Abstract:
The invention relates to a method, which comprising initiating the establishment of a security association between a client node and a gateway node. User data is obtained from an authentication server and the user is authenticated. Authorization is obtained for the user for certain network services from a separate authorization node. An authorized address is provided to the client node. The authorization is checked by the gateway node for the allowing outbound packets to specific destinations.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the providing of packet data access services in a communication system. Particularly, the invention relates to a method for the routing and control of packet data traffic in a communication system. 
     2. Description of the Related Art 
     The amount of packet data traffic continues to increase with the introduction of new multimedia services. It becomes important for packet data access networks to be able to transmit packet data in an efficient and a scalable way that avoids introducing bottlenecks to the architecture of the network. However, simultaneously it must be possible to control the packet data traffic and to apply a variety of policies for the packet data traffic. It must be possible to control the attaching of users to different sub-networks, for instance, in the form of deciding on the providing of addresses from a given access point only to authorized users. The routing and policy control must be efficient irrespective of the type of an access network. 
     A problem associated with prior art networks is that the burden of the routing of packet data traffic and the interfacing of external networks for the packet data traffic has been centralized to network elements in the same position in the network topological without taking into consideration the type of packet data traffic or the type of access network used. 
     Reference is now made to  FIG. 1 , which illustrates a Universal Mobile Telecommunications System (UMTS) and an IP multimedia Subsystem (IMS) in prior art. The IP multimedia architecture for UMTS and GPRS mobile communication networks is referred to as an IP Multimedia Subsystem (IMS). The IMS is defined in the 3G Partnership Project (3GPP) specification 23.228 version 6.14.0, June 2006. The GPRS is defined in the 3GPP specification 23.060, version 6.13.0, June 2006. In  FIG. 1  there is shown a mobile station  100 , which communicates with a Radio Network Controller (RNC)  114  within a Radio Access Network  110 . The communication occurs via a Base Transceiver Station (BTS)  112 . The radio access network  110  is, for example, a 2G GSM/EDGE radio access network or a 3G UMTS radio access network. An IP Connectivity Access Network (IP-CAN) functionality connected to access network  110  comprises at least a Serving GPRS Support Node (SGSN)  122  and a Gateway GPRS Support Node (GGSN)  124 . An IP connectivity access network can also been seen as to comprise both a packet switched core network functionality  120  and an access network  110 . The main issue is that an IP-CAN provides IP connectivity to user terminals towards an IP network such as the Internet or an Intranet. SGSN  122  performs all mobility management related tasks and communicates with a Home Subscriber Server (HSS)  160  in order to obtain subscriber information. GGSN  124  provides GPRS access points. There is an access point, for example, to a Media Gateway (MGW)  126 , to a first router  142  attached to an IP network  140 , and to a Proxy Call State Control Function (P-CSCF)  152 . The access point to IP network is used to relay packets to/from an IP network node (IP-N) such as  147 . The packets may be related to, for example, Internet browsing or File Transfer Protocol (FTP) file transfer. The access point for P-CSCF  152  is used to convey signaling traffic pertaining to IP multimedia. GGSN  124  establishes Packet Data Protocol (PDP) contexts, which are control records associated with a mobile subscriber such as mobile station  100 . A PDP context provides an IP address for packets received from or sent to mobile station  100 . A PDP context has also associated with it a UMTS bearer providing a certain QoS for mobile station  100 . In GGSN  124  there is a primary PDP context for the signaling packets associated mobile station  100 . For the user plane data packets carrying at least one IP flow there is established at least one secondary PDP context. The at least one IP flow is established between a calling terminal and a called terminal in association with an IP multimedia session. An IP flow carries a multimedia component, in other words a media stream, such as a voice or a video stream in one direction. For voice calls at least two IP flows are required, one for the direction from the calling terminal to the called terminal and one for the reverse direction. In this case an IP flow is defined as a quintuple consisting of a source port, a source address, a destination address, a destination port and a protocol identifier. 
