The software-defined wide area network (SD-WAN) is an application of software-defined networking (SDN) technology for WAN connections, which are used to connect enterprise networks such as branch offices and data centres over large geographic distances. Traditionally, WAN connections require special proprietary hardware. SD-WAN solutions, on the other hand, adopt a software-based approa­ch to migrate a large part of the network control to cloud.

Branch networks are currently facing several challenges. For one, increasing the bandwidth availability in existing and new branch offices is expensive and time consuming. Further, the presence of numerous single-function devices in the network makes it difficult to deploy new solutions while monitoring and troubleshooting the existing ones. Besides, the transmission of branch WAN traffic through data centres degrades the performance of cloud applications. The provisioning of new applications for branch use requires reconfiguration and is IT intensive.

In this context, SD-WAN offers several advantages for distributed organisations with critical branch operations. These include the benefits of business agility, im­proved application performance and low cost of bandwidth. While SD-WAN products and services vary by vendor, most enterprises deploy hybrid WAN by dyna­mi­cally routing traffic over both private and public links, such as leased multi protocol label switching (MPLS).

Advantages of SD-WAN

SD-WAN technology undertakes real-time WAN link performance monitoring and data packet inspection to autono­mo­us­ly manage network traffic distribution across multiple heterogeneous WAN links. Further, SD-WAN solutions shift traffic monitoring and management from physical devices to applications by leveraging SDN’s flexibility and agility. This helps create a secured pool of private and public connections, brings in automation, agility and centralised network control, and provides real-time traffic management over multiple links. In addition, the technology helps the network administrator to remotely program appliances through a central controller, thereby reducing the provisioning time and minimising or eliminating the need to manually configure traditional routers at branch locations.

SD-WAN solutions also improve application performance by protecting applications against network failures and dynamically changing paths when their performance degrades. Another benefit is that the SD-WAN infrastructure separates the control plane and the data plane, which means that network changes can be controlled and updated through software. By decoupling the control and data planes, the control elements can be shifted to a software framework and centralised. SD-WANs enable a configuration that is pushed out to all the devices simultaneously.

SD-WAN solutions have inbuilt encryption and firewall features and make security management more centralised. They help businesses manage traffic flows over their networks.

Issues and concerns

The potential disadvantages of SD-WAN stem largely from the fact that the technology is at a nascent stage (only a few years old) as compared to traditional networking concepts and hence is not mature enough to fit all applications. Many SD-WAN solutions are not yet able to support WAN optimisation, which means that while enterprises do get some provisioning and automation capabilities, their network speed has not improved.

Further, while evaluating the decision to adopt SD-WAN technologies, the principal concern of enterprises is return on investment. The capex and opex of an SD-WAN solution needs to be compared with the overall cost of the WAN. Another consideration is that of vendor lock-in. There are several SD-WAN products, and they are all different and incompatible. While some get incorporated into the existing WAN, others replace the WAN hardware completely. The evaluation process should consider the long-term commitment to the vendor.

Future prospects

The key objective of SD-WAN technology is to deliver a secure and simple cloud-enabled WAN connection with as much open and software-based solutions as possible. The technology can be used to deliver basic WAN connectivity, or premium business services such as virtual private networks, WAN optimisation and applications delivery control. The adoption of SD-WAN is expected to increase significantly in the coming years as organisations seek to optimise network costs and improve application performance. According to research firm Gartner, spending on SD-WAN products will rise from $129 million in 2016 to $1.24 billion in 2020.

SD-WAN is rapidly moving beyond its initial functionality of delivering hybrid WAN architecture or services. Going forward, the technology is expected to be characterised by improved centralised management, orchestration and administration; more granular analytics and high application visibility; and better built-in security as well as the ability to work with third-party network security solutions.

Further, while the public cloud traffic has been the key demand driver for SD-WAN so far, SD-WAN suppliers are now expanding their capabilities to ensure high-speed, low-latency connectivity bet­ween multiple cloud providers and enterprise networks. To this end, many SD-WAN vendors have started partnering with cloud companies. For instance, Citrix has partnered with Equinix and Viptela with Microsoft Azure.