Why does 5G need the NETCONF system (3)?

1. Protocol Framework As shown in the following figure (1), NETCONF adopts a layered structure, where each layer encapsulates specific functions and provides services to the upper layer. This structure allows each layer to focus on a single aspect of NETCONF and reduces the dependencies between layers. Changes within a layer have minimal impact on other layers.

NETCONF can be divided into four layers: the transport security layer, the message layer, the operation layer, and the content layer. These layers are:

• The transport security layer: This layer is responsible for communication between the client and server. NETCONF can be layered on top of any transport protocol that meets basic requirements, such as SSH, TLS, and HTTPS. SSH is the preferred transport protocol for transmitting XML messages in NETCONF.
• The message layer: This layer provides transport-independent RPC and notification encoding mechanisms. The client encapsulates an RPC request in an element and sends it to the server. The server encapsulates the result of processing this request in an element and sends it to the client.
• The operation layer: This layer defines a set of basic protocol operations, which are called as RPC methods with XML-encoded parameters.
• The content layer: This layer is defined by the data model for management data. Currently, mainstream data models include Schema and YANG.        
• Schema is a set of rules for describing XML files. Devices use schema files (similar to MIB files in SNMP) to provide device configuration and management interfaces to network management systems (NMSs).
• YANG is a data modeling language designed for NETCONF. The client can compile RPC operations into XML messages to achieve client-server communication that conforms to the constraints of the YANG model.

2. Message Format The following figure (2) is a complete NETCONF YANG request message structure;

3. Communication Framework In NETCONF, the RPC request initiated by the client and the reply from the server are both encoded in XML and contained in the and elements respectively. This request-reply framework is independent of the transport layer protocol; some basic RPC elements are listed below:

• The element is used to encapsulate the request sent by the NETCONF client to the NETCONF server.
• The NETCONF server sends an element in response to each request.
• If any error or alarm occurs during the processing of the request, the NETCONF server will return an message containing only the element to the NETCONF client.
• If no errors or alarms occur during the processing of the request, the NETCONF server returns an message containing only the element to the NETCONF client.

IV. Database Configuration NETCONF defines a complete set of device configuration parameters. NETCONF defines the existence of one or more configuration databases and allows configuration operations on them. In the basic NETCONF model, only the configuration database is available. Other configuration databases can be defined based on capabilities and are only available on devices that support those capabilities. These include:

• : The running configuration database. This database stores all currently active configurations on a network device. There is only one configuration database on a device, and it always exists.

• : The candidate configuration database. This database stores configuration data to be committed to the configuration database on the device. Operations on the configuration database can be performed without affecting the device's current configuration. The operation is used to commit a candidate configuration. To support the configuration database, a device must support the candidate configuration capability, a standard NETCONF capability.

• : The startup configuration database (similar to a saved configuration file). It stores the configuration data that needs to be loaded when the device starts. To support the configuration database, the device must support independent startup capability, which is a standard NETCONF capability.