CSU / DSU (Channel Service Unit / Data Service Unit)
1.6.6
Week 3

By alan janson

WHAT!?!?!
A CSU/DSU (Channel Service Unit/Data Service Unit) is a hardware device about the size of an external modem that converts a digital data frame from the communications technology used on a local area network (LAN) into a frame appropriate to a wide-area network (WAN)
And… vice versa.

CSU DSU Channel Service Unit
csu_dsu.jpg

For example
If you have a Web business from your own home and have leased a digital line (perhaps a T-1 or fractional T-1 line) to a phone company or a gateway at an Internet service provider, you have a CSU/DSU at your end and the phone company or gateway host has a CSU/DSU at its end.

Applications of CSU/DSU
csu_dsu_diagram.jpg

CSU
The Channel Service Unit (CSU) receives and transmits signals from and to the WAN line and provides a barrier for electrical interference from either side of the unit.
The CSU can also echo loopback signals from the phone company for testing purposes.

CSU Device
DSU
The Data Service Unit (DSU) manages line control, and converts input and output between RS-233C, RS-449, or V.xx frames from the LAN and the time-division multiplexed (TDM) DSX frames on the T-1 line.
The DSU manages timing errors and signal regeneration.
It also provides a modem-like interface between the computer as Data Terminal Equipment (DTE) and the CSU.

DSU Device
Extra
CSU/DSUs are made as separate products or are sometimes part of a T-1 WAN card.

References
http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci211866,00.html