Abstract:
A method of transmitting a communication event from a calling entity to a called entity located in a communication system comprising a first network and a second network, said method comprising determining a first identity associated with the calling entity and a first and second identity associated with the called entity, wherein the first identities are recognizable in the first network and the second identity is recognizable in the second network; associating at a first node located in the second network the first identities with the second identity; establishing a connection between the calling entity and a second node; wherein the connection with second node is established using the first identity associated with the called entity; querying the first node with the first identity associated with the called entity and the first identity associated with the calling entity to determine the second identity associated with the called entity; and transmitting the communication event to the called entity using the second identity associated with the called entity.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 11/986,977, filed Nov. 27, 2007, which 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 0723120.2 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 interne. 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 communication 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 communication networks when each device is located in a different communication network. 
         [0007]    In order to place a call from a device located in one network, such as a PSTN network, to a device located in a different network, such as one connected to the internet, it is necessary for the user of the device connected to the internet to register for a PSTN dial in number with the network provider so that calls can be made to the internet user from devices in the PSTN network. 
         [0008]    One disadvantage of this arrangement is that a device in the PSTN network can only place calls to devices connected to the internet if the user of the device has registered to have a PSTN number. A further disadvantage of this arrangement is that even if the internet user has registered to have a PSTN number, the user in the PSTN network may only call the user connected to the internet if he is aware of the PSTN number registered to the internet user. 
       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 present invention there is provided a method of transmitting a communication event from a calling entity to a called entity located in a communication system comprising a first network and a second network, said method comprising the steps of: determining a first identity associated with the calling entity and a first and second identity associated with the called entity, wherein the first identities are recognizable in the first network and the second identity is recognizable in the second network; associating at a first node located in the second network the first identities with the second identity; establishing a connection between the calling entity and a second node; wherein the connection with second node is established using the first identity associated with the called entity; querying the first node with the first identity associated with the called entity and the first identity associated with the calling entity to determine the second identity associated with the called entity; and transmitting the communication event to the called entity using the second identity associated with the called entity. 
         [0011]    According to a second aspect of the present invention there is provided a communication system comprising a first network and a second network, wherein the communication system is arranged to transmit a communication event from a calling entity to a called entity located in the communication system, said communication system comprising: a first network node located in the second network arranged to determine a first identity associated with the calling entity and a first and second identity associated with the called entity, wherein the first identities are recognizable in the first network and the second identity is recognizable in the second network; and to associate the first identities with the second identity; and a gateway node arranged to receive a connection established by the calling entity wherein the connection is established using the first identity associated with the called entity; wherein the first node is further arranged to provide the second identity associated with the called entity in response to receiving the first identity associated with the called entity and the first identity associated with the calling entity from the gateway node, such that the gateway node may transmit the communication event to the called entity using the second identity associated with the called entity. 
         [0012]    Since the caller is allocated a PSTN number to establish a call to another party, there is no need for the caller to have prior knowledge of a fixed PSTN number that is used by the other party to receive calls. 
         [0013]    A further advantage of embodiments of the present invention is that since both the caller identity and the allocated PSTN number are used to identify the called party, the same PSTN number may be allocated for use by more than one caller. 
         [0014]    As the PSTN number is allocated to a caller for the duration of a session, the caller may make more than one call the same party during a session without requiring a new number each time the call is established. 
         [0015]    A further advantage of embodiments of the present invention is that no information is required to be transmitted from the calling device in order to establish a call after a connection has been established with the PSTN network. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    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: 
           [0017]      FIG. 1  is a schematic representation of a communication network in accordance with an embodiment of the invention; 
           [0018]      FIG. 2   a  is a diagram showing the protocol stack of a client program in accordance with an embodiment of the present invention; 
           [0019]      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; 
           [0020]      FIG. 3  is a schematic representation of part of the communication network shown in  FIG. 1 ; 
           [0021]      FIG. 4  is a schematic representation of part of the communication system shown in  FIG. 1  according to an embodiment of the present invention; 
           [0022]      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. 
           [0023]      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 
           [0024]      FIG. 7  is a diagram showing the initiation of a call in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Reference will first be made to  FIG. 1 , in which is shown a communication network  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. 
         [0026]    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). 
         [0027]    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 . 
         [0028]    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 network  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). 
         [0029]    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 . 
         [0030]    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.    
         [0031]      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. 
         [0032]      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. 
         [0033]    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 . 
         [0034]    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. 
         [0035]    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 . The communication instance may include a protocol adapter for handling communications using different protocols.  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 . 
         [0036]    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. 
               
