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Official Lammle User Forum

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  1. #1
    Join Date
    Dec 2008
    Posts
    88

    Default CSU/DSU and DCE Quesion

    Hey everyone,

    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. I am a little confused in how that differs from a DCE. I am not really sure on what a DCE is. I understand from Page 30 of Lammle 6th Ed that the DCE is usually located at the service provider. I have researched it online and to me is sounds very similar to a CSU/DSU.

    Wikipedia says: A Data circuit-terminating equipment (DCE) is a device that sits between the data terminal equipment (DTE) and a transmission circuit.
    It also says that the DCE is a modem.

    I though it was the CSU/DSU that sits between the DTE and Transmission Circuit, and I thought the CSU/DSU was the modem.

    This has been really confusing...

    Any help would be appreciated.

    Thank you.
    Last edited by typesh; 12-27-2008 at 10:59 PM.

  2. #2
    Join Date
    Mar 2008
    Location
    Winston Salem, NC
    Posts
    432

    Default

    Yep, a DCE provides clocking, and the CSU/DSU also provides the clocking.... The service providers DCE is usually the CSU/DSU...

    In the enterprise over here, they have their routers (DTE) connected to the jack, which is the Demarc point, and the Service providers CSU/DSU provides the clocking rate and ect, so the DTE device.
    Cisco---------------------- CompTIA
    -CCNA ----------------------Security +
    -CCNP (BSCI,BCMSN,ISC W)

  3. #3
    Join Date
    Dec 2008
    Posts
    88

    Default

    Thank you! This has been really confusing...

    If I understand correctly....

    The router (DTE) connects to a CSU/DSU which actually is the DCE?

    So, would it be correct to say a CSU/DSU is the DCE, and that they both can be referred to as a modem?

  4. #4
    Join Date
    Mar 2008
    Location
    Winston Salem, NC
    Posts
    432

    Default

    yep,, thats why in lab environments, you have to have one router the DCE which provides the clocking , which is basically substituting the CSU/DSU
    Cisco---------------------- CompTIA
    -CCNA ----------------------Security +
    -CCNP (BSCI,BCMSN,ISC W)

  5. #5
    Join Date
    Dec 2008
    Posts
    88

    Default

    Sounds good! It makes sense now.

    Just wanted to clarify the word "clocking."

    Does clocking tell the DTE how many bits to send and receive per second?

    For example:

    When using the "clock rate ?" command, are we telling the DTE how many bits per second to send, or to receive?

  6. #6
    Join Date
    Nov 2007
    Location
    Dortmund, Germany
    Posts
    554

    Default

    Quote Originally Posted by typesh View Post
    [...]

    When using the "clock rate ?" command, are we telling the DTE how many bits per second to send, or to receive?
    Hello,
    always remember: DCE => Do Clock Enable

    You have to set the clock rate on the DCE end. Usually only in a lab, where else you have to take care of the DCE equipment?!
    Bye, Tore

  7. #7
    Join Date
    Dec 2008
    Posts
    88

    Default

    If i set the clock on the DCE Router like this:

    clock rate 64000

    Is that telling the DCE how many bits per second to send/receive?

  8. #8
    Join Date
    Mar 2008
    Location
    Winston Salem, NC
    Posts
    432

    Default

    From my conception yes, the clock rate is basically the CIR, if running frame-relay, that the SP provides to you...

    but yep 64000 = 64kps
    Cisco---------------------- CompTIA
    -CCNA ----------------------Security +
    -CCNP (BSCI,BCMSN,ISC W)

  9. #9
    Join Date
    Dec 2008
    Posts
    88

    Default

    Thanks guys!

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