FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See section 10, rule 13) 1. Title of the invention: CONTROL PLANE OPTIMIZATION OF COMMUNICATION NETWORKS 2. Applicant(s) NAME NATIONALITY ADDRESS TATA CONSULTANCY SERVICES LIMITED Indian Nirmal Building, 9th Floor, Nariman Point, Mumbai, Maharashtra 400021, India 3. Preamble to the description COMPLETE SPECIFICATION The following specification particularly describes the invention and the manner in which it is to be performed. 1 2 TECHNICAL FIELD [0001] The present subject matter relates, in general, to communication networks and, in particular, to optimization of control plane in Software Defined 5 Network (SDN). BACKGROUND [0002] Communication networks are vastly utilized and relied upon across the globe to share information between two or more end users. A communication network, also referred to as a network, typically involves one or more network 10 devices, such as network switches and network routers, apart from other components, for the purpose of transferring information amongst the end users. [0003] The information is transferred in the form of digitized data packets, simply referred to as packets. At a network device, packets are received at one or more input ports of and are forwarded to one or more output ports of the network 15 device. The forwarding is based on a path or a route of the packet, for being forwarded to an end user, which may in turn be based on the configuration of the network. Typically, each forwarder in a network is configured with an in-built control logic, also referred to as the control plane. The control plane determines forwarding rules or conditions that allow the network device to control the 20 forwarding behaviour or flow of packets between the input and output port(s) of the network device. [0004] More recently, computer networks with dynamic architectures, such as Software Defined Networks (SDNs) that allow the control logic to be decoupled from the network device and be moved to external central controllers are 25 increasingly being used. The SDN architecture decouples the control plane of the 3 network from the data plane and provides direct control of the network devices such that the network may be managed with greater flexibility and efficiency. BRIEF DESCRIPTION OF DRAWINGS [0005] The detailed description is described with reference to the 5 accompanying figure(s). In the figure(s), the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figure(s) to reference like features and components. Some embodiments of systems and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with 10 reference to the accompanying figure(s), in which: [0006] Figure 1 illustrates a network environment implementing a system for network control plane optimization in software defined network (SDN), according to an implementation of the present subject matter. [0007] Figure 2 illustrates a network controller, according to an 15 implementation of the present subject matter. [0008] Figure 3 illustrates a central optimization controller, according to an implementation of the present subject matter. [0009] Figure 4 illustrates a network control plane optimization method, according to an implementation of the present subject matter. 20 [0010] Figure 5(a) illustrates an SDN topology implementing the non-zero sum game based network control plane optimization operation, according to an implementation of the present subject matter. [0011] Figure 5(b) illustrates an SDN topology implementing the non-zero sum game based network control plane optimization operation for a decreasing 25 network load, according to an implementation of the present subject matter. 4 [0012] Figure 6(a) illustrates an SDN topology implementing the non-zero sum game based network control plane optimization operation, according to an implementation of the present subject matter. [0013] Figure 6(b) illustrates an SDN topology implementing the non-zero 5 sum game based network control plane optimization operation for an increasing network load, according to an implementation of the present subject matter. [0014] Figure 7(a) illustrates an SDN topology implementing the non-zero sum game based network control plane optimization operation, according to an implementation of the present subject matter. 10 [0015] Figure 7(b) illustrates an SDN topology implementing the non-zero sum game based network control plane optimization operation for a change in network load, according to an implementation of the present subject matter. [0016] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the 15 principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. 20 DETAILED DESCRIPTION [0017] Software Defined Network (SDN) technology provides customization and optimization of data forwarding in communication networks. Modern communication networks are simplified by the SDN technology by decoupling a data-forwarding layer and control layer, for example, the data plane and the control 25 plane. In conventional communication networks, the control plane function, such as routing, resourcing, and management functionality are performed in the network devices, such as a switch or a router itself, whereas, in case of communication 5 networks supporting SDN, the network devices are configured to implement the data plane functions, while the control plane functions are provided by an SDN controller mapped to the network devices. Open Application Programming Interface (API) services, such as Open Flow protocol are implemented to manage the