Abstract:
A method of receiving a communication event from a calling entity located in a communication network comprising a first network and a second network, at a receiving device associated with a user located in the communication system, said method comprising associating a first identity recognisable in the first network with a second identity recognisable in the second network for both the user and the calling entity at a data store located in the second network; providing the first and second identities for the calling entity to the receiving device via the second network; receiving at a node in the second network associated with the user, the communication event together with the second identity for the calling entity via the second network, wherein the communication event is addressed with the second identity of the user; querying the data store with the second identity of the calling entity and the second identity of the user to determine the first identity of the calling entity and the first identity of the user; receiving at the receiving device associated with the user the communication event together with the first identity for the calling entity via the first network, wherein the communication event is addressed with the first identity of the user; and determining the second identity of the calling entity at the receiving device associated with the user using the first identity of the calling entity.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. § 119 or 365 to Great Britain Application No. 0623621.0, filed Nov. 27, 2006 and Great Britain Application ______ filed Nov. 23, 2007. The entire teachings of the above applications are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a method for handling communication in a communication system. 
       BACKGROUND 
       [0003]    Communication systems link together two communication devices so that the devices can send information to each other in a call or other communication event. Information may include voice, text, images or video. 
         [0004]    One such communication system is a peer to peer system, in which a plurality of end users can be connected for communication purposes via a communications structure such as the internet. The communications structure is substantially decentralised with regard to communication route switching therein for connecting the end users. That is, the end users can establish their own communication routes through the structure based on exchange of one or more authorisation certificates (user identity certificates—UIC) to acquire access to the structure. The structure includes an administration arrangement issuing the certificates to the end users. Such a communication system is described in WO 2005/009019. 
         [0005]    Peer-to-peer systems and other communication systems that use the internet or any other packet switched network employ voice over IP (internet protocol) protocols (VoIP) to transmit data. These systems are commonly referred to as VoIP systems. VoIP systems are beneficial to the user as they are often of significantly lower cost than communication networks, such as fixed line or mobile networks, otherwise referred to as public switched telephone networks (PSTN). This may particularly be the case for long distance calls. 
         [0006]    The connection of two communication devices using more than one type of network is becoming increasingly common. In some cases a call may be transmitted via more than one network in an attempt to reduce the cost of the call. For example a call between two devices located in a PSTN network may be transmitted via the internet. In other cases it is necessary to transmit the call via two networks when each device is located in a different network. 
         [0007]    Gateways are provided at the interface between different networks to translate call data from a form required by a protocol of one network into a form required by a protocol of another network. However in some cases some data associated with the call may not be supported by the protocol of one of networks. In this case the data associated with the call is lost. 
         [0008]    For example a communication device such as a mobile phone located in a PSTN network may be arranged to identify the origin of an incoming call. However if the call has originated from a device located in the internet the PSTN network cannot recognise and transmit the identity of user of the device to the mobile phone. As such the identity of the calling party will be lost. 
       SUMMARY 
       [0009]    It is therefore an aim of embodiments of the invention to address at least one of the above identified problems. 
         [0010]    According to a first aspect of the invention there is provided a method of receiving a communication event from a calling entity located in a communication network comprising a first network and a second network, at a receiving device associated with a user located in the communication system, the method comprising: associating a first identity recognisable in the first network with a second identity recognisable in the second network for both the user and the calling entity at a data store located in the second network; providing the first and second identities for the calling entity to the receiving device via the second network; receiving at a node in the second network associated with the user, the communication event together with the second identity for the calling entity via the second network, wherein the communication event is addressed with the second identity of the user; querying the data store with the second identity of the calling entity and the second identity of the user to determine the first identity of the calling entity and the first identity of the user; receiving at the receiving device associated with the user the communication event together with the first identity for the calling entity via the first network, wherein the communication event is addressed with the first identity of the user; and determining the second identity of the calling entity at the receiving device associated with the user using the first identity of the calling entity. 
