ZyXEL Communications XGS4700 Series, Manual

Page: 217 / 485

XGS4700-48F User’s Guide
217
C
H A P T E R
2 2
Queuing Method
This chapter introduces the queuing methods supported.
22.1 Queuing Method Overview
Queuing is used to help solve performance degradation when there is network
congestion. Use the Queuing Method screen to configure queuing algorithms for
outgoing traffic. See also Priority Queue Assignment in Switch Setup and
802.1p Priority in Port Setup for related information.
Queuing algorithms allow switches to maintain separate queues for packets from
each individual source or flow and prevent a source from monopolizing the
bandwidth.
22.1.1 Strictly Priority
Strictly Priority (SP) services queues based on priority only. As traffic comes into
the Switch, traffic on the highest priority queue, Q7 is transmitted first. When that
queue empties, traffic on the next highest-priority queue, Q6 is transmitted until
Q6 empties, and then traffic is transmitted on Q5 and so on. If higher priority
queues never empty, then traffic on lower priority queues never gets sent. SP
does not automatically adapt to changing network requirements.
22.1.2 Weighted Fair Queuing
Weighted Fair Queuing is used to guarantee each queue's minimum bandwidth
based on its bandwidth weight (the number you configure in the Weight field)
when there is traffic congestion. WFQ is activated only when a port has more
traffic than it can handle. Queues with larger weights get more guaranteed
bandwidth than queues with smaller weights. By default, the weight for Q0 is 1,
for Q1 is 2, for Q2 is 3, and so on.
The weights range from 1 to 15 and the actual guaranteed bandwidth is calculated
as follows: