Subscribers initiate all connections. OpenYield accepts connections only during agreed hours and from secure endpoints.
HeartBtInt (108) defaults to 30 seconds. Send a Heartbeat (35=0) whenever no other message has been sent within that interval.
Sessions disconnect if two consecutive heartbeats are missed and a Test Request (35=1) goes unanswered.
Market Data and Order Book sessions reset sequence numbers on every reconnect, and prior session messages are not retransmitted. On reconnect, Market Data resends a full snapshot. Order Book sends no snapshot: you receive IOIs only as the book changes, so reset your cached book when you reconnect.
Trading, Summon, and Drop Copy sessions reset sequence numbers daily only. Intraday sequence resets (141=Y or Sequence Reset) are not supported on these sessions; contact OpenYield support if a reset is needed.