FIELD OF THE INVENTION 
   The present invention relates to a node for providing a file service to a mobile terminal, particularly, but not exclusively, for use in a Next Generation Network. 
   BACKGROUND ART 
   Next Generation Networks (NGNs) allow operators to incorporate voice, video and data services into customised service bundles. Thus, a need arises to provide mobile users with the facility to organise and share files. A need also arises to allow mobile users to access services through local and global networks, regardless of access environment, location and operator. 
   Existing wireless telecommunication networks allow subscribers to make and receive voice calls using their terminals via a wireless network other than one with which they are registered (usually referred to as a “visited network” and a “home network” respectively). This service is known as “roaming”. 
   Much effort has been directed to providing fast, seamless voice roaming. However, little attention has been paid to the problem of how to allow mobile users to access and share files easily and conveniently. In most cases, mobile users access files located in their home network by accessing a portal via an Internet connection. 
   The present invention seeks to provide a node for providing a file service to a mobile terminal. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of certain embodiments of the present invention there is provided a node for providing a file service to a mobile terminal, the node comprising an interface for interfacing with a mobile terminal, a system for managing files for a plurality of users, each user having a user folder, and at least one processing module configured, in response to receiving a request for file access from a mobile terminal, to identify a user folder, to determine whether the file managing system manages the user folder and, in dependence upon whether the file managing system manages the user folder, to retrieve an entry point for the user folder and to transmit the entry point to the mobile terminal. 
   Thus, a user can access their files seamlessly through such nodes. 
   The node may further comprise storage for storing metadata for the file system, wherein the at least one processing module is configured to retrieve the entry point from the metadata. 
   The at least one processing module may be configured, in response to determining that the file managing system does not manage the user folder, to identify another node which manages the user folder, to request metadata for the user folder from the other node, to receive the metadata from the other node, to retrieve the entry point from the metadata and to transmit the entry point to the mobile terminal. The node may comprise storage for storing metadata, wherein the at least one processing module is configured to store received metadata in the metadata storage for at least a predetermined duration of time. 
   The at least one processing module may be configured to identify a user from the request and, in dependence upon a user identity, to identify the user folder. The at least one processing module may be configured, in response to receiving a command to grant permission to a second user to access a first user&#39;s file or folder, to identify a node managing the second user&#39;s user folder and to send a message to the node, the message including metadata for the file or folder. 
   The node may further comprise storage for storing metadata for the file system, wherein the at least one processing module is configured, in response to receiving a message from another node granting permission to the user to access another user&#39;s file or folder and which includes metadata for the file or folder, to stored the metadata in the metadatastorage. 
   The at least one processing module may be configured to inspect a network identifier provided by the mobile terminal so as to determine whether the file managing system manages the user folder. The entry point may comprise a security identifier. The at least one processing module may be configured, in response to receiving a request for file access from a mobile terminal, to authenticate the mobile terminal. 
