Re: Comcast Telephone Service????

[Frank Olson <Use_the_email_links@xxxxxxxxxxxxxxxxxxxxxx>]

Robert L Bass wrote:
>>Even when using a "full rate" codec such
>>as the G.711, it helps if "echo cancellation"
>>and "silence suppression" are turned off,
>>but I have no idea who does that, or how...
>
>
> Silence suppression is a means of making a VoIP call sound more like a telephone call by creating background noise (BGN) similar to
> what is heard on a POTS call when no one is speaking.  BGN is sometimes referred to as "comfort noise" because it makes the user
> comfortable that he is still connected.  Needless to say, BGN is undesirable in a digital call between an aloarm system and the
> central monitrong station receiver.
>
> Echo cancellation has been used on POTS phone systems for years.  There is an inherent delay in processing long distance calls.  The
> microphone picks up some of the receiver's signal and sends it back, a little bit later, creating an annoying echo.  Echo
> cancellation systems are employed by telco's to kill the echo.  The process typically employs two technologies.  An adaptive filter
> picks up the echo, recognizes it as a delayed copy of previously transmitted waveforms (or, in more modern systems, bit patterns)
> and cancels most of the unwanted signal.
>
> Adaptive filters are not perfect.  They leave an aufdible component of the original echo (hmm; is "original echo" a contradiction in
> terms:))?  A non-linear amplifier is employed to clean up what remains.  The precise manner in which this is done is beyond my
> limitd knowledge of the subject but it involves suppression of the local signal and the remaining echo component.
>
> One problem with adaptive filters and echo suppression apparently is they tend to see repetitive waveform (data signals are often
> repetitive) as noise and kill the signal.  Also, some systems filter out high frequency sounds since they're not an expected
> component of normal speach.
>
> Almost every ATA device's CODEC can handle DTMF (touch-tine) signalling.  Becaue some alarm transmission formats employ DTMF, these
> may be better suited for use with VoIP service than others, especially pulse formats.  NBo guarranty here that some particular unit
> will work.  You just have to experiment.
>
>
>>So, the key to determining whether an alarm system will work on a VOIP
>>system may be to determine the type of codec that is used by the VOIP
>>interface.  Assuming the cable companies won't tell or don't know, googling
>>the part number might produce some useful information.
>
>
> Most major manufacturers list the CODEC's and lots of other stuff about their VoIP devices online.  Worst case, you have to make a
> phone call.
>


Amazing what a few seconds on "Google" will turn up, isn't it??