ZTE Issues SDON Whitepaper, Explaining in Detail the Key. Technologies for Optical Network Evolution

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1 ZTE Issues SDON Whitepaper, Explaining in Detail the Key Technologies for Optical Network Evolution Ever-changing service demands and uncontrollable traffic and traffic direction are two major causes which urge operators to introduce the Software Defined Network (SDN) over optical network. As a spokesperson from an operator said on a forum, it is practicable now to introduce the SDN to optical transport networks. The optical forwarding plane and control plane are both ready for supporting the SDN. The open-source technology for controllers is gradually enhanced. The optical forwarding-plane technology is practicable to support the SDN in terms of many aspects, for example, ultra-long distance transmission of 100G/400G, large-capacity OTN, ROADM, and multi-granularity dispatching. "It is an extremely large project for China to gradually develop SDN-based optical networks. It can't be made overnight. What we need to do is to protect existing investment, make breakthroughs in terms of northbound and southbound interfaces of the control layer, and implement smooth evolution for existing equipment", mentioned the operator when talking about the actual challenges they face during SDN introduction. It is obvious that relevant enterprises in the industrial chain have considered the feasibility of technologies and the problems that may occur during the actual deployment of SDN. The Software Defined Optical Network (SDON) strategy proposed by ZTE features intelligent, virtualized and cloud-based, which greatly draws the market's attention. Wei Xiaoqiang, head of the Bearer Network Planning Department of ZTE, said "The ZTE SDON solution can provide varieties of apps such as BoD, OVPN and IP+ optical collaboration to help operators fast provision services, adjust bandwidth on demands, build a cross-regional large network, simplify OAM, and reduce OPEX."

2 As from 2016, the SDN will experience a pre-commercial deployment and long-term evolution phase. To define the processes, key technologies and applicable scenarios of the SDON, ZTE will issue the SDON Whitepaper (hereafter referred to as the Whitepaper) at the end of June when the NGON Next-Generation Optical Network Forum will be held in Nice France. The Whitepaper details the core technologies that may be involved in the SDON development and gives deployment suggestions. SDON Evolution Process After a series of research and trial operations, operators focus on how to solve the current network problems by gradually deploying typical SDN scenarios over existing networks. The SDON evolution process defined in the Whitepaper is: Network Management Centralized Configuration > Distributed Control (With PCE) > SDN Control, as shown in Table 1. Table 1 SDON Evolution Process According to the Whitepaper, the control plane and PCE of an optical network have laid a solid technical foundation for smooth evolution of the SDN solution in terms of route computing, resource dispatching, and discovery and synchronization of

3 engineering information over a multi-layer multi-domain heterogeneous network. This is a great milestone for the optical network to evolve towards a new generation of SDN architecture. As shown in Figure 1, the control plane and PCE architecture are closely related to the SDN controller architecture in terms of the applied technologies. Figure 1 Control Plane, PCE Architecture and SDN Architecture At present, the PCE technology has been widely applied to products. China Mobile jointly cooperates with the Transport Institution of the Ministry of Industry and Information Technology to test the PCE interoperability over multiple OTN domains and verify the PCE-based centralized control system over optical network and the route computing, resource dispatching, multi-domain service dispatching, and protection/restoration over multi-domain multi-layer PCE collaboration. The test fully shows that the PCE system lays a solid technical foundation for smooth evolution towards the new generation of SDN optical network, and is a predominant milestone for the optical network to evolve towards the new generation of SDN architecutre. SDON Key Technologies The Whitepaper defines in detail the overall SDON architecture which consists of the application layer, control layer and equipment layer, as shown in Figure 2. The interfaces are classified into southbound interfaces and northbound interfaces. At present, the SDN solution for optical network has been gradually practicable and a three-layer framework with southbound and northbound interfaces has been formed. In addition, some other layers can be deployed according to different applicable scenarios. Figure 2 Overall Architecture of the SDN Optical Network Solution

4 The elastic optical network is the core of the SDON architecture. It takes advantage of the optical channels over flexible grid-based dispatching and chooses the integrated filter component through the high-performance programmable optical channels. In addition, it supports flexible Mesh-based switching and processing for the signals with different intervals and code types. The SDN optical-network controller is mainly used for route computing, resource dispatching and unified connection control. It supports global network view, forwarding state control, and network-wide resource information and utilization information. In addition, it properly controls and balances network traffic and forwarding traffic by implementing unified computing and issuing continuous commands based on the preset network policy and load balance policy. Regarding the southbound and northbound interfaces concerned a lot by operators, the Whitepaper defines that the interface between the controller over SDON architecture and the app-layer or upper-layer controller is northbound interface (CVNI), and that the interface between the controller and the NE is southbound interface (CDPI). The northbound interface API should be open, flexible and highly extensive to meet different user demands for network configuration, management and application. The interface protocols can be OPENFLOW, PCEP or Restful according to the requirements of the app layer.

