Let me explain it like this. In the olden days, after Alexander Bell invented the telephone, man had end-to-end communication, and this is what most panels used. They would dial a number, establish communications, communicate and then break the connection. This is how the once-a-day, or once a week communication worked. People were happy for the most part. This was called "circuit-switched" communications.
Then one day, Al Gore invented the Internet and the world would be changed. No longer would you need to use your 300 baud modem to establish a connection. You could have 100% 24/7 connections that were always on. This was called "packet-switched" communications.
Cellular did go through its own transformation, first using circuit-switched analog (making a call) and this was called 1st Generation, or 1G for short. But in the early 90's, packet-switched data became available in cellular, and it was called 2nd Generation, or 2G. This was digital.
Today we are at 3G or 4G with cellular, and packet-switched networks are very common. So YES, the technology does exist today to have a completely monitored connection over a digital link. Its not magic, and information on if a connection exists or not is actually built into the standard, as with a wired standard. Look at where an Ethernet cable plugs into your device and you usually see a green and yellow LED. Remove the connector and the LEDs go out. Cellular has the same concept but maybe not the green and yellow LEDs. This is connection and data information. So YES, it does REALLY exist.
By the way, even with circuit-switched networks, places like banks commonly used a constantly monitored analog connection, so if the line was cut, both sides would know it, and this was in the 1800's.
