!!! Overview
[{$pagename}] implies the [Protocol] provides [assurance] of the delivery of [data] to the __intended recipient(s)__, as opposed to an [unreliable protocol], which does not provide notifications to the sender as to the delivery of transmitted [data] or [messages]. [Reliability] is a synonym for [assurance], which is the term used by the [ITU] and [ATM] Forum in the [context] of the [ATM] Service-Specific Coordination Function, for [example] for transparent assured delivery with [AAL]5.

[{$pagename}]s 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].

[TCP], the main [protocol] used on the [Internet], is a [unicast] [{$pagename}]. [UDP], often used in computer games or in other situations where speed is an issue and the loss of a little [data] is not as important because of the transitory nature of the data, is an [unreliable protocol].

Often, a [unicast] [{$pagename}] is also connection-oriented. For [example], [TCP] is connection-oriented, with the virtual-circuit ID consisting of source and destination [IP Address] and port numbers. 

Some [unreliable protocols] are connection-oriented as well. These include [ATM] and [frame] relay. There are also reliable connectionless protocols, such as AX.25 when it passes data in I-frames. But this combination occurs rarely: reliable-connectionless is uncommon in commercial and academic networks.

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