interactions 5 between the data plane and control plane. SDN in conjunction with an Open API service provides flexibility and increased control over the network devices. [0018] Conventionally, communication networks implemented based on SDN architecture provides a logically centralized control of a physically distributed control plane. Such systems implement a distributed SDN controller with the 10 mapping between a network device, such as a switch or a router and a controller being statically configured. The terms SDN controller, network controller and controller have been used interchangeably in the specification. Statically configured controllers make it difficult for the control plane to adapt to traffic load variations in the communication networks, such as data centre networks, enterprise networks, that 15 have significant variations in temporal traffic and spatial traffic characteristics. In such scenarios of statically configured controllers, a controller may become overloaded if the network devices mapped to this controller observe a large traffic. Further, some controllers in the communication network may be in an overload condition while other controllers may be underutilized. The load may shift across 20 controllers over time, depending on the temporal and spatial variations in traffic conditions and static mapping can result in non-optimal performance. [0019] Majority of the techniques follow a centralized control plane architecture, where a central controller can decide the number of controllers required and their allocation to network devices. Also, certain conventional techniques 25 provide distributed control plane architecture for communication networks implemented based on SDN architecture. The load in such architecture is dynamically shifted to allow the controllers to operate within a specified load restriction. As the load on the communication network changes, the load on each 6 controller also changes and the architecture dynamically expands or shrinks the controller pool as based on the change in the network load. As load imbalance occurs, a controller with heavy network load transfers its load on to another controller with relatively less load. The algorithm and techniques underlying the 5 architecture to provide change in control pool are generally based on the existing Open Flow standard. [0020] However, the presently available methods and systems for distributed controller architecture, as described above, do not provide optimal solutions for controller placement. Further, such methods and systems provide for addition and 10 deletion of controllers based on the load of the communication network, but the number of the controllers in the network may not be optimum. If the non-optimum number of controllers in the communication network is high, it may lead to underutilization of some controllers and further result in delay in the control resolution, result in more electricity consumption, and cause high operational 15 expenditure and capital expenditures for the communication network. On the other hand, if the number of controllers in the communication network is low, it may result in poor Quality-of-Service (QoS) of the communication network due to packet drops and delayed resolution of flows. Moreover, the decision of addition and deletion of network controllers based on the load of the communication network is taken by a 20 centralized control entity. More often than not, a malfunctioning of the centralized control entity results in failure or improper functioning of the communication network. [0021] Further, conventionally available methods are topology specific and may not be compatible with different types of communication networks. Also, 25 conventionally available methods are often not backward compatible making them difficult to be implemented in existing communication networks. Also, some conventionally known techniques provide solution that require incurring significant cost and expenditure of resources for their implementation. 7 [0022] The present subject matter describes systems and methods for control plane optimization in a communication network. In an embodiment, the systems and methods allow determination of optimum number of network controllers in the communication network. Further, according to an implementation of the present 5 subject matter, the determined optimum number of controllers may be placed at optimal locations in the control plane of the communication network. Placement of the controllers may be defined as mapping of controller on network devices, such as network switch in order to achieve a uniform load over the network, maximum utilization of the controllers, and minimum delay of control resolution. 10 [0023] According to an implementation of the present subject matter, the communication network may be implemented based on SDN architecture. In one implementation, the optimum number of controller(s) is determined based on the load on the communication network. Since the load on a communication network is a function of time and changes dynamically, the number of controllers to support the 15 load may also change dynamically. Providing optimal number of controllers may include addition or deletion of controllers dynamically. Accordingly, in one implementation of the present subject matter, network controllers may be dynamically added or deleted in the communication network, such as a SDN. Further, in one embodiment, the placement of the network controllers in the control 20 plane may be dynamically varied. [0024] In one embodiment of the present subject matter, the optimization of the number of the controllers and their respective placement may be determined in accordance with a non-zero sum game based network control plane optimization operation. In the non-zero sum game based network control plane optimization 25 operation, hereinafter referred to as control plane optimization operation; each network controller in the communication network computes its self payoff value. The self payoff value is indicative of whether the controller is optimally utilized, underutilized or overutilized. 