Splitterless modem with integrated off-hook detector

Details Splitterless modem with integrated off-hook detector Splitterless modem with integrated off-hook detector

1999-02-04

2001-07-31

Woo, Stella (Department: 2643)

Telephonic communications

Telephone line or system combined with diverse electrical...

Having transmission of a digital message signal over a...

C379S093310, C379S093090

Reexamination Certificate

active

06269154

ABSTRACT:

This application is related to U.S. patent application Ser. No. 09/216,082 by Ibrahim, Polley, and Payne entitled “Residential Power Cutback for Splitterless DSL Operation,” filed Dec. 18, 1998, the entirety of which is incorporated herein by reference.
TECHNICAL FIELD
The invention relates generally to modems, and more particularly to a means by which a remote splitterless DSL modem maintains a high quality communications link to a central office modem by rapid detection of ring events, on-hook to off-hook transitions, on-hook to off-hook transitions preceded by ring events, and off-hook to on-hook transitions, followed by rapid configuration of modem operating parameters to minimize errors and disconnects.
BACKGROUND OF THE INVENTION
The increased use of telephone twisted pair wiring for data communications has resulted in a push for faster modems and improved signaling protocols compatible with the public switched telephone network (PSTN). Examples of such improved protocols include the emerging modem communication standards which have pushed the limit of transmission speeds close to 56 Kbps. Other examples include the emerging variety of digital subscriber line (DSL) communications protocols—including asymmetric digital subscriber line (ADSL), symmetric digital subscriber line (SDSL), hi-bit rate digital subscriber line (HDSL), and very high rate digital subscriber line (VDSL). Each DSL variant represents a different transmission speed over a different distance of copper pair wiring. Currently, industry is manufacturing communication equipment capable of implementing one or more of the DSL protocols. Modems, routers, line cards, and digital loop carrier systems are all examples of such equipment.
Theoretically, a DSL modem and a plain old telephone system (POTS) or other voice band device should be able to operate simultaneously over the same wire line pair since they use different frequency bands. Splitterless modems try to take advantage of this principle to transmit both voice band and digital DSL signals simultaneously. An example of such a splitterless modem architecture is disclosed in related U.S. patent application Ser. No. 09/216,082 (the “Related Application”), entitled “Residential Power Cut-back for Splitterless DSL Operation”.
The Related Application discloses a splitterless DSL modem capable of operating in at least two steady states: one during which normal DSL data transmission occurs and another in which voice transmissions occur simultaneously with DSL. The modem can also operate in a “transient” state that occurs in the brief time it takes to transition from one of the first steady states to another.
Unfortunately, the connection of a POTS to the same wire line pair as a DSL modem can suffer from several problems that occur during the presence of transient signals. One transient, called the “off-hook transient” can cause data disruptions and/or a disconnect from the line. Typically, the off-hook transient occurs as the POTS device coupled to the same wire line pair goes from the on-hook condition (handset down) to the off-hook condition (handset up) or state. Thus, the activation of the POTS device creates an off-hook transient that may appear as a spike or other signal form over the wire line pair coupling both the DSL modem and the POTS device to the central office. Other transients, including on-hook and ring signals may cause similar problems.
The Related Application discusses other changes in line conditions such as a change in the line impedance as the POTS changes states. While such changes in line condition can be short-lived, they oftentimes interrupt or disconnect the DSL modem from the line and cause data to be lost. It would therefore be advantageous to have a system and method of accommodating changes in line condition that occur as a POTS device coupled to the same line as the DSL modem goes from one steady state to another. A system and/or method of preventing data loss and/or disconnects due to transients would provide many benefits in the context of a DSL environment.
SUMMARY OF THE INVENTION
The present invention is a solution to the problems associated with transient signals that permits concurrent operation of a plain old telephone system (POTS) device, such as a facsimile, telephone or other similar voiceband device that operates within the traditional voiceband and a digital subscriber line (DSL) modem to prevent disconnects of the DSL modem, the unrecoverable loss of data, or other disruptions of a DSL session. The present invention thus enables a customer to plug the splitterless DSL modem in any normal telephone phone jack similar to the way voice band modems are installed today.
According to one embodiment, disclosed is a system for transient and ring signal detection in a splitterless DSL communications system in which a DSL modem and a POTS device operate together over the same wire line pair. The system includes a splitterless DSL modem at the remote end of a communications link with an integrated transient and ring detector circuit or other similar means of detecting transients and ring signals. The remote splitterless DSL modem includes a digital signal processor (DSP), a hybrid interface to the wire line pair, and a signal converter circuit. The splitterless DSL modem may also include various filters for appropriate bandwidth filtering.
In one embodiment, the transient and ring detector circuit is coupled to the hybrid interface on the analog side of the DSL modem. The transient and ring detector circuit may also be connected on the digital side of the signal converter thus providing for both digital and analog hardware as well as software implementations of the system.
Also disclosed is a splitterless DSL modem having a means of transient and ring signal detection. The splitterless DSL modem include a DSP, a hybrid interface to a twisted pair wire line connection, a D/A converter, an A/D converter, and various filters as appropriate for bandwidth filtering. The transient and ring detector circuit is coupled to the hybrid interface on the analog side of the DSL modem in one embodiment. The transient and ring detector may also be coupled on the digital side of the D/A and A/D converters.
Further disclosed is a method of preventing a splitterless DSL modem from disconnecting or losing data due to transients during a DSL communication session. The method can be employed across a link coupling both a voice band device and a DSL modem to a central office facility. The method includes the step of detecting when a ring signal from the central office is transmitted over the link. Next, if this is the first time a ring signal has been detected, the DSL modem computes a set of operating parameters corresponding to a first (typically the on-hook steady state) steady state of the voiceband device; otherwise, the DSL modem recalls a set of operating parameters previously computed and stored for the first steady state. Next, when a transition to a second steady state is detected, a set of operating parameters corresponding to a second steady state are recalled or, if this is the first time the transient has been detected, the operating parameters are generated for the first time, stored and utilized following detection of the transient signal. Likewise, operating parameters that correspond to the first steady state are stored, recalled and utilized when a transient preceding a change to the first steady state is detected.
The method may also include any one of the following steps: detecting the start of a transient and reacting immediately to prepare both remote and CO modems for further effects of the transients and for calculating a set of new operating parameters for the second steady state; alerting both the splitterless remote DSL modem and the modem in the central office that a transient has occurred; placing the central office modem on stand-by. As discussed in the Related Application, examples of the type of operating parameters which may be computer, stored, recalled and utilized include the equalizer filter coefficients, fram

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