Configuring Csctl - Brocade Communications Systems StoreFabric SN6500B Administrator's Manual

5

Configuring CSCTL

Configuring CSCTL

Unlike QoS Zone-based FC flow prioritization method, CSCTL enables the same SID/DID pair
exchange frames with different priorities.
To be able to prioritize a frame flow between two end nodes, Fabric OS v7.0.0 and later provide
support for up to 32 Virtual Channels (VCs) per port. This categorizes the frames entering into a
fabric on the basis of preset behavior defined with these VCs, and conserves the frame's behavior
until it is transmitted out of fabric. However, out of the 32 VCs for each external port, only 16 are
used.
With the CSCTL method of prioritization, there is no need to have explicit traffic segregation, such
as QOS_H, QOS_M and QOS_L. The classification is entirely based upon CSCTL database
programmed into the ASIC. As the name suggests, CSCTL bits in each frame are used to define the
VC number on the transmit port.
In order to achieve this kind of classification, Fabric OS v7.0.0 and later provides a CSCTL database
table on each chip, capable of storing 256 entries. Each entry in the database table is populated
with a VC number which, if this feature is enabled, is retrieved by indexing the CSCTL value into the
table for each frame entering the fabric.
Irrespective of the type of frame classification method used, the flow priority of a frame is primarily
determined by the VC number used to transmit the frames across the ISL ports. In both methods of
classification, the VC number for a frame is determined at the ingress Fabric port or Fabric Loop
port (F/FL), when the frame enters the fabric for the very first time. To maintain the same flow
priority for a frame across all the ISL hops in a fabric, the same VC number is used while
transmitting the frame at the egress E_Port until it is out of the fabric thru a F/FL port. The main
difference between QoS Zone method of classification and CSCTL VC based method of
classification is how the VC number is computed when the frame enters into the fabric thru an F/FL
port and, of course, the manner of setting up these two frame classification methods.
Once the CSCTL mode is enabled on an F/FL port in a switch, the CSCTL value in the frame header
of all the incoming frames on that F/FL port are used to index into the ASIC's CSCTL database table
to compute the VC number, which will define the frame's flow priority throughout its life in the fabric
until it exits out of the fabric thru another F/FL port. The QoS links (ISLs) preserve this classification
during frame's traversal across all the hops in the fabric.
NOTE
When CSCTL mode and QOS zones are enabled, QoS zones lose priority to CSCTL mode.
To enable CSCTL mode, perform the following steps.
1. Select the Port Admin tab.
2. Select View > Advanced mode.
3. Select the F_Ports to configure.
4. Select Enable from the CSCTL drop-down button.
To disable CSCTL mode, perform the following steps.
1. Select the Port Admin tab.
2. Select View > Advanced mode.
3. Select the F_Ports to configure.
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