Abstract:
Communication systems and methods for providing premium multiparty communication sessions between a plurality of callers. The plurality of callers may comprise an initiating caller who initiates the premium multiparty communication session but who does not have a status in the communication system which is recognized by an operator of the communication system for allowing the premium multiparty communication session to proceed; and a premium multiparty caller who has a status in the communication system which is recognized by the operator of the communication system such that the operator allows the premium multiparty communication session to proceed, wherein the premium multiparty caller is a different caller to the initiating caller. The premium multiparty caller funding the premium multiparty communication session may be transferred and assigned during communication sessions.

Description:
RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 or 365 to Great Britain Application No. 1014614.0, filed Sep. 2, 2010. The entire teachings of the above application are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to premium communication sessions, such as multiparty video communication sessions between a plurality of callers in a communication system. 
     BACKGROUND 
     Communication systems allow communication sessions, such as calls or instant messaging sessions, to occur between two or more users (or callers) in the communication system. As well as transferring audio data between the callers in a call, video data (or “image data”) can also be transmitted between the callers in a communication session. 
     In one example, the communication system is a packet-based communication system which allows 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. 
     The transmission of some types of data, e.g. video data, in a communication session may result in large quantities of data being transmitted, as compared to the amount of data transmitted when other types of data, e.g. audio data, is transmitted in a communication session. In some communication systems, callers may be required to have a different level of authorisation to engage in communication sessions involving the transmission of video data, as compared to that required to engage in communication sessions involving the transmission of only audio data. Authorisation for engaging in video communication sessions may be provided, for example, by an operator of the communication system. In one example, a caller can initiate audio communication sessions (i.e. communication sessions involving the transmission of audio data, but not video data) without being required to provide funds to the operator of the communication system, whereas in order for a caller to initiate other types of communication session, the caller may be required to provide funds to the operator of the communication system. By providing funds to the operator of the communication system, a caller can acquire a subscription status in the communication system which can be recognized by the operator such that the caller can engage in certain types of communication session for which a subscription status is required. For example the subscription status may be a premium video subscription status which allows a caller to initiate video calls between more than two callers over the communication system. 
     For example, in one known communication system, when two callers are engaging in a one-to-one video call neither caller is required to have a premium video subscription status for the video call to proceed. This scenario is depicted in the communication system  100  shown in  FIG. 1 . Communication system  100  comprises a first caller  102  and a second caller  106  who can communicate over a communications network, such as the Internet. The first caller  102  is associated with a first webcam  104 . The webcam  104  may be part of a first user device. The second caller  106  is associated with a second webcam  108 , which may be part of a second user device. The first user  102  can transmit data to, and receive data from, the second user  106  over the communications network, as represented by arrow  110  in  FIG. 1 . For example, data may be transmitted between the first and second user devices over the communications network. The first and second webcams  104  and  108  are used for capturing image data for use in a video call between the first and second users  102  and  106 . In the communication system  100 , neither the first user  102  nor the second user  110  are required to have a premium video subscription status for the one-to-one video call between the two users to proceed. 
     However, if two users are engaging in a one-to-one video call with the additional functionality that there is screen sharing in the call along with the video data then in order to initiate the video call a user would be required to have a premium video subscription with the communication system. For example, the communication system  200  shown in  FIG. 2  shows a first user  202  who is associated with a first webcam  204  and a first screen  212 , and a second user  206  who is associated with a second webcam  208 . The first and second users  202  and  206  can communicate with each other over a communications network. For example, the first webcam  204  and the first screen  212  may be part of a first user device whilst the second webcam  208  may be part of a second device, wherein the first and second user devices can transmit and receive data over the communications network. As shown by arrow  210  in  FIG. 2  video data captured by the first and second webcams  204  and  208  can be transmitted between the first and second users  202  and  206 . Furthermore, the arrow  214  represents that image data representing the image displayed on the first screen  212  can be transmitted between the first and second users  202  and  206 . In this way the second user  206  is able to view the images that are being displayed on the first screen  212 . It can be seen in  FIG. 2  that the first user transmits two image data streams (represented by arrows  210  and  214 ). One of the image data streams ( 210 ) includes video data (which is image data) captured by the first webcam  204 , whilst the other data stream ( 214 ) includes image data representing an, image displayed on the first screen  212 . 
     The transmission of two image data streams from the first user  202  requires a high bandwidth and a high level of network resources. The operator of the exemplary communication system  200  has decided that in order to be provided with enough bandwidth and network resources for participating in the communication session shown in  FIG. 2  at least one of the users  202  and  206  is required to have a premium video subscription. The communication session shown in  FIG. 2  is a premium communication session. 
