Openness Matters: Exploring Network Convergence 

In my previous blog introducing the “Openness Matters” series, I looked at what is driving service providers to undergo a digital transformation and to choose open standards-based solutions. In this blog on network convergence, I will explore how service provider can deploy a variety of radio and broadband access technologies to deliver connectivity to both commercial and residential subscribers. 

Today, there is a wide variety of devices available, including smartphones, tablets, PCs, CPEs, access points, routers, gateways, IoT endpoints, and voice and video activated equipment. And there are new applications and services being deployed across a multitude of industry verticals. And there is near insatiable demand for ultra-high-speed mobile broadband, extreme low latency, massive density, and the ability to connect anywhere, anytime.  

Service providers have many technologies to choose from when it comes to bridging the digital divide. On the wireless side, they can look to 3GPP-based cellular technologies such as 4G and 5G, dual and tri-band Wi-Fi/Wi-Fi 6e, and low power Wi-Fi variants such as Bluetooth or Zigbee. For wireline, service providers can choose fiber, Coax, or copper. Service providers can also consider satellite technologies to deploy in the most remote regions. 

These architectures and their continued evolution are a result of coordinated efforts from various standards bodies including 3GPP, the O-RAN Alliance, Broadband Forum (BBF), the Open Networking Foundation (ONF), IETF, ITU-T, IEEE, CableLabs and others. Radisys is active in many of these industry organizations and is developing open and disaggregated mobile and broadband access solutions.  

So what exactly is Wireless Wireline Convergence?

Wireless Wireline Convergence (WWC) is a joint project between the BBF and the 3GPP standards working groups which is defining how wireline access can be integrated into the 5G system via a common 5G core network. 

This project was kicked off by a group of major service providers in 2017 with the intent to serve wireline subscribers with a 5G system. The objective was to adapt any required changes in a 5G system to be able to support wireline users with a common set of protocols and network functions within the core network and have the BBF develop corresponding set of specifications. The 3GPP changes required to accommodate these wireline networking functions were incorporated in Release 16. 

This turned out to be a huge effort from the 3GPP working groups given the nature of wireline/fixed access networks design where each of their service areas were independent/self-contained and they did not have ubiquitous mobility requirements as are found in the wireless domain. There was no one architecture required. The definition of a path towards 5G Convergence made operators rethink their investment patterns and operations strategies. The BBF has published its second round of specifications, moving from the fundamentals of convergence to feature enhancements and work continues to include 3GPP technologies as well as use cases in driving this initiative.

What does WWC look like?

Figure 1: High Level Convergence Architecture

Figure 1 above shows a high-level view of the WWC architecture and basic deployment scenarios. 

On the left, there are a variety of digital endpoints including smartphones and residential gateways (Customer Premises Equipment/CPE) that are 5G capable (5G-RG) and legacy fixed network assets (FN-RG). The 5G enabled CPE could support wireline, wireless in the form of fixed wireless access or both accesses, and hybrid either for resiliency or for intelligent bandwidth aggregation. This is also dependent on the CPE capabilities and configurations. 

Wireless access is specified as 4G/5G as we anticipate the transition to ubiquitous 5G radio enabled standalone architectures globally will happen over a much longer time period. This hybrid 4G/5G access is critical for operators to continue to leverage their investments over the last decade in 4G and the maturity of the technology in providing various mobility services, while 5G networking infrastructure designs are being built with software-defined cloud-native architectures adapted to telecom environments. 

The Wireline access network is shown in the middle of the picture, and this could encompass legacy technologies such as Copper based (DSLAMs), Hybrid Fiber Coax (HFC DOCSIS-Cable), Fiber (PON) and more advanced technologies such as Cable (HFC-DOCSIS 4.0) and PON (XGS-PON/NG-PON) that are still in the early stages of deployment and maturity. There could be a lot of scenarios wherein this wireline access network is a third-party network and, in some instances, there are significant barriers to upgrade the outside plant. The unmodified part of the wireline access network raises a key requirement to maximize the deployable footprint for 5G Convergence. 

The wireline access network connects to the 5G system via wireline access gateway function (W-AGF). This is a mediation platform that bridges/supports calls from the 5G and non-5G capable RG endpoints into the 5G system via wireline access empowering the 5G service providers to manage their wireline subscribers with 5G core. Such an architecture simplifies the digital transformation by consolidating networking assets across disparate wireless (3GPP/Non-3GPP ) as well as wireline domains and drives a common converged 5G core framework for handling critical functions such as end user/device authentication, authorization, identity management, subscription, policy, charging, billing, network exposure, core data network analytics etc. Operators looking for ways to drive enhanced customer satisfaction as well as improve revenue margins will benefit from the definition and adoption of such a converged core infrastructure. More importantly, it offers the promise of full convergence, thereby enabling a seamless subscriber experience across multi-access networking domains. 