5 The southbound interface is mainly used to establish connections over optical network, and remove and maintain end-to-end optical/electrical-layer connections. The interface protocols can be OPENFLOW, PCEP or SNMP. With the development of SDN and its extensive application, southbound and northbound interfaces will have more enhanced functions, open capabilities, and standardized protocols. Regarding the interoperability of the SDN with traditional optical networks, the Whitepaper defines that one of the basic ideas for the SDN is unified control over multiple heterogeneous networks. The existing networks have multiple control modes, for example, traditional networks controlled by EMS/NMS and the networks deployed with distributed control planes (GMPLS). For new SDN optical networks, the interoperability with traditional networks should be taken into consideration to implement automatic establishment for end-to-end connections over multi-layer heterogeneous network. SDON Values and Its Way of Evolution The Whitepaper emphasizes the two main values of SDON. First, the SDON functions as a service layer to perceive service characteristics under global unified dispatching, supports finer management, and enhances the efficiency and quality of data by applying different policies on time and space dimensions. Second, from the perspective of the operation over smart channels, the SDON supports many VAS functions like OVPN through varieties of technologies such as the virtualization technology. This helps fully utilizing optical network channels. In the path of evolution, the SDN shows its great innovativeness and power. During actual deployment, the industrial chain needs to work out periodical solutions and technologies regarding the specific demands in different scenarios. The Whitepaper also shows many technological and non-technological challenges that the SDON will face during its future deployment. As a software defined network architecture, its major challenges come from unified software control, elastic management, software complexity and efficiency, and security. As an open system, its major challenges to the unified control come from migration of equipment and

6 management functions of different hardware providers, smooth evolution from existing hardware platforms towards virtualized networks, compatibility with traditional networks, and other long-term co-existent challenges. SDON Practices of ZTE Before issuing the SDON Whitepaper, ZTE has carried out a lot of research and practical work regarding the SDN over optical network. From 2014, ZTE cooperated with the three mainstream operators to finish the SDON tests in labs and existing networks, which further enhanced the support of ZTE equipment such as ZTE 9700 to the SDON. At present, operators deploy SDON over their existing networks, with the purpose of solving existing problems, protecting existing investment and focusing primarily on the management and utilization of optical network resources. From July to September 2015, ZTE cooperated with China Telecom to finish the testing on the typical scenarios oriented to BoD and VTS, including lab tests and existing network tests in two provinces. All the tests had resulted in the expected achievements. According to the rules for the innovation circle, ZTE proposed that the SDON could be tested in a few scenarios first to re-build and verify the existing software functions over SDN architecture. Under the cooperation with China Telecom for trial operation, ZTE acted as a single-domain controller and equipment provider and took part in the functional tests regarding the establishment, deletion and query for ODUk and L2 Ethernet services over a cross-vendor and cross-routing-domain network, VTS service protection and restoration, BoD, and L2 Ethernet service statistics. All the functional tests provided the most valuable reference for the commercial use of SDON in the future. In addition, ZTE maintained the enhancement of SDON architecture during its cooperation with operators. To be specific, ZTE highlighted module functions, enhanced southbound and northbound interfaces according to operator standards and relevant ONF standards, and submitted many SDON proposals which had been

7 accepted by the ISO. Zhu Yongxing, Vice President of ZTE, said "Due to the differences in transport equipment from different providers, it is recommended to deploy the SDON phase by phase over the transport and control planes to manage the controllers from the same provider. Concerning equipment from different providers, it is more reasonable to implement unified management through an upper-layer collaborator and deploy the SDON phase by phase." From 2016, the SDN will experience the commercial use and long-term evolution phase. ZTE will gradually deploy the typical SDN scenarios over existing networks to solve the existing problems which operators face now. CWW