Abstract:
A method of controlling an audio output device at a user terminal connected to a communication network and executing a communication client is provided. The method comprises: establishing a connection between a user of the user terminal and a further user over the communication network; responsive to establishing the connection, analysing the status of the audio output device with the communication client; in the case that the communication client determines that the audio output device is in a muted state, controlling the audio output device to deactivate the muted state such that audio information transmitted from the further user via the connection can be heard by the user of the user terminal.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119 or 365 to Great Britain, Application No. 0811194.0, filed Jun. 18, 2008. The entire teachings of the above application are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    This invention relates to an audio device control method and apparatus. 
       BACKGROUND 
       [0003]    Packet-based communication systems allow the user of a device, such as a personal computer, to communicate across a computer network such as the Internet. Packet-based communication systems include voice over internet protocol (“VoIP”) communication systems. These systems are beneficial to the user as they are often of significantly lower cost than fixed line or mobile networks. This may particularly be the case for long-distance communication. To use a VoIP system, the user must install and execute client software on their device. The client software provides the VoIP connections as well as other functions such as registration and authentication. In addition to voice communication, the client may also provide further features such as video calling, instant messaging, voicemail and file transfer. 
         [0004]    One type of packet-based communication system uses a peer-to-peer (“P2P”) topology built on proprietary protocols. To enable access to a peer-to-peer system, the user must execute P2P client software provided by a P2P software provider on their computer, and register with the P2P system. When the user registers with the P2P system the client software is provided with a digital certificate from a server. Once the client software has been provided with the certificate, communication can subsequently be set up and routed between users of the P2P system without the further use of a server. In particular, the users can establish their own communication routes through the P2P system based on the exchange of one or more digital certificates (or user identity certificates, “UIC”), which enable access to the P2P system. The exchange of the digital certificates between users provides proof of the users&#39; identities and that they are suitably authorised and authenticated in the P2P system. Therefore, the presentation of digital certificates provides trust in the identity of the user. It is therefore a characteristic of peer-to-peer communication that the communication is not routed using a server but directly from end-user to end-user. Further details on such a P2P system are disclosed in WO 2005/009019. 
         [0005]    The correct configuration of the audio devices used to place a call over a VoIP system is a very important issue. A large proportion of users who have problems making VoIP calls report issues such as one caller not being able to hear the other, echo on the call, or background noise. Most frequently, these problems are technical problems related to the configuration of audio devices. Configuration problems such as these therefore result in large numbers of potential users ceasing to use a VoIP system. 
       SUMMARY 
       [0006]    The inventors have appreciated that a particular problem exists because the audio devices connected to the device of the user can be controlled by many different software elements executed on the device. For example, the audio devices can be independently controlled by the operating system, the client software and third party software. The inventors have found that this often leads to user confusion, as the user does not appreciate that setting the state of an audio device using, for example, the operating system affects the operation of the VoIP client software. The result of this is that users incorrectly configure their audio devices, and are consequently unable to make calls over the VoIP system. 
         [0007]    According to one aspect of the present invention there is provided a method of controlling an audio output device at a user terminal connected to a communication network and executing a communication client, comprising: establishing a connection between a user of the user terminal and a further user over the communication network; responsive to establishing the connection, analysing the status of the audio output device with the communication client; in the case that the communication client determines that the audio output device is in a muted state, controlling the audio output device to deactivate the muted state such that audio information transmitted from the further user via the connection can be heard by the user of the user terminal. 
         [0008]    Because the communication client determines that the user wishes to proceed with communication with the further user (as the connection is established) and determines that the audio output device is muted, a situation is detected which would otherwise prevent the communication from continuing. The communication client changes the settings of the audio output device to counter this, and, hence the communication client enables the communication between the user and further user to proceed successfully, with the user being able to hear the further user. The communication client therefore prevents a communication problem from being experienced by the user, thereby improving the usability and quality of the communication system. 
