Abstract:
A system, method, and apparatus for providing an embedded controller in a modem device for enabling data communication between different networks. Management and control capabilities for a gateway function are embedded into a communication controller of the modem device so as to enable direct connection between wired and wireless devices while eliminating a separate gateway controller. A single controller in the modem device, wired or wireless, manages its own designated communication functions and data exchange between the two different networks.

Description:
FIELD OF INVENTION 
   The present invention relates in general to data communication, and more particularly to a system, method, and apparatus for bridging two networks for data communication. 
   BACKGROUND OF INVENTION 
   Modems are typically used as a means for inexpensive data communications. A modem is referred to herein as a device to connect two hosts through a data link. Modems typically convert signals produced by one type of device, e.g., a computer, to a form compatible with another device, e.g., a telephone. Many applications use modems connected to a telephone line accessible through a public switched telephone network (PSTN) to pass data to an application controller, typically a central management server. PSTN refers to the international public telephone system that carries analog voice and data signals. The term modem stands for mo(dulator)-dem(odulator) since a stream of digital data or binary bits (0&#39;s and 1&#39;s) is modulated for transmission into an analog signal within the bandwidth of the PSTN and the received analog signal is demodulated back to digital data. 
   Applications providing communication between different types of networks typically include a gateway device for bridging the networks. For example, one network may comprise a local wireless linked network having one or more wireless modems and the other network comprises a wired telephone line link network having one or more wired modems.  FIG. 1  is a block diagram depicting an exemplary prior art system  10  for applications having wired modems and wireless modem devices for data communications. System  10  includes a microprocessor-based remote application micro-controller  12   a  for providing system control for a corresponding node  14   a  in system  10 . An identical remote application micro-controller  12   b  is shown for a node  14   b . The remote application micro-controllers  12   a ,  12   b  are also referred to herein as micro-controllers or “remote app” micro-controllers as shown in  FIG. 1 . System  10  includes a requesting application controller  30  which typically is a server that originates data requests to the rest of the system. 
   Each remote application micro-controller  12   a ,  12   b  typically includes a microprocessor, random access memory, non-volatile memory, and input and output signal interfaces (not shown). The remote application micro-controller  12   a ,  12   b  provide control based on an application program loaded therein through a loading means (not shown). The application program for each remote application micro-controller  12   a ,  12   b  is typically loaded as firmware stored in the non-volatile memory of the system, but is not limited to this form. 
   As shown in the system in  FIG. 1 , each micro-controller  12   a ,  12   b  interfaces with a corresponding wireless device  20   a ,  20   b  via a data interface bus which is typically a serial port  26   a ,  26   b . Each wireless device  20   a ,  20   b  has a pre-determined protocol to enable communication with its corresponding remote application micro-controller  12   a ,  12   b . The protocol may be a defined command set and syntax for every command, or through addressable register settings of each remote application micro-controller  12   a ,  12   b . Each remote application micro-controller  12   a ,  12   b  can be programmed to provide management and control via a corresponding I/O interface with other devices or sensors (not shown). 
   When data communication is required which is event driven or pre-scheduled, the micro-controller  12   a ,  12   b  typically issues commands to its connected wireless device to initiate a communication session with another wireless device. For applications using a wireless device for data communication, the controller  12   a ,  12   b  executes its stored application program for managing all necessary functions and for preparing reports to be forwarded to the higher level requesting application controller  30 . 
   The application controller  30  interfaces with a wired modem  28   b  via a data interface bus which is typically a serial port  26   e , as seen in  FIG. 1 . The wired modem  28   b  is not limited to a modem; any suitable wired device may be used. As seen in  FIG. 1 , the wired modem  28   b  is coupled to nodes  14   a  and  14   b  for communication via gateway  2 . Gateway  2  comprises a wireless modem  20   c , a wired modem  28   a , a wired to wireless gateway controller  24 , and serial ports  26   c ,  26   d . The wireless modems  20   a ,  20   b  communicate with a wireless modem  20   c  via a wireless link  16   a ,  16   b  using a corresponding antenna  22   a ,  22   b ,  22   c . The gateway controller  24  connects to wireless modem  20   c  and wired modem  28   a  via corresponding serial ports  26   c ,  26   d . The gateway controller  24  provides a bridge between the wireless modem  20   c  and the wired modem  28   a . The wireless modem  20   c  communicates to the wired modem  28   a  which in turn communicates via the PSTN to another wired modem  28   b.    
   The gateway controller  24  is typically implemented using a standalone processor for managing the two different data communication devices, i.e., the wireless modem and the wired modem. The standalone processor runs a program to manage the communication between the wired and wireless links. Gateway controller  24  enables data from a wireless linked device  20   a ,  20   b  to be passed to a remote application controller  30  through the telephone network, i.e., PSTN. Alternatively, gateway controller  24  enables data from telephone line linked equipment, i.e. wired modems  28   a ,  28   b  to be passed to the wireless networked devices  20   a ,  20   b ,  20   c.    
   The standalone processor includes two serial ports for managing the two different serial ports linked devices. A program running in the processor in gateway controller  24  typically passes modem “AT” commands to the two devices for initializing the devices and to prepare each device to accept communication from either side. The modem “AT” command, also known as “the AT command set” for modems is a set of predefined commands initially developed by the Hayes Micro Computer Company in the mid 1980&#39;s to control their proprietary modem equipment used for connecting data terminals to host computing devices over the public telephone network. The AT command set is now the industry standard adopted by most modem manufacturers for controlling modems and serial data transmission over telephone lines. The AT command set has a string of characters for each command, preceded by the prefix “AT”, for sending instructions to the modem. The original AT Command set has been augmented many times as modem speeds and feature sets have increased. Special commands have been added by many vendors to control new features of their wired and wireless communication products. 
