Appeal No. 2001-2270
Application 09/235,529
telephones are not detected by the central office, but these
signals were often detected by variability in central office
sensitivity, telephone network attenuation, and dialing signal
strength (spec. at 2, line 20 to spec. at 3, line 6). It is
stated (Br4): "The research of the present inventors into the
Bellcore specifications and the real characteristics of central
office receivers has led to the conclusion that much more
attenuation is needed. As a result, the present claims require a
substantially higher attenuation of 30 dB or higher."
Eaton discloses a telephone dialing code processor for
intercepting outgoing DTMF codes (i.e., preventing them being
received by the central office) and then either redialing a
modified sequence of telephone numbers or barring the call
(col. 3, line 63 to col. 4, line 3). The device is located in
series with one of the telephone line conductors (Fig. 2; col. 5,
lines 51-53). Eaton disclose that in the mute (interception)
mode the loss is typically 30 dB (col. 9, lines 3-5).
The examiner concludes (FR2-3; EA5):
It would have been obvious to one of ordinary skill in
the art at the time of [sic] the invention was made
to utilize the teachings of Eaton (e.g., choosing an
impedance or an AC load that can attenuate the tone signals
to a certain threshold level, e.g., 30-38 dB) so that the
central office does not recognize the outgoing dialing
signals (e.g., the DTMF tones), and a conventional telephone
system can be economically used as an intercom system.
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