8 [0025] In one implementation, any controller of the communication network which is underutilized and has a capacity to take over more load, may be considered as a greedy controller. Based on the control plane optimization operation, the greedy controller may increase its utilization by sharing load of one or more neighboring 5 controllers. However, in case the controller is significantly underutilized, it may transfer its existing load to one or more neighboring greedy controllers and enter an inactive mode. This approach not only enables equal distribution of load across the various controllers but also ensures that the controllers that have a significantly low utilization are no longer active, thus allowing optimization of the operational cost of 10 the communication network. [0026] In another embodiment, an over-utilized controller may off-load some of its load to one or more neighboring controllers to balance its load. For example, the load may be off-loaded to a neighboring controller that is underutilized. In one embodiment, in case the over-utilized controller is unable to off-load it load to a 15 neighboring controller or is facing excessive load in spite of the off-loading, the overutilized controller may generate a request for activation of an additional controller in the communication network. This, again, ensures equal distribution of load across the various controllers. Also, instances where additional controllers may have to be added in the communication network are promptly identified such that 20 there is no loss of QoS. Activation of the additional controller only at such instances ensures optimization of the operational cost of the communication network. [0027] The control plane optimization operation is carried out by each of the controllers in the communication network. The decision to add or delete network controllers to the communication network is not taken by a centralized control entity 25 but is rather distributed across the various controllers of the communication network. Thus, the performance of the communication network is unaffected by any delay or failure in functioning of the centralized control entity. Further, the systems and methods for control plane optimization as described in accordance with various 9 embodiments of the present subject matter are backward compatible and may also be implemented in legacy communication networks. Furthermore, the systems and methods for control plane optimization described herein are independent of the topology of the communication network. Additionally, the systems and methods for 5 control plane optimization provide a scalable solution for network control plane optimization that may be implemented in any communication network irrespective of the size of the communication network or the amount of load that the communication network handles. [0028] The following disclosure describes systems and methods for control 10 plane optimization in a communication network. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope. Furthermore, all 15 examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and 20 embodiments of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof. [0029] While aspects of the described system and method can be implemented in any number of different computing systems, environments, and/or configurations, embodiments for the information extraction system are described in 25 the context of the following system(s) and method(s). [0030] Figure 1 illustrates a network environment implementing a system 100 for control plane optimization in communication network 102, such as a software defined network (SDN), according to an implementation of the present 10 subject matter. In one implementation, the communication network 102 can be a public network, including multiple computing devices 104-1, 104-2......104-N, individually and commonly referred to as computing device(s) 104 hereinafter. The computing devices 104, such as personal computers, laptops, various servers, such as 5 blade servers, and other computing devices connected to the communication network 102 to communicate with each other. In another implementation, the communication network 102 can be a private network with a limited number of computing devices 104, such as personal computers, servers, laptops, and/or communication devices, such as PDAs, tablets, mobile phones and smart phones connected to the 10 communication network 102 to communicate with each other. [0031] The network environment allows the computing devices 104 to transmit and receive data to and from each other. The computing devices 104 may belong to an end user, such as an individual, a service provider, an organization or an enterprise. The network environment may be understood as a public or a private 15 network system, implementing the system 100 for control plane optimization of the communication network 102 over which the computing devices 104 may