Software-defined optical network (SDON) combines software-defined network (SDN) and transport network. It is a research hotspot in the field of transport network management. It has many applications in packet transport network (PTN) and optical transport network (OTN). And in the network management structure, information model, north-south interface, and other aspects, formed a series of standards. With the emergence of control requirements such as 5G network technology and cloudized private lines, the interaction requirements of the transport network management and control system and the upper-layer service collaborative orchestration are more clear, and it is required to be able to achieve coordinated management and automation network slice control with the upper-layer business management and control system. From the perspective of improving the efficiency of operation and maintenance, it is necessary to have new features such as unified management and control and intelligent operation and maintenance of the transmission network management and control system.

First, SDON international and domestic standardization system is basically perfect

In terms of international standardization, the standardization work of the transmission network SDON is mainly completed by several standardization organizations such as ITU-T, ONF, and IETF.

The ITU-T main ITU-T focuses on the management and control architecture of the 5G transport network, the network slice control, and the information model of the L0 layer to the L2 layer. At present, ITU-T has completed two specifications for G.7701 general control and ITU-T G.7702 transport network SDN control architecture in terms of management and control architecture; ITU-T G.7711 general information in terms of network information model The model defines a protocol-independent information model, ITU-T G.854.1 defines the L1 layer network model, and ITU-T G.807 (G.media) defines the L0 layer medium optical network management architecture, ITU-T G.876 ( G.media-mgmt) executive functions and control mode of optical network media type is defined, ITU-T G.807 and G.876 is expected to be completed around July 2019 and developed through the review. The follow-up ITU-T Q12/14 working group will focus on the 5G management architecture and model research in the transmission network SDN management and control, and adopt the virtual network (VN) management model and the client/server Context architecture to support the upper network segmentation. To realize the slice control of the transport network, and to study the network recovery technology under the centralized controller architecture.

ONF mainly focuses on the work related to the SDN information model of the transport network. It is mainly carried out by the Network Information Model (OTIM) working group. It has developed relevant standards such as the TR-512 Core Information Model (CIM) and the TR-527 Transport API (TAPI) interface function specification. Follow-up mainly focuses on network protection, OAM information modeling, L0 layer OTSi information modeling and other related work.

The IETF mainly focuses on the control model of transport network, IP network and network virtualization, and defines the network model based on YANG. Its TEAS working group is currently refining the ACTN-based virtual network (VN) control model. Its traffic engineering (TE) tunnel and TE topology models have been basically completed. These models can be used for protocol-independent connection-oriented network management. The network management and models related to the protocol are formulated in the CCAMP working group, including OTN tunnels, topologies, and business models. The IETF will continue to develop standards for network virtualization, network slicing, 5G management and other aspects, and improve the related IETF YANG model and its applications.

In general, the international standardization organizations such as ITU-T, ONF, and IETF have basically completed the standardization work for SDON. Currently, the research on 5G control technology and the improvement of the relevant information model of the transport network are focused. In terms of domestic standardization work, China Communications Standards Association (CCSA) has developed a relatively complete software-defined optical network standard system, including general-purpose SDON management and control technology, software-defined optical transport network (SDOTN), and software-defined packet transport network (SPTN). Series of standards.

Second, software-defined optical network (SDON) new research hotspots appear

With the advent of 5G technology and cloud network collaboration applications, software-defined optical networks (SDON) have emerged some new research hotspots, including unified collaborative management and control, multi-layer network management and control, network slice management, intelligent operation and maintenance, and control. Protection of the device, etc.

(1) Unified control becomes the mainstream solution for SDON controller deployment

Smooth evolution from the network, protect existing network investment, and at the same time make the network controller’s control function and traditional management functions have a consistent user experience, and the operator network has the need for unified management and control. The main technical features of unified management and control include the adoption of a unified management and control platform to achieve unified deployment of management, control, and intelligent operation and maintenance; the adoption of a unified data model to prevent data conflicts between different systems and reduce system performance degradation caused by data synchronization; The unified northbound interface is used to provide an open interface based on the YANG model to realize the programming of network resources. Unified control system In actual network deployment, the region division may be based on network performance requirements of a distributed control protocol, the protocol defines a diffusion region of a certain range of the internal network, to reduce the signaling transport network resources consumption , improve service protection Restore performance. The domain controller can directly access the carrier service coordinator to implement flat deployment of the controller, or a multi-level network architecture. Through the unified functions of the manufacturer EMS/OMC and the domain controller (DC), the unified management and control of the resources in the transport domain can be realized; through the unification of the upper-level asset management system and the collaborative orchestrator and the multi-domain collaborative controller (SC) of the transport network, Unified orchestration of cross-domain business.

