Measure DSL speed?|
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Posted by Vic Dura on February 20, 2009, 6:50 am
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I have a question about how download DSL speed is measured. Previously I had 1.5Mb DSL service. When I went to a site such as SpeakEasy <http://www.speakeasy.net/speedtest/> to measure my d/l
speed, it would show approximately 1.1 - 1.3 Mb which is what I would
expect. However when I would use a .bat script in a WinXP console window to measure the speed I would only calculate about half that speed. The .bat script works as follows: 1) turn on a timer 2) use ftp to download a 1.5MB file from the server of my ISP. 3) turn off timer & save elapsed time 4) calculate d/l speed from the known file size and d/l time I've recently upgraded to 3Mb service and I have seen my d/l speeds double. However I still see the same relative disparity between the two methods of d/l speed measurement as described above; i.e. the speed measured at SpeakEasy is about 2.9Mb/sec but the speed calculated by the script is about 1/2 that. Can anyone offer any insight as to why the large disparity? Thanks -- At first they laugh at you, then they ignore you, then they fight you, then you win. | ||||||||||||||||||||||
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Posted by Bert Hyman on February 20, 2009, 8:39 am
Please log in for more thread options > Can anyone offer any insight as to why the large disparity?
You're including all the Windows and program overhead in your timing. It takes time for Windows to load and close your FTP program, and a significant amount of time for your FTP program to look up and connect to the remote server, negotiate with the remote server to open the file and then save the downloaded file on your PC at the end. I suppose you could try to swamp the overhead by downloading a very large file, but the overhead will still be there. -- Bert Hyman St. Paul, MN bert@iphouse.com | ||||||||||||||||||||||
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Posted by Peter on February 20, 2009, 5:27 pm
Please log in for more thread options Hi Vic,
> I have a question about how download DSL speed is measured.
Unfortunately, you are chasing shadows there.....;-) > Previously I had 1.5Mb DSL service. When I went to a site such as
> SpeakEasy <http://www.speakeasy.net/speedtest/> to measure my d/l > speed, it would show approximately 1.1 - 1.3 Mb which is what I would > expect. However when I would use a .bat script in a WinXP console > window to measure the speed I would only calculate about half that > speed. There are so many variables that are added in there it almost seems pointless to do any "testing" because all testing is moot. If you REALLY want to know what your Hardware NEGOTIATED Line rate is, then let your Hardware tell you what speed it obtained. For a DSL service, most DSL H/W provides a status display similar to this one (please excuse the formatting) - ATU-R (DS) ATU-C (US) Modem Status: Showtime (DMTDSL_SHOWTIME) DSL Mode: ITU G.992.1 (G.DMT) ITU STD NUM: 0x01 0x01 Vendor ID: 'ALCB' 'BDCM' Vendor Specific: 0x0000 0x9191 Vendor Country: 0x00 0xB5 Capacity Used: 99% 39% Noise Margin: 12.0 dB 29.0 dB Output Power: 16.5 dBm 11.5 dBm Attenuation: 57.5 dB 31.5 dB Defect Status: None None Last Fail Code: None Selftest Result: 0x49 Subfunction: 0x02 Interrupts: 52250 (78 spurious) Activations: 280 SW Version: 3.8129 FW Version: 0x1A04 Interleave Fast Interleave Fast Speed (kbps): 1344 0 160 0 Reed-Solomon EC: 499 0 0 0 CRC Errors: 7 0 0 0 Header Errors: 10 0 0 0 Bit Errors: 0 0 BER Valid sec: 0 0 BER Invalid sec: 0 0 The line to note is this one - Speed (kbps): 1344 0 160 0 Also useful is tihs one - Noise Margin: 12.0 dB The SPEED tells me that this ADSL line has negotiated a DS (DOWNSTREAM) connection speed of 1.344 Mb, and an US (UPSTREAM) connection speed of 160Kbps, and the NOISE MARGIN tells me that the Router NEGOTIATE a rate that is likely to be LOWER than the rate that is possible ON THIS LINE. Ideally, the NOISE MARGIN should be somewhere around 4 - 8db to be closer to optimal (note there is no 1 guaranteed value that is truly optimal) This can be for a number of reasons, some inside your (or your ISP) control, some outside you control. EG Currently its extremely wet outside and such weather can play havoc with the performance of the Copper cable in our area, so the displayed rate is likely to be lower what than I am normally able to get (I normally get about 2.0Mb Down, 160 Up), which is close to my contracted service, I get less due to my large distance from the DSLAM. That is the most accurate form of line speed between YOUR house and your CONNECTION point and it is EXACTLY correct! Nothing else is in the equation. Thre are 2 things to note - 1. This is an ATM (DSL) line rate so the framing on that line will be in ATM cell (block) size of 53 Bytes, using a 48 Byte payload, meaning effectively the USER visible operating speed is 1.334Mb LESS about 5/53 or something like 9-10%. 