Browse Prior Art Database

Hybrid Transmission System for Functional Digital Telephones

IP.com Disclosure Number: IPCOM000087110D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Esteban, D: AUTHOR

Abstract

The proposed system is based on the use of a two-wire hybrid transmission (analog and digital) consisting of a 4 kHz bidirectional analog voice channel (300 - 3400 Hz telephone bandwidth) compatible with conventional equipment (telephone or data adapters), and a full duplex out-of-band frequency signaling at an intermediate transmission rate (600 to 1200 bauds).

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Hybrid Transmission System for Functional Digital Telephones

The proposed system is based on the use of a two-wire hybrid transmission (analog and digital) consisting of a 4 kHz bidirectional analog voice channel (300 - 3400 Hz telephone bandwidth) compatible with conventional equipment (telephone or data adapters), and a full duplex out-of-band frequency signaling at an intermediate transmission rate (600 to 1200 bauds).

The lower part of the voice band link (0 to 4 kHz) is allocated to the voice signal, the upper part (12 to 20 kHz) to the signaling signal (data information being considered signaling), as depicted in Fig. 1.

The voice signal is transmitted over the two-wire link in the same way as for conventional analog telephones (bidirectional link with analog hybrid). The signaling signal consists of two independent digital subchannels centered, for instance, at 12 and 22 kHz.

The proposed hybrid interface is shown in Fig. 2. This implementation assumes the voice/signaling spectra depicted in Fig. 1, the allocation for these spectra being justified by the need to optimize the switching interface and the telephone together. The main features of this implementation are the following:

- The system outgoing signaling is centered at 12 kHz so as to benefit from the attenuation provided at this frequency by the input analog filter (about 40 dB at 12 kHz), in order to compensate for the unbalance of the line circuit hybrid. On the terminal side the signaling is re...