Browse Prior Art Database

Reliable Transmission of Voice Messages

IP.com Disclosure Number: IPCOM000034466D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Locke, ME: AUTHOR

Abstract

As users of voice store and forward equipment require more flexible transmission of messages, it has become necessary to transmit messages between remote equipment. For example, a corporation may have large offices in New York and Los Angeles and desire transmission of voice messages between these two sites. Dedicated transmission facilities between such sites may be prohibitively expensive. A cost-effective mechanism is to use the public telephone network. The public telephone network has the following notable disadvantages: 1) insufficient bandwidth for economical digital transmission of high quality voice messages, 2) variable and sometimes unacceptable impairments for analog transmission of high quality voice messages, and 3) control information cannot be transmitted at the same time as a high quality analog voice message.

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Reliable Transmission of Voice Messages

As users of voice store and forward equipment require more flexible transmission of messages, it has become necessary to transmit messages between remote equipment. For example, a corporation may have large offices in New York and Los Angeles and desire transmission of voice messages between these two sites. Dedicated transmission facilities between such sites may be prohibitively expensive. A cost-effective mechanism is to use the public telephone network. The public telephone network has the following notable disadvantages: 1) insufficient bandwidth for economical digital transmission of high quality voice messages, 2) variable and sometimes unacceptable impairments for analog transmission of high quality voice messages, and 3) control information cannot be transmitted at the same time as a high quality analog voice message. This article seeks to solve the second and third disadvantages listed above so that analog transmission of high quality voice messages is feasible. Several previously used techniques are used together to ensure reliable transmission of high quality analog voice messages over the public telephone network.

First, impairments that might affect message quality are measured. Second, a modem is used with an error detection and correction mechanism for the purpose of transmitting control information.

Third, synchronizing tones are transmitted for delimiting the beginning and end of the analog message transmission. Fourth, control information is transmitted via the modem both before and after analog message transmission to ensure that message transmission was completed correctly and successfully. The sequence of operation is described below. This is followed by a description of each of the mechanisms used in implementation. 1) System A calls System B via the public telephone network (or a private telephone network, if such is available). 2) System B answers the call and responds with a test transmission usable for characterizing the telephone line. 3) System A analyzes the test transmission of system B. If the telephone line characteristics are adequate, system A responds by making a test transmission. If the telephone line characteristics are not adequate, system A drops the telephone line, and restarts the sequence at a later time. 4) System B analyzes the test transmission of system A. If the telephone line characteristics are adequate, system B responds by transmitting modem carrier. If the telephone line characteristics are not adequate or the line is dropped, system B drops the telephone line. 5) System A waits for modem carrier. If carrier is not established within a prescribed amount of time or the line is dropped, system A drops the telephone line, and restarts the sequence at a later time. When carrier is established, system A responds with an alternate modem carrier. 6) Systems A and B may now identify each other and request transmission of messages from one to the...