     The communication system illustrated in  FIG. 1  comprises also the IP Multimedia Subsystem (IMS) functionality. The IMS is used to set-up multimedia sessions over IP-CAN. The network elements supporting IMS comprise at least one Proxy Call State Control Function (P-CSCF), at least one Inquiring Call State Control Function (I-CSCF), at least one Serving Call State Control Function S-CSCF, at least one Brakeout Gateway Control Function (BGCF) and at least one Media Gateway Control Function (MGCF). As part of the IMS there is also at least one Home Subscriber Server (HSS). Optionally, there is also at least one Application Server, which provides a variety of value-added services for mobile subscribers served by the IP multimedia subsystem (IMS). 
     P-CSCF  152  receives signaling plane packets from GGSN  124 . Session Initiation Protocol (SIP) signaling messages are carried in the signaling plane packets. The signaling message is processed by P-CSCF  152 , which determines the correct serving network for the mobile station  100  that sent the signaling packet. The determination of the correct serving network is based on a home domain name provided from mobile station  100 . Based on the home domain name is determined the correct I-CSCF, which in  FIG. 1  is I-CSCF  154 . I-CSCF  154  hides the topology of the serving network from the networks, in which mobile station  100  happens to be roaming. I-CSCF  154  takes contact to home subscriber server  160 , which returns the name of the S-CSCF, which is used to determine the address of S-CSCF  156  to which the mobile station  100  is to be registered. If I-CSCF  156  must select a new S-CSCF for mobile station  100 , home subscriber server  160  returns required S-CSCF capabilities for S-CSCF selection. 
     Upon receiving a registration, S-CSCF  156  obtains information pertaining to the profile of the mobile station  100  from HSS  160 . The information returned from HSS  160  may be used to determine the required trigger information that is used as criterion for notifying an application server  162 . The trigger criteria are also referred to as filtering criteria. Application server  162  may be notified on events relating to incoming registrations or incoming session initiations. Application server  162  communicates with S-CSCF  156  using the ISC-interface. The acronym ISC stands for IP multimedia subsystem Service Control interface. The protocol used on ISC interface is SIP. AS  162  may alter SIP INVITE message contents that it receives from S-CSCF  156 . The modified SIP INVITE message is returned back to S-CSCF  156 . 
     If the session to be initiated is targeted to a PSTN subscriber or a circuit switched network subscriber, the SIP INVITE message is forwarded to a BGCF  158 . BGCF  158  determines the network in which interworking to PSTN or the circuit switched network should be performed. In case PSTN interworking is to be performed in the current network, the SIP INVITE message is forwarded to MGCF  159  from BGCF  158 . In case PSTN interworking is to be performed in another network, the SIP INVITE message is forwarded from BGCF  158  to a BGCF in that network (not shown). MGCF  159  communicates with MGW  126 . The user plane packets carrying a media bearer or a number of interrelated media bearers for the session are routed from GGSN  124  to MGW  126  as illustrated in  FIG. 1 . 
     If the session to be initiated is targeted to a terminal  146 , which is a pure IP terminal, S-CSCF  156  forwards the SIP INVITE message to terminal  146 . Terminal  146  communicates with a second router  144 , which interfaces IP network  140 . IP network  140  is used to carry the user plane IP flows associated with the session established between mobile station  100  and terminal  146 . The user plane IP flows between first router  142  and GGSN  124  are illustrated with line  128 . The user plane IP flows between second router  144  and terminal  146  are illustrated with line  148 . 
     Generally, in  FIG. 1  user plane is illustrated with a thick line and control plane with thinner line. 
     One problem in the architecture illustrated in  FIG. 1  is, for example, that if there are other types of IP-CANs (not shown) that are used to access IMS  150  or the amount of user plane traffic grows by way of a myriad of IP multimedia sessions specifically GGSN  124  may be required to process significant packet data traffic. Therefore, it would be beneficial to have an architecture, which may provide for access point gateway functionality at different points in the network topology and avoids the buildup of network bottlenecks. 
