Core Network: The Backbone of Mobile Communications

Introduction: Why the Core Network Matters

If the Radio Access Network (RAN) is the handshake between your phone and the tower, then the Core Network is the brain, nervous system, and beating heart of the mobile ecosystem. It’s the part of the network where decisions are made, subscribers are authenticated, services are delivered, and—unfortunately—where attackers often find their way in.

In 2G it was mostly about voice switching, in 3G about mobile data, in 4G about all-IP convergence, and in 5G the Core is now software-defined, cloud-native, and more exposed than ever. Whether you’re streaming Netflix, placing a VoLTE call, or connecting a private 5G factory robot, the Core Network makes it happen.

Core Network Functions: What It Does

At its simplest, the Core Network handles four fundamental tasks:

1. Authentication & Security – Verifying that you are a legitimate subscriber (and that your phone isn’t cloned).
2. Mobility Management – Keeping your session alive as you move between cells, cities, or even countries.
3. Session & Service Management – Allocating IP addresses, creating bearers, and ensuring your traffic gets to the right place with the right quality of service.
4. Interconnection & Charging – Linking mobile subscribers to the internet, other operators, and legacy systems, while keeping track of billing.

Evolution of the Core Network

• 2G (GSM Core Network): Based on circuit switching (MSC, HLR, VLR, AuC). Focused on voice calls and SMS.
• 3G (UMTS Core): Introduced packet-switched nodes (SGSN, GGSN) to handle mobile internet.
• 4G (Evolved Packet Core, EPC): Fully IP-based, with key nodes like the MME, SGW, PGW, HSS. Enabled LTE’s high-speed data and VoLTE.
• 5G Core (5GC): Cloud-native, service-based architecture (SBA) built on APIs and microservices. Introduces the AMF, SMF, UPF, and NRF. Much more flexible, but also significantly increases the attack surface.

Protocols in the Core Network

The glue holding everything together is a mix of telecom protocols—many of which were designed decades ago without security in mind:

• SS7 (2G/3G): Still widely used for signaling, but notoriously insecure and exploited for location tracking and SMS interception.
• Diameter (4G): Introduced with LTE, supports encryption, but optional—leaving many deployments exposed.
• HTTP/2 + SBI (5G): API-driven signaling between Network Functions, offering flexibility but also API-level vulnerabilities.
• GTP (GPRS Tunneling Protocol): Still crucial for user data transport, often targeted for fraud and DoS attacks.

Key Components of the Core

• Authentication & Subscriber Databases: HLR (2G/3G), HSS (4G), UDM/AUSF (5G).
• Mobility Anchors: MSC/SGSN in 2G/3G, MME in 4G, AMF in 5G.
• Data Gateways: GGSN in 3G, PGW/SGW in 4G, UPF in 5G.
• Policy & Charging Functions: PCRF (4G), PCF (5G).
• Interconnection Elements: STP for SS7, DRA for Diameter, SEPP for 5G interconnect security.

Security Challenges in the Core

The Core Network has always been a prime target for attackers because it’s where subscriber data, signaling control, and billing information live. Some of the most pressing security risks include:

• Legacy Protocol Attacks: SS7 and Diameter vulnerabilities that remain active even in modern networks.
• Interconnection Threats: Malicious signaling from roaming partners or compromised operators.
• GTP Exploits: Used to bypass billing, inject traffic, or perform denial-of-service.
• API Abuse in 5G: Poorly secured service-based interfaces can be exploited just like in enterprise IT.
• Configuration & Exposure: Misconfigured firewalls, open test nodes, or internet-exposed core elements.

As operators migrate from hardware-based EPCs to virtualized and cloud-native 5G cores, the attack surface multiplies: containers, orchestration systems, cloud supply chains, and misconfigured Kubernetes clusters all become part of the mobile security equation.

Why Core Network Security Matters

When the Core is compromised, attackers don’t just snoop on calls—they can hijack subscriber sessions, steal identities, manipulate billing, and disrupt entire national services. In fact, many nation-state APT groups target core networks precisely because it gives them leverage over entire populations.

With the EU’s NIS2 directive, the Cyber Resilience Act, and national security agencies pushing stricter telecom security, operators are under pressure to protect their core with the same rigor as critical infrastructure.

Conclusion

The Core Network is the invisible backbone of mobile connectivity, evolving from simple circuit-switched nodes in 2G to cloud-native microservices in 5G. It enables billions of connections daily, but its complexity and exposure also make it one of the most attractive targets for attackers.

Understanding the Core—its functions, protocols, and vulnerabilities—isn’t optional. It’s the first step in reducing the attack surface of mobile networks and securing the foundation on which modern digital society depends.

🔐 Looking for the full picture? Explore the Ultimate Guide to Mobile Network Security — your complete resource on telecom security, from architecture to audits.