3. Advanced Functions
To help a better understanding about the software management interfaces, this chapter describes some advanced functions provided by the switch.
3.1 QoS Function
The switch provides a powerful Quality of Service (QoS) function to guide the packet forwarding in two priority levels. The versatile classification methods can meet most of the application needs. The following figure illustrates the QoS operation flow when a packet received on the input port until it is transmitted out from the output port:
3.1.1 Priority Level
Each output (egress) port in the switch is equipped with two transmission priority queues to store the packets for transmission. The high priority queue stores the high priority packets and low priority queue stores the low priority packets.
3.1.2 Egress Service Policy
The packets in high priority queue and low priority queue are transmitted out from a port based on a user configured round robin ratio, called egress service policy between high priority queue and low priority queue. The switch provides four ratio options for the service policy:
•[ 4:1 ] : 4 high priority packets then 1 low priority packet
•[ 8:1 ] : 8 high priority packets then 1 low priority packet
•[ 16 :1 ] : 16 high priority packets then 1 low priority packet
•[Always high priority first] : Packets in high priority queue are sent first until the queue is empty
3.1.3 Packet Priority Classification
Each received packet is determined and classified into one of two priority levels, high priority and low priority upon reception. The switch provides many classification methods including:
•Port based
•802.1p based
•IP DSCP based
•IP network address based
They all can be configured to be activated or not. Some are per port configuration and some are global configuration for the switch. More than one classification method can be enabled at the same time. If a packet is classified as high priority in any one of the enabled (applied) classifications, the packet is forwarded to the high priority queue of the output port. Otherwise, it is classified as low priority.
