Stop Bit Encoding

Stop bit encoding is a process incorporated in FAST that eliminates redundancy at the data field level by using a stop bit instead of the traditional separator byte. In FAST, a stop bit is used instead of FIX’s traditional <SOH> separator byte. Thus 7 bits of each byte are used to transmit data and the eighth bit is used to indicate the end of a field.

FAST 7-Bit Binary Representation

FAST renders numbers into binary across the 7 data bits in each byte. Thus a number equal to or less than 2^7-1, (127) occupies one byte, a number between 2^7 and 2^(7*2)-1(16,383), occupies two bytes, etc.