Core technologies for building 5G networks: the differences and connections between SDN and NFV

We often hear network operators and equipment vendors mention SDN and NFV as the core technologies for building future 5G networks. So what are these two technologies, and what are the differences and connections between them?

What is SDN?

SDN, or Software Defined Network, is a new type of innovative network architecture and a way to implement network virtualization. Its core idea is to separate the control plane from the data plane of network devices, thereby achieving flexible control of network traffic and making the network smarter.

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SDN originated from research projects in universities. In 2006, the Clean Slate project at Stanford University, funded by the US GENI project, and a research team led by Professor Nick McKeown of Stanford University proposed the concept of OpenFlow. The OpenFlow protocol standardized the interfaces of the control plane and the data plane, bringing programmable features to the network. On this basis, Professor Nick McKeown and his team further proposed the concept of SDN.

Early network protocol research generally used some network simulators to simulate real network environments, but researchers still wanted to test the network protocols and algorithms that were in the research stage in a real network environment. The original purpose of studying the Openflow protocol was to provide a test platform for new protocols and algorithms. Deploying the Openflow network test platform in the campus network is closer to the complexity of the real network.

Later, researchers realized that Openflow-based SDN technology can not only be used for research, but also be deployed in actual network environments to make network control more flexible. Especially in data center deployment, it can achieve path optimization and avoid data congestion. With the development of cloud computing, the scale of data centers is also getting larger and larger, and SDN technology can play an increasingly important role.

SDN network architecture: separation of control plane and data plane

What are the benefits of separating the control plane and data plane of SDN? The biggest benefit is programmability.

The original various network protocols are fixed in the network equipment. The functions of the network equipment are determined by its internal programs and configurations. It can be said that the functions are dead and cannot be dynamically adjusted according to traffic changes. If you want to change, you must reconfigure or deploy the network equipment.

After separation, network managers can develop application software on the A-CPI interface of the SDN controller and dynamically adjust the routing protocol of the SDN controller in combination with traffic monitoring, thereby affecting the network elements (Openflow switches) in the data plane to control traffic forwarding, thus turning the network from dead to alive.

Another benefit is that the routing protocol of the traditional network is a distributed system composed of all the routers on the network, which means that the bandwidth resource scheduling is distributed, and it is inevitable that there will be inappropriate allocation and network congestion. With the SDN controller, it is equivalent to centralizing the flow control functions originally distributed on each router, which can allocate resources more effectively.

SDN can also be combined with cloud computing. For example, the SDN controller and the network application software on it can run on the virtual machines of cloud computing.

What is NFV?

NFV, or Network Function Virtualization, uses general-purpose hardware such as x86 and virtualization technology to carry the software functions of dedicated hardware, thereby reducing expensive equipment costs. By decoupling software and hardware and abstracting functions, network device functions no longer rely on dedicated hardware, enabling rapid development and deployment of new services, and automatic deployment, elastic scaling, fault isolation, and self-healing based on actual business needs.

The NFV concept originated from network operators. With the continuous upgrading of network technology, each technology upgrade requires new network equipment. Network operators deploy network equipment with different functions each time, which is not only costly but also very complicated for network management.

Due to equipment costs and management difficulties, operators hope to use general-purpose hardware to carry network functions that were previously dedicated hardware, such as load balancing and firewalls.

NFV technology can be easily combined with cloud computing virtualization technology. For example, general hardware that carries various network functions can be directly replaced by virtual machines. If network functions need to be upgraded, operators do not need to purchase dedicated hardware, but can directly deploy new network software to run on it. If computing resources are insufficient, more virtual machines can be deployed.

The Differences and Relationships between SDN and NFV

The design ideas of SDN and NFV are actually to improve the flexibility of the system through decoupling and make the system more intelligent. In terms of design ideas, they are very similar. So what is the difference between the two?

The most obvious difference between SDN and NFV is that SDN decouples the control plane and the data plane, while NFV mainly decouples software and hardware. In addition, SDN deals with layers 2-3 in the OSI model, involving switches, routers, etc., while NFV deals with layers 4-7, such as load balancing, firewalls, etc.

SDN and NFV technologies are highly complementary and do not depend on each other. NFV can be deployed independently of SDN, and vice versa. In the implementation of data centers, SDN and NFV technologies can coexist and play their respective roles.