   According to a second aspect of certain embodiments of the present invention there is provided a node for providing a file service to a mobile terminal, the node comprising an interface for interfacing with a mobile terminal, a system for managing files for a plurality of users, each user having a user folder, and at least one processing module configured, in response to receiving a command to grant permission to a second user to access a first user&#39;s file or folder, to identify a node managing the second user&#39;s user folder and to send a message to the node, the message including metadata for the file or folder. 
   Thus, a user can share files easily through such nodes. 
   According to a third aspect of certain embodiments of the present invention there is provided a node for providing a file service to a mobile terminal, the node comprising an interface for interfacing with a mobile terminal, a system for managing files for a plurality of users, each user having a user folder, and at least one processing module configured in response to receiving a message from another node granting permission to a second user to access a first user&#39;s file or folder and which includes metadata for the file or folder, to store the metadata in the metadatastorage. 
   According to a fourth aspect of certain embodiments of the present invention there is provided a system for serving a file comprising the node and storage, remotely located from the node, for storing the files. 
   According to a fifth aspect of certain embodiments of the present invention there is provided a communications network including the file serving system. 
   The communications network may include at least one access point configured, in response to receiving a request for connection to a node from a mobile terminal, to return an address for the node to the mobile terminal. 
   According to a sixth aspect of certain embodiments of the present invention there is provided a method of operating a node for providing a file service to a mobile terminal, the method comprising receiving a request for file access from a mobile terminal, identifying a user folder, determining whether the node manages the user folder, retrieving an entry point for the user folder and transmitting the entry point to the mobile terminal. 
   The method may further comprise identifying another node which manages the user folder, requesting the metadata for the user folder from the other node, receiving the metadata from the other node, retrieving the entry point from the metadata. 
   According to a seventh aspect of certain embodiments of the present invention there is provided a method of operating a node for providing a file service to a mobile terminal, the method comprising receiving a command to grant permission to a second user to access a first user&#39;s file or folder, identifying a node managing the second user&#39;s user folder and sending a message to the node, the message including metadata for the file or folder. 
   According to an eighth aspect of certain embodiments of the present invention there is provided a method of operating a node for providing a file service to a mobile terminal, the method comprising receiving a message from another node granting permission to a second user to access a first user&#39;s file or folder and which includes metadata for the file or folder, and storing the metadata in metadatastorage. 
   According to a ninth aspect of certain embodiments of the present invention there is provided a computer-readable medium storing a computer program comprising instructions which, when executed by at least one computer causes the at least one computer to perform the method. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: 
       FIG. 1  shows a system of data networks accessible by mobile terminals; 
       FIG. 2  is a functional block diagram of a node for providing a file service to mobile terminals; 
       FIG. 3  is a block of a computer system for implementing at least some of the functions of the node shown in  FIG. 2 ; 
       FIG. 4  is a sequence flow diagram illustrating a method of discovering a node in a home network; 
       FIG. 5  illustrates structure of metadata entry point; 
       FIG. 6  is a sequence flow diagram illustrating a method of discovering a node in a visited network; 
       FIG. 7  illustrates structure of metadata; 
       FIG. 8  is a sequence flow diagram illustrating a method of sending an invitation to share a file; 
       FIG. 9  illustrates structure of the invitation sent in the method described with reference to  FIG. 7 ; 
       FIG. 10  is a sequence flow diagram illustrating a method of downloading a file; and 
       FIG. 11  is a sequence flow diagram illustrating a method of uploading a file. 
   


