clock synchronization units(CSU)

yes "thejim =D0=B4=B5=C0=A3=BA "

CSU is not "clock synchronization unit". The definition of CSU and DSU refers to "Channel Service Unit" and "Data Service Unit" respectively. In simply words, DSU is where data flow begins or ends, and CSU is a "channel", through which data flow. Check the following link for definitions:

Mike

------ Cisco IP Phone Headset Adapters

The second and last paragraph in that url seem to sontradict each other, but a decent link just the same.

My two cents:

The DSU is best described in the last paragraph. The DSU will terminate to the data source/sinks via a serial interface such as RS232, V.35, etc. The DSU's job is to convert the electrical format on the terminal interface to one which is compatible with the (telco/line) transmission facility, such as a bipolar/ami signal. It also adds the required framing and control mechanisms for the line side. In the case of a T1 DSU, the device also allows for 'mapping' of the data presented by the source terminal onto timeslots in either an Nx56 (7 bit) or Nx64 (8 bit) manner.

The CSU allows for 'grooming' of the signal to/from the DSU on the terminal side and the line/network side. Examples of 'grooming' include pulse density enforcement, line build out on either side, frame format conversion, alwarm support such as yellow/remote/AIS/blue, defining the format of these alarms such as being framed or unframed or in/out of channel, loopback capability, and test/monitoring access, etc.

Once upon a time, these two functions were in two seperate boxes - one being a DSU and the other being a CSU. DataSource --------DSU-------CSU------telco line..............

More recently the two seperate functions have been located in a single box. DataSource--------DSU/CSU-------------telco line..............