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EP0069595A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Data transmission over long distance circuits

Assignee: General Datacomm Inc
•
Filing: 1982-07-07
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Granted: —
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Expires: 2002-07-07
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Abstract

Abstract This invention relates to a method and apparatus providing a common handshaking protocol for the 201, 202 and 208 modems in long distance data transmission. According to the present invention a novel handshaking sequence trains up any echo canceller 74 in the circuit, detects the presence of any echo suppressor 82 and uses a conventional signal preamble in the presence of echo cancellers 74 and a sacrificial carrier sequence in the presence of echo suppressors 82. As in the prior art, a ringing signal is applied to an answer modem 40 in response to a signal from an originate modem 30. The answer modem 40 is connected to the communication line after receipt of the ringing signal, and an answerback tone is transmitted from the answer modem to the originate modem after a period of silence following connection of the answer modem to the line. After receipt of the answerback tone, the originate modem 30 is connected to the communication line. In accordance with the invention, this is followed by a period of silence that is sufficiently long to reactivate any echo suppressors 82 in the communication line. Thereafter at least two training sequences are transmitted, one from the originate modem 30 to the answer modem 40 and the other from the answer modem 40 to the originate modem 30, each training sequence being sufficiently long to train up any echo canceller 74 in the line. The lengths of the training sequences as received are compared with their lengths as transmitted to determine if the length of the sequence was shortened by an echo suppressor 82. If the length of the training sequences as received are significantly shorter than their lengths as transmitted, a sacrificial carrier is transmitted at the beginning of each transmission of data in a new direction. In the event the training sequences as received are not significantly shorter, each transmission of data in a new direction begins without a sacrificial carrier. As a result, greater data throughput can be achieved in the absence of echo suppressors 82 and errors can be avoided while echo cancellers 74 are being trained.

Inventors

  • 👤 Martin N.Y. Shum

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-10-28 16:46
CPC Classifications
H; H04; H04B; H04B3/00; H04B3/02; H04B3/20; H04L; H04L5/00; H04L5/14; H04L5/16

Claims Analysis

Total Claims: 4
Claim 1
Independent Claim 226 words
A method of handshaking between an originate modem.(30).and an answer modem.(40).interconnected by a communication line comprising the steps of: causing a ringing signal to be applied to the answer modem.(40). in response to a signal from the originate modem.(30); connecting the answer modem.(40).to the communication line after receipt of the ringing signal; transmitting an answerback tone from the answer modem.(40).to the originate modem.(30).after a period of silence following connection of the answer modem.(40).to the line; connecting the originate modem.(30).to the communication line after receipt of the answerback tone; waiting sufficiently long to reactivate any echo suppressors .(82).in the communication line; thereafter transmitting first and second training sequences, one from the originate modem.(30).to the answer modem.(40).and the other from the answer modem.(40).to the originate modem.(3O), said first and second training sequences being sufficiently long to train up any echo canceller.(74). in the line; detecting if the lengths of the first and second training sequences as received are significantly shorter than their lengths as transmitted; and in the event the training sequences as received are significantly shorter than their lengths as transmitted, transmitting a sacrificial carrier at the beginning of each transmission of data in a new direction and in the event that the training sequences are not significantly shorter as received than as transmitted beginning each transmission of data in a new direction without a sacrificial carrier.
Claim 2
Independent Claim 226 words
A method of handshaking between an originate modem.(30).and an answer modem.(40).interconnected by a communication line comprising the steps of: causing a ringing signal to be applied to the answer modem.(40). in response to a signal from the originate modem.(30); connecting the answer modem.(40).to the communication line after receipt of the ringing signal; transmitting an answerback tone from the answer modem.(40).to the originate modem.(30).after a period of silence following connection of the answer modem.(40).to the line; connecting the originate modem.(30).to the communication line after receipt of the answerback tone; waiting sufficiently long to reactivate any echo suppressors .(82).in the communication line; thereafter transmitting first and second training sequences, one from the originate modem.(30).to the answer modem.(40).and the other from the answer modem.(40).to the originate modem.(3O), said first and second training sequences being sufficiently long to train up any echo canceller.(74). in the line; detecting if the lengths of the first and second training sequences as received are significantly shorter than their lengths as transmitted; and in the event the training sequences as received are significantly shorter than their lengths as transmitted, transmitting a sacrificial carrier at the beginning of each transmission of data in a new direction and in the event that the training sequences are not significantly shorter as received than as transmitted beginning each transmission of data in a new direction without a sacrificial carrier.
Claim 3
Independent Claim 224 words
An apparatus for performing a handshaking procedure between an originate modem.(30).and an answer modem.(40). interconnected by a communication line, said apparatus comprising: means for applying a ringing signal to the answer modem.(40).in response to a signal from the originate modem.(30); means for connecting the answer modem.(40).to the communication line after receipt of the ringing signal; means for transmitting an answerback tone from the answer modem.(40).to the originate modem .(30).after a period of silence following connection of the answer modem.(40).to the line; and means for connecting the originate modem.(30).to the communication line after receipt of the answerback tone; characterised in that: said apparatus is provided with means for transmitting a first and second training sequences, one from the originate modem.(30).to the answer modem.(40).and the other from the answer modem.(40).to the originate modem .(30), after a period of silence that is sufficiently long to reactivate any echo suppressors.(82).in the communication line, said first and second training sequences being sufficiently long to train up any echo cannceller.(74).in the line; means for detecting if the lengths of the first and second training sequences as received are significantly shorter than their lengths as transmitted; and in the event the training sequences as received are significantly shorter than their lengths as transmitted, means for transmitting a sacrificial carrier at the beginning of each transmission of data in a new direction.
Claim 4
Independent Claim 224 words
An apparatus for performing a handshaking procedure between an originate modem.(30).and an answer modem.(40). interconnected by a communication line, said apparatus comprising: means for applying a ringing signal to the answer modem.(40).in response to a signal from the originate modem.(30); means for connecting the answer modem.(40).to the communication line after receipt of the ringing signal; means for transmitting an answerback tone from the answer modem.(40).to the originate modem .(30).after a period of silence following connection of the answer modem.(40).to the line; and means for connecting the originate modem.(30).to the communication line after receipt of the answerback tone; characterised in that: said apparatus is provided with means for transmitting a first and second training sequences, one from the originate modem.(30).to the answer modem.(40).and the other from the answer modem.(40).to the originate modem .(30), after a period of silence that is sufficiently long to reactivate any echo suppressors.(82).in the communication line, said first and second training sequences being sufficiently long to train up any echo cannceller.(74).in the line; means for detecting if the lengths of the first and second training sequences as received are significantly shorter than their lengths as transmitted; and in the event the training sequences as received are significantly shorter than their lengths as transmitted, means for transmitting a sacrificial carrier at the beginning of each transmission of data in a new direction.

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