TMC(Traffic Message Channel) in Car GPS Navigation Player System

March 4, 2015 - PRLog -- TMC(Traffic Message Channel) in navigation function is a technology for delivering traffic and travel information to motor vehicle drivers. It is digitally coded, using the Radio Data System on conventional FM radio broadcasts in car DVD player (http://www.car-gpsdvd.com/). It can also be transmitted on Digital Audio Broadcasting or satellite radio. TMC in gps (http://www.car-gpsdvd.com/Supply-special-car-dvd-gps_c1) allows silent delivery of dynamic information suitable for reproduction or display in the user's language without interrupting audio broadcast services. Both public and commercial services are operational in many countries. When data is integrated directly into a navigation system, traffic information can be used in the system's route calculation.

Operation in TMC in the Car navigation system
Each traffic incident is binary-encoded and sent as a TMC message. Each message consists of an event code, location code, expected incident duration, affected extent and other details.
The message is coded according to the Alert C standard. It contains a list of up to 2048 event phrases (1402 as of 2007) that can be translated by the receiver into the user's language. Some phrases describe individual situations such as a crash, while others cover combinations of events such as construction causing long delays.
In Europe, location code tables are maintained on a national level. Those location tables are integrated in the maps provided by in-vehicle navigation system companies such as Nokia and TomTom and by vehicle manufacturers such as Ford. In other countries, such as the U.S. and Canada, private companies maintain the location tables and market TMC services commercially.
Sources of traffic information typically include police, traffic control centers, camera systems, traffic speed detectors, floating car data, winter driving reports and roadwork reports.

Functionality on TMC in the Car navigation system
This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2012)RDS-TMC is a low-bandwidth system, with each RDS-TMC message comprising 37 data bits sent at most 1–3 times per second, using a basic data channel primarily designed for FM radio tuning and station name identification. Compressing traffic incident descriptions in multiple languages into 16 bits for a location, 11 bits for an event code, plus 5 bits for an extent and a few more bits for the duration and system management was necessary due to constraints in the RDS standard (almost all broadcast data bits were already assigned).
One design challenge of RDS-TMC was to find a way of using 16 bits (about 65,000 combinations) to describe locations across an entire state or country. Such a system could not convey latitude-longitude data (available 25 years later using GPS). Instead, RDS-TMC relies on the use of location tables that point only to significant highway junctions. The precision of each traffic event's location is low compared to modern GPS devices. The user's navigation system locates a driver to about 3 metres (9.8 ft), but only knows, for example, that a crash took place between Exit 3 and Exit 4, northbound on a particular motorway. This limitation is because traffic events (accidents, congestion, burst water mains, faulty traffic lights, etc.) have to be superimposed onto maps by matching the reported location with the location table. If the nearest location table point is distant from the point of the incident, then it appears on a section of main road between two junctions instead of at its exact location. The limited precision can make a significant difference as to how navigation devices interpret the incident, possibly leading to a poor route choice.
In the USA and elsewhere, systems such as Cable television relay service station (CARS) exist[citation needed] that can track and pinpoint event locations with one-meter precision. These real-time data are published in XML for access by companies such as Google and TomTom. These incident reports can be delivered to mobile phones and handheld devices in vehicles.[citation needed] They are not currently in use in most navigational systems for reasons that are unclear.

Security on TMC in car gps navigation system
In April 2007, two Italian security researchers presented research about RDS-TMC at the CanSecWest security conference. The presentation, entitled "Unusual Car Navigation Tricks", raised the point that RDS-TMC is a wireless cleartext protocol and showed how to build a receiver and transmitter with inexpensive electronics capable of injecting false and potentially dangerous messages.
Detailed instructions and schematics were published in Issue No. 64 of Phrack hacking magazine.
The TMC Forum responded by stating that the effects of any 'pirate' TMC broadcasts would be non-existent on users not on routes affected by fake obstruction messages and that such broadcasts would directly interfere with that country's TMC carrier station, which would lead to criminal or civil liability. They stated that it was therefore unlikely that such activity would take place.

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