   DETAILED DESCRIPTION OF EMBODIMENTS 
   Referring to  FIG. 1 , a system of data networks  1 ,  2 ,  3  in accordance with some embodiments of the present invention is shown. The data networks  1 ,  2 ,  3  are accessed via respective access networks  4 ,  5 ,  6  and interconnected by a backbone network  7 . 
   In this example, the data networks  1 ,  2 ,  3  are General Packet Radio Services (GPRS) core networks and the access networks  4 ,  5 ,  6  are UMTS Terrestrial Radio Access Networks (UTRANs). However, the data networks  1 ,  2 ,  3  and access networks  4 ,  5 ,  6  need not be third-generation mobile telephone networks or even mobile telephone networks. For example, the access networks  4 ,  5 ,  6  (which can be unified with their respective data networks  1 ,  2 ,  3 ) can be wireless networks, for example conforming to IEEE 802.11, often referred to as a “wireless local area network” or WLAN, or IEEE 802.16, usually known as “WiMax”, or even wired networks. Each data network  1 ,  2 ,  3  may be accessible via more than one access network (not shown) using different forms of connectivity. In this example, the data networks  1 ,  2 ,  3  are Internet Protocol (IP) networks, although they need not be IP networks. 
   The data networks  1 ,  2 ,  3  are controlled by different network operators (not shown) and serve different geographic regions. However, different networks  1 ,  2 ,  3  can serve the same region(s). 
   In a first location  8 , a user (not shown) subscribes or is registered to use the first network  1  and is able to store and access data via the first network  1  (referred to as their “home” network) using a mobile terminal  9  (or “user equipment”). As will be explained in more detail later, in a second location  10 , the user can also access their data via the second network  2  (referred to as their “visited” or “roamed” network). Furthermore, the user can also share their data with another user (not shown) through their corresponding terminal  11 . 
   Each data network  1 ,  2 ,  3  includes at least one node  12 ,  13 ,  14  (hereinafter referred to as “service nodes”) for providing a file service, for example providing access to the user&#39;s files  15 , to mobile terminals  9 ,  11 . Responsibility for the user&#39;s files  15  is taken by the node  12  in the user&#39;s home network  1  (hereinafter referred to as “the home node”). However, if there is more than one service node in the user&#39;s home network  1 , then one of the service nodes is chosen to be the home node  12 , for example, when the user first registers with the network  1 . 
   Each data network  1 ,  2 ,  3  has a respective storage farm  16 ,  17 ,  18  each comprising at least one storage device  19   1 , . . . ,  19   N . Only storage devices  19   1 , . . . ,  19   N  for a first storage farm  16  are illustrated for clarity. If a home node  12  receives a request  20  from a subscriber to access their files  15  and the subscriber is located in their home network  1 , then the home node  12  returns, to the mobile terminal  9 , a metadata entry point  21  for accessing the files  15 . However, if a different node  13  receives the request  20 , e.g. because the subscriber is visiting the second network  2 , then the node  13  identifies the home node  12 , retrieves and caches metadata  22 , and returns the metadata entry point  21  to the mobile terminal  9 . 
   To help identify and/or authenticate mobile terminals  9 ,  11 , the service nodes  12 ,  13 ,  14  may interrogate operator databases  23 ,  24 ,  25 , such as home subscriber servers or user profile server. 
   As shown in  FIG. 1 , the service nodes  12 ,  13 ,  14  can be accessed via respective gateways  26 ,  27 ,  28 . 
   Referring to  FIG. 2 , the service node  12 ,  13 ,  14  is shown in more detail. 
   The service nodes  12 ,  13 ,  14  are provided by servers  42  ( FIG. 3 ) implemented in the network domain (i.e. ISO/OSI layer 3) with interfaces to the core network  1 ,  2 ,  3  ( FIG. 1 ), storage pools  16 ,  17 ,  18  and operator databases  23 ,  24 ,  25 . In this example, the service nodes  12 ,  13 ,  14  are neither part of the core network  1 ,  2 ,  3  ( FIG. 1 ), nor sit on network elements (not shown), such as switches. 
   Each service node  12 ,  13 ,  14  interfaces with network elements through protocols, such as DIAMETER for interfacing with the operator&#39;s subscriber register  15 ,  16 ,  17 , and session initiation protocol (SIP) for session initiation and control. 
   Each service node  12 ,  13 ,  14  includes an access function  29  (hereinafter referred to as the “access point”), a home network interfacing function  30  (hereinafter referred to as the “home point”) and a file serving function  31  (hereinafter referred to simply as the “serving point”). A function may also be referred to as a “component” or “module”. 
   The access point  29  includes a session manager  32 , a home point identifier module  33  and a routing request manager  34 . 
   The access point  29  is configured to manage sessions between the service node  12 ,  13 ,  14  and mobile terminals  9 ,  11 , to identify the mobile terminal&#39;s home point  30  and to route messages between the mobile terminal  9 ,  11  and the home point  30  and the serving point  31 , which may be attached to the same or a different node  12 ,  13 ,  14 . 
