SD-WAN is an acronym for software-defined networking in a wide area network (WAN). SD-WAN simplifies the management and operation of a WAN by decoupling the networking hardware from its control mechanism. This concept is similar to how software-defined networking implements virtualization technology to improve data center management and operation.
A key application is to allow companies to build higher-performance WANs using lower-cost and commercially available Internet access, enabling businesses to partially or wholly replace more expensive private WAN connection technologies such as MPLS.
WANs allow companies to extend their computer networks over large distances, connecting remote branch offices to data centers and to each other, and delivering applications and services required to perform business functions. Due to the physical constraints imposed by the propagation time over large distances, and the need to integrate multiple service providers to cover global geographies (often crossing nation boundaries), WANs face important operational challenges, including network congestion, packet delay variation, packet loss,and even service outages. Modern applications such as VoIP calling, videoconferencing, streaming media, and virtualized applications and desktops require low latency. Bandwidth requirements are also increasing, especially for applications featuring high-definition video.It can be expensive and difficult to expand WAN capability, with corresponding difficulties related to network management and troubleshooting.
SD-WAN products are designed to address these network problems. By enhancing or even replacing traditional branch routers with virtualization appliances that can control application-level policies and offer a network overlay, less expensive consumer-grade Internet links can act more like a dedicated circuit. This simplifies the setup process for branch personnel. MEF Forum has defined an SD-WAN architecture consisting of an SD-WAN Edge, SD-WAN Controller and SD-WAN Orchestrator. The SD-WAN Edge is a physical or virtual network function that is placed at an organization’s branch/regional/central office site, data center, and in public or private clouds cloud platforms. MEF Forum has published the first SD-WAN service standard, MEF 70 which defines the fundamental characteristics of an SD-WAN service plus service requirements and attributes.
The SD-WAN Orchestrator, which typically also includes the SD-WAN Controller functionality, is used to set centralized policies which are used to make forwarding decisions for application Flows. Application flows are IP packets that have been classified to determine their user application or grouping of applications to which they are associated. The grouping of application flows based on a common type, e.g., conferencing applications, is referred to as an Application Flow Group in MEF 70. Per MEF 70, the SD-WAN Edge classifies incoming IP packets at the SD-WAN UNI, determines, via OSI Layer 2 through Layer 7 classification, which application flow the IP packets belong to, and then applies the policies to block the application flow or allow the application flows to be forwarded based on the availability of a route to the destination SD-WAN UNI on a remote SD-WAN Edge. This helps ensure that application performance meets service level agreements (SLAs).
Research firm Gartner has defined an SD-WAN as having four required characteristics:
- The ability to support multiple connection types, such as MPLS, Last Mile Fiber Optic Network or through high speed cellular networks e.g. 4G LTE and 5G wireless technologies
- The ability to do dynamic path selection, for load sharing and resiliency purposes
- A simple interface that is easy to configure and manage
- The ability to support VPNs, and third-party services such as WAN optimization controllers, firewalls and web gateways
Features of software-defined networking in a wide area network (WAN) include resilience, quality of service (QoS), security, and performance, with flexible deployment options; simplified administration and troubleshooting; and online traffic engineering.