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Resend Request logic is the FIX session mechanism by which a given system, upon detecting a higher than expected message sequence number from its counterparty, requests a range of ordered messages resent from the counterparty. The counterparty resends the requested message range sequentially until both systems are back in sequence. 

Info
Customers must wait for in-flight resend requests to be fulfilled before logging out or failing over to the backup gateway.

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If the client system exceeds this value, CME Globex sends a Session Level Reject (tag 35-MsgType=3) message. Tag 58-Text in this message will contain the following: "Range of messages to resend is greater than maximum allowed 2500."

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The following example illustrates the use of the Gap Fill message during resend processing. The iLink 2 Sequence Reset message is identified as a Gap Fill by tag 123-GapFillFlag equal to 'Y'.

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  1. The message sent by CME Globex has tag 34-MsgSeqNum=11 and is higher than the client system is expecting.
  2. The client system responds with a iLink 2 Resend Request with tag 7-BeginSeqNo=10 and tag 16-EndSeqNo=0 indicating infinity.
  3. Before CME Globex receives the Resend Request, it has already sent messages 12 and 13.
  4. When the client system receives messages 12 and 13, the absence of the tag 122-OrigSendingTime and tag 369-LastMsgSeqNumProcessed = 199 indicates that messages 12 and 13 are not the resend responses it is expecting.
  5. The client system, therefore, issues duplicate Resend Requests with tag 43-PossDupFlag=Y.
  6. When CME Globex receives the original Resend Request, it processes it by re-sending messages 10 - 13 with tag 43-PossDupFlag =Y and tag 122-OrigSendingTime tag populated.
  7. Since the subsequent Resend Requests were sent as duplicates with tag 43-PossDupFlag=Y and CME Globex has already processed the original message, per the FIX Protocol, CME Globex ignores the duplicate Resend Requests.

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