A 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. Note 1: A self-synchronizing code permits the proper framing of transmitted code words provided that no uncorrected errors occur in the symbol stream. Note 2: External synchronization is not required. Note 3: High-level data link control (HDLC) and Advanced Data Communication Control Procedures (ADCCP) frames represent self-synchronizing code words.