Network throughput: Difference between revisions

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===Asymptotic throughput===

The '''asymptotic throughput''' (less formal '''asymptotic bandwidth''') for a packet-mode [[communication network]] is the value of the [[maximum throughput]] function, when the incoming network load approaches [[infinity]], either due to a [[Message passing|message size]],<ref>''Modeling Message Passing Overhead'' by C.Y Chou et al. in Advances in Grid and Pervasive Computing: First International Conference, GPC 2006 edited by Yeh-Ching Chung and José E. Moreira {{ISBN|3540338098}} pages 299-307</ref> or the number of data sources. As with other [[bit rate]]s and [[data bandwidth]]s, the asymptotic throughput is measured in [[bits per second]] {{nowrap|(bit/s)}} or (rarely) [[byte]]s per second {{nowrap|(B/s)}}, where {{nowrap|1 B/s}} is {{nowrap|8 bit/s}}. [[Decimal prefix]]es are used, meaning that {{nowrap|1 Mbit/s}} is {{nowrap|1000000 bit/s}}.<!--[[User:Kvng/RTH]]-->

Asymptotic throughput is usually estimated by sending or [[network simulation|simulating]] a very large message (sequence of data packets) through the network, using a [[greedy source]] and no [[flow control (data)|flow control]] mechanism (i.e., [[User Datagram Protocol|UDP]] rather than [[Transmission Control Protocol|TCP]]), and measuring the networkvolume pathof throughputdata received inat the destination node. Traffic load between other sources may reduce this maximum network path throughput. Alternatively, a large number of sources and sinks may be modeled, with or without flow control, and the aggregate maximum network throughput measured (the sum of traffic reaching its destinations). In a network simulation model with infiniteinfinitately large packet queues, the asymptotic throughput occurs when the [[Network latency|latency]] (the packet queuing time) goes to infinity, while if the packet queues are limited, or the network is a multi-drop network with many sources, and collisions may occur, the packet-dropping rate approaches 100%.

A well-known application of asymptotic throughput is in modeling [[point-to-point communication]] where (following Hockney) [[Network latency|message latency]] <math>T(N)</math> is modeled as a function of message length <math>N</math> as <math>T(N) = (M + N)/A</math> where <math>A</math> is the asymptotic bandwidth and <math>M</math> is the half-peak length.<ref>''Recent Advances in Parallel Virtual Machine and Message Passing Interface'' by Jack Dongarra, Emilio Luque and Tomas Margalef 1999 {{ISBN|3540665498}} page 134</ref>

As well as its use in general network modeling, asymptotic throughput is used in modeling performance on [[massively parallel]] computer systems, where system operation is highly dependent on communication overhead, as well as processor performance.<ref>M. Resch et al. ''A comparison of MPI performance on different MPPs''in Recent Advances in Parallel Virtual Machine and Message Passing Interface, Lecture Notes in Computer Science, 1997, Volume 1332/1997, 25-32</ref> In these applications, asymptotic throughput is used in Xu and Hwang model (more general than Hockney's approach)modeling which includes the number of processors, so that both the latency and the asymptotic throughput are functions of the number of processors.<ref>''High-Performance Computing and Networking'' edited by Angelo Mañas, Bernardo Tafalla and Rou Rey Jay Pallones 1998 {{ISBN|3540644431}} page 935</ref><!--[[User:Kvng/RTH]]-->

===Peak measured throughput===