[TriLUG] IP Phone

[Jim Ray]

Prolly a function of the A/D and D/A in the PCI card.  If Brother Nyquist
really rules, then the designers of that card have the sampling rate and
dynamic range set properly.  Me thinks 3.4 kHz BW would be a piece of cake
yet would recommend testing prior to making a claim.

/jim

-----Original Message-----
From: trilug-bounces at trilug.org [mailto:trilug-bounces at trilug.org] On Behalf
Of Rob Lockhart
Sent: Wednesday, January 21, 2004 11:05 AM
To: Triangle Linux Users Group discussion list
Subject: Re: [TriLUG] IP Phone


Jon I meant to ask you a question at the last meeting, but it is perhaps a
bit technical in nature.

How does the VoIP system handle POTS sample rate recovery and NTR for
sampling over an IP network without such capabilities?  Otherwise, I would
assume that things like Tivos and such (you have to have a land line for
unhacked DirecTivo) that require POTS modem access for pay-per-view and
other such things would not work reliably (due to a high connect rate
causing a high bit-per-symbol allocation) the QAM signalling getting screwed
up by the irregularly-arriving packets.  I could even imagine that, say,
network latency being very low and consistent during training, and then a
few seconds later having different latency (or jitter) characteristics than
during training, that this may cause the CPE modem to train up at a higher
rate than the VoIP system can compensate for, thus it may cause the
narrowband modem link to drop and attempt retrain.

Just curious....

Of course this is very hard to detect with your ear and the right
decoding/encoding techniques but I doubt they'll work very well for a
33.6kbps or higher connect rate (due to the density of the constellation).

Regards,
  -Rob


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