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This article mainly introduces the relevant knowledge of SDN architecture, the content is detailed and easy to understand, the operation is simple and fast, has a certain reference value, I believe you will gain something after reading this SDN architecture article, let's take a look at it.

SDN is a new network architecture which separates the network control function from the forwarding function and realizes the control programmable. This architecture will transfer from the control layer from network devices to external computing devices, so that the underlying infrastructure is transparent and abstract for applications and network services, and the network can be regarded as a logical or virtual entity.

Not just the controller.

SDN (Software Defined Network) is a new type of network innovation architecture put forward by the clean slate Research Group of Stanford University in the United States. Its core technology OpenFlow realizes the flexible control of network traffic by separating the control plane of network equipment from the data plane, and provides a good platform for core network and application innovation. With the continuous development of the SDN practice of equipment manufacturers and operators in the industry, SDN has become a vague marketing name, which refers to any network architecture that allows software to program or configure the network, and the implementation of a variety of technologies and interface protocols. ONF (Open Network Foundation) is the most important standards organization in the field of SDN. It defines the concept of SDN in its newly released SDN Architecture Issue 1.1 in 2016. it believes that SDN is a network architecture that meets the following four principles:

● control and forwarding separation principle: the control entity of the network is independent of the network forwarding and processing entity and is deployed independently. It should be noted that the deployment of control and forwarding separation is not a new network architecture principle. In fact, the deployment mode of traditional optical network has always been the separation of controller and forwarding, while the traditional packet network (IP/MPLS/Ethernet) is a distributed deployment mode of control and forwarding. The advantage of the separation of control and forwarding is that control can be centralized to achieve more efficient control, and control software and network hardware are independently optimized for release.

● centralized control principle: the principle of centralized control mainly pursues the efficient use of network resources. The centralized controller has a broader view of network resources and status, and can schedule resources more effectively to meet the needs of customers. At the same time, the controller can also abstract the details of the network resources, so as to simplify the customer's operation to the network.

● network service programmability: the purpose of this principle is to allow customers to change business attributes to meet their own changing needs by exchanging information with the controller throughout the business life cycle. The purpose of this principle is the agility of the business, customers can assist the business, start the business, change the business, cancel the business, and so on.

● open interface: the principle of SDN technology implementation of this principle, which requires the interface technology to be standardized and contributed to the whole industry. This principle is mainly to standardize the general and common functional interfaces in the network field, so as to ensure the deconstruction of the application with the network and prevent manufacturers from locking. This principle does not oppose the functional extension of manufacturers on the premise of meeting the common interface standards and compatibility.

SDN schema defined by ONF

Like SDN, the architecture of SDN does not have an industry standard. The description of the architecture in the latest architecture document "SDN Architecture Issue 1.1" released by ONF is quite different from that of "SDN Architecture Issue 1.0". Other leading operators and vendors also have their own descriptions of the architecture. Here, citing the "SDN Architecture Issue 1.1" released by ONF in 2016, the architecture description of SDN is summarized as follows:

The core of the SDN architecture above is the controller, and the core work of the controller is Orchestration & Virtualization. The controller controls and manages the network resources through D-CPI (Data-Controller Plane Interface) to the south, and communicates with the application or higher controller through A-CPI (Application-Controller Plane Interface) to the north. The key names in the architecture diagram are explained below: Resource: any resource that can deliver network business, including physical network resources (topology, links and ports) and logical resources (labels, etc.), or virtualized network resources (NFV).

Resource group: network resources are combined into sets according to certain technologies or management boundaries, such as IGP autonomous domain of IP network, optical network and so on. Different network resources and controllers can be controlled and managed by different protocols.

Server context: the necessary and sufficient information created within the controller to manage feature network resources. It can also be understood as the adapter or driver of the controller for characteristic network resources.

Virtualization: the process of abstracting resources and assigning them to feature users. Customers will only see their own abstract resources.

Orchestration: the process of selecting network resources to meet customer needs, and continuously optimize network resources according to the changes of users or the changes of the network.

Client context: an information environment created within the controller to maintain management and control interaction with customers. We can see that the core of the above SDN architecture is the controller, and the key functions of the controller are collaboration and virtualization, and provide programming interfaces. So what's the difference between the controller and the traditional network management? ONF's description of this problem is that the controller must be a positive feedback system, that is to say, the controller should continuously monitor the state changes of network resources and continuously optimize resources according to certain strategies to meet the business needs of customers. The traditional network management system is mainly a unilateral management system, which lacks the function of real-time control to the network.

