Full-duplex start-up for modems

Details Full-duplex start-up for modems Full-duplex start-up for modems

1993-04-27

1994-10-04

Safourek, Benedict V.

Multiplex communications

Wide area network

Packet switching

375121, H04L 2908

Patent

active

053532805

ABSTRACT:
The start-up time for typical current generation modems for full-duplex data transmission over the Public Switched Telephone Network (PSTN) as specified in CCITT Recommendations V.32 and V.32bis is about 4 to 8 seconds. This invention reduces that start-up time to about 0.5 to 1 second by applying interleaved and overlapping sending and receiving operations of two connected modems, the calling modem and the answering modem. Both modems send and receive simultaneously in a predetermined sequence at different frequency ranges, channel probing tones (e.g. for evaluating the channel bandwidth), repetitive identification messages (e.g. for determining reference times, identifying modulation rates and center frequencies), repetitive response messages (e.g. for transmitting the determined bandwidths and reference times to the other modem and determining round-trip delays), and training sequences (e.g. for determining echoes, frequency shifts, and receiver settings). The modems then transmit data in a full-duplex mode at the modulation rate and center frequency appropriate for the channel and at an initial bit rate. The maximum achievable bit rate may be achieved later during the full-duplex transmission through rate negotiations.

REFERENCES:
patent: 4680781 (1987-07-01), Amundson et al.
patent: 4953210 (1990-08-01), McGlynn et al.
patent: 5023869 (1991-06-01), Grover et al.
patent: 5214637 (1993-05-01), Sridhar et al.
IEEE Transactions on Communications vol. 38, No. 5, May 1990, New York, USA: pp. 629-639 CIOFFI "A fast echo canceller initialization method for the CCITT V.32 modem".

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