PATENT ABSTRACT
Standard telephone handset ports provide a bias voltage for any attached peripheral devices. The present invention provides bi-directional control signaling where telephone sets vary the bias voltage for detection by peripheral devices and where the peripheral devices provide short, load, and no-load conditions for detection by the telephone sets using the bias voltage.

PATENT DESCRIPTION
FIELD OF INVENTION 
     This invention relates to telephones and in particular to a signaling system between telephones and peripheral devices. 
     BACKGROUND OF THE INVENTION 
     Attaching a peripheral device to a telephone via the handset (or headset) port creates a number of difficulties. The most obvious difficulty is that the handset port was only designed with a very limit purposes i.e. receiving and sending voice respectively to a speaker and from a microphone. Thus, there is little or no control signaling through handset ports. This is not a problem if only handset sets were connected to the handset ports. However, this is increasingly not the case. 
     The most obvious example is that of a headset and a handset connected to a handset port of a telephone set. Thus, the question arises, how is the telephone set to determine which device, the headset or the handset, is active. Typically, the handset must be left off hook either by some mechanical device or by a secondary cradle. Gancarcik in U.S. Pat. No. 5,832,075 disclose a further solution by monitoring the telephone bias voltage of the handset ports. Thus, the telephone set takes action when a switch on the headset interrupts the bias. 
     The solution disclosed by Gancarcik works well with a passive device such as a headset. However, if one wishes to use more sophisticated peripheral devices such as an add-on speakerphone or a wireless headset, it is desirable for the telephone set to have bi-directional control signaling or communication with the peripheral devices. It is therefore desirable to provide a signaling system, which addresses, in part, some of the shortcomings of handset ports noted above. 
     SUMMARY OF THE INVENTION 
     Standard telephone handset ports provide a bias voltage for any attached peripheral devices. The present invention provides bi-directional control signaling where telephone sets vary the bias voltage for detection by peripheral devices and where the peripheral devices provide short, load, and no-load conditions for detection by the telephone sets using the bias voltage. 
     According to an aspect of the invention, there is provided a signaling system for a telephone set to communicate with a peripheral device connected thereto, the system comprising a circuit for detecting short, load, and no load conditions in the peripheral device; and a power circuit for toggling a bias voltage supplied by the telephone set to the peripheral device, wherein the peripheral device generates said short, load and no-load conditions in accordance with predetermined first patterns to communicate with the telephone set and the telephone set toggles the bias voltage in accordance with predetermined second patterns to communicate with the peripheral device. 
     According to another aspect of the invention, there is provided a method of communications a telephone set and a peripheral device connected thereto, the method comprising detecting short, load, and no load conditions in the peripheral device; and toggling a bias voltage supplied by the telephone set to the peripheral device, wherein the peripheral device generates said short, load and no-load conditions in accordance with predetermined first patterns to communicate with the telephone set and the telephone set toggles the bias voltage in accordance with predetermined second patterns to communicate with the peripheral device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in detail with reference to the accompanying drawings, in which like numerals denote like parts, and in which 
         FIG. 1  is a block diagram of a telephone set connected to a peripheral device in accordance with one embodiment of the invention; 
         FIG. 2  is a block diagram of a circuit for the telephone set  50  to vary bias voltage and to monitor conditions in the peripheral device; 
         FIG. 3  is a block diagram of a circuit for the peripheral device of  FIG. 1  to generate conditions and monitor bias voltage; 
         FIG. 4  are voltage diagrams (A) and (B) of input bias voltage V 2  and corresponding bias voltage V 1  respectively of  FIG. 1  showing signaling for initializing the peripheral device; 
         FIG. 5  are voltage diagrams (C) and (D) of the input bias voltage V 2  and the corresponding bias voltage V 1  respectively of  FIG. 1  showing signaling for terminating a call by the telephone set; 
         FIG. 6  are voltage diagrams (E) and (F) of the input bias voltage V 2  and the corresponding bias voltage V 1  respectively of  FIG. 1  showing signaling for terminating a call by the peripheral device; 
         FIG. 7  are voltage diagrams (G) and (H) of the input bias voltage V 2  and the corresponding bias voltage V 1  respectively of  FIG. 1  showing an example of signaling for the telephone set to communicate an event to the peripheral device; and 
         FIG. 8  is a block diagram of an alternate circuit for a peripheral device to generate conditions and monitor bias voltage. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , there is shown a block diagram of a telephone set  50  connected to a peripheral device  60  in accordance with one embodiment of the invention. A handset  52  and the peripheral device  60 , a conference unit, is connected to the telephone set  50  via a handset port  55 . 
