I last covered how the control channel is the software brains behind modern day trunked radio repeaters. But how exactly does a control channel work? The system itself can be compared to an air traffic controller.
An air traffic controller is the logistical gateway for airplane movement both on the ground and in the air. The airplane pilot may steer the plane, but he isn’t allowed to move or fly until authorized by the controller. The controller also keeps planes separated on the ground and in the air ensuring no ramp or mid-air collisions occur.
The Control Channel
The control channel of a repeater performs these same operations. No communication occurs until the control channel gives the go ahead just as an air traffic controller would for airplanes. From the moment the two-way radio is turned on, the radio checks in with the control channel and electronically asks permission to join the radio network. Once approved by the controller, the radio is told to hold until for its next task is issued by the control channel. Just like an airplane pilot, the two-way radio must communicate with the controller before being allowed to talk with other radios on the network. And similar to runways at an airport, the control channels separates radio traffic to different frequencies (think runways) ensuring no two-way radio traffic collides with each other.
It gets even better
Certain radio towers are part of a regional network and have the potential to be part of a global network using IP based technologies. This regional network has its own separate control channel which regulates regional traffic just like ATC regions (aka: air centers).
Why the Need?
I agree the systems I am describing are much more complicated than 1990 systems, but there is a need as evidenced in hurricane Katrina when all communication stopped including cell phones. Temporary satellite towers were strategically positioned in the affected areas after days of no power, towers, or communication in the area. The resulting advancement of the MSWIN radio and data network is a good example of mission-critical vendor neutral communication network. Pre-trunk systems were sporadically located and loosely funded resulting in lackluster communication across the full state of MS. There is a lot of politics involved considering this is a government funded entity working through governmental delays and bureaucratic administration, but today’s MSWIN network is extremely advanced post-Katrina.
As a final side note, you may be wondering how Mississippi inherited the MSWIN network considering New Orleans got all the news coverage of Katrina. That’s cause the majority of the state was without power in the aftermath as highlighted by Katrina’s path in the adjacent picture. As a result, most of Mississippi was dark and off-grid for days in major cities and weeks in rural areas.