Abstract:
A modem adapter is provided to adapt a modem to operate with a telephone system. The modem adapter includes a conductor detector, a voltage generator, and a dial-tone generator. The conductor detector is configured to detect live conductors on a telephone jack. The voltage generator is configured to generate an on-hook line voltage comparable to that normally expected by the modem and to deliver the generated on-hook line voltage to the modem. The dial-tone generator is configured to generate and deliver to the modem a first dial tone different from the second dial tone delivered by a telephone system to which the modem is attempting communication. A method for adapting a modem to a telephone system is also provided.

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention relates generally to modem adapters. More specifically, the present invention relates to a universal adapter for a modem, such as a PSTN modem, that allows for modem connectivity over a variety of telephone systems. 
   2. Background of the Invention 
   Computers manufactured for use in North America, and the communications programs that are intended to operate on these computers, typically expect certain line conditions for proper operation, for example, line voltage, presence of a physical RJ11 connection, dial tone, etc. In some locations both inside and outside of North America, some of these conditions may not be present. This can result in faulty operation, including complete failure, of computer modems. 
   In most North American countries, the PSTN connection is made via the inner two conductors on an RJ11 jack. Outside of these countries, this connection may be made via the outer two conductors. In this scenario no physical connection would be made between the computer modem and the actual PSTN connection. 
   Another problem arises from differences in dial tones. The dial tone cadence in some countries can be different enough from what is expected by the computer that the modem fails to detect the dial tone or may even incorrectly interpret the dial tone as a busy tone, among other problems. In either of these cases, or other similar situations whereby the modem is confused by an unfamiliar dial tone, the modem will not dial. 
   Some modems also require detection of line voltage within a certain range in order to qualify that the line condition is appropriate for dialing. Central office switches in countries outside North America may or may not confirm these requirements. Such discrepancies between North American and other countries can cause modem failure. 
   In many cases, computers used in hotels suffer from similar problems. A computer used at a hotel will often access a PSTN connection through a PBX, which can affect the dial tone cadence and line voltage. Either of these conditions can cause the modem to fail. 
   To overcome some of these problems various solutions have been attempted. For example, certain hardware is available that allows connectivity between different kinds of telephone jacks. These adapters, however, do not sense which of the conductors are “live,” nor do they switch the inner pair for the outer pair as may be required. 
   Software solutions have also been tried. For example, some communications programs allow for disabling of some of the dialing safeguards such as dial tone detection. This solution often results in inconsistent operation and may be difficult to locate within the program. Often times, even with such a solution in place, users do not have the requisite computer skills to implement the necessary software changes, resulting in poor modem performance. 
   BRIEF SUMMARY OF THE INVENTION 
   According to one exemplary embodiment, a modem adapter of the invention includes a conductor detector to detect live conductors on a telephone jack, a voltage generator to generate an on-hook line voltage comparable to that normally expected by the modem and to deliver the generated on-hook line voltage to the modem, and a dial-tone generator to generate and deliver to the modem a first dial tone different from the second dial tone delivered by a telephone system to which the modem is attempting communication. 
   According to another exemplary embodiment, a method for adapting a modem to a foreign telephone system includes detecting which conductors on a telephone jack are live and routing an active connection to the live conductors, generating an on-hook line voltage comparable to that expected by the modem and delivering the generated on-hook line voltage to the modem, and generating and delivering to the modem a dial tone different from the dial tone delivered by the foreign telephone system. 
   According to another exemplary embodiment, a modem adapter of the invention includes a main control unit, one or more comparators connected to the telecommunications line for sensing a live connector pair, a first switch for connecting to the live connector pair, and a second switch for connecting the modem to the telecommunications line. The main control unit generates and sends a dial tone different from a dial tone received from the telecommunications line to the modem and, upon detecting modem tones from the modem, sends a control signal to the second switch to connect the modem to the telecommunications line. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic functional diagram showing an exemplary embodiment of a universal modem adapter according to the present invention; and 
       FIG. 2  is a schematic diagram of an exemplary embodiment encompassing functions depicted in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  depicts a functional diagram of an exemplary modem adapter system  100  according to the present invention. System  100  is used to provide a connection between a phone jack  110  and a computer modem  150 . A telephone line  105  capable of supporting many different types of telephone connections found around the world is connected to jack  110 . Jack  110  is preferably an RJ11 connection or other phone jack capable of providing a PSTN connection to a central office switch for handling communication signals to and from a computer modem. 
   An analog switch  120  is connected to jack  110  to switch to a live, or active, Tip/Ring pair of the jack. With most phone jacks, there are four conductors. In some locations or localities the live connection includes the outside pair of conductors and in other locations or localities, the live connection includes the inside pair. Analog switch  120  is capable of connecting the signal to either of the two sets of conductors. 
   A pair of comparators  122  and  124  are provided to monitor the signal available at jack  110  and along with a main control unit (MCU)  130  are capable of determining which two of the four conductors available at jack  110  are “live”. As used herein, “live” is intended to mean connected to tip and ring at a central control office switch. Comparators  122  and  124  communicate with MCU  130 , which, in turn, communicates with switch  120 . MCU  130  processes the information from comparators  122  and  124  and sends a control signal to switch  120 . Upon receiving the control signal from MCU  130 , switch  120  then routes the active connection to the conductors it detected as being live. 