         [0009]    In one embodiment, the step of establishing a connection comprises the user of the user terminal initiating a call with the further user. Preferably, the step of establishing a connection comprises the further user answering a call initiated by the user of the user terminal. 
         [0010]    Because the step of establishing the connection requires the call to be answered it is ensured that the call is actually taking place before any changes to the audio output device settings are made. The user must make a positive decision to answer the call, signalling an intention that the call should proceed, before the audio output device settings are altered. 
         [0011]    In another embodiment, the step of establishing a connection comprises the further user initiating a call with the user of the user terminal. Preferably, the step of establishing a connection comprises the user of the user terminal answering a call initiated by the further user. 
         [0012]    As the audio output device is only un-muted after an incoming call is answered by the user, then the incoming call will not disturb the user by producing a ringing tone. This is advantageous, because if the user has deliberately muted the audio output device, the communication client should not ring when there is an incoming call. However, by answering the call the user has indicated a positive intention to continue with the call, thereby indicating that the communication client should determine whether to change the audio output device settings. 
         [0013]    In one embodiment, the call is a voice call. In another embodiment, the call is a video call. 
         [0014]    Preferably, the step of controlling the audio output device further comprises the communication client accessing user preference data stored at the user terminal to determine whether the communication client is permitted to control the audio output device. In the case that the communication client is permitted to control the audio output device, the method comprises the communication client deactivating the muted state automatically without interaction from the user of the user terminal. In the case that the communication client is not permitted to control the audio output device, the method comprises displaying a notification message in a user interface of the user terminal such that the user is notified that the audio output device is in a muted state. 
         [0015]    By displaying the notification message to the user, the user is informed of the muting of the audio output device, such that it becomes clear that the output audio device settings, which can be controlled through the OS, can affect the operation of the communication client. This increases user awareness and avoids similar problems occurring in subsequent calls. 
         [0016]    Preferably, the notification message comprises a user-operable control arranged to deactivate the muted state upon actuation by the user. Preferably, the method further comprises the step of removing the notification message from the user interface after the notification message has been displayed for a predetermined length of time if the user-operable control is not actuated by the user. 
         [0017]    Preferably, the step of controlling the audio output device to deactivate the muted state comprises storing an indicator that the status of the audio output device has been changed in a storage means. Preferably, the method further comprises the steps of detecting at the communication client that the connection between a user of the user terminal and a further user has been terminated; reading the indicator from the storage means; and restoring the status of the audio output device to the muted state if the status of the audio output device has been changed. 
         [0018]    By restoring the muted state of the audio output device, it can be ensured that the removal of the mute setting only occurs for the duration of the call. The user has given his approval to un-mute the audio output device for the purposes of the call over the communication system, but not for any other purpose. The restoration of the mute setting prevents user being disturbed by the user terminal subsequently emitting sounds, for which has not explicitly selected to un-mute the audio output device. 
         [0019]    Preferably, the communication network is a packet-based communication network. In one embodiment, the packet-based communication network is a voice over internet protocol communication network. In another embodiment, the packet-based communication network is a peer-to-peer communication network. 
         [0020]    According to another aspect of the present invention, there is provided a user terminal, comprising: means for connecting the user terminal to a communication network; an audio output device; and processing means arranged to execute a communication client, wherein the communication client is arranged to establish a connection between a user of the user terminal and a further user over the communication network, analyse the status of the audio output device responsive to establishing the connection, and, in the case that the communication client determines that the audio output device is in a muted state, control the audio output device to deactivate the muted state such that audio information transmitted from the further user via the connection can be heard by the user of the user terminal. 
