Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M1/00—Substation equipment, e.g. for use by subscribers
  • H04M1/82—Line monitoring circuits for call progress or status discrimination
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M1/00—Substation equipment, e.g. for use by subscribers
  • H04M1/60—Substation equipment, e.g. for use by subscribers including speech amplifiers
  • H04M1/6033—Substation equipment, e.g. for use by subscribers including speech amplifiers for providing handsfree use or a loudspeaker mode in telephone sets
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M3/00—Automatic or semi-automatic exchanges
  • H04M3/22—Arrangements for supervision, monitoring or testing
  • H04M3/2272—Subscriber line supervision circuits, e.g. call detection circuits
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M3/00—Automatic or semi-automatic exchanges
  • H04M3/42—Systems providing special services or facilities to subscribers
  • H04M3/42314—Systems providing special services or facilities to subscribers in private branch exchanges
  • H04M3/42323—PBX's with CTI arrangements

Definitions

• This invention relates to detection of the activity state of a telephone handset (handset on-hook/off-hook), especially in Internet or LAN telephone communications.
• the terminal equipment used is usually a computer provided with multimedia characteristics and connected to a telecommunication network.
• the structure of the system is shown in Figure 1.
• the connection with the other party to the call is set up by way of a datacommunication network, such as a LAN or the Internet.
• Control operations of the call are performed by software in the computer, to which a mouse and a keyboard are connected.
• the outgoing speech is input by a separate microphone to an audio card, and the incoming speech is heard from loudspeakers connected to the audio card.
• the separate microphone and loudspeakers may also be replaced by a telephone handset used in the conventional telephone or by a headset, whereby the environment can not hear the incoming speech.
• CTI Computer Telephony Integration
• the programme reads the incoming speech from the signal received from the datacommunication network and controls the audio card so that it replays the speech from the loudspeakers.
• the programme also maintains information on the state of the call, such as if the terminal equipment is in a passive (on-hook) or an active (off-hook) call state, whether a call is going on, whether a call is coming in, whether dialling is going on etc., and through the datacommunication network it sets up a connection with the other participant or participants of the call.
• the CTI programme tells the audio card to send an alerting signal through the loudspeakers. Differing from the use of a conventional telephone, the incoming call is typically answered by announcing the call by using the mouse and clicking on the reply key on the CTI programme's display or by striking some predetermined key in the keyboard, such as the Enter key. If it is desired to change over the audio signals from the loudspeakers and from a separate "hands-free" microphone to a handset, this can be done with a separate mechanical switch. Usually, the headset is constantly active, and change-over to loudspeakers takes place when required by disconnecting the headset from its connectors or by using a separate switch belonging to the headset. When making an outgoing call, the target is chosen by using the computer's user interface, and if a confidential handset or headset call is desired, the signals are changed over to the handset by changing the position of the switch element.
• the peripheral equipment intended for these is already connected to these, for which reason they can not be used without problems.
• the audio output of the audio card is simply the loudspeaker/line output located in the same connector.
• Some special cards have a separate output connection for loudspeakers and for the line level, but these again can not be separately controlled by the programme.
• detection of the handset state to the programme controlling the call in the computer by using only the existing connections of the audio card is a state-of-the-art problem.
• the present invention aims at eliminating this problem. This objective is achieved with the method and equipment defined in the independent claims.
• the inventive idea is to cause in the microphone line such an echo of a measuring signal to be sent to the loudspeaker line, which is a response to the handset state.
• the measuring signal used may be a normal dial signal, a speech signal conducted to the loudspeaker line or a separate measuring signal to be summed into the speech signal.
• the arrangement according to the invention includes means for leaking the measuring signal from the handset's loudspeaker line to its microphone line and means responsive to the handset state for turning off the leak.
• the response or echo of the measuring signal sent to the loudspeaker line, which echo can be perceived from the microphone signal may be defined e.g. by the programme.
• the handset's loudspeaker signal is connected by way of an attenuator to the handset's microphone line.
• a relay or switch which is responsive to the handset's activity state and which connects the line to equipment earth, if the handset is on- hook. When the switch is open, an electric echo of short delay obtained through the attenuator can be detected in the audio card's microphone input.
• the electric loudspeaker signal arriving by way of the attenuator will not be relayed to the audio card's microphone output, and an electric echo is no longer found in the microphone input, but only an acoustic echo which has travelled on the air path and which is of longer delay and which also has different frequency characteristics.
• the handset's activity state is determined by measuring the delay or frequency characteristics of the echo signal on the audio card and by defining the handset as active, if the echo is found to contain an electric echo component.
• FIG. 1 shows a CTI system