   Requests from mobile terminal  9 ,  11  are directed to the access point  29  of the node  12 ,  13 ,  14  in the network  1 ,  2 ,  3  to which the mobile terminal  9 ,  11  is connected. Thus, taking the example of the first mobile terminal  9 , if the mobile terminal  9  is connected to its home network  1  ( FIG. 1 ), then it will connect to the access point  29  of the node  12  of its home network  1  ( FIG. 1 ). If the mobile terminal  9  is connected to a visited network  2  ( FIG. 1 ), then it will connect to the access point  29  of the node  13  of the visited network  2  ( FIG. 1 ). 
   The node  12  in the subscriber&#39;s home network  1  (hereinafter referred to as the subscriber&#39;s “home node”) and its corresponding home point  30  (“the subscriber&#39;s home point”) is identified using the subscriber&#39;s network identifier, which in this example is in the form of a telephone number. However, the subscriber&#39;s network identifier may take other forms, such as data stored on a subscriber identity module (SIM) or data entered into the mobile terminal  9  by the user. 
   The subscriber&#39;s network identifier is used by the access point  29  to identify the subscriber&#39;s home network  1 . A configuration of the home point  30  for the home network  1  is retrieved from a table (not shown) listing peer nodes  12 ,  13 ,  14 , for example stored in each operator database  23 ,  24 ,  25  or in another database (not shown). 
   The access point  29  manages sessions and profiles by caching file system metadata and user information, including credential information and information about the configuration of the subscriber&#39;s home point  30 . 
   A new session is established each time a client  51  ( FIG. 4 ) is started on the mobile terminal  9 . An existing session ends when the client  51  ( FIG. 4 ) terminates, the session times out or a new session is established for the same network identifier. 
   The home point  30  includes a subscriber identification and authentication module  35 , a home point identifier module  36  and a request routing module  37 . 
   The home point  30  interfaces with the operator database  23 ,  24 ,  25  in its network  1 ,  2 ,  3  which stores subscription-related records (also referred to as “user profiles”) and authentication and authorisation data. 
   The home point  30  also maps the subscriber&#39;s network identifier (e.g. telephone number) to the user&#39;s security identity in the serving point  31  of each network  1 ,  2 ,  3 . The home point  30  stores a table including entries, each entry listing a network identity (herein also referred to as “NetworkID”), for example in the form of a country and area code, a user identity for example in the form of a telephone number (within given country and area) and a corresponding security identity (herein also referred to as a “SID”). The security identity is generated at a service node  12 ,  13 ,  14  where a file is hosted, which may be the user&#39;s service node or an inviter&#39;s service node. 
   The serving point  31  includes a file system facade  38  and stores metadata  39  (including user&#39;s meta data  22 ) and a file system  40 . 
   The serving point  31  provides an interface with the network operator&#39;s file system  40  and respective storage farms  16 ,  17 ,  18 . In this example, each storage farm  16 ,  17 ,  18  is located in its respective data network  1 ,  2 ,  3 . For example, the storage farm  16 ,  17 ,  18  may be physically co-located with the service point  31 . However, the storage farm  16 ,  17 ,  18  need not be located in the data network  1 ,  2 ,  3  and storage devices  19   t , . . . ,  19   N  providing the storage farm  16 ,  17 ,  18  may be distributed. 
   Referring to  FIG. 3 , the access point  29 , home point  30  and serving point  31  are implemented by respective servers  42 . However, more than one server  42  can be used to implement each component  29 ,  30 ,  31 . In some embodiments, the servers are co-located. In other embodiments, the servers  42  are distributed. 
   Each server  42  includes a processor  43 , memory  44  and an input/output (I/O) interface  45  operatively connected by a bus  46 . A server  42  may include more than one processor. The I/O interface  45  is operatively connected to a network interface  47 , storage  48  in the form of hard disc drives and, optionally, removable storage  49 . Other elements, including peripheral devices such as keyboards (not shown) and displays (not shown), may be temporarily or permanently provided. 
   Respective computer program codes  50  which, when executed by a server  42 , causes the server  42  to provide a components  29 ,  30 ,  31  are stored on a hard drive  48  and loaded into memory  44  for execution by the processor  43 . The computer program codes  50  may be stored on and transferred from removable storage  49  or through network interface  47  from a remote source (not shown). 
   Referring to  FIGS. 1 ,  2  and  4 , a method of discovering a service node  12  in a home network  1  will now be described, in which a mobile terminal  9  contacts its home operator&#39;s service node  12  and creates a session which enables the user to proceed with file and folder operations, such as storing, updating and reading files. 