         [0011]    According to a second aspect of the present invention there is provided a network node for receiving a communication event for a user of a communication network from a calling entity, said communication network comprising a first network and a second network, said network node executing a communication instance arranged to store a first identity recognisable in the first network in association with a second identity recognisable in the second network for both the user and the calling entity; to transmit the first and second identities for the calling entity to a receiving device associated with the user via the second network; to receive the communication event together with the second identity for the calling entity via the second network, wherein the communication event is addressed with the second identity of the user; and to determine the first identity of the calling entity and the first identity of the user using the second identity of the calling entity and the second identity of the user; wherein the communication instance is further arranged to transmit the communication event together with the first identity for the calling entity to the receiving device via the first network using the first identity of the user such that the receiving device may determine the second identity of the calling entity using the first identity of the calling device. 
         [0012]    According to a third aspect of the present invention there is provided a receiving device arranged to receive a communication event from a calling entity via a communication system comprising a first network and a second network, said receiving device comprising: a processor executing a client program arranged to receive a first identity recognisable in the first network and a second identity recognisable in the second network for the calling entity; a receiver arranged to receive a communication event together with the first identity of the calling entity via the first network; wherein the client program is further arranged to determine the second identity of the calling entity using the first identity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For a better understanding of the present invention and as to how the same may be carried into effect, embodiments of the present invention will now be described by way of example only with reference to the following drawings: 
           [0014]      FIG. 1  is a schematic representation of a communication system in accordance with an embodiment of the invention; 
           [0015]      FIG. 2   a  is a diagram showing the protocol stack of a client program in accordance with an embodiment of the present invention; 
           [0016]      FIG. 2   b  is a schematic diagram showing the transmission of data between the client protocol stack and the GSM protocol stack in a user device in accordance with an embodiment of the present invention; 
           [0017]      FIG. 3  is a schematic representation of part of the communication system shown in  FIG. 1 ; 
           [0018]      FIG. 4  is a schematic representation of part of the communication system shown in  FIG. 1  according to an embodiment of the present invention; 
           [0019]      FIG. 5  shows the call connections made when placing calls between a user device and entities located in the communication system according to an embodiment of the present invention; 
           [0020]      FIG. 6  shows the logical connections between a call manager, a session node, an inbound gateway and an outbound gateway according to an embodiment of the present invention; and 
           [0021]      FIG. 7  is a diagram showing the reception of a call in accordance with an embodiment of the present invention. 
           [0022]      FIG. 8  is a diagram showing the reception of a command in accordance with an alternative embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Reference will first be made to  FIG. 1 , in which is shown a communication system  100 , including a packet switched network  104  and circuit switched networks  112  and  120 . In one embodiment the packet switched network  104  may be the internet. Data may be transmitted via the internet  104  via a peer to peer system. The circuit switched networks  112 ,  120  may be PSTN (Public Switched Telephone Network) networks. 
         [0024]    A user device  102  is shown to be connected to the internet  104  via a session node  106 . The user device  102  is also connected to the PSTN network  120 . In one embodiment of the invention the user device is connected to the PSTN network  112  via a circuit switched connection  222  and to the session node  106  via a packet switched connection  111 . The circuit switched connection  222  and the packet switched connection  111  may be provided by a GSM (Global System for Mobile Communications) network (not shown). For example the packet switched connection may be provided by a GPRS (General Packet Radio Service) connection of the GSM network whilst the circuit switched connection may be provided by a GSM audio connection of the GSM network. In a preferred embodiment of the invention the packet switched connection  111  is used to transmit packet data according to an internet protocol such as Transmission Control Protocol (TCP). 
