FIX Antenna follows two main rules:

  1. An outgoing message is stored to the file and then sent
  2. An incoming message is stored to the file after it is processed

There are two very important consequences of these rules that in combination with FIX sequencing and retransmission make losing a message in FIX Antenna impossible:

  1. If application crashes during the incoming message processing, it will not be stored and after restoring a session the sequence number too high will be identified and resend request will be sent.
  2. If application crashes before a message is delivered to a counter-party, the counter-party will identify a gap and send a request for retransmission after restoring a session.

Gap fill

Gap fill is a standard FIX mechanism designed to indentify and resolve message loss. It is based on sequencing messages in each direction, resend request mechanism, PosDup flag and sequence reset.

When session identifies the "sequence number too high" problem it sends a resend request message asking for retransmission of lost messages. The opposite side resends requested messages with PosDupFlag set to "Y". Session level messages are not resent. The sequence reset is used to keep sequence numbers consistent during resending.

FIX Antnenna automatically resolves gap fill, i.e. no manual work is required. However it is possible to intervernt into standard mechanism.


FIX Antenna comes with a basic failover mechanism. If application crashes, FIX Antenna will fully restore its state as it was before the crash after the next initialization. No information will be lost.

Generated on 10 Feb 2022 for FIXAntennaJava by  doxygen 1.6.1