     In another example, a communication system  300  as shown in  FIG. 3  includes four callers  302 ,  306 ,  310  and  314  which are engaging in a multiparty video communication session. In order to engage in a multiparty communication session (be it an audio or a video communication session) one of the callers initiates the communication session and acts as the host for the communication session. The first caller  302  is associated with a first webcam  304  for capturing video data for the first caller  302 . The data captured by the first webcam  304  can be transmitted over a communications network (not shown in  FIG. 3 ) to each of the other callers  306 ,  310  and  314 . Similarly, the second caller  306  is associated with a second webcam  308  for capturing video data for the second caller  306 . The data captured by the second webcam  308  can be transmitted over the communications network to each of the other callers  302 ,  310  and  314 . Similarly, the third caller  310  is associated with a third webcam  312  for capturing video data for the third caller  310 . The data captured by the third webcam  312  can be transmitted over the communications network to each of the other callers  302 ,  306  and  314 . Similarly, the fourth caller  314  is associated with a fourth webcam  316  for capturing video data for the fourth caller  314 . The data captured by the fourth webcam  316  can be transmitted over the communications network to each of the other callers  302 ,  306  and  310 . 
     The host caller mixes the audio streams of the different callers in the communication session and transmits the mixed audio stream to each of the callers in the communication session. For example, the user terminal of the host caller  302  may be running client software for communicating over the communications network and the client software may receive and decode the audio streams from each of the other callers. The audio streams are mixed and transmitted to each of the other callers ( 306 ,  310  and  314 ) such that that each caller is provided with a mixed audio stream that includes the audio streams of each of the other callers, but does not include the audio stream of the caller for which the mixed stream is intended. Each of the mixed streams are then encoded and sent to the appropriate caller. The reason that a different stream needs to be mixed and encoded for each caller is that it is not desirable for a caller&#39;s own voice to be heard returning to the same caller. This is particularly the case since there is a delay incurred in the transmission of the audio stream, and in the decoding/encoding process, and the caller would therefore hear their own voice delayed by a short period of time, which would be disconcerting to the caller. 
     Since video data streams comprise many times more data than audio data streams, the video data streams are not mixed using the client of the host caller  302 . Instead, the video data streams are sent to a server (not shown in  FIG. 3 ) in the communication system  300 , and the video data streams are retransmitted to each of the callers in the communication session from the server. 
     In order for the host caller  302  to initiate the multiparty video communication session shown in  FIG. 3  the operator of the communication system  300  may require that he has a premium video subscription (as shown in  FIG. 3 ). In this case, if the host caller  302  does not have a premium video subscription then he cannot initiate the multiparty video communication session shown in  FIG. 3 . Since the multiparty video communication session shown in  FIG. 3  requires multiple video data streams to be transmitted over the communications network (and also uses a server to mix the video data streams) the operator of the communication system  300  requires that the host caller  302  has a premium video subscription before allowing the host caller  302  to initiate the multiparty video communication session. 
     Although  FIG. 3  shows a multiparty video communication session between four callers, in the exemplary communications system  300  shown in  FIG. 3 , the host  302  would require a premium video subscription with the communication system  300  to initiate any multiparty video communication session involving more than two participants. As shown in  FIG. 3 , the host caller  302  is one of the participants in the multiparty video communication session. The other callers in the multiparty video communication session may be referred to as “non-hosts”. 
     SUMMARY 
     The inventors of the present invention have realised that the requirements regarding subscriptions for engaging in premium communication sessions, such as multiparty video communication sessions, can advantageously be made more flexible than in the prior art. In particular, the inventors have realised that it can be advantageous for a caller to be able to benefit from having a subscription with the communication system even when he does not initiate a particular premium communication session (i.e. even when he is not the host of the particular premium communication session). The inventors have also realised that it can be advantageous for a premium communication session, such as a multiparty video call, to be maintained (i.e. not dropped) when the original funding party leaves the call. 
     The term “premium communication session” is used in this application to mean a communication session between callers which is allowed to proceed on the basis of one of the callers having a particular status in the communication system. This status may be a premium subscription status. Premium communication sessions may include “multiparty video communication sessions” which are communication sessions involving the transmission and reception of video data streams between at least three callers. This includes the case in which at least one participant caller is transmitting one video stream to more than one other caller, e.g. when a first caller (caller A) is in a call with three other callers (callers B, C and D) and caller A is transmitting video data to callers B and C but no other video data streams are transmitted. Premium communication sessions may also include video calls between two callers involving the transmission of at least three image data streams, such as when one of the callers is screen sharing in addition to transmitting video captured from his webcam. Premium communication sessions may also include a call between two callers wherein one caller transmits a video data stream whilst the other caller is screen sharing. 
     According to a first aspect of the invention there is provided a communication system configured to provide a premium multiparty communication session between a plurality of callers, the plurality of callers comprising: an initiating caller who initiates the premium multiparty communication session but who does not have a status in the communication system which is recognized by an operator of the communication system for allowing the premium multiparty communication session to proceed; and a premium multiparty caller who has a status in the communication system which is recognized by the operator of the communication system such that the operator allows the premium multiparty communication session to proceed, wherein the premium multiparty caller is a different caller to the initiating caller. 