         [0025]    The user device  102  may be, for example, a personal computer, a gaming device, a personal digital assistant, a suitably enabled mobile phone, or other device able to connect to the network  104 . 
         [0026]    In accordance with an embodiment of the invention the session node  106  runs a communication instance  122  defining a session dedicated to a user of the user device  102 . The communication instance  122  enables the user of the user device  102  to communicate across the communication system  100 . The session node  106  is able to concurrently run a plurality of communication instances for a number of other users operating other user devices (not shown). 
         [0027]    The user device  102  runs a client software program  124  that provides a client interface on the user device and allows the user of the user device  102  to communicate with the communication instance  122  running on the session node  106 . 
         [0028]    The client program  124  running on the user device has a number of different components or layers for implementing various functions, including a protocol layer  402  ( FIG. 2   a ) for managing the interface with the GSM network. The interface with the GSM network will be described hereinafter with reference to  FIG. 2   b.    
         [0029]      FIG. 2   a  shows a protocol stack for the client program  124  according to an embodiment of the present invention. The protocol stack shows an operating system layer  401 , a protocol layer  402 , a client engine layer  404  and a client user interface layer  406 . 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. 2   a . The operating system layer  401  manages the hardware resources of the user device  102  and handles data being transmitted to and from the session node  106 . The operating system layer also handles the data being transmitted to and from the network  112 . The client protocol layer  402  of the client software communicates with the operating system  401 . Processes requiring higher level processing are passed to the client engine layer  404 . The client engine  404  also communicates with the user client user interface layer  406 . The client engine may be arranged to control the client user interface layer  406  to present information to the user via user interface means of the user device and to receive information from the user via the user interface means of the user device. The user interface means may comprise a speaker, a microphone, a display screen and a keyboard. This list is not exhaustive. 
         [0030]      FIG. 2   b  is a schematic diagram showing the transmission of data between the client protocol stack and the GSM protocol stack in the user device  102 . As shown in  FIG. 2   b  the user device  102  further comprises a GSM protocol stack  501  and a radio transceiver  502 . Information transmitted from the GSM network to the user device is received by the transceiver  502 . The data received from the GSM network is processed by GSM protocol stack  501  before it is transmitted to the client program  124 . Similarly, information to be transmitted to the GSM network from the client program  124  is processed by the GSM protocol stack  501  before it is transmitted to the GSM network via the transceiver  502 . The operation of the GSM protocol stack  501  is known in the art and will not be described in detail herein. 
         [0031]    Reference is again made to  FIG. 1 . As shown in  FIG. 1  the peer to peer system on the internet  104  comprises an inbound gateway  114  and an outbound gateway  116 . The inbound gateway  114  and the outbound gateway  116  are connected to PSTN gateways  188  located in the PSTN networks. The inbound gateway  114  is arranged to receive data for the peer to peer system on the internet  104  from the PSTN gateways  188 . The outbound gateway  116  is arranged to transmit data from the peer to peer system on the internet  104  to the to the PSTN gateways  188 . 
         [0032]    Also shown in  FIG. 1  is a profile node  128 . The profile node  128  is responsible for storing user profile information for users of the peer to peer system. The user profile information includes login information for logging into the peer to peer system and a contact list  132  associated with each user of the peer to peer system. The contact list  132  comprises the addresses of, for example, other users of the communication system stored as contacts by a user. 
         [0033]    The communication instance  122  running on the session node  106  manages the communication between the client program  124  running on the device  102  and the peer to peer system on the internet  104 .  FIG. 3  shows the connection path between the communication instance  122  on the session node  106  and the client program  124  running on the user device  102 . As shown in  FIG. 3 , the session node  106  further comprises a core module  205  for allocating a communication instance  122  to a client program  124 . 
         [0034]    In accordance with an embodiment of the invention the client program  124  running on the user device  102  is arranged to set up a connection with the session node  106 . The client program  124  sends the session node  106  data relating to the user device  102  via the packet switched connection  111  in a data packet. The data packet may include the attributes listed in table 1: 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 KEY 
                 TYPE 
                 ATTRIBUTE 
               
