Open Island

Communications State Parameter Bits Description Sync state (seebelow) 2 0 UTC direct (sync from own integral GPS receiver ) 1 UTC indirect (own GPS unavailable - UTC sync from GPS receiver on nearby ship or base station) 2 Station is synchronized to a base station (base direct - GPS unavailable). 3 Station is synchronized to another station based on the highest number of received stations or to another mobile station, which is directly synchronized to a base station (GPS unavailable) Slot time-out 3 Specifies frames remaining until a new slot is selected 0 means that this was the last transmission in this slot 1-7 means that 1 to 7 frames respectively are left until slot change Sub message 14 The sub message depends on the current value in slot time-out as described in Table 19 * The communication state field covers 19 bits and this is general to both message 1, message 2 and message 3. The * content is though different for the different communication

For my boat tracking system, I found out that using AIS format seems to be a good idea, at least I don't have to worry about how to present boat data, since there are already plenty things for do this on mobile phone or PC. Here is what I read: http://catb.org/gpsd/AIVDM.html Looking into AIS NMEA0183, it has much more application then I think. Such as MOB device, epir, aid to navigation device...etc, all are included. it use the first few char to indicate the function: Table 1. AIS talker IDs !AB NMEA 4.0 Base AIS station !AD MMEA 4.0 Dependent AIS Base Station !AI Mobile AIS station !AN NMEA 4.0 Aid to Navigation AIS station !AR NMEA 4.0 AIS Receiving Station !AS NMEA 4.0 Limited Base Station !AT NMEA 4.0 AIS Transmitting Station !AX NMEA 4.0 Repeater AIS station !BS Base AIS station (deprecated in NMEA 4.0) !SA NMEA 4.0 Physical Shore AIS Station It can also be used between device on boat for message communication, AIVDO The