The sending application will initiate the sequence reset. The message in all situations specifies NewSeqNo <36> to reset as thevalue of the next sequence number to be transmitted.
If the GapFill field is not present (or set to N), it can be assumed that the purpose of the Sequence Reset <4> message is to recover from an out-of-sequence condition. The MsgSeqNum <34> in the header should be ignored (i.e. the receipt of a Sequence Reset <4> message with an out of sequence MsgSeqNum <34> should not generate resend requests).
If the Gap Fill field is present (and equal to Y), the MsgSeqNum <34> should conform to standard message sequencing rules (i.e. the MsgSeqNum <34> of the SequenceReset-GapFill<4> message should represent the beginning MsgSeqNum <34> in the GapFill range because the remote side is expecting that next message).
The sequence reset can only increase the sequence number. If a sequence reset is received attempting to decrease the next expected sequence number the message should be rejected and treated as a serious error. It is possible to have multiple ResendRequests issued in a row (i.e. 5 to 10 followed by 5 to 11). If sequence number 8, 10, and 11 represent application messages while the 5-7 and 9 represent administrative messages, the series of messages as result of the Resend Request <2> may appear as SeqReset-GapFill<4> with NewSeqNo <36> of 8, message 8, SeqReset-GapFill with NewSeqNo <36> of 10, and message 10. This could then followed by SeqReset-GapFill with NewSeqNo <36> of 8, message 8, SeqReset-GapFill with NewSeqNo <36> of 10, message 10, and message 11. One must be careful to ignore the duplicate SeqReset-GapFill which is attempting to lower the next expected sequence number. This can be detected by checking to see if its MsgSeqNum <34> is less than expected. If so, the SeqReset-GapFill is a duplicate and should be discarded.
The '^' character is used to represent SOH character.