There exist many tools to passively monitor a link for traffic flows. They are typically used near the edge of the network, but not necessarily at the termination point of data flows - usually within a few hops of end-points. Round trip time (RTT) values for individual flows is of interest for network management purposes and can be used to indicate user experienced network delay, and in network design decisions. Determining the RTT when not at an end-point of a data flow is complicated by the fact that packets may be seen out of order and that witnessed packets may not reach their destination. In this paper we present an algorithm to estimate running RTT and jitter characteristics of TCP streams monitored at the midpoint of a TCP flow.