               
                   
               
             
             
               
                 CHUNKTYPE 
                 integer 
                 CLIENTDATA 
               
               
                 DEVICE_PSTNNUMBER 
                 string 
                 device PSTN number in 
               
               
                   
                   
                 international notation. 
               
               
                   
               
             
          
         
       
     
         [0035]    As shown in table 1, the data packet includes an attribute defining an IP address of the user device and an attribute defining a PSTN number of the device. The PSTN address identifies the user device  102  in the PSTN network  112 . 
         [0036]    After a connection between the client program  124  and the session node  106  has been established the user of the user device may then provide login information to the session node  106  in order to log into the peer to peer system on the internet  104 . 
         [0037]    The session node may verify the login information provided from the user device against the profile information for the user of the user device  102  stored on the profile node  128 . On verification of the login information provided from the user device  102  the core module  205  will assign a dedicated communication instance  122  to the client program  124 . 
         [0038]    The communication instance  122  associates the identity user of the user device as defined by at least part of the login details of the user with the identity of the device as defined by the PSTN number of the device. In one embodiment of the invention the communication instance may store the identity of the user together with the identity of the user device in a data store  129  associated with the communication instance. 
         [0039]    According to an embodiment of the invention it is possible for the user of the user device to log into the peer to peer system using more than one user device. According to this embodiment of the invention the communication instance will associate the identity of each device with the identity of the user in the peer to peer system. 
         [0040]    Once the session node  106  has assigned a communication instance  122  to the user device  102  the communication instance  122  will provide the client program  124  with data to enable to the client program to establish a communication event with an entity in the communication system  100 . 
         [0041]    The entity may be any node in the communication system  100  that is capable of transmitting information to the user device  102 . For example the entity may be another user device or a network node in the communication system  100 . The entity may correspond to voice mail records, or other data records associated with the user of the user device. Additionally the entity may be an entity arranged to instruct the client program to carry out control commands. 
         [0042]    An entity is located by an address in the network in which it resides. The address of an entity that resides in the internet  104  may be for example an IP address, a URI (Uniform Resource Indicator), a username, of a VoIP device. The address of an entity that resides in the PSTN network may be a PSTN number associated with the entity. 
         [0043]    In one embodiment of the invention the entity may be located in more than one network. For example the entity may be a user that is logged into the peer to peer system of the internet using two or more user devices. In this case an entity will have more than one associated addresses. 
         [0044]    The user device  102  may transmit or receive a communication event with an entity via more than one network of the communication system. For example the user device  102  may receive a call via the PSTN network  112  from an entity located in the internet  104 . 
         [0045]    In accordance with an embodiment of the invention the communication instance  122  is arranged to allocate an entity an identity that may be transmitted and interpreted by both the PSTN network and the peer to peer system on the internet. In this case the identity of the entity may be resolved to the address of the entity by a node located in the internet  104 . In a preferred embodiment of the invention the allocated identity is a PSTN number. 
         [0046]    For example, if the entity is located in the internet, the IP address of the entity the will not be recognized by the PSTN network. The communication instance  122  is arranged to allocate a PSTN number to the entity that may be used to identify the entity during a call with the entity via the PSTN network. 
         [0047]    As shown in  FIG. 1  a call manager  118  is connected to the session node  106 , the inbound gateway  114  and the outbound gateway  116 . The call manager has access to the data store  126 . In  FIG. 1  the data store  126  is shown as being associated with the call manager  118 . In an alternative embodiment of the invention the data store  126  may be associated with the call session node  106 . 
         [0048]    In the embodiment shown in  FIG. 1  the call manager  118  is shown as being located separately from the session node  106  and the gateways  114  and  116 . In alternative embodiments the call manager  118  may however form part of either the session node  106  or of one of the gateways  114  or  116 . The logical connections between the call manager, the session node, the inbound gateway and the outbound gateway are shown in  FIG. 6 . 
         [0049]    The call manager  118  is arranged to provide the communication instance  122  with a PSTN number to be allocated to an entity in response to a request from the communication instance. The communication instance is arranged to allocate the PSTN number to the entity and to provide the address of the entity to the call manager. The call manager is then arranged to store the allocated PSTN number in the data store  126  together with the address of the entity. 
         [0050]    In a preferred embodiment of the invention the address of an entity is determined from the contact list  132  provided from the profile node  128 . This embodiment of the invention will be described with reference to  FIG. 4 . 
         [0051]      FIG. 4  is a diagram showing the steps for allocating a PSTN number to an entity in accordance with a preferred embodiment of the invention. 
         [0052]    In step S 1  the communication instance  122  is arranged to retrieve the addresses of the entities of that are listed as contacts in the contact list  132  associated with the user of the user device  102 . The addresses of the entities are retrieved from the profile node  128 . 
         [0053]    In step S 2  the communication instance stores the address of each entity in the data store  129 . In a preferred embodiment of the invention the entire contact list  132  is stored in the data store  129 . 
         [0054]    In step S 3  the communication instance  122  is then arranged to retrieve a PSTN number for each entity listed in the contact list from the call manager. 
         [0055]    In step S 4  the communication instance is arranged to allocate each PSTN number to each entity listed in the contact list and to report the addresses of each entity allocated a PSTN number to the call manager. 
         [0056]    In step S 5  the call manager  118  is arranged to store in the data store  126  a PSTN number in association with the address for each entity listed in the contact list. 
         [0057]    In one embodiment of the invention the call manager is arranged to additionally store in the data store  126  the PSTN number of the user device  102  in association with the PSTN number allocated to the entity. The PSTN number of the user device may be reported to the call manager in either step S 3  or step S 4 . In this embodiment of the invention the address of the entity may be resolved using the PSTN number allocated to the entity and the PSTN number of the device. In this case one PSTN number may be allocated for use by more than one user. 
         [0058]    The contact list  132  together with the PSTN numbers allocated to each entity in the contact list are transmitted from the communication instance to the client program  124 . 
         [0059]    In a preferred embodiment of the invention the allocated PSTN numbers and the contact list  132  are transmitted to the client program  124  in data packets via the data connection  111 . The allocated PSTN numbers may be provided in a separate data packet from the contact list  132 . 
         [0060]    At least part of the PSTN numbers may be provided to the client program in a ‘call set up’ data packet comprising the attributes listed in table 2: 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 KEY 
                 TYPE 
                 ATTRIBUTE 
               