               
                   
               
             
          
         
       
     
         [0037]    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 . 
         [0038]    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 interne  104 . 
         [0039]    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 . 
         [0040]    The communication instance  122  associates the identity of the user of the user device, as defined by at least part of the login details of the user, with the identity 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  122 . 
         [0041]    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. 
         [0042]    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 network  100 . 
         [0043]    The entity may be any node in the communication system  100  that is capable of receiving information from the user device  102 . For example the entity may be another user device or a 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. 
         [0044]    Additionally an entity may be a node arranged to carry out control commands in the network. 
         [0045]    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 
         [0046]    (Uniform Resource Indicator), a username, or a VoIP device. The address of an entity that resides in the PSTN network may be a PSTN number associated with the entity. 
         [0047]    In one embodiment of the invention the entity may relate to more than one end point in the communication network  100 . 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. 
         [0048]    In accordance with an embodiment of the invention the user device  102  may establish a communication event with an entity via more than one network of the communication system. For example the user device  102  may establish a call using the PSTN network  112  to an entity located in the internet  104 . 
         [0049]    In order to establish a communication event with an entity over more than one network it is necessary to identify the entity in each network. 
         [0050]    In accordance with an embodiment of the invention the communication instance  122  is arranged to allocate an identity to an entity 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. 
         [0051]    For example, if the entity is located in the internet, the public IP address of the entity in the internet will not be recognized by the PSTN network. According to an embodiment of the invention the communication instance  122  is arranged to allocate a PSTN number to the entity that may be used to establish a call to the via the PSTN network. The allocated PSTN number may then be resolved to the IP address of the entity at a location in the internet. 
         [0052]    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 a data store  126 . In  FIG. 1  the data store  126  is shown as being associated with the call manager  118 . 
         [0053]    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 . 
         [0054]    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. 
         [0055]    In a preferred embodiment of the invention the address of an entity may be determined by the communication instance from the contact list  132  provided from the profile node  128 . This embodiment of the invention will be described with reference to  FIG. 4 . 
         [0056]      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. 
         [0057]    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 . 
         [0058]    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 . 
         [0059]    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. 
         [0060]    In step S 4  the communication instance  122  is arranged to allocate each PSTN number to each entity listed in the contact list and to report the address of each entity to the call manager, together with an indication of which PSTN number has been allocated to which entity. 
         [0061]    In step S 5  the call manager  118  is arranged to store in the data store  126  the address of each entity listed in the contact list in association with the allocated PSTN number. 
         [0062]    In a preferred embodiment of the invention the call manager  118  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 device may be reported to the call manager in either step S 3  or step S 4  by the communication instance. 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 having a communication instance running on the session node  106 . 
         [0063]    The allocated PSTN numbers may be stored in association with the address of each entity and the PSTN number of the user device  102  for the duration of the session between the client program  124  running on the device  102  and the session node  106 . A session is started when the session node  106  assigns a dedicated communication instance  122  to the client program  124 . A session may be closed when the client program  124  transmits a logout request to the session node, or when a session is timed out. 
         [0064]    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 . The contact list  132  and the allocated PSTN numbers may then be stored in a data store accessible to the client program  124 , located in the user device  102 . 
         [0065]    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 . 
         [0066]    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 
               
