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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.<ref name=ITU-T-X.213>"Section 3: Definition of the Connectionless-Mode Service", ITU-T Recommendation X.213: Open Systems Interconnection – Network service definition, International Telecommunication Union, October 2001</ref><ref name=CISCOIS-IS>"ISO Connectionless Network Service" Template:Webarchive, Chapter 2, Section 1 in IS-IS Network Design Solutions, Cisco Press, 7 February 2002, Template:ISBN</ref> As such it is a "best-effort" rather than a "reliable" delivery service. 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,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> the OSI Network Service Definition (which also defines the connection-oriented service, CONS.)
Connectionless-mode Network ProtocolEdit
Connectionless-mode Network Protocol (CLNP) is an OSI protocol deployment. 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.<ref>Link Letter, Volume 4, No. 3 (Sept/Oct 1991), p. 1, NSFNET Information Services, Merit Network, Inc., Ann Arbor</ref> However, CLNP usage remained low compared to TCP/IP.
Transport Protocol Class 4 (TP4) in conjunction with CLNSEdit
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.
Protocols providing CLNSEdit
Several protocols provide the CLNS service:<ref name=CISCOIS-IS/>
- Connectionless-mode Network Protocol (CLNP), as specified in ITU-T Recommendation X.233.<ref>ITU-T Recommendation X.233: Protocol for providing the connectionless-mode network service: Protocol specification, International Telecommunication Union, August 1997</ref>
- 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),<ref>{{#invoke:citation/CS1|citation
|CitationClass=web }}</ref> the OSI equivalent of BGP.
- Signalling Connection Control Part (SCCP), as specified in ITU-T Recommendation Q.711<ref>ITU-T Recommendation Q.711: Specifications of Signalling System No. 7 – Signalling connection control part (SCCP), International Telecommunication Union, March 2001</ref> is a Signaling System 7 protocol.
See alsoEdit
- X.25 protocol suite, an OSI Connection Oriented Network Service (CONS)
ReferencesEdit
External linksEdit
- What is CLNS? - a brief introduction by Ivan Pepelnjak