In telecommunication

Telecommunication

Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

s, a self-synchronizing code is a line code

Line code

In telecommunication, a line code is a code chosen for use within a communications system for baseband transmission purposes...

 in which the symbol stream formed by a portion of one code word

Code word

In communication, a code word is an element of a standardized code or protocol. Each code word is assembled in accordance with the specific rules of the code and assigned a unique meaning...

, or by the overlapped portion of any two adjacent code words, is not a valid code word. Put another way, a set of strings (called "code words") over an alphabet is called a self-synchronizing code if for each string obtained by concatenating two code words, the substring starting at the second symbol and ending at the second-last symbol does not contain any code word as substring.

A synonym for self-synchronizing code is comma-free code. However, sometimes the term comma-free code is used in the meaning of prefix code

Prefix code

A prefix code is a type of code system distinguished by its possession of the "prefix property"; which states that there is no valid code word in the system that is a prefix of any other valid code word in the set...

. The latter is a broader concept: every self-synchronizing code is a prefix code

Prefix code

A prefix code is a type of code system distinguished by its possession of the "prefix property"; which states that there is no valid code word in the system that is a prefix of any other valid code word in the set...

, but not all prefix codes are self-synchronizing.

A self-synchronizing

Synchronizing

In telecommunication, the term synchronizing has the following meanings:# Achieving and maintaining synchronism.# In fax, achieving and maintaining predetermined speed relations between the scanning spot and the recording spot within each scanning line....

 code permits the proper framing

Frame 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...

 of transmitted code words provided that no uncorrected errors occur in the symbol stream; external synchronization

Synchronization

Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....

 is not required. Self-synchronizing codes also allow recovery from uncorrected errors in the stream; with most prefix codes, an uncorrected error in a single bit may propagate errors further in the stream and make the subsequent data unreadable.

Examples

• High-Level Data Link Control
  High-Level Data Link Control
  High-Level Data Link Control is a bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization...
  
   (HDLC)
• Advanced Data Communication Control Procedures
  Advanced Data Communication Control Procedures
  In telecommunication, Advanced Data Communication Control Procedures is a bit-oriented data link layer protocol used to provide point-to-point and point-to-multipoint transmission of data frames that contain error control information. It places data on a network and ensures proper delivery to a...
  
   (ADCCP)
• UTF-8
  UTF-8
  UTF-8 is a multibyte character encoding for Unicode. Like UTF-16 and UTF-32, UTF-8 can represent every character in the Unicode character set. Unlike them, it is backward-compatible with ASCII and avoids the complications of endianness and byte order marks...