It was derived from IBM's Synchronous Data Link Control protocol, which is the layer 2 protocol for IBM's Systems Network Architecture developed around 1975.
2.
Flag sequences are used in bit-oriented protocols, such as Advanced Data Communication Control Procedures ( ADCCP ), Synchronous Data Link Control ( SDLC ), and High-Level Data Link Control ( HDLC ).
3.
ADCCP is an ANSI standard, X3.66, derived from IBM's Synchronous Data Link Control ( SDLC ) protocol, and is functionally equivalent to the ISO High-Level Data Link Control ( HDLC ) standard.
4.
To satisfy such needs, IBM 3767 serial printer and IBM 3770 communications system ( including a line printer ) became available as part of the " Advanced Function in Communications " announcement which included the new System Network Architecture ( SNA ) and Synchronous Data Link Control ( SDLC ) communications protocol set, followed by another announcement in July, 1975, which included IBM 3760 Data Entry Station and the new models of IBM 3270 display stations, and IBM 3790 communication system.
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