Date: Mon, 17 Jan 2000 20:17:24 -0800 (PST) From: David Wolfskill <dhw@whistle.com> To: freebsd-isp@FreeBSD.ORG, xiyuan@yahoo.com Subject: Re: net speed Message-ID: <200001180417.UAA73885@pau-amma.whistle.com> In-Reply-To: <20000118033637.5783.qmail@web2106.mail.yahoo.com>
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>Date: Mon, 17 Jan 2000 19:36:37 -0800 (PST) >From: xiyuan qian <xiyuan@yahoo.com> >Hi, how to express the net speed between the client >and the server? with ping ??? First, I would contend that "speed" (as such) is not a very meaningful term with respect to networks. Indeed, your query relates to that lack of meaningfulness, as the text below should show. There are a couple of different (but related) ways to refer to how fast data gets from its source to its destination. The relevant terms are "latency" and "bandwidth". Absent a fair amount of context, determining which is meant can be challenging. Essentially, latency is a measure of the minimal amount of time that any quantum of information could spend in getting from the source to the destination. Typically, this will be measured with a small amount of data -- a single datagram (or packet, depending on the level you are measuring). Ping can be a useful tool for measuring this (at the datagram level). You can see the effect of changing the size of the datagram by specifying different sizes and noting the difference in the amount of time it takes, or latency. At the same time, this latency will vary, depending on network conditions, so it is likely that the best estimate of latency will be of a statistical nature. Bandwidth, on the other hand, is a measure of how much data can transit the network in a given amount of time. This, also, can be rather dependent on network conditions, as well as the load on the source and destination machines. Further, for useful (from the user's perspective) measures of bandwidth, higher-level protocols tend to be involved, such as FTP, and these have additional overhead. The commonly-quoted "speeds" of networks are measured in terms of bandwidth, rather than latency (i.e., a certain amount of data in a unit of time, vs. a certain amount of time for a unit of data). All that said, this is based on my observations, for the most part -- I haven't studied network theory; I'm not sure it existed as such back when I was in school... so please take all of this with a suitably-sized "grain of salt". Cheers, david -- David Wolfskill dhw@whistle.com UNIX System Administrator voice: (650) 577-7158 pager: (888) 347-0197 FAX: (650) 372-5915 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
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