     According to a second aspect of the invention there is provided a method of providing a premium multiparty communication session between a plurality of callers in a communication system, the method comprising an initiating caller initiating the premium multiparty communication session, wherein the plurality of callers comprises: the initiating caller who does not have a status in the communication system which is recognized by an operator of the communication system for allowing the premium multiparty communication session to proceed; and a premium multiparty caller who has a status in the communication system which is recognized by the operator of the communication system such that the operator allows the premium multiparty communication session to proceed, wherein the premium multiparty caller is a different caller to the initiating caller. 
     In preferred embodiments, the premium multiparty caller is a funding caller who acquired said status by providing funds to the operator of the communication system for allowing the premium multiparty communication session to proceed. The status may be a subscription status, such as a premium video subscription status. 
     By providing for the case in which the initiating caller of the multiparty video communication session is a different caller to the funding caller, the funding caller is able to use his subscription status with more flexibility. In particular, the funding caller is able to engage in premium communication sessions, such as multiparty video communication sessions, using his subscription status even when he has not initiated the communication session. This also means that a caller can initiate a multiparty video communication session without having a required status (e.g. without having the premium video subscription status) provided that one of the other callers in the multiparty video communication session does have the required status. The initiating caller may establish the premium communication session by requesting that an established non-premium multiparty communication session between the plurality of callers is converted into the premium multiparty communication session. Alternatively the initiating caller may establish the premium communication session by establishing the premium multiparty communication session including transmitting an indication of the plurality of callers to a server in the communication system, wherein the server determines that the premium multiparty caller has said status and on that basis that the premium multiparty communication session is to be allowed to proceed. 
     According to a third aspect of the invention there is provided a method of handling a communication session between a plurality of callers in a communication system, the method comprising: receiving a request from one of the plurality of callers to convert the communication session into a premium communication session; determining whether another one of the plurality of callers has a status which indicates that premium communication sessions are to be allowed to proceed; and if it is determined that said other one of the plurality of callers has said status, converting the communication session into a premium communication session. 
     According to a fourth aspect of the invention there is provided a communication system configured to handle a communication session between a plurality of callers, the communication system comprising: receiving means for receiving a request from one of the plurality of callers to convert the communication session into a premium communication session; determining means for determining whether another one of the plurality of callers has a status which indicates that premium communication sessions are to be allowed to proceed; and converting means for converting the communication session into a premium communication session if it is determined that said other one of the plurality of callers has said status. 
     Said other one of the plurality of callers who has said status is not necessarily the initiator of the call. It may be determined whether at least one of the callers in the communication session has permission to facilitate a premium communication session, (e.g. a multiparty video call). In preferred embodiments of the invention the status of the callers is a subscription status which can be used to provide permission for multiparty video communication sessions to proceed. The permission for a multiparty video communication session to proceed may be based on whether or not at least one caller in the multiparty video communication session has a valid subscription status to ‘fund’ the call. A caller with a suitable valid subscription status may be referred to as a funding caller. 
     Depending on the operator of the communication system, a communication session may be allowed to proceed without requiring any of the callers to have a particular subscription status if, for example, the communication session is a multiparty audio communication session (which involves no transmission of video data). However, if one of the callers then requests that the communication session is converted into a premium communication session, the operator of the communication system may require that at least one of the callers has a valid status for allowing premium communication sessions to proceed. The inventors have realised that it is not necessary for the caller who is requesting the conversion of the communication session into a premium communication session to necessarily be the caller who has the valid status for allowing premium communication sessions to proceed. In this way the status of another caller in the communication session can be used to allow the communication session to be converted into a premium communication session. In preferred embodiments, any participant will be able to convert an audio call to a video call, provided at least one participant on the call has the appropriate subscription status. 
     According to a fifth aspect of the invention there is provided a method of handling a premium communication session between a plurality of callers in a communication system, wherein a first of the plurality of callers is in a validating condition which indicates that the premium communication session is allowed to proceed, the method comprising: during the premium communication session, determining that the first caller is no longer in the validating condition; determining whether a second of the plurality of callers is in the validating condition which indicates that the premium communication session is allowed to proceed; and responsive to the determination that the first caller is no longer in the validating condition, if it has been determined that the second caller is in the validating condition, maintaining the premium communication session. 
     According to a sixth aspect of the invention there is provided a communication system configured to handle a premium communication session between a plurality of callers, wherein the communication system is configured to allow the premium communication session to proceed on the basis that a first of the plurality of callers is in a validating condition, the communication system comprising: first determining means for determining, during the premium communication session, that the first caller is no longer in the validating condition; and second determining means for determining whether a second of the plurality of callers is in the validating condition which indicates that the premium communication session is allowed to proceed, wherein the communication system is configured to maintain the premium communication session responsive to the determination that the first caller is no longer in the validating condition if it has been determined that the second caller is in the validating condition. 