(2) SDON needs to solve the problem of multi-layer network management and control

The next-generation transport network supports multiple network layers, including L0 layer to L3 layer network technologies. Different network technologies may be used in different domains, or multiple layers of network technology layers in the same network domain. Software-defined optical networks should have multi-layer, multi-domain network management functions.

The management of multi-layer and multi-domain networks can adopt a unified multi-layer management network model, which can be realized by cutting and expanding the model under the common model architecture. ITU-T G.7711/ONF TR512 defines a common network information model. IETF also defines technology-independent TE network models and IP network models under unified model architecture, ETH, ODU, L3VPN, optical layer, and other network technologies. The information modeling model can be performed on the basis of the above model, tailoring and expanding, and defining the operator’s unified northbound interface information model.

In addition, the transport network management and control system should have the planning and optimization functions of multi-layer network resources to achieve the optimal configuration of multi-layer network resources. For the connection-oriented service routing policy, a unified connection-oriented service routing policy and constraints, including L0 layer optical channel, L1 layer ODU/FlexE channel, L2 layer ETH service, L3 layer SR-TP tunnel, etc., may be adopted. A unified routing calculation strategy and routing constraint policies, such as minimum hop count, minimum cost, minimum delay, load balancing, path separation/inclusion/exclusion network resources, and link protection type constraints are adopted. For L3 layer connectionless routing policies, such as SR-BE, dynamic routing can be implemented using SDN centralized routing or distributed BGP routing protocols.

For the coordination of multi-layer routing strategies, the routing parameters should be transmitted between different network layers first, such as the routing cost of the service layer, SRLG and other parameters, which can be passed to the client layer. The link routing cost parameters of the service layer can be used for the client. Layer routing calculation. Secondly, multiple levels of route joint optimization should define multi-layered joint route optimization objectives, strategies and constraints to achieve multi-layer route optimization.

(III) Automated full-cycle operation and maintenance is the basic requirement of network slice control

The segmentation requirements of the 5G bearer network are gradually clear. It is necessary to provide the bearer of the bearer network for different service types such as eMBB, uRLLC, and mMTC. The control of the network slice becomes an important part of the control system. First, for the slice management architecture, the current bearer network management structure, information model, and interface interaction process support the slice network management and control function; secondly, the network slice requires intelligent planning, and the network slice control has the characteristics of network planning and optimization. The bearer network management and control system should Introduce new slice planning and optimization deployment functions; for the slice management process, automatic deployment and monitoring are the basic requirements of 5G network slicing, and a closed-loop process of discovery, creation, operation and maintenance of slice resources should be formed to realize automatic deployment and operation of the slice network. Dimensions, the bearer network should support the manual slicing function; finally, based on the requirements of the upper controller and the orchestration system, based on the technical characteristics of each layer network, the slice management and control of the multi-layer network resources, based on the slicing requirements of the upper layer network and the technology of the bearer network Features implement this layer slice network management.

(4) Intelligent operation and maintenance brings new features to SDON technology

Artificial intelligence ( AI) technology brings new features to network management and control. By introducing big data analysis to the bearer network and introducing machine learning capabilities, it can realize business-centric intelligent troubleshooting, AI-based intelligent fault analysis, and intelligent fault self- Intelligent network operation and maintenance capabilities such as planning and optimization based on business performance monitoring. The network intelligent operation and maintenance function should support the automation, closed loop and intelligent operation and maintenance of the network operation and maintenance life cycle. In a multi-vendor, multi-regional, multi-technology network environment, a unified data model should be defined to extract data from the bearer network for analysis of network behavior. In addition, behavioral models should be defined, such as developing fault management templates and traffic warning models to guide the intelligent operation and maintenance of the network.

Third, summary

With the advent of 5G technology and the emergence of network application requirements such as cloud-dedicated lines, software-defined optical networks have brought many new research hotspots. From the current status of standardization, both the international and domestic standards systems have been formed with software-defined optical networks. The next research hotspot will be multi-layer network management and control architecture, network slice management, multi-layer network information model, and controller-based controllers. Protection recovery, etc. Software-defined optical network (SDON) will evolve toward unified collaborative management, intelligent operation and maintenance, and further improve the network’s intelligent management and control capabilities and operation and maintenance efficiency.