Telecom operators have suffered from complex dedicated hardware devices for many years. With the penetration of IT virtualization and cloud computing into the communications technology (CT) field, network function virtualization (NFV) has become the first choice of operators for their network evolution. According to the market research, the compound average growth rate (CAGR) of the global NFV market is 51.57% from 2013 to 2018, and it will reach 45 billion US dollars by the end of 2020. However, NFV also faces some inevitable issues during the network evolution. Pushing NFV into maturity in a rapid manner is key to successful 5G commercialization.
Challenges Faced by NFV Maturity
Unified Management and Interoperability of Cloud Native VNFs
The microservice architecture required by cloud native virtual network functions (VNFs) not only helps operators get rid of dedicated hardware devices, but also allows them to dynamically expand their network functions and improve the flexibility and efficiency of service deployment. However, the majority of current VNFs are transplanted from legacy platforms to virtual machines. The microservice re-architecture by different vendors is implemented based on their own software frameworks, so these microservices are difficult to integrate or interoperate with each other for unified management in a multi-vendor cloud environment.
Effective NFV Operations with Vertical Industries
At present, the unified management and orchestration (MANO) only provides the deployment and orchestration capabilities of NFV network services, but fails to be efficiently collaborated with the BOSS system to deliver end-to-end network services from different vendors and different network domains. Therefore, the demands for tailor-made differentiated services by various vertical industrial customers cannot be met, nor can their needs for microservice self-management like monitoring, optimization, and DevOps be satisfied.
Evolution of Infrastructure Capabilities
NFV is constructed on the infrastructure that is composed of universal hardware and virtual resource management systems. Along with the continuous development of telecom networks, the IT infrastructure also needs to be optimized continuously in terms of reliability, performance, timeliness, maintainability, security, and lightweight so as to meet the application demands of CT networks.
Balancing Between Openness and Integration
The multi-vendor component-based environment makes operators quite difficult to integrate their own network services. The interoperability of the multi-layer decoupling architecture is facing bigger challenges than what is expected. Therefore, it is necessary to redefine technical specifications on practical NFV implementations based on various open source frameworks and ETSI specifications.
5G Pushing NFV into a New Phase of Development
On June 13th, 2018, 3GPP plenary session (TSG#80) approved the freeze of 5G standalone (SA) networking function, which marks the official birth of the complete international 5G standards. 5G SA network based on SDN/NFV enables the smart development of vertical industries, bringing new business modes to operators and industrial collaborators. By using a brand-new network different from 4G, 5G SA requires standard service-based architecture (SBA), slice-based operations, and distributed cloud infrastructure. All this will help address the challenges related to NFV and will push NFV into a new phase of development.
Standard Service-Based Architecture
3GPP SBA realizes the service-based standardization of VNFs. It has three major characteristics: service-based components, standard API for telecom services, and service-based framework. SBA decouples existing network elements (NEs) by their functions into mutually-independent modular functions, and organizes them through the unified service-based framework. The standard APIs are used to provide services for external applications. Each service component can be iterated and updated independently for easy development and openness to other third parties. In this way, flexible orchestration and rapid service innovation can be realized.
The SBA-based 5G network has many advantages. One advantage is agility. 5G network services can be upgraded rapidly and conveniently. Another advantage is easy scalability. New network elements and services can be added to the network without introducing new interface design. Services enable plug and play as well as automatic registration and discovery. A third one is flexibility. Network functions can be combined to meet the need for flexible network slicing. The last advantage is openness. Network functions can be easily called for creating new third-party services.
The concept of network service orchestration is proposed for operations in NFV environments. MANO is a used for unified service and resource orchestration. Furthermore, slice-based operations are also adopted to effectively interoperate with BOSS and MANO.
The end-to-end 5G network slicing services include terminal, base stations, bearer, core network, and even vertical industrial services (Fig. 1). 5G slices can be divided based on different service types such as eMBB, uRLLC, and mMTC or be created based on users from different vertical industries. A user can access multiple slices at the same time, and one slice can also serve different users. Each slice has its own SLA assurance and is isolated from other slices. The slice services can be temporarily and dynamically created or deleted to release network resources. The 5G network slicing provides a basis for smart allocation of service-based pipeline resources and capabilities, allowing operators to offer differentiated services in different scenarios.
Distributed Cloud Infrastructure
Traditional virtual technologies such as KVM and OpenStack cannot completely meet the latency and reliability needs of telecom networks. These problems are more serious especially when ultra-reliable and low-latency communications (uRLLC) and multi-access edge computing (MEC) are introduced to 5G networks. The container technology is characterized by lightweight operation and efficient application deployment, so it can be used to guarantee real-time communication while improving the flexibility in deploying telecom services and the upgrade capability without service interruption. The service-based architecture has been prepared to some extent for containers used in a 5G network.
As new requirements are placed on the NFV-based 5G network, the container technology is also enhanced for NFV, which involves higher network performance and SDN multi-plane adaptation. Although NFV has not yet been put into large-scale commercial applications based on the containers, the demands for multiple services in a 5G network will certainly give rise to the distributed telecom cloud infrastructure that can be built on the hybrid resource pool from the network center to the edge (Fig. 2).
After developing over a certain period of time, NFV has become an important fundamental technology for re-architecturing telecom networks. The 5G development depends on the advantages of cost, openness, and flexibility that NFV has brought about. As the 5G network speeds up its commercial process, the NFV-related challenges with 5G commercialization will be addressed as soon as possible. This will push NFV into a new phase of development.