Cajun P220G, Configuration And Operation Manual

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Managing Buffers and Queues
Cajun P220G Switch Configuration and Operation Guide 4-5
Table 4-1. Fabric Port Information
Memory The amount of physical memory associated with this buffer.
Age Timer The amount of time a packet remains in the queue before being
discarded as a stale packet. You may want to increase the timer
value for ports connected to 10 Mb/s ports, particularly 10 Mb/s
shared media, because you may want to queue packets longer
before discarding them.
High Priority
Allocation Percent of the buffer’s queueing space allotted to high priority
traffic. Because the high-priority queue is serviced more
frequently than the normal priority queue, raising this value
may not necessarily provide better service. In fact, if you are
using the high-priority queue for delay-sensitive traffic, you
may want to reduce the amount of memory devoted to the
high-priority queue. This ensures that packets that cannot be
delivered in a timely manner are discarded. If instead you want
the high priority queue to guarantee delivery of as many
packets as possible, regardless of delay, increase this value.
Note:
The change does not take effect until you reset
the switch.
Priority Threshold Some priority schemes have more than two queues (the IEEE
allows up to 8, numbered 0 through 7). Set this parameter to
the value at which the P220G switch starts sending packets to
the high-priority queue. The default value (4) causes all traffic
with a priority greater than 4 (5, 6, and 7) to be assigned to the
high-priority queue.
High Priority
Service Ratio Determines how many times the high priority queue is serviced
for each time the low priority queue is serviced. The ideal value
changes from queue to queue, but the goal is to ensure that
traffic mix guarantees optimal mix between high-priority and
best effort traffic.
High and Normal
Overflow Drops Number of packets dropped because the associated buffer is full.
Indicates that the device immediately before the queue is
processing traffic faster than the next downstream element can
process the same volume of traffic. For example, overflow drops
on the input buffer indicate that traffic is arriving faster than the
switch matrix can process it. Overflow drops on the output
buffers indicates that the output port cannot handle the volume
of the load being offered.
High and Normal
Stale Drops Number of packets dropped because they timed out waiting for
service (using the age timer value). In the high-priority queue,
this can help determine how efficiently the switch is processing
“better never than late” traffic. Excessive stale drops on the
high-priority queue may indicate the need to increase the
service ratio on the high-priority queue.
Congestion Drops Number of packets dropped because the switch controller has
sensed congestion at the outbound port.