• Deutsche Telekom is working towards commercial Open RAN deployments
• It trialled a non-real-time RAN intelligent controller with rApps and management tools from multiple vendors to assess the potential of a programmable Open RAN architecture 
• The integration of multiple elements presented challenges and key specifications do not exist or are still not finalised
• But DT is encouraged by the potential of best-of-breed opportunities

Deutsche Telekom has shared some key and important takeaways from a recent multivendor Open RAN proof-of-concept (PoC) set of tests that highlight the potential of disaggregated radio access network (RAN) architectures but also point towards ongoing systems integration and specifications challenges. 

The German giant has had a tougher time than it expected with Open RAN. It is one of the five European operators – along with Orange, Telecom Italia (TIM), Telefónica and Vodafone Group – that signed a memorandum of understanding (MoU) in early 2021 with the aim of accelerating Open RAN developments in Europe. But the results from its main trial sites in Neubrandenburg – which has been dubbed O-RAN Town – were, by the admission of its own executives, disappointing and forced the operator to reassess its strategy. Despite that, at the beginning of this year DT reaffirmed its commitment to Open RAN and announced plans for commercial rollouts starting this year.    

As it moves towards those rollouts, it is testing multiple scenarios to figure out the best way to plan, deploy and operate Open RAN-based networks: Its latest PoC focused on a multivendor deployment of a service management and orchestration (SMO) platform, multiple non-real-time RAN intelligent controllers (RIC) platforms and rApps that run on non-real-time RICs. The non-real-time RIC is, as previously noted, one of two forms of the RIC – the non-real-time system runs applications that are used for network management, optimisation and automation tasks that can be performed quickly but which do not require sub-second response times, whereas the near real-time RIC performs tasks that require response times as quick as 10 milliseconds.    

The SMO platform used in the recent tests was one that DT developed itself based on ONAP (Open Network Automation Platform), the open-source network management software stack that is part of the Linux Foundation: DT’s Petr Ledl, head of network trials and integration lab, highlighted that internal development last year – see Deutsche Telekom's six steps to Open RAN success.

That SMO platform was integrated with a non-real-time RIC developed by DT, based on code developed by the O-RAN Software Community (a collaboration between the O-RAN Alliance and the Linux Foundation), as well as non-real-time RICs provided by Juniper Networks and VMware. The RIC platforms were then loaded with two rApps provided by AirHop – a physical cell identity optimisation (PCI) rApp, which was used to focus on the detection and resolution of PCI confusion and collision scenarios, and an AI/ML energy savings dynamic multi-carrier management (ESMC) rApp, which was used to “determine the optimum time to enable/disable sleep-mode on capacity cells in order to save energy while maintaining user quality of experience (QoE),” noted Deutsche Telekom in its announcement about the PoC.

DT also used a RIC test platform/network emulator from Viavi to “validate rApp logic and stress test the RIC components to benchmark the various solutions,” noted DT, while some initial tests were completed using a small Open RAN network setup using technology from Mavenir “to validate end-to-end configuration and performance management (CM & PM) integration for a real network environment,” the operator added.

“With this PoC, we set out to assess the technical integration complexity of the components delivered by each party, the level of customisation required, to gauge the maturity of products and to identify potential future standardisation requirements,” said Ledl in DT’s announcement. 

“At DT our primary focus is always on driving innovation to support the best customer experience. The RIC and rApps are key to programmability, automation, and optimisation in radio access networks. Taking the learnings from this successful trial, we will now continue the work with our ecosystem partners to accelerate non-RT RIC/rApp development towards production readiness,” added Ledl. 

But there is still plenty of work to be done around the integration of elements from multiple suppliers and, in a related challenge, the development of industry specifications that are needed for workable Open RAN deployments. 

In its whitepaper that provided in-depth detail about the PoC, DT noted that the O-RAN Alliance, the industry body developing the specs that will enable industry-wide interoperability between the various elements of an Open RAN architecture, has not yet “defined a detailed internal SMO architecture and internal interfaces between the functional building blocks, including the interface(s) towards the non-RT RIC,” and those interfaces will be vital if operators wanting to use Open RAN systems are to avoid lengthy integration testing and duplicated efforts. 

“As there is still no standard interface defined between SMO and non-RT RIC, this presents significant integration and maintenance challenges when both components are coming from different vendors,” noted the DT team in the whitepaper.

Also, the various RIC and rApp vendors “provide their own dashboards and UIs [user interfaces]. There is no clear picture of how these can be centrally integrated within the SMO framework. This may lead to a disjointed, cumbersome way of working for an operations engineer, requiring multiple applications from various sources (rApp/non-RT RIC/SMO) to maintain and validate system performance,” added the DT team.

In addition, current O-RAN Software Community (OSC) specifications for the R1 interface between non-real-time RIC systems and rApps “are still incomplete and the OSC RIC still misses essential elements,” noted DT. 

As part of its PoC, DT developed functions, including a configuration management service (CMS) and enhancements to the OSC RIC control panel, “to enable the PoC use case execution and… make the OSC fragments more mature.”    

The DT whitepaper provides additional detail and insight both into these challenges and the recommendations it makes for the community to overcome them. 

But while there is clearly plenty of work still to be done if Open RAN deployments are to be seen as viable by the broader operator community, DT is encouraged by developments and the outcome of its PoC, particularly as it is keen to be able to bring together the best-of-breed elements it wants to use from multiple suppliers and not rely on a single vendor to provide a pre-integrated package. 

Despite the integration challenges, “this PoC has shown from a high-level perspective that the adoption of the SMO, non-RT RIC and rApp framework is promising in how it allows for the decoupling of optimisation algorithm development, the supporting platform development and the system integration – so that components from different parties can form a truly disaggregated RAN optimisation concept,” it noted. 

News of DT’s PoC comes only days after Vodafone, one of its Open RAN MoU peers, announced it has started to replace Huawei equipment in the UK with Open RAN systems – see Vodafone starts swapping Huawei gear for Open RAN systems.

- Ray Le Maistre, Editorial Director, TelecomTV