Atlantis Land 111U User Manual

Page 45

7.4 Traffic Shaping

Traffic Shaping is an agreement between the carrier and the subscriber to regulate the

average rate and “burstiness” or fluctuation of data transmission over an ATM

network. This agreement helps eliminate congestion, which is important for

transmission of real time data such as audio and video connections.

Peak Cell Rate (PCR) is the maximum rate at which the sender can send cells. This

parameter may be lower (but not higher) than the maximum line speed. 1 ATM cell is

53 bytes (424 bits), so a maximum speed of 832 Kbps gives a maximum PCR of 1962

cells/sec. This rate is not guaranteed because it is dependent on the line speed.

Sustained Cell Rate (SCR) is the mean cell rate of a bursty, on-off traffic source that

can be sent at the peak rate, and a parameter for burst-type traffic. SCR may not be

greater than the PCR; the system default is 0 cells/sec.

Maximum Burst Size (MBS) is the maximum number of cells that can be sent at the

PCR. After MBS is reached, cell rates fall below SCR until cell rate averages to the SCR

again. At this time, more cells (up to the MBS) can be sent at the PCR again.The

following figure illustrates the relationship between PCR, SCR and MBS.