CLNS is an abbreviation of Connectionless Network Service.

It is an OSI network layer service that does not require a circuit to be established before data is transmitted. CLNS routes messages to their destinations independently of any other messages.

In a OSI protocol deployment, CLNS would be the service provided by CLNP (Connection Less Network Protocol) and used by TP4 (Transport Protocol 4). However CLNP is not used on the Internet, instead its function is provided by IP. CLNP is still widely used today in many telecommunications networks (mainly the transmission area) around the world. Still the new systems delivered utilise this.