# A Survey on Efforts to Evolve the Control Plane of Inter-Domain Routing
## 5 Classification of Efforts for Evolving the Control Plane
### The Criteria  
#### 5.1.1 Concepts  
The concept type used in the proposals is one classification criterion for works to evolve the control plane. The concept is the set of principles and designs adopted by a work in the literature to approach the network research problem. Thereby, this survey classifies two concept types: _Traditional_ and _Software-Defined Networking (SDN)_.  
Figure 4: The total number of ASs and stub ASs on the Internet from December of 2015 to April of 2018.  
Figure 3: The Internet scalability issue caused by the application of traffic engineering of stub ASs. **(a)** The exponential growth of routing table size captured by active BGP entries at FIB since 1989. Furthermore; **(b)** is the unique number of ASs on the Internet from 1997 until 2018. The data were extracted from [[http://www.cidr-report.org/as2.0/](http://www.cidr-report.org/as2.0/)]([http://www.cidr-report.org/as2.0/](http://www.cidr-report.org/as2.0/)).  
* Traditional: The traditional networks are characterized as all the network logic embedded into network appliances. They have a distributed nature, and to solve a specific networking problem they, need to act individually on the affected appliances and apply manual changes in their configuration.  
Traditional network protocols have been developed and deployed by combining software and hardware into network devices (e.g., TCP/IP). In other words, closed and proprietary network systems have been produced with long development cycles (usually years) and bring new network functionalities that frequently require the acquisition of new hardware with such features. Besides, proprietary boxes often alter the configuration, as well as the compatibility of APIs (Application Programming Interfaces) across vendors (and even across different products from the same vendors [43]). Therefore, legacy and discontinued products make the integration with new network devices a hard to often impossible task [44].  
* SDN: Software-Defined Networking (SDN) is emerging as a new network paradigm [45; 46; 47; 48]. SDN proposes a separation of software-hardware from devices (vertical integration). Thereby, SDN has the potential to enable new technologies, network programmability and the flexibility of functionalities on network devices.  
A major feature of SDN is the decoupled control and data plane. This allows a centralization logic of the control to be fully aware of the network state, enforce network policies, routing decisions, forwarding information, and so forth. Many technologies apply the concepts of SDN. The most notable one is the OpenFlow protocol [49]. OpenFlow is an instantiation of the concepts of SDN [43], which is becoming a standard de facto instance of SDN in the academic and industry field [50].  
Touching upon OpenFlow, it provides a programmable interface between the OpenFlow controller (the network logic) and OpenFlow Switches (forwards packets based on controller logic). Besides, OpenFlow rules follow the concept of flow, which is a sequence of packets sent from a particular source to a particular destination following a given path [39]. The OpenFlow rules are capable of identifying and matching TCP/IP header fields, which can provide fine-grained rules for the definition of traffic flows inside OpenFlow networks.