Tuning Your Switch Performance (Layer 2 & Layer 3)

Table 13-2.Buffer Detailed Configuration Parameters (Continued)

Parameter

Definition

 

 

High Priority

Percent of the buffer’s queueing space allotted to high priority

Allocation

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

Determines how many times the high priority queue is serviced

Service Ratio

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

Number of packets dropped because the associated buffer is full.

Overflow Drops

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

Number of packets dropped because they timed out waiting for

Stale Drops

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.

 

 

6.To manage your Physical Port buffers, repeat Steps 1-4to 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.

13-4

Cajun P550/P220 Switch Operation Guide