Top of Book Update Messages

There are extended, expanded, long and short forms of bid and ask updates. Short form messages are sent if the symbol is less than five characters, the price is less than or equal to 999.99, and the size can be expressed in five characters. Expanded form messages are sent if the symbol is greater than six characters and accommodate larger symbol sizes possible through the ISRA plan. Extended form messages are sent if the price exceeds the maximum allowed for a long form price data type.