Harmonized API Layer (HAL)

Deutsche Telekom (and T-HT as part of group) has been using TM Forum Open APIs to meet a large business initiative to transform their complex back-end systems and introduce a single mobile application (OneApp) across Europe. Project goal was to implement a central system for setting mandatory standards for most of functionalities including common data models for implemented APIs for different National Companies (NatCos), and describing the work flows of recurring business processes. The purpose of a central HAL system is to provide a common context for most of telecommunication operators operating under Deutsch Telekom Group.


  • Complex back-end systems
  • Ever changing process of revising and defining a common ground processes and documentation within group.

Software Architecture

Custom Software Development

Business Analysis

Technologies used:

  • Enterprise Architecture
  • OpenAPI
  • Java
  • Spring Boot

Team composition:

  • 2 Solution Architects
  • 2 Full stack software developers
  • Project highlights:

    Emphasize was on a new approach of telco IT landscape transformation, through the changes on architectural, process, technological, and integration level. Overall new solution was created through a larger number of independent digital microservices rather than through several monolith enterprise systems.


    Solution enabled introduction of one single mobile application (OneApp) across Europe where previously each country had its own app, all with differing architectural approaches and larger maintenance costs. HAL enabled abstraction of each NatCo within group to benefit from existing OSS BSS investment and harmonise through implementation of TMForum OpenAPI recommendations.

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