SD-WAN

Do we look at the egress interface from the point of view of that session's forward flow, and measure both forward and reverse flows on that ""egress"" interface?  Or do we measure each flow's bandwidth on its respective egress interface, relative to its direction?

Based on my own observations and testing, I believe that we measure the total bandwidth of a session by adding bandwidth consumption by its two bi-directional flows, as seen at the session's (forward flow's) egress interface. But I would like to make sure that my conclusion is correct. Thanks!

Good question. Actually, the interface is not factored into the calculation of session bandwidth. While most all sessions have only two flows, based on the type of traffic or service-policy configuration, certain flows can actually have one or many flows. It is for this reason that the session bandwidth is calculated by enumerating all of the flows within a session, totaling the number of bytes transmitted for flows destined to the service (forward direction) and the number of bytes received for flows from that service (reverse direction). That being said, your observation is correct. For the typical session, the following diagram helps illustrate the point.