Wait4Bus revision 2 – Group B Altered from: Huanwen Qu, Jeroen Zuijderwijk, Rudy van Wandelen & Roy van den Broek Richard Nieuwenhuis, Kang Ning and Jeroen Zuijderwijk

The challenge Provide an initial specification, that: is high-level is maximally flexible is modular gets the message to the bus stands Our part focuses on the front-end and back-end parts

Two different set-ups Central server Bus contacts server, server contacts bus stands R&S-AS on the bus Bus contacts bus stands

Central server BUSSERVERBUS STAND R&SAS Send 2 M4 GPS UNIT LED Display Receive 2 M3 M1 Send 1 M2 Receive 1

R&S-AS on the Bus R&SAS Send 2 M4 GPS UNIT LED Display Receive 2 BUSBUS STAND M3 M1 Send 1 M2 Receive 1

Communication We defined communication M(1,2,3,4) as: messages sent from and to the different modules The messages contain different information

Message M1 The message from GPS unit to microprocessor contains: Current bus location Only longitude and latitude are transmitted Current time All busses have the same time because when they are in reach of 4 GPS satellites the time in the GPS units are automatically corrected The microprocessor asks the GPS unit for this information periodically the only pull in the system

Message M2 The message from microprocessor to the R&SAS contains: Information from the GPS Current bus location and current time Unique bus number These correspond to the bus line and direction The microprocessor knows address the message should be sent to This can be a phone number or a direct connection The microprocessor receives a confirmation from the server

Message M3 The message from the R&SAS to the server phone contains: Expected arrival time Bus line number Phone number of the bus stand the expected time is computed for

Message M4 The message from the server phone to the bus stand contains: Information from R&SAS Expected arrival time Bus line number Confirm the receipt of the message to the server that sent it

Special cases When there is some special things happened, such as strike, traffic accident, road repairing, etc. Message M3 will contains: Special case information Expected recover time Bus line number Phone number of the bus stand the message will send to

Special cases (continue) When there is some special things happened, such as strike, traffic accident, road repairing, etc. Message M4 will contains: Special case information Expected recover time Bus line number

Special cases (continue) When the bus location message in M2 are always the same. an operator is contacted to check the problem (traffic accident, traffic jam, microprocessor or GPS error, etc)

Error handling Message M1 is not received The microprocessor on the bus tries to get it again if the GPS unit never answers the microprocessor notes this Message M2 is not received No confirmation received The message is send again

Error handling (continued) Message M3 will always be received because it is internal on the server Message M4 not received No confirmation received Message sent again In all cases a message is not send successfully it is sent again After a threshold of resends is passed an operator is contacted

Example GPS sends time and location Time (t) Location (lo,la) The microprocessor on the bus adds the unique bus number Bus number (bnr) This information is send to the R&SAS

Example (continued) The R&SAS computes for each bus stand in the bus line the expected arrival time: Arrival time (at) Computed from (t) and (lo,la) Bus line number (blnr) Derived from (bnr) This information is send to each bus stand separately using the phone number provided by the system

Example (continued) The bus stand displays the expected time and bus line number on a LED display Arrival time (at) Bus line number (blnr)