               
                   
               
             
             
               
                 CHUNKTYPE 
                 integer 
                 CALLSETUP 
               
               
                 CALLMETHOD 
                 integer 
                 a numeric value identifying 
               
               
                   
                   
                 calling method to use 
               
               
                 DIALIN_NUMBER_PREFIX 
                 string 
                 first number in dial-in number 
               
               
                   
                   
                 range, for example “ +3725521000” 
               
               
                 DIALIN_NUMBER_RANGE_SIZE 
                 integer 
                 # of numbers in dial-in block, 
               
               
                   
                   
                 for example 1000 
               
               
                 VOICEMAIL_NUMBER_PREFIX 
                 string 
                 dial-in number range for 
               
               
                   
                   
                 listening voicemails 
               
               
                 VOICEMAIL_NUMBER_RANGE_SIZE 
                 integer 
                 # of numbers in voicemail 
               
               
                   
                   
                 number block 
               
               
                   
               
             
          
         
       
     
         [0061]    In one embodiment of the invention each PSTN number for calling an entity may be listed separately in the data packet. However in a preferred embodiment, each PSTN number may be determined by the client program  124  from a first number and a second number corresponding to an index number identifying the contact in the contact list (see table 3). The range of indexes may be limited by of a number range defined in the data packet, as shown in table 2. 
         [0062]    Table 3 shows the attributes of the data packet containing the contact list  132 . Each entity in the contact list is given an index value starting from 1. The attribute container containing the contact list may further include the contacts username, or URI for contacting the contact using the peer to peer system, and the name of the contact. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 KEY 
                 TYPE 
                 ATTRIBUTE 
               
