Synchronous data link control

Synchronous Data Link Control ( SDLC ) is a proprietary, bit-synchronous data communication protocol for transparent bit-serial data transmission . It covers layer two of the SNA developed by IBM . The data exchange can take place via permanently switched lines or via switched lines in the operating modes half or full duplex . The transmission path can be configured as a point-to-point connection, multipoint connection or as a loop.

SDLC is the basis for the extended HDLC protocol, which has an extended frame . As with HDLC, so-called stuffing bits are also used for channel coding in SDLC .

With SDLC, messages are divided into short frames with a uniform format and transmitted. The most important distinguishing feature of SDLC from the older byte-oriented network protocol BSC is a uniformly formatted frame structure.