# A Comprehensive Survey on Knowledge-Defined Networking
## 3 Knowledge Plane
### Knowledge Distribution and Management Plane  
Knowledge management in the context of knowledge-defined networking refers to the process of capturing, storing, sharing, and utilizing knowledge and rules within a networked environment. Knowledge management aims to improve the performance of the networked environment by ensuring that the required knowledge and rules are provided to the necessary parties. It involves knowledge and rule sharing, which involves establishing processes and systems for capturing and disseminating knowledge and rules across the network. This plane basically consists of a Knowledge Base (KB) that necessarily consists of generated knowledge by knowledge generation models, composed knowledge by ontology editors, generated rules by rule generators, collected data from the network, and control messages, as evident from Figure 3. Data models such as Yet Another Next Generation(YANG) or Common Information Model (CIM) can be used to store and disseminate network data, which are discussed in detail in Section 4.5.3. Raw data are received to this plane from the control and management planes, while the received data can be stored in the knowledge base and provided to the knowledge generation plane when required. Knowledge and rules can be shared from this knowledge base to the application plane, the control plane, the management plane, and the knowledge composition sub-plane (generated knowledge). Thus, it is required to have standards for knowledge and rules storing, sharing, and utilization in order for multiple KDN systems to be interoperable. As the network has limited networking capabilities and resources, there should be transmission rules for transmission of knowledge related traffic (generated knowledge, composed knowledge, or rules generated from composed knowledge). One of the purposes of the knowledge distribution plane is to derive transmission rules for knowledge-related traffic to be exchanged within the knowledge plane and between the knowledge plane and the application, management, and control planes. For instance, rules generated by the knowledge composition plane are relatively smaller in size compared to descriptive knowledge produced from the knowledge generation plane. Therefore, transmission of generated rules from knowledge requires higher reliability, high priority, and high latency, whereas relatively larger-volume descriptive knowledge transmission may need low reliability and low priority, and may tolerate some higher latency. In other words, the data flows for each rule and descriptive knowledge have their own QoS parameters. QoS is the ability of a network to provide the required services for selected network traffic. The descriptive knowledge may be optionally distributed to end devices at the discretion of the controller. For example, in a vehicular network, if knowledge is generated related to the status of vehicular traffic congestion, that knowledge is required to be sent to all the nodes in the network controlled by the controller. 5.1 Review on Existing Work on Flow Scheduling and Prioritization to Apply Knowledge and Rule Dissemination  
The OpenFlow protocol has different tactics to control QoS parameters in data flows. It has an enqueuing feature to maintain different queues for different flows, matching and tagging of Virtual Local Area Network (VLAN) and Multi Protocol Label Switching (MPLS) labels with traffic classes, rate limiting functionality by means of meter tables, and a flow monitoring framework [226]. However, OpenFlow does not provide support for queue configuration, as it is currently handled by OF-CONFIG, which has been standardized by the Open Network Foundation (ONF). There are a few open-source SDN controller projects with QoS support, such as OpenDaylight, Open Network Operating System (ONOS), Floodlight (FL), etc. In order to disseminate descriptive knowledge and generated rules having different QoS parameters, QoS-motivated routing with per-flow routing can be employed [79].