     SUMMARY OF THE INVENTION 
     The invention relates to a method comprising: initiating the establishment of a security association between a client node and a first gateway node; obtaining at least one user identity and user authentication data from an authentication server; authenticating the user with the authentication data; providing said at least one user identity to a second gateway node; obtaining for the user authorization pertaining to at least one access point in said second gateway node; providing said authorization pertaining to said at least one access point and an address for said client node to said first gateway node; providing said address to said client node from said first gateway node; transmitting a packet from said client node to said first gateway node, said packet comprising said address as source address; allowing said packet based on said authorization pertaining to said at least one access point; and routing said packet to a destination node in said first gateway node based on at least said address. 
     The invention relates also to a method comprising: initiating the establishment of a security association between a client node and a first gateway node; obtaining at least one user identity and user authentication data from an authentication server; authenticating the user with the authentication data; providing said at least one user identity to a control node; obtaining for the user authorization pertaining to at least one access point to said first gateway node from said control node; obtaining an address for said client node in said first gateway node; providing said address to said client node from said first gateway node; transmitting a packet from said client node to said first gateway node, said packet comprising said address as source address; allowing said packet based on said authorization pertaining to said at least one access point; and routing said packet to a destination node in said first gateway node based on at least said address. 
     The invention relates also to a method comprising: initiating the establishment of a security association between a client node and a first gateway node; obtaining at least one user identity and user authentication data from an authentication server; authenticating the user with the authentication data; requesting the creation of a packet data protocol context from a second gateway node; creating a packet data protocol context in said second gateway node; determining session control node information in said second gateway node; providing said session control node information in at least one protocol configuration option to said first gateway node; providing said session control node information to said client node in a configuration payload of a security association related message. 
     The invention relates also to a communication system, comprising: a client node configured to initiate the establishment of a security association with a first gateway node, to transmit a packet to said first gateway node, said packet comprising an address as source address; a first gateway node configured to establish a security association with said client node, to obtain at least one user identity and user authentication data from an authentication server, to authenticate the user with the authentication data, to providing said at least one user identity to a second gateway node, to provide said address to said client node from said first gateway node, to receive said packet comprising said address as source address, to allow said packet based on said authorization pertaining to said at least one access point and to route said packet to a destination node based on at least said address; and a second gateway node configured to obtain for the user an authorization pertaining to at least one access point and to provide said authorization pertaining to said at least one access point and an address for said client node to said first gateway node. 
     The invention relates also to a communication system comprising: a client node configured to initiate the establishment of a security association towards a first gateway node; and a first gateway node configured to obtaining at least one user identity and user authentication data from an authentication server, to authenticate the user with the authentication data, to provide said at least one user identity to a control node, to obtain for the user authorization pertaining to at least one access point, to obtain an address for said client node, to providing said address to said client node, to receive a packet from said client node, said packet comprising said address as source address, to allowing said packet based on said authorization pertaining to said at least one access point and to route said packet to a destination node in said first gateway node based on at least said address. 
     The invention relates also to a communication system, comprising: a client node configured to initiate the establishment of a security association to a first gateway node; said first gateway node configured to obtain at least one user identity and user authentication data from an authentication server, to request the creation of a packet data protocol context from a second gateway node, to authenticate the user with the authentication data and to providing said session control node information to said client node in a configuration payload of a security association related message; and said second gateway node configured to create a packet data protocol context in said second gateway node, to determine session control node information in said second gateway node, to providing said session control node information in at least one protocol configuration option to said first gateway node. 
     The invention relates also to a network node, comprising: a security entity configured to establish a security association with a client node, to obtain at least one user identity and user authentication data from an authentication server, to authenticate the user with the authentication data, to providing said at least one user identity to a gateway node, to provide an address to said client node; a communication entity configured to receive said packet comprising said address as source address; a filtering entity configured to allow said packet based on said authorization pertaining to said at least one access point; and a router entity configured to route said packet to a destination node based on at least said address. 