         [0021]    According to another aspect of the present invention there is provided a computer program product comprising program code means which, when executed by a computer implement the steps according to the above-described method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    For a better understanding of the present invention and to show how the same may be put into effect, reference will now be made, by way of example, to the following drawings in which: 
           [0023]      FIG. 1  shows a P2P VoIP communication system; 
           [0024]      FIG. 2  shows a user interface of a VoIP communication client; 
           [0025]      FIG. 3  shows a user terminal on which is executed a communication client; 
           [0026]      FIG. 4A  shows an operating system audio control; 
           [0027]      FIG. 4B  shows an audio properties window; 
           [0028]      FIG. 5  shows a flowchart for handling the control of output audio devices; 
           [0029]      FIG. 6  shows a communication client options window; and 
           [0030]      FIG. 7  shows a user interface of a VoIP communication client with a notification message. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Reference is first made to  FIG. 1 , which illustrates a P2P communication system  100 . Note that whilst this illustrative embodiment is described with reference to a P2P communication system, other types of communication system could also be used, such as non-P2P, VoIP systems. A first user of the communication system (named “Tom Smith”  102 ) operates a user terminal  104 , which is shown connected to a network  106 . Note that the network  106  utilises a communication system such as the Internet. The user terminal  104  may be, for example, a personal computer (“PC”) (including, for example, Windows™, Mac OS™ and Linux™ PCs), a personal digital assistant (“PDA”), a mobile phone, a gaming device or other embedded device able to connect to the network  106 . The user device is arranged to receive information from and output information to a user of the device. In a preferred embodiment of the invention the user device comprises a display such as a screen and a keyboard and mouse. The user device  104  is connected to the network  106  via a network interface  108  such as a modem, and the connection between the user terminal  104  and the network interface  108  may be via a cable (wired) connection or a wireless connection. 
         [0032]    The user terminal  104  is running a communication client  110 , provided by the software provider. The communication client  110  is a software program executed on a local processor in the user terminal  104 . The user terminal  104  is also connected to a handset  112 , which comprises a speaker and microphone to enable the user to listen and speak in a voice call. The microphone and speaker does not necessarily have to be in the form of a traditional telephone handset, but can be in the form of a headphone or earphone with an integrated microphone, or as a separate loudspeaker and microphone independently connected to the user terminal  104 . 
         [0033]    An example of a user interface  200  of the communication client  110  executed on the user terminal  104  of the first user  102  is shown illustrated in  FIG. 2 . The client user interface  200  displays the username  202  of “Tom Smith”  102  in the communication system, and the user can set his own presence state (that will be seen by other users) using a drop down list by selecting icon  204 . 
         [0034]    The client user interface  200  comprises a button  206  labelled “contacts”, and when this button is selected the contacts stored by the user in a contact list are displayed in a pane  209  below the button  206 . In the example user interface in  FIG. 2 , four contacts of other users of the communication system are shown listed in contact list  208 . Each of these contacts have authorised the user of the client  110  to view their contact details and presence state and mood message information. Each contact in the contact list has a presence status icon associated with it. For example, the presence status icon for “Kevin Jackson”  210  indicates that this contact is “online”, the presence icon for “Maria Jones”  212  indicates that this contact is “away”, the presence icon for “Roger White”  214  indicates that this contact&#39;s state is “do not disturb”, the presence icon for “Sarah Rowling”  216  indicates that this contact is “offline”. Further presence indications can also be included. Next to the names of the contacts in pane  209  are mood messages  220  of the contacts. 
         [0035]    The contact list for the users (e.g. the contact list  208  for “Tom Smith”) is stored in a contact server (not shown in  FIG. 1 ). When the client  110  first logs into the communication system the contact server is contacted, and the contact list is downloaded to the user terminal  104 . This allows the user to log into the communication system from any terminal and still access the same contact list. The contact server is also used to store the user&#39;s own mood message (e.g. a mood message  222  of the first user  102 ) and a picture  224  selected to represent the user (known as an avatar). This information can be downloaded to the client  110 , and allows this information to be consistent for the user when logging on from different terminals. The client  110  also periodically communicates with the contact server in order to obtain any changes to the information on the contacts in the contact list, or to update the stored contact list with any new contacts that have been added. Presence state information is not stored centrally in the contact server. Rather, the client  110  periodically requests the presence state information for each of the contacts in the contact list  208  directly over the communication system. Similarly, the current mood message for each of the contacts, as well as a picture (avatar—e.g. picture  226  for “Kevin Jackson”) that has been chosen to represent the contact, are also retrieved by the client  110  directly from the respective clients of each of the contacts over the communication system. 
