What is the function of CSU/DSU Device?

Hi, I am having a bit confusion in a topic, What exactly is the function of CSU / DSU Device?

I am answered with different answers from my friends, teachers and google, all answers are different,

For now what I have studied from answers.com and wikipedia is that CSU/DSU is a modem like device used to connect in-house network to dedicated internet (T1, E1 etc) while teachers are focusing on bandwidth allocation, that csu/dsu are only used for bandwidth allocation like the ptcl provides us 10mb dsl, 4mb and other different bandwidth options is only because of CSU/DSU.

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YuckTheFankees

From my CCENT studies, here are my notes regarding CSU/DSU: it connects the router to a T1 WAN connection that converts WAN signals into signals that the LAN can understand

jash.exe

Thanks for the answer bro.
What does the clock rate thing do in this process? any idea?

Teachers are keep telling me that it synchronizes DTE and DCE devices, I know what DTE and DCE is in clock rate, But what exactly means that is synchronizes?
According to them it is just bandwidth allocation process, like if you are an ISP and you want to provide a customer 2MB connection only, then you will use the clockrate accordingly, I am sure this is not only what DSU /CSU do, or may be this is a small part of its functionality.

Also if some CCIE student can help us with perfect answer, This would help me and other users having the same question, I am sure there are more than 80% ccna / ccent students to whom this is not clear and they also donot ask this question from instructors.

YuckTheFankees

Have you started to lab yet?

jash.exe

lab, mmm i am not sure what kinda lab, I have used basic configuration of routers switches, two routers connection using serial, serial dte and ethernet cables, I have setup clockrate on one router while using serial clock cable. everything works fine. We have not yet used csu/dsu devices, I have idea how they look like, but not yet used.

YuckTheFankees

I was having a hard time with the same things you are right now but then I started to lab. Everything begins to make sense when you're actually using the commands to set the clock rate for the device that is connceted to the DCE cable. You can use the command "show controllers" to see if the router is connected to the DCE or DTE cable, if it's the DCE cable then use the command "clock rate 64000" (example) to set the clock rate.

Edit: The clock rate defines the speed of the link, which is supplied by your telco just like you said.

jash.exe

yeah I have done that, but still have no idea what exactly this clock rate is doing, like if we use command "enable password cisco" we know that we are enabling password for configuration mode. But what does it means that we are setting up clock rates for two routers to communicate with each other, why clockrate, what exactly is the process that clock rate works with?

YuckTheFankees

The clock rate serves to synchronize the receiver on the other side of the link. Meaning the DCE device is letting the DTE device know what the speed of the link is.

fadhil

jash.exe wrote: »

Hi, I am having a bit confusion in a topic, What exactly is the function of CSU / DSU Device?

I am answered with different answers from my friends, teachers and google, all answers are different,

For now what I have studied from answers.com and wikipedia is that CSU/DSU is a modem like device used to connect in-house network to dedicated internet (T1, E1 etc) while teachers are focusing on bandwidth allocation, that csu/dsu are only used for bandwidth allocation like the ptcl provides us 10mb dsl, 4mb and other different bandwidth options is only because of CSU/DSU.

CSU/DSU device is the translating device that prepares data for transmission across the service provider network. it is like modem and place into a customer area connected directly to a service provider.
the function of CSU manages control functions while of DSU converts data.

TheShadow

jash.exe wrote: »

yeah I have done that, but still have no idea what exactly this clock rate is doing, like if we use command "enable password cisco" we know that we are enabling password for configuration mode. But what does it means that we are setting up clock rates for two routers to communicate with each other, why clockrate, what exactly is the process that clock rate works with?

Don't read too much into it my friend. Long ago clock rate was called Bit time, in other words it was simply a voltage pulse that said expect to send or receive a bit during this pulse time. There were two types of communication in early telecommunication ASYNChronous and SYNChronous which used to this day terms from telegraphy. Mark and Space which indicated an ink pen marking or not marking on a roll of paper.

An async line sending no bit information was in a marking state as a simple check to make sure the telegraph lines had not been cut. Bits going down the line were a series of marks and spaces on paper or voltage and no voltage. To speed up transmission eliminating two or three bits per character i.e. start and stop bits, along came synchronous transmission which now required a clock at a specific speed to tell each end when bits were valid. So each end of the transmission knows how many bits to expect per second and when to expect them. The ASCII syn character is used to indicate the lack of useful characters during transmission which now gives us syn flood hacking on the net. New persons normally figure out the true use of clock when trying to get their terminal program to talk to a router the first time i.e. crazy characters which make no sense.