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Typical branch offices can have multiple WAN connection types, including MPLS, Internet (such as LTE and ADSL), and so on. In these traditional networks, the MPLS-based connection typically includes performance guarantees known as service level agreements (SLAs) to ensure business-critical applications can function properly. The Internet connection often provides an alternative link for backup and load balancing purposes. However, with Internet access offerings providing ever-increasing bandwidth, many applications can now reasonably be routed over the Internet link.

Software-defined wide area networking (SD-WAN) is primarily thought of as a connectivity solution, implemented as an overlay on top of traditional WAN access. An SD-WAN solution provides the ability to make use of the links in whichever way an enterprise customer wishes, as shown in Figure 1.

In an SD-WAN environment, low-priority traffic can use the lower-cost Internet link(s), while more important traffic can travel across better quality links (such as those provided by an MPLS network). Link usage can also be assigned per application. With an SD-WAN solution, an enterprise customer can mix and match cost optimization with SLA requirements as they see fit.