ZyXEL Communications P-2602HWLNI, Руководство пользователя, Страница: 104 / 496

Chapter 7 WAN Setup
P-2602HWLNI User’s Guide
104
For example, if the normal route has a metric of "1" and the traffic-redirect route has a metric
of "2" and dial-backup route has a metric of "3", 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. In the same manner, the ZyXEL Device uses the dial-backup route
if the traffic-redirect route also fails.
If you want the dial-backup route to take first priority over the traffic-redirect route or even the
normal route, all you need to do is set the dial-backup route’s metric to "1" and the others to
"2" (or greater).
IP Policy Routing overrides the default routing behavior and takes priority over all of the
routes mentioned above.
7.3 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 49 Example of Traffic Shaping