In an
audio receiver receiving a
bit stream of data, an example of a syncword is 0x0B77 for an
AC-3 encoded stream. An
Ethernet packet with the Ethernet preamble, 56 bits of alternating 1 and 0 bits, allowing the receiver to synchronize its clock to the transmitter, followed by a one-octet start frame delimiter byte and then the header. All
USB packets begin with a sync field (8 bits long at low speed, 32 bits long at high speed) used to synchronize the receiver's clock to the transmitter's clock. A receiver uses a physical layer preamble, also called a physical layer training sequence, to synchronize on the signal by estimating frequency and clock offsets. Some documentation uses "preamble" to refer to a signal used to announce a transmission, to wake-up receivers in a low-power mode. While some systems use exactly the same signal for both physical-layer training and wake-up functions, others use 2 different signals at 2 different times for these 2 functions, or have only one or the other of these signals. The
Bisync protocol of the 1960s used a minimum of two ASCII "
SYN" characters (0x16…0x16) to achieve character synchronization in an undifferentiated bit stream, then other special characters to
synchronize to the beginning of a frame of characters. The syncwords can be seen as a kind of
delimiter. Various techniques are used to avoid
delimiter collision, orin other wordsto "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). ==Alternatives==