[ntp:questions] Accuracy of audio tones via VOIP

Garrett Wollman wollman at bimajority.org
Wed Jul 10 02:31:38 UTC 2013

In article <E1Uwh0W-000Hn2-ML at stenn.ntp.org>,
Harlan Stenn  <stenn at ntp.org> wrote:
>I have heard (and I haven't checked in to this) that a good number of
>local calls are converted to digital pretty quickly, too.

For all intents and purposes, all of them are.  Over on
comp.dcom.telecom people used to post about how the last #1AESS in
various states was about to be replaced by something digital; I do not
believe that there are any analog CO switches left in traditional Bell
territory -- whatever tiny independents are left may still have some.
Obviously the situation will be different in other countries.

However, this does not imply that the clocks aren't synchronized.  If
there were significant clock skew in the PSTN, fax machines wouldn't
work (as indeed they don't over a naive VOIP connection).


Garrett A. Wollman    | What intellectual phenomenon can be older, or more oft
wollman at bimajority.org| repeated, than the story of a large research program
Opinions not shared by| that impaled itself upon a false central assumption
my employers.         | accepted by all practitioners? - S.J. Gould, 1993

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