   The user starts a client  51  on their mobile terminal  9 . If not already connected to the data network  1 , the client  51  automatically (e.g. without further user instruction) causes the mobile terminal  9  to establish a connection with the data network  1 . 
   The client  51  sends a query  52  to the gateway  26  asking for availability and an address of the network&#39;s access point  29  (step S 401 ). The gateway  26  returns a message  53  which includes the address (e.g. an access point name or an IP address) of the network&#39;s access point  29  (step S 402 ) and the client  51  sends a request  54  to the identified access point  29  to be connected thereto (step S 403 ). 
   The access point  29  creates a session (step S 404 ), identifies the home point  30  of the home node  12  (i.e. the “user&#39;s home point”) (step S 405 ) and retrieves an access address of the user&#39;s home point  30  (step S 406 ). 
   The access point  29  contacts the user&#39;s home point  30  and sends a request  55  to authenticate the user (step S 407 ). The request  55  identifies the user using a network identity (e.g. country and area codes) and a user identity (e.g. telephone number). The user&#39;s home point  30  returns a message  56  verifying (or not) that the user is authenticated (step S 408 ). The verifying message  56  includes a security identifier for the file system  40 . If the user is authenticated, then the process continues, otherwise it terminates. 
   The access point  29  determines whether the user is camped in their home network (i.e. whether the service node  12  is the user&#39;s home node) (step S 409 ). If the service node  12  is the user&#39;s home node, then the access point  29  sends a message  57  to inform the client  51  that it is connected and identifies the session (step S 410 ). In the event that the service node  12  is not the user&#39;s home node (i.e. that the user&#39;s home point is provided by a different service node  13 ,  14 ), the access node  29  responds differently and the response is described hereinafter with reference to  FIG. 6 . 
   The client  51  sends a request  20  to the access point  29  for the user&#39;s entry point of metadata (step S 411 ). The request  20 , which may be referred to as a “call function”, can specify whether an entry point to a root folder or a specific folder is required. For example, a request “GetMDSEntryPoint( )” can be used to ascertain the entry point to the root folder. Alternatively, a request “GetMDSEntryPoint(EntityID)” can be used to find entry point for a folder specified by the argument, namely EntityID. If the client  51  knows the EntityID for the root folder, then GetMDSEntryPoint(EntityID) can be used to find the entry point for the root folder. As will be described in more detail later, the entry point metadata  21  describes a folder and its content. The access node  29  checks whether the user is in its home network (step S 412 ). If the user is in its home network, then the access node  29  sends a request  20  to the home point  30  requesting the user&#39;s entry point of metadata (step S 413 ). The request  20  is forwarded to the serving point  31  (step S 414 ). The serving point  31  retrieves the user&#39;s metadata entry point  21  from metadata  39  ( FIG. 2 ) and returns the metadata entry point  21  to the home point  30  (step S 415 ), which in turn forwards it to the access point  29  (step S 416 ). The access point  29  forwards the metadata entry point  29  to the client  51  (step S 417 ). 
   The user&#39;s metadata entry point  21  is stored locally (i.e. in the mobile terminal  9 ) until a predefined event or timeout occurs. Using the metadata entry point  21 , the user is able to proceed with other operations, such as uploading, downloading, sharing or changing the file and folder attributes. 
   Referring to  FIG. 5 , the structure  60  of the metadata entry point  21  is shown in the form of an XML schema diagram. 
   A metadata entry point  21  includes information  61  about a folder (e.g. a root folder) and information  62  about its content. 
   The folder information  61  may include an entity identifier  63  (herein also referred to as “EntityID”), an entity name  64  and an entity type  65 . 
   Likewise, the content information  62  may include information  66  about each entity in the form of a set of attributes  67  which may include an entity identity  68 , an entity name  69  and an entity type  70 . The entity may be a file or a folder. The entity identity  68  can be used by a client  51  in subsequent requests for information about sub-directories. 
   The metadata entry point  21  for a root folder may also include invitations  72  from other users to access files. Each invitation  72  includes information  73  about the file or folder that the user has been invited to access and includes an inviter identity  74 , an invitee identity  75 , an entity identity  76 , a security identity  77  and a network identity  78 . 
   An example of a metadata entry point  21  for a root folder conforming to the structure  60  shown in  FIG. 5  is given below: 
   