   The gateway controller  24  enables the wired modem  28   a  and wireless modem  20   c  to exchange data through the gateway if both modems are enabled to connection through the gateway controller  24  to their counterpart modem. A drawback of the system shown in  FIG. 1  is that a separate gateway controller is needed to provide bridging between the wired and wireless network devices. 
   A need exists to reduce cost and device size by eliminating the separate gateway controller for bridging of two communication networks. A system, method, and apparatus are therefore needed which solves the above described drawbacks of the prior art. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method and corresponding system which overcomes the drawbacks of known systems and methods. 
   Broadly stated, the present invention provides a system for providing a virtual host for enabling data communication between different networks the system having an application controller and comprising a wired device in a wired network coupled to the application controller via a first bus; one or more wireless devices in a wireless network, each wireless device is coupled to a corresponding host controller via a corresponding bus, the wireless devices for communicating via a corresponding wireless link; a gateway module for enabling communication between the wired network and the wireless network comprising a wired modem for communicating with said wired device via said wired network; and a wireless module coupled to the wired modem via a serial port and comprising a wireless transceiver and communications controller; wherein the gateway module enables communication between each wireless device in the wireless network and the wired device in the wired network; such that the gateway module enables communication between the host controllers and the application controller. 
   Broadly stated, according to another embodiment, in a system having an application controller, a wired modem in a wired network coupled to the application controller via a first serial port, one or more wireless modems in a wireless network, each wireless modem is coupled to a corresponding host controller via a corresponding serial port, the wireless modems for communicating via a corresponding wireless link, a wired device for communicating with the wired modem via the wired network, a wireless module coupled to the wired device via a second serial port for enabling communication between the wired and the wireless network and between the host controllers and the application controller comprising a wireless transceiver; a user configurable communications controller; and programmable I/O pins connected to the second serial port; and wherein the wireless module provides for the switching of direction of its serial port signals for enabling connection to the wired modem. 
   Broadly stated, according to another embodiment, the present invention provides a method or enabling communication between the wired and the wireless network and between the host controllers and the application controller, in a system having an application controller, a wired device in a wired network coupled to the application controller via a first serial port, one or more wireless modems in a wireless network, each wireless modem is coupled to a corresponding host controller via a corresponding serial port, the wireless modems for communicating via a corresponding wireless link, a gateway module for enabling communication between the wired network and the wireless network having a wired modem for communicating with the wired device via a wired network link and a wireless module coupled to the wired modem via a second serial port and having a wireless transceiver and communications controller; comprising the steps of initializing the wireless module for preparing the gateway module to accept communication via the wireless link; managing communication for four operating modes of the gateway module, each mode representing a different connection state of the wired modem and the wireless module comprising managing communication for a first mode wherein the wired modem is not connected to the application controller and the wireless modem is not connected to one of the host controllers; managing communication for a second mode wherein the wired modem is connected to the application controller and the wireless module is not connected to one of the host controllers; managing communication for a third mode wherein the wireless modem is connected to one of the host controllers and the wired modem is not connected to the application controller; managing communication for a fourth mode wherein the wired modem is connected to one of the application controller and the wireless modem is connected to the host controller; selectively switching between the modes as a function of the connection state of the wired modem and the wireless module; responsive to a predetermined command transmitted from one of the wireless modems, selectively enabling the commanding wireless modem to communicate with the wired modem through the gateway module; and responsive to a predetermined command transmitted from the wired device, selectively enabling the wired device to communicate with the wireless module through the gateway module. 
   An advantage of the present invention is that it eliminates the need for a separate application microcontroller in a gateway application. In a preferred embodiment, the present invention enables direct connection of a wired modem to a wireless modem having a transceiver and a communications controller. The present invention enables management and control capabilities to be embedded into the communications controller of the wireless device so as to enable direct connection from the wireless device to the wired modem, eliminating the separate gateway controller. In other words, the present invention enables a single controller in the wireless device to manage wireless communication and modem operation so as to eliminate the gateway controller. As a result, equipment cost is reduced because there is no need for a separate gateway controller for bridging two networks. 
   These and other embodiments, features, aspects, and advantages of the invention will become better understood with regard to the following description, appended claims and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and the attendant advantages of the present invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a block diagram depicting an exemplary prior art system  10  for applications using wired and wireless modem devices for data communications; 
       FIG. 2  is a block diagram depicting a system, method, and apparatus for a virtual host according to an embodiment of the present invention; 
       FIG. 3  is a flow diagram  110  illustrating modes and the flow between modes according to the system, method, and apparatus in  FIG. 2 ; 
       FIGS. 4-7  are flow charts illustrating details regarding one of the operating modes in  FIG. 3  according to an embodiment of the present invention. 
   

