Asynchronous APIs: a much-needed evolution for telcos?

How can CSPs truly keep pace with customer demands and the rapid evolution of digital services? As the industry shifts from rigid, request-response architectures to flexible, event-driven integrations, Leonardo Hodgson explores how asynchronous APIs are unlocking new levels of efficiency and innovation across the telco ecosystem.

CSPs are under constant pressure to innovate and modernise their BSS/OSS platforms to meet evolving customer expectations and enable new business models. Integration has always been one of the biggest challenges in this digital transformation.

For decades, Service-Oriented Architecture (SOA) and synchronous APIs were the backbone of BSS/OSS interoperability, but as networks and services grow more complex and customer expectations continue to rise, these models are reaching their limits.

Asynchronous and event-driven APIs are the natural, necessary next-step. By complementing and enhancing traditional request-response APIs, they provide CSPs with the flexibility to handle long-running processes and real-time interactions, providing better support for loosely coupled ecosystems. TM Forum's Open Digital Architecture (ODA) and its REST-based Open APIs are at the centre of this shift, guiding the industry towards more resilient and adaptable integration models.

From SOA to ODA: the evolution of telco integration

SOA introduced the principle of modular services, accessible through well-defined interfaces. This reduced duplication and improved interoperability, giving CSPs a framework to manage complex BSS/OSS processes.

However, SOA implementations were often rigid, dependent on central orchestration layers like enterprise service buses (ESBs) and focused on synchronous interactions.

ODA builds on these principles, adapting them for the cloud-native era and modern integration demands. Instead of monolithic stacks, ODA promotes a composable BSS/OSS architecture with modular components (such as Product Catalogue, Service Inventory or Order Management), each exposing standard Open APIs. It also embraces containerisation, microservices, DevOps practices like CI/CD, and an API-first mindset.

Now, TM Forum’s new Gen5 Open APIs support the latest event-driven architectures, acknowledging that not all interactions work well with the traditional synchronous request-response flows.

Why asynchronous and event-driven APIs are essential

CSP operations typically involve interactions across multiple systems and actions can happen over extended periods. For example, Service Activation, Provisioning or Order Fulfilment may involve dozens of steps, including some with external dependencies that may take time to complete. A purely synchronous model forces clients to wait for completion or continuously poll, leading to inefficiency and tight coupling dynamics.

An asynchronous approach addresses this situation by decoupling the request from the final response. A system can accept a request, acknowledge it immediately, and complete the work in the background. Clients can then monitor the status or receive a callback when the operation finishes.

Event-driven APIs go further, enabling systems to react automatically to changes in state. Instead of repeatedly querying for updates, an order management system can subscribe to "order completed" events, or a partner platform can receive real-time notifications when a customer activates a new service – this is exactly how the Cerillion Notification System (CNS) works. This decoupling makes integration more scalable, efficient and responsive, especially in multi-vendor or partner ecosystems.

Evolving Open APIs & ODA

TM Forum's Open APIs have become a global standard, adopted by major CSPs, technology partners, system integrators and vendors.

While originally designed for synchronous REST interactions, the latest version of the API design guidelines document (TMF630) explicitly supports and details asynchronous and event-driven patterns:

• Asynchronous operations
  Describe patterns such as the "monitor" resource, allowing clients to check the progress of long-running operations.
• Notifications and events
  APIs can expose subscription mechanisms so that external systems receive callbacks when relevant state changes occur. 
• Hybrid adoption
  New asynchronous APIs are being added to the Open API Directory, complementing the existing REST set. TM Forum also highlights the use of AsyncAPI specifications to define event contracts, aligning with modern event streaming technologies.

Together, these developments ensure that ODA can support both traditional RESTful integration and newer event-driven approaches in a consistent and standardised way.

Challenges and considerations

Moving towards the latest generation of APIs brings benefits, but also gives rise to new and complex challenges for CSPs to address:

• Correlation
  Linking responses or events back to the original request.
• Reliability
  Handling retries, duplicates and ordering in event streams.
• Security
  Ensuring only authorised consumers receive sensitive events.
• Governance
  Managing schemas, versioning and the lifecycle of APIs and events.
• Legacy systems
  Coexistence of older, synchronous systems with newer, event-driven components.

These challenges require careful design and robust operational practices to ensure reliability – TM Forum's specifications and guidelines provide a shared foundation to address these issues.

Conclusion

As more CSPs adopt ODA, event-driven architectures and asynchronous APIs will become standard practice rather than optional enhancements. They enable CSPs to scale integrations, support real-time digital services, and accelerate time-to-market in dynamic partner ecosystems.

The industry is unlikely to stop using synchronous REST APIs anytime soon, because they will remain the most suitable and effective method for many integration scenarios.

However, the future of integration is hybrid, with: 

• synchronous APIs for straightforward, immediate operations; and
• asynchronous or event-driven patterns for long-running use cases.

Telco integration has always evolved with the industry's needs. REST APIs simplified interoperability and adoption. Now, asynchronous and event-driven APIs extend this evolution, offering CSPs the flexibility to operate and integrate systems in a more efficient, adaptable and scalable manner.