     
       
             
             
           
         
             
                 
                 
             
           
           
             
                 
               &lt;MDSEntryPoints &gt; 
             
             
                 
                &lt;MDSEntryPoint EntityID=“5” EntityName=“John Root” 
             
             
                 
                EntityType=“Folder”&gt; 
             
             
                 
                 &lt;EntityContent&gt; 
             
             
                 
                  &lt;SubEntity EntityID=“7” EntityType=“Folder” 
             
             
                 
                  EntityName=“My Documents”/&gt; 
             
             
                 
                  &lt;SubEntity EntityID=“6” EntityType=“File” 
             
             
                 
                  EntityName=“picture.jpg”/&gt; 
             
             
                 
                 &lt;/EntityContent&gt; 
             
             
                 
                &lt;/MDSEntryPoint&gt; 
             
             
                 
                &lt;Invititions&gt; 
             
             
                 
                 &lt;Invitation EntityID=“201” InviteeID=“6192244” 
             
             
                 
               InviterID=“437981” NetworkID=“441234” SID=“31” /&gt; 
             
             
                 
                &lt;/Invititions&gt; 
             
             
                 
               &lt;/MDSEntryPoints&gt; 
             
             
                 
                 
             
           
        
       
     
   
   The root folder is called “John Root” and is identified in the file system by an EntityID “5”. The root folder contains a folder called “My Documents” and a file called “picture.jpg” identified by EntityIDs “7” and “6” respectively. 
   The root folder also includes an invitation from another user to access a folder (not shown). The invitation does not specify the name of the folder. However, the invitation identifies the file in the inviter&#39;s file system using an EntityID and a SID assigned by the inviter&#39;s service node and identifies the inviter&#39;s network using an inviter&#39;s network ID, in this case, using country and area codes, and the inviter&#39;s user ID, in this example, using a telephone number within the network (i.e. excluding any county and area codes). The invitation also specifies the invitee, in this instance, using the invitee&#39;s telephone number within the network. 
   It will be appreciated that the example just given is simplified and that a metadata entry point  21  may contain many more sub-entities. 
   A metadata structure is a whole set of ordered data organized in a parent-child hierarchy in which each element contains information about its own and its underlying name, type, structure, contents, and invitation characteristics. 
   A metadata entry point is a subset of a metadata structure which only contains information about a particular entry point and its underlying files and folders, with no further information about other elements in the hierarchy and no information about the contents of its subfolders. Hence, the entry point represents a peek into a certain point in the metadata structure. 
   As will be explained in more detail later, in certain circumstances, initial queries are for the metadata structure so as to cache the whole structure in a visited network and, thus, minimize traffic. Subsequent queries are for entry points in the cached metadata structure. Therefore, most of the user&#39;s requests are querying for entry points. 
   Below is an illustration in XML notation of a metadata structure and a certain metadata entry point in that metadata structure: 
   
     
       
             
           
         
             
                 
             
           
           
             
               &lt;MDS &gt; 
             
             
                &lt;Invititions&gt; 
             
             
                 &lt;Invitation EntityID=“201” InviteeID=“6192244” InviterID=“437979” 
             
             
               NetworkID=“441223” SID=“31”/&gt; 
             
             
                &lt;/Invititions&gt; 
             
             
                &lt;Entity EntityID=“5” EntityName=“John Root” EntityType=“Folder”&gt; 
             
             
                 &lt;EntityContent&gt; 
             
             
                  &lt;Entity EntityID=“7” EntityName=“My Documents” EntityType=“Folder”&gt; 
             
             
                   &lt;EntityContent&gt; 
             
             
                    &lt;Entity EntityID=“14” EntityName=“Work Related” EntityType=“Folder”&gt; 
             
             
                     &lt;EntityContent&gt; 
             
             
                      &lt;Entity EntityID=“63” EntityName=“Proposals” EntityType=“Folder”/&gt; 
             
             
                      &lt;Entity EntityID=“112” EntityName=“BusinessPlan.doc” EntityType=“File”/&gt; 
             
             
                     &lt;/EntityContent&gt; 
             
             
                    &lt;/Entity&gt; 
             
             
                    &lt;Entity EntityID=“17” EntityName=“Entertainment” EntityType=“Folder”&gt; 
             
             
                     &lt;EntityContent&gt; 
             
             
                      &lt;Entity EntityID=“211” EntityName=“MJ.avi” EntityType=“File”/&gt; 
             
             
                     &lt;/EntityContent&gt; 
             
             
                    &lt;/Entity&gt; 
             
             
                    &lt;Entity EntityID=“72” EntityName=“pim.db” EntityType=“File”/&gt; 
             
             
                   &lt;/EntityContent&gt; 
             
             
                  &lt;/Entity&gt; 
             
             
                  &lt;Entity EntityID=“6” EntityName=“Picture.jpg” EntityType=“File”/&gt; 
             
             
                 &lt;/EntityContent&gt; 
             
             
                &lt;/Entity&gt; 
             
             
               &lt;/MDS&gt; 
             
             
               &lt;MDSEntryPoints &gt; 
             
             
                &lt;MDSEntryPoint EntityID=“5” EntityName=“John Root” EntityType=“Folder”&gt; 
             
             
                 &lt;EntityContent&gt; 
             
             
                  &lt;SubEntity EntityID=“7” EntityType=“Folder” EntityName=“My Documents”/&gt; 
             
             
                  &lt;SubEntity EntityID=“6” EntityType=“File” EntityName=“picture.jpg”/&gt; 
             
             
                 &lt;/EntityContent&gt; 
             
             
                &lt;/MDSEntryPoint&gt; 
             
             
                &lt;Invititions&gt; 
             
             
                 &lt;Invitation EntityID=“201” InviteeID=“6192244” InviterID=“437981” 
             
             
               NetworkID=“441234” SID=“31” /&gt; 
             
             
                 
             
           
        
       
     
   