     In preferred embodiments, for a caller to be in the validating condition the caller must be a participant in the premium communication session and must also have a status in the communication system which allows premium communication sessions to proceed (e.g. a premium video subscription status as described above). When a caller is in the validating condition and he has a subscription status which is being used to fund the premium communication session then the caller is a funding caller for the premium communication session. 
     The inventors have realised that if, during the premium communication session, the condition of the funding caller changes such that he is no longer in the validating condition the system can determine if there is another caller in the premium communication session who can fund the call. The condition of the funding caller may change from the validating condition if the funding caller leaves the premium communication session or if the status of the funding caller changes such that it no longer indicates that premium communication sessions are allowed to proceed, such as for example if the caller&#39;s subscription expires. 
     If there is another caller in the premium communication session who is in the validating condition when it is determined that the first caller is no longer in the validating condition then the premium communication session is allowed to proceed on the basis of that other caller&#39;s validating condition. However, if there are no callers in the validating condition in the premium communication session when it is determined that the first caller is no longer in the validating condition then the communication system may terminate the premium communication session. Alternatively, if there are no callers in the validating condition when it is determined that the first caller is no longer in the validating condition then the communication system may start a grace period of x minutes for which the premium communication session can continue before being dropped. However, if one of the callers in the premium communications session enters into the validating condition during the grace period then the premium communication session may be allowed to proceed. At the start of the grace period the communication system may notify all of the callers in the premium communication session that unless one of the callers enters into the validating condition before the end of the grace period then the premium communication session will be dropped. In order to enter into the validating condition the callers may be required to acquire a subscription status, for example by paying a subscription to the operator of the communication system. 
     There is described herein methods and systems for allowing funding callers to utilize their status in the communication system with more flexibility. This allows a greater number of premium communication sessions to proceed which is beneficial to both the operator of the communication system and to the users of the communication system. The inventors have made the realisations that the funding party for a premium communication session can be assigned and transferred during a communication session and that it is not necessary for the initiator of a premium communication session to be the caller with a suitable status for allowing multiparty premium sessions to proceed provided that one of the other callers in the premium communication session has the suitable status. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  shows a first prior art communication system; 
         FIG. 2  shows a second prior art communication system; 
         FIG. 3  shows a third prior art communication system; 
         FIG. 4  shows a schematic representation of a user terminal according to a preferred embodiment; 
         FIG. 5  shows a communication system according to a preferred embodiment; 
         FIG. 6  is a flow chart for a process of handling a multiparty communication session; and 
         FIG. 7  is a flow chart for a process of handling a multiparty video communication session. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the invention will now be described by way of example only. It will be apparent to a person skilled in the art that the invention is not limited by the features of the preferred embodiments described below, but is instead determined by the scope of the appendant claims. Various modifications may be made to the preferred embodiments described below without departing from the scope of the invention as would be apparent to a person skilled in the art. 
     With reference to  FIGS. 4 and 5  there is now described a user terminal  401  and a communication system  500  according to preferred embodiments. 
       FIG. 5  shows a communication system  500  according to preferred embodiments. Communication system  500  is similar to communication system  300  of the prior art shown in  FIG. 3  in that it comprises four callers who can all communicate with each other in a multiparty video communication session. However, in contrast to the communication system  300  shown in  FIG. 3 , the host caller  502  does not have a premium video subscription status in the communication system  500 , and the caller  510  does have a premium video subscription status for allowing the multiparty video communication session to proceed. In the communication system  500  a multiparty video communication session is allowed to proceed on the basis of the premium video subscription of the caller  510  even though the host caller of the multiparty video communication session is a different caller (caller  502 ). 
     The communication system  500  is a packet-based communication system. For example, the communication system  500  could be a packet-based communication system that uses a peer-to-peer (“P2P”) topology built on proprietary protocols. To enable access to a peer-to-peer system, the caller must execute P2P client software provided by a P2P software provider on their user terminal, and register with the P2P system. When the caller 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 callers of the P2P system without the further use of a server. In some other embodiments, the communication system  500  is a different type of communication system that does not use a P2P topology, and instead uses a server based system for handling communication sessions as is known in the art. 
       FIG. 4  illustrates a detailed view of a user terminal  401  on which is executed client software for communicating over the communication system  500  as described above. The user terminal  401  can be used by a caller (e.g. the host caller  502 ) for communicating over the communication system  500  with the other callers ( 306 ,  510  and  314 ) in the communication system  500 . The user terminal  401  comprises a central processing unit (“CPU”)  402 , to which is connected a display  404  such as a screen, input devices such as a keypad (or a keyboard)  406 , a pointing device such as a joystick (or mouse)  408  and a webcam  426  for capturing video data. The display  404  may comprise a touch screen for inputting data to the CPU  402 . An output audio device  410  (e.g. a speaker) and an input audio device  412  (e.g. a microphone) are connected to the CPU  402 . The display  404 , keypad  406 , joystick  408 , webcam  426 , output audio device  410  and input audio device  412  are integrated into the user terminal  401 . In alternative user terminals one or more of the display  404 , the keypad  406 , the joystick  408 , webcam  426 , the output audio device  410  and the input audio device  412  may not be integrated into the user terminal  410  and may be connected to the CPU  402  via respective interfaces. One example of such an interface is a USB interface. The CPU  402  is connected to a network interface  426  such as a modem for communication with a communications network for communicating over the communication system  500 . The network interface  426  may be integrated into the user terminal  401  as shown in  FIG. 4 . In alternative user terminals the network interface  426  is not integrated into the user terminal  401 . 
