The "ALL" tradingSession means that the order can trade in any available session at the venue where it is sent. For example, if an exchange only has REG tradingSession, the order may be reported with a tradingSession of “REG” or "ALL". If an exchange has multiple sessions, and the order is not allowed to trade in all sessions based on a customer instruction or understanding, then the specific trading sessions in which the order is allowed to participate must be identified.