A router is connected to an HDLC circuit via a T1 physical interface. The SLA for this link only allows for a sustained rate of 768 kb/s. Bursts are allowed for up to 30 seconds at up to line rate, with a window Tc of 125 ms. What should the Bc and Be setting be when using generic traffic shaping?
A.
Be = 46320000 , Bc = 96000
B.
Be = ,768000 Bc = 32000
C.
Be = ,128000 Bc = 7680
D.
Be = ,0 Bc = 96000
Explanation:
From the formula Tc=Bc/CIR => Bc = Tc * CIR = 125ms * 768kb/s = 96000 bits
(In fact you should calculate with the default units, that is 0.125s * 768000b/s)
The T1 speed is 1.544 Mbps = 1544000bps. Bursts are allowed for up to 30 seconds at up to line rate ->Be = 1544000bps * 30 = 46320000 bits.
Terminologies: The term CIR refers to the traffic rate for a VC based on a business contract.
Tc is a static time interval, set by the shaper.
Committed burst (Bc) is the number of bits that can be sent in each Tc.
Be is the excess burst size, in bits. This is the number of bits beyond Bc that can be sent after a period of inactivity.