       FIG. 4  also illustrates an operating system (“OS”)  414  executed on the CPU  402 . Running on top of the OS  414  is a software stack  416  for the client. The software stack shows a client protocol layer  418 , a client engine layer  420  and a client user interface layer (“UI”)  422 . 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. 4 . The operating system  414  manages the hardware resources of the computer and handles data being transmitted to and from the network via the network interface  426 . The client protocol layer  418  of the client software communicates with the operating system  414  and manages the connections over the communication system. Processes requiring higher level processing are passed to the client engine layer  420 . The client engine  420  also communicates with the client user interface layer  422 . The client engine  420  may be arranged to control the client user interface layer  422  to present information to the user via a user interface of the client and to receive information from the user via the user interface. 
       FIG. 5  also shows that a server  504  is present in the communication system  500 . In preferred embodiments, audio data streams are mixed by the host caller  502  (the call initiator) as described above, and sent from the host caller  502  to each of the other callers ( 306 ,  510  and  314 ) in the communication session. The video data streams are retransmitted from the server  504  to each of the callers in the multiparty video communication session. Other embodiments are also possible. For example, the data streams may be transmitted using a mesh architecture in which different routing options are available for transmitting the data streams through the network. In another alternative embodiment, the audio data streams are mixed at the server  504  instead of by the host caller  502 . 
     The server  504  is used to store subscription information relating to the status of the callers in the multiparty video communication session. The status of each of the callers in the communication system  500  can be monitored and any changes to the status of the callers are stored in the server  504  in real-time. In this way the server  504  can maintain an up to date record of the status of each of the callers in the communication system  500 . Therefore, the server  504  can be used to determine whether the status of the callers in a multiparty video communication session is sufficient to allow the multiparty video communication session to proceed (e.g. that at least one of the callers in the multiparty video communication session has a status indicating that multiparty video communication sessions are to be allowed to proceed). 
     Before a communication session has started the callers in the communication system  500  are in a pre-call state. A caller (e.g. host caller  502 ) can select a group of callers with which to start a communication session. When the host caller  502  selects a group of three or more callers in total (including the host caller himself), a ‘Group Video Call’ button will be displayed on the display  404  of the user terminal  401  of the host caller  502 . The Group Video Call button will be displayed on the display  404  regardless of the premium video subscription status of the callers in the selected group. 
     However, multiparty video calls (e.g. video calls between three or more participants, including the host) require a premium video subscription in the communication system  500 . Therefore when the host caller  502  clicks on the Group Video Call button, the system will check whether the host caller  502  has a premium video subscription status which is sufficient for proceeding with the multiparty video call. The subscription status required may vary depending upon the number of callers selected to be in the multiparty video communication session. The subscription status information may be stored locally at the host caller&#39;s user terminal  401 , or on the server  504  as described above. Where the host caller  502  initiates a multiparty video communication session that is within the limits of his premium video subscription status, no additional communication will be displayed to the host caller  502  and the multiparty video communication session will proceed. However, if the host caller  502  does not have a premium video subscription status sufficient for the multiparty video communication session to proceed, then the multiparty video communication session may not be allowed to proceed. In alternative embodiments, the multiparty communication session may be connected as a multiparty audio communication session, but the video will not start. The multiparty audio communication session is allowed to proceed because the communication system  500  does not require any of the callers in a multiparty audio communication session to have a particular subscription status before allowing the multiparty audio communication session to proceed. This is because the transmission of an audio data stream over the network requires much less bandwidth and network resources than the transmission of a video data stream. In other embodiments, the host caller  502  may transmit a list of the participants intended to be in the multiparty video communication session to the server  504 . The server  504  may then determine whether any of the participants in the list have a suitable subscription status for allowing the multiparty video communication session to proceed, and if any of the participants do have a suitable subscription status then the multiparty video communication session may be allowed to proceed. 
     If a caller who has been included in a multiparty video communication session does not have the appropriate software or hardware for participating in video calls then they are able to participate in the multiparty communication session on an audio basis only. This allows callers to join in a multiparty communication session even though they do not have the required equipment for transmitting and receiving video data streams and even though the other callers in the communication session are transmitting video data streams in the multiparty communication session. 
     A video data stream transmitted in a multiparty video communication session may comprise for example (i) video data captured from a caller&#39;s webcam, or (ii) image data representing images displayed on a caller&#39;s screen. When the video data stream comprises video data representing images displayed on a caller&#39;s screen the communication session can include screen sharing of the caller&#39;s screen. 
