Syncword
Encyclopedia
In computer network
s, a syncword, sync character or preamble is used to synchronize a transmission by indicating the end of header information and the start of data.
encoded stream.
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.
Various techniques are used to "disguise" bytes of data at the data link layer
that might otherwise be (incorrectly) recognized as the sync word. For example, HDLC uses bit stuffing
or "octet stuffing", while other systems use ASCII armor.
For example, the FSK441 protocol achieves character synchronization by synchronizing on any "space" characters in the message -- in effect, every "space" character in the message does double duty as a syncword.
For example, CRC-based framing
achieves character and start-of-header synchronization.
In a self-synchronizing code
, every character is, in effect, a syncword, and can be used to achieve character synchronization in an undifferentiated bit stream..
such as for Ethernet frame
s, as well as channel estimation.
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
s, a syncword, sync character or preamble is used to synchronize a transmission by indicating the end of header information and the start of data.
Examples
For example an audio receiver is receiving a bit stream of data. An example of a syncword is 0x0B77 for an AC-3AC-3
AC-3 can be:* AC-3 algorithm , one of a series of algorithms used for the solution of constraint satisfaction problems* Comte AC-3, a 1920s Swiss bomber/transport aircraft.* Dolby AC-3, a Dolby Digital, audio codec...
encoded stream.
The bisync protocol of the 1960s used a minimum of two ASCII "SYN
Synchronous idle
Synchronous Idle is the ASCII control character 22 , represented as ^V in caret notation. Synchronous Idle is used in some synchronous serial communication systems such as Teletype machines or the bisync protocol to provide a signal from which synchronous correction may be achieved between data...
" 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.
Various techniques are used to "disguise" bytes of data at the data link layer
Data link layer
The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....
that might otherwise be (incorrectly) recognized as the sync word. For example, HDLC uses bit stuffing
Bit stuffing
In data transmission and telecommunication, bit stuffing is the insertion of noninformation bits into data...
or "octet stuffing", while other systems use ASCII armor.
Alternatives
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 message -- in effect, every "space" character in the message does double duty as a syncword.
For example, CRC-based framing
CRC-based framing
The concept of CRC-based framing was developed by StrataCom, Inc. in order to improve the efficiency of a pre-standard Asynchronous Transfer Mode link protocol. This technology was ultimately used in the principal link protocols of ATM itself and was one of the most significant developments of...
achieves character and start-of-header synchronization.
In a self-synchronizing code
Self-synchronizing code
In telecommunications, a self-synchronizing code is a line code in which the symbol stream formed by a portion of one code word, or by the overlapped portion of any two adjacent code words, is not a valid code word...
, every character is, in effect, a syncword, and can be used to achieve character synchronization in an undifferentiated bit stream..
Preamble
In digital communication, preamble is a sequence of known bits are sent in each frame. It is used for both frame synchronizationFrame synchronization
While receiving a stream of framed data, frame synchronization is the process by which incoming frame alignment signals, i.e., distinctive bit sequences , are identified, i.e., distinguished from data bits, permitting the data bits within the frame to be extracted for decoding or retransmission...
such as for Ethernet frame
Ethernet frame
A data packet on an Ethernet link is called an Ethernet frame. A frame begins with Preamble and Start Frame Delimiter. Following which, each Ethernet frame continues with an Ethernet header featuring destination and source MAC addresses. The middle section of the frame is payload data including any...
s, as well as channel estimation.
See also
- Start Frame DelimiterStart Frame DelimiterThe Start Frame Delimiter is the 8-bit value marking the end of the preamble of an Ethernet frame. The SFD is immediately followed by the destination MAC address. It has the value 10101011....
- Synchronous idleSynchronous idleSynchronous Idle is the ASCII control character 22 , represented as ^V in caret notation. Synchronous Idle is used in some synchronous serial communication systems such as Teletype machines or the bisync protocol to provide a signal from which synchronous correction may be achieved between data...
- Magic number (programming)Magic number (programming)In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following:* A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures...
- Bit slip marks