Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1997-12-16
2001-11-13
Luther, William (Department: 2664)
Pulse or digital communications
Transceivers
Modems
C375S231000, C375S366000
Reexamination Certificate
active
06317455
ABSTRACT:
TECHNICAL FIELD
This invention relates to data communications, and more particularly to data communications using modem devices requiring training prior to data transmission.
BACKGROUND
Data communications often involves the use of modulator/demodulators (modems) or modem-like devices (e.g. Digital Subscriber Line devices, 56 kbps digital “modems”, etc.) to communicate over a network system having at least one network link that uses an analog signaling scheme. For example, as shown in
FIG. 1
, two computers
1
,
2
may each have a modem link
3
,
4
(land-line or wireless) to the public switched telephone network
5
. Generally, at least part of the virtual circuit connecting the two computers
1
,
2
will be analog in nature.
A characteristic of analog links is that various components in the link, such as 2-wire to 4-wire hybrids, can cause echos in the link. Further, variations in analog component values can change operating characteristics of the link. Accordingly, under many current standards, such as the ITU V.34 standard defining a 33,600 kbps data signaling rate, modems conforming to the standard perform various training routines to set equalization and echo canceling parameters before commencing data transmission. For example,
FIG. 2
shows a bi-directional signaling diagram of one type of routine, in which modem A is conducting identification and line probings routines with a second modem B (not shown). Initially, modem A transmits a known training sequence, PSA, to modem B for a preset, minimum time period (for example, about 0.15 secs.). Using the PSA sequence, modem A trains its echo canceling circuitry while modem B trains its equalizer circuitry, in known fashion. After the PSA sequence is transmitted for no more than a preset, maximum time period, modem A transmits an end-of-sequenice marker, EOSA.
After receiving the EOSA marker, modem B transmits a known training sequence, PSB, to modem A for a preset, minimum time period (for example, about 0.15 secs.). Using the PSB sequence, modem B trains its echo canceling circuitry while modem A trains its equalizer circuitry, in known fashion. After the PSB sequence is transmitted for no more than a preset, maximum time period, modem B transmits an end-of-sequence marker, EOSB.
Under the V.34 standard, this initial round of training is at a relatively low rate, typically about 6,000 bps. A second round of training at a low-to-mid rate (e.g., about 12,000 bps) then takes place, in similar fashion. That is, after receiving the EOSB marker, modem A transmits a known training sequence, PSA′, to modem B for a preset, minimum time period (for example, about 0.15 secs.). Using the PSA′ sequence, modem A trains its echo canceling circuitry for a higher data rate while modem B trains its equalizer circuitry, in known fashion. After the PSA′ sequence is transmitted for no more than a preset, maximum time period, modem A transmits an end-of-sequence marker, EOSA′. Modem A is then fully trained, and may begin to transmit user data, DataA, at the full connected modem rate. Meanwhile, modem B performs this second round of training concurrently with training for modem A. That is, essentially immediately alter the EOSB marker, modem B transmits a known training sequence, PSB′, to modem A for a preset, minimum time period (for example, about 0.15 secs.). Using the PSB′ sequence, modern B trains its echo canceling circuitry for a higher data rate while modem A trains its equalizer circuitry, in known fashion. After the PSB′ sequence is transmitted for no more than a preset, maximum time period, modem B transmits an end-of-sequence marker, EOSB′. Modem B is then fully trained, and may begin to transmit user data. DataB, at the full connected modem rate.
Such standard training may take from 5 to 15 seconds for high-speed (e.g., 14,400 bps or faster) modems before user data can be transmitted or received by either modem. Such a delay is undesirable for “transaction modems”, which are typically used at point-of-sale (POS) terminals to conduct such transactions as check verification, credit card validation, etc. Slower modems (e.g., 300-1,200 bps) having faster training times have often been used as transaction modems, and can be satisfactory if transactions always involve a small amount of data (e.g., ten's of bytes of data, sufficient, for example, for validating a credit card number). However, such modems are undesirable if a substantial amount of data must be transmitted more than occasionally. Thus, more and more frequently, high-speed modems are being used for transaction applications. Similarly, such training times for standard modems adversely impacts the response time of modem access to the Internet.
One way of shortening the training time of high-speed modems is to only train for the minimum time allowed by a data signaling standard. However, this approach results in a lower data rate at the end of the training period than if training had been performed for a greater time period.
Thus, the inventors have determined that it would be desirable to make high-speed modems more efficient, particularly for transaction and Internet applications.
SUMMARY
The invention includes a system and method for modern information transfer before connection. The invention makes high-speed modems more efficient, particularly for transaction and Internet applications by providing for transmission of pre-connection user data during modem training. A training sequence for a modem in accordance with the invention may be summarized as follows:
(1) beginning training of the modem at a first data rate using a defined training sequence;
(2) after a selected amount of training transmitting pre-connection user data from the modem at up to the first data rate while continuing training of the modem;
(3) ending training;
(4) enabling transmission of user data at a full connected data rate of the modem.
The invention may also include the following training sequence before enabling transmission of user data at the lull connected data rate of the modem:
(5) beginning secondary training of the modem at a second data rate using a defined training sequence;
(6) after a selected amount of secondary training, transmitting pre-connection user data from the modem at up to the second data rate while continuing secondary training of the modem;
(7) ending secondary training.
In a typical implementation complying with the ITU V.34 standard, the time available for each modem to transmit pre-connection user data during training is about 1.6 secs. at about 6,000 bps in the initial training sequence, and about 1.8 secs. at about 12,000 bps in the secondary training sequence. Thus, a total of more than about 9,000 bits, and generally more than about 20,000 bits, and possibly more than about 31,000 bits, can be sent in each direction during the training cycles. This amount of data would often be adequate to complete many transactions or exchanges of Internet protocol setup information. Thus, the invention would allow a high speed modem to have response times comparable to lower speed modems while having the ability to communicate at much higher speeds for larger amounts of data.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
REFERENCES:
patent: 5394346 (1995-02-01), Milsom
patent: 5751701 (1998-05-01), Langberg et al.
patent: 5790594 (1998-08-01), Peng
patent: 5852631 (1998-12-01), Scott
patent: 5864714 (1999-01-01), Tal et al.
Rosenlof John
Williams Richard G. C.
3Com Corporation
Luther William
McDonnell Boehnen Hulbert & Berghobb
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