A Study of Internet Round-Trip Delay

We present the results of a study of Internet round-trip delay. The links chosen include links to frequently accessed commercial hosts as well as well-known academic and foreign hosts. Each link was studied for a 48-hour period. We attempt to answer the following questions: (1) how rapidly and in what manner does the delay change -- in this study, we focus on medium-grain (seconds/minutes) and coarse-grain time-scales (tens of minutes/hours); (2) what does the frequency distribution of delay look like and how rapidly does it change; (3) what is a good metric to characterize the delay for the purpose of adaptation. Our conclusions are: (a) there is large temporal and spatial variation in round-trip time (RTT); (b) RTT distribution is usually unimodal and asymmetric and has a long tail on the right hand side; (c) RTT observations in most time periods are tightly clustered around the mode; (d) the mode is a good characteristic value for RTT distributions; (e) RTT distributions change slowly; (f) persistent changes in RTT occur slowly, sharp changes are undone very shortly; (g) jitter in RTT observations is small and (h) inherent RTT occurs frequently. (Also cross-referenced as UMIACS-TR-96-97