CPC Main Group
H04M 9/00 Arrangements for interconnection not involving centralised switching
6 direct subcodes
Child Classifications
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- H04M 9/02 involving a common line for all parties
- H04M 9/04 involving a separate line for each pair of parties
- H04M 9/06 involving combinations of interconnecting lines
- H04M 9/08 Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic