Hi,
It depends upon the connector. For example below is the Pin Out for a standard RJ45.
| 1 | RX (input) |
| 2 | RX (input) |
| 3 | -- |
| 4 | TX (output) |
| 5 | TX (output) |
| 6 | -- |
| 7 | -- |
| 8 | -- |
Below is the link.
http://www.cisco.com/c/en/us/support/docs/routers/1600-series-routers/46795-wic-1dsu-t1.html
If it is being connected to another RJ45 via T1 link, Tx and Rx pair has to be interchanged.
HTH
-Amit
