IDG Contributor Network: Why WAN metrics are not enough in SD-WAN policy enforcement
On the topic of measuring WAN metrics, most engineers think to look at the standard statistics of loss, latency, jitter, and reachability for determining path quality. This is good information for a routing protocol that is making decisions for packet flow at layer 3 of the OSI model. However, it is incomplete information when looking at it from the perspective of the overall user experience. In order for an SD-WAN solution to provide materially better value than a typical packet router, it must look beyond the metrics considered by the router.
SD-WAN devices shouldn’t be considered routers in the conventional sense. Routers use local tables and algorithms such as Dijkstra to determine the shortest path to a destination for a packet. The term packet is important here. It is all that the router cares about. If you look up the definition of a router, it is a device that functions at layer 3 to deliver packets to their destination network. When there is a problem the router will process the topology change and compute new routing table entries that are a point in time decision of the available paths. These topology changes take time to process. This can cause packet loss, latency, and jitter for anything traversing that segment. Hence why we use those measurements to determine the health of our legacy networks.