     Whilst a multiparty audio call is in progress between three or more participant callers, a ‘Convert to Video Call’ button will be displayed on the display of a user terminal of each of the callers. In one embodiment the ‘Convert to Video Call’ button will be displayed to the callers in the multiparty audio call regardless of the permission status of the participant callers on the call. In an alternative embodiment of the invention the ‘Convert to Video Call’ button will only be displayed to the callers in the multiparty audio call if it is determined that one of the participant callers has the required permission status for converting the multiparty audio call into a multiparty video call. Any of the participant callers in the multiparty audio call will be able to convert the multiparty audio call to a multiparty video call, provided at least one of the participant callers on the multiparty audio call has the appropriate subscription status for allowing multiparty video calls (e.g. a premium video subscription status). 
       FIG. 6  shows a flowchart for a process of handling a multiparty communication session. Initially the multiparty communication session is not a multiparty video communication session. For example, it may be a multiparty audio call or a multiparty instant messaging communication session. Then in step S 602  a request is received from one of the callers in the multiparty communication session for converting the multiparty communication session into a multiparty video communication session. Any of the callers in the original multiparty communication session can attempt to convert the multiparty communication session into a multiparty video communication session, for example by clicking on the Convert to Video Call button displayed on the screen of their user terminal. 
     After the request has been received (e.g. after the Convert to Video Call button has been clicked), in step S 604  it is determined that the requesting caller does not have a required status for allowing multiparty video communication sessions to occur (e.g. he does not have the required premium video subscription status). Note that if the requesting caller does have the required status then the multiparty video communication session can proceed on the basis of the requesting caller&#39;s status. 
     In step S 606  it is determined whether any of the participant callers in the original multiparty communication session has a valid subscription status sufficient for converting the multiparty communication session into a multiparty video communication session. In a preferred embodiment of the invention, the determination in step S 606  comprises transmitting a message to the server  504  to check the subscription status of participants in the multiparty communication session. The message indicates each participant caller of the multiparty communication session. In response the server  504  looks up the subscription status of each participant of the multiparty communication session on a database containing subscription information stored at the server  504 . 
     If the server  504  determines that there are no participants able to fund a multiparty video call then the server transmits a reply message to the requesting caller indicating that the multiparty video call cannot start. Then, as shown in step S 608 , the multiparty communication session is not converted into a multiparty video communication session, and instead may be maintained as a multiparty communication session which does not involve the transmission of video data streams. When none of the callers in the multiparty communication session have the required subscription status for allowing a multiparty video communication session, the requesting caller will be shown a pop-up message on the display of his user terminal indicating that this is the case to thereby explain why a multiparty video call cannot proceed. The caller could also be informed about ways in which subscription may be purchased such that the caller could acquire the required subscription status for allowing multiparty video communication sessions to proceed. 
     However, if there is one participant caller (a “funding caller”) that is able to fund multiparty video communication sessions (due to their status) then the server  504  may, in some embodiments, transmit a reply message to the requesting caller indicating that the multiparty video call may start, and the multiparty video communication session may be allowed to proceed. In these embodiments, no additional communication will be displayed to the requesting caller and the multiparty video communication session will commence. In some embodiments permission to use the status of the funding caller is requested from the funding caller before proceeding with the multiparty video communication session, and the multiparty video communication session can only proceed on the basis of the funding caller&#39;s subscription status if the funding caller provides permission to do so. 
     In other embodiments, as shown in  FIG. 6 , if there is one participant caller that is able to fund multiparty video communication sessions (due to their status) then the method may proceed by passing to step S 610  in which it is determined whether more than one caller in the original multiparty communication session has the required status for converting the communication session into a multiparty video communication session. This determination is performed by the server  504 . If only one caller has the required status then the method passes to step S 612  in which permission is requested from the caller with the required status for using his status to allow the multiparty video communication session to commence. The permission may be requested by way of sending a message to the caller with the required status with the request in the message. If the caller with the required status does not provide permission to use his status then the communication session cannot be converted into a multiparty video communication session on the basis of his status and so the communication session is not converted into a multiparty video communication session. However, if the caller with the required status provides his permission then the multiparty communication session is converted into a multiparty video communication session in step S 614 . 
     If it is determined in step S 610  that more than one caller in the multiparty communication session has the required status then the method passes to step S 616  in which one of those callers is selected. The selection may be a random selection. Alternatively, the selection may be based on the particular status of the callers. For example, a caller with a subscription status that allows unlimited multiparty video calls may be selected in preference to a caller with a subscription status which indicates that they have a prepaid balance for funding multiparty video calls. When one of the callers has been selected in step  516  the method proceeds to step S 618  in which permission is requested from the selected caller for using his status to allow the multiparty video communication session to commence. The permission may be requested by way of sending a message to the selected caller with the request in the message. If the selected caller does not provide permission to use his status then the communication session cannot be converted into a multiparty video communication session on the basis of his status and so the communication session is not converted into a multiparty video communication session. However, if the selected caller provides his permission then the multiparty communication session is converted into a multiparty video communication session in step S 620 . 