   Also connected to MCU  130  is a dial tone detect device  126 . Dial tone detect device  126  is provided between jack  110  and MCU  130  and may include a high impedance differential amplifier that feeds the analog dial tone signal to MCU  130  for analysis. As seen in  FIG. 1 , dial tone detect device  126  is positioned between switch  120  and MCU  130 . A second detecting device  128  that is used for detecting modem tones is provided on the modem side of the system to detect if modem tones are being generated by modem  150 . When modem tones are detected by device  128 , MCU  130  closes switch  160  to complete the connection between the computer and the PSTN line if this connection has not already been made. 
   Connected between switch  160  and modem  150 , is a voltage generator  130  capable of generating on-hook line voltages comparable to what a typical telephone company would provide. When activated, voltage generator  130  delivers this on-hook line voltage to the modem connection to “fool” the modem into thinking it is receiving its normal expected input of on-hook line voltage. In providing this voltage, generator  130  allows modem  150  to believe it is operating under its normal operating conditions. 
   One function provided by MCU  130  is to act as a dial-tone generator to provide a dial tone to modem  150  that is in accordance with dial tones for which modem  150  is programmed. When system  100  determines that modem tones are being generated, switch  140  is closed so that the dial tone generated by MCU  130  can be sent to modem  150  and allow modem  150  to operate in its expected environment. 
   In addition, an isolation device  160  is provided as part of the exemplary system. Isolation device  160  isolates modem  150  from the PSTN connection until MCU  130  determines that both sides of the communications session (e.g., the modem and the PSTN connection) are ready to be connected. Once system  100  determines that both the modem and PSTN connection are ready to be connected, MCU  130  sends a control signal to isolation device  160  to complete the circuit and allow for communication between the PSTN connection and modem  150 . In essence, system  100  sits between the PSTN connection on one side and modem  150  on the other side and isolates each side from the other by providing expected connection environments to each side. Once both sides have been properly set up to be connected, system  100  removes a barrier created by isolation device  160  and completes the connection. 
   A listening device  170  may also be included in the system for listing in on the audible tones active on the PSTN line. This listener preferably operates so as not to load down the PSTN line. 
   System  100  thus allows for a standard modem to connect to telephone systems around the world without the associated difficulties encountered with foreign systems. System  100  may also be modified so as to allow for a foreign modem to operate according to its expected conditions outside of its expected input conditions. For example, rather than being programmed to provide North American dial tones, etc., the system may be set up to provide European dial tones and operating conditions if a European modem is being connected to a foreign telephone system. 
     FIG. 2  depicts a schematic diagram of a modem connection system  200  according to one exemplary embodiment of the present invention. On the left side of  FIG. 2  is a PSTN connection that would be provided via a jack similar to that described above with respect to jack  110 . On the right side of  FIG. 2  sits a modem. System  200  sits between the PSTN connection and ultimately allows for connection of the modem to the PSTN connection. Where possible, similar reference numerals are used to refer to elements of  FIG. 2  that correspond with functional elements described in  FIG. 1 . 
   In the center of system  200  resides MCU  230 . MCU  230  is connected to a variety of detection and monitoring devices as well as to several switches to allow for proper connection of the modem to the PSTN connection. MCU  230  processes information sent to it and provides control signals to operate the various switches that ultimately connect the modem to the PSTN system. MCU  230  also provides some of the functionality described above with respect to “fooling” each side into believing it is operating under its expected operating conditions. 
   First, a pair of comparators  222  and  224  are provided to sense when line voltage is present on a given tip or ring connection and then feed that information to MCU  230  at a correct logic level. MCU  230  then processes that information and generates a control signal to be sent to switch  220 . Switch  220 , based on the control signal sent from MCU  230 , then connects to the proper live pair of connectors. 
   Also connected between MCU  230  and the PSTN connection is a high impedence differential amplifier  226 . Amplifier  226  feeds the analog dial tone signal to MCU  230  for analysis. On the other side of MCU  230  is connected another differential amplifier  228 , which is connected to the line going to/from the modem. Differential amplifier  228  acts in a similar capacity to amplifier  226 , but is used to detect modem tones. Once modem tones are detected, MCU  230  will need to expediently closes switches  240  and  260  to complete the connection between the computer modem and the PSTN line, if this has not already occurred. 
   Switch  240  is provided between the modem on one side and switch  260  and MCU  230  on the other side. Switch  240 , through DAC output  1  of MCU  230  feeds an artificial dial tone to the computer modem to simulate an off-hook condition. Switch  235  connects −48VDC to the tip connection of the computer modem to simulate a normal on-hook condition. 
   Three amplifiers  280 ,  282 , and  284  feed DTMF output from DAC output  2  of MCU  230  to the PSTN line. These amplifiers will typically be needed only if manual dialing is required. Audio speaker  270  and its associated amplifier  272  are connected to the line to allow for an audible indication of what is occurring on the line. This may be useful for a user to monitor what is occurring with the modem connection. 
   It may be possible to allow for hands free operation within system  200  by adding a 2:4 wire hybrid circuit, a microphone, and a microphone pre-amp as well as speakerphone switching circuitry. Such hands free operation and the associated componentry should be well known to those of skill in the art. A keypad  290  may also be provided to aid in manual interface with system  200 . 
   The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents. 
   Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.