WAN Devices

eng_ahmedas

Hi All
I wish u r all in good health.first of all , i want to thank u for these fantastic forum and i wish we could help each other.I am very confused about some WAN devices and want u to help be answer these questions
1) Does CSU/DSU and DCE are the same device or they are different devices ??? what are their jobs in WAN ????
2) Does CSU/DSU is CPE (Customer Premises Equipment) or it is located at C.O. ????
Thanks in Advance

evanderburg

The CSU/DSU is a device. The DCE is a cable. The CSU/DSU would be CPE if it is owned by the customer. It is not if it is owned by the ISP.

autoartist

evanderburg wrote:

The CSU/DSU is a device. The DCE is a cable. The CSU/DSU would be CPE if it is owned by the customer. It is not if it is owned by the ISP.

This is pretty much correct.
However DCE is more than just a cable.

http://www.cisco.com/en/US/products/hw/routers/ps380/products_installation_guide_chapter09186a008007ce3e.html

Data communications equipment (DCE) is more often a device like a modem or mux or perhaps channel bank or CSU/DSU. I know routers can be configured as DCE devices but more often than not they are configured as DTE because they usually interface a DCE like a mux or CSU/DSU.
Unless you are in a lab more often than not you must have DTE going to DCE so that is why a router is configured as DTE.

Think of a CSU/DSU as a type of line conditioning equipment. It converts the signals from the router into a format that can travel long distances and can be accepted by the COs equipment (another CSU/DSU or mux w/ built in CSU/DSU, etc). The signals from the router carry various information, multi signals (RS-530, 449 etc). The transmissions from the CSU/DSU are simply four signals, 2 transmits and 2 receives. They can travel long distances, serial signals from a router (RS-530, 449 etc) cannot travel long distances. Now some routers have the CSU/DSU as part of the router so in that case a T-1 can terminate at the router directly.

This does a much better job than me

http://searchnetworking.techtarget.com/sDefinition/0,290660,sid7_gci211866,00.html

www.whatis.com is a fantastic website for looking up telecom terms

eng_ahmedas

Thanks toooo much for ur useful replays

autoartist

Just a side note about DCE and DTE.

When talking about frame relay, the router is considered the DTE and the Frame relay switch located at the CO is the DCE.
Now the DTE to DCE device discritptions still apply b/t the router and what every line driver (mux, CSU/DSU, channelbank, etc) that it connects to actually reach the CO.

Pretty much what ever provides timing for the circuit (ckt) is the DCE and what ever references the timing is the DTE). Remember in a back to back Cisco router lab setup one Router must provide timing and use the clock rate command, notice how that is the one setup as the DCE.

Your question about CPE.

Anything located at the customers site is the customer primises equipment (CPE), even if they don't own it (the customer). I think you might have been confused w/ the term Demarcation. The Demarcation is the point where responsibility of a circuit shifts from the CO/ISP to the customer.

My network

Demarc point (see note A: )
________________|
LAN----ROUTER

---

Channel-bank

---

T-1

---

[Central Office]


Note A: I own the router and everything to the left of the Demarc point. The ISP installed the Channel-bank, they own it and control it. Bascially I cannot control anything and don't own anything from the right of the demarc point "|". That equipment belongs to the CLEC (phone company) and ISP.

Hey there is a great book you should have, get it used at half.com
Encyclopedia of Networking and Telecommuncations (latest one published in 2001)

Don't let the date discourage you. Telecom stuff doesn't change as fast as software technology. The book looks like this
http://www.linktionary.com/about.html
The book also lists websites for further study of a topic

PS: If you work at company perhaps you kind find the person w/ the lock and key to the Demarc point and get them to show you around.

eng_ahmedas

Thanks tooooo much auto artist. ur replay was very useful to me and help me understand what i didn't understand.
Thanks again