               
                   
               
             
             
               
                 CHUNKTYPE 
                 integer 
                 CONTACT 
               
               
                 CONTACTINDEX 
                 integer 
                 contact index value, starting from 1 
               
               
                 SKYPENAME 
                 string 
                 contact username 
               
               
                 FULLNAME 
                 string 
               
               
                 PSTNNUMBER 
                 string 
               
               
                   
               
             
          
         
       
     
         [0063]    The client program  124  may determine the PSTN number by arithmetically adding the first number to the second number. For example if the first number is defined as: 
         [0064]    +3725521020 
         [0065]    and the second number, corresponding to an index, is: 
         [0066]    33 
         [0067]    the PSTN number for the contact identified by index 33 will be: 
         [0068]    +3725521053 
         [0069]    Alternatively the client program may determine the PSTN number by appending the second number corresponding to a member of the number range to the first number. For example, if the first number is: 
         [0070]    +37255210 
         [0071]    and the index corresponding to the entity is: 
         [0072]    33 
         [0073]    the PSTN number will be: 
         [0074]    +3725521033 
         [0075]    In one embodiment of the invention the call method attribute referred to in table 2 may indicate how the PSTN number should be determined from the information provided in the data packet. For example, the call method may specify whether the PSTN number should be determined by arithmetically adding the member of the number range to the first number, or by appending the member of the number range to the first number, or whether the entire PSTN number is listed in the data packet. 
         [0076]    The communication instance  122  is arranged to send the contact list  132  to the client program  124 . In the case where the call method requires that part of the PSTN number is derived using the index of the contract, the client program  124  may generate a PSTN number for each contract having an index. In the case where the call method indicates that a list of entire PSTN numbers are provided in the call set up data packet the client program may determine which PSTN number corresponds to which entity by correlating the position of a PSTN number in the list with the index number provided for each entity in the contact list. 
         [0077]    In an embodiment of the invention a predefined PSTN number, or index, is reserved for communication events that occur with entities that are not listed in the contact list. In a preferred embodiment of the invention the index ‘0’ is reserved for entities that are not listed on the contact list. Additionally, other numbers may be reserved for transmitting control commands from the network  104  to the client program  124 . This will be described in more detail hereinafter. 
         [0078]    In accordance with an embodiment of the invention the user device  102  may receive calls from an entity located in the communication network via the PSTN network. The user device  102  may also establish a call to an entity located in the communication network  100  via the PSTN network using the PSTN number allocated to the entity. 
         [0079]      FIG. 5  shows the call connections made when placing calls between the user device  102  and entities located in the communication network. More specifically  FIG. 6  shows the following call connections: 
         [0080]    (1) an outbound call from the user device  102  to an entity  110   b  located in the PSTN network; 
         [0081]    (2) an outbound call from the user device  102  to an entity  110   a  located in the internet  104 ; 
         [0082]    (3) an inbound call to the user device  102  from an entity  110   b  located in the PSTN network; and 
         [0083]    (4) an inbound call to the user device  102  from an entity  110   a  located in the PSTN network. 
         [0084]    As shown in  FIG. 5 , inbound calls made to the client running on the user device  102  are routed to the session node  106  from the calling entity. The session node  106  is then able to determine the PSTN number of the device and the PSTN number allocated to the entity by querying the data store  126 . The method of receiving a call at the user device  102  will now be describe in detail in relation to  FIG. 7 . 
         [0085]      FIG. 7  is a diagram illustrating the reception of a call at the user device  102 . In  FIG. 7  the control data connection for handling the call set up and the media data connection for transmitting the media data are shown separately. The control data connection is shown as a solid line and the media data connection is shown as a broken line. 
         [0086]    The call may originate from an entity located in the packet switched network  104  or from an entity located in the circuit switched network  112 . The following method will be described the case where a call is initiated from an entity located in the internet  104 . 
