The RJ48 electrical test interface, on the PDH/DSn port group, follows the standard pin-out for balanced E1, T1 and 64k Codirectional links
The RJ48 G.703 electrical test interface, on VeEX's test sets PDH/DSn port group, follows the standard pin-out for balanced E1, T1 and 64k Codirectional links. Balanced interfaces use a pair of differential signals, with +/- or A/B or Tip/Ring, in a twisted pair, to counter external interference.
There is a common misconception where some people may mistakenly refer to the RJ48 interface as "RJ45" simply because they share the same connector. It is important to note that while RJ45 interface cables are commonly used in Ethernet applications, they have a different (incompatible) pin-out compared to RJ48 interfaces. Therefore, users must exercise caution when selecting test cords to avoid any compatibility issues.
Depending on world regions or vendors, the transmit data (TxD) and receive data (RxD) signal polarities are labeled in different ways:
- Tip ≡ Positive (+) ≡ A ≡ Earth ≡ Ground Side
- Ring ≡ Negative (-) ≡ B ≡ Battery Side
The term "Negative" comes from the -48V nomenclature used in POTS (plain old telephone systems)
1. Terminal Mode (RJ48C)
Used for traditional applications, like BER testing and ISDN PRI, in normal point-to-point (single port) mode, the 8-pin female modular plug connector is configured in RJ48C mode, with the following pin-out:
| RJ48C E1/T1 (Female) | |
| Pin | Signal |
| 1 | RxD- (B/Ring) |
| 2 | RxD+ (A/Tip) |
| 3 | |
| 4 | TxD- (B/Ring) |
| 5 | TxD+ (A/Tip) |
| 6 | |
| 7 | |
| 8 | |
2. Dual-Port Monitor Applications (RJ48M)
When used for bi-directional monitoring applications (usually in high-impedance mode), the 8-pin female modular connector is configured in RJ48M mode, with two receivers and the following pin-out:
| TX-series RJ48M E1 (Female) | |
| Pin | Signal |
| 1 | Rx1- (B/Ring) |
| 2 | Rx1+ (A/Tip) |
| 3 | |
| 4 | Tx1- (B/Ring) |
| 5 | Tx1+ (A/Tip) |
| 6 | |
| 7 | Rx2- (B/Ring) |
| 8 | Rx2+ (A/Tip) |
Note: In certain dual receiver (monitor) modes, the Tx1 interface may remain active, transmitting a valid signal to keep the link alive.
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