Frame Relay

[Ash!]

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.Remember 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 ?

Cheers