Without classification all packets are treated the same

Classification is the process of identifying traffic and categorizing that traffic into different classes. Packet classification uses a traffic descriptor to categorize a packet within a specific group in order to define that packet. Typically used traffic descriptors include class of service (CoS), incoming interface, IP precedence, differentiated services code point (DSCP), source or destination address, application, and Multiprotocol Label Switching (MPLS) Experimental Bits (EXP). After the packet has been defined (that is, classified), the packet is then accessible for QoS handling on the network.

Using packet classification, you can partition network traffic into multiple priority levels or classes of service. When traffic descriptors are used to classify traffic, the source agrees to adhere to the contracted terms and the network promises a QoS. Different QoS mechanisms, such as traffic policing, traffic shaping, and queuing techniques use the traffic descriptor of the packet (that is, the classification of the packet) to ensure adherence to that agreement.

Classification should take place at the network edge, typically in the wiring closet, within IP Phones or at network endpoints. It is recommended that classification occur as close to the source of the traffic as possible.

This topic describes the purpose of packet marking.

This topic describes the purpose of packet marking.

Marking is related to classification. Marking allows network devices to classify a packet or frame based on a specific traffic descriptor. Typically used traffic descriptors include CoS, DSCP, IP precedence, QoS group, and MPLS experimental bits. Marking can be used to set information in the Layer 2 or Layer 3 packet headers.

Marking a packet or frame with its classification allows network devices to easily distinguish the marked packet or frame as belonging to a specific class. After the packets or frames are identified as belonging to a specific class, QoS mechanisms can be uniformly applied to ensure compliance with administrative QoS policies.

This topic describes IP packet classification and marking options that are available at the datalink layer.

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