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Re: [PLUG] VoIP over ADSL?
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There is a very good description of ADSL modulation techniques here:
http://homepage.ntlworld.com/martin.hubert1/index.htm
as well as the reasoning behind asymetrical data rates. It seems it has
more to do with crosstalk differences in one direction vs. the other which
was surprising to me.
Depending on the modulation technique - a 6Mb ADSL line takes about
1.1-1.5 Mhz of BW on the copper.
The specs on VoIP for AT&T say 90Kb up and down minimum. As was pointed
out, other services offer reduced BW requirements at the expense of
reduced quality. Any DSL line should give at least the 90Kb required.
I find a good 'down' test to be the MS HD video download site:
http://www.microsoft.com/windows/windowsmedia/content_provider/film/
ContentShowcase.aspx
Download a large clip - 50 MB or more and let the download rate meter
bottom out. This is your rate in kilobytes/sec - multiply it by roughly 10
to get the Mbit rate. For me it is consistently 190Kbyte/sec or 1.9
Mbits/sec. That is my download rate. So the VoIP 90Kb would be about 5% of
the available download BW.
I have not been able to find a reliable way to determine upload rates. If
anyone has a good method let me know? Having a directory on your providers
system and uploading a large test file would be one method.
I find that DSL (at least mine) is VERY consistent. So long as nothing
else on my local network is eating up BW the 1.9Mb rate is dead
consistent. I am not sure if this is true on cable where nodes are shared.
Doug
****************************
* Doug Crompton *
* Richboro, PA 18954 *
* 215-431-6307 *
* *
* doug@crompton.com *
* wa3dsp@wa3dsp.ampr.org *
* http://www.crompton.com *
****************************
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