Traffic Classifiers and Traffic Behaviors
Traffic Classifiers
Traffic classification technology allows a device to classify packets that enter a DiffServ domain in order for the device to identify the packet service type and to apply any appropriate action upon the packet.
Traffic Classification Techniques
Packets can be classified based on QoS priorities (for details, see sectionQoS Priority Fields), or packet information such as the source IP address, destination IP address, MAC address, IP protocol, and port number, or specifications in an SLA. Therefore, traffic classification can be classified as behavior aggregate classification or multi-field classification. For details, see section BA Classification and MF Classification.
After packets are classified at the DiffServ domain edge, internal nodes provide differentiated services for classified packets. A downstream node can accept and continue the upstream classification or classify packets based on its own criteria.
Traffic Behaviors
A traffic classifier is configured to provide differentiated services and must be associated with a certain traffic control or resource allocation behavior, which is called a traffic behavior.
The following table describes traffic behaviors that can be implemented individually or jointly for classified packets on a NE20E.
| Traffic Behavior | Description | |
|---|---|---|
| Marking/Re- marking | External marking | Sets or modifies the priority of packets to relay QoS information to the next device. |
| Internal marking | Sets the class of service (CoS) and drop precedence of packets for internal processing on a device so that packets can be placed directly in specific queues. Setting the drop precedence of packets is also called coloring packets. When traffic congestion occurs, packets in the same queue are provided with differentiated buffer services based on colors. |
|
Traffic policing |
Restricts the traffic rate to a specific value. When traffic exceeds the specified rate, excess traffic is dropped. |
|
Congestion management |
Places packets in queues for buffering. When traffic congestion occurs, the device determines the forwarding order based on a specific scheduling algorithm and performs traffic shaping for outgoing traffic to meet users' requirements on the network performance. |
|
Congestion avoidance |
Monitors network resources. When network congestion intensifies, the device drops packets to prevent overloading the network. |
|
Packet filtering |
Functions as the basic traffic control method. The device determines whether to drop or forward packets based on traffic classification results. |
|
Policy-based routing (also called redirection) |
Determines whether packets will be dropped or forwarded based on the following policies:
|
|
Load balancing |
Load balancing is configured to be session-by-session or packet-by-packet. Load balancing applies only to packets that have multiple forwarding paths available. There are two possible scenarios:
|
|
Packet fragmentation |
Modifies the Don't Fragment (DF) field of packets. NOTE:
Some packets sent from user terminals are 1500 bytes long.
PCs generally set the DF value to 1 in the packets. When packets traverse
network devices at various layers, such as the access, aggregation,
or core network layer, additional information is added so that the
packet length will exceed the maximum transmission unit (MTU) of 1500
bytes. If such a packet carries the DF value of 1 in the header, the
packet will be dropped. A DF value of 1 specifies that a datagram
not be fragmented in transit. To prevent such packet loss and to keep
users unaware of any change, the device involved is allowed to set
the DF field in an IP header. |
|
Flow mirroring |
Allows a device to copy an original packet from a mirrored port and to send the copy to the observing port. |
|
Flow sampling |
Collects information about specific data flow, such as timestamps, source address, destination address, source port number, destination port number, ToS value, protocol number, packet length, and inbound interface information, to intercept specific users. |
|
Modifying the TTL value |
Modifies the Time To Live (TTL) value of IP packet headers. |
|
