Four classes of service in SCCP
	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