         [0036]    Calls to the users in the contact list may be initiated over the communication system by selecting the contact and clicking on a “call” button  228  using a pointing device such as a mouse. Referring again to  FIG. 1 , the call set-up is performed using proprietary protocols, and the route over the network  106  between the calling user and called user is determined by the peer-to-peer system without the use of servers. For example, the first user “Tom Smith”  102  can call a second user “Kevin Jackson”  114 . 
         [0037]    Following authentication through the presentation of digital certificates (to prove that the users are genuine subscribers of the communication system—described in more detail in WO 2005/009019), the call can be made using VoIP. The client  110  performs the encoding and decoding of VoIP packets. VoIP packets from the user terminal  104  are transmitted into the network  106  via the network interface  108 , and routed to a computer terminal  116  of the called party  114 , via a network interface  118 . A client  120  (similar to the client  110 ) running on the user terminal  116  of the called user  114  decodes the VoIP packets to produce an audio signal that can be heard by the called user using the handset  122 . Conversely, when the second user  114  talks into handset  122 , the client  120  executed on user terminal  116  encodes the audio signals into VoIP packets and transmits them across the network  106  to the user terminal  104 . The client  110  executed on user terminal  104  decodes the VoIP packets, and produces an audio signal that can be heard by the user of the handset  112 . 
         [0038]    The VoIP packets for calls between users (such as  102  and  114 ) as described above are passed across the network  106  only, and the public switched telephone network (“PSTN”) ( 124 ) is not involved. Furthermore, due to the P2P nature of the system, the actual voice calls between users of the communication system can be made with no central servers being used. This has the advantages that the network scales easily and maintains a high voice quality, and the call can be made free to the users. Additionally, calls can also be made from the client ( 110 ,  122 ) using the communication system to fixed-line or mobile telephones ( 126 ), by routing the call to the PSTN network ( 124 ). Similarly, calls from fixed-line or mobile telephones ( 126 ) can be made to the communication system via the PSTN ( 124 ). 
         [0039]    In addition to making voice calls, the user of the client  110  can also communicate with the users listed in the contact list  208  in several other ways. For example, an instant message (also known as a chat message) can be sent by typing a message in box  230  (as shown in  FIG. 2 ) and sending it by selecting the “send message” button  232 . Additionally, the first user  102  can use the client  110  to transmit files to users in the contact list  208 , send voicemails to the contacts or establish video calls with the contacts (not illustrated in  FIG. 2 ). 
         [0040]      FIG. 3  illustrates a detailed view of the user terminal  104  on which is executed client  110 . The user terminal  104  comprises a central processing unit (“CPU”)  302 , to which is connected a display  304  such as a screen via a display interface  305 , an input device such as a keyboard  306  and a pointing device such as a mouse  308  connected via an interface  309  such as USB. An output audio device  310  (e.g. a speaker) and an input audio device  312  (e.g. a microphone) are connected via an audio interface  313 . The output audio device  310  and input audio device  312  may be integrated into a handset  112  or headset, or may be separate. The CPU  302  is connected to a network interface  108  as shown in  FIG. 1 . 
         [0041]      FIG. 3  also illustrates an operating system (“OS”)  314  executed on the CPU  302 . Running on top of the OS  314  is a software stack  316  for the client  110 . The software stack shows a protocol layer  318 , a client engine layer  320  and a client user interface layer (“UI”)  322 . Each layer is responsible for specific functions. Because each layer usually communicates with two other layers, they are regarded as being arranged in a stack as shown in  FIG. 3 . The operating system  314  manages the hardware resources of the computer and handles data being transmitted to and from the network via the network interface  108 . The client protocol layer  318  of the client software communicates with the operating system  314  and manages the connections over the communication system. Processes requiring higher level processing are passed to the client engine layer  320 . The client engine  320  also communicates with the client user interface layer  322 . The client engine  320  may be arranged to control the client user interface layer  322  to present information to the user via the user interface of the client (as shown in  FIG. 2 ) and to receive information from the user via the user interface. 
