Over at the Boundary Blog, Steven Strowes writes that understanding network delay is key to understanding some important aspects of your network performance.
This post describes how Boundary uses a well-known TCP mechanism to calculate round-trip times (RTTs) between any two hosts by passively monitoring TCP traffic flows, i.e., without actively launching ICMP echo requests (pings). The post is primarily an overview of this one aspect of TCP monitoring, it also outlines the mechanism we are using, and demonstrates its correctness.
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