I am guessing that the data feed requirements of ATC telemetry are fairly modest, well within the range that a pair of analog modems could handle. You don't hav

I am guessing that the data feed requirements of ATC telemetry are fairly modest, well within the range that a pair of analog modems could handle. You don't have to send a raw radar feed to the airport, just put the intelligence (object detection, delta computation, etc) at the endpoints and transmit the results. I'm also guessing that they do this every day at hundreds of other airports, and it works just fine. Moving to fiber gives you greater bandwidth, reliability, multipath redundancy, etc. But I bet the real motivation is access to newer and more general communications equipment. Maintaining the old, perfectly adequate but increasingly unusual hardware/software is more of a pain than replacing with new stuff that exceeds requirements but is maintained just like all the other modern stuff everywhere. All guesses. I do not work in ATC, but I've seen the pattern in other industries with similarish requirements.