What is going on?

This panel provides explanations of the demo.

As you click on the buttons this panel changes, displaying explanations of what is happening.

The three vertical panels represent the three computers: the LPS and PPS servers and the OBU in the car.

The middle panel represents the OBU in car. Select a car and a time band. Then drag the two markers on the map to simulate a journey and click on the "Travel" button.

When you need to you can clear the databases using an option in the main navigation bar. From this bar you can explore other features, including itemised bills, in more detail.

Drive Somewhere

When you click on the "Travel" button the journey between the two markers is committed, and the colour change indicates this. Also, the number of trips to report to the LPS is incremented.

You can drag the markers and click on "Travel" several times before reporting the journeys to the LPS.

The panel below the buttons tell you how many journeys have been recorded but not sent to the LPS for pricing.

Journey details sent to Location Procesing Service

When you click the "Report travel" button, one of the unreported journeys is selected at random. See that it turns white on the OBU map.

The journey details are sent across the Internet to the LPS server. You can see the message sent by the OBU in box with the arrow, below the buttons. Along with the (compressed) journey data are the time band (Peak, Off-peak or Weekend, in this example), a pseudo-random journey ID and a digital signature.

When the LPS gets the message it prices the journey, adds the journey to its database, and sends the price back to the OBU. You can see the message sent by the LPS in box with the arrow in the left-hand panel.

You can see the journey being recorded in the LPS database, and appearing on the LPS map. The LPS does not know the identity of the OBU (this is indicated by the black colour). Journeys for all cars (not just yours) are displayed.

When the OBU receives the acknowledgement from the LPS it accumulates the price, and then deletes the journey data (you will see the journey disappearing from the OBU map).

Accumulated price sent to Payment Processing Service

When you click the "Report charges" button a message is sent from the OBU across the Internet to the PPS.

You can see the message sent by the OBU in box with the arrow, below the buttons. The OBU identifies itself and sends a sequence number, the accumulated price and a digital signature.

When the PPS gets the message it adds the message to its database, increments the sequence number and sends these back to the OBU as an acknowledgement. You can see the message sent by the PPS in box with the arrow in the right-hand panel.

You can see the journey being recorded in the PPS database. Note that the PPS knows the identity of the OBU, but not where it has been. Charges for all cars (not just yours) are displayed.

When the OBU receives the acknowledgement from the PPS it zeros the outstanding charges and notes the new sequence number.