ZyXEL Communications Prestige 791R, User Manual

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Prestige 791R G.SHDSL Router
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.
If the PCR, SCR or MBS is set to the default of “0”, the system will assign a
maximum value that correlates to your upstream line rate.
The following figure illustrates the relationship between PCR, SCR and MBS.
Figure 7-1 Example of Traffic Shaping
7-4 Internet Access