**3. Key technologies in SDON**

(5) NBI can optionally support path computation function when the controller is controlled

(6) NBI should support post controller resource data updating request. When network re‐ source data is updating directly, instead of based on network notifications, new request will be needed through northbound interface to update data. And resource should be

(7) Northbound should support triggering the function of resynchronizing controller re‐

(1) OpenFlow protocol: OpenFlow protocol for network devices should correspond to the re‐ quirement of ONF TS‐024 (OpenFlow Switch Specification 1.4.1) and ONF TS‐022 (Opti‐ cal Transport Protocol Extensions Ver1.0) or higher version. OpenFlow protocol supports

(2) OF‐Config protocol: As a supplementary of OpenFlow protocol, it is used for configuring

(4) ASON/GMPLS control panel protocol: Signaling protocol should correspond to GB‐T 21645.4‐2010(ASON) and Request For Comments (RFC) 3471; routing protocol should correspond to GB/T 216545.8‐2012 and RFC4203. Automatic discovering protocol should

(5) Path computation element protocol (PCEP): Corresponding to the requirement of Inter‐ net Engineering Task Force (IETF) RFC 5440 (PCE communication protocol) and other

SDON NBI can be implemented by SDN‐specific protocols (RESTCONF, PCEP, etc.) or other

In some cases, notification function is mandatory for NBI to push update information to cus‐ tomers. RESTCONF is one option, which supports notification event defined in YANG model. RESTCONF clients receive notifications by means of subscribing URL of notification mes‐ sage's resource. NBI protocol can follow RESTCONF protocol defined in IETF draft‐ietf‐net‐

It is JSON or XML format that content encoding of northbound interface communication

popular protocols used in current software engineering (Restful, Protobuf, etc.).

should use, which corresponds to RFC7159 and RFC3032, respectively.

(3) Traditional management protocols: Qx, SNMP, TL1 protocols, and so on.

(a) Support posting routing computation request and offering path computation func‐

(b) Support posting reconfiguring path request, adjusting path connected, in order to

by other upper layer orchestrators.

6 Optical Fiber and Wireless Communications

satisfy new requirement.

released after connections are deleted.

source data.

**2.2. Protocols**

tion according to demand of service strategy.

There are several protocols that can be used to implement SBI:

resource reporting and network device configuring.

correspond to GB/T 21645.7‐2010 and RFC4204.

OpenFlow network devices.

derived RFC documents.

conf‐restconf‐07 to realize functions above.

SDON is stretching optical network intelligence. It represents the fact that the control panel of optical network changes from switching intelligence to a comprehensive automatic one, where services diversity and management automation are also considered. In order to adapt to this revolution, SDON needs to make breakthroughs on key technologies like ser‐ vices assignment strategies, heterogeneous networks, and programmable optical transmit devices.

#### **3.1. Sliceable transponder**

Sliceable transponder is a kind of photonic, which can be divided into several sub‐transpon‐ ders, and each sub‐transponder can be used to construct an independent lightpath without "O‐E‐O" switching on transit nodes. From the perspective of optical layer, multiple optical flows can be multiplexed into one optical transponder. And the de‐multiplexing procedure for each optical flow will be operated in the receiver at destination node of that flow. **Figure 2** shows a sliceable flexible optical transponder.

A physical transponder can generate different ligthpaths with different spectrum segments. Multi‐flow optical transponder has been proposed and proved by experiment [11]. In addi‐ tion, multi‐spectrum sliceable and bandwidth‐extendable coherence optical transponder based on any waveform optical generator, which can also generate multiple optical paths, has been proposed and proved [12].

The most significant difference between sliceable transponder and unsliceable transponder is that there are multiple send‐receive interfaces in sliceable transponder, which means multiple clients' signals can be handled by one transponder. Consequently, there should be a program‐ mable switch matrix between interface card and sliceable transponder, in order to routing

**Figure 2.** Sliceable optical transponder schematic diagram.

signals between them. In this case, the number of interface cards M and transponder slices are the key factor, which decide the network capability and networking cost.

### **3.2. Wavelength‐selective switching (WSS)**

The advent of all‐optical switches based on wavelength‐selective switching (WSS) has a sig‐ nificant impact on the development of extensibility and flexibility on optical networking. It makes the structure of all‐optical switches change unexpectedly. This kind of WSS lets each wavelength in an input Wavelength‐Division Multiplexing (WDM) signal transmit to anyone of the output ports, while the N×1 WSS has the contrary function.

Each WSS chooses an output previously configured wavelength from each input optical fiber. The number of WSS will grow according to the expansion of its dimensions. As to interfaces on client side, several WSS can be deployed as multiplexing/de‐multiplexing role, instead of deploying one WSS for each add/drop fiber.

**Figure 3** shows an example flexible switching node, which can realize high‐spectral efficient multi‐grid grade switching.