2. Usually, DSl H/W continually evaluates its connection parameters and adjusts the line signaling to obtain values that usually work best. It is CRITICAL to understand that copper in the ground is NOT a static environment, there are MANY variables that mean it's performance can and will vary, sometimes by wide margins. ALL of this is usually OUTSIDE your control, all a user can do is ensure they operate their hardware within its working parameters, and these days there is very little required from the user in this respect. . > The .bat script works as follows:
> > 1) turn on a timer > 2) use ftp to download a 1.5MB file from the server of my ISP. > 3) turn off timer & save elapsed time > 4) calculate d/l speed from the known file size and d/l time For really accurate readings you are adding in too many uncontrollable variables into your figures to worry about trivia like this. Please dont waste your time... HOWEVER, having said all that the REAL issue for users is the bandwidth between YOUR machine and the destination Server for EACH site you are trying to communicate with, with whatever SERVICE you are trying to reach. All thee factors will affect performance and are near impossible to calculate on a public network such as the internet. The reality is that it all comes down to the question "Is your ISP delivering the service they promised?",and that can be a really tough question to PROVE, let alone answer. > Can anyone offer any insight as to why the large disparity?
Simple, the methodology used for calculating these figures is flawed, and its like a cat chasing its own tail. This does not stop cats desiring to catch their own tail.....;-) I hope this helps.........................pk. -- Peter from Auckland. | ||||||||||||||||||||||
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Posted by Bert Hyman on February 20, 2009, 4:32 pm
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> There are so many variables that are added in there it almost seems
> pointless to do any "testing" because all testing is moot. If you > REALLY want to know what your Hardware NEGOTIATED Line rate is, then > let your Hardware tell you what speed it obtained. Testing can be useful if you have reason to think that something funny is going on upstream. My router usually trains up at 6592/896 Kbps and I usually get 5Mbps downloads from close-in, capable sites. When things seemed to go sour a few months ago, I was able to use test results to first convince myself that something was going on and to get The Phone Company and my ISP to look into things. Unbelievable as it seems, The Phone Company actually admitted that they'd over-committed the DSLAM at the local central office, and my ISP did some load balancing on their circuits and things have been fine since then. -- Bert Hyman St. Paul, MN bert@iphouse.com | ||||||||||||||||||||||
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Posted by Robert Redelmeier on February 20, 2009, 6:33 pm
Please log in for more thread options > The .bat script works as follows:
> > 1) turn on a timer > 2) use ftp to download a 1.5MB file from the server of my ISP. > 3) turn off timer & save elapsed time > 4) calculate d/l speed from the known file size and d/l time > > I've recently upgraded to 3Mb service and I have seen my d/l speeds > double. However I still see the same relative disparity between the > two methods of d/l speed measurement as described above; i.e. the > speed measured at SpeakEasy is about 2.9Mb/sec but the speed > calculated by the script is about 1/2 that. > > Can anyone offer any insight as to why the large disparity? Try a larger file. At 3 Mbps, a 1.5 MB file takes 4 seconds raw. Most ftp transfers take a while to startup. -- Robert | ||||||||||||||||||||||
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