communicate with each other. [0032] The communication network 102 may be a wireless network, wired network, or a combination thereof. The communication network 102 can be a 20 combination of individual networks, interconnected with each other and functioning as a single large network, for example, the Internet or an intranet. The communication network 102 may be any public or private network, including a local area network (LAN), a wide area network (WAN), the Internet, an intranet, a peer to peer network, and a virtual private network (VPN). According to an implementation 25 of the present subject matter, the communication network 102 may be a software defined network. Further, embodiments of the present subject matter, the concepts of SDN may be extended to non-SDN networks also. 11 [0033] In an implementation, the communication network 102 may include a plurality of network devices 106-1, 106-2, 106-3, …, 106-N, individually and commonly referred to as network device(s) 106 hereinafter. The network device 106 may be any network hardware device, such as network switch, simple forwarders, 5 routers, gateways, network bridges, and hubs for mediation of data in the communication network 102. Further, a network device 106 may be hybrid network device, such as multilayer switches, proxy servers, or firewalls. The network device 106 may be utilized for communication process through the communication network 102. The network devices 106 may communicate with other network devices 106 of 10 the communication network 102 based on communication links 108. [0034] The communication network 102 may further include a plurality of network controllers 110-1, 110-2, …, 110-N, individually and commonly referred to as controller(s) 110 hereinafter. The controller(s) 110 may be employed on a control plane of a communication network 102 and may manage the flow control of the 15 communication network 102. The controller(s) 110 may receive data from the network devices 106 employed on a data plane of the communication network 102. Further, the controller(s) 110 may obtain a forwarding path for the requests coming from networking devices 106 and configures the networking devices 106 such that networking devices 106 may forward data to other network devices 106 or to a 20 computing device 104-1, 104-2......104-N. The controller(s) 110 may be a virtual controller or a physical controller. [0035] In one embodiment of the present subject matter, the system 100 determines an optimum number of controller(s) 110 for the communication network 102 based on the load on the communication network 102. In one embodiment, the 25 system 100 performs a non-zero sum game based network control plane optimization operation, interchangeably referred to as control plane optimization operation, to determine the optimum number of controller(s) 110 for the communication network 12 102. The control plane optimization operation has been explained in details later in this specification. [0036] In accordance with one implementation of the present subject matter, the system 100 includes a central optimization controller (COC) 112 in the 5 communication network 102. In another embodiment of the present subject matter, the COC 112 may be a controller 110 of the communication network 102, assigned to work as COC 112. The COC 112 may optimize the number of controllers 110 in the communication network 102. The COC 112 may be communicatively coupled to the controllers 110 through communication link(s) 108-1, 108-2, …, 108-N. The 10 COC 112 may receive requests from one or more of the ccontrollers 110 for activation or deactivation of additional controllers in the communication network 102. Based on factors, such as a current traffic profile of the controller that sends the request, the network load and quality of service parameters, the COC 112 may allow or refuse the request for activation or deactivation of virtual controllers. 15 [0037] Activation of an additional network controller may include addition of a virtual network controller or invoking an existing dormant physical network controller. Deactivating a network controller may include deleting a virtual controller or putting an active physical controller in a dormant mode. In one example, controllers 110 may run on virtual machines. In such a network configuration, the 20 COC 112 may provide for logical addition and deletion of the controllers 110 in the communication network 102. Logical addition and deletion of controllers 110 may be achieved through the virtual machines running the controllers 110. For instance, each controller 110 runs on a separate virtual machine. The capacity of each virtual machine, such as number of cores or CPUs, memory, disk, may be assigned 25 dynamically. In another example, where the network configuration includes physical network controllers, the physical controllers may be dynamically invoked from a dormant mode or put in a dormant mode. The dormant mode may be a sleep mode or a switch-off mode. The COC 112 may determine to put a physical network controller 13 on either mode based on factors, such as time or traffic profile variation of the communication network 102. [0038] To explain, the functioning of the COC 112 to optimize the number of controllers 110 in the communication network 102, the number of controllers 110 in 5 the communication network 102 may be represented by k, wherein the value of k may vary dynamically. At any instant, the value of k controllers 110 may be within the range of k1 and k2, such that k1