Graph models are commonly used in studying solutions to internetworking problems. This paper considers several random graph models that have been used to model internetworks, and considers ways to characterize the properties of these graphs. By matching the characteristics of the random graphs to the characteristics of real internetworks, more accurate modeling can be achieved. College of Computing Georgia Institute of Technology Atlanta, Georgia 30332--0280 1 Introduction Accompanying the rapidly increasing use of large networks and internetworks has been a corresponding growth in research on internetworking. Researchers working in internetwork communication generally adopt one of three methods to evaluate their ideas: ffl They implement their ideas on a real internetwork. This approach has obvious difficulties, including the problem of getting access to an internetwork of reasonable size that can tolerate experimentation. ffl They implement their ideas on a smaller network and e...

Measurements of network tra c have shown that self-similarity is a ubiquitous phenomenon spanning across diverse network environments. In previous work, we have explored the feasibility of exploiting long-range correlation structure in self-similar tra c for congestion control. We have advanced the framework of multiple time scale congestion control and shown its e ectiveness at enhancing performance for rate-based feedback control. In this paper, we extend the multiple time scale control framework to window-based congestion control, in particular, TCP. This is performed by interfacing TCP with a large time scale control module which adjusts the aggressiveness of bandwidth consumption behavior exhibited by TCP as a function of \large time scale " network state, i.e., information that exceeds the horizon of the feedback loop as determined by RTT. How to e ectively utilize such information|due to its probabilistic nature, dispersion over multiple time scales, and a ection on top of existing window-based congestion controls|is a nontrivial problem. Our contribution is threefold. First, we de ne a modular extension of TCP|a function call with a simple interface|that applies to various avours of TCP|e.g., Tahoe, Reno, Vegas|

With the proliferation of workstation clusters connected by high-speed networks, providing efficient system support for concurrent applications engaging in nontrivial interaction has become an important problem. Two principal barriers to harnessing parallelism are: one, efficient mechanisms that achieve transparent dependency maintenance while preserving semantic correctness, and two, scheduling algorithms that match coupled processes to distributed resources while explicitly incorporating their communication costs. This paper describes a set of performance features, their properties, and implementation in a system support environment called DUNES that achieves transparent dependency maintenance—IPC, file access, memory access, process creation/termination, process relationships—under dynamic load balancing. The two principal performance features are push/pull-based active and passive end-point caching and communication-sensitive load balancing. Collectively, they mitigate the overhead introduced by the transparent dependency maintenance mechanisms. Communication-sensitive load balancing, in addition, affects the scheduling of distributed resources to application processes where both communication and computation costs are explicitly taken into account. DUNES ’ architecture endows commodity operating systems with distributed operating system functionality while achieving transparency with respect to their existing application base. DUNES also preserves semantic correctness with respect to single processor semantics. We show performance measurements of a UNIX based implementation on Sparc and x86 architectures over high-speed LAN environments. We show that significant performance gains in terms of system throughput and parallel application speed-up are achievable.

Asynchronous parallel computing can result in high message generation rates, thus triggering network congestion. This paper investigates the network congestion problem that can result from asynchronous parallel programs' high message generation rates. First, we characterize the communication requirements of a large class of supercomputing applications falling under the category of fixed-point problems amenable to solution by parallel iterative methods. In particular, we concentrate on asynchronous iterative algorithms whose communication/computation ratio is especially high resulting in degraded effective throughput if communication is not managed properly. Second, we show the effects of network contention and asynchrony on application performance in a local-area network environment and investigate methods of solution. Our approach is based on a congestion control algorithm called Warp Control whose adaptive properties are exploited to yield significant performance enhancements when ne...

15.26> 1. Introduction Measurements of local area and wide area trac have shown that network trac exhibits variability at a wide range of time scales and that this is an ubiquitous phenomenon which has been observed across diverse networking contexts [6,8,11,17,21]. A number of performance studies have shown that self-similarity can exert a detrimental impact on network performance leading to amplied queueing delay and packet loss rate [1, 12,13]. From a queueing perspective, a principal distinguishing characteristic of longrange dependent trac is that queue length distribution decays much more slowly|i.e., polynomially|vis-a-vis short-range-dependent trac sources which exhibit exponential decay. These performance eects, to some extent, can be curtailed by delimiting the buer This work was supported in part by NSF grants ANI-9714707 and EIA-9972883. y Contact author. E-mail: park@cs.purdue.edu; tel.: +1-765-494-7821, fax.: +1-765-494-07

Recent measurements of network traffic [3, 8] have shown that scale-invariant burstiness---self-similarity--- is a ubiquitous phenomenon found in both LANs and WANs as well as many types of traffic including compressed video. In [5], a generic high-level (application layer) causal mechanism was advanced for inducing self-similar link traffic when incorporating the effects of the transport layer. The performance impact was investigated in [4] showing the sensitive dependence of the delay-throughput relation on self-similarity. This paper studies the problem of provisioning quality of service (QoS) to real-time applications in the presence of self-similarity, first, with respect to network design, and second, with respect to congestion control. In the context of network design, two of the principal design variables are bandwidth and buffer capacity. The marginal utility of buffer capacity with respect to QoS provision is low due to the amplified queueing behavior exhibited by self-simil...