Challenges Facing Access Offices in the 5G Era
The access office (AO) is the telecommunications equipment room nearest to end users. It houses OLTs and typically covers broadband users in a 3 to 5 km radius. In the 4G era, BBUs are usually pooled, and operators tend to deploy a large quantity of BBUs in their AOs to reduce the number of equipment rooms. Although wireline and wireless devices already share an AO in the 4G era, wireline and wireless are independent of each other in terms of service and network.
Typical application scenarios defined for 5G include enhanced mobile broadband (eMBB) with peak data rates of up to 10 Gbps, massive machine-type communication (mMTC) characterized by a density of one million connections per square kilometer, and ultra-reliable low latency communication (uRLLC) with a low latency of 1ms required for such applications as the internet of vehicles (IoV). 5G will enable the internet of everything (IoE), where humans, machines and the environment will be more closely and efficiently linked, and there will be continuous innovation of the production modes, business models and people lifestyles. Network service provision will be based on services instead of access modes because whether access is wired or wireless will be irrelevant to users. Service integration is bound to drive network convergence.
To ensure the delivery of rich services and applications, the 5G network employs a brand-new architecture:
● The 5G core network uses a cloud-based architecture that separates control and forwarding functions and allows for fast deployment of services as needed. The introduction of multi-access edge computing (MEC) technology pushes service processing closer to the edge and reduces latency. A unified 5G core network provides mobile users with consistent services and enables fixed-mobile convergence (FMC), thereby ensuring a seamless service experience across wireline and wireless scenarios.
● The 5G access network adopts an architecture where the AAU, DU and CU are separated, and the practice of distributing AAUs and pooling DUs is still heavily used. The introduction of high-frequency base stations vastly increases base station density. The scale and complexity of the fronthaul network is substantially expanded, which presents an unprecedented fiber resource consumption challenge.
As the access portal for users in the 5G era, the AO must offer super-high bandwidth, ultra-low latency and differentiated QoS assurances, as shown in Fig. 1. More importantly, it has to accommodate dynamic connections brought by cloudification of the 5G core network. The introduction of MEC can move some of the service processing to the NFV infrastructure (NFVI) of the AO. Moreover, the traffic inside the AO between the wireline and wireless services and between the NFV services on the NFVI also surges. Faced with these 5G requirements, traditional AO architecture falls short and needs a transformation.
Objectives of Access Office Construction in the 5G Era
The AO for the 5G era will be an intelligent FMC equipment room that is superfast, easy to maintain, flexible, and reliable. While the existing power supply system (including power backup equipment), cooling system, monitoring system and wiring routes of the AO are kept intact, its internal network is divided into four functions as shown in Fig. 2:
● Connection function: Using a leaf-spine data center topology, the AO can build a high-bandwidth, scalable and reliable internal communication network to support complex communications among the DU (wireless), OLT (wireline), uplink transmission equipment, and NFVI with QoS assurance.
● Access function: The DU is used for wireless access processing, while the OLT for wireline access processing.
● NFVI (computing and storage function): The NVFI is deployed in the AO to ensure that low-latency, real-time services can be rapidly processed to improve user experience. Because the NFVI provides computing and storage capabilities, it can be seen as a remote module of the edge data center (EDC) and the NFV services running on it are centrally orchestrated and managed by the 5G core network.
● Transport function: The AO provides network-side interfaces to centrally carry wireline and wireless traffic from the OTN, IPRAN or SPN equipment.
Principles of Access Office Construction in the 5G Era
Since AOs exist in large numbers and vary greatly in their hardware conditions and environments, transforming all of them in one stroke will incur an enormous workload and a huge investment. Instead, they should be evolved step by step based on the following principles:
● Openness: The interfaces among access function, connection function, NFVI (computing and storage function) and transport function should be open. The NFVI is shared by all the functions and users of the AO.
● Scalability: AOs vary significantly in their hardware conditions including the floor area, power supply system and cooling equipment. The access, connection, computing & storage, and transport equipment in the AO can be trimmed according to service needs and smoothly expanded as per functionality and capacity.
● Flexibility: The reconstruction of the AO should be based on smooth evolution of the AO’s existing architecture. Functions can be flexibly deployed according to the conditions of the AO and without affecting the operation of the existing services.
Steps of Access Office Construction in the 5G Era
Considering the above-mentioned principles, we suggest building an AO in three steps, which can be merged or adjusted if needed:
● Step 1: Setting up an NFVI: Low-latency, real-time NFV services of the 5G era need to be deployed as close to end users as possible. To achieve this aim, the NFVI and the internal communication network supporting the NFVI have to be installed in the AO. The NFVI, as a remote module of the EDC, is managed and controlled by the EDC, and enables service deployment under centralized orchestration of the 5G core network, thereby ensuring a smooth switchover of services and consistent user experience across wireline and wireless. Such services include video acceleration, location service, and TCP acceleration.
● Step 2: Smartening up the AO: The access, transport and connection functions of the AO are centrally managed to separate equipment management and service management. Service management by incorporating SDN&NFV can enable fast end-to-end deployment as well as intelligent operation and maintenance.
● Step 3: Integrating and optimizing the AO: The access function, transport function, connection function, and NFVI (computing and storage function) of the AO are performed by separate devices. To save space, simplify deployment, boost reliability and provide QoS assurances for different services, related functions can be integrated to reduce the number of network elements. The AO can also be optimized using a standard module. The module can selectively house access, connection and transport functions while at the same time solving cooling and monitoring issues. After being tested and verified in the factory, the module can be directly installed in the AO to cut the engineering workload. By adding modules as needed, the AO can be conveniently expanded to keep up with service demands.
The numerous AOs are an important asset of operators. With the trend towards FMC, operators should modernize their AOs in stages so that the AOs can support full-service bearing, smart operation, centralized management, fast service deployment, and smooth scalability. Only through such modernizations can the business value of the AOs be fully tapped in the 5G era.
[Keywords] Access office, 5G, fixed-mobile convergence, FMC, AO