# PSTN trunk interfaces

Analog trunks with loop start signaling are the most common type of telephone trunks found in residential installations. The network uses the presence or absence of current flow in the telephone circuit as signaling information when establishing and processing connections.

Digital trunks multiplex
the signal of many different channels into one interface. Digital trunks follow two basic standards around the world:

- T1 trunk lines have a capacity of 1.544 Mbps, and typically handle 24 simultaneous telephone channels. T1 trunks are used in the United States, Canada, Hong Kong, and Japan.

- E1 trunk lines have a capacity of 2.048 Mbps and typically handle 30 simultaneous telephone channels. E1 trunks are used mainly in Europe, Asia, and South America.

Digital trunks use signaling bits associated with voice channels to carry signaling information. For a detailed description of T1 and E1 communications, see the appropriate board installation and developer's manual.

## Trunk interface boards and the CT bus

NMS trunk interface boards can connect to other boards in the same chassis over the CT bus. The CT bus is a high-speed, time-division multiplexed digital telephony bus between telephone line interface boards (such as AG 2000 boards), that allows boards to share data, signaling, and switching information. You can add additional DSP resources, analog line interfaces, or loop start line interfaces, by using other AG 2000 boards or board sets.

You can also use MVIP-compatible products from other manufacturers with NMS boards.

For detailed information about a particular NMS board, refer to the appropriate board installation manual.

Warning: | NMS obtains board-level approval certificates for supported countries. Some countries require you to obtain system-level approvals before connecting a system to the public telephone network. To learn what approvals you require, contact the appropriate regulatory authority in the target country.