scope:

This standard specifies a) five classes of procedures when operating over the connection-mode network service; 1) class 0: simple class; 2) class 1: basic error revocery class; 3) class 2: miltiplexing class; 4) class 3: error recovery and multiplexing class; 5) class 4: error detection and recovery class; for the connection-mode transfer of data and control information from one transport entity to a peer transport entity; b) one class (class 4) of procedure when operating over the connectionless-mode network service; c) the means of negotiating the class of procedures to be used by the transport entities; d) the structure and encoding of the transport protocol data units used for the transfer of data and control information.