ZyXEL Communications GS-4012F, User Manual

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GS-4012F User’s Guide
Chapter 20 Queuing Method 131
C
H A P T E R
20
Queuing Method
This chapter introduces the queuing methods supported.
20.1 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.
The switch has eight physical queues, Q0 to Q7. Q7 has the highest priority and Q0 has the
lowest.
20.1.1 Strict Priority Queuing (SPQ)
Strict Priority Queuing (SPQ) services queues based on priority only. As traffic comes into the
switch, traffic on the highest priority queue, Q3 is transmitted first. When that queue empties,
traffic on the next highest-priority queue, Q2 is transmitted until Q2 empties, and then traffic
is transmitted on Q1 and so on. If higher priority queues never empty, then traffic on lower
priority queues never gets sent. SPQ does not automatically adapt to changing network
requirements.
Table 40 Physical Queue Priority
QUEUE PRIORITY
Q7 8 (Highest)
Q6 7
Q5 6
Q4 5
Q3 4
Q2 3
Q1 2
Q0 1 (Lowest)