Software defined wide area networking (SD-WAN) requires more than one internet circuit (unless managed as the ISP end) and allows for the customisation of outbound traffic dependant on metrics such as bandwidth, latency, speed etc. It can pro-actively monitor the circuits to determine which circuit is performing the best at the time, and can switch traffic between them based on which is functioning the best at the time. An example might be using a certain circuit for voice traffic due to its dependency on a low latency/packet loss level, and using the other circuit for web browsing, due to the relatively low impact it would have on searching the web. SD-WAN is becoming more and more common and is a great feature not only for performance, but also for redundancy. Due to its generally lower cost and higher level of customisation, companies have been replacing their legacy MPLS circuits with it, although MPLS does still have its use cases.