         [0042]    There are several reasons why users of a communication system such as that shown in  FIG. 1  have problems making calls. These are often technical problems related to the configuration of the audio devices. Frequently, the cause is user mismanagement of audio devices and the lack of call environment optimisation in the client  110 . Thus, users (particularly new or non-technical users) often give up and stop using the communication system. By enhancing the audio device handling in a smart and automated way, the users have an increased likelihood of making successful calls using the communication system, and therefore are more likely to continue using it. 
         [0043]    A particular problem exists because the audio devices ( 310 ,  312 ) of the user terminal  104  can be controlled by several different software elements executed on the user terminal  104 . For example, the state of the audio devices ( 310 ,  312 ) can be controlled by both the operating system  314  and the communication client  316 . In addition, there may be further software elements (not shown in  FIG. 3 ) executed on the user terminal  104  that can also set the state of the audio devices. This can lead to confusion on the part of the user, as he may set the state of an audio device using, for example, the operating system control, and this will affect the operation of the communication client  316 . 
         [0044]    For example, the user  102  of the user terminal  104  can select an operating system control, such as that illustrated in  FIG. 4A , by selecting an icon  402  provided by the operating system. Selecting the icon  402  displays a pop-up window  404  that allows the user to set the output audio device  310  (e.g. the speakers, headphones or handset) to be muted by actuating a check box  406 . The user may select this control to prevent the user terminal from producing any sounds, for example when in a meeting or other quiet location. The mute control  406  applies to the user terminal as a whole, and therefore mutes the output audio device  310  for other applications executed on the user terminal  104 . In particular, the mute control  406  will mute the output audio device  310  when the communication client  110  is used. 
         [0045]    Therefore, if the user  102  forgets that he has muted the output audio device  310  using the control  406 , and later attempts to make a call using the communication client, then he will be unable to hear what the called party is saying. An inexperienced or non-technical user can interpret this as being a problem with the communication client  110  or the communication system, and may not appreciate that this is due to an operating system setting. 
         [0046]    The output audio device  310  can also be muted using other controls, such as from an audio properties window  408  as illustrated in  FIG. 4B , which includes a check box  410  to mute the speakers. In addition, third party software (i.e. not the OS  314  or the communication client  110 ) can also control the output audio device  310 . It can therefore be seen that the muting of output audio devices can happen very readily in the user terminal  104 , and the consequence of this is significant if the user does not appreciate that this affects communication over the communication system. 
         [0047]      FIG. 5  illustrates a flow chart for a technique of automating the control of output audio devices in the case that they are muted, and for surfacing information about the audio devices in the UI of the client, so that users are better informed and can manage the audio devices in a more reliable and efficient manner. As a result, the users are much less likely to experience a call over the communication system in which they are unable to hear the called party. The call quality perceived by the users is therefore higher. 
         [0048]    The flowchart in  FIG. 5  applies in the circumstance where either the call is initiated by the user whose output audio device is muted, or where a call is received at the terminal of a user whose output audio device is muted. For example, referring to  FIG. 1 , if the terminal  104  of the first user “Tom Smith”  102  has an output audio device  310  muted, then the flowchart of  FIG. 5  is applied at the terminal  104  if “Tom Smith”  102  initiates a call to “Kevin Jackson”  114  (i.e. “Tom Smith” is the calling party and “Kevin Jackson” is the called party) or if “Tom Smith”  102  is called by “Kevin Jackson”  114  (i.e. “Kevin Jackson” is the calling party and “Tom Smith” is the called party). Note also that this technique applies equally to the case where a VoIP user is calling a PSTN user, or where a PSTN user is calling a VoIP user. 
