what means E1, E2, E3, E4 . . T1,T3, . . ?
These are Data-Line definitions for internet connections
| Signal | Speed | Channels |
| E-0 | 64 Kbps | 1 x E-0 |
| E-1 | 2.048 Mbps | 32 x E-0 |
| T-1/DS1 | 1.544 Mbps | |
| multiple E1 with Cisco | n x 2.048 Mbps | up to 240 |
| E-2 | 8.448 Mbps | 128 x E-0 |
| DS2/T-2 | 6.312 Mbps | |
| E-3 | 34.368 Mbps | 16 x E-1 |
| T-3 | 44.736 Mbps | |
| E-4 | 139.264 Mbps | 4 x E3 |
| E-5 | 565.148 Mbps | 4 x E4 |
optional there are 155 Mbps and 622 Mbps and more on fiber optics
Some Electrical Characteristics for En
| Cabling | Coaxial or one symmetrical pair (4 wires) for each direction |
| Mark | Balanced: 3.0 Vdc Unbalanced: 2.37 Vdc |
| Space | Balanced: 0 Vdc +/- 0.237 Vdc Unbalanced: 0 Vdc +/- 0.3 Vdc |
| Pulse width | 488 nsec |
| Encoding | AMI or High Density Bipolar of order 3 (HDB3) |
| Speed | 2048 kbps +/- 50 ppm |
Pinning Specifications
Sub-D15 Male Female
| Signal | RJ45 Description | DTE RJ45 | BNC Description | DTE BNC |
| RxA | Receive Input Negative | 1 | Receive Input | Tip |
| RxB | Receive Input Positive | 2 | Receive Ground | Ring |
| TxA | Transmit Output Negative | 4 | Transmit Output | Tip |
| TxB | Transmit Output Positive | 5 | Transmit Ground | Ring |
| S1 | Transmit Ground | 3 | ||
| S2 | Receive Ground | 6 |