     The invention relates also to a network node, comprising: means for establishing a security association with a client node; means for obtaining at least one user identity and user authentication data from an authentication server; means for authenticating the user with the authentication data; means for providing said at least one user identity to a gateway node; means for to providing an address to said client node; means for receiving a packet comprising said address as source address; means for allowing said packet based on said authorization pertaining to said at least one access point; and means for routing said packet to a destination node based on at least said address. 
     The invention relates also to a network node, comprising: a security entity configured to obtain at least one user identity and user authentication data from an authentication server, to authenticate the user with the authentication data, to provide said at least one user identity to a control node, to obtain for the user authorization pertaining to at least one access point, to obtain an address for said client node, to providing said address to said client node; a communication entity configured to receive a packet from said client node, said packet comprising said address as source address; a filtering entity configured to allow said packet based on said authorization pertaining to said at least one access point; and a routing entity configured to route said packet to a destination node based on at least said address. 
     The invention relates also to a network node, comprising: means for obtaining at least one user identity and user authentication data from an authentication server; means for authenticating the user with the authentication data; means for providing said at least one user identity to a control node; means for obtaining for the user authorization pertaining to at least one access point; means for obtaining an address for said client node; means for providing said address to said client node; means for receiving a packet from said client node, said packet comprising said address as source address; means for allowing said packet based on said authorization pertaining to said at least one access point; and means for routing said packet to a destination node based on at least said address. 
     The invention relates also to a network node, comprising: a security entity configured to establish a security association with a client node, to obtain at least one user identity and user authentication data from an authentication server, to request the creation of a packet data protocol context from a second gateway node, to authenticate the user with the authentication data and to providing said session control node information to said client node in a configuration payload of a security association related message. 
     The invention relates also to a network node, comprising: means for establishing a security association with a client node; means for obtaining at least one user identity and user authentication data from an authentication server; means for requesting the creation of a packet data protocol context from a second gateway node; means for authenticating the user with the authentication data; and means for providing said session control node information to said client node in a configuration payload of a security association related message. 
     The invention relates also to a computer program embodied on a computer readable medium, when executed on a data-processing system, the computer program being configured to perform: establishing a security association with a client node; obtaining at least one user identity and user authentication data from a server; authenticating the user with the authentication data; providing said at least one user identity to a gateway node; providing an address to said client node; receiving a packet comprising said address as source address; allowing said packet based on said authorization pertaining to said at least one access point; and routing said packet to a destination node based on at least said address. 
     The invention relates also to a computer program embodied on a computer readable medium, when executed on a data-processing system, the computer program being configured to perform: obtaining at least one user identity and user authentication data from an authentication server; authenticating the user with the authentication data; providing said at least one user identity to a control node; obtaining for the user authorization pertaining to at least one access point; obtaining an address for said client node; providing said address to said client node; receiving a packet from said client node, said packet comprising said address as source address; allowing said packet based on said authorization pertaining to said at least one access point; and routing said packet to a destination node based on at least said address. 
     The invention relates also to a computer program embodied on a computer readable medium, when executed on a data-processing system, the computer program being configured to perform: establishing a security association with a client node; obtaining at least one user identity and user authentication data from an authentication server; requesting the creation of a packet data protocol context from a second gateway node; authenticating the user with the authentication data; and providing said session control node information to said client node in a configuration payload of a security association related message. 
     In one embodiment of the invention, the communication system further comprises a communication entity in the second gateway node, which is configured to provide said at least one user identity to a control node. The control node, in other words, a control server, is, for example, an IP Multimedia Register (IMR), a Remote Authentication Dial In User Service (RADIUS) server, a Lightweight Directory Access Protocol (LDAP) database server or an Online Charging Server (OCS). A database entity in the control node is configured to determine said authorization pertaining to said at least one access point node with said at least one user identity. The communication entity in the control node is configured to indicate said authorization to said second gateway node. 
