6.3.2.2 TransactionId

A TransactionId (UInt64) is used to uniquely identify a deliver request. It is generated by the payment service and distributed to other components of the Vending Machine. The uniqueness can only be guaranteed for a certain amount of time in order to identify different deliver requests at the same time, which must be unique at least for the whole time the transaction is active. A reasonable strategy to assign the TransactionId is increasing the number every time by one and roll over to 0 at the maximum of UInt64. However, the strategy of assigning a TransactionId is vendor-specific and other components shall not make assumptions about this.

The TransactionId will not protect against false delivery request; there is protection given using the OPC UA security mechanisms, i.e., only specific Clients can communicate and request deliveries.