Hi folks,
In South Africa there is a rather upsetting requirement to make the PSTN
front end of a DAA or trunk interface circuit immune to these meter pulse
signals, which are applied to tip and ring at 8Vrms behind a 200Ohm
resistor. Most chipsets would fold under this onslaught and result in
broken/interrupted transmission if you should be on an international call,
say, with meter pulses pouring through at one second intervals, for example.
Is this requirement, or rather this practice, peculiar only to SA? or do
other countries have similar requirements?
What is strange is that these signals originate in our Siemens exchanges,
which would seem to suggest that it is not necessarily of our own making, or
maybe I am being naive here.
Although it is not too difficult to provide either a low-pass filter on tip
and ring, or an LC notch filter across the line, the impedances of these
networks is such as to violate the requirements for the on-hook impedance
required by CLI (CID) specifications.
I look forward to your esteemed comments.
Colin Botha
Chief Development Engineer
Tellumat (Pty) Ltd
+27 21 710 2252 (Tel)
+27 21 710 2692 (Fax)
cbo...@tellumat.com
http://www.tellumat.com
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