David,

Until the standard that gives voip packets higher priority is
implemented, there can be problems with voip circuit quality. Most of
that problem is in the last link of the  end user data connection
(bri/pri/dsl/t1/ocx).  We have customers trying to run voip on dsl,
which will work fine until they move beyond 5 voip circuits or try to
move a lot of internet (http, ftp, etc) data at the same time.  Each
voip will take about 80k EACH way for a quality voice signal.  Those
voip packets don't have a chance of arriving on-time and in order when
the customer starts a file download stream while a call is in progress.
Most Dsl is asymmetric in bandwidth, typ 1-3M to and only 400K max from
the customer.  If the backbone has 400 http and 100 voip packets to push
to the customer, the voice channel is going to "break-up" since the
packets are either missing or out of order when the codec trys to
reassemble the audio.  Once a standard becomes practice, the http stuff
can be delayed until the voip packets are sent on.

We have customers successfully moving voip (and some vpn that can be
throttled) on symmetric ip circuits provided by tier one providers. Less
important ip is passed on separate, cheaper dsl.  It's all a matter of
pipes, and what and how stuff is pushed thru them.

All the neat features of voip and virtual switches will change telephony
forever, but be prepared to become a network expert along the way ;-)

btw, most voip providers have links to test programs that can be run in
the background (for days) to test quality of service on isp
connections.  routing, error rate, burstiness, los, and a whole list of
other values that can predict how well or poorly voip will work.
www.broadbandreports.com
<http://www.google.com/url?sa=U&start=1&si=1&oi=smap&q=http://www.dslreports.com/>  
has these tools and very good forums about voip.

-larry

David Lesher wrote:

>Our Left Coast office had Vonage on 768K and soon gave up; the
>quality was unusable.
>
>This especially applied to FAX; it was 100% unusable.
>
>Are there are VIOP adapters/systems that handle fax as I think they
>should: stop trying to carry digitized modem sound; rather use
>some kind of packetized scheme end-to-end.  Telebit trailblazers
>used this 'spoofing' to great success for UUCP.
>
>User reports welcome
>
>
>
>  
>


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