Frame Relay Traffic Shapping

From: spycharlies@hotmail.com
Date: Fri Jul 14 2006 - 01:17:59 ART

Hey Guys, i came across this question in one of the workbooks(IEWB), i totally have no idea on how the Bc was calculated.

R1,R2 & R3's serial interface connects to the frame cloud

R1 supports maximum transmission rate of 896kbps
R2 -> max. of 640kbps
R3 -> max. of 1536kpbs

Task
-----
Configure Frame Relay traffic shaping on these devices to allow
the highest possible average rate without any circuit becoming overwhelmed.

R1 & R3 shld be able to transmit a max of 3584 bytes per shaping interval
on the circuit btw them, while R2 & R3 shld be able to transmit a max of 2560 bytes.

Here is the solution
---------------------
R1:
map-class frame-relay 896Kbps
frame-relay cir 896000
frame-relay bc 28672
!
interface Serial0/0
frame-relay class 896Kbps
frame-relay traffic-shaping

R2: 

----
map-class frame-relay 640Kbps
frame-relay cir 640000
frame-relay bc 20480
!
interface Serial0/0
frame-relay class 640Kbps
frame-relay traffic-shaping

R3:
----
map-class frame-relay 640Kbps
frame-relay cir 640000
frame-relay bc 20480
!
map-class frame-relay 896Kbps
frame-relay cir 896000
frame-relay bc 28672
!
interface Serial1/0
frame-relay traffic-shaping
frame-relay interface-dlci 301
class 896Kbps
frame-relay interface-dlci 302
class 640Kbps

Any hints on how the Bc was calculated????

thanks in advance

cheers
uyota

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