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Can anyone explain this weird modem phenomenon?!?

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I'm still on dial-up (long story), so for long downloads I usually just let a file download in the background while I do things like hang in the forum or answer email.


I needed to download a 14 MB photo file from the Alesis site for my upcoming Summer NAMM show report for EQ, so I started the process. Just a few minutes later, an alert box said the file had been downloaded. That seemed waaaay too fast, so I checked the file size, expecting that it had been corrupted and truncated...but all 14 MB were there. Huh?


Well, I needed to download a second picture file, and this time I looked at the box showing the calculated transfer time and rate. The thing was going along at DSL speeds -- about 115kbps!! Normally I get about 48kbps on a good day.


So I thought okay, I'll go download some big updates while things are working fast. I went to the Steinberg site to download the latest Wavelab5 patch, but transfer time was back to normal speed. I figured my magic high-speed window had closed, so just for kicks, I went back to the Alesis site and downloaded another picture that I hadn't planned on using in the report. This time it was chugging along at about 96kbps. However, it did slow down linearly over the course of the download; at the end of the transfer, it had slowed to a little over its normal speed (about 48kbps).


What's even weirder is I'm using a truly cheap US Robotics 56k modem I picked up at WalMart a couple years ago for $30 when my previous modem got fried by a nearby lightning strike.


Anyone got a theory about why my modem transfer time was over twice as fast as normal, albeit temporarily? And why, with the third picture, did the transfer start off real fast and end up slower?


Beats me. My only theory is that our area just got DSL recently. Maybe the data normally moves at that rate, but the phone company slows things down if it detects you're not a DSL subscriber. And maybe for some reason the "slow down" routine got bypassed or something. Weird........

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Hi Craig,


I find this does happen with graphics files in particular. I have no idea WHY it happens but have experienced exactly the same thing, but only with graphics files.

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Hi all,


Fairly straightforward - the actual data rate is limited to 56kbps, but modems have some clever realtime, lossless data-compression routines on top of that - so, if the data is relatively compressible (which high quality, large image files are) you can get higher reported speeds, as the modem is able to squash the data on the fly. Other things that compress nicely are text files and HTML.


However, for already-compressed data like ZIP or SIT files, low-quality JPEGs, or MP3 audio, there's no additional headroom that the modem is able to squeeze out, so you're stuck at regular download speeds.

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Would this be taking advantage of an ISP's "accelerated download" features also,(they all seem to advertise it lately), with respect to data compression and mirroring? Could it be that the pipeline was relatively uncluttered at certain points, and was getting busier when things slowed down? I don't know. Just curious.

What intrigues me is the fact that a 56K modem was reporting higher speeds. I didn't know they could do that. Of, course, I've never really checked. I do know that it's much faster downloading early in the morning, but I just attributed that to Internet traffic.


Tele Kinesis

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I think Angus has it right. The modem's built in compression is increasing your apparent data rate. You didn't mention whether the modem is internal or external, but either way the speed of the link between the modem and the pc is likely much faster than 56K.


It's definately nothing to do with DSL - a different kind of modem is required for that.



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I had the same with a 6mb mp3 once one a 56k modem,... it took 3 seconds,....amazing! I never figuered out how come. I tried svereal times and each time it worked but only if I downloaded from the same site.


With my adsl modem I one time had something similar. I have a1 mbit connection which changed for no reason to 4mbit and then changed back again.


I could download at aproxx 470b/second...


Sometimes I think people who make computers allready know how to transfer at awesome speeds but don't tell it to us ignorants cause now we keep buying new modems each year.

Fan, nu pissar jag taggtråd igen. Jag skulle inte satt på räpan.


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DSL requires a separate modem which interfaces between the phone line and the ethernet port in your computer. It also has special treatment at the telco's central office, and often a fiber optic carrier translator between your neighborhood and the office. Standard phone service, known as POTS (Plain Old Telephone Service), uses a limited voice range that is filtered in the central office, or switch. This was originally set up so that signalling (commands for changes in the status of the line and for routing the call) could "ride" in the frequencies outside the voice range. That filtering is what gives phone calls their distinctive thin sound, and why music played over a phone line sucks, as there are no upper and lower harmonics.


A standard dial-up modem uses the voice freqs to transmit data. This is why you can't be on the phone when the modem is active. DSL is actually ADSL, Asynchronous Digital Subscriber Line. It uses the full range of frequencies (broadband) that are outside the voice range. It works independent of the POTS line and could be active even if you didn't have voice service.


Craig, I really hope you can get broadband someday. It's probably projected for your area, but local telephone companies have been taking it in the shorts lately from both cell phone competition and cable TV broadband, so their capital budgets are often frozen. The cable companies have to install equipment to make their broadband work, too, and often don't extend facilities for a small customer base.


If you want to use my DSL, you're welcome to come here anytime. I'll heat up the soldering iron in case you have any tips for my Silvertone 1484 project.



He not busy being born

Is busy dyin'.


...Bob Dylan

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Originally posted by LiveMusic:

I dunno but I've always wondered WHY when I'd download on an ISP, it would start off at a rate and continually degrade (time-wise) as it transferred.

I'm no expert, but what appears to happen is that the software lies to you a little bit. When you right-click a link and select 'Save to file' for example, the browser will instantly start caching the file in a temp directory. Meanwhile, it requests a 'file save' dialog from the OS. After a time, the OS responds, and lets you browse to a directory, edit the filename maybe, and click OK.


By now the tmp file is up to, say 150Kb or so, but the timer on measuring the download rate is still at zero because the file hasn't been written to until now. So you get unrealistically high numbers in bytes/sec (for example, if it takes 1 second to transfer the 150K into its final destination, the browser reports an average rate of 150K/sec. The next second, you get the normal 5Kbytes, so the browser reports 77.5 Kb/s (155Kb/2sec). And so on.


Eventually, if download is big enough, the reported average rate will be back to 56K/s.


I'm not sure of this, I'm just theorized based on what I've seen. I would also agree that Modem compression will inflate reported transfer rates as well.

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Let us not forget that the theoretical limit of a filtered (standard) phone line is only 53k, not the modem's 56k upper limit. So actual speeds will never exceed 53k of actual information on a standard U.S. phone line.


How they managed to compress a 14mb file to a small enough size for you to get the apparent speeds you've described, Craig, is beyond my comprehension. :freak:


I'm quite sure you're not complaining, though. ;)

It's easiest to find me on Facebook. Neil Bergman




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USR Modems were some of the best, and I am betting that the modem you dial in to uses the same chipset, so there is no translation in the compression. They 'play nice'. It is possible the ISP replaced a modem recently, and that is why is just seemed to happen. And, the modem you bought...If it is external, they are generically better because they have their own processing. Most of the last round of internal modems were 'winmodems' which off loaded the processing for stuff like compression to the CPU in the OC. Many of the USR modems were NOT win modems.


Could just be luck as well.. ;)

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