TL;DR
- Mobile networks consist of radio base stations, backhaul links and a core network — each element handles a distinct part of delivering your call or data.
- Each generation (2G through 5G) uses different radio techniques and spectrum bands, producing progressively higher speeds and lower latency.
- When you move between coverage areas, a process called handover transfers your active session between base stations without dropping the connection.
- Ofcom licences and auctions the radio spectrum that operators need to run their networks across the UK.
- 3G networks are being progressively shut down by UK operators; 2G is being retained longer to support IoT and basic voice services.
The three layers of a mobile network
Every mobile network can be understood as three cooperating layers. The radio access network (RAN) is what most people picture — the masts and base stations that broadcast radio signals within a defined geographic area called a cell. Your handset communicates wirelessly with the nearest base station using a licensed frequency band. The physical mast you see on a hilltop or rooftop typically carries antennae serving several directional sectors, each of which forms its own cell.
The backhaul layer connects each base station back to the operator’s internal infrastructure, usually via fibre or microwave links. Finally, the core network handles authentication (verifying that your SIM is allowed on the network), routing of calls and data packets, charging, handover coordination, and interconnection with other operators and the public internet. In 4G and 5G, the core is almost entirely software-defined, meaning operators can reconfigure functions without touching hardware.
How a call or data session begins
When you switch on your phone, it scans available frequencies, selects the strongest signal from a base station on its home network (or a roaming partner), and registers its location with the core. This idle-mode registration lets the network page your phone when an incoming call arrives. When you initiate a call or open an app, your handset and the base station negotiate a radio channel, agree on modulation and coding rates that suit the signal quality, and open a bearer — a logical pipe through the network.
Voice calls on modern 4G networks typically travel as VoLTE (Voice over LTE) packets, treated with high priority so that jitter and delay remain imperceptible. On 2G and 3G, voice used circuit-switched connections that reserved a fixed channel for the duration of the call. The shift to packet-switched voice is one reason operators can carry more simultaneous calls on the same spectrum.
Handover: moving between cells without dropping the call
Because cells cover finite areas, a moving handset must transfer its active session from one base station to another. This process, called a handover (or handoff), is coordinated by the network. Your phone continuously measures signal strength from neighbouring cells and reports those measurements to the serving base station. When the serving station determines a neighbouring cell would provide a better connection, it signals the target base station to prepare resources, then instructs your handset to switch — all within milliseconds.
In 4G LTE, handovers are managed by the base station itself (called an eNodeB) with minimal core-network involvement, reducing latency. In 5G New Radio (NR), a similar distributed architecture (gNodeB) manages handovers, and additional techniques such as dual connectivity allow the handset to maintain simultaneous connections to both a 4G anchor cell and a 5G cell, improving continuity at the edge of 5G coverage areas.
Mobile generations: what actually changed
The “G” in 2G, 3G, 4G and 5G refers to distinct generations of standardised radio technology, each defined by international bodies including 3GPP (3rd Generation Partnership Project). Each generation brought new modulation schemes, spectral efficiency improvements and architectural changes — not merely faster speeds, though that is the most visible consumer outcome.
2G (GSM/GPRS/EDGE) digitised voice and introduced rudimentary data. 3G (UMTS/HSPA) enabled mobile broadband at speeds sufficient for web browsing. 4G (LTE/LTE-A) was engineered as an all-IP network from the outset, delivering speeds that could substitute home broadband in many scenarios. 5G NR introduces network slicing (partitioning one physical network into virtualised slices for different use cases), massive MIMO antenna arrays, and millimetre-wave bands capable of multi-gigabit peak speeds in dense areas.
| Generation | UK Launch Era | Typical Peak Speed | Primary Use | Current Status (UK) |
|---|---|---|---|---|
| 2G (GSM/GPRS/EDGE) | Early 1990s | Up to ~0.3 Mbit/s (EDGE) | Digital voice, SMS, basic data | Active; retained for IoT and basic voice coverage |
| 3G (UMTS/HSPA+) | Early 2000s | Up to ~42 Mbit/s (HSPA+) | Mobile broadband, video calls | Being phased out by UK operators |
| 4G (LTE/LTE-A) | 2012 | Up to ~300 Mbit/s (LTE-A) | All-IP voice (VoLTE), streaming, mobile broadband | Dominant; extensive UK coverage |
| 5G NR (Sub-6 GHz) | 2019 | Typically 100–600 Mbit/s in commercial conditions | Enhanced mobile broadband, fixed wireless access, IoT slicing | Expanding; primarily urban and suburban |
| 5G NR (mmWave) | Limited UK trials | Multi-Gbit/s peak in line-of-sight | High-density venues, industrial use cases | Early deployment; limited coverage |
Spectrum: the invisible resource operators compete for
Radio spectrum is the range of electromagnetic frequencies over which wireless signals travel. For mobile networks, spectrum is divided into licensed bands — ranges of frequencies that an operator pays to use exclusively within a geographic area. Ofcom, the UK’s communications regulator, is responsible under the Wireless Telegraphy Act 2006 for managing spectrum in the national interest. It publishes a UK Frequency Allocation Table that records every allocated band and its permitted uses.
