High-speed MODEM operating over two or more telephone lines

Details High-speed MODEM operating over two or more telephone lines High-speed MODEM operating over two or more telephone lines

1999-05-04

2002-12-03

Yao, Kwang Bin (Department: 2662)

Multiplex communications

Communication techniques for information carried in plural...

Adaptive

C370S536000, C375S222000

Reexamination Certificate

active

06490295

ABSTRACT:

BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention generally relates to communication devices used within a communication system or network, and, more particularly, to a device for transceiving signals over multiple telephone lines or similar transceiving lines.
2. Present State of the Art
Throughout the ages man has initiated and developed numerous methods to communicate information. Communication in one form or another is used continuously, whether it be face to face conversation involving both body and verbal communication or through pictures, music, or art. With the advances in technology, however, individuals wish to spend more time communicating to discuss business, entertainment, and other daily events, but wish communication, in all its forms, to be more easily accomplished.
The modern society in almost every respect is crucially dependent on its ability to communicate signals or data, whether in digital or analog form, from one point to another. With the advances in technology the Internet has become ubiquitous for business and electronic commerce, education, entertainment, etc. As such, individuals, companies and other entities demand faster and faster communication speeds to manufacture, distribute and sell their products and services. In many situations, the speed of signal transmission or receiving (“transceiving”) directly impacts the quality of the services provided via the Internet, for example real-time video conferencing requires a minimum transceiving speed to be feasible.
The communication channels over which data is transceived is almost always the widespread public switched telephone network (PSTN). The core of the PSTN in the United States and other industrialized countries is completely digital, while the connection to the digital backbone is traditionally analog. A digital connection to the PSTN is possible through a service such as the Integrated Services Digital Network (ISDN). The ISDN provides 2 digital channels that are each capable of transceiving signals or data at a rate of 64,000 bits per second (“b/s”) and a control channel that can transceive signals or data at 16,000 b/s.
To use the ISDN, a user's central office (“CO”), such as a local telephone company's switching office, must be upgraded to provide lines and other equipment capable of transceiving signals. Therefore, the user must replace the analog on-premises equipment with digital equivalents, while the individual lines at the CO must be modified to carry digital data such as fiber optic cable. The installation costs and monthly charges for connectivity through an ISDN are significant, such that most users do not have a digital connection to the PSTN. Furthermore, ISDN digital connections are infrequently offered in rural and sparsely populated areas since it is difficult for telephone companies to recoup their investment in equipment and installation. In light of this, most users continue to have an analog connection to their CO.
The analog portion of the PSTN was designed to carry voice as inexpensively as possible. In particular, most analog connections to a CO are bandlimited and carry signals with a bandwidth ranging from about 200 Hz to about 3200 Hz in the United States and from about 300 Hz to about 3400 Hz in some other countries. The band ranges were chosen decades ago, as the narrowest possible band which could contain specific important characteristics of the human voice. Any signals outside these ranges are typically sharply attenuated.
To transceive data over an analog connection to the CO requires a modem. A modem performs two tasks: modulation, which converts the digital signal into an analog signal in the upstream direction, and demodulation, which converts the analog signal into a digital signal in the downstream direction. Most modems today convert a digital data stream into an analog signal within the bandwidths referenced in regard to the PSTN.
In recent years substantial progress has been achieved in modem design. While earlier modems could operate only at rates of 2400 b/s, modem speeds have increased up to 33,600 b/s. See International Telecommunications Union, Telecommunication Standardization Sector (ITU-T) Recommendation V.34, Geneva, Switzerland (1994) which is hereby incorporated as a reference.
Unfortunately rates of up to 33,600 b/s are insufficient for many of the newer applications envisioned with the advent of the Internet, such as video conferencing. While text transmission is fast, facsimile and especially still image transmission is slow. Furthermore, even with current sophisticated audio compression algorithms only low-quality video and audio is possible.
There are fundamental limitations that reduce the quality of data transmission in addition to lowering the maximum achievable data rate over the PSTN. The capacity of a communication channel on the PSTN, as discussed in C. Shannon, “A Mathematical Theory of Communication,” Bell System Technical Journal volume 27, pp. 379-423 and pp. 623-656, 1948, which is incorporated herein by reference, is given by
C
=
W
⁢
 
⁢
(
1
+
log
⁢
 
⁢
S
N
)
(
1
)
where C is the maximum achievable data rate in b/s, W is the bandwidth of the channel in Hertz, and S/N is the signal to noise ratio. For most of the PSTN of the United States S/N at present is below 2000 (approximately 30 dB). If we substitute these numbers into the above equation we can easily find out that C≈3000×12=36,000 b/s. Regardless of the sophistication of current signal processing algorithms or the speed of current processors, the maximum achievable data rate remains the same for a single PSTN line. It is clear that current modem standards have achieved a rate which is very close to the maximum possible. Thus the speed of modems is limited not by available technology, but by the limited bandwidth of the telephone system.
The bandwidth limitation becomes more acute when combined with the changing usage of the PSTN. In the past most of the traffic over the PSTN was voice, with very little percentage of the total traffic being data. At the beginning of the next century, however, the ratio of voice to data traffic is expected to become reversed; with more data traffic than voice traffic.
A significant portion of the increase data traffic is caused by the availability of the Internet access. Most users today connect to the Internet through their Internet Service Provider (“ISP”). ISPs usually have a high-bandwidth direct digital connection to the PSTN. Normally high-rate of communication is necessary in one direction only, from the ISP to the user (the downstream direction). This arrangement allows speeds of up to 56,000 b/s in the downstream direction. Currently modems capable of receiving data at speeds up to 56,000 b/s are available from several modem vendors, such as the 3Com Corporation, Santa Clara, Calif.
Many 56,000 b/s modems are capable of transceiving signals at various rates. Furthermore, the ITU-T V.90 standard for modems that can operate at rates up to 56,000 b/s actually envisions several possible modem data rates that vary based on the telephone line conditions, such as the effects of signal-to-noise ratio. Thus, unlike previous modem standards ITU-TV.90 does not specify a single data rate in the downstream direction. The allowed rates in the downstream direction range from about 28,000 to 56,000 in 1,333 b/s increments.
In normal communication sessions, two modems that are in communication will evaluate the telephone line conditions according to a line probing technique. Such line probing techniques are discussed for example in U.S. Pat. No. 5,515,398 entitled “Modem line probing signal techniques,” issued to Walsh et al. which is assigned to the assignee of the present invention. The superior the line conditions, the higher the data rate at which the two modems will choose to operate.
Line characteristics of the PSTN lines can change with time, however, and may be varied through influence of electric and magnetic fields that are in close proximity to the PSTN

Affiliated with

Also associated with

Rating

High-speed MODEM operating over two or more telephone lines does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with High-speed MODEM operating over two or more telephone lines, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High-speed MODEM operating over two or more telephone lines will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2955769