Message SequenceReset Scenario base

SYNOPSIS: The Sequence Reset message has two modes: **Gap Fill mode** and **Reset mode**.
ELABORATION: ### Gap Fill mode Gap Fill mode is used in response to a Resend Request when one or more messages must be skipped over for the following reasons: 1. During normal resend processing, the sending application may choose not to send a message (e.g. an aged order). 2. During normal resend processing, a number of administrative messages are skipped and not resent (such as Heart Beats, Test Requests). Gap Fill mode is indicated by GapFillFlag (tag 123) field = \"Y\". If the GapFillFlag field is present (and equal to \"Y\"), the MsgSeqNum should conform to standard message sequencing rules (i.e. the MsgSeqNum of the Sequence Reset GapFill mode message should represent the beginning MsgSeqNum in the GapFill range because the remote side is expecting that next message sequence number). ### Reset mode Reset mode involves specifying an arbitrarily higher new sequence number to be expected by the receiver of the Sequence Reset-Reset message, and is used to reestablish a FIX session after an unrecoverable application failure. Reset mode is indicated by the GapFillFlag (tag 123) field = \"N\" or if the field is omitted. If the GapFillFlag field is not present (or set to N), it can be assumed that the purpose of the Sequence Reset message is to recover from an out-of-sequence condition. In Sequence Reset - Reset mode, the MsgSeqNum in the header should be ignored (i.e. the receipt of a Sequence Reset - Reset mode message with an out of sequence MsgSeqNum should not generate resend requests). ***Sequence Reset -- Reset should NOT be used as a normal response to a Resend Request (use Sequence Reset -- Gap Fill mode). The Sequence Reset -- Reset should ONLY be used to recover from a disaster situation which cannot be recovered via the use of Sequence Reset -- Gap Fill. Note that the use of Sequence Reset -- Reset may result in the possibility of lost messages.*** ### Rules for processing all Sequence Reset messages The sending application will initiate the Sequence Reset. **The message in all situations specifies NewSeqNo to reset to as the** **value of the *next* sequence number** to be expected by the message recipient **immediately following the messages and/or sequence numbers being skipped**. 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 Resend Requests 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 may appear as Sequence Reset-GapFill mode with NewSeqNo of 8, message 8, Sequence Reset-GapFill with NewSeqNo of 10, and message 10. This could then followed by Sequence Reset-GapFill with NewSeqNo of 8, message 8, Sequence Reset-GapFill with NewSeqNo of 10, message 10, and message 11. One must be careful to ignore the duplicate Sequence Reset-GapFill mode which is attempting to lower the next expected sequence number. This can be detected by checking to see if its MsgSeqNum is less than expected. If so, the Sequence Reset-GapFill mode is a duplicate and should be discarded.

ID	MsgType	Abbr	Flow
5	4	SequenceReset

Pedigree

Added	EP	Updated	EP	Deprecated	EP
FIX.2.7

Responses

None

Members

SequenceReset base members

ID	Name	Abbr	Presence	Description
1024	StandardHeader	Hdr	required	SYNOPSIS: The standard FIX message header ELABORATION:
123	GapFillFlag	GapFillFlag	optional	SYNOPSIS: Indicates that the Sequence Reset message is replacing administrative or application messages which will not be resent.
36	NewSeqNo	NewSeqNo	required	SYNOPSIS: New sequence number
1025	StandardTrailer	Trlr	required	SYNOPSIS: The standard FIX message trailer ELABORATION: