Evolving the Network Toward 5G
How the Network Evolved And Made 5G easier
Mobile networks used to be more complex than they are now because they were a hybrid ➖ you might even say chimera ➖ that combined a circuit switched telephone network with a packet switched data network. Phone calls were carried over dedicated synchronous channels from the phone to the cell site and from there to a telephone switch. Data was carried on separate channels, one for customer data and another for control signals from the network. (We've skipped mobile telephones that didn't connect to the internet. Wikipedia has a good history here: https://en.wikipedia.org/wiki/History_of_mobile_phones)
When People Talked On Telephones
The telephone network was designed to best serve people talking to one another. Quaint. At its height, the fixed-line telephone network could deliver your voice with minimal latency by building a "virtual circuit" from one side of the planet to the other, where the analog signal from your home phone would arrive at a telephone switch, get digitized, and put on a digital virtual circuit that could guarantee that the digital bits representing your voice arrived, synchronously, on the far side of the planet, or anyplace else, within a few milliseconds, and there get turned back into a voltage on a copper wire that moves the diaphragm in the earpiece of another telephone. This technological triumph was called the Synchronous Digital Hierarchy (SDH). Mobile phones were an adjunct to the SDH, and the design of the mobile network reflected that.
Access to the telephone network is limited to subscribers. There are multiple network operators, each with their own network and their own subscribers. Within that network, subscribers who were all previously tethered to copper wires running to their homes were now untethered. The databases of subscribers had to be networked within and among the mobile network operators, and subscribers had to be tracked and identified wherever they went. Complex charging, rating, and billing had to be implemented to bill subscribers accurately for how much they talked, and how much data they consumed. Data was not treated quite like internet packets of data. Within the parts of the network from a so-called "serving node" to the mobile device, a kind of "tunnel" of packets within packets was created so that each user's tunnel could follow him or her around the mobile network. But then, things got simpler.
The Evolved Packet Core
Voltages on copper wires and the Synchronous Digital Hierarchy are relics of a past glory. People talk on computers, using apps, especially when they want to talk to their relatives around the planet without straining their budgets. Latency and jitter can be worse, but, evidently, people don't care. Increasingly, internet voice quality is, depending on the app, better than that on the telephone network. Voice is now a tiny amount of the traffic carried on global telecommunications networks. The internet ate the telephone network, and is eating every other specialized type of network such as cable TV and satellite TV networks as well.
There is no longer a reason to support virtual circuits in the mobile network, or any telephone network, for that matter. "Telephone" is now just another app that uses telephone numbers as a means of identifying users. Network operators can save equipment and operating costs by adopting internet packet switching for everything. In fact, your phone probably supports a technology called Voice over LTE, or VoLTE. If your network operator supports VoLTE, your voice, when making a phone call, is carried in packets from the phone to wherever it is destined.
To take advantage of the packetizing of everything in Internet Protocol (IP) packets, network operators have replaced their circuit switched network with a technology call the Evolved Packet Core (EPC).
The Evolved Packet Core, and VoLTE, plays an important role in smoothing the transition to 5G, especially to Non-Standalone (NSA) 5G networks that work alongside the LTE network. Except for needing to handle more bits, and some new signaling, the EPC is mostly the same for 5G as it is for LTE.
You might therefore be excused for thinking that NSA 5G networks are really just part of a Long Term Evolution.