3com 3031 Instruccion De Instalación
946
C
HAPTER
68: C
ONGESTION
M
ANAGEMENT
If there is only one FIFO-based output/input queue on router's interface, malicious
applications may occupy all network resources and seriously affect transmitting
mission-critical data.
applications may occupy all network resources and seriously affect transmitting
mission-critical data.
Within each queue the sending (sequence) of packets is defaulted as FIFO.
PQ (Priority Queuing)
Figure 234 Priority Queueing
Priority queuing is designed for mission-critical applications. Those applications
have an important feature, i.e. when congestion occurs they require preferential
service to reduce the response delay. PQ can flexibly design priority sequence
according to different network protocols (e.g. IP and IPX), interface receiving
packets, packet length, source/destination IP address etc. Priority queuing classifies
the packets into four different types: top, middle, normal and bottom in
descending order. By default, the data flow enters the normal queue.
have an important feature, i.e. when congestion occurs they require preferential
service to reduce the response delay. PQ can flexibly design priority sequence
according to different network protocols (e.g. IP and IPX), interface receiving
packets, packet length, source/destination IP address etc. Priority queuing classifies
the packets into four different types: top, middle, normal and bottom in
descending order. By default, the data flow enters the normal queue.
During queues dispatching, PQ strictly comply with the priority sequence from
high to low, and it will send packets in the high-priority queue first. When that
queue is empty PQ will begin to send packets in lower priority queue. So packets
of mission-critical application are put into higher priority queue, and packets of
normal application, into lower priority queue. It guarantees that the packets of
mission-critical application are sent with priority, and the packets of normal
application are sent at the free interval of operating mission-critical application.
high to low, and it will send packets in the high-priority queue first. When that
queue is empty PQ will begin to send packets in lower priority queue. So packets
of mission-critical application are put into higher priority queue, and packets of
normal application, into lower priority queue. It guarantees that the packets of
mission-critical application are sent with priority, and the packets of normal
application are sent at the free interval of operating mission-critical application.
The disadvantage of PQ is that packets in the lower queues will be neglected if
there are packets in the higher queues for a long time.
there are packets in the higher queues for a long time.
incoming packets
top queue
middle queue
classify
outgoing packets
normal queue
bottom queue
transmit
queue
interface
scheduler