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FMC access in the 5G era

24 Sep 2018
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Development background of FMC

Fixed Mobile Convergence (FMC) allows fixed and mobile networks to interwork and collaborate for full-service and integrated-service operation. The technology provides users with diverse quality services, including communications, information and entertainment, independent of the terminal, network, application and location.

Mobile broadband and fixed broadband both compete with and rely on each other. In areas such as Internet access and data service, mobile broadband replaces some of the fixed network functions. For example, smartphones have gradually taken the place of fixed terminals including computers as the primary mode of accessing the Internet. On the other hand, mobile and fixed networks are interdependent. A heterogeneous network based on cellular and Cloud-RAN (C-RAN) technologies requires a large amount of mobile backhaul networking. In the access segment, in particular, mobile and fixed networks both need a great deal of optical infrastructure.

As competition intensifies in an increasingly mature communications market, operators are compelled to find ways to prevent customer churn and attract new users. Starting in 2012, some operators in Europe endeavored to gain more mobile or fixed users by engaging in Mergers and Acquisitions (M&A) and tapping the potential of existing users. Notable cases include the acquisition of wireless operators EE by fixed-network incumbent BT and the success of Deutsche Telekom (DT) in signing up 70% of its mobile users to its fixed broadband services. FMC has become an effective weapon used by operators in their battle for users.

In the LTE era, an IP Multimedia Subsystem (IMS)-based FMC solution can provide fixed and mobile users with services including voice, data and video that are unified to improve Quality of Experience (QoE). By adopting the new operating model of binding fixed and mobile users, operators can retain customers, boost Average Revenue Per User (ARPU) and improve profitability.

In the 5G era, the deep integration of a cloudified network architecture, Virtual Network Functions (VNFs) and service functions brings new opportunities and challenges for FMC.

Analysis of application scenarios and technical architecture

FMC services need to have the following characteristics:

  • Connection between the equipment and network levels is seamless, and diverse applications can be transported between different network platforms. Handover between different networks does not interrupt or degrade services.
  • Users can be connected in a variety of ways. Integrated services and devices can employ different access technologies such as Wi-Fi or cellular according to the user location, required application, Quality of Service (QoS) and amount of calling.
  • Users can use one terminal, instead of the multiple terminals needed in the past, to implement all the applications.
  • End users can set services and the user interface. Fixed network terminals also support diverse settings like smartphones.

As shown in Figure 1, User Equipment (UE) in the 5G era falls into two types:

One type is the 5G RG, which is an upgraded version of the traditional RG and is connected as a UE to the 5G core network through a fixed or mobile network. The 5G RG can be connected to the core network via a wired, Fixed Wireless Access (FWA) or hybrid link.

The other type is the NG UE, which is an upgraded version of the original UE and can be connected to the 5G core network through a WLAN or cellular network. The NG UE is connected via Wi-Fi or cellular to offload some traffic. Another way is for the NG UE to be connected via both a WLAN and cellular link.

In both cases, the RG serves as a trusted node to provide Wi-Fi access.

Figure 1 Overall FMC Architecture in the 5G Era

5G FMC mainly involves two integrations at the access network:

1. Resource sharing and architecture integration

In the 5G era, scenarios such as dense urban or hotspot areas need to adopt a C-RAN architecture where DUs are centralized. For fixed network access, the distance from the DU pool to the user is basically the same as that from the access office to the user. In areas where the access office has ample resources, fixed and mobile equipment can be co-located so that the resources can be shared to reduce CAPEX. The existing fixed network resources including the access office, power supplies, air-conditioners and transmission equipment can be shared, which facilitates the centralized management of equipment.

Figure 2 Fixed-Mobile Architecture Integration Prompted by the New 5G Architecture

2. Network simplification and function integration

Network architecture, operation and maintenance is simplified to reduce OPEX. The overlapping parts of the authentication, control and management functions of the fixed and mobile networks are integrated to provide users with a consistent service experience and boost operation and maintenance. The integration takes the following forms:

1. A standard interfaces. The 5G core network becomes more functionally independent. It is decoupled from access modes and gradually transforms into an agnostic architecture. By reducing AN-CN interface coupling, standardization implements seamless and agnostic access.

2. Unified authentication. In the past, fixed and mobile users were authenticated by different operating systems. The FMC architecture allows the users to be authenticated in the view of one operator, saving network resources and simplify management.

3. Unified resource management. With virtualization and programmable technologies, some overlapping functions of the fixed and mobile networks can be abstracted and integrated, while the operator’s resources can be orchestrated in a unified manner.

Figure 1 shows all the three typical 5G FMC access modes currently being discussed by the standards bodies 3GPP and BBF.

1. Integration mode: The Access Gateway Function (AGF) is provided at the access node, where it is directly connected to the 5G CN. Key modules include the 5G RG and AGF.

2. Interworking mode: In the existing access mode, the existing transmission equipment, such as the Broadband Network Gateway (BNG), that interconnects with the CN supports the Fixed-Mobile Interworking Function (FMIF) interface. Key modules include the FN-RG and FMIF. The FN-RG is the traditional RG and can provide Wi-Fi access.

3. Hybrid mode: Fixed access and cellular access co-exist in this mode.

Of the three modes, integration is the most recommended mode because its network architecture is the straightforward. As L3 is moved downwards to the access node, the control plane and user plane interfaces to the 5G CN are more direct, thus reducing the amount of intermediary transmission equipment.

Access Office (AO) re-architecture makes it easier to deploy SDN and NFV services, such as the 5G AGF, in the future. In terms of functionality and location, the 5G AGF will best run on the NFVI of the access office. That enables the NFV platform in the re-architected access office to be fully used to implement the deep architecture and function integrations required by FMC.

Figure 3 Interfaces Between 5G AN and Core Network in Integration Mode

In integration mode, all mobile users are connected by wired access and 5G CN functionality is integrated. The N1’/N2’/N3’/N4’ interfaces in Figure 3 are interfaces between wired AN and core network. All the mobile devices are connected to the NG-RG (also called 5G RG), where user access to the core network is authenticated. The core network only needs to authenticate and charge the NG-RG, but does not individually perform these operations on the mobile devices connected to the NG-RG, including UEs, tablets and laptops.

Industry development and network evolution

FMC has attracted widespread industry attention, with a number of big-name players with both fixed and mobile network resources, including AT&T, BT, China Mobile, DT, KT, NTT, Orange, Telecom Italia, Telefonica, Telenor and Vodafone, engaged in discussions on 5G FMC standards at 3GPP and BBF.

The latest development of 5G FMC standardization by BBF is contained in the document “SD-407: 5G Fixed Mobile Convergence Study”, while that by 3GPP is included in Release 15 SA2 TS23.706. Meanwhile, research at 3GPP corresponding to the Release 16 timetable will soon kick off.

Evolution of the FMC network in the 5G era is intended to achieve: 1) a non-3GPP access network based on the 5G core network to implement agnostic access; 2) software-driven function development based on software modularization to make 5G networks more flexible; 3) a future-proof architecture design to support new 5G use cases including industrial, public and user networks; and 4) a converged network platform based on a cloud platform to integrate more access network services in addition to the existing mobile network use cases.

The 5G FMC architecture is still being discussed. For it to be perfected, many issues need to be resolved with input from operators and vendors.


Li Yufeng, Chief Engineer for FM Product Planning, ZTE Corporation

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