         [0049]    In step S 502 , a call is initiated by the calling party. For the purposes of explaining  FIG. 5 , it is assumed that the output audio device  310  of “Tom Smith”  102  is muted. The calling party can either be “Tom Smith”  102  or “Kevin Jackson”  114 . In step S 504 , the call is answered by the called party. It is preferable that the process of  FIG. 5  is only executed once the call is answered. This is because this ensures that the call is actually taking place before any changes to the audio device settings are made. In other words, the user must make a positive decision to answer the call, signalling an intention that the call should proceed, before the audio settings are altered. 
         [0050]    This is particularly advantageous when a call is received at the terminal which has the muted output device (i.e. the called party has the muted output device). Because the terminal is muted, it will not produce any ringing tone when the incoming call is received. This is desirable, because if the user has deliberately placed the output audio device  310  onto mute, he would not wish for the communication client to ring when there is an incoming call. However, by answering the call (which the user can be alerted to by a message displayed on the screen rather than a ringing tone) the user has indicated a positive intention to continue with the call, thereby indicating that the communication client  110  should determine whether to change the audio settings. 
         [0051]    However, it should be noted that, in simpler embodiments, step S 504  can be omitted, and the process of  FIG. 5  can be executed as soon as the call is intitated rather than once it is answered. 
         [0052]    In step S 506  the client engine layer  320  of the communication client  10  analyses the state of the output audio device  310 . Specifically, the client engine  320  accesses the OS  314  to determine whether the output audio device  310  is set to be muted. If, in step S 508 , it is determined that the output audio device  310  is not muted, then the call can proceed as normal in step S 510 . If, however, it is determined in step S 508  that the output audio device  310  is muted, then in step S 512  the user preferences set by the user of the communication client  110  are analysed. Specifically, the client engine  320  accesses user preference information that is stored on the user terminal  104 . The user preferences in question here relate to whether the communication client  110  is permitted to make changes to the audio device settings. In particular, they relate to whether the communication client  110  is able to change the mute settings of the output audio device  310 . 
         [0053]    The user preferences are controlled through an options window  602 , as illustrated in  FIG. 6 . The options window  602  is accessed by the user selecting a menu item from the tools menu  234  shown in  FIG. 2 . A category of options is labelled “Audio settings”  604 , and when selected by the user the audio settings preferences  606  are displayed. In particular, this display allows the user to select the output audio device  310  using a drop-down menu  608 . In addition, a check-box  610  enables the user to select whether he would prefer the communication client  110  to automatically adjust the output audio device  310  settings. More specifically, this option determines whether the communications client  110  can change whether the output audio device  310  is muted. 
         [0054]    In step S 514 , if the check-box  610  has been selected by the user such that the communication client  110  can automatically adjust the output audio device settings, then in step S 516  the output audio device  310  is automatically un-muted. This enables the call to continue in step S 510  with the output audio device  310  un-muted so that the user is able to hear the other party in the call. Therefore, the communication client  110  has determined that the user wishes to proceed with the call (as it was answered), detected that the output audio device  310  was muted, which would prevent the call from continuing successfully, and automatically changed the settings of the output audio device  310  to counter this. In this way, the communication client  110  has prevented a problem with calling from being experienced by the user, thereby improving the user experience of the communication system. 
         [0055]    If, in step S 514 , it is determined that the user has not selected the check-box  610 , then the communication client  110  is not able to automatically adjust the output audio device settings. In this case, the communication client  110  displays a notification message to the user in step S 518 , instead of automatically un-muting the output audio device  310 . The user interface (client UI  322 ) of the communication client  110  displaying the notification message is shown in  FIG. 7 . 
         [0056]    The user interface shown in  FIG. 7  shows that a call with “Kevin Jackson” has started, as indicated by the presence of a call status bar  702 , and an “End call” button  704 . A notification message  706  is displayed at the top of the user interface to indicate to the user that the output audio device  310  of his terminal is muted. The message  706  reads “Your speakers are on mute”. Below this is a further message  708  which elaborates on the consequences of the audio device being muted. The further message  708  reads “You won&#39;t be able to hear anything. To unmute your speakers, click the button”. The purpose of the further message  708  is to educate the user, such that it becomes clear that the output audio device settings, which can be controlled through the OS, can affect the operation of the communication client  110 . This increases user awareness and avoids similar problems occurring in subsequent calls. 