         [0087]    In step S 10 , an incoming call from the packet switched network  104  is received at the communication instance  122  running on the session node  106 . The control data of the incoming call will identify the destination of the call with the username associated with user of the user device  102 . The username of the user is used to locate the communication instance  122  in the peer to peer system on the internet  104 . The control data may also identify the origin of the call by including username of the calling entity. 
         [0088]    In step S 20  the communication instance searches the data store  129  to determine the PSTN number of the device  102 . The communication instance may also search the contact list  132  associated with the user of the device  102  to determine if the username of the calling entity matches an entity listed in the contact list  132 . If calling entity is listed in the contact list  132 , the PSTN number allocated to the calling entity will be retrieved from the data store  129 . If the calling entity is not listed in the contact list the PSTN number reserved for entities not listed on the contact list will be retrieved. 
         [0089]    In step S 30 , the control data connection comprising the PSTN number of the device  102  is transmitted, together with the media data connection, to the outbound gateway  116 . The control data may also include the PSTN number retrieved from the data store  129  to identify the calling entity. 
         [0090]    In step  40  the call is transmitted from the outbound gateway  116  to the PSTN gateway  188  using the PSTN number of the device. The PSTN number retrieved from the data store  129  to identify the calling entity is also transmitted with the call. 
         [0091]    In step S 50  the call is transmitted to the user device  102  via the PSTN network. The PSTN number retrieved to identify the calling entity is recognised by the PSTN network and may be transmitted by the PSTN network to identify the origin of the call. 
         [0092]    If the calling entity has an allocated PSTN number, in step S 60  the client program  124  running on the user device  102  is arranged to resolve the allocated PSTN number to the associated contact details of the entity provided in the contact list  132 . This may be achieved by mapping the PSTN number of the calling entity to the username of the contact using the mapping method described previously. For example if the PSTN number associated with the calling entity is generated at the client program  124  using the index representing the entity, the client program may be arranged to subtract the first number from the PSTN number to derive the index and identify the contact. The username of the contact may then be displayed on the display of the user device to show that there is an incoming call from that contact. 
         [0093]    Alternatively, if the reserved PSTN number was transmitted with the call to identify that the calling entity was not stored on the contact list  132 , the client program  124  may be arranged to display the predefined text on the display of the user device which states that the caller is ‘unknown’. 
         [0094]    In an alternative embodiment of the invention the media data connection is not established via the communication instance  122  as shown in  FIG. 7 . Instead steps S 10  to S 30  may be used to set up the control data connection only. The media data connection may then be established between the outbound gateway and the calling entity after the control data connection is established. 
         [0095]    In an alternative embodiment of the invention the identity calling entity in the peer to peer system may be arranged to transmit a command to be carried out by the client program  124 . The command may for example relate to an instruction for the client program  124  to establish a connection with the session node  106 . The command may originate either from another node located in the network  104  or from the session node  106 . This embodiment of the invention will be described in relation to  FIG. 8 . 
         [0096]    In step S 101  the node  166  transmitting the communication event comprising the command is arranged to address the communication event to the username of the user of the device  102 . The command is identified as the caller identity of communication event. 
         [0097]    In step S 102  the communication instance receives the communication event. The communication instance is arranged to search the data store  129  to retrieve a PSTN number corresponding to the command listed in the contact list  132 . Additionally the communication instance is arranged to retrieve the PSTN number of the user device associated with the username. 
         [0098]    In step S 103  the communication event is routed to the user device  102  via the PSTN network using the PSTN number of the user device  102 . The PSTN number allocated to the command is transmitted with the communication event as the caller identity of the communication event. 
         [0099]    In step S 1104  the client program is arranged to resolve the caller identity of the communication event to the command listed in the contact list. The client program is then arranged to carry out the command. For example, if the command is ‘connect’ the client program will establish a connection with the session node  106 . 
         [0100]    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 claims.