The methodology with which the communication circuit is allocated and retained between the communicating N_Ports and by the level of delivery integrity required for an application.
Class of service (established during login)
Class 1: Dedicated Connection
Full bandwidth allocated, in-order delivery guaranteed
Class 2: Multiplex
More like a LAN: connectionless transmission, dropped frames okay but get a notification.
Class 3: Datagram
Similar to class 2 but no notification
Class 4: Fractional
Establishes a bandwidth-limited Virtual Circuit (VC) path across the fabric.
Class 6: Multicast
Multicast capabilities
Note : Classes 1, 2, and 3 may be supported with any of the three topologies. Classes 4 and 6 are only supported with the Fabric topology.
Class 3 : Datagram
- Provides connection-less service without any notification of non-delivery (BSY or RJT), delivery (ACK), or end-to-end flow control between two communicating Nx_Ports.
- Allows one Nx_Port to transmit consecutive frames to multiple destinations without establishing a dedicated connection with any specific Nx_Port.
- The Fabric, if present, and the destination Nx_Port are allowed to discard Class 3 frames without any notification to the transmitting Nx_Port.
- Allows one Nx_Port to receive consecutive frames from one or more Nx_Ports without having established dedicated connections.
- Class 3 service is requested by an Nx_Port on a frame by frame basis.
- The Fabric, if present, routes the frame to the destination Nx_Port.
- Nx_Port supporting Class 3 service is required to have logged in with the Fabric or the Nx_Ports.
- F_Port exercises buffer-to buffer flow control with the Nx_Port.
- R_RDY is used for buffer-to-buffer flow control.
- If the Fabric is unable to deliver the frame to the destination Nx_Port, the frame is discarded and the source is not notified.
- If the destination Nx_Port is unable to receive the frame, the frame is discarded and the source is not notified.
- End-to-end Credit is not used.
