BBF lays out converged network specs

The 5G network will be as much made up of wireline technologies as wireless, not just for dense fiber backhaul and fronthaul, but as operators move towards converged access and core. These trends have brought the Broadband Forum (BBF) into increasingly close contact with the mobile standards bodies, and recently the Forum submitted proposals for 5G fixed/mobile convergence to the 3GPP.

These proposals were drawn up at the request of operators which take part in both standards bodies, the BBF said, after a “comprehensive cycle of iterative feedback between the two organizations”.

“Two years ago, 10 of the world’s biggest operators came to us with their concerns that the 5G infrastructure which was being developed would not let them take advantage of both their wireless and wireline networks,” said Geoff Burke, CMO of the BBF. “Today, we are able to deliver a set of recommendations which will not only address how the 5G core can be evolved to support the fixed networks of these operators but provide them with the capabilities to launch new innovative combined subscriber offerings.”

Among the resulting submissions are a number of common interfaces between the access and 5G core networks to support convergence of wireline and wireless. The next step will be for 3GPP members to evaluate these, as well as other recommendations on signaling changes and other enhancements, which would help integrate wireless access fully into the core.

It is encouraging to see substantial work resulting from a close cooperation between the 3GPP and another group, given its patchy track record in the past on developing joint standards with the IEEE and others. The BBF even has a wireless and wireline convergence work area director, Dave Allan.

He said in a statement: “This is an exciting moment for the 5G market, as well as for Broadband Forum, 3GPP and their memberships … In many ways this is just the beginning and, as Release 16 progresses and 5G further expands, our work with 3GPP will continue to ensure standardization of this new technology is successful. With 5G promising a variety of new and innovative applications such as autonomous driving and healthcare, this work is crucial to enabling converged operators to unlock these opportunities – empowering them to deliver a uniform experience to their customers irrespective of the access media type, technology, or appliance they are using.”

David Aders, in charge of converged control plane engineering at Australia’s Telstra – which contributed to the proposals – said: “The alignment and collaboration between Broadband Forum and 3GPP are essential to delivering an ecosystem that is truly game-changing and providing a globally supported framework for operators such as ourselves to develop many next generation services.”

Another aspect of the BBF’s fixed/mobile convergence activity is to develop a specification for a 5G Access Gateway Function (AGF) that adapts fixed access onto the 5G core; as well as specifications for 5G-capable CPE; and for interworking of existing fixed access subscribers and equipment with a 5G core, in various deployment scenarios.

Georg Mayer, chair of 3GPP’s core networks and terminals group, added: “The recommendations from Broadband Forum allow us to develop a truly access-agnostic and common 5G core network, which will allow seamless user and service mobility between 3GPP and non-3GPP accesses.”

The new specs are expected to be included in 3GPP Release 16, which is due at the end of this year, or if not fully incorporated, it will be a complementary set of specs.

In another 5G-related activity, the BBF has released specs for a new approach to the Dynamic Bandwidth Assignment (DBA) function, to enhance the quality of service of optical access systems, which should support time-critical 5G applications that require fiber xHaul.

The work has defined an application programming interface (API) which would replace the current DBA software module and allow services – including 5G fronthaul – to be deployed on optical access systems more easily. Two telcos, NTT of Japan and Chunghwa Telecomof Taiwan, jointly proposed use cases for the DBA software module and developed the API specs.

“These technical advances will enable carriers to use a common access system for a diverse range of services including the accommodation of base stations for 5G mobile systems, which place strict requirements on acceptable latency thresholds,” said Jun Terada, general manager at NTT Access Network Service System Laboratories. “We believe that the widespread use of the API as an international standard will lead to the drastic expansion of the application area of optical access systems.”

The new standards are part of the Forum’s work on an abstraction interface for time-critical applications on passive optical networks (PON), a project kicked off in 2017 by NTT.

It comprises two technical reports, TR-402 and TR-403. The former gives an overview of how to capture the DBA function in a module, including a use case for 5G base stations over an optical access network, and it also specifies the functional requirements of the API. The latter provides more details of the API, including format and performance requirements.

The next stage will be to encapsulate the remaining access functions in modules, working with operators, vendors, other standards bodies and open source communities.

Robin Mersh, CEO of the Forum, said: “The work fits perfectly with our other initiatives around next-generation access and will enable operators to cost-effectively upgrade their optical access networks as they prepare for the 5G era.”

The work builds on previous efforts led by NTT to support the concept of a Flexible Access System Architecture (FASA), which has been the basis of new BBF architectures and interfaces developed since 2017. Last year, NTT demonstrated optical line terminal (OLT) modularization and tested OLT prototypes with the API to enable the smooth replacement of DBA software modules.