   Reference symbols or names are used in the Figures to indicate certain components, aspects or features shown therein, with reference symbols common to more than one Figure indicating like components, aspects or features shown therein. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will now be described in more detail with reference to  FIGS. 2-7 . The term “wireless device” herein refers to a device for wireless data communication purposes that functions as the “carrier” for the system, method, and apparatus according to embodiments of the present invention. 
     FIG. 2  is a block diagram depicting a system  100  and method for a virtual host according to an embodiment of the present invention.  FIG. 2  also illustrates the data flow between the different devices in the system. System  100  in  FIG. 2  includes the elements of system  10  of  FIG. 1  except for gateway  102  replacing gateway  2 . Gateway  102  includes comprises a “wireless modem with virtual host”  120  coupled to the wired modem  28   a  via a serial port  126 . The “wireless modem with virtual host”  120 , also referred to herein as wireless virtual host modem, wireless module, or virtual host, comprises wireless modem  20   c  plus the virtual host functionality. In an alternative embodiment (not shown) the virtual host functionality is implemented in the wired modem  28   a  instead of the wireless modem  20   c.    
   Wireless virtual host modem  120  replaces the wireless modem  20   c  and the gateway controller  24 . According to an embodiment of the present invention, devices coupled to either side of gateway  102 , i.e., the PSTN  18  or the wireless links  16   a ,  16   b , can send AT commands to a modem on either side of gateway  102 . The present invention provides a pass-through function wherein a remote device, e.g., wireless modem  20   a , can send AT commands to a modem on the other side of gateway  102 , e.g., wired modem  28   a . For this example, the system  100  enables a wireless networked device  20   a  to first make a call to the wireless virtual host modem  120  that provides the gateway and connect to it. The system then enables the remote wireless modem, e.g.,  20   a ,  20   b , to send AT commands to the wired modem  28   a  to control it. The remote wireless modem can control wired modem  28   a  to call wired modem  28   b  linked to the application controller  30  in order to make a connection to the application controller  30 . According to this example, the pass-through function in wireless virtual host modem  120  enables a gateway connection for enabling a remote wireless modem, e.g.,  20   a ,  20   b , to communicate with the application controller  30 . In this example, the gateway linked path for communication is via a linked path that includes gateway  102 , wired modem  28   b , and serial port  26   e  to application controller  30 . More specifically, the path from wireless modem  20   a ,  20   b  includes the wireless link  16   a ,  16   b  to wireless virtual host modem  120 , serial port  126 , wired modem  287   a , wired device  28   b , serial port  26   e , and application controller  30 . Thus, wired devices connected to gateway  102  can communicate when both sides of gateway  102 , i.e., wired modem  28   a  and wireless virtual host modem  120 , are connected. 
   The initialization of the virtual host  120  prepares the gateway  102  to accept remote calls via a wireless link. An AT command ATSO=1 sent to a modem in gateway  102  will direct it to connect automatically when it receives a call. 
   The pass-through function is implemented in the firmware in the wireless virtual host modem  120 . The pass-through function according to the present invention enables a connected remote host to gain control of a modem on one side of the gateway  102  by calling the other side of the gateway  102 , i.e., either the wired modem  28   a  or wireless virtual host modem  120 , from a remote counterpart host and making the connection. For example, the present invention enables a micro-controller  12   a  to send AT commands to the wired modem  28   a  of the gateway  102  for controlling modem  28   a  if the wireless virtual host modem  120  of the gateway  102  has connected with the micro-controller  12   a . The present invention enables two host controllers in two different networks, e.g., application controller  30  and micro-controller  12   a  in  FIG. 1 , to exchange data through the gateway transparently if wired modem  28   a  and wireless virtual host modem  120  of the gateway  102  are connected with the corresponding host controller, i.e., application controller  30  and micro-controller  12   a.    
   A modem device typically has a serial port to communicate with a host computer or host controller. Devices which use serial ports for their communication are split into two equipment categories. The modem has been defined as a Data Communication Equipment (DCE) and the host computer or host controller is defined as a Data Terminal Equipment (DTE). In a standard serial port, signals are defined either ways. Table 1 shows a description and designation for an RS-232 standard serial port signal set having 9 signals/pins. 
   
