Implementing switched 56 service

To provide dial-up capable digital lines for support of switched 56 requires special CSU/DSUs to be installed on the 56 kbps circuit at the Central Office. The channel service unit (CSU) is a device that is installed between the customer's multiplexer and the service provider's network switch. It manages the physical characteristics of the signal such as the network protection, diagnostics, signal format, clocking and one's density. It is also used here to extract signaling information from the data stream to control the switching of the circuit.

The data service unit (DSU) is installed between the CSU and the user. This unit provides for things such as proper termination specifications, data isolation, and proper mechanical connection specifications. In other words, the data service unit would be the actual physical connection between a user and the data circuit channel service unit. The connections for switched 56 service are illustrated in Figure 6.9.

AT&T use their 4ESSTM switch for 4-wire switching and use the 700 56X XXXX number for switched 56 services. The installation of a Northern Telecomm (Nortel) data unit at the customer's premises is all that is required to support 2-wire switched 56. Once in the PSTN, the individual switched 56 circuits can be routed or switched to any other termination point connected to the PSTN.

Figure 6.9

Switched 56 service implementation

Figure 6.9

Switched 56 service implementation

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