I am having some problems understanding the CSU/DSU and DCE. I understand that a CSU/DSU is used to connect a DTE (such as a router or computer) to a T1/T3 line. From what I understand, the DTE connects to the CSU/DSU box, and then the CSU/DSU box connects to the circuit. What i dont understand is that are CSU/DSU and DCE the same device because they both provide clocking or they both are different?
Other thing is that DCE device is usually at the service provider side so it means that we home users are first connected to a CSU/DSU box and then at the service provider they connect to DCE and both CSU/DSU provide clocking so is the data also clocked at the DCE before entering the WAN?
DSU/CSU is a DCE (generic term) that provides the transition to the Telco service. DSU handles the interface with the DTE and CSU handles the interface with the telcom service.
In addition to the vmiller's answer, I would like to correct a slight misinformation. You wrote:
Other thing is that DCE device is usually at the service provider side
As far as my knowledge goes, this is not correct. The DCE device is still at the customer's premises, usually connected to the customer's edge router via a short cable, and subsequently connected to the local loop provided by the telco. There is another DCE component at the other end of the local loop, and the two DCEs - the one at the customer's premises, and the other at the ISP - talk to each other directly. Between two routers, the interconnection is DTE-DCE-DCE-DTE.
Here is an example for frame relay using a router as a frame relay switch.
back to back HDLC
what are you trying to accomplish ?