• Figure 2 shows the principle of the invention
• Figure 3 shows an example of how the invention functions
• Figure 4 shows another example of how the invention functions
• Figure 5 shows hardware used for defining the handset state in accordance with the invention
• Figure 6 shows a call signal sent to a loudspeaker line and echo signals to be found on its microphone line, when the handset is on-hook and off-hook respectively.
• a measuring signal is supplied from an audio card's loudspeaker connection to loudspeaker line 201.
• the signal of loudspeaker line 201 is connected intentionally to microphone line 211 by an echo connection 203 dependent on the handset state 200.
• the connection is just an attenuation, but from the viewpoint of the invention the only essential thing is that, when turned on, the connection will produce a response of the loudspeaker line signal to the microphone line.
• This response which is dependent on the handset state is detected by a specification programme 204 which compares the signals of the loudspeaker and microphone lines with one another and which specifies the handset state according to the detected response.
• the handset state may also be identified just by listening to the microphone line.
• the microphone and the amplifier connected to it are mute, whereby the computer programme perceives first level background noise.
• the computer programme perceives a second higher-level signal and deduces that the handset is off- hook.
• FIG. 3 shows an example of how the invention is embodied in principle.
• the signal of the handset's loudspeaker line 301 is connected to the handset's microphone line 311 by a switch 303 causing an echo with a short delay.
• Switch 303 is preferably an attenuator, which controls a suitable echo strength so that it will not interfere with the outgoing speech signal but is still easily perceivable.
• Microphone line 311 has a handset state 300 responsive muting switch 304, which mutes the microphone line, when the handset is on-hook, that is, in an inactive state.
• Both the echo switching and the muting of the microphone line may be embodied either in the handset or in some equipment component which is separate from the handset, such as e.g. in the handset hook.
• all those echoes of the loudspeaker signal which can be perceived in the audio card's microphone input are such acoustic echoes caused by parallel equipment such as separate loudspeakers and microphones, which have a relatively long echo delay.
• the muting switch 304 will not mute the microphone signal.
• a short-delay echo component caused by intentional switching 303 of the echo and with frequency characteristics different from the acoustic echo is hereby perceived on the microphone line.
• the echo occurring on the microphone line is examined by the means 305 for specifying echo characteristics.
• the characteristics may be specified by a separate equipment component designed for the purpose, but it is preferable to specify the delay with the aid of a programme integrated with the CTI programme.
• the handset state is preferably specified based on echo characteristics measured by means 306 by comparing the measured characteristics, such as the delay or the echo strength, with limit values which are established in advance at predetermined frequencies. If the specification is based e.g. on a measurement of the echo delay time, the handset will be defined as being off-hook, if the delay is shorter than the established limit value, and if the delay is longer than the limit value, then the handset will be defined as being on-hook.
• FIG. 4 shows the principle of another example of the operation of the method of finding out the handset state in accordance with the invention.
• the signal of the handset's loudspeaker line 401 is connected to the handset's microphone line 411 by a switch 403 causing a short-delay echo and by a switch 404 responsive to the handset state.
• Both the switch 403 and the switch 404 may be embodied either in the handset or in some equipment component which is separate from the handset, such as e.g. in the handset hook.
• Switch 403 is preferably an attenuator, with which a suitable echo strength is controlled, so that it will not interfere with an outgoing speech signal, but is still easy to perceive.
• the attenuated signal of the loudspeaker line is allowed to cause a short-delay echo on the microphone line when the handset is on-hook and it is turned off by switch 404 when the handset is off-hook.
• the echo occurring on the microphone line is examined by means 405 for specifying the echo characteristics.
• the characteristics may be specified by a separate equipment component designed for the purpose, but they are preferably specified by a programme integrated with a CTI programme.
• the handset state is specified based on echo characteristics measured by specification means 406 preferably by comparing the measured characteristics with pre-established limit values. If e.g. the delay is short, the handset is defined as being on-hook, and if the delay is long, the handset is defined as being off-hook.
• FIG. 5 shows detection of the handset's activity state in a CTI system in accordance with the invention.
• the hook switch 2 used in handset 1 is e.g. a Reed relay or a mechanical switch, which will mute the handset by short-circuiting it to equipment earth.
• the switch may be either fixedly in the handset or separate from the handset, e.g. in the handset hook, provided that the microphone will be connected to earth when the handset is in its place.
• the microphone of the handset is connected by way of summing element 4 to such a microphone port 5 of the computer's audio card, which has a direct current supply connected through resistance 6 for an amplifier (an impedance matcher) in the microphone.
• hook switch 2 When the handset is on-hook, hook switch 2 will short-circuit the microphone to approximately zero volt against equipment earth.
• a separate hands-free microphone 7 is connected to the other input of the summer 4. If desired, the separate microphone 7 may be muted by switch 8 controlled by level detector 15.