   Referring again to  FIG. 4 , once a client  51  has sent a request  20  for an entry point to the user&#39;s root folder, e.g. using GetMDSEntryPoint( ), and received a metadata entry point  21  for the root folder, then the client  51  can send further requests  20  for an entry point to sub-folders, e.g. using GetMDSEntryPoint(EntityID). 
   Referring to  FIGS. 1 ,  2  and  6 , a method of discovering a service node  13  in a visited network  2  will now be described, in which a user wishes to access files and folders in their home network  1 . 
   The user starts a client  51  on their mobile terminal  9 . If not already connected to the data network  2 , the client  51  automatically (e.g. without further user instruction) causes the mobile terminal  9  to establish a connection with the data network  2 . 
   The client  51  sends a query  52  to a gateway  27  asking for availability and an address of the network&#39;s access point  19  and requests connection in the same way as steps S 401  to  403  hereinbefore described (steps S 603 ). The access point  29  of the visited service node  13  creates a session (step S 604 ), identifies the home point  30  of the home node  12  (i.e. the “user&#39;s home point”) (step S 605 ) and retrieves an access address of the user&#39;s home point  30  (step S 606 ) in the same way as steps S 604  to  606  hereinbefore described. Also, the access point  29  may contact the user&#39;s home point  30  (step S 607 ) and send a request  55  to authenticate the user, to which the user&#39;s home point  30  returns a message  56  verifying (or not) that the user is authenticated and, if authenticated, the security identity (step S 608 ). 
   The access point  29  determines whether the network  2  is home to the user or whether the user is visiting (step S 609 ). If the service node  13  is visiting, then the access point  29  sends a request  79  to the user&#39;s home node to be sent metadata  22  (step S 610 ). 
   The home point  30  at the user&#39;s home node  12  forwards the request  79  to the service point  31  (step S 611 ). 
   The service point  31  returns metadata  21  for the user to the home point  30  (step S 612 ), which in turn forwards the metadata  22  to the access point  29  (step S 613 ). The metadata  22  describes the user&#39;s file structure including a top-level folder and sub-folders, and files therein. 
   The access point  29  caches the metadata  22  locally (step S 614 ). The access point  29  sends a message  57  to inform the client  51  that it is connected and identifies the session (step S 616 ). 
   The client  51  sends a request  20  to the access point  29  for the user&#39;s metadata entry point  21  (step S 617 ). The access node  29  checks whether the user is in its home network (step S 618 ). If the user is visiting, then the access node  29  retrieves the user&#39;s metadata entry point  21  stored locally and returns the metadata entry point  21  to the client  51  (step S 619 ). 
   Using the metadata entry point  21 , even though they are located in a visited network  2 , the user is able to proceed with other operations, such as uploading, downloading, sharing or changing the file and folder attributes in the same way that they could in their home network  1 . 
   Referring to  FIG. 7 , the structure  80  of the metadata  22  is shown. 
   Metadata  22  includes information  81  about the user&#39;s folder and information  82  about its content, i.e. each entity, such as a file or folder. 
   The folder information  82  includes an entity identifier  84 , an entity name  85  and an entity type  86 . 
   The content information  82  includes information  87  about each entity including a set of attributes  88  which may include an entity identity  89 , an entity name  90  and an entity type  91 . The entity may be a file or a folder. 
   The metadata  22  includes invitations  92  (if any) from other users to access files. 
   Each invitation  92  includes information  93  about the folder or file that the user has been invited to accesses and includes an inviter identity  94 , an invitee identity  95 , an entity  96 , a security identity  97  and a network identity  98 . 
   Once a user has discovered their local service node  12 ,  13 ,  14 , they can carry out several file and folder operations, such as storing files, and this is hereinafter described in more detail. Furthermore, the user can share their files and folders with other users from the same or different network  1 ,  2 ,  3  or share files and folders of other users. 
   Referring to  FIGS. 1 ,  2  and  8 , a method of sending an invitation from a user (“the inviter”) to another user (“the invitee”) to view or share a file will now be described. The access network gateway is omitted for clarity. 
   The client  51  (of the inviter&#39;s mobile terminal  9 ) establishes a connection with a service node  12 ,  13 , as hereinbefore described. 
   The client  51  sends an invitation  100  to share a file to the access point  29  (step S 901 ). The invitation  100  specifies a user identity of the invitee (e.g. the telephone number of a mobile terminal  11 ) and a file identity of the file or folder to be shared. 
