3Com 3824 Implementation Guide - Page 49
Traffic Classification, traffic, for example, a telephone conversation from Web surfing
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How Traffic Prioritization Works 49 Traffic prioritization in your Switch may be applied dependent upon following factor: ■ The level of service requested by an end-station - the transmitting end-station sets the priority of each stream of traffic. Received traffic at the Switch is forwarded through the appropriate queue depending on its priority level for onward transmission across the network. A QoS network can differentiate between time critical data, business critical data and opportunistic data (such as email, File Transfer Protocol (FTP) and Web traffic). A QoS network also has the ability to stop unauthorized usage of the network, such as online gaming. To achieve quality of service the Switch will use four processes: ■ Traffic Classification - a QoS network examines the traffic to identify which application or device generated the traffic. ■ Traffic Marking - after traffic is identified, it is Marked so that other network devices can identify the data and give it the correct level of service. ■ Traffic Re-marking - if a traffic packet enters the Switch with a priority marking requesting an unacceptable level of service, the Switch can Re-mark it with a different priority value to downgrade its level of service. ■ Traffic Prioritization - once the network can differentiate types of traffic, for example, a telephone conversation from Web surfing, prioritization can ensure that a large download from the Internet does not disrupt the telephone conversation. The Switch is configured to handle priority tagged packets and NBX phone traffic. Traffic Classification To determine the service level to be applied to each incoming traffic type, each packet or frame must first be classified. Traffic classification is the means of identifying which application, device or user generated the traffic. The Switch employs several methods of classifying (identifying) traffic. These can be based on any combination of fields in the first 64 bytes of the packet, and at different levels of the 7 layer OSI model as shown in Table 5.