# CSU/DSU

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A **CSU/DSU** (**channel service unit/data service unit**) is a digital-interface device used to connect [data terminal equipment](/source/Data_terminal_equipment) (DTE), such as a [router](/source/Router_(computing)), to a [digital circuit](/source/Digital_circuit), such as a [Digital Signal 1](/source/Digital_Signal_1) (DS1) T1 line. The CSU/DSU implements two different functions. The [channel service unit](/source/Channel_service_unit) (CSU) is responsible for the connection to the [telecommunication](/source/Telecommunication) network, while the [data service unit](/source/Data_service_unit) (DSU) is responsible for managing the interface with the DTE. A CSU/DSU can have an external connection point or it can be integrated into a modular card installed in a router.

A CSU/DSU is the equivalent of the modem for an entire [LAN](/source/LAN). The [DCE](/source/Data_circuit-terminating_equipment), commonly a modem or CSU/DSU, is the device used to convert the user data from the DTE into a form acceptable to the WAN service provider transmission link. [1]

## WAN interface

The [WAN Interface Card](/source/WAN_Interface_Card) (WIC) may contain an integrated CSU/DSU that can be inserted into a router slot. An example of a WIC is the 1-port 56/64-kbit/s DSU/CSU WIC (WIC-1DSU-56K4) by Cisco Systems. DTE is generally a router, but can also be a terminal, computer, printer, or fax machine if they connect directly to the service provider network.

## References

1. Microsoft Official Academic Course (2012). [*98-366: MTA Networking Fundamentals*](http://customselect.wiley.com/book/9780470901830). Hoboken, NJ: John Wiley & Sons. p. 151. ISBN 978-0-470-90183-0.

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Adapted from the Wikipedia article [CSU/DSU](https://en.wikipedia.org/wiki/CSU%2FDSU) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/CSU%2FDSU?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.