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."

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

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

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.

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

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

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.

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