The interconnection of local area networks is increasingly important, but little data are available on the characteristics of the aggregate traffic that LANs will be submitting to the interconnection media. In order to understand the interactions between LANs and the proposed interconnection networks (MANs, WANs, and BISDN networks), it is necessary to study the behavior of this external LAN traffic over many time scales – from milliseconds to hundreds of seconds. We present a high time-resolution hardware monitor for Ethernet LANs that avoids the shortcomings of previous monitoring tools, such as traffic burst clipping and timestamp jitter. Using data recorded by our monitor for several hundred million Ethernet packets, we present an overview of the short-range time correlations in external LAN traffic. Our analysis shows that LAN traffic is extremely bursty across time domains spanning six orders of magnitude. We compare this behavior with simple formal traffic models and employ the data in a trace-driven simulation of the LAN-BISDN interface proposed for the SMDS SM service. Our results suggest that the pronounced short-term traffic correlations, together with the extensive time regime of traffic burstiness, strongly influence the patterns of loss and delay induced by LAN interconnection. 1.

This paper examines the phenomenon of congestion in order to better understand the congestion management techniques that will be needed in high-speed, cell-based networks. The first step of this study is to use high time-resolution local area network (LAN) traffic data to explore the nature of LAN traffic variability. Then, we use the data for a trace-driven simulation of a connectionless service that provides LAN interconnection. The simulation allows us to characterize what congestion might look like in a high-speed, cell-based network. The most

Dynamics of Internet load are investigated using statistics of round-trip delays, packet losses and out-of-order sequence of acknowledgments. Several segments of the Internet are studied. They include a regional network (the Jon yon Neumann Center Network), a segment of the NSFNet backbone and a cross-country network consisting of regional and backbone segments.

The performance of a system is determined by its characteristics as well as by the composition of the load being processed. Hence, its quantitative description is a fundamental part of all performance evaluation studies. Several methodologies for the construction of workload models, which are functions of the objective of the study, of the architecture of the system to be analyzed, and of the techniques adopted, are presented. A survey of a few applications of these methodologies to various types of systems (i.e., batch, interactive, database, network-based, parallel, supercomputer) is given.

We propose to characterize the burstiness of packet arrival processes with indices of dispersion for intervals and for counts. These indices, which are functions of the variance of intervals and counts, are relatively straightforward to estimate and convey much more information than simpler indices, such as the coefficient of variation, that are often used to describe burstiness quantitatively.

Binary exponential backoff is a randomized protocol for regulating transmissions on a multiple access broadcast channel. Ethernet, a local area network, is built upon this protocol. The fundamental theoretical issue is stability: does the backlog of packets awaiting transmission remain bounded in time, provided the rates of new packet arrivals are small enough? It is assumed n 2 stations share the channel, each having an infinite buffer where packets accumulate while the station attempts to transmit the first from the buffer. Here, it is established that binary exponential backoff is stable if the sum of the arrival rates is sufficiently small. Detailed results are obtained on which rates lead to stability when n = 2 stations share the channel. In passing several other results are derived bearing on the efficiency of the conflict resolution process. Simulation results are reported that, in particular, indicate alternative retransmission protocols can significantly improve performanc...

During a bulk data transfer over a high speed network, there is a high probability that the next packet received from the network by the destination host is the next packet in the transfer. An optimistic implementation of a bulk data transfer protocol takes advantage of this observation by instructing the network interface on the destination host to deposit the data of the next packet immediately into its anticipated final location. No copying of the data is required in the common case, and overhead is greatly reduced. Our optimistic implementation of the V kernel bulk data transfer protocols on SUN-3/50 workstations connected by a 10 megabit Ethernet achieves peak process-to-process data rates of 8.3 megabits per second for l-megabyte transfers, and 6.8 megabits per second for 8-kilobyte transfers, compared to 6.1 and 5.0 megabits per second for the pessimistic implementation. When the reception of a bulk data transfer is interrupted by the arrival of unexpected packets at the destination, the worst-case performance of the optimistic implementation is only 15 percent less than that of the pessimistic implementation. Measurements and simulation indicate that for a wide range of load conditions the optimistic implementation outperforms the pessimistic implementation.

v Abstract Caching has long been recognized as a powerful performance enhancement technique in many areas of computer design. Most modern computer systems include a hardware cache between the processor and main memory, and many operating systems include a software cache between the file system routines and the disk hardware. In a distributed file system, where the file systems of several client machines are separated from the server backing store by a communications network, it is desirable to have a cache of recently used file blocks at the client, to avoid some of the communications overhead. In this configuration, special care must be taken to maintain consistency between the client caches, as some disk blocks may be in use by more than one client. For this reason, most current distributed file systems do not provide a cache at the client machine. Those systems that do place restrictions on the types of file blocks that may be shared, or require extra communication to confirm that...

Recently, Ethernet celebrated its twentieth anniversary. Over those years, the processing speed of the attached hosts has increased by several orders of magnitude, to the point where the relative bandwidth of a 10 Mbps Ethernet has fallen from more than adequate to support large enterprise networks (whose utilizations were typically only a few percent, anyway), to marginally fast enough to support a single high performance desktop workstation. At the same time, the Ethernet standard has also evolved to incorporate new technology at the physical layer, including new media, new signalling methods, and support for higher data rates. However, the MAC layer protocols have remained essentially unchanged from the early days of undemanding applications running on large numbers of slow hosts. In this paper, we argue that it is time to review the MAC layer and incorporate advances made in the protocol performance field over the last twenty years. First, we describe several little-known facts abo...

In this paper, a simulation model for incorporation within a performance-oriented parallel software development environment is presented. This development environment is composed of a graphical design tool, a simulation facility, and a visualisation tool. Simulation allows parallel program performance to be predicted and design alternatives to be compared. The target parallel system models a virtual machine composed of a cluster of workstations interconnected by a local area network. The simulation model architecture is modular and extensible which allows re-configuration of the platform. The model description and the validation experiments which have been conducted to assess the correctness and the accuracy of the model are also presented. 1 Introduction The key obstacle to the widespread adoption of parallel computing is the difficulty in program development. Firstly, an application has to be decomposed into parallel objects (processes, or tasks) according to the computational model ...