Reliable byte stream
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A reliable byte stream is a common service paradigm in computer networking; it refers to a byte stream in which the bytes which emerge from the communication channel at the recipient are exactly the same, and in the exact same order, as they were when the sender inserted them into the channel.
The classic example of a reliable byte stream communication protocol is the Transmission Control Protocol, one of the major building blocks of the Internet.
A reliable stream is not the only reliable service paradigm which computer network communication protocols provide, however; other protocols (e.g. SCTP) provide a reliable message stream, i.e. the data is divided up into distinct units, which are provided to the consumer of the data as discrete objects.
[edit] Mechanism
Communication protocols which implement reliable byte streams, generally over some unreliable lower level, use a number of mechanisms to provide that reliability.
All data items are identified with a sequence number, which is used both to make sure that the data are delivered to the entity at the other end in the correct order, and to check for lost data items. The receiver sends back acknowledgements for data items which have been successfully received; a timer at the sender will cause a timeout if an acknowledgement is not received within a reasonable round trip time, and the (presumably lost) data will then be re-transmitted. To check that no data items are damaged, a checksum is used; one is computed at the sender for each block of data before it is sent, and checked at the receiver. Erroneous or missing data are reported to the sender, in order that it may retransmit the same. Any duplicated data items are discarded.