     Referring to  FIG. 2 , there is illustrated a block diagram of a circuit  100  for the telephone set  50  to vary bias voltage and to monitor conditions in the peripheral device  60 . The circuit  100  comprises a power circuit  101  to vary a bias voltage V 1  between zero and 2.52 volts (D.C.) under control of a microprocessor (not shown), a first comparator circuit  102  for detecting a short circuit condition in the peripheral device from an input bias voltage V 2 , and a second comparator circuit  103  for detecting a load condition in the peripheral device from the input bias voltage V 2 . The combination of the first comparator circuit  102  and the second comparator circuit  103  further detects a no-load condition in the peripheral device from the input bias voltage V 2 . The input bias voltage V 2  is supplied to the peripheral device  60 , for example, an add-on speakerphone: the conference unit. A resistor R 2  is thus used to so that a voltage drop appears for the input bias voltage V 2  when a load is placed across the input bias voltage V 2  for the load condition. 
     The first comparator circuit  102  is configured by a resistance network R 3 , R 4  and R 5  to detect changes in the input bias voltage V 2  of 35 to 40% to indicate the short condition. The second comparator circuit  103  is also configured by the resistance network R 3 , R 4  and R 5  to detect changes in the input bias voltage V 2  of 3 to 4% to indicate the load condition. The configuration of the resistance network R 3 , R 4  and R 5  is well known in the art and is also disclosed in U.S. Pat. No. 5,830,075 by Gancarik. A resistor R 1  is provided to further differentiate the input bias voltage V 2  from the bias voltage V 1 , but is not necessarily required. Preferably, the circuit  100  is contained within a single integrated chip such as a Mitel (trade mark) MT 92303 dual CODEC. 
     Under the control of the microprocessor, the bias voltage V 1 , the output of the power circuit  100 , is switch ON and OFF for the telephone set  50  to signal the peripheral device  60 . The outputs of the first and the second comparator circuits  102 ,  103  is received by the microprocessor for the telephone set  50  to receive the signals of the peripheral device  60 . Thus, bi-directional control signaling between the telephone set  50  and the peripheral device  60  is provided. 
     Referring to  FIG. 3 , there is illustrated a block diagram of a circuit  200  for the peripheral device  60  of  FIG. 1  to generate the conditions and monitor bias voltage. The circuit  200  receives the input bias voltage V 2  and comprises a switch Pi  204  and a resistor Rp for providing the load condition, a switch Si  205  for providing the short condition, and a third comparator circuit  206  for monitoring changes in the input bias voltage V 2 . The peripheral device  60 , in the case of the conference unit, further comprises two blocking capacitors C and a microphone/speaker Sp. The switches Si and Pi are under the control of a peripheral microprocessor (not shown), a controller, for signaling the telephone set  50 . The output Bi of the third comparator circuit  206  is received by the controller to indicate signals from the telephone set  50 . 
     The controller closes switch Pi  204  to provide a load, the resistor Rp, across the input bias voltage V 2  to generate the load condition. The controller closes switch Si  205  to short the input bias voltage V 2  to thus generate the short condition. The third comparator circuit  206  monitors ON and OFF status of the input bias voltage V 2  for control signals from the telephone set  50 . 
     Referring to  FIG. 4 , there are voltage diagrams (A) and (B) of the input bias voltage V 2  and the corresponding bias voltage V 1  respectively of  FIG. 1  showing signaling for initializing the peripheral device  60 , the conference device. When the conference unit adjunct wishes to inform the telephone set  50  that it is ready for use (for example, on power up or on a user pressing an on/off switch on the conference unit), the controller of the conference unit closes switch Pi  204 , which generates the load condition or device presence signal  402  for the telephone set  50  to detect. The controller then closes switch Si  205  for 100 ms, which generates the short condition or a hook switch signal for the telephone set  50  to detect. At this point, the telephone set  50  is able to detect a headset as disclosed in U.S. Pat. No. 5,832,075 by Gancarcik. It is, however, not able to reliably detect between one headset and another peripheral device  60 . 