     
       
             
             
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               # 
               Signal 
               Description 
               DTE 
               DCE 
             
             
                 
             
           
           
             
               1 
               DCD 
               Data Carrier Detect 
               Input 
               Output 
             
             
               2 
               RXD 
               Receive Data 
               Input 
               Output 
             
             
               3 
               TXD 
               Transmit Data 
               Output 
               Input 
             
             
               4 
               DTR 
               DTE Ready 
               Output 
               Input 
             
             
               5 
               GND 
               Ground 
               N/A 
               N/A 
             
             
               6 
               DSR(DCR) 
               DCE Ready 
               Input 
               Output 
             
             
               7 
               RTS 
               DTE enable DCE to send 
               Output 
               Input 
             
             
               8 
               CTS 
               DCE enable DTE to send 
               Input 
               Output 
             
             
               9 
               RI 
               Ring Indicator 
               Input 
               Output 
             
             
                 
             
           
        
       
     
   
   A modem is typically a Data Communication Equipment (“DCE”) device. The serial port signals for the wireless virtual host modem  120 , however, must be changeable so that the modem functions like a DTE device since for communication for the virtual host function the wireless virtual host modem  120  is connected directly to the wired modem  28   a  via serial port  126 , rather than being connected to wired modem  28   a  through the gateway controller  24 . According to this connection for the virtual host function, the wireless virtual host modem  120  functions as a DTE and the wired modem  28   a  as a DCE. For example, for the pass-through function, a remote calling party will see “through” the wired link and see the AT command interface of the wireless virtual host modem  120  if the remote calling party calls wired modem  28   a  and gets connected thereto. Thus, the pass-through function of the present invention enables wired modem  28   a  to control the wireless virtual host modem  120  in order to connect to another wireless modem device, e.g., wireless modem  20   a.    
   The wireless virtual host modem  120  must provides for switching its serial port signal direction from its DCE status to DTE status to enable connection to another wired modem device (DCE). According to the present invention, wireless virtual host modem  120  is software configurable and includes programmable I/O pins for providing the switching. For enabling the virtual host function of wireless virtual host modem  120 , all of its serial port signals reverse directions so as to change the serial port signals, i.e., in Table 1, of wireless virtual host modem  120  from DCE to DTE without changing the signal names. 
   The main virtual host functions of wireless virtual host modem  120 , other than serial port signal management and control, are provided through software as will be described in further detail below. The virtual host function of wireless virtual host modem  120  is provided through control of its initialization to configure its serial port as DTE&#39;s along with management and controls of four operational modes. 
   The four operational modes of the wireless virtual host modem  120  according to the embodiment of system, method, and apparatus of the present invention shown in  FIG. 2  are shown in more detail in  FIGS. 3-7 .  FIG. 3  is a flow diagram  110  illustrating modes and the flow between modes according to the system, method, and apparatus in  FIG. 2 . According to Mode  00  “standby” at node  130 , neither modem on either side of gateway  102  is connected. According to Mode  01  at node  140 , only the wired modem  28   a  side of gateway  102  is connected. According to Mode  10  at node  150 , only the wireless virtual host modem  120  side of gateway  102  is connected. According to Mode  11  at node  160 , both the wired modem  28   a  and wireless virtual host modem  120  are connected. 
