The resend request is sent by the receiving application to initiate the retransmission of messages. This function is utilized if a sequence number gap is detected, if the receiving application lost a message, or as a function of the initialization process.
The resend request can be used to request a single message, a range of messages or all messages subsequent to a particular message.
Note: the sending application may wish to consider the message type when resending messages; e.g. if a new order is in the resend series and a significant time period has elapsed since its original inception, the sender may not wish to retransmit the order given the potential for changed market conditions. (The Sequence Reset <4>-GapFill message is used to skip messages that a sender does not wish to resend.)
Note: it is imperative that the receiving application process messages in sequence order, e.g. if message number 7 is missed and 8-9 received, the application should ignore 8 and 9 and ask for a resend of 7-9, or, preferably, 7-0 (0 represents infinity). This latter approach is strongly recommended to recover from out of sequence conditions as it allows for faster recovery in the presence of certain race conditions when both sides are simultaneously attempting to recover a gap.
The '^' character is used to represent SOH character.