Information About Fibre Channel Interfaces; Forward Error Correction; Dynamic Bandwidth Management; Out-Of-Service Interfaces - Cisco MDS 9000 Series Configuration Manual

Configuring Fibre Channel Interfaces

Information About Fibre Channel Interfaces

Forward Error Correction

The Transmitter Training Signal (TTS) is defined in FC-FS-4(Clause 5.5). It provides the capability for FC
ports to negotiate the following two capabilities:
1. Transmitter training, which enables a receiver to send feedback to a transmitter to assist the transmitter
in adapting to the characteristics of the link that connects them.
2. FEC usage.
The TTS is not used by 4 and 8-gigabit FC ports. From 32-gigabit speed and higher, its use is mandatory. For
16-gigabit FC ports, EA variants must transmit the TTS during the link speed negotiation, but the use of it by
the receiver is optional, and EL variants must not use TTS.
Forward Error Correction (FEC) is defined in IEEE 802.3TM clause 74 and is implemented in FC without
modification. FEC is not supported on 4, 8 and 16-gigabit EL ports. Its use is optional on 16-gigabit EA ports.
The TTS is the mechanism that allows FEC negotiation on such ports.
For more information on configuring FEC and TTS, see the

Dynamic Bandwidth Management

On port switching modules where bandwidth is shared, the bandwidth available to each port within a port
group can be configured based on the port rate mode and speed configurations. Within a port group, some
ports can be configured in dedicated rate mode while others operate in shared mode.
Ports configured in dedicated rate mode are allocated the required bandwidth to sustain a line rate of traffic
at the maximum configured operating speed, and ports configured in shared mode share the available remaining
bandwidth within the port group. Bandwidth allocation among the shared mode ports is based on the operational
speed of the ports.
Unutilized bandwidth from the dedicated ports is shared among only the shared ports in a port group as per
the ratio of the configured operating speed. A port cannot be brought up unless the reserved bandwidth is
quarantined for the shared ports. For dedicated ports, configured bandwidth is taken into consideration while
calculating available bandwidth for the port group. This behavior can be changed using bandwidth fairness
by using the rate-mode bandwidth-fairness module number command.

Out-of-Service Interfaces

On supported modules and fabric switches, you might need to allocate all the shared resources for one or more
interfaces to another interface in the port group or module. You can take interfaces out of service to release
shared resources that are needed for dedicated bandwidth. When an interface is taken out of service, all shared
resources are released and made available to the other interface in the port group or module. These shared
resources include bandwidth for the shared mode port, rate mode, BB_credits, and extended BB_credits. All
shared resource configurations are returned to their default values when the interface is brought back into
service. Corresponding resources must be made available in order for the port to be successfully returned to
service.
Configuring FEC, on page 93
Cisco MDS 9000 Series Interfaces Configuration Guide, Release 8.x
Information About Fibre Channel Interfaces
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