Hi @chris.xiao
HIGH_1 and LOW_1 will update in real-time when there are new high or new low trades during trading hours.
However, they can be in a separate update message from the TRDPRC_1.
As Warat mentioned, this functionality is dependent on the linehandler for that venue. For most exchanges, Low and High are included in the trade price packet, which sets the new Low/High.