**4. Novel applications**

SDON is a promising solution for next‐generation high‐speed optical transport network, which embraces a wide application perspective. Here are some sample applications, which can make optical network being used in a more flexible manner. The sample applications include bandwidth on demand [29], Virtual Optical Network (VON) services [30], and some emerging applications [31, 32].

#### **4.1. Bandwidth on demand**

Based on the centralized control plane of SDON, providers are able to predict resource occupation status in time dimension, and accordingly arrange and accommodate users' requests to avoid spectrum conflicts and fragmentations. One application, which is called time‐aware bandwidth on demand, has already been implemented and demonstrated to do such things. Bandwidth on demand can improve the utilization of spectrum resource in SDON. The overall feasibility and efficiency of this time‐aware Bandwidth on demand architecture is experimentally verified on a testbed with real OpenFlow‐enabled tunable optical modules in terms of blocking probability and resource occupation rate, as shown in **Figure 7**. First, the users' requests are sent to the controller, and then the controller will schedule these requests to make the spectrum resource utilization optimized, finally the controller will send messages to optical nodes to set up lightpaths. As one of the basic types of services in intelligent optical network, bandwidth on demand can prove the integrity and availability of networking by offering bandwidth resource directly. Also, bandwidth on demand can be a basic measurement index of network automation.

### **4.2. Virtual optical network**

**4. Novel applications**

12 Optical Fiber and Wireless Communications

emerging applications [31, 32].

**4.1. Bandwidth on demand**

SDON is a promising solution for next‐generation high‐speed optical transport network, which embraces a wide application perspective. Here are some sample applications, which can make optical network being used in a more flexible manner. The sample applications include bandwidth on demand [29], Virtual Optical Network (VON) services [30], and some

**Figure 6.** Architecture and procedure of OaaS: (a) architecture, (b) CSO procedures, (c) module diagram.

Based on the centralized control plane of SDON, providers are able to predict resource occupation status in time dimension, and accordingly arrange and accommodate users' requests to avoid spectrum conflicts and fragmentations. One application, which is called time‐aware bandwidth on demand, has already been implemented and demonstrated to do such things. Bandwidth on demand can improve the utilization of spectrum resource Virtual optical network (VON), which aims to provide multiple dedicated virtual network over shared network infrastructure, has gained a lot of attention by network providers. By VON, service providers can request a dedicated network for each application on a per‐need basis and have full control ability over that network. Network virtualization technologies can partition/composite of network infrastructure (i.e., the physical optical nodes and links) into independent virtual resource, adopting the same functionality as the physical resource. Also, the composition of these virtual resource (i.e., virtual optical nodes and links) allows deploying multiple VON. A VON must be composed of not only a virtual transport plane but also a virtual control plane, with the purpose of providing the required independent, and full control functionalities. In datacenter optical network, since the computing resources are highly distributed, it is impossible to build a dedicated optical network for a special ser‐ vice. So joint considering computing and networking resource is very important if they are under the control of same provider. Network virtualization can eradicate the ossification of the network, stimulate innovation of new network architectures and applications, and enable network operators to operate different VON that share a common physical infrastructure. **Figure 8** shows the schematic of SDN‐based VON provisioning.

There are many challenges in VON provisioning, such as VON design and VON resource management. VON design refers to the procedures to find a subset of the underlying physical

**Figure 7.** Time‐aware bandwidth on demand: (a) without SS, three slots occupied; (b) with SS, two slots occupied, one slot resource is saved.

**Figure 8.** VON provisioning.

network topology connecting the computing resources with virtual nodes hosted on the physi‐ cal nodes and virtual links spanning over the physical links. The VON design problem is related to the traffic demand model and the entire physical network topology information. VON resource management includes two schemes, that is, dedicated scheme and shared scheme. The dedicated VON assumes that the link resources are exclusively assigned to a VON user, so each VON topology runs independently, and its reserved link resources cannot be occupied by other VON. The dedicated VON is relatively easier to achieve, but it has a drawback that it increas‐ ingly decreases the efficiency of resource utilization. Note that the sharing VON scheme can be fully or partially shared, and partially shared VON manner is more profitable. On each physical link belonging to a VON, a minimum guaranteed capacity must be assigned to it, while residual capacity is shared by all the VON on that link. The challenge in employing the partially shared VON approach is that the service provider should treat the dedicated and shared resources with different policies, which inevitably increases implementation complexity and difficulty.

## **5. Conclusions**

In this chapter, we summarize the basic principles and key technologies of SDON. First, the architecture of SDON is described with southbound and northbound interfaces and proto‐ cols. Then, several key technologies of SDON are introduced, including sliceable transponder, WSS, BV‐OXC, routing and spectrum assignment, virtual optical network mapping, and CSO algorithms. Finally, two novel applications are prospected, such as bandwidth on demand and VON. More studies need to be conducted to promote the evolution of SDON in the future.

## **Author details**

Yongli Zhao\*, Yuqiao Wang, Wei Wang and Xiaosong Yu

\*Address all correspondence to: yonglizhao@bupt.edu.cn

State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing, China
