Recent measurements of local-area and wide-area traf®c [8, 28, 42] have shown that network traf®c exhibits variability at a wide range of scales. What is striking is the ubiquitousness of the phenomenon, which has been observed in diverse networking contexts, from Ethernet to ATM, LAN and WAN, compressed video, and HTTPbased WWW traf®c [8, 15, 23, 42]. Such scale-invariant variability is in strong contrast to traditional models of network traf®c, which show burstiness at short time scales but ar