In order to ensure the most efficient data transmission possible for the different types of traffic, Fibre Channel (FC) distinguishes between six different service classes for data transmission between end devices, of which, however, only some are implemented in products.
The Class 1 service (Dedicated Service) is a connection-oriented, receiptless service between two node ports. The Class 1 connection is dedicated between two ports and provides full bandwidth to the user. The transmission is acknowledgmentless. The connection cannot be used for other purposes.
Class 2 (Multiplex Service) is a connectionless service that works with datagrams and multiplexes the frames from one or more N_Ports or NL ports. This service operates with acknowledgement mechanisms and end-to-end flow control.3(Datagram Service) is comparable to Class 2, but operates without acknowledgement according to the best-effort principle with link flow control.
Class 4(Virtual Circuit Fractional Bandwidth) is a connection-oriented service with bandwidth allocation. Only part of the available bandwidth is used for transmission. The remaining bandwidth can be used for other purposes. Class 4 service requires maximum time to transfer the data packets between sender and receiver.
Class 6 is a connection-oriented service for multicast services. This service class supports unidirectional multicast connections.