Link Load Balancing
Link Load Balancing or WAN Link Balancing provides not only a balanced load, but also a high availability of a WAN connection. Different Vendors are using different methodologies, but all serve a common goal. Load balance the WAN Link and make sure the business continues (Business Continuity). During some of my projects, there was a requirement to prioritize Business Critical Traffic from Internet Traffic. With a Traffic Shaper not a big deal. Just define policies for different traffic types. However, when it comes to the requirement to send Business Critical Traffic to ISP-1 & ISP-2, and Internet Traffic only to ISP-3 with a redundancy to ISP-2 than it gets complex. Policy based Routing may help, but not if you have to prioritize within different business critical applications.
Link Load Balancer are deployed inline between Edge Routes and Firewalls. To monitor the quality and status of WAN connections, they perform different kind of health and performance checks to proof reliability of attached ISPs. By knowing all this information, the Link Load Balancer could intercept inbound and outbound traffic and switch users or applications to preferred ISP connections.