Classes Of Service - EMC Connectrix EC-1200 Planning Manual

Fibre Channel Switching Concepts
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Classes of Service

The two classes of service typically used in the storage area network
environment are Class 2 and Class 3. Class 2 provides acknowledged
connectionless service and Class 3 provides unacknowledged
connectionless service.
For devices using Class 2 service, there is also a higher-level N_Port
login process where the end ports establish a session and determine
the flow control rules to be used between them.
The current HBA/driver solutions use Class 3.
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