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48-21
Cisco MDS 9000 Family Fabric Manager Configuration Guide
OL-17256-03, Cisco MDS NX-OS Release 4.x
Chapter 48 Configuring FCIP
Using the FCIP Wizard
• If the average rate of the Fibre Channel traffic is greater than min-available-bandwidth multiplied
by the RTT, but less than max-bandwidth multiplied by the RTT, then if the Fibre Channel traffic is
transmitted in burst sizes smaller than the configured CWM value the entire burst is sent
immediately by FCIP at the max-bandwidth rate.
• If the average rate of the Fibre Channel traffic is larger than the min-available-bandwidth multiplied
by the RTT and the burst size is greater than the CWM value, then only a part of the burst is sent
immediately. The remainder is sent with the next RTT.
The software uses standard TCP rules to increase the window beyond the one required to maintain the
min-available-bandwidth to reach the max-bandwidth.
Note The default burst size is 50 KB.
Tip We recommend that this feature remain enabled to realize optimal performance. Increasing the CWM
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.
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.
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.
Note Use the default if the FCIP traffic is passing through a high throughput WAN link. If you have a
mismatch in speed between the Fibre Channel link and the WAN link, then time stamp errors occur in
the DMA bridge. In such a situation, you can avoid time stamp errors by increasing the buffer size.
Advanced FCIP Interface Configuration
This section describes the options you can configure on an FCIP interface to establish connection to a
peer and includes the following topics:
• Configuring Peers, page 48-22
• Active Connections, page 48-25
• Number of TCP Connections, page 48-25
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