     In order to ensure the privacy of each participant of the original multiparty communication session, the caller that converts a multiparty audio call to a multiparty video call will not be able to switch on the video stream for each participant. Instead each participant must separately choose to start transmitting a video data stream in order for a video data stream to be transmitted from that participant. 
     A caller may change his status during a communication session. If this happens then the status stored in the server  504  is updated in real-time. A caller may for example change his status by successfully subscribing via a website of the communication system  500 . If a caller has updated his status during a communication session their subscription status stored on the database at the server  504  will be updated immediately such that they will be able to convert the communication session to a multiparty video communication session immediately thereafter. 
       FIG. 7  shows a flowchart for a process of handling a multiparty video communication session. A first caller, for example caller  510  shown in  FIG. 5 , is initially funding the multiparty video communication session. In other words, the multiparty video communication session is allowed to proceed on the basis of the subscription status of the first caller  510 . In this sense the first caller  510  is considered to be in a “validating condition” meaning that he is in a condition which allows the multiparty video communication session to proceed. In order to be in the validating condition the first caller  510  must be a participant in the multiparty video communication session and must also have a status which is recognised in the communication system  500  as indicating that multiparty video communication sessions are to be allowed to proceed. For example, the first caller  510  may have a premium video subscription status. 
     However, in step S 702  it is determined that the first caller  510  is no longer in the validating condition. In order to perform this determination the server  504  may monitor changes to the callers participating in the multiparty video communication session by monitoring a heart beat message provided from the host caller  502 . The host caller  502  is arranged to transmit a heart beat message to the server  504  throughout the multiparty video communication session indicating the current participants in the multiparty video communication session. The server  504  may also monitor the subscription status of the participants (including the funding caller  510 ) throughout the multiparty video communication session. In one embodiment the server  504  may query a subscription database to determine the funds available to the funding caller  510  on receipt of each heartbeat message from the host caller  502 . 
     If the server  504  determines that the first caller  510  has left the multiparty video communication session or that the status of the first caller  510  has changed such that he no longer has a status which indicates that multiparty video communication sessions are to be allowed to proceed then it is determined in step S 702  that the first caller  510  is no longer in the validating condition, and the method passes to step S 704 . 
     In step S 704  it is determined whether there is another caller in the multiparty video communication session who is in the validating condition (i.e. participating in the multiparty video communication session and having a sufficient subscription status for allowing multiparty video communication sessions to proceed). In this way the system will check for the presence of a caller in the multiparty video communication session having a sufficient subscription status (i.e. an identical, or higher, subscription status than that originally held by the first caller  510 ) for allowing the multiparty video communication session to proceed. In some embodiments, if there is another caller in the validating condition then the multiparty video communication session continues without any visible system activity. In some embodiments permission to use the status of the other caller is requested from the other caller before proceeding with the multiparty video communication session, and the multiparty video communication session can only proceed on the basis of the other caller&#39;s subscription status if the other caller provides permission to do so. 
     In other embodiments, as shown in  FIG. 7 , if there is another caller in the validating condition then the method proceeds with step S 706  in which it is determined whether there is more than one caller is in the validating condition. This determination is performed by the server  504 . If only one caller is in the validating condition then the method passes to step S 708  in which permission is requested from the caller who is in the validating condition for using his status to allow the multiparty video communication session to be maintained. The permission may be requested by way of sending a message to the caller who is in the validating condition with the request in the message. If the caller who is in the validating condition does not provide permission to use his status then the multiparty video communication session cannot be maintained on the basis of his status and so the multiparty video communication session is not maintained. However, if the caller who is in the validating condition provides his permission then the multiparty video communication session is maintained in step S 710 . 
     If it is determined in step S 706  that more than one caller in the multiparty video communication session is in the validating condition then the method passes to step S 712  in which one of those callers is selected. The selection may be a random selection. Alternatively, the selection may be based on the particular status of the callers. For example, a caller with a subscription status that allows unlimited multiparty video calls may be selected in preference to a caller with a subscription status which indicates that they have a prepaid balance for funding multiparty video calls. When one of the callers has been selected in step the method proceeds to step S 714  in which permission is requested from the selected caller for using his status to allow the multiparty video communication session to be maintained. The permission may be requested by way of sending a message to the selected caller with the request in the message. If the selected caller does not provide permission to use his status then the multiparty video communication session cannot be maintained on the basis of his status and so the multiparty video communication session is not maintained. However, if the selected caller provides his permission then the multiparty video communication session is maintained in step S 716 . 
     Returning to step S 704 , if it is determined that there is not another caller who is in the validating condition (i.e. who is participating in the multiparty video communication session and who has a sufficient subscription status for allowing multiparty video communication sessions to proceed) then the multiparty video communication session is not allowed to proceed unless the condition of at least one caller becomes the validating condition. 
