[kwlug-disc] [OT] Diagnosing voip and Tomato

John Johnson jvj at golden.net
Mon Feb 28 19:40:43 EST 2011


On 2011-02-25 11:02, Paul Nijjar wrote:
> On Thu, Feb 24, 2011 at 10:21:52PM -0500, Insurance Squared Inc. wrote:
>    
>> Here's where I'm puzzled.  Seems like plenty of people using Voip on the
>> list.  Am I the only one experiencing this problem repeatedly?  Or does
>> everyone else's calls degrade as soon as the kids get home from school?
>>      
> I have mentioned this before, but our Sympatico routers are
> configurable so that our ATAs get priority bandwidth. I don't remember
> how I did this; it may have been through IP address. So if you could
> prioritize your Asterisk box's IP, you might win.
>
> I agree with John that the "A" in ADSL is a big pain. Fortunately we
> have not experienced much degradation, but I worry about it a fair
> amount.
>
> - Paul
Execulink (in my case Golden.net) resells Bell's DSL and they tell me 
that the service is ADSL2+.

see: various wikipedia hits on ADSL and ADSL2+ and *ITU G.992.x*

http://whirlpool.net.au/wiki/ADSL_Theory and
http://www.ee.kth.se/php/modules/publications/reports/2005/IR-SB-EX-0509.pdf

"Under good conditions the newest ADSL technology (ADSL2+) can offer 
downloads at 25
Mbit/s, which is more than sufficient for most "in home"-applications 
today and should be
compared to a V.90 modem's top bit rate at 56 kBit/s (0,056 Mbit/s)."

Whether ADSL or ADSL2+ , the signal format uses multiple frequencies, 
above the voice band, as carriers each modulated with a combination of 
phase shift and amplitude signal changes to encode as few as one or two 
bits. Each of the multiple carriers is not unlike one of the two 
carriers used in the 56 kBits/s modem mentioned above, one used for 
upstream, one for downstream.

IMO: The DSL  signal between the DSLAM has about as digital content as 
an AM or FM radio signal, one carrier with amplitude or frequency shift 
keying. Many forget that the transmission media whether RF or CAT5 cable 
all live in an analog world. And the signals pumped over the media are 
usually, except in the flat ribbon cables in one's PC are analog 
signals. (The SATA standards, too, take the analog environment into 
account.)

Fibre?: The days of binary on/off are long gone. Here too, wavelength 
modulation (aka frequency modulation) comes into play. And the big boys 
use multiple wavelengths on one fibre cable.

As for the OP's original question: I dunno. The issue may be solved with 
a better downstream protocol, e.g. ADSL2+.

JohnJ




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