Telephonic communications – Telephone line or system combined with diverse electrical... – Having transmission of a digital message signal over a...
Reexamination Certificate
1998-06-09
2001-06-12
Woo, Stella (Department: 2643)
Telephonic communications
Telephone line or system combined with diverse electrical...
Having transmission of a digital message signal over a...
C379S093310
Reexamination Certificate
active
06246754
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to modems and more particularly to a mechanism for changing the modem technology that is selected by a pair of modems to be used as the basis for communications between the modems.
2. Description of the Relevant Art
In order to establish communications between two modems, it is necessary to define a framework within which the modems will communicate. This communication framework is related to the technologies employed by the respective modems. The process of selecting the proper framework is referred to as inter-working or handshaking. At the beginning of the handshaking process, the modems select a particular modem technology which will be used in the communications. Although a modem may employ a modern modem technology, most modems implement older technologies as well. This allows a given modem to be compatible with other modems which use the older technologies.
The selection of the modem technology to be used in communications between a pair of modems is referred to herein as negotiation. During the negotiation stage, one modem identifies the technology of the other. If one modem uses a newer technology, this modem will detect the older technology of the other modem and “fall back” or use the older technology. In this manner, the modems will typically select the most recent technology which is common to both modems.
Each modem technology allows communications to be conducted at a range of speeds, or bit rates. Typically, more recently developed technologies have higher allowable bit rates than older technologies. One of the bit rates allowed by the selected technology is selected by the modems for the connection. The bit rate selected by the modems is a function of the quality of the telephone line used for the connection—the more noise on the line, the slower the bit rate that will be chosen. The selection of the appropriate bit rate is referred to herein as training.
The handshaking process thus consists of a negotiation to select a modem technology and training to select the highest speed allowed by the selected technology and the line quality. At the conclusion of the handshaking process, the modems can begin transmitting data to each other (although it is not necessary that data be transferred—the modem connection may have been established in anticipation of future data transfers.)
Some modems are configured to re-enter the training stage if the condition of the telephone connection changes during communications between the modems. This process is referred to herein as re-training. While re-training can be used to select a speed suitable to the changed condition of the telephone line, the speed must be one allowed by the previously selected modem technology. The selected modem technology cannot be changed during re-training. In order to select a different modem technology, the telephone connection must be dropped and re-established, after which the entire handshaking process must be repeated. Changing the modem technology in the prior art thus incurs all of the overhead associated with establishing a new connection. There is also the possibility that there may not be a line available or that the quality of the connection may have more noise than the previous connection.
SUMMARY OF THE INVENTION
The present invention is directed to dynamically reconfigurable modems. That is, it allows a pair of modems which have already completed the handshaking process to re-enter negotiation and select a modem technology different from the one originally selected without having to disconnect and then re-establish the connection between the modems.
The invention includes means for one modem to interrupt data transfer and transmit a signal to the other modem indicating a request that a different modem technology be used. The request may be made as a result of changing line conditions, changing system demands, changing data transfer requirements, or other altered conditions under which the modems are operating. If the modem receiving the request accepts the request, both modems re-enter negotiation to select the best modem technology which suits the changed conditions. The modems are then re-trained to select the highest available bit rate within that technology which is appropriate to the line conditions. After the new modem technology and bit rate are selected, the modems resume transferring data.
REFERENCES:
patent: 4771417 (1988-09-01), Maxwell et al.
patent: 4905282 (1990-02-01), McGlynn et al.
patent: 4928305 (1990-05-01), Yui
patent: 5343515 (1994-08-01), Treffkorn
patent: 5450438 (1995-09-01), Landry et al.
patent: 5726765 (1998-03-01), Yoshida et al.
patent: 5802153 (1998-09-01), Sridhar et al.
patent: 5818913 (1998-10-01), O'Mahony
Boswell, Jr. Charles Ray
Cole Terry Lynn
Conley & Rose & Tayon P.C.
Kivlin B. Noäl
Legerity Inc.
Woo Stella
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