     FIGS. 4-7  are flow charts illustrating details regarding one of the operating modes in  FIG. 3  according to an embodiment of the present invention.  FIG. 4  illustrates the flow  130  for the process according to Mode  00  in  FIG. 3 . The gateway  102  is in idle state in Mode  00  such that the gateway  102  is not connected to any of wired or wireless counterpart host controller, i.e.,  30 ,  12   a ,  12   b . In Step  131 , the Mode  00  process is entered. The mode designation comprises two bits having mode bit  0  as the least significant bit (LSB) on the right and mode bit  1  as the most significant bit (MSB) on the left. In Step  132 , the software checks a buffer A to determine if a “CONNECT” command is input to the wired modem side. In Step  133 , a determination is made as to whether a CONNECT string has been received on the wired modem side. In Step  134 , the LSB of the mode is set to 1 if buffer A indicates that a CONNECT string has been received on the wired modem side, that is, the mode bits change to Mode  01 , and the process proceeds to Step  135 . The process also proceeds to Step  135  if buffer A indicates that a CONNECT string has not been received on the wired modem side. In Step  135 , the software checks a buffer B to determine if a “CONNECT” string is input to the wireless virtual host modem  120  side of gateway  102 . In Step  136 , a determination is made as to whether a CONNECT string has been received on the wireless modem side. In Step  137 , the MSB of the mode is set to 1 if buffer B indicates that a CONNECT string has been received on the wireless modem side and the process proceeds to Step  138 . The process also proceeds to Step  138  if buffer B indicates that a CONNECT string has not been received on the wireless modem side. 
     FIG. 5  illustrates the flow  140  for the process according to Mode  01  in  FIG. 3 . In Mode  01 , the wired modem is connected to a remote host counterpart, i.e., application controller  30  via wired device  28   b , but the wireless virtual host modem  120  is not connected to a remote counterpart, i.e., wireless links  16   a ,  16   b , in Mode  01 . In Mode  01 , the pass-through function according to the present invention enables the remote host to be in control of the AT command interface of the wireless virtual host modem  120 . According to Mode  01 , all input from the remote host will be forwarded to an AT command handler of the wireless virtual host modem  120  for execution as an AT command for operating the wireless virtual host modem  120 . In Mode  01 , for example, the remote host may change certain settings of wireless virtual host modem  120 , attempt to initiate a connection, i.e., changing modes, to another wireless modem, e.g.,  20   a , or attempt a count-off command to collect information from multiple wireless modems within working distance. The count-off command is described in copending commonly assigned U.S. patent application Ser. No. 10/830,750, which is incorporated herein by reference. In Mode  01 , although the remote host can “attempt” to initiate a connection to wireless modem  20   a , for example, it should be appreciated that since the wireless virtual host modem  120  is not connected to wireless modem  20   a  in Mode  01 , a change in modes is required such that wireless virtual host modem  120  connects to wireless modem  20   a  before the “attempt” can be successful. 
   Turning to further details of the specific process steps for the process  140  for Mode  01  shown in  FIG. 5 , in Step  141 , the Mode  01  process is entered. In Step  142 , the port A input, i.e., on the wired modem side is forwarded to port B, i.e., on the wireless virtual host modem  120  side, while filtering the input in order to detect a “NO CARRIER” string for checking the connection state of the wired modem. In Step  143 , a determination is made as to whether a “NO CARRIER” string has been received, indicating that the wired modem has been disconnected. In Step  144 , the LSB of the mode is set to 0 if the “NO CARRIER” string has been received so as to cause the mode to change to Mode  00  and the process proceeds to Step  145 . The process also proceeds to Step  145  if a determination is made that a “NO CARRIER” string has not been received, i.e., remain at Mode  01 . In Step  145 , the port B input is filtered for detection of a “CONNECT” string, indicating the wireless virtual host modem  120  is connected, while discarding other strings. In Step  146 , a determination is made as to whether a CONNECT string has been received on the wireless modem side. In Step  147 , the MSB of the mode is set to 1 if the CONNECT string has been received on the wireless modem side and the process proceeds to Step  148 . The process also proceeds to Step  148  if a CONNECT string has not been received on the wireless modem side. 