Controller + Collaborator Network Architecture of operator Network

The network of operators is a complex network composed of multiple technologies, multiple levels and multiple manufacturers. In the process of transition to SDN, it is impossible for operators to overthrow the large-scale network stock in operation and build a new SDN network. Therefore, the SDN practice of the operator network must be step by step, from the SDN transformation of a small number of sub-networks to the whole network, but this process is long-term, at least 10 years. The service provided by the operator to the end customer must be the whole network. Regardless of whether the operator's network is SDN or not, the operator must ensure the quality requirements of users and business access experience. The business goal of SDN transformation for operators is business agility, providing users with self-defined capabilities, opening network programming interfaces, and providing customers with applications to invoke network services in the way of API. The external users of operators will certainly require operators to provide a unified service distribution platform and programming interface, rather than a variety of multiple controller platforms. This unified business management and distribution platform is the collaborator. The < The Third Network: Lifecycle Service Orchestration Vision > white paper published by MEF puts forward the concept of LSO. MEF defines the functions and supporting application program interfaces (API) of LSO from the perspective of users and business. The functions and interfaces defined by MEF support end-to-end operations in the business lifecycle, including implementation, control, performance, security, analysis, policy management across operator networks, and so on. The purpose of LSO is to overcome the complexity of the existing business management system, by defining the abstraction of services, hiding the underlying network technology, and simplifying the application interface and user service experience. By using a model-driven approach and abstract products, services, and resources, you can ensure that agile operations and maintenance throughout the business lifecycle are simplified and automated in a sustainable manner. In the new situation where SDN/NFV/Cloud technology goes hand in hand, the collaboration layer needs to address at least the following challenges:

● service and network separation: service coordinator is service-oriented. Its main function is to abstract all kinds of atomic network services and freely combine them to form new service types according to the needs of users. The business model maintained by the collaborative layer should be decoupled from the specific network technology, and the change and evolution of the lower network technology do not affect the business experience and programming interface of the customer interface.

The coordination of ● SDN network and traditional stock network: the deployment of SDN will not be achieved overnight, it must be local first and then the whole, and may start from the data center, and a large number of networks also rely on the existing management and control means. The collaborator needs to integrate the latest SDN technology, adapt to a variety of existing OSS/EMS systems, and provide a unified northbound business programming interface to users.

Collaboration between ● physical network and virtual network: with the maturity of NFV technology, some network functions in the network will gradually become software. end-to-end service delivery needs to cooperate with network resources and virtual network resources to provide services together.

The integration and cooperation of ● CT and IT: with the IT, cloud and app of operators' business, customers' business needs are also facing the integration of CT technology and IT technology. Enterprise-oriented businesses, in particular, need to integrate network capabilities, private and public cloud capabilities, and application software capabilities. ICT synergy is also a huge challenge. At present, when operators consider the architecture of network transformation, collaborators play a key role. Suppliers have also provided a variety of collaborator products. SDN controller, NFV's MANO, traditional OSS system and collaborator will work together to complete the operator's business and network transformation. At present, no standards organization can give a standard architecture diagram for the transformation of operators' networks. The following figure can be used as a reference.

From the figure above, we can see that the SDN controller is an important part of the operator's network transformation. the controller controls both the physical network and part of the virtual network, and northward provides the interface to the collaborator. The collaborator is a user-oriented business programming platform and provides management means for the whole life cycle of the business. The collaborator adapts to the traditional OSS system, SDN network and NFV management system at the same time to the south, and can also manage the NFV function directly.

Northbound interface of SDN controller

The core of SDN is to realize the programmable control of the network and promote the innovation of network services, and the northbound interface is the most key driving force of this trend. Through the northbound interface, network business developers can call all kinds of network resources in the form of software programming. At the same time, the upper network resource management system can globally control the resource state of the whole network through the northbound interface, and schedule the resources uniformly. Because the northbound interface serves the business application directly, its design must be able to describe the business intention and have good maneuverability, and the complexity and diversity of network services require the SDN northbound interface to be flexible and extensible to meet the complex and changeable business innovation requirements. Different from the international standards such as openflow and netconf of SDN southbound interface, the standardization of SDN northbound interface is still in its infancy. At present, all kinds of controllers opendaylight, floodlight, onos and so on in SDN market have their own set of northbound interface. However, the opening levels of these northbound interfaces are uneven, either from the point of view of users, operation or product capability. Unable to form a unified standard northbound interface, which brings great confusion to the upper application, and the learning cost is also very high. At present, the protocol formulation of northbound interface has become the focus of competition in the field of SDN.

This is the end of the article on "what is the SDN architecture?" Thank you for reading! I believe you all have a certain understanding of "what the SDN architecture is like". If you want to learn more, you are welcome to follow the industry information channel.

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