   The access point  29  forwards the invitation  100  to the inviter&#39;s home point  30  (step S 902 ). The inviter&#39;s home point  30  identifies the invitee&#39;s home point  30  (step S 903 ) and retrieves the configuration for the invitee&#39;s home point  30  (step S 904 ). 
   The inviter&#39;s home point  30  sends an instruction  101  to the inviter&#39;s service point  31  to share the specified file or folder (step S 905 ). The inviter&#39;s service point  21  returns a message  102  to the inviter&#39;s home point  30  which specifies a metadata entry point and a security identity (step S 906 ). The inviter&#39;s home point  30  also sends an invitation  103  to the invitee&#39;s home point  30  notifying it that the invitee is invited to share the specified file or folder (step S 907 ). The invitee&#39;s home point  30  forwards the invitation  103  to the invitee&#39;s service point, which in turn updates invitee&#39;s metadata to indicate that a shared file (step S 908 ). 
   Referring to  FIG. 9 , the structure  104  of the invitation  103  is shown in more detail. 
   Each invitation  103  has a set of attributes  105  which includes an inviter identity  106 , an invitee identity  107 , an entity identifier  108 , a security identity  109  and a network identity  110 . The network identity  110  is specified to avoid generating multiple security identities  109  for a given invitee. 
   Referring to  FIGS. 1 ,  2  and  10 , a method of downloading a file will now be described, in which a user downloads a file from a so-called “file home point” which may be the user&#39;s home point  12  or the inviter&#39;s home point  14 . 
   The client  51  (which may be running on the first or second mobile terminal  9 ,  11 ) establishes a connection with a service node  12 ,  13 ,  14  as hereinbefore described. 
   The client  51  sends a request  111  to the access point  29 , which may be in a home network  1  or a visited network  2  (step S 1001 ). The request specifies a file identity and a network identity which identifies the network  1 ,  2 ,  3  in which the file is stored. Thus, if the user wishes to download their own file(s), then the network identity specifies, in the case of first mobile terminal  9 , the first data network  1  or, in the case of the second mobile terminal  11 , the third data network  3 . If, however, the user wishes to download shared file(s), then the network identity specifies, in the case of second mobile terminal  11 , the first data network  1 . 
   The access point  29  forwards the request  111  to the user&#39;s home point  30  (step S 1002 ). The home point  30  checks if the file is located in the attached service point  31  (step S 1003 ). 
   The home point  30  sends a request  112  to the service point  31  to return the specified file(s)  13  (steps S 1004  &amp; S 1005 ). In the case where the file is not located in the attached service point  31 , the request  103  is sent via the invitee&#39;s home point  30 . 
   The service point  31  returns the specified file(s)  13  to the user&#39;s home point  30  (steps S 1006  &amp; S 1007 ), which in turn forwards the file(s) to the mobile terminal  9  (steps S 108  &amp;  1009 ). 
   Referring to  FIG. 11 , a method of uploading a file will now be described, in which a user uploads a file from their mobile terminal  9  to their home point  12 . In this example, the user can only upload a file to their folder and not to a folder belonging to another user. Thus, the “file home point” is the user&#39;s home point  12 . The access network gateway is omitted for clarity. 
   The client  51  establishes a connection with a home node  12 ,  13 ,  14 , as hereinbefore described. 
   The client  51  sends a request  113  to the access point  29 , which may be in a home network  1  or a visited network  2  (step S 1101 ). The request  113  specifies a folder identity and the file. 
   The access point  29  forwards the request  113  to the user&#39;s home point  30  (step S 1102 ). The home point  30  forwards the request  113  to the file service point  30 , in this case, the service point  30  of the user&#39;s home point  12  (step S 1103 ). 
   The file service point  30  returns a file identity  114  to the home point  30  which updates the metadata (step S 1104 ) and forwards the file identity  109  to the mobile terminal  9 . 
   It will be appreciated that many modifications may be made to the embodiments hereinbefore described. For example, file services may be accessible through the Internet. Each node can be used to provide a file service to a plurality of different mobile terminals. File services may overlap. For example more than two users may be invited to access the same file(s). Furthermore, users can exchange invitations. For example, a user may invite another to access one or more of their files and vice versa.
A node for providing a file service to a mobile terminal, the node comprises mobile terminal interface, and a file system for a plurality of users, each user having a user folder. The node is configured, in response to receiving a request for file access from a mobile terminal, to identify a user folder, to determine whether the file managing system manages the user folder and, in dependence upon whether the file managing system manages the user folder, to retrieve an entry point for the user folder and to transmit the entry point to the mobile terminal.