While receiving a stream of framed data, frame synchronization is the process by which incoming frame alignment signals, i.e., distinctive bit sequences (a syncword), are identified, i.e., distinguished from data bits, permitting the data bits within the frame to be extracted for decoding or retransmission. This is sometimes referred to as "framing".
A common practice in telecommunications, for example in T-carrier, is to insert, in a dedicated time slot within the frame, a noninformation bit or framing bit that is used for the actual synchronization of the incoming data with the receiver. In a bit stream, framing bits are used in determining the beginning or end of a frame. They occur at specified positions in the frame, do not carry information, and are usually repetitive.
If the transmission is temporarily interrupted, or a bit slip event occurs, the receiver must re-synchronize.
References
This article incorporates public ___domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22. (in support of MIL-STD-188).
Scientific Articles
J. L. Massey. "Optimum frame synchronization ". IEEE trans. comm., com-20(2):115-119, April 1972.
R Scholtz. "Frame synchronization techniques", IEEE Transactions on Communications, 1980
P. Robertson. "Optimal Frame Synchronization for Continuous and Packet Data Transmission", PhD Dissertation, 1995, Fortschrittberichte VDI Reihe 10, Nr. 376 PDF