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RJ-48X jack patched to AS5300 CSU/DSU RJ-45 jack

Is it possible to pin-out a cable to run from a jackfield with RJ-45X jacks to a CSU/DSU on a AS5350 with an RJ45 jack? What would the pinout be? Both jacks appear to use the 1,2,4, and 5 pins for T1, but there is a lot of contradictory info on which pins are used to for tx and rx.


Re: RJ-48X jack patched to AS5300 CSU/DSU RJ-45 jack

A T1 does indeed use 1&2, 4&5.

IF you are going between two similar devices (i.e., CSU/DSU to CSU/DSU) then you can create a crossover cable with 1->4, 2->5, 4->1, 5->2

If you are going between complimentary devices (i.e., smartjack/NIU->CSU/DSU, then a straight-through should be used.

Also note that for long runs, UTP (i.e., Cat{anything} ) should not be used, it is not the "spec" cabling for T1. You need "premises" cabling, which is individually shielded pair, inside a shielded jacket.

If you want to see what it looks like, go to, select "online catalog," then put in "premises cable" for the search.

UTP / Cat{3,4,5,5e,6) is OK for shorter runs.

Good Luck


Community Member

Re: RJ-48X jack patched to AS5300 CSU/DSU RJ-45 jack

Hi Scott,

Understood on the pins, but what puzzles me is why a straight through does not work with this jackfield and its RJ-48x ports. I even tried a cross over. None of these cables exceed 3 meters in length.

I don't have this problem with my RJ-45 jacks in my old jackfields and panels. Just this new one with the RJ-48x (emphasis on "x".) A search on the RJ-48x turns up two issues.

1) It puts the port into loopback as soon as a cable is removed. I thought about the key on the RJ-48 connector, but even with an RJ-45 connector the 15310 show alarm when a cable is connected to the port.

2) I notice different notation for pin assignments as follows:





I can?t tell from this notation if T is transmit ring, and T1 is transmit tip? or what. Any ideas?


Re: RJ-48X jack patched to AS5300 CSU/DSU RJ-45 jack

From the explanation above, T and T1 are transmit leads and R and R1 are receive leads. You can say T for both T and T1 leads are the TIP and R and R1 are the RING. T-1 wiring is full duplex and requires two leads for the transmit and two leads for the receive. The two leads are the signal and signal return . In high speed electronics using low voltage you see two leads that run as a set. This is very similiar to the phonejack loop for your local phone. You only use two wires. Well in a T-1 you use two wires for the transmit and two wires for the receive....


Re: RJ-48X jack patched to AS5300 CSU/DSU RJ-45 jack

You absolutely want to keep transmit as a pair and receive as the other pair .. (i.e., 1&2, 4&5 ***NOT*** 1&4, 2&5).

Using both pair for transmit and receive would blow your crosstalk halfway to the moon.

Think of it as a "Plus" & "Minus," where the "T" is the plus lead and the "R" lead is the minus. SO you have a Transmit Plus & Transmit Minus and a Receive Plus & Receive Minus .... each must stay in their own pair (same color wires, Blue/Blue-White and (probably) Green/Green-White but could be Orange/Orange-White).

(T=Tip/R=Ring of one pair, T1=Tip, R1=Ring of the second pair)

One of the usual questions is why a cable that can carry 100Meg Ethernet (or Gig) is bad to use for "only" 1.5 meg T1 (or 2 Meg E1) ... the signaling is different; T1/E1 are much more likely to cause crosstalk. T1/E1 are straight bi-polar pulse trains, Ethernet, Fast tehernet, and Gig Ethernet are differential signals.

For the sake of an electrical connection, an RJ45x is the same as an RJ45.

Did you make the jumper cables, or are they "store bought" pre-fab cables?

What is feeding this jackfield, and what are you connecting into it?

Let us know

Good LUck


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