• Earpiece 9 of the handset is connected by summer and attenuator element 10 to loudspeaker output 11 of an audio card.
• the loudspeakers 12 are connected by attenuator element 14 to the handset microphone, whereby a side tone is brought about, which is called an electric echo in this application.
• the level detector controls the switches 8 and 13 so that when the handset is on-hook and the microphone line in equipment earth, the separate microphone 7 and the loudspeakers 12 are active. When the handset is lifted off its hook, the voltage of the handset's microphone line will rise, and the level identifier will (if so desired) mute the loudspeakers and the separate microphone.
• the computer's call programme On perceiving an incoming call, the computer's call programme sends an alerting sound through the audio card's loudspeaker output to the loudspeakers and to the handset earpiece. In the earphone, an electric connection of side tone takes place to the handset microphone which is short-circuited.
• the computer programme will monitor the keyboard, the mouse and any signal arriving from the audio card's microphone.
• Figure 6 shows a signal Sk transmitted from the audio card to the loudspeaker line and signals Sm1 and Sm2 which are formed on the microphone line during different handset states. If the handset is on-hook, switch 2 in Figure 5 is closed and the handset microphone 3 is thus mute.
• a so-called acoustic echo signal Sm1 is perceived on the audio card's microphone line 5, which echo signal is caused acoustically by the ring sound Sk sent to the loudspeaker line from loudspeakers 12 to the separate microphone 7.
• the sound propagates in the air approximately one centimetre in 29 microseconds, so e.g. the delay D1 of an acoustic echo perceived from a microphone placed at a distance of 10 centimetres from the loudspeaker is approximately 290 microseconds.
• the length of the acoustic delay must be no less than one sample interval. If the chosen sampling rate is 8000 samples a second, which is used in conventional telephone technology, the additional delay caused by the acoustic path can be detected, if the distance between loudspeaker and microphone is longer than 1 dmm ⁇ 8000X * 29 - 10- 6 m ⁇ 4 ' 3cm - (1 )
• a call may be answered by using the keyboard or the mouse or by lifting the handset. That the handset is lifted can be noticed from a change in the ringing tone delay.
• the programme performed on a computer perceives the shortening of the delay of the ringing signal in the microphone input and from this it deduces that there is a wish to answer the call. Based on this, it may carry out the signalling required for starting the call in the direction towards the network. If it is desired to receive the incoming call as a loudspeaker call, then according to the state of the art, answering is done with the keyboard or with the mouse without lifting the handset, whereby the separate microphone and the loudspeakers or, correspondingly, the headset, will be active.
• the computer programme constantly performs measuring of the delay between the signal sent to the loudspeaker line and its echo signal received from the microphone line and it compares the result it obtains with the delay limits mentioned above.
• the delay measuring may be based e.g. on an analysis of the actual speech signal or on an analysis of the delay of a additional signal which is added to the speech signal and which is easy to detect.
• An example of a suitable additional signal is a sinusoidal signal, which is sent at a relatively high audio frequency and burst and which is easily filtered away from the speech signal. Suitable frequencies are e.g.
• Such signals in a frequency range of 5000 Hz - 20,000 Hz, which are filtered away in such a speech signal processing that filters away all frequency components having a frequency of more than 4000 Hz, but which are easy to detect from samples taken by the audio card at a higher sampling frequency.
• the programme When the programme finds that a delay which has been short (the handset off-hook, electric echo) becomes long (the handset on-hook, acoustic echo), it deduces that the handset has been placed on its hook.
• the programme triggers off a predetermined function which may be e.g. a call release, a suitable signal level adjustment for a loudspeaker call, a muted pause or any other state established by the programme's settings.
• the programme if it is found during a call that a long delay has become short, the programme deduces that the handset has been lifted off its hook and it may again carry out the steps defined for this situation, such as e.g. an adjustment of the signal level so that it is suitable for a handset call.
• the existence of an electric echo can be determined also in other ways than by measuring the delay, such as e.g. based on the different frequency characteristics of the electric echo and the acoustic echo.
• the acoustic echo has passed through the loudspeaker and microphone.
• the normally used capacitor microphones typically are very broadband, but the frequency band of ordinary loudspeakers connected to a multimedia computer is limited at the lower end to a range of 50...100 Hz.
• a low-frequency, e.g. 5 Hz, identifier signal the acoustic echo is filtered in the loudspeakers to a very low level.
• an intentionally caused electric echo is of a considerably higher level.
• This embodiment depends a little more than the embodiment based on echo delay specification on the characteristics of computer components, mainly the amplifier, the loudspeakers, the microphone and the audio card's input degree.

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Cited By (2)

Citations (3)

• 1997
  • 1997-06-27 FI FI972801A patent/FI103623B/fi active
• 1998
  • 1998-06-26 EP EP98929470A patent/EP0997025A1/en not_active Withdrawn
  • 1998-06-26 AU AU79220/98A patent/AU7922098A/en not_active Abandoned
  • 1998-06-26 WO PCT/FI1998/000563 patent/WO1999000963A1/fi not_active Application Discontinuation

Patent Citations (3)

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