Blasting the way to synchronous communications
P. Charbonnet, Georgellen Smith · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 1984
Minicomputer and microcomputer users now have several new options in data communications software. Most of these packages fall into the rapidly growing category of file-transfer utilities-that is, programs that exchange computers. The key factor in the development of these products is that most micros and minis have only asynchronous communications capability. They cannot use mainframe data communications protocols. All of the asynchronous protocols that have emerged use the standard synchronous technique for error detection: the data stream is divided into blocks, and the integrity of each block is monitored by appending a check-sum that is recomputed and compared with the original check-sum when the block is received. Full-duplex protocols such as blocked asynchronous transmission (blast) transmit a continuous stream of data blocks while using the other half of the communications channel to receive block acknowledgements simultaneously. This structure is combined with the use of sliding window or pipelining techniques as employed by sophisticated synchronous protocols such as SNA/SDLC and x.25/HDLC. The end result is that full-duplex asynchronous protocols can endure significant propagation delay without losing efficiency. They are suitable for use in a variety of communications environments.