Traffic Shapping in Frame Relay
Imagine you have a router connected to ISP’s network. and you are using frame relay with the following specification:
- the physical connection can support up to 256 kbps.
- Your ISP is provisioning 128 kbps in average.
- However, the ISP guarantee that the throughput will not lower than 32 kbps
- To maintain the average bandwidth, every 50 millisecond the router send Bc bits
Then we have the following graph as illustration:
(picture taken from: http://linuxbrit.co.uk)
Based on the spefication above, we have some parameter:
- CIR = 128 kbps
- MINCIR = 32 kbps
- access rate = 256 kbps
- Tc = 50 ms
ps: in above illustration and picture, the maximum traffic should be CIR. but for some case, there are some traffic that exceed the provisioning bandwidth. I can not get a good picture to ilustrate that. The thoughput which reach access rate should be spike only.
Then we can calculate Bc and Be
- Bc = Tc * Cir / 1000 = 6400
- Be = (AR – CIR) * TC / 1000 = 6400
Bc is the amount of traffic which sent during Tc period.
Be is the amount of traffic which exceed the provisioning bandwidth during Tc Period.
For some cases, Bc is zero, which mean that the CIR is the same value as access rate. this is the ideal case.
