Today's telecom market demands flexibility and rapid service deployment from operators, yet growth is held back by legacy monolithic BSS/OSS systems. The transition to 5G networks requires transforming infrastructure into a scalable, cloud-native environment. Since the telecom core cannot be shut down for updates, modernization must occur in phases by building integration layers.
What is at stake for the industry
Monolithic architecture tightly couples billing, routing, and profile management, which slows down the launch of new services. Furthermore, legacy signaling protocols like SS7 and Diameter have significant vulnerabilities. According to the ENISA Threat Landscape 2025 report, the exploitation of these protocols remains a constant threat. According to the CFCA 2025 study, global losses from telecom fraud reach approximately $41.82 billion annually.
Architectural benchmarks: ODA and SBA
To overcome the limitations of monoliths, the industry uses two standardized approaches:
- Open Digital Architecture (ODA) by TM Forum involves replacing monoliths with a component-based, API-first architecture where modules operate autonomously.
- Service-Based Architecture (SBA) by 3GPP transforms network elements into software functions that interact via APIs, ensuring dynamic scaling.
The Strangler Fig strategy
The safest modernization method is the Strangler Fig strategy, which involves three stages:
- Creating an API-first integration layer on top of the monolith to intercept requests.
- Gradually decoupling individual functions into independent, ODA-compliant modules.
- Migrating network functions to a 3GPP-compliant SBA architecture for the 5G core.
Security and integration solutions
During the transition period, legacy traffic is isolated using signaling firewalls, while a Zero Trust approach is implemented for new microservices. Specialized platforms, including low-code tools like UnityBase by Intecracy Group, are used to build transit architectures and integrate OSS/BSS. They allow for the rapid generation of REST APIs to connect the legacy core with new microservices based on a unified metadata model.
Infrastructure maturity levels
- Level 1 (Legacy Monolith): Proprietary hardware, monolithic BSS/OSS, unsecure protocols.
- Level 2 (Hybrid Integration): API-first layers on top of the monolith, basic traffic monitoring.
- Level 3 (ODA-Compliant): Component-based architecture, interaction via open APIs.
- Level 4 (Cloud-Native): Microservices-based 5G core architecture, Zero Trust security.
Action plan
To successfully modernize telecom infrastructure without disrupting ongoing operations, operators should adopt a structured transition plan:
- Apply the Strangler Fig strategy to gradually replace monolithic functions with microservices without shutting down the core.
- Deploy integration platforms like UnityBase to quickly build API-first transit architectures and connect legacy systems.
- Protect vulnerable legacy protocols with signaling firewalls while implementing a Zero Trust framework for all new cloud-native services.
Prepared by a Software Ukraine member. Original publication.