Date: Mon, 12 Apr 1999 10:02:58 +0200 From: Stefano Riva <sriva@alice.it> To: Rudi Opperman <rudi@askas.co.za> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: how to determine the speed of a connection dynamically ? Message-ID: <3.0.5.32.19990412100258.009387e0@relay.alice.it> In-Reply-To: <37119D1E.8E6FF98F@askas.co.za>
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At 09.13 12/04/99 +0200, you wrote: >Suppose i have a server (eg http) that wants to respond dynamically to >various clients connecting at variable speeds .. (eg no compression for >fast links, lossy compession for slow links ). >What is the best way to determine such characteristics of a connection >(assuming a connection oriented protocol) and what does one do with >connectionless protocols? >Also how would a proxy/gateway complicate analysis? >I seems too simplistic to ping based on source address and then use >derived timing info as accurate - but this was suggested as a solution! >I would assume that there would be some protocol dedicated to deriving >this info The timing info derived from ping is a round-trip value that has no real meaning regarding the "speed" of a link (assuming you're talking about bandwidth, since compression would be almost pointless otherwise). Probing a link for available bandwidth is expensive, because the only reliable way to proceed is to transfer something, something not so small if you want to obtain an average, fairly correct result. As far as I know, the only wide-spread products that probe a link for bandwidth are clients like GetRight for Windows; they start a file download and "probe" alternate sites by doing "fragments" of downloads. If they find a faster site, they drop the connection with the first one and resume the download from the faster one. Of course, they must have a list of mirrors to work, mirrors capable of resuming. They usually work well with sites like Tucows, but if you know for sure which is the faster mirror for you, they effectively slow down large downloads, because they probe a bunch of other sites, eating up part of your bandwidth. Concerning the presence of a proxy, you can probe only the link between you and the proxy. --- Stefano Riva Software Engineer - Systems Administrator Informazioni Editoriali I.E. Srl Phone +39-027528400, Fax +39-027528451 Email sriva@alice.it To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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