     In some embodiments, if it is determined that there is not another caller who is in the validating condition then the multiparty video communication session is dropped. The communication session may be dropped entirely or may be converted into a multiparty communication session which does not involve the transmission of video data streams, e.g. a multiparty audio communication session or a multiparty instant messaging communication session. 
     However, in other embodiments, as shown in  FIG. 7 , if it is determined that there is not another caller who is in the validating condition then the method passes to step S 718  in which a grace period of x minutes is started. In step S 720  the callers in the multiparty video communication session are notified that a subscription status (e.g. a premium video subscription status) is required to continue with the multiparty video communication session and that the multiparty video communication session will be dropped at the end of the grace period unless one of the callers successfully acquires a sufficient subscription status before the end of the grace period. 
     Then in step S 722  it is determined whether any of the callers are in the validating condition. If it is still the case that none of the callers are in the validating condition then the method passes to step S 724  in which it is determined whether the grace period of x minutes has expired. If the grace period has not yet expired then the method passes back to step S 722 . This cycle of steps S 722  and S 724  will continue until either one of the callers enters into the validating condition or the grace period expires. 
     If the grace period expires before any of the callers enters into the validating condition then the method will pass to step S 726  in which the multiparty video communication session is dropped. In other embodiments, instead of dropping the multiparty video communication session, the multiparty video communication session may instead be converted into a multiparty communications session which does not involve the transmission of video data streams, e.g. a multiparty audio communication session or a multiparty instant messaging communication session. 
     However, if one of the callers enters into the validating condition before the grace period expires then the multiparty video communication session may be allowed to be maintained on the basis of the new validating condition of the one of the callers. In some embodiments, if one of the callers enters into the validating condition before the grace period expires then the multiparty video communication session is maintained. In some embodiments permission to use the status of the caller is requested from the caller before proceeding with the multiparty video communication session, and the multiparty video communication session can only proceed on the basis of the caller&#39;s validating condition if the caller provides permission to do so. 
     In other embodiments, as shown in  FIG. 7 , if one of the callers enters into the validating condition before the grace period expires then the method will pass to step S 706 . The method then proceeds as described above whereby permission is requested from the caller before maintaining the multiparty video communication session on the basis of their subscription status. 
     It can therefore be seen that by following the method shown in  FIG. 7 , if a participant successfully acquires a sufficient subscription status before the end of the grace period, then the multiparty video communication session will continue as it was before the determination that the first caller  510  was no longer in the validating condition. If no participant acquires a sufficient subscription status for the multiparty video communication session before the end of the grace period, then the video aspect of the multiparty video communication session will drop. Any payment received whilst the multiparty video communication session is proceeding must be cleared before the subscription status is available to be used as the basis for allowing the multiparty video communication session to proceed. 
     It can be seen in the embodiments described above that multiparty video communication sessions can be allowed to proceed on the basis of the subscription status of callers in the multiparty video communication session with more flexibility than in the prior art. This provides a much more user-friendly communication system and promotes use of the communication system for engaging in multiparty video communication sessions. 
     A number of factors may be considered in selecting a funding caller to fund a multiparty video communication session. In some embodiments, a potential funding caller is any participant in a multiparty video communication session with a subscription status that allows unlimited multiparty video communication sessions. In other embodiments a potential funding caller is any participant in a multiparty video communication session who has credit in a prepaid balance with the operator of the communication system. In further embodiments a potential funding caller is any participant in a multiparty video communication session with sufficient funds for the allowing the multiparty video communication session to proceed (e.g. a subscriber or a caller with credit) and who has previously indicated that he is willing to fund multiparty video communication sessions. 
     As described above, where there is more than one potential caller for funding the multiparty video communication session, the server may select the funding caller at random or may transmit a request to a selected caller to confirm that the he is happy to fund the multiparty video communication session. 
     When a funding caller is selected by the system a record of the start billing event is created. When the system determines from the heart beat message that the funding caller is no longer a participant of the call, or that the call has ended, a record of the end billing event is created. In this way the funding caller can be charged correctly for funding the multiparty video communication session. The funds required for the multiparty video communication session may also depend upon the number of callers in the multiparty video communication session. The funds required for the multiparty video communication session may also depend upon the amount of data transmitted over the communication system during the multiparty video communication session. The funds required for the multiparty video communication session may also depend upon other factors as would be apparent to a person skilled in the art. 
     In the preferred embodiments described above for a caller to acquire a required status for allowing multiparty video communication sessions to proceed they are required to provide funds to the operator of the communication system. In other embodiments, a caller may acquire the status in other ways. For example, some callers may be granted the status without providing any funds to the operator of the communication system for reasons such as that they are a particularly frequent user of the communication system or that they have administrator rights in the communication system. 
     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 changes in form and detail may be made without departing from the scope of the invention as defined by the appendant claims.