Automatic or semi-automatic exchanges

Child Classifications

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• H04M 3/002
• H04M 3/005
• H04M 3/02 Calling substations, e.g. by ringing (selective calling H04Q)
• H04M 3/08 Indicating faults in circuits or apparatus
• H04M 3/16 with lock-out or secrecy provision in party-line systems
• H04M 3/18 with means for reducing interference ; with means for reducing effects due to line faults
• H04M 3/20 with means for interrupting existing connections; with means for breaking-in on conversations
• H04M 3/22 Arrangements for supervision, monitoring or testing
• H04M 3/38 Graded-service arrangements, i.e. some subscribers prevented from establishing certain connections (queuing arrangements H04Q3/64)
• H04M 3/40 Applications of speech amplifiers
• H04M 3/42 Systems providing special services or facilities to subscribers (specially adapted for wireless communication networks H04W4/00)
• H04M 3/60 Semi-automatic systems, i.e. in which the numerical selection of the outgoing line is under the control of an operator