With a leased line you bandwidth is guaranteed. If you ask for 2MB then that's what you get and your service provider has to ensure that their available bandwidth on their network is greater than the total combined maximum bandwidth of all their customers.
With frame relay the bandwidth through the frame "cloud" is contended. However, when you sign up for a frame relay circuit you agree to a CIR (Committed Information Rate). This is the rate at which you will not drop below. For example, if you ask for a 2MB line with a CIR of say 512K, then your available bandwidth might drop below 2MB if you are not using it so that other customers can make use of the bandwidth. However, it will not drop below your CIR (512K). The total bandwidth required by the service provider on their fr network is the total of all the CIR's. In practice this would be much higher, but you get the idea.
Chris.
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Chris Andrew, CCNA
chrisac@gmx.co.uk
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