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When aircraft are detected by radar and their transponders 'ping' back to the radar site, this data is passed over data network cables to the air traffic controllers.
Is there typically any specialist equipment (high safety certification?) to send the data from the radar site on to the data network? Or is it something as simple as a server/PC with a network card?
I'll describe the typical Mode-S radar system based on my mostly European experience. Details will vary but the general concept applies world wide.
The radio signal received from the aircraft is digitized, CRC checked, compared to and combined with data from earlier transmissions from the aircraft. This data is usually encoded in ASTERIX format (typically category 048PDF) and transmitted over a datalink to a surveillance data processing system (SDPS) in the ATC centre. From the SDPS the data is further distributed to various client systems, among which the air traffic controller display system is one.
The radar processing itself is partly dedicated hardware and partly COTS (commercial-off-the-shelf) infrastructure. This is housed in a standard server cabinet. Network components are typically COTS high quality systems and duplicated for redundancy.
The datalink from the radar site to the ATC facilities can take many forms. Every country has its own regulator and local telecom market peculiarities, leading to a variety of implementations. Often a dedicated line will be used, usually with a backup line as well. Sometimes two telecom providers are used that have to provide fully independent data paths to the ATC centre. In a few cases radio links are used to connect surveillance systems, I know of surveillance systems (not radars) that use satellite links.
Within the ATC centre usually duplicated or triplicated networks are used for redundancy. These can be UTP or glassfibre networks. These are again based on COTS high availability/integrity components.
While I think that DeltaLima is the most suitable to answer that question, I will make an attempt from my experience in Hellenic airspace.
The territory you want to controll has several RADAR installations. They may be primary, secondary or both. Each of these RADARs are connected to the ACC with a leased line (leased from National Telecomunications Organization in the case of Greece). I don't know of any specific protocols used (ASTERIX maybe? And I think X.25 on the data link layer). Then radar data from each individual RADAR is processed by the RDP (RADAR Data Procesor). RDP is a computer (maybe more than one) but you can't easily call it PC. The end result (containing position, ground speed, direction and altitude and Mode A code for the case of secondary radar covered track) is sent to the controller positions using a LAN protocol.
You can say that while the concept is similar to "one PC with a network card" the reality is much more complex, and has to do with safety, redundancy and very ofter with old hardware (you can't change RADARs or any other ATM equipment every 1 or 2 years just to have the latest of them).
