Have a suspicion of what RCL is but can you amplify? Is it in additional to track code signaling? Since the line from Greensboro = Raleigh went straight from dark to CTC is RCL somewhat new or is it a NS standard using it system wide in places? Exactly how is the line from Raleigh= Selma signaled as have read it is different?
I am no expert on this but I am willing to type out what I think I know and my short history in the hobby of ATCSMon.
I think RCL came about in the late 1980s or early 1990s. Many RR's use this type of network that has CTC and it is used to control switches and signals and I think it might also help with hot boxes and FREDs at the end of the train. Basically RCL replaced "telegraph" lines with wireless transmission using some frequencies set aside by the FCC. The signal was not encoded and the AAR may have even published whtie papers on the tech for anyone to read. Someone figured out how to decode the signal and make sense of all the data. From what I can tell most railroads that are Class I used this technology and many still do use it, such as NS. CSX dropped this for bouncing the signal off of satellites about a decade ago. (I am not arond CSX much but in the few cases I am near CSX control boxes at switches and signals the boxes have small parabolic antennas pointing to the sky. ) Other railroads I think have moved to fiber in the ground if they are off RCL. Right now the FCC is forcing, from my understanding, the RRs to drop the frequencies being used (I think there may be plans to use the RCL frequencies for cell phone in the future or maybe government emergency/first responder communications. I read about this but I don't remember) and this is going to be done in 2 or 3 years or maybe even less time than that. From what I can gather this process is happening as I type this. Some RR's will go to fiber, some may adopt the satellite tech used by CSX and some may continue with RCL but at a different frequency AND, heres the kicker, with encrypted data, and that will be hard to get the docs to decrypt and most think reverse engineering would be breaking the law around decrypting data that is not allowed by the encrypting party.
I moved to my home on the extreme east of Greensboro in 2009 and I can't remember if I stumbled on ATCSMon then or before I lived here. We moved from the extreme south side of Greensboro and near the dark CF line that runs south from Greensboro towards Sanford. But one way or another I found out about it and was asked to help and I passed on it for a decade almost as I did not want to spend money running a computer and have to devote internet bandwidth to the cause with a family of 5 all needing internet.
Now I have gigafiber with ATT so plenty of bandwidth and the wife and I are empty-nesters so no worries about 5 people needing to use the internet at once. The person that installed my system donated the antenna, wiring and software defined radio to connect to the computer. I donated an old Win7 machine but they have that ready to go as well. He set everything up so I never had to read any documentation that would have explained all this tech in detail. I log on every other day or so just to make sure my system is sending the signal out to the servers but I don't watch it that much. It is interesting and I am glad I can serve a need for railfans that do lots of sitting by track-side to watch trains come by. My software defined radio moves off the frequency some so I know how to fix that. A few months after I finally got this up and running is when I first started hearing rumors about it going away over the next couple of years.
ATCSMon can be a bit hard to set up but it works fine for the one track I have which is the NC-Line by my house. Connected and separate to this is TrainMon5 which takes the data going to ATCS servers around the country and converts that to something that a web browser can show. I use that on my phone and it allows coverage around the country. Not every ATCS route is converted to TrainMon5. From what I can tell some people running ATCS do not want to work with TrainMon5 for some reason so TrainMon5 is a subset of what is available on ATCSMon. The other caveat is that people have to agree to host and be near the signal boxes. I am about a mile from the McLeansville control point and about 2-3 miles from the Superior Control Point. McLeansville gives me a clean signal about 95% of the time and Superior is about 80% of the time. I can sometimes pick up Fields, which is just to the east of the Greensboro station and about 6-7 miles from me. Fields is very sporadic for me. Sometimes I can pick up a signal 50 or more miles away such as Nelson, but I never seem to get anything to the west of Greensboro's station which are quite close, at least compared to control point Nelson. Something about Nelson and geography I guess. I need to check out that area on Google Earth. Recently some signals around Cary went off line for ATCSMon when a restaurant closed and they served as our computer location. That happens. There is a consolidated route on TrainMon5 that is the NC main from Atlanta up into Virginia and then also the NC-line from Greensboro to Raleigh and also the line from Winston-Salem to Roanoke and Charlotte to Columbia.
I hope I answered your question. I started rambling. Sorry for the long post and it is a bit off Amtrak discussion.