Priority queuing (PQ) can give strict priority to latency-sensitive applications (for example, e-commerce applications). PQ gives priority to specific packets by placing those packets in a high-priority queue. Other packets are placed in a medium, normal, or low queue. However, if any packets are in the high queue, none of the packets in lower-priority queues are sent.
Similarly, when packets are in the medium queue, no packets are sent from the normal or low queues. Although this approach does accomplish the goal of giving priority to specific traffic, it can lead to protocol starvation.
- Legacy priority queueing uses four queues (high, medium, normal and low), which gets serviced from high-to-low.
- PQ is prone to starvation.
- The queueing strategy will be 'priority-list' as listed with "show interface" command.
- Similar to custom queueing, the 'gt', 'lt' and 'fragments' keywords are also available.
Router(config)# priority-list 1 protocol ip high tcp www
Router(config)# priority-list 1 protocol ip medium tcp telnet
Router(config)# priority-list 1 default low
!
Router(config)# interface serial 0/1
Router(config-if)# priority-group 1
Router(config-if)# ip rtp priority starting-udp-port
port-number-range bandwidth
The port-number-range is not the last port number in the range. Rather, it is the number of ports in the range. For example, the following command specifies that 64 kbps of bandwidth should be made available for packets using UDP ports in the range 16,384 through 32,767:
Router(config-if)# ip rtp priority 16384 16383 64
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