Connectionless-mode Network Service
OSI network layer datagram service
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. As such it is a "best-effort" rather than a "reliable" delivery service. CLNS is one of the two primary OSI network-layer services, the other being Connection-Oriented Network Service (CONS). CLNS is not an Internet service, but provides capabilities in an OSI network environment similar to those provided by the Internet protocol suite. The service is specified in ISO/IEC 8348, the OSI Network Service Definition (which also defines the connection-oriented service, CONS.)
01Connectionless-mode Network Protocol
02Transport Protocol Class 4 (TP4) in conjunction with CLNS
CLNS is used by ISO Transport Protocol Class 4 (TP4), one of the five transport layer protocols in the OSI suite. 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. TP4 provides reliable transport service and functions with either connection-oriented or connectionless network service. TP4 is the most commonly used of all the OSI transport protocols and is similar to the Transmission Control Protocol (TCP) in the Internet protocol suite.
03Protocols providing CLNS
Several protocols provide the CLNS service:
- Connectionless-mode Network Protocol (CLNP), as specified in ITU-T Recommendation X.233.
- End System-to-Intermediate System (ES-IS), a routing exchange protocol for use in conjunction with the protocol for providing the CLNS (ISO 9542).
- Intermediate System-to-Intermediate System (IS-IS), an intradomain routing exchange protocol used in both the OSI and Internet environments (ISO/IEC 10589 and RFC 1142).
- Interdomain Routing Protocol (IDRP), the OSI equivalent of BGP.
- Signalling Connection Control Part (SCCP), as specified in ITU-T Recommendation Q.711 is a Signaling System 7 protocol.
Sources and credits
This article is adapted from the Wikipedia article “Connectionless-mode Network Service”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
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