The job of the multiplex is to accept data from one supplier and to transfer it to many suppliers.
This task may seem trivial at first, but closer review reveals that it presents quite a few unique challenges. Data are not supplied in one one shot, but rather in a continuous manner. It must be transfered without loss, therefore both the connections to suppliers and consumers have to be precisely monitored. If a connection is lost, the repective subscriptions are automatically renewed. The DDIP ensures as much as possible that the lost or backed up data packets are resent.
The individual data subscribers can set up and end subscriptions completely independantly of one another in mulitplexer mode. The DDIP maintains an overview of who has received which data and to whom the data must still be sent.
In addition to the simple transmission of a real-time data format, the DDIP also permits conversion of intended uses/formats. In this way, different formats to supply journey planning systems can be converted to one another:
- VDV 454 AUS to SIRI ET
- SIRI ET to VDV 454 AUS
- VDV 454 to GTFS RT
- SIRI ET to GTFS RT
Not only format can be converted, but actual data use can as well. For example, data intended for timetable information can also be used for display on departure boards:
- VDV 454 AUS to VDV 453 DFI
- SIRI ET to SIRI SM