Operators acquire spectrum through Ofcom auctions or trading of existing licences. Different bands have different physical properties: lower frequencies (such as 700 MHz or 800 MHz) travel further and penetrate buildings better, making them valuable for wide-area rural coverage; higher frequencies (such as 3.4–3.8 GHz used for 5G) carry more data but over shorter distances. A large operator typically holds spectrum across several bands to balance coverage and capacity.
The core network and what it does
The core network is the operator’s central nervous system. In 4G, it is called the Evolved Packet Core (EPC); in 5G Standalone (SA), it becomes the 5G Core (5GC), built on cloud-native microservices. Key functions include the Home Subscriber Server (HSS) or Unified Data Management (UDM) in 5G, which holds SIM authentication credentials; the Mobility Management Entity (MME) or Access and Mobility Management Function (AMF), which tracks device location and manages handovers; and the Packet Gateway, which routes data to the internet and enforces charging policies.
When you roam abroad, your home network’s core communicates with the visited network’s core to authorise use and record usage for billing. This interoperability is governed by GSMA technical specifications and bilateral agreements between operators, meaning the architecture is intentionally standardised internationally even while each operator’s commercial implementation differs.
What this means in practice
Consider Priya, commuting by train from Leeds to York. As the train leaves the station, her phone connects to a 4G base station on the city fringe. The train accelerates and the signal from that cell weakens; her handset measures a stronger signal from a roadside mast ahead and reports this to the network. Within milliseconds, a handover is executed — her VoLTE call continues without interruption even though the serving base station has changed. Between two villages where 4G coverage is thinner, her phone may briefly fall back to 2G for voice, then re-attach to 4G once the train reaches a more densely covered area. This seamless generation-switching happens automatically, governed by parameters the operator configures in its radio access network, and is invisible to Priya unless she notices the status indicator on her screen.
Related Guides
How we verified this
This article draws on Ofcom’s Connected Nations reports, the Wireless Telegraphy Act 2006 (legislation.gov.uk), Ofcom’s UK Frequency Allocation Table, 3GPP published standards documentation, and GSMA technical background papers on network architecture and roaming interoperability.
Disclaimer: Kaeltripton.com is an independent UK editorial publisher. We are not regulated by Ofcom or the FCA and we do not sell or arrange mobile services, insurance, or financial products. This content is for general information only and is not legal, financial, or technical advice. Rules, prices, and operator policies change. Verify the current position with Ofcom, GOV.UK, the ICO, or your provider before acting. ICO registered ZC135439. Last reviewed: 2026-06-05.
Frequently Asked Questions
What is a mobile network?
A mobile network is a radio communications infrastructure that allows devices fitted with a SIM card to make calls, send messages and access the internet wirelessly. It consists of radio base stations (masts), backhaul links carrying traffic to the operator’s core, and a core network that handles authentication, routing and charging. In the UK, Ofcom licences the spectrum that each network operator uses.
What is the difference between 4G and 5G?
4G LTE delivers typical real-world speeds of tens to low hundreds of megabits per second and latency around 30–50 milliseconds. 5G NR, using mid-band spectrum such as 3.4–3.8 GHz, can deliver faster speeds and lower latency — often sub-20 ms — and supports network slicing, which lets operators dedicate virtualised portions of the network to specific services. In practice, the gap is most noticeable in dense urban areas where 5G capacity reduces congestion.
How does a mobile call travel from my phone to another?
Your voice is digitised and packetised by your handset, then transmitted over radio to the nearest base station. The base station forwards the packets via backhaul to the operator’s core network, which routes them to the destination — either across the same operator’s infrastructure or via an interconnect to another network. The recipient’s core delivers the packets to their serving base station, which transmits them to the destination handset. On modern 4G networks this entire path uses Voice over LTE (VoLTE).
What is spectrum?
Spectrum refers to the range of radio frequencies used to transmit wireless signals. For mobile networks, specific bands of spectrum are licensed to operators, giving them the exclusive right to use those frequencies in defined geographic areas. Different frequency ranges have distinct physical properties — lower bands cover wider areas, higher bands carry more data but over shorter distances. Spectrum is a finite, shared national resource managed in the UK by Ofcom under the Wireless Telegraphy Act 2006.
Who assigns mobile spectrum in the UK?
Ofcom is the statutory regulator responsible for managing the radio spectrum in the UK, acting under powers granted by the Wireless Telegraphy Act 2006. It awards licences through competitive auctions, administered assignments or trading schemes. Ofcom also publishes the UK Frequency Allocation Table, which maps every frequency band to its permitted use, and publishes conditions attached to each spectrum licence, including coverage obligations that operators must meet.
