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{{Short description|Protocol acknowledgement capability}}
{{Use American English|date=January 2020}}
In [[computer networking]], a '''reliable''' protocol is a [[communication protocol]] that notifies the sender whether or not the delivery of data to intended recipients was successful. [[Reliability engineering|Reliability]] is a synonym for '''assurance''', which is the term used by the [[ITU]] and [[ATM Forum]], and leads to '''[[fault-tolerant]] messaging'''.
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.
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There are a number of protocols that are capable of addressing real-time requirements for reliable delivery and timeliness:
[[MIL-STD-1553B]] and [[STANAG 3910]] are well-known examples of such timely and reliable protocols for [[avionics#Aircraft networks|avionic data buses]]. MIL-1553 uses a 1 Mbit/s shared media for the transmission of data and the control of these transmissions, and is widely used in federated military [[avionics]] systems.<ref name="Ekman_SAAB">{{citation |author=Mats Ekman |title=Avionic Architectures Trends and challenges |url=https://www.kth.se/polopoly_fs/1.146328!/Menu/general/column-content/attachment/3_Ekman_Saab.pdf |publisher=KTH |url-status=dead |archive-url=https://web.archive.org/web/20150203164824/https://www.kth.se/polopoly_fs/1.146328!/Menu/general/column-content/attachment/3_Ekman_Saab.pdf |archive-date=2015-02-03 |quote=Each system has its own computers performing its own functions}}</ref> It uses a bus controller (BC) to command the connected remote terminals (RTs) to receive or transmit this data. The BC can, therefore, ensure that there will be no [[network congestion|congestion]], and transfers are always timely. The MIL-1553 protocol also allows for automatic retries that can still ensure timely delivery and increase the reliability above that of the physical layer. STANAG 3910, also known as EFABus in its use on the [[Eurofighter Typhoon]], is, in effect, a version of MIL-1553 augmented with a 20 Mbit/s shared media bus for data transfers, retaining the 1 Mbit/s shared media bus for control purposes.
The [[Asynchronous Transfer Mode]] (ATM), the [[Avionics Full-Duplex Switched Ethernet]] (AFDX), and [[Time Triggered Ethernet]] (TTEthernet) are examples of packet-switched networks protocols where the timeliness and reliability of data transfers can be assured by the network. AFDX and TTEthernet are also based on IEEE 802.3 Ethernet, though not entirely compatible with it.
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With both AFDX and TTEthernet, there are additional functions required of the interfaces, e.g. AFDX's Bandwidth Allocation Gap control, and TTEthernet's requirement for very close synchronization of the sources of time-triggered data, that make it difficult to use standard Ethernet interfaces. Other methods for control of the traffic in the network that would allow the use of such standard IEEE 802.3 network interfaces is a subject of current research.<ref name="Charlton et al 2013">{{citation |author=D. W. Charlton |display-authors=etal |title=An Avionic Gigabit Ethernet Network |work=Avionics, Fiber-Optics and Photonics Conference (AVFOP) |year=2013 |publisher=IEEE |pages=17–18 |doi=10.1109/AVFOP.2013.6661601|isbn=978-1-4244-7348-9 |s2cid=3162009 }}</ref>
==See also==
*{{anl|Robustness of complex networks}}
*{{anl|Cascading failure}}
==References==
{{reflist}}
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