Appeal No. 2001-2270
Application 09/235,529
We agree that Eaton's teaching of an attenuation between the
telephone and the central office of 30 dB, albeit in a series
device, would have suggested to the artisan modifying Stevens'
parallel attenuator to provide an attenuation of 30 dB between
the telephone and the central office. The important fact is the
attenuation of DTMF tones between the telephone and central
office, not the kind of connection (serial or parallel) which
provides the attenuation. In addition, even without Eaton, the
"at least 30 dB" limitation appears to be an obvious limitation
which is determinable by routine investigation by one of ordinary
skill in the art in view of the guidance provided by Stevens that
the attenuation should be sufficient "so that the amplitude of
the signals on the telephone line is below a threshold of the
central office, so that the central office does not recognize the
signals as representing a telephone number entered by the user"
(col. 2, lines 42-45). Appellants note that "[t]he signaling
chapter of 'BOC Notes on the LEC Network - 1990' states that a
central office DTMF receiver should register DTMF digits with a
power per frequency of -25 to 0 dBm" (spec. at 9, lines 2-4),
which teaches that the attenuation should be greater than 25 dB;
"[t]he Mitel MT8870D integrated DTMF receivers are claimed to be
'central office quality'; and they accept a DTMF low group or
high group tone of -29 to +1 dBm" (spec. at 9, lines 9-10), which
teaches that the attenuation should be greater that 29 dB (e.g.,
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