               
                   
               
             
          
         
       
     
         [0067]    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 corresponding to a ‘DIAL IN NUMBER PREFIX’ and a second number corresponding to an index number identifying the contact in the contact list (see table 3). The index number will fall within the number range, referred to as the ‘DIAL IN NUMBER RANGE’ as shown in table 2. 
         [0068]    The index number for each contact is transmitted in the contact list from the communication instance  122  to the client program  124 . 
         [0069]    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 
                 ENTITY 
               
               
                 ENTITYINDEX 
                 integer 
                 entity index value, starting from 1 
               
               
                 USERNAME 
                 string 
                 entity username 
               
               
                 FULLNAME 
                 string 
               
               
                 PSTNNUMBER 
                 string 
               
               
                   
               
             
          
         
       
     
         [0070]    The client program  124  may determine the PSTN number for each entity in the contact list by arithmetically adding the first number to the index for the entity. For example if the first number is defined as: and the index for an entity is: 
         [0000]    33
 
the PSTN number for the entity will be:
 
+3725521053
 
         [0071]    Alternatively the client program may determine the PSTN number by appending the index to the first number. For example, if the first number is: 
         [0000]    +37255210
 
and the index corresponding to an entity is:
 
33
 
the PSTN number for the entity will be:
 
+3725521033
 
         [0072]    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. 
         [0073]    Accordingly, the PSTN number allocated to an entity may be determined at the client program  124 , the communication instance  122  and the call manager  118 . 
         [0074]    In accordance with an embodiment of the invention the user device  102  may establish a call to an entity located in the communication network  100  via the PSTN network using the PSTN number allocated to the entity. The user device  102  may also receive calls from an entity located in the communication network via the PSTN network. 
         [0075]      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. 5  shows the following call connections: 
         [0076]    (1) an outbound call from the user device  102  to an entity  110   b  located in the PSTN network; 
         [0077]    (2) an outbound call from the user device  102  to an entity  110   a  located in the internet  104 ; 
         [0078]    (3) an inbound call to the user device  102  from an entity  110   b  located in the PSTN network; and 
         [0079]    (4) an inbound call to the user device  102  from an entity  110   a  located in the PSTN network. 
         [0080]    As shown in  FIG. 5 , outbound calls made from the user device  102  to an entity are routed to the inbound gateway  114 . The inbound gateway is then able to determine the address of the entity by querying the data store  126  via the logical connections illustrated in  FIG. 6 . The method of calling an entity from the user device  102  will now be describe in detail in relation to  FIG. 7 . 
         [0081]    A call comprises both a media data connection and a control data for handling the call set up. In  FIG. 7  the control data connection for transmitting control data 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 call connection is shown as a broken line. 
         [0082]    In step S 100  the user of the user device  102  initiates a call to an entity listed in the contact list  132 . The contact list  132  may be displayed by the user interface layer of the client program  124  as selectable links on a display of the user device  102 . The user may initiate a call to the entity by selecting a link for that entity. When the user initiates the call the client program  124  is arranged to dial the PSTN number allocated to that entity. The call placed by the client program  124  will therefore include control data that defines the allocated PSTN number. The control data will also include the PSTN number of the user device  102 . The dialled PSTN number allocated to entity is used to establish a media data connection and control data connection with the PSTN gateway  188  via the GSM audio connection  222 . 
         [0083]    In step  200  the media data connection is held at the PSTN gateway  188 . The PSTN gateway  188  is arranged to transmit the control data to the inbound gateway located in the internet  104 . The PSTN gateway  188  is arranged to transmit control data comprising recognised PSTN numbers to the inbound gateway  114 . The PSTN gateway may recognise numbers that have been provided for use by the call manager  118  by the operator of the PSTN network. 
