# Future Internet Architectures on an Emerging Scale--A Systematic Review
## 3 Evolutionary and Clean Slate Approaches
### Evolutionary Approach
#### 3.1.1 Software-Defined Networking  
SDN offers solutions to the future internet architecture by incorporating network intelligence as a component of the network and separating the data plane (the part of the network that carries the user traffic [20]) from the control plane (the part of the network that controls the forwarding of data packets [21]). The controllers, which emerge from the routing process in the control plane, act as the \"brain\", and contain complete intelligence. However, the centralization of network intelligence in SDN can lead to poor scalability and security, making it a central issue [22]. To promote SDN, the Open Networking Foundation (ONF) was established in 2011 to support the standardization of the OpenFlow protocol and its technologies. The goal of the ONF is to scale this innovation through simple software changes in data centers, which can bring potential benefits such as an enhanced configuration, improved performance, and improved architecture [23]. In 2020, ONF announced Aether, which is the first open-source platform that supports 5G, LTE, and edge as cloud services. Aether's open-source architecture runs on a Kubernetes orchestrated environment and is built on CORD (Central Office Re-directed as a Data Center) and ONOS (Open Network Operating System) platforms, allowing for an easy assembly and deployment with remarkable speed [24]. Figure 1: Architecture of evolutionary approach. CORD  
Small or large central offices (COs) often use service gateways to provide services to their customers, such as residential, mobile, or enterprise users. However, these service edges face challenges such as high capital expenditures and operational costs, as there are hundreds of heterogeneous, closed proprietary systems that accumulate over decades in the telecommunications (Telco) edge. These systems are often not programmable, which limits innovation and the creation of new platforms and services. Therefore, the main objective is to reduce these costs (capital and operational) to enable Telcos to offer new services. In essence, CORD [25] aims to bring the economies of a data center, which relies on commodity servers, open-source software, and cloud intelligence, to the edge of a Telco network. This approach, known as access as a service, allows for the disaggregation of legacy virtual machines (VMs) into smaller elements, enabling greater innovation. As an open-source project, it is important to understand the entire ecosystem surrounding CORD. CORD utilizes SDN to interconnect physical and virtual elements, adding value not just to VMs, but also to switches. By doing so, CORD enables the provision of innovative services. The primary objective of the CORD project was to create a customizable and extensible platform that could support multiple access technologies and services, while adhering to the best practices for building and operating scalable multi-tenant cloud services, including support for multitenancy. From an architectural perspective, the reference platform, as shown in Figure 2, is critical. The developers sought to design a minimal kernel that could support thousands of CO edges. In 2017, the third release of CORD was announced, which enabled the cloud community to run a variety of projects independently. It can be seen that the CORD platform is no longer in use [26], but its legacy lives on in the form of several ONF broad-band projects, such as SEBA (SDN Enabled Broadband Access), VOLTHA (Virtual Optical Line Terminal Hardware  
Figure 2: Elements of CORD project. connected edge cloud, etc. These projects are built upon the foundation that was laid by CORD to provide innovative solutions to the challenges that are faced by Telco networks. SEBA, for instance, provides a cloud-native, open-source platform for software-defined access networks that enables service providers to offer next-generation services. VOLTHA is an open-source software platform that provides hardware abstraction for optical line terminals (OLTs) and is designed to work with multiple hardware vendors.