Abstract
The connection of billions of devices to the internet poses numerous challenges to the networking infrastructure. The traditional networking paradigm is anticipated to be unable to cope with a scenario of myriad heterogenous devices connected through both wireless and wired links. The mobility and instability of a significant portion of the devices of the IoT demand a flexible and agile response of the network to adapt and keep the appropriate policies in effect. Software-defined networking (SDN) moves the intelligence of the network to a central controller with a global vision of the network capable of issuing timely instructions to the network nodes to accommodate the constant changes. This chapter presents the SDN paradigm, covering its architecture, functional blocks, interfaces, and protocols. The focus is put on the application of SDN to IoT environments supporting different applications, each with its specific difficulties, exploring current trends to tackle the identified challenges.
TopBackground
In the previous decades, Internet connectivity has rocketed from being available to a few government and research institutions, to companies, to homes, and finally to virtually everybody in the planet. The ultimate democratization of Internet access among residential users has been made possible by the advent of several successive access network technologies. First, CATV providers included Internet access in their catalog service with DOCSIS. Along the way, telcos found the way to claim their market share using the ubiquitous telephone line with ADSL and related technologies (xDSL). In these days, providers are pushing the rollout of their FTTH access networks struggling to outperform competitors in getting their optic fibers to the homes. In the meanwhile, digital cellular telephony has evolved through several generations (GSM, CDMA, UMTS, LTE) with ever-increasing bandwidth in the radio interface. Currently, most mobile telcos have deployed their 4G (Advanced LTE) radio access network, providing speed enough to watch multimedia contents on-line on smartphones and other portable devices. In addition, public and private wireless networks are being implemented in companies, hospitals, airports, stores, restaurants, public spots, etc. As a consequence, user traffic keeps soaring as these continuous upgrades of both fixed and wireless access networks are introduced, and this forces network owners to increase their core network capacity accordingly.
The next step in deepening the Internet access ubiquity is the 5th generation (5G) of mobile communications. Many telcos and network equipment providers have been deploying pilot projects for testing and demonstration in the last years (e.g., in the Winter Olympic Games in South Korea in February 2018). A few telcos around the world are already offering commercial service as of the last quarter of 2019. 5G improvements over the previous generation include not only the required increase of bandwidth, which determines the hop to a new generation. Very important aspects are the reduction of latency, essential to real-time conversational applications, and the increment of the number of connected devices, with an impressive 106 per square kilometer. The driver for this capability is obviously not the need to connect one million people in such a reduced area. The aim is to be able to connect one million things to the Internet with wireless links, opening the door to another conception: the Internet of Things (IoT) (Ejaz, Imran, Jo, Muhammad, Qaisar & Wang 2016). Cisco Systems defines the Internet of Everything to be an expanded IoT connecting virtual entities as well as “physical” things (Evans, 2012). Devices can be connected to the IoT by fixed line access, but it is the availability of a wireless access that will lead to the birth of a new generation of the Internet. The 5G radio access network will play a central role by facilitating the connection and mobility of a massive number of devices.
Key Terms in this Chapter
Application Plane: Part of the SDN architecture consisting of applications implementing services provided to users/devices through the network. Applications interact with the SDN controller through APIs (the northbound interface) to get an abstract global vision of the network they are using and to communicate the network behavior they need at the moment.
Control Plane: Part of the networking function that determines the treatment given to each traffic flow, and lastly to each packet, including switching, routing, quality of service, security, and fault tolerance aspects. It is placed in each network element in the traditional networking paradigm, whereas it is centralized in SDN, allowing for network programmability.
Network Edge: Part of the network consisting of access nodes and the wired lines or wireless links to connect user devices. These access nodes are network elements specialized in handling numerous user links, aggregating their traffic flows, and sending them to the core network through high-speed communication lines.
Core Network: Part of the network consisting of network elements connected by high-speeds communication lines (optic fibers and/or point-to-point radio links), typically covering a wide geographical region. It does not include the network infrastructure to connect user devices.
SDN Controller: Central part of the SDN control plane. Through the southbound interfaces, it interacts with SDN network elements through APIs to get notifications about new traffic flows and network changes, and to install forwarding rules in the switches. Through the northbound interfaces, it receives the network behavior needed by applications, translating it to instructions to network elements.
Flow Table: List of rules in an SDN network element matching specific traffic flows. For a given flow, actions are specified as to how to treat a packet belonging to that flow. An SDN network element can organize packet processing as a sequence or pipeline of flow tables through which a packet flows from the ingress interface to the egress interface.
SDN Network Element: A piece of networking equipment consisting of several input/output interfaces and the data plane functions. An SDN Network Element, or SDN switch, also provides APIs to interact with the SDN controller (the southbound interface) to receive instructions to install flow table entries to handle new traffic flows.
Data Plane: Part of the networking function that handles packets in network elements, including the buffering of the packet, the decision on dropping or forwarding it, the output interface, the queuing policy, and the modification of its headers/contents. The way each of these functions process packets is decided by the control plane. Network elements typically perform these functions at line rate (the speed at which packets enter the element through the input interfaces) in specialized hardware.
Orchestrator: An SDN controller that has a view of the entire network and coordinates other local SDN controllers covering portions of the network to implement global network policies.
Software-Defined Networking (SDN): A networking paradigm in which the control plane is removed from the network elements and placed in a central SDN controller. The controller installs appropriate forwarding rules in the relevant network elements for each new traffic flow, according to the network policies requested by applications.