Connectionless-mode Network Service (CLNS) or simply Connectionless Network Service is an OSI network layer datagram service that does not require a circuit to be established before data is transmitted, and routes messages to their destinations independently of any other messages.
CLNS is the service provided by the Connectionless-mode Network Protocol (CLNP).
From August 1990 to April 1995 the NSFNET backbone supported CLNP in addition to TCP/IP.
TP4 offers error recovery, performs segmentation and reassembly, and supplies multiplexing and demultiplexing of data streams over a single virtual circuit.
TP4 sequences PDUs and retransmits them or re-initiates the connection if an excessive number are unacknowledged.