CPDLC Ground Initiated Continuity

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The CPDLC Ground Initiated Continuity is a part of the performance statistics gathered for ground initiated transactions. It is the probability that a ground initiated CPDLC transaction completes before the expiration timer expires (120 seconds). Note uplink messages which are responded to automatically (e.g. Next Data Authority exchanges) are not considered in the calculation of continuity; they complete almost immediately and so would skew the results and do not really reflect the continuity of the service as perceived by the controller.

All ground initiated requests and associated closing responses are analysed. For transactions that do not complete within the permitted delay (120s) an expired event is counted.

CPDLC Ground Initiated Transactions Continuity = 1 – (number of ground initiated CPDLC expired events / total number of ground initiated CPDLC requests made)


Expired events can occur for one of two reasons: i) the transactions are completed by a downlinked error message indicating that the transaction could not be completed due to some temporary problem with the system (see below for the list of such error messages), or ii) because no closing response is received within 120 seconds (the expiration timer).

Note transactions that do not complete as the result of Provider Abort are not considered as expired events, since in the definition of Continuity the communication system has to be available when the transaction is initiated and in the case of a PA the communication system is not available.

The error messages that are considered as expired events are as follows:

  • UPLINK DELAYED IN NETWORK AND REJECTED. RESEND OR CONTACT BY VOICE
  • RESPONSE TIMER EXPIRED
  • AIR SYSTEM TIMEOUT