     In one embodiment of the invention, a session signaling entity in the client node is configured to add a session signaling message pertaining to a session to said packet. A session control node is configured to provide an indication of said session to the control node, which supervises, for example, user specific prepaid accounts. The control node configured to detect a session release condition for said session and to send a release request message to said first gateway node. The security entity in the first gateway node configured to delete a second security association. 
     In one embodiment of the invention, the second gateway node is a Gateway General Packet Radio Service Support Node. 
     In one embodiment of the invention, the user is a mobile subscriber, which is identified to the client node using a subscriber identity module or any other card. 
     In one embodiment of the invention, the first gateway node comprises a Virtual Private Network (VPN) gateway. In one embodiment of the invention, the first gateway node comprises a Serving GPRS Support Node. 
     In one embodiment of the invention, the communication system comprises an Internet Protocol Connectivity Access Network (IP-CAN) and a proxy network node with an application entity configured to receive signaling messages from a terminal via said Internet Protocol Connectivity Access Network (IP-CAN). The application entity may comprise Session Initiation Protocol (SIP) functionality. The proxy network node may be, for example, a Proxy CSCF (P-CSCF). 
     In one embodiment of the invention, the Internet Protocol Connectivity Access Network comprises a Serving General Packet Radio Service Support Node and a Gateway General Packet Radio Service Support Node. The first gateway node may be a Serving GPRS Support Node, which is configured to a communication entity that allows the first gateway node to communication towards a control node via the Radius protocol or the Diameter protocol. The second gateway may be a Gateway GPRS Support Node. 
     In one embodiment of the invention, the signaling messages comprise Session Initiation Protocol (SIP) session invitation messages. 
     In one embodiment of the invention, said communication system comprises a mobile communication network. In one embodiment of the invention, said terminal comprises a mobile station or generally a mobile terminal. In one embodiment of the invention a user of a mobile terminal is identified using a subscriber module, for example, User Services Identity Module (UMTS) or a Subscriber Identity Module (SIM). The combination of Mobile Equipment (ME) and a subscriber module may be referred to as a mobile subscriber. 
     In one embodiment of the invention, the communication system comprises at least one of a Global System of Mobile Communications (GSM) network and a Universal Mobile Telephone System (UMTS) network. The mobile station may be, for example, a GSM mobile station or a UMTS mobile station with a dual mode or multimode functionality to support different access types. 
     In one embodiment of the invention, the computer program is stored on a computer readable medium. The computer readable medium may be a removable memory card, a removable memory module, a magnetic disk, an optical disk, a holographic memory or a magnetic tape. A removable memory module may be, for example, a USB memory stick, a PCMCIA card or a smart memory card. 
     The embodiments of the invention described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment of the invention. A method, a communication system, a network node or a computer program to which the invention is related may comprise at least one of the embodiments of the invention described hereinbefore. 
     The benefits of the invention are related to the increased scalability. Packet data traffic may be distributed more evenly in different points within the network topology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings: 
         FIG. 1  is a block diagram illustrating a Universal Mobile Telecommunications System (UMTS) and an IP multimedia Subsystem (IMS) in prior art; 
         FIG. 2  is a block diagram illustrating a communication system with two gateway nodes in one embodiment of the invention; 
         FIG. 3  is a block diagram illustrating a single gateway node communication system in one embodiment of the invention; 
         FIG. 4  is a block diagram illustrating the distribution of session control node information in one embodiment of the invention; 
         FIG. 5A  is a flow chart illustrating a first part of a method for the transmitting of signaling plane information in one embodiment of the invention; 
         FIG. 5B  is a flow chart illustrating a second part of a method for the transmitting of signaling plane information in one embodiment of the invention; and 
         FIG. 6  is a block diagram illustrating a network node in one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 2  is a block diagram illustrating a communication system with two gateway nodes in one embodiment of the invention. 