         [0084]    In step S 300  the inbound gateway  114  transmits the control data comprising the allocated PSTN number of the called entity and the PSTN number of the user device to the call manager  118 . The media data connection is held at the PSTN gateway  188  until the allocated PSTN number of the called entity is resolved to the address of the entity. 
         [0085]    At step S 400  the call manager  118  uses the PSTN number of the device  102  to search the data store  126  for the contact list  132  associated with the user of the device  102 . The PSTN allocated to the entity is then used to locate the address of the entity as defined in the contact list  132 . In one embodiment of the invention the call manager may also retrieve the username of the user associated with the user of the user device  102 . 
         [0086]    In step S 500  the address of the entity is transmitted to the inbound gateway  114 . The call manager  118  may also transmit the username of the user of the user device  102  to the inbound gateway  114 . 
         [0087]    In step S 600  the inbound gateway  114  accepts the media data from the PSTN gateway and uses the address of the entity received from the call manager  118  to transmit the call via the packet switched network  104 . If the address of the entity is located in the PSTN network the inbound gateway will transmit the call to the PSTN network via the outbound gateway  116  (shown in  FIG. 1 ). 
         [0088]    In step S 700  the call is received at the called entity, e.g. device  110   a  or  110   b . If the called entity is located in the internet  104  the username of the user of the device  102  retrieved in step S 500  may be displayed on the device  110   a  to indicate the origin of the call. 
         [0089]    In an alternative embodiment of the present invention the entity that the user of the user device  102  places a call to is not listed as a contact in the contact list  132 . In this embodiment of the invention the user device  102  is arranged to provide the communication instance  122  with the address of the entity via the data connection  111  before initiating a call with the entity. In this embodiment of the invention a PSTN number defined in the ‘call set up’ message described in relation to table 2 is reserved for an entity that is not listed in the contact list. When the communication instance receives the address of the entity from the user device, the address of the entity is stored in the data store  126  in association with the reserved PSTN number. A call may then be placed to the entity via the PSTN network in accordance with the method steps described in relation to  FIG. 7 . 
         [0090]    In a further alternative embodiment of the invention, for predefined addresses stored in the data store  126  the call manager is arranged to instruct the inbound gateway to not accept the call and instead to provide the PSTN gateway  188  with the address to route the call via the PSTN network. In a preferred embodiment these addresses may relate to emergency numbers e.g. ‘999’. 
         [0091]    In one embodiment of the invention the address of an entity may specify the location of a voicemail record associated with the user. The address of a voicemail record may be determined using the username of the user and the address of a voicemail node. The address of the voicemail node may be prestored in the data store  126 . Alternatively the address of the voicemail record may be provided in the contact list associated with the user. 
         [0092]    In an further embodiment of the invention the address of an entity may specify a control command that may be implemented by a node. For example the address of the entity may define a specific action to be implemented for the user&#39;s voicemail record by the voicemail node. For example the control command may cause the voicemail node to delete all messages stored in the user&#39;s voicemail record. 
         [0093]    In one embodiment of the invention the communication instance is arranged to provide information relating to the geographical location of the user device  102  to the call manager  118  when requesting a PSTN number. In this embodiment of the invention the call manager is arranged to provide the communication instance  122  with PSTN numbers that relate to PSTN gateways that are local to the user device, otherwise referred to as a local number. 
         [0094]    In an alternative embodiment of the addresses of the entities having an allocated PSTN number may be stored at a data store associated with the inbound gateway. In this embodiment of the invention the address may be resolved at the inbound gateway. 
         [0095]    In an alternative embodiment of the addresses of the entities having an allocated PSTN number may be stored at a data store associated with the PSTN gateway In this embodiment of the invention the address may be resolved at the PSTN gateway. 
         [0096]    In an alternative embodiment of the invention the call data may be held at the PSTN gateway until the address of the entity is resolved. In this case the inbound gateway  114  instructs the PSTN gateway to forward the call data after the address of the entity is resolved. 
         [0097]    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.