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Thread: Frame Relay

  1. #1
    Join Date
    Jul 2008

    Default Frame Relay

    Hi lammle

    One paragraph your book ( study guide 6 th ed page 801) confuses me a under heading Data link Connection Identifiers (DLCIs)

    You explain how much saving using frme relay compare to leased line.

    Let me explain suppose you have a central HQ with three branch offices.If you were to connect each branch office to HQ using T1 , you would need serial interfaces on your router at HQ, one for each T1 ( understandable).Suppose you use Frame Relay PVCs instead. You could have a T1 at each branch connected to a service provider and only a siingle TI at HQ ( Does this mean even though we use Frame relay cloud our three branche routers connected to their switches through T1 leased lines and similarly our HQ will connect its router to Frame relay switch through another leased lines T1.These are small leased lines as compare to dedicated point point three leased lines connected individually to HQ)

    There would be three PVCs on the single TI AT HQ one going to each branch.And even though there's only a single interface and a single CSU/DSU, the three PVCs function as three separate circuits.Rememb er what I said about saving money? How much for two additional T1 interfaces and a pair of CSU/DSUs? Answer : A lot

    since in first case if we use three TIs terminating at HQ there are four ,two pairs CSU/DSU ( three on each branch and on HQ).

    Please expain , how many CSU/DSU in frame relay when there are three branches and one HQ?
    And do we still use leased lines even though we use frame relay ( Branch1router ---switch , Branch2router ----swtch, Branch3router ---swtch , HQ4router ----swtch ) or in other word do our LMI connection using leased lines in this example ?

    I do not know if my question make any sense ?

    Last edited by Ash!; 10-05-2008 at 01:44 PM.

  2. #2
    Join Date
    Mar 2008
    Winston Salem, NC


    I believe, i will research this...

    But i am pretty sure.. Sine the CSU/DSU supplies the clock rate, then the the Frame -relay provider ( the FR switch is the DCE side)
    so for every curcuit the FR there will be a CSU/DSU supplying the clock,.

    one at Hq, and all the branches.

    again,, ima do some research, and come back with another post.
    Cisco---------------------- CompTIA
    -CCNA ----------------------Security +

  3. #3
    Join Date
    Dec 2006

    Default Frame Relay - very important on CCNA

    You only have one CSU/DSU at the Corp or Central site if you use FR.
    For T1 you would have a CSU/DSU for each T1.

    This why we use to use FR - to same money.

    However, we would use MPLS today.

    BUT - you need to understand your Frame Relay to pass the CCNA so read and re-read my Frame Relay section carefully and use a simulator to practice it.

    Todd Lammle

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