Colin,
in Germany similar metering/AoC signals are occasionally to be found in the
analogue network, and we had very similar requirements.
The values are 16kHz at -23 to +21 dBm (!) across 200 ohms.
If You look into the NET4 (ETS/EN300001)(1.7.8) You will find more.
In the European countries metering is (thank god) only available on special
subscription for an extra fee (for example for charge phones and hotels).
In Germany 99.9% of subscriber lines do NOT use it. In the others it is quite
similar. Switzerland is the only exeption with 12kHz metering signalling is
always
on, filters are required.
A relatively simple parallel resonance in series with the line may prevent
hangup.
If You cannot accept interruptions and retrain You need a much better filter or
You are out of luck if You cannot have metering switched off. A suitable filter
configuration will have two parallel resonances and one series resonance. I am
not
an expert on filters.
I remember that there has been an attempt to define special signalling at the
start
of a call to switch off metering on demand but have no information if it has
ever
been implemented.
Note 1: Siemens exchanges are supposed to be fully configurable. Many German
exchanges
use the very same equipment.
Note 2: ETS/EN300001 is available for free download at www.etsi.org
Regards
Robert
Robert Pausch, Regulatory Compliance Engineer
and Compliance Project Manager
Hewlett-Packard EMEA GmbH, Einsteinring 30, 85609 Dornach, Germany
Tel: +49 (89) 9392 2352, FAX: +49 (89) 9392 2336
Mailto: robert.pau...@hp.com
-----Original Message-----
From: Colin Botha [mailto:cbo...@tellumat.com]
Sent: Friday, November 15, 2002 5:29 PM
To: Treg (E-mail)
Subject: 12/16kHz meter pulse signal amplitudes . . . .
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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