Appendix A Quality of Service

Configure the following parameters:

Tx Bandwidth - Tx bandwidth limits the Router’s bandwidth transmission rate. The purpose is to limit the bandwidth of the WAN device to that of the weak- est outbound link.. This forces the Router to be the network bottleneck, where sophisticated QoS prioritization can be performed.

Rx Bandwidth - In the same manner, this Rx bandwidth limits the Router’s bandwidth reception rate.

TCP Serialization - Enable TCP Serialization from its drop-down list, either for active voice calls only or for all traffic. The screen will refresh, adding a “Maximum Delay” text box. This function allows the maximum allowed trans- mission time frame (in milliseconds) of a single packet to be defined. Any packet requiring a longer time to be transmitted will be fragmented to smaller sections. This avoids transmission of large, bursty packets that can cause delay or jitter for real-time traffic, such as VoIP.

Shaping Classes

The bandwidth of a device can be divided to reserve constant portions of band- width to predefined traffic types. Such a portion is known as a shaping class. When not used by its predefined traffic type or owner (for example VoIP), the class will be available to all other traffic. However, when needed, the entire class is reserved solely for its owner. Also, the maximum bandwidth that a class uses can be limited, even if the entire bandwidth is available.

When a shaping class is defined for a specific traffic type, two shaping classes are created. The second class is the “Default Class”, which is responsible for all the packets that do not match the defined shaping class, or any other classes that might be defined on the device. This can be viewed in the “Class Statistics” screen.

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