Tc (timing interval) = Bc/CIR

Origin of Tc Time Interval:

125ms DEFAULT or 1/8 of a second
1500byte packet serialization delay (time to put it on the wire) on 64kbps line

Tc (interval) = Bc/CIR
125ms = 8000/64000

CIR * Tc = Bc

With voice 1/100 of a second or 10ms Tc, sample size of a voice packet (20ms two voice packets)

AR = Access Rate – full line speed in bps, max transmit value
CIR = Committed Information Rate – targe value for transmission, nominal transmit value
Bc = Normal burst – Equals CIR/Tc
Be = Excess burst – Equals (AR/Tc)-Bc – “These are leftovers”
Tc will vary. 1/8 sec (125ms) in data, 1/100 in voice (10ms)


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