ABSTRACT: We measured and analyzed the variability in round trip times (RTTs) within TCP connections using passive measurement techniques. We collected eight hours of bidirectional traces containing over 22 million TCP connections between end-points at a large university campus and almost million remote locations. Of these, we used over 1 million TCP connections that yield 10 or more valid RTT samples, to examine RTT variability within a TCP connection. Our results indicate that contrary to observations in several previous studies, RTT values within a connection vary widely. Our results have implications for designing better simulation models, and understanding how round trip times affect the dynamic behavior and throughput of TCP connections.