In mobile telecom, security at the signaling layer is still catching up with attacker capabilities. Even as networks evolve toward 5G and cloud-native cores, legacy signaling protocols like SS7, DIAMETER, and GTP remain deeply embedded—and persistently vulnerable.
This is why signaling firewalls are essential. But as attack surfaces grow and adversaries become more sophisticated, firewalls alone are no longer enough. Operators need Intrusion Detection Systems (IDS) purpose-built for telecom—like PTM (P1 Telecom Monitor)—to gain real-time visibility into what firewalls miss.
Let’s break down why.
SS7 Firewalls: Defending a 1970s Protocol in 2025
The risk:
SS7 was never designed with security in mind. It enables call setup, roaming, SMS delivery, and more in 2G and 3G networks—but lacks authentication and encryption by default.
Firewall role:
SS7 firewalls inspect signaling messages (MAP/CAP), applying policy rules to:
- Block location tracking (SRI-SM abuse)
- Stop SMS interception (ForwardSM spoofing)
- Prevent denial of service to HLR, MSC, or VLR
Beyond firewalls:
SS7 attacks can be stealthy and subtle. A misconfigured roaming partner, for instance, might send messages that appear legitimate but exploit outdated rules. That’s where an IDS becomes critical—detecting behavioral anomalies across days or weeks, even when firewalls permit the message.
DIAMETER Firewalls: 4G’s Core Needs Core Security
The risk:
DIAMETER is the backbone protocol in LTE—used for authentication (S6a), charging (Gy), and policy control (Gx). But many deployments still operate without TLS encryption or robust peer validation.
Firewall role:
DIAMETER firewalls inspect AVPs and validate:
- Session states
- Origin-host correctness
- AVP length and content
- Interface-specific policies
Why you also need IDS:
Firewalls can enforce static policy, but can’t always detect slow misuse or data leakage. A compromised peer may gradually exfiltrate user data over allowed interfaces. An IDS like PTM can observe this over time and raise alerts based on behavioral baselines—something a rule-based system won’t catch.
GTP Firewalls: Protecting the Data Plane Tunnel
The risk:
GTP enables user plane data tunneling (GTP-U) and control plane session signaling (GTP-C). It’s critical for 4G and 5G NSA networks but is vulnerable to:
- IMSI spoofing
- Rogue session creation
- IP address conflicts
- DoS via tunnel floods
Firewall role:
A GTP firewall monitors control plane messages and:
- Validates CreateSessionRequest and TEIDs
- Tracks tunnel lifecycles
- Ensures integrity between control and user planes
Why an IDS is vital:
Attackers may exploit slow tunnel manipulations, malformed GTP-U payloads, or abuse roaming peer connections with erratic but non-blockable behavior. Firewalls may miss these unless explicitly configured. PTM continuously analyzes all GTP traffic—both control and user plane—to detect anomalies at the tunnel level.
The Role of Telecom Intrusion Detection Systems (IDS)
Unlike traditional firewalls that block known bad traffic, IDS are built to observe — identifying unknown, novel, or stealthy threats through continuous monitoring.
An IDS like PTM (P1 Telecom Monitor):
- Parses SS7, DIAMETER, GTP in real-time
- Builds session-level behavioral baselines
- Detects anomalies, misuse, and slow-burning attacks
- Tags and alerts on unknown or zero-day signaling behaviors
- Offers forensic search across past signaling traffic
Why both are necessary:
- Firewalls = real-time enforcement
- IDS = real-time visibility + long-term detection
In modern telecom security architecture, they are complementary—not redundant. Firewalls provide defense-in-place, while IDS gives you a radar view of your mobile core.
Summary: You Need Both Shields and Sensors
Telecom signaling protocols are a prime target—and attackers often fly under the radar. Firewalls for SS7, DIAMETER, and GTP are essential to enforce baseline hygiene, but Intrusion Detection Systems like PTM are your best bet for catching what slips through.
With hybrid networks still running 2G to 5G NSA protocols in parallel, telecom operators need layered defenses:
- Firewalls to block.
- IDS to detect.
- Forensics to understand.
Don’t just build walls—build visibility.
🔐 Looking for the full picture? Explore the Ultimate Guide to Mobile Network Security — your complete resource on telecom security, from architecture to audits.
