Traffic Shaping; Figure 37 Example Of Traffic Shaping - ZyXEL Communications P-660HN FxZ Series User Manual

The metric sets the priority for the ZyXEL Device's routes to the Internet. If any two of the
default routes have the same metric, the ZyXEL Device uses the following pre-defined
priorities:
• Normal route: designated by the ISP (see
• Traffic-redirect route (see
For example, if the normal route has a metric of "1" and the traffic-redirect route has a metric
of "2", then the normal route acts as the primary default route. If the normal route fails to
connect to the Internet, the ZyXEL Device tries the traffic-redirect route next.

5.7 Traffic Shaping

Traffic Shaping is an agreement between the carrier and the subscriber to regulate the average
rate and fluctuations 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 832Kbps 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 each bursty traffic source. It specifies the
maximum average rate at which cells can be sent over the virtual connection. SCR may not be
greater than the PCR.
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 37 Example of Traffic Shaping

P-660HN-FxZ Series User's Guide
Section 5.2 on page
Section 5.8 on page 86)
Chapter 5 WAN Setup
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85