     The telephone set  50  then toggles the bias voltage V 1  in a first predetermined pattern (OFF/ON/OFF/ON/OFF/ON)  406 . The controller, by the third comparator circuit  206 , detects these changes and, in response, opens the switch Pi  204  for a 100 ms interval  408 , which generates a no-load condition in the peripheral device  60 , and then re-closes the switch Pi  204 . The telephone set  50  then knows that the peripheral device  60  is a conference unit connected to the handset port and signals the conference unit for operation by toggling the bias voltage V 1  in a second predetermined pattern (OFF/ON/OFF/ON)  410 . The conference unit upon detecting the signal of the second predetermined pattern  410  in the input bias voltage V 2  thus starts operating. 
     Referring to  FIG. 5 , there are voltage diagrams (C) and (D) of the input bias voltage V 2  and the corresponding bias voltage V 1  respectively of  FIG. 1  showing signaling for terminating a call by the telephone set  50 . The telephone set  50  thus toggles the bias voltage V 1  in a third predetermined pattern  510 . The peripheral device  60  upon detecting the changes in the input bias voltage V 2  accordingly to the third predetermined pattern thus terminates operation accordingly. 
     Referring to  FIG. 6 , there are voltage diagrams (E) and (F) of the input bias voltage V 2  and the corresponding bias voltage V 1  respectively of  FIG. 1  showing signaling for terminating a call by the peripheral device  60 . The peripheral device  60  closes the switch Si  205  for 100 ms  610  to request termination of the call and, in response, the telephone set  50  thus toggles the bias voltage V 1  in a third predetermined pattern  620  and terminates the call. The peripheral device  60  upon detecting the changes in the input bias voltage V 2  in the third predetermined pattern thus terminates operation accordingly. 
     Referring to  FIG. 7 , there are voltage diagrams (G) and (H) of the input bias voltage V 2  and the corresponding bias voltage V 1  respectively of  FIG. 1  showing an example of signaling for the telephone set  50  to communicate an event to the peripheral device  60 . In the peripheral device  60 , there is implemented an adaptive filter (not shown). Under certain conditions (such as, for example, generating local comfort DTMF tones), the telephone set  50  generates signals that could significantly disrupt the adaptive filter. Thus, when the telephone set  50  is instructed to generate a local comfort tone (for example, a DTMF key is pressed), the telephone set  50  signals to the peripheral device  60  to halt adaptation of coefficients by a toggle of the bias voltage V 1   710 . The telephone set  50  then waits an appropriate time interval  720  to ensure the adaptation in the peripheral device  60  is halted. The telephone set  50  then proceeds to generate the comfort tone  730 . Once the generation is complete it signals (with the same signal  710 ), the peripheral device  60  to resume adaptation. 
     Referring to  FIG. 8 , there is a block diagram of an alternate circuit for a peripheral device to generate conditions and monitor bias voltage. The alternate circuit  800  comprises a switch Pi  804  in series with a resistor Rp and a coupling transformer  808 , a switch  805 , and a fourth comparator circuit  806 . The switches and the comparator circuit of the alternate circuit  800  are operated in the same pattern as those in  FIG. 3 . The resistor Rp of  FIG. 8 , as a load, however can be of lower resistance than the corresponding part of  FIG. 3 . 
     It will be understood by those skilled in the art that many other commands can be exchanged between the telephone set and the peripheral device. The choice of using a start and only two signals from the peripheral device to the telephone set  50  was dictated by the desire to simplify the signaling as much as possible but more complex symbols are certainly possible. 
     It will be understood by those skilled in the art that the present invention can also be implemented in headset ports, or other ports, of telephone sets. 
     Although preferred embodiments of the invention have been described herein, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the invention or the appended claims.