Syncword

In computer networks, a syncword, sync character, sync sequence or preamble is used to synchronize a data transmission by providing bit/symbol clock or word boundary information, or to indicate the beginning of actual data. The syncword is a known sequence of data used to identify the start of a frame, and is also called reference signal or midamble in wireless communications.

Prefix codes allow unambiguous identification of synchronization sequences and may serve as self-synchronizing code.

‍—‌to "disguise" bytes of data at the data link layer that might otherwise be incorrectly recognized as the syncword. For example, HDLC uses bit stuffing or "octet stuffing", while other systems use ASCII armor or Consistent Overhead Byte Stuffing (COBS).

In some communication systems, a receiver can achieve character synchronization from an undifferentiated bit stream, or start-of-header synchronization from a byte stream, without the overhead of an explicit syncword. For example, the FSK441 protocol achieves character synchronization by synchronizing on any "space" characters in the messageJohn R. Freer (1996). Computer communications and networks (2nd ed.). Taylor & Francis. p. 12. ISBN 978-1-85728-379-2.