A passive method to estimate TCP round trip time from nonsender-side

TCP round trip time is an important subject of network measurement research. And it is widely utilized in congestion control and network tomography. Compared with active methods to measure round trip time, passive ones are superior for low cost and not injecting traffic into networks. However, all present passive measurement methods have deficiencies. Some of them are not accurate enough, some others are only applied in just one phase of TCP connection, so none of them can well satisfy the demand of network management. This paper presents a passive method named cross to estimate TCP round trip time from nonsender-side. With cross correlation function, it precisely finds the correspondence between the sequence of ACK packets and that of data packets, and then gets round trip time of TCP connection. The experiment upon PlanetLab shows that this method is able to precisely estimate TCP round trip time in any phase of TCP connection no matter the network is idle or congested.