Estimating Maximum Jitter; Buffer Size - Cisco DS-X9530-SF1-K9 - Supervisor-1 Module - Control Processor Configuration Manual

Chapter 33 Configuring FCIP
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m .
We recommend that this feature remain enabled to realize optimal performance. Increasing the CWM
Tip
burst size can result in more packet drops in the IP network, impacting TCP performance. Only if the IP
network has sufficient buffering, try increasing the CWM burst size beyond the default to achieve lower
transmit latency.
To change the CWM defaults, follow these steps:
Command
Step 1
switch(config-profile)# no tcp cwm
switch(config-profile)# tcp cwm
switch(config-profile)# tcp cwm burstsize 30
switch(config-profile)# no tcp cwm burstsize
25

Estimating Maximum Jitter

Jitter is defined as a variation in the delay of received packets. At the sending side, packets are sent in a
continuous stream with the packets spaced evenly apart. Due to network congestion, improper queuing,
or configuration errors, this steady stream can become lumpy, or the delay between each packet can vary
instead of remaining constant.
You can configure the maximum estimated jitter in microseconds by the packet sender. The estimated
variation should not include network queuing delay. By default, this parameter is enabled in Cisco MDS
switches when IPS modules or MPS-14/2 modules are present.
The default value is 1000 microseconds for FCIP interfaces.
Note The default value for FCIP interfaces is 1000 microseconds.
To configure the maximum jitter value, follow these steps:
Command
Step 1
switch(config-profile)# no tcp max-jitter
switch(config-profile)# tcp max-jitter
switch(config-profile)# tcp max-jitter 300
switch(config-profile)# no tcp max-jitter 2500

Buffer Size

You can define the required additional buffering—beyond the normal send window size —that TCP
allows before flow controlling the switch's egress path for the FCIP interface. The default FCIP buffer
size is 0 KB.
OL-6973-03, Cisco MDS SAN-OS Release 2.x
Advanced FCIP Profile Configuration
Purpose
Disables congestion monitoring.
Enables congestion monitoring and sets the
burst size to its default size.
Changes the burst size to 30 KB. The valid
range is from 10 to 100 KB.
Leaves the CWM feature in an enabled state but
changes the burst size to its factory default.
Purpose
Disables delay jitter estimation.
Enables the delay jitter feature and sets the time
to its factory default.
Changes the time to 300 microseconds. The
valid range is from 0 to 10000 microseconds.
Leaves the delay jitter feature in an enabled
state but changes the time to its factory default.
Cisco MDS 9000 Family Configuration Guide
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