help needed understanding frame relay tfaffic shaping

[cormon]

Hi , Im studying for my bcran and am fine except for the concepts involved in frame relay taffic shaping .

I understand what CIR and MINCIR are but its the relationship between Bc(committed burst) and Tc(Committed Rate Measurement Interval) that I dont understand . I searched everywhere for logical expalantion (that i can understand) to no avail.

thanks in advance for your time

 

[Nazgulero]

Hello,

the best way to explain the relationship between Bc and Tc might be through an example. Basically, it all boils down to the following mathematically related values:

Bc=CIR*Tc
CIR=Bc/Tc
Tc=Bc/CIR

Let´s say you have a CIR of 256000. The default Tc is 125ms, so in this case, the Bc would be 16000. That means, 16000bps are sent every 125ms, and 8 of those intervals fit into 1 second (1000ms). The Tc determines the amount of traffic sent with every interval. Now let´s say you want to use Frame Relay Traffic Shaping for voice traffic, and you want the traffic sent with every interval to be as small as possible. You would configure the Tc as 10ms (which is the lowest value possible). With a Tc of 10ms, the Bc would be 2560. That means that 2560bps will be sent with every interval.
You might want to check this link, it has a really good explanation of how the math works:

Frame Relay Traffic Shaping

http://www.internetworkexpert.com/resources/01700368.htm

Does that make sense ?

Regards,

GP

 

[cormon]

Ya it does actually , I was using the Cisco Book for the exam and I find it falls sort on explanations sometimes . That makes it alot clearer....

thanks for taking to time to explain it