Reliability (computer networking): Difference between revisions

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In [[computer networking]], a '''reliable''' protocol is a protocol which notifies the sender of data whether or not the delivery of data to intended recipients was successful. Reliability is a synonym for '''assurance''', which is the term used by the [[ITU]] and [[ATM Forum]] in the context of the [[Asynchronous Transfer Mode|ATM]] Service-Specific Coordination Function, for example for transparent assured delivery with [[ATM Adaptation Layer 5|AAL5]].<ref>Young-ki Hwang, et al., ''Service Specific Coordination Function for Transparent Assured Delivery with AAL5 (SSCF-TADAS)'', Military Communications Conference Proceedings, 1999. MILCOM 1999, vol.2, pages 878 - 882, DOI: 10.1109/MILCOM.1999.821329</ref><ref name="ATMF-INTRO" >ATM Forum, The User Network Interface (UNI), v. 3.1, {{ISBN|0-13-393828-X}}, Prentice Hall PTR, 1995.</ref><ref name ="AAL-5 spec">ITU-T, ''B-ISDN ATM Adaptation Layer specification: Type 5 AAL'', Recommendation I.363.5, International Telecommunication Union, 1998.</ref>

Reliable protocols typically incur more overhead than unreliable protocols, and as a result, function more slowly and with less scalability. This often is not an issue for [[unicast]] protocols, but it may become a problem for [[reliable multicast]] protocols.

[[Transmission Control Protocol|TCP]], the main protocol used on the [[Internet]], is a reliable unicast protocol. [[User Datagram Protocol|UDP]], is an unreliable protocol and is often used in [[computer games]], [[streaming media]] or in other situations where speed is an issue and the loss of a littlesome data isloss notmay asbe importanttolerated because of the transitory nature of the data, is an unreliable protocol.<!--[[User:Kvng/RTH]]-->

Often, a reliable unicast protocol is also [[connection-oriented]]. For example, TCP is connection-oriented, with the [[virtual circuit|virtual-circuit]] ID consisting of source and destination [[IP address]]es and port numbers. However, some unreliable protocols are connection-oriented, such as [[Asynchronous Transfer Mode|ATM]] and [[frame relay]]. In addition, some protocols are reliable-connectionless, such as [[IEEE 802.11]], where the sending station will resend a frame if the sending station doesn't receive an ACK frame within a predetermined period of time, and [[AX.25]] when it passes data in [[I-frame]]s.

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Strong reliability properties are offered by [[group communication system]]s (GCS) such as [[IS-IS]], [[Appia framework]], [[Spread (group communication system)|Spread]], [[JGroups]] or [[QuickSilver Scalable Multicast]]. The [[QuickSilver Properties Framework]] is a flexible platform that allows strong reliability properties to be expressed in a purely declarative manner, using a simple rule-based language, and automatically translated into a hierarchical protocol.

==Asynchronous Transfer Mode==

In the context of the [[Asynchronous Transfer Mode|ATM]] Service-Specific Coordination Function, for example for transparent assured delivery with [[ATM Adaptation Layer 5|AAL5]].<ref>Young-ki Hwang, et al., ''Service Specific Coordination Function for Transparent Assured Delivery with AAL5 (SSCF-TADAS)'', Military Communications Conference Proceedings, 1999. MILCOM 1999, vol.2, pages 878 - 882, DOI: 10.1109/MILCOM.1999.821329</ref><ref name="ATMF-INTRO" >ATM Forum, The User Network Interface (UNI), v. 3.1, {{ISBN|0-13-393828-X}}, Prentice Hall PTR, 1995.</ref><ref name ="AAL-5 spec">ITU-T, ''B-ISDN ATM Adaptation Layer specification: Type 5 AAL'', Recommendation I.363.5, International Telecommunication Union, 1998.</ref>

==Reliable delivery in real-time systems==