Class 0:
Basic connectionless class. Each
information block (SCCP message) is
transmitted from one SCCP user to
another SCCP user independently.
Class 1:
Sequenced (MTP) connectionless class.
All messages use the same SLS
code.
Class 2:
Basic connection-oriented class.
Virtual connections are set-up and
released + using same SLS code +
segmentation & reassembly (SAR)
Class 3:
Flow-control connection-oriented class.
VC control + same SLS codes + SAR
+ flow control