The converged core network further simplifies the interfaces to OSS/BSS systems associated with traffic handling across wireline and wireless access domains with a common set of APIs. The traditional 4G/5G radio access network as shown in Figure 1 terminates its control and user plane data traffic in the converged 5G core network that allows seamless transition of users as they switch the radio access technologies due to lack of 5G overlay coverage in certain geographic areas.

Figure 2: Data Flows in a Converged WWC Architecture

Figure 2 shows an expanded view of the converged 5G system with various core networking functions that handle the control and user plane data traffic from legacy (FN-RG) as well as 5G capable RGs connected via the wireline and wireless access domains. The W-AGF is an integral function for WWC and acts as Access Gateway Function (AGF) when supporting 5G-RG and FN-RG terminals. It also acts as Fixed Mobile Interworking Function (FMIF) when supporting FN-RG only in the case of presence of Broadband Network Gateway (BNG). In both scenarios associated with FN-RG, the AGF/FMIF have identical interfaces towards the 5GC. In other words, the 5GC is transparent to the use of AGF or FMIF when serving FN-RG. The definition of W-AGF in the case of Wireline Broadband Access network and Cable Access network is governed by specific BBF (TR-456/WT-457) and CableLabs (WR-TR-5WWC-ARCH) standards. The W-AGF along with the other core networking functions can be fully virtualized, run as containers on commercial off-the-shelf (COTS) hardware platforms in cloud native environments.

You can see that the 3GPP/Non-3GPP Access and the W-AGF serving wireline Access technologies terminate their control plane signaling in a common entity called the Access and Mobility Management function (AMF) and user plane data traffic in the User Plane Function (UPF). The AMF becomes a converged access controller in this scenario for handling all the signaling interactions originating from these access domains to establish the call processing required for end user service delivery. 

The various control plane functions within the 5G converged core network interface with each other over a services-based architecture that simplifies the peer network functions interaction using a common protocol layer (HTTPS) as opposed to the previous generation of core technologies. 

Digital transformation in the next-generation of connected society using multiple access technologies is simplified by having a common converged core infrastructure with network functions built in with standards-based interfaces towards the access domain. The multi-access and core network domains are connected via a transport networking domain which is not explicitly indicated in the above Figures. Various telecom service providers including the traditional MNOs, MSOs, FTTX and other local WISPs/ISPs etc. may have differing requirements for their transport networks based on their incumbent architecture, targeted services delivery and roadmap for their infrastructure evolution to meet next generation services in a brownfield/greenfield deployment. In a software-defined disaggregated telecom environment, convergence of their management layers across multiple networking domains is critical for service providers to have a single pane of glass management approach of their end-to-end network infrastructure. While this approach presents data in the form of dashboard metrics, indicators, status and state information from multiple sources/networking domains in a unified manner, the underlying common set of tools, standards-based interfaces, and APIs being used for management and monitoring become extremely important. Such a converged networking domain architecture and management strategy simplifies the overall conversational voice and video services delivery as well as regulatory, lawful intercept services that are critical to meet specific requirements from certain geographic regions.

With no end in sight to ever-increasing demand from consumers and enterprises for high-bandwidth, reliable and secure connectivity, service providers must deploy the right mix of technologies with cloud capabilities. No single access technology can meet this demand on its own. 

A smart converged network solution enables a more seamless and optimized experience independent of the user location, provides consistent treatment of traffic flows with quality of service across multi-access domains, application prioritization, security, integrated analytics, and thus can improve the way we live, work, learn and play while adopting the use of next-generation applications and services. The timing is right to focus on openness in network architectures that are becoming more user centric and can deliver significant value via the convergence of wireless and wired networks in a cloud native environment. 

Quality of Service is extremely important in Wireless Wireline Convergence as it provides end users with the flexibility to take advantage of the best possible access networking technologies available in a given location and at a given time. Service providers need to ensure seamless interworking of wireless and wireline networks to guarantee consistent end-to-end converged QoS to all subscribers irrespective of the access technology.

Stay tuned for the next blog in my Openness Matters series where I’ll address the move towards containerization and how it is impacting the telecom industry.