Wide-Area Traffic: The Failure of Poisson Modelling

Network arrivals are often modeled as Poisson processes for ana-lytic simplicity, even though a number of traffic studies have shown that packet interarrivals are not exponentially distributed. We eval-uate 24 wide-area traces, investigating a number of wide-area TCP arrival processes (session and connection arrivals, FTP data con-nection arrivals within FTP sessions, and TELNET packet arrivals) to determine the error introduced by modeling them using Poisson processes. We find that user-initiated TCP session arrivals, such as remote-login and file-transfer, are well-modeled as Poisson pro-cesses with fixed hourly rates, but that other connection arrivals deviate considerably from Poisson; that modeling TELNET packet interarrivals as exponential grievously underestimates the bursti-ness of TELNET traffic, but using the empirical Tcplib [Danzig et al, 1992] interarrivals preserves burstiness over many time scales; and that FTP data connection arrivals within FTP sessions come bunched into “connection bursts, ” the largest of which are so large that they completely dominate FTP data traffic. Finally, we of-fer some results regarding how our findings relate to the possible self-similarity of wide-area traffic.