Browse Prior Art Database

ISDN S BUS EXTENSION TELEPHONE

IP.com Disclosure Number: IPCOM000006808D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2002-Feb-04
Document File: 2 page(s) / 102K

Publishing Venue

Motorola

Related People

Neil Wellenstein: AUTHOR

Abstract

Digital telephone systems, including ISDN, do not allow adding extension phones simply by plugging another telephone onto the line, as analog systems do.

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MOTOROLA INC. Technical Developments Volume 18 March 1993

ISDN S BUS EXTENSION TELEPHONE

by Neil Wellenstein

INTRODUCTION

  Digital telephone systems, including ISDN, do not allow adding extension phones simply by plugging another telephone onto the line, as analog systems do.

  The ISDN S Bus is a 4-wire digital bus, with iso- lated transmit and receive pairs. This invention uses these isolated pairs to establish an analog signal path between extension phones on the S Bus. This permits these phones, up to the maximum of 8 allowed on the S Bus, to be conferenced on the S Bus and to be conferenced into the ISDN system. Circuitry is provided to maintain constant audio levels regardless of the number of exten- sion phones in use.

DESCRIPTION

Fire 1 is a simpliied diagram showing the princi- ple of operation. Dialiig, ringing, and hook switch cir-

cuitry is not shown. The voice signal between the ana- log side of the codec and microphone and earphone of the telephone handset is 4-wire analog. This 4-wire ana- log signal is converted to 2-wire analog by the 2-to-4 wire hybrid (shown as a transformer but which may be either a transformer or a solid state implementation). The 2-wire analog signal is then inserted on the 4-wire S Bus through the center taps ofthe transmit and receive transformers which couple the digital signals to and from the S Bus transceiver. This isolates the analog signal from the digital signals so there is no crosstalk.

  All signaling between stations may be done in the ISDN D Channel, using the Electronic Key Telephone System option, although an analog tone signaling scheme could be used as well. Any one, but only one, of the up to eight ISDN telephones on the S Bus can initiate or receive an ISDN call. Any or all of the other telephones on the bus can then be alerted and conferenced into the call.*A local intercom system could be set up as well.

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MOTOROLA INC. Technical Developments Vo...