| Internet-Draft | Network Working Group | July 2023 |
| Chen, et al. | Expires 11 January 2024 | [Page] |
The interfaces of Digital Twin Network can be divided as twin network southbound interface, internal interface and northbound interface. In order to build a digital twin network and realize its many advantages, different interfaces should be able to meet different requirements. And this memo introduces the requirements and design about interfaces of the Digital Twin Network.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].¶
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As defined in the[I-D.irtf-nmrg-network-digital-twin-arch] , the digital twin network is defined as "a network system with a physical network entity and a virtual twin, and the two can interact with each other in real time". And it has four core elements: data, model, mapping and interaction. Accordingly, a "three-layer, three-domain and double-closed loop" architecture is adopted.¶
Based on the above architecture definition of three-layer, three-domain and double-closed-loop, the interfaces of each layer and their positions of the digital twin network are shown in Figure 1. The network elements in the physical entity network exchange network data and network control information with the twin network layer through the twin southbound interface. The twin network layer contains three key subsystems, which are data sharing warehouse, service mapping model and digital twin management. Through the corresponding interface protocol, the construction and interaction requirements of the three key subsystems should be met. And through the internal interface of the twin layer, the interaction between the three key subsystems and the physical network layer and network application layer is realized. Network applications input requirements to the twin network layer through the twin northbound interface, and deploy services in the twin network layer through the model example. To sum up, there are differences in interface protocol requirements between different layers of DTN and within twin layers. In addition, the protocols supported by different devices in the physical network layer are also different, so the construction of DTN also needs to consider how to achieve efficient collaboration between different protocols.¶
+---------------------------------------------------------------------+
| |
| Network Application Layer |
| |
+-------^-------------------------^----------------------^------------+
| | |
| | | Twin
| | | Northbound
| | | Interface
+-------v-------------------------v----------------------v-----------+
| Twin Network Layer |
| |
| +------------+ +----------+ +---------------+ |
| | data | | service | | digital | |
| | sharing <-----------> mapping <----------> twin | |
| | warehouse | Twin | model | | management | |
| +------------+ Internal +----------+ +---------------+ |
| Interface |
+--------^------------------------^-----------------------^----------+
| | | Twin
| | | Southbound
| | | Interface
+--------v------------------------v-----------------------v-----------+
| |
| Physical Network Layer |
| |
+---------------------------------------------------------------------+
Twin northbound interface¶
The twin northbound interface is the interface between the network application layer and the twin network layer. The network application requirements are input from the twin northbound interface to the twin network layer. The twin northbound interface can support the rapid deployment of network applications such as network operation and optimization, network visualization, intent verification, and network automatic driving with lower cost, higher efficiency, and less impact on live network services. Therefore, the twin northbound interface should have the characteristics of the following 4 aspects.¶
Twin Internal interface¶
As shown in the "three-layer, three-domain, double-closed loop" of DTN architecture, the twin network layer contains three key subsystems, namely, data sharing warehouse, service mapping model and digital twin management, which is the most critical part of the digital twin network. The internal interface of the twin layer refers to the interface within and between the three subsystems: data sharing warehouse, service mapping model and digital Twin management. In order to support the functions of the three subsystems in the twin network layer and the interaction between the three subsystems, the internal interface of the twin layer should have the following four functions.¶
Twin southbound interface¶
The twin southbound interface is the interface between the twin network layer and the physical entity network. Control updates are delivered from the twin southbound interface to the physical entity network, and various nes in the physical entity network exchange network data and network control information with the twin network layer through the twin southbound interface. Therefore, the southbound twin interface should have three functions.¶
With the development of communication networks, many North-South and intra-network communication protocols have been formed in the network, such as RESTCONFRFC 8527 [RFC8527], NETCONFRFC 8526 [RFC8526], OpenFlow, XMPPRFC 7622 [RFC7622], East-West Bridge, etc.. Because different communication protocols have different characteristics, the existing protocols are suitable for different twin network interfaces. In this draft, we attempt to give some suggestions about the applicability of some existing general protocols suitable for DTN construction.¶
As mentioned above, the physical network in DTN covers various network types, such as mobile access network, core network, and data center network. Therefore, there are many types of network element (NE) devices, and the protocols supported by devices of different manufacturers are different. At the same time, the network application layer in DTN also should support a variety of protocols for different network applications. Therefore, the internal interface of the twin layer must be able to achieve multi-protocol collaboration to meet the diversified protocols and differentiated data formats supported by NEs or network devices of different manufacturers. In addition, the internal interface of the twin network layer must also support changes in requirements and adaptation changes of interface protocols brought about by different applications and application upgrades. At the same time, since the construction of the twin network layer is not only a simple, 1:1 complete copy of the physical network, but a physical network mapping through model abstraction, the implementation of protocol conversion and other processing through multi-protocol collaboration within the twin layer can not only achieve the simplification of the internal protocol of the twin layer, but also will not affect the original DTN system construction.¶
At present, in view of the problem that there are many types of protocols in the network, the industry has also carried out related research. It can be seen that the research of multi-protocol conversion and fusion has a certain basis, but how to achieve multi-protocol collaboration in DTN remains to be studied. In addition, for protocols of the twin northbound interfaces and twin southbound interfaces need to process are different, the protocol adaptation functions of the northbound interfaces and southbound interfaces are different.¶
Twin southbound interface protocol adaptation function¶
+------------------------------------------------------------+ | Collaborative Adaptation of Southbound Interfaces | | +-------------+ +------------+ +-------------+ +---------+ | | |Configuration| | Analysis | | Identif. | | Data | | | | Management | |& Conversion| |& Matching | | Manag. | | | +-------------+ +------------+ +-------------+ +---------+ | +------------------------------------------------------------+
The twin-layer southbound interface protocol adaptation function identifies, analyzes, and converts multiple protocols used by different terminals and devices at the physical network layer. It simplifies information exchange among the three sub-systems at the twin-layer and between the twin-layer and the physical network layer, and implements protocol-independent information processing and data forwarding functions at the twin-layer. By introducing the southbound interface protocol adaptation unit, the network devices in the underlying physical network do not need to be modified too much, and the protocol conversion and adaptation work can be completed by the southbound multi-protocol adaptation unit, which makes the functions of the twin network layer easier to realize and further reduces the complexity of the construction of digital twin network.¶
Compared with the wide variety of protocols supported by NEs at the physical layer, the number of protocols used by applications at the current network application layer is small, and most applications based on Rest API are implemented. Therefore, compared with the protocol adaptation function of the southbound interface, the protocol adaptation function of the twin northbound interface is simpler. Similar to the southbound interface protocol adaptation function, the northbound interface protocol adaptation function also requires a protocol parsing and conversion module to convert the service requirements of Rest API-based network applications into protocols that can be executed at the network twin layer.¶
This document has no requests to IANA.¶