How does it work? In order to provide data, the Ground Station needs to be "Pinged" to identify who you are and it needs to know WHERE you are. The 'Ping' is generated by the ADS-B Out equipment and the 'Where' is determined by your WAAS GPS (hence the need for the WAAS GPS). Your GPS provides position data to your ADS-B Equipment and your ADS-B equipment then sends your position to the ADS-B Ground Station as it 'Pings' the station. The Ground Station in turn, knowing where you are and what aircraft are around you, will transmit a TIS-B Cylinder of Surveillance to your ADS-B In equipment placing your aircraft right smack in the middle of the cylinder. If equipped with a complete ADS-B UAT System with display and/or an additional portable ADS-B system, your Cylinder of Surveillance will be displayed accordingly on the display. Note: This is the data that is only partially supplied or MISSING completely when equipped with ONLY a Portable type system (not ADS-B OUT compliant).
Another key note in this discussion is to recognize that installing a new 'ES' transponder (or grading an existing Mode S transponder to 'ES'), combined with a WAAS GPS, does NOT give you a Cylinder of Surveillance, it only gives you the SAME TIS-A traffic that would have been achieved from a non-ES Mode S transponder and that is assuming that you are within range of one of the remaining terminal radars that support TIS-A Broadcast. However, combining this upgrade with a portable ADS-B system WILL provide you with a Cylinder of Surveillance as displayed on your portable display. An exception to the is the Garmin GTX345 series Transponders which are not just ADS-B OUT compliant but also have a complete dual-band ADS-B receiver built in. See Chart Below.
For the purpose of simplifying the following chart, lets define "Cylinder of Surveillance" (Abbreviated COS) - It is defined as the area 15nm radius and +/-3500 ft. surrounding your aircraft (or other ADS-B aircraft) which contains traffic data.