     FIG. 6  illustrates the flow  150  for the process according to Mode  10  in  FIG. 3 . In Mode  10 , the wireless virtual host modem  120  is connected to another wireless counterpart, e.g.,  20   a . In Mode  10 , the wireless modem linked device, e.g.,  20   a  is in control of the AT command interface of the wired modem  28   a  in gateway  102  through use of the pass-through function. According to the pass-through function, all input from a host, i.e.,  12   a , linked via wireless link  16   b  through wireless modem  20   a  to gateway  102  is forwarded to the serial port of wired modem  28   a  for execution as an AT command for operating the wired modem  28   a . Thus, in Mode  10 , a wireless modem linked host, e.g.,  12   a , may change the settings of the wired modem  28   a  remotely, or attempt to initiate a connection with another remote server, i.e.,  30 , through the PSTN system. 
   Turning to further details of the specific process steps for the process  150  for Mode  10  shown in  FIG. 6 , in Step  151 , the Mode  10  process is entered. In Step  152 , the port B input, i.e., on the wireless virtual host modem  120  side, is forwarded to port A, i.e., on the wired modem side, while filtering the input in order to detect a “DISCONNECT” string for checking the connection state of the wireless virtual host modem  120 . In Step  153 , a determination is made as to whether a “DISCONNECT” string has been received, indicating that the wireless virtual host modem  120  has been disconnected. In Step  154 , the MSB of the mode is set to 0 if the “DISCONNECT” string has been received so as to cause the mode to change to Mode  00  and the process proceeds to Step  155 . The process also proceeds to Step  155  if a determination is made that a “DISCONNECT” string has not been received, i.e., remain at Mode  10 . In Step  155 , the port A input is filtered for detection of a “CONNECT” string, indicating the wired virtual  28   a  is connected, while discarding other strings. In Step  156 , a determination is made as to whether a CONNECT string has been received on the wired modem side. In Step  157 , the LSB of the mode is set to 1 if the CONNECT string has been received on the wired modem side and the process proceeds to Step  158 . The process also proceeds to Step  158  if a CONNECT string has not been received on the wired modem side. 
     FIG. 7  illustrates the flow  160  for the process according to Mode  11  in  FIG. 3 . In mode  11 , all data coming in to one side of the gateway  102  is sent from the other side. For example, if a data byte into gateway  102  comes from the connected telephone line modem  28   b , the data byte will be passed through the wireless virtual host modem  120  in gateway  102  and sent to wireless modems  20   a  or  20   b  connected to wireless virtual host modem  120  via wireless links  16   a ,  16   b.    
   Turning to further details of the specific process steps for the process  160  for Mode  11  shown in  FIG. 7 , in Step  161 , the Mode  11  process is entered. In Step  162 , the port A input, i.e., on the wired modem side is forwarded to port B, i.e., on the wireless virtual host modem  120  side, while filtering the input in order to detect a “NO CARRIER” string for checking the connection state of the wired modem. In Step  163 , a determination is made as to whether a “NO CARRIER” string has been received, indicating that the wired modem has disconnected. In Step  164 , the LSB of the mode is set to 0 if the “NO CARRIER” string has been received so as to cause the mode to change to Mode  10  and the process proceeds to Step  165 . The process also proceeds to Step  165  if a determination is made that a “NO CARRIER” string has not been received, i.e., remain at Mode  11 . In Step  165 , the port B input, i.e., on the wireless virtual host modem  120  side is forwarded to port A, i.e., on the wired modem  28   a  side, while filtering the input in order to detect a “DISCONNECT” string for checking the connection state of the wireless virtual host modem  120 . In Step  166 , a determination is made as to whether a DISCONNECT string has been received on the wireless modem side. In Step  167 , the MSB of the mode is set to 0 if the DISCONNECT string has been received on the wireless modem side and the process proceeds to Step  168 . The process also proceeds to Step  168  if a DISCONNECT string has not been received on the wireless modem side. In Mode  11 , if one of the connections drops off due to environmental, noise, reasons, etc., the other connection is dropped within a predetermined time interval (not shown). 
   According to an embodiment of the present invention, when filtering for the “DISCONNECT” or “NO CARRIER” string from the serial port input, the system, apparatus, and method includes detection of hardware signals, e.g., the DCD signal in Table 1, for determining if the connection has been lost. 
   Having disclosed exemplary embodiments, modifications and variations may be made to the disclosed embodiments while remaining within the scope of the invention as described by the following claims.