1. A means of providing synchronization in a data link control protocol such as HDLC where, for example, a 0 is automatically inserted whenever a predetermined number of 1s is present in a data stream at the sending end of the link. The receiving equipment automatically deletes the extra 0s before delivering the received message to the receiving terminal.

2. A means of inserting and deleting bits on multiply connected high-speed digital transmission links that are not synchronously clocked.