the other?

Thanks,
Dave

This is like a function of binary math. It's one or the other and depends on whose side you're on.

Yes and no. Normally the transmit goes on top and receive on the bottom. The question is what mood the installer was in when he did it. It's either YOUR transmit or THEIR transmit.

Hope I answered your question LOL

Carl

I have had a heck of a time finding info on this topic. RJ-48 interfaces don't ever seem to be labeled like serial interfaces that use a DCE/DTE label and reference their functions to the DTE. This would eliminate the "who's transmit are we talking about" problem. So I guess you are saying try it one way and see it it comes up and if not then swap'em?

I can tell you the way it is suppose to be, can't guarantee it's this way. The first pair should be the customers receive and the 2nd pair the customers transmit.

RJ48X's are wired:
1/2 -transmit from CO to CPE
4/5 -transmit from CPE to CO

RJ48C's are the same way, without the auto 1/4 2/5 shorting.

Always remember when working with a PRI: send a loop back toward the CO, and you won't generate any alarms or lock your D Channel out.

And just to add something here, so people understand it-- if your carrier needs to extend the demarc and wants to know what type of RJ48 block to install-- go with an 'X' block (they sometimes call them 'biscuits'). The X means it will automatically loop up, if you disconnect your connection from it.

If you want to make your own loopback jack, to let you do 'hardloops' on your own. Take an RJ45 plug, a single 3" pair of UTP, and connect pins 1 to 4, and 2 to 5. Others blank/empty. Orient the plug so that the flexible tab is on the side away from you, the gold pins are on the side facing you and at the top. Leftmost gold-in is "1", rightmost gold-in is "8".