Network arrivals are often modeled as Poisson processes for analytic simplicity, even though a number of traffic studies have shown that packet interarrivals are not exponentially distributed. We evaluate 24 wide-area traces, investigating a number of wide-area TCP arrival processes (session and connection arrivals, FTP data connection 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 remotelogin and file-transfer, are well-modeled as Poisson processes with fixed hourly rates, but that other connection arrivals deviate considerably from Poisson; that modeling TELNET packet interarrivals as exponential grievously underestimates the burstiness 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 offer some results regarding how our findings relate to the possible self-similarity of widearea traffic.

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In this paper a new switching technique called virtual cut-through is proposed and its performance is analyzed. This switching system is very similar to message switching, with the difference that when a message arrives in an intermediate node and its selected outgoing channel is free (just after the reception of the header), then, in contrast to message switching, the message is sent out to the adjacent node towards its destination before it is received completely at the node; only if the message is blocked due to a busy output channel is a message buffered in an intermediate node. Therefore, the delay due to unnecessary buffering in front of an idle channel is avoided. We analyze and compare the performance of this new switching technique with that of mes-sage switching with respect to three measures: network delay, traffic gain and buffer storage requirement. Our analysis shows that cut-through switching is superior (and at worst identical) to message switching with respect to the above three performance measures.

Graphs are commonly used to model the topological structure of internetworks, to study problems ranging from routing to resource reservation. A variety of graphs are found in the literature, including fixed topologies such as rings or stars, "well-known" topologies such as the ARPAnet, and randomly generated topologies. While many researchers rely upon graphs for analytic and simulation studies, there has been little analysis of the implications of using a particular model, or how the graph generation method may a ect the results of such studies. Further, the selection of one generation method over another is often arbitrary, since the differences and similarities between methods are not well understood. This paper considers the problem of generating and selecting graph models that reflect the properties of real internetworks. We review generation methods in common use, and also propose several new methods. We consider a set of metrics that characterize the graphs produced by a method, and we quantify similarities and differences amongst several generation methods with respect to these metrics. We also consider the effect of the graph model in the context of a speciffic problem, namely multicast routing.

We analyze 2.5 million TCP connections that occurred during 14 wide-area traffic traces. The traces were gathered at five "stub" networks and two internetwork gateways, providing a diverse look at wide-area traffic. We derive analytic models describing the random variables associated with telnet, nntp, smtp, and ftp connections, and present a methodology for comparing the effectiveness of the analytic models with empirical models such as tcplib [DJ91]. Overall we find that the analytic models provide good descriptions, generally modeling the various distributions as well as empirical models and in some cases better.

A program's working set W(t, T) at time t is the set of distinct pages among the T most recently referenced pages. Relations between the average working-set size, the missing-page rate, and the interreference-interval distribution may be derived both from time-average definitions and from ensemble-average (statistical) definitions. An efficient algorithm for estimating these quantities is given. The relation to LRU (least recently used) paging is characterized. The independent-reference model, in which page references are statistically independent, is used to assess the effects of interpage dependencies on working-set size observations. Under general assumptions, working-set size is shown to be normally distributed. Key Words and Phrases: working-set model, paging, paging algorithms, program behavior, program

Many application-level traffic streams, or conversations, are multiplexed at the points where local-area networks meet the wide-area portion of an internetwork. Multiplexing policies and mechanisms acting at these points should provide good performance to each conversation, allocate network resources fairly among conversations, and make efficient use of network resources. In order to characterize wide-area network traffic, we have analyzed traces from four Internet sites. We identify characteristics common to all conversations of each major type of traffic, and find that these characteristics are stable across time and geographic site. Our results contradict many prevalent beliefs. For example, previous simulation models of wide-area traffic have assumed bulk transfers ranging from 80 Kilobytes to 2 Megabytes of data. In contrast, we find that up to 90% of all bulk transfers involve 10 Kilobytes or less. This and other findings may affect results of previous studies and should be taken into account in future models of wide-area traffic. We derive from our traces a new workload model for driving simulations of wide-area internetworks. It generates traffic for individual conversations of each major type of traffic. The model accurately and efficiently reproduces behavior specific to each traffic type by sampling measured probability distributions through the inverse transform method. Our model is valid for network conditions other than those prevalent during the measurements because it samples only network-independent traffic characteristics. We also describe a new wide-area internetwork simulator that includes both our workload model and realistic models of network components. We then present a simulation study of policies for multiplexing datagrams over virtual circu...

ABSTRACT. Scheduling algorithms for time shared computing facilities are considered in terms of a queueing theory model. The extremely useful limit of "processor sharing " is adopted, wherein the quantum of service shrinks to zero; this approach greatly simplifies the problem. A class of algorithms is studied for which the scheduling discipline may change for a given job as a function of the amount of service received by that job. These multilevel disciplines form a natural extension to many of the disciplines previously considered. The average response time for jobs conditioned on their service requirement is solved for. Explicit solutions are given for the system M/G/1 in which levels may be first come first served (FCFS), feedback (FB), or round-robin (RR) in any order. The service time distribution is restricted to be a polynomial times an exponential for the case of RR. Examples are described for which the average response time is plotted. These examples display the great versatility of the results and demonstrate the flexibility available for the intelligent design of discriminatory treatment among jobs (in favor of short jobs and against long iobs) in time shared computer systems.

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Abstract — Network traffic generators allow video and audio streams to be modelled. ‘Bursty ’ traffic patterns imply packetby-packet rather than time-averaged analysis to determine the impact on network routers. Due to computer operating system time event scheduling dependencies, the ability to generate accurate packet delivery is compromised. A real-time operating system on an x86 commodity machine is shown to result in greater accuracy and range, but with some loss in precision outside its operating range, compared to a general-purpose Linux kernel. I.