Lucent Technologies P550 - Manual (Page 240)

Tuning Your Switch Performance (Layer 2 & Layer 3)
13 -4 Cajun P550/P220 Switch Operation Guide
6. To manage your Physical Port buffers, repeat Steps 1-4 to tune Physical Port (Fast
Ethernet) buffers. Physical Port ports have additional buffers on both the input and
output ports.
7. Click APPLY to save your changes, or CANCEL to restore previous settings.
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 you want the
high priority queue to guarantee delivery of as many packets as
possible, regardless of delay, increase this value. 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 Cajun P550 switch
starts sending packets
to the high-priority queue. The default value (4) causes all
traffic with a priority greater than or equal to 4 (4, 5, 6, and 7)
to be assigned to the high-priority queue. Lucent recommends
that you do not change this parameter.
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.
Table 13-2. Buffer Detailed Configuration Parameters (Continued)
Parameter Definition