         [0057]    Once the notification message  706  is displayed in the user interface, a timer is started in step S 520  of  FIG. 5 . The timer is used to control the length of time that the notification message  706  is displayed in the user interface. It is preferable that the notification message is not displayed indefinitely in the user interface, as it is possible that the user has deliberately placed the output audio devices on mute. 
         [0058]    If the user wishes to continue the call with the output audio device  310  un-muted, he can select an unmute button  710  displayed alongside the notification message  706 . Referring again to  FIG. 5 , in step S 522 , if the user has selected to unmute the output audio device  310  using the button  710 , then in step S 524  the output audio device  310  is un-muted by the communication client  110 . The user is then able to hear the other party in the call. When the unmute button  710  is selected by the user, the notification message  706  is removed from the UI. 
         [0059]    If the user wishes to dismiss the notification message  706  without un-muting the output audio device  310 , then he can select a close button  712 . If the close button  712  is selected in step S 526 , then in step S 528  the call proceeds, but with the output audio device  310  remaining muted. In this case, the user will not be able to hear any sounds from the other party. However, since the user has been notified of this, and has actively selected to remove the notification without un-muting the output audio device  310 , it can be assumed that this state is desired by the user. 
         [0060]    If the user does not select either the unmute button  710  or the close button  712 , then the notification message  706  will remain displayed in the UI until the timer started in S 520  expires. When a timeout occurs in step S 530  the notification message  706  is removed from the UI and the call continues in S 528  with the output audio device  310  in the muted state. 
         [0061]    The process illustrated in  FIG. 5  therefore provides a technique for avoiding the situation where the user has placed their output audio device  310  into a muted state, but wants to proceed with a call over the communication system. The communication client  10  will either automatically unmute the output audio device  310  (if permitted by user preferences) or will inform the user of the situation, thereby allowing them to unmute the device if desired. 
         [0062]    In addition to un-muting the output audio device  310  when a call is answered over the communication system, it is also preferable that the communication client restores the state of the output audio device  310  to be the same as before the call was answered. To achieve this, the communication client  110  can store a flag to indicate when the output audio device  310  us un-muted (i.e. in step S 516  or S 524  in  FIG. 5 ). When the call over the communication system is completed, the communication client  110  (specifically the client engine  320 ) reads the status of the flag to determine whether the output audio device  310  was changed from muted to un-muted. If it was, then the communication client changes the output audio device  310  back to the muted state. 
         [0063]    Restoring the state of the output audio device  310  is advantageous because the user may have deliberately set it to mute in order to prevent his user terminal from making sounds (e.g. if he is in a meeting or other quiet location). The user may choose to take a call over the communication system, and the output audio devices can be automatically un-muted to allow the call to proceed (as described above). However, if the output audio devices are not restored to a muted state then the user may be surprised if his user terminal subsequently begins emitting sounds, as he has not deliberately selected to un-mute the output audio device  310 . Therefore, by restoring the muted state of the output audio device  310 , it can be ensured that the removal of the mute setting only occurs for the duration of the call. The user has given his approval to un-mute the output audio device  310  for the purposes of the call over the communication system (in S 514  or S 522 ), but not for any other purpose. 
         [0064]    While this invention has been particularly shown and described with reference to preferred embodiments, it will be understood to those skilled in the art that various  5  changes in form and detail may be made without departing from the scope of the invention as defined by the appendant claims. In particular, the above technique was described with reference to a P2P VoIP communication system. The technique can equally be applied to non-P2P VoIP communication systems. In addition, the technique can be applied in the case where a VoIP user is either receiving a call from the PSTN,  10  or making a call to the PSTN network. Furthermore, the technique can also be used for devices that connect to a circuit switched network (such as the PSTN or mobile networks) if the output of such devices can be muted.