where:
Lines of subscribers are connected into the EX exchange. Standard connection surface of the exchange towards the network is realized by the ET (usually PCM trunk) exchange terminal. Exchanges are connected into a MUX digital multiplex equipment, which joins more digital signal streams with each other with a primer speed to the signal stream with higher speed. Standard output connection surface of the digital multiplex is adapted by the LT line terminal to the digital line section. Distorted and noisy line signals at the line section are refreshed by the R line regenerator(s).
Elements of the network are connected to each other through standardized access point. Standardized access points generate a hierarchy system.
Standard bit rates of hierarchy access points in case of European (2048 kbit/s) PDH (Pleisochronous Digital Hierarchy):
| Hierarchy level | Bit rate | Speech |
|---|---|---|
| kbit/s | channel | |
| 64 | 1 | |
| 1 (E1, primer) | 2048 | 30 |
| 2 (E2, secondary) | 8448 | 4x30=120 |
| 3 (E3, tertiary) | 34368 | 4x120=480 |
| 4 (E4, quarter) | 139264 | 4x480=1920 |
In PDH systems theres bit rates are only nominally (within a given tolerance) the same at the nodes of the network.
Standard bit rates in case of American (1544 kbit/s) PDH systems:
| Hierarchy level | Bit rate | Speech |
|---|---|---|
| kbit/s | channel | |
| 64 | 1 | |
| 1 (T1,DS1) | 1544 | 24 |
| 2 | 6312 | 4x24=96 |
| 3 (DS3) | 44736 | 7x96=672 |