**Figure 3.** Software‐defined flexible switching node.

#### **3.3. Bandwidth‐variable optical cross‐connect**

Bandwidth‐variable optical cross‐connect (BV‐OXC) is an important kind of switching node in flexible spectrum optical network. A multi‐dimension BV‐OXC is composed of some splitters and some bandwidth‐variable wavelength‐selective switches (BV‐WSS) as shown in **Figure 4**.

Software‐Defined Optical Networking (SDON): Principles and Applications http://dx.doi.org/10.5772/intechopen.68294 9

**Figure 4.** Bandwidth‐variable optical switching node schematic diagram.

signals between them. In this case, the number of interface cards M and transponder slices are

The advent of all‐optical switches based on wavelength‐selective switching (WSS) has a sig‐ nificant impact on the development of extensibility and flexibility on optical networking. It makes the structure of all‐optical switches change unexpectedly. This kind of WSS lets each wavelength in an input Wavelength‐Division Multiplexing (WDM) signal transmit to anyone

Each WSS chooses an output previously configured wavelength from each input optical fiber. The number of WSS will grow according to the expansion of its dimensions. As to interfaces on client side, several WSS can be deployed as multiplexing/de‐multiplexing role, instead of

**Figure 3** shows an example flexible switching node, which can realize high‐spectral efficient

Bandwidth‐variable optical cross‐connect (BV‐OXC) is an important kind of switching node in flexible spectrum optical network. A multi‐dimension BV‐OXC is composed of some splitters and some bandwidth‐variable wavelength‐selective switches (BV‐WSS) as shown in **Figure 4**.

the key factor, which decide the network capability and networking cost.

of the output ports, while the N×1 WSS has the contrary function.

**3.2. Wavelength‐selective switching (WSS)**

8 Optical Fiber and Wireless Communications

deploying one WSS for each add/drop fiber.

**3.3. Bandwidth‐variable optical cross‐connect**

**Figure 3.** Software‐defined flexible switching node.

multi‐grid grade switching.

Bandwidth‐variable optical cross‐connect (BV‐OXC) changes the switching granularity from wavelength to sub‐carrier level. The basic unit bandwidth of sub‐carrier is 12.5 GHz, while the interval is 6.25 GHz, both of which are much less than 50 GHz—the International Telegraph Union Telecommunication Standardization Sector (ITU‐T) standard wavelength.

In addition, each wavelength in OXC is isolated from the others. Even though there is a block‐ ing interval between two adjacent wavelengths, this feature makes it impossible for a band‐ width that is more than a wavelength to pass inviolately. However, BV‐OXC eliminates the slot between sub‐carriers and makes it possible for multiple sub‐carriers to bind together and become a broadband. BV‐OXC makes it possible to switch a signal as a super‐channel.

Thus, BV‐OXC has not only better switching granularity but also makes switching capability rise dramatically. Subsequently, this technique can be used in elastic optical network (EON), for the reason that the core idea of EON is to provide necessary spectrum resource with better granularity for users' different connection requirements.

#### **3.4. Routing and spectrum assignment**

In elastic optical network, high‐spectral efficiency and expansibility have been already real‐ ized. Meanwhile, the flexibility introduces new challenges in network research. For instance, taking route and spectrum assignment into account, it is not suitable for traditional routing and wavelength assignment (RWA) algorithm being used in flexible spectrum network any longer. One of the reasons is that there lies a new feature—constraint condition of spectrum continuity in flexible spectrum network, which means that network needs to assign a slot of continuing and available spectrum resource for each lightpath. In addition, the flexibility of grid makes the network model more complicated, resulting in higher difficulties of optimization.

In elastic optical network, spectrum is further divided into a series of sub‐carriers that has lower data rate and finer granularity than those in WDM network [13]. Compared with RWA problem in traditional network schedule, the primary problem in elastic network is to allocate contiguous spectrum resources to provision high bandwidth demand connections. This prob‐ lem is called Routing and Spectrum Allocation (RSA) [14].

According to required bitrates and modulation format, lightpath is constructed from source node to destination node in frequency domain by means of allocating continuous sub‐carriers on all links. In order to demodulate easily on receivers, one or more sub‐carriers are needed as gap between adjacent spectrum paths. There are three kinds of constraints that we should obey when operating RSA computation:


When connections are deleted, the allocated spectrum resource will be released and can be provided for other coming services. However, due to the fact that network being usually used to serve multiple applications, lightpaths may be constructed and deleted randomly, which leads to the appearance of spectrum fragments inevitably. When contiguous spectrum is divided into fragmentary segments, new coming requests might be blocked for lacking wider contiguous spectrum segment, though there are still lots of unused spectrum slots. This means that the spectrum is not used efficiently. Some heuristic algorithms have been proposed for RSA problems [18–20] and defragmentation problems [21–23].

