Store and forward

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Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in a networking context, verifies the integrity of the message before forwarding it. In general, this technique is used in networks with intermittent connectivity, especially in the wilderness or environments requiring high mobility. It may also be preferable in situations when there are long delays in transmission and variable and high error rates, or if a direct, end-to-end connection is not available.

This technique originates the delay-tolerant networks. No real-time services are available for these kinds of networks.

Manually operated relay[edit]

Store and forward networks predate the use of computers. Point-to-point teleprinter equipment was used to send messages which were stored at the receiving end on punched paper tape at a relay center. A human operator at the center removed the message tape from the receiving machine, read the addressing information, and then sent it toward its destination on appropriate outbound point-to-point teleprinter link. If the outbound link was in use, the operator placed the message in tape in a physical queue, usually consisting of a set of clips or hooks. A major relay center in the mid 1900s might have dozens of inbound and outbound teleprinters, scores of operators, and thousands of messages in the queues during peak periods. Operators referred to these centers as "torn-tape relay centers," a reference to removing the received message from the inbound teleprinter by tearing the paper tape to separate one message from the next. The U.S. military term for such a center was "Non-Automated Relay Center" (NARC).

Automatic relay[edit]

Plan 55-A was an automatic, electromechanical store and forward message switching system. All message storage was performed by paper tape punches paired with paper tape readers, with a bin in between.

UUCP[edit]

Main article: UUCP

Prior to the deployment of the Internet, computers were connected via a variety of point-to-point techniques, with many smaller computers using dial-up connections. The UUCP store-and-forward protocols allowed a message (typically e-mail) to move across the collection of computers and eventually reach its destination. Late in the 20th century, store and forward techniques evolved into packet switching which replaced it for most purposes.

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