Channel Service Unit / Data Service Unit

A Channel Service Unit / Data Service Unit (CSU / DSU) is a hardware component that is roughly the size of an external modem and performs a similar function as a modem: modems prepare data packets so that they can be transported via analog Telephone connections are suitable. In contrast, a CSU / DSU takes care of the adaptation of data packets to digital WAN connections such as frame relay , primary multiplex or T1 .

A company that operates its own web server and has rented a digital connection (e.g. a T1 connection) can be used as an example of the use of a CSU / DSU. The company is connected to a telecommunications service provider or to the gateway of an Internet service provider. In a constellation of this type, there must be a CSU / DSU on the company side as well as on the telephone company or the gateway.

A CSU / DSU is two devices in one:

Channel Service Unit (CSU)

The CSU forms a barrier to electrical interference from either side of the link. It ensures that malfunctions of the DSU are prevented and is also responsible for buffering and flow control .

The CSU offers diagnostic options and makes it possible for the connection to be tested remotely using loopback signals.

Data Service Unit (DSU)

The DSU takes care of timing errors and signal refreshment. It converts the input and output between RS-232C, RS-449, or V.xx frames that come from the LAN and DSX frames that are used for the time division multiplex (TDM) method on a T -1 connection are provided.

variants

The CSU and DSU are manufactured as separate products, but can also be part of a T1 WAN card. Most of the device variants have the DSU and CSU in the same housing. The DSU can, however, also be built into a multiplexer , i.e. a device that is used to combine digital signals for high-speed connections.

A CSU / DSU is often connected to a router .