#### **3.5. Virtual optical network mapping**

Virtual optical network (VON) is a new kind of transport service, which aims to allocate spectrum resource to customers at topology level. Compared with RSA, VON mapping is more complex because it needs not only spectrum allocation but also mapping virtual topol‐ ogy to physical substrates. **Figure 5** shows a use case of virtual network mapping. The left is abstracted topology and the right is the physical topology. If node mapping method is adopted, node 1 on the abstracted topology is mapped on node 2 on physical topology. Similarly, nodes 2 and 3 are mapped on nodes 4 and 1 on physical topology. If link map‐ ping method is adopted, link 1–2 on abstracted topology is mapped on link 2‐3‐4 on physical topology, and link 1–3 is mapped on link 2–1 on physical topology. The procedure of virtual network mapping can be divided into two phases:


From the perspective of VON mapping, all of the mapping algorithms can be summarized as:

Software‐Defined Optical Networking (SDON): Principles and Applications http://dx.doi.org/10.5772/intechopen.68294 11

**Figure 5.** An example of virtual optical network mapping.

contiguous spectrum resources to provision high bandwidth demand connections. This prob‐

According to required bitrates and modulation format, lightpath is constructed from source node to destination node in frequency domain by means of allocating continuous sub‐carriers on all links. In order to demodulate easily on receivers, one or more sub‐carriers are needed as gap between adjacent spectrum paths. There are three kinds of constraints that we should

(1) Spectrum consistency constraint, namely each link in the path needs to allocate the same

(2) Spectrum continuity constraint, only to make sure that each sub‐carrier in the path must

(3) Spectrum conflict constraint, allocated spectrum in different paths on the same fiber can‐

When connections are deleted, the allocated spectrum resource will be released and can be provided for other coming services. However, due to the fact that network being usually used to serve multiple applications, lightpaths may be constructed and deleted randomly, which leads to the appearance of spectrum fragments inevitably. When contiguous spectrum is divided into fragmentary segments, new coming requests might be blocked for lacking wider contiguous spectrum segment, though there are still lots of unused spectrum slots. This means that the spectrum is not used efficiently. Some heuristic algorithms have been

Virtual optical network (VON) is a new kind of transport service, which aims to allocate spectrum resource to customers at topology level. Compared with RSA, VON mapping is more complex because it needs not only spectrum allocation but also mapping virtual topol‐ ogy to physical substrates. **Figure 5** shows a use case of virtual network mapping. The left is abstracted topology and the right is the physical topology. If node mapping method is adopted, node 1 on the abstracted topology is mapped on node 2 on physical topology. Similarly, nodes 2 and 3 are mapped on nodes 4 and 1 on physical topology. If link map‐ ping method is adopted, link 1–2 on abstracted topology is mapped on link 2‐3‐4 on physical topology, and link 1–3 is mapped on link 2–1 on physical topology. The procedure of virtual

(1) Node mapping: Map virtual nodes to different real physical nodes and satisfy virtual

From the perspective of VON mapping, all of the mapping algorithms can be summarized as:

(2) Link mapping: Map virtual links between virtual nodes to real physical links.

proposed for RSA problems [18–20] and defragmentation problems [21–23].

lem is called Routing and Spectrum Allocation (RSA) [14].

obey when operating RSA computation:

spectrum resource.

10 Optical Fiber and Wireless Communications

connect with the others.

not be overlapped [15–17].

**3.5. Virtual optical network mapping**

network mapping can be divided into two phases:

nodes' resources demand.


As for mapping algorithm, concepts like sliceable ability of link, optical transponder, and switching nodes are proposed to describe resource abstraction method in flexible spectrum network. And based on that above, LS‐based virtual optical network mapping strategy and NS‐based virtual optical network mapping strategy are proposed [27]. Result from experi‐ ment shows that LS‐based virtual optical network mapping and NS‐based virtual optical net‐ work mapping, compared to baseline virtual optical network mapping, get lower blocking probability and higher profit.

#### **3.6. Cross stratum optimization algorithm**

In datacenter network, network‐based services are provisioned by both IT and network resource. In order to achieve the optimization of IT and network resource, cross stratum opti‐ mization (CSO) is proposed [28], which can enable a joint optimization of IT and network resource and take optical as a service (OaaS).

The SDN‐based control architecture with CSO between optical network and application stra‐ tum resource in inter‐datacenter network is proposed to partially meet the QoS requirement.

Unified control architecture is proposed as depicted in **Figure 6(a)**, which especially emphasizes on the cooperation between application controller (AC) and service controller (SC) based on OpenFlow to realize the CSO of application and network resource. According to the requirement, AC customizes appropriate virtual resource through related SC with extended OpenFlow pro‐ tocol. In addition, dynamic global load balancing strategy is implemented based on both appli‐ cation and network resource, while SC can trigger service‐aware Path Computation Element algorithm based on the result of dynamic global load balancing strategy. SC interacts with each other for the security and virtual network information. OpenFlow‐enabled routers and optical transport nodes are realized by extending match domain in extended OpenFlow protocol. The responsibilities and interactions among entities are provided as shown in **Figure 6(b)** and **(c)**.

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