     In  FIG. 2  there is a client node  250 . It communicates with an IP access network  252 . The IP access network may be any wired or wireless network. In  FIG. 2  there is also a Virtual Private Network gateway VPN-GW  268 . VPN-GW  268  provides IP Security (IP-SEC) security associations for client nodes such as client node  250 . The security associations are provided over IP access net-work  252 . In  FIG. 2  there are two authentication authorization and accounting servers, namely AAAv  262  and AAAh  264 . AAAv  262  acts as the AAA server within the network of VPN-GW  268 , whereas AAAh  264  acts as the AAA server within the home network of the mobile subscriber associated with client node  250 . VPN-GW  268  communicates with AAAv  262  using either the Radius protocol or the Diameter protocol. Similarly, AAAv  262  communicates with AAAh  264  using the Radius or the Diameter protocol. There is also an interface from AAAh  264  to the Home Subscriber Server (HSS) of the mobile sub-scriber. In  FIG. 2  there is also an IP multimedia subsystem  270 . There is a Proxy Call State Control Function (P-CSCF)  274  and a media gateway  276  in IP multimedia subsystem (IMS)  270 . There is also a home subscriber server  272  within IMS  270 . HSS  272  is configured to communicate with AAAh  264 . There is also a Control Server (CTRL)  278 . Control server  278  may be, for example, an LDAP server storing a directory database, an Online Charging Server (OCS) or an IP Multimedia Register (IMR). Control server  278  is, for example, in charge of providing user data and user service subscription information. Mobile subscriber subscription information indicates, for example, information on access point names that are allowed for specified mobile subscribers. The subscriber information also indicates what sub-networks are allowed as destination networks for specified subscribers and what quality of service may be provided for the packet traffic pertaining to the specified subscribers. There may also be information on pre-paid accounts associated with the mobile subscriber. Control server  278  may also be a session information repository. In one embodiment of the invention, the control server is merely a software component or a separate computer plug-in unit directly comprised in a GGSN  266  or a similar gateway node. There is also a sub-network  280  which comprises a server  282 . In  FIG. 2  there is also a second sub network  140 , which comprises a node  147  and an ingress router  142  and an egress router  144 . There is also a second terminal  146  which is configured to communicate with sub-network  140  via user plane connection  148 . In  FIG. 2  there is also gateway GPRS support node GGSN  266 . 
     At time T 1  client node  250  wishes to establish an IPSEC security association towards VPN-GW  268 . The security association initiation is performed, for example, with Internet Key Exchange (IKE) IKEv2 protocol defined in Internet Engineering Task Force (IETF) document 4306, December, 2005. It should be noted that other versions of IKE, may as well be used for the purposes of the disclosed method. Also other key exchange protocols may be used for the establishing of security associations or secure tunnels. 
     The security association initiation phase, called IKE_SA_INIT in IKEv2, between client node  250  and VPN-GW  268  is illustrated with double-headed arrow  201 . Thereupon, the IKEv2 authentication phase, called IKE_AUTH in IKEv2, is commenced. The IKEv2 authentication phase is illustrated with double-headed arrow  202 . First, client node  250  sends an IKEv2 authentication message to VPN-GW  268 . The authentication message does not have an IKEv2 AUTH payload, which indicates the desire of client node  250  to use extensible authentication, for example, the Encapsulated Authentication Protocol (EAP), which is defined, for example, in the IETF RFC 4187. The IKEv2 authentication message provides the identity of the current user of client node  250  and the name of the access point desired by the user. The identity of the user is expressed as a Network Access Identifier (NAI). The user may, for example, be identified within NAI using a logical name such as the ones used in E-mail address username parts or an MSISDN number. Upon obtaining the NAI in VPN-GW  268 , the NAI is provided by VPN-GW  268  to AAAh  264  via AAAv  262 . This message chain is not shown in  FIG. 2 . The correct AAAh is found using the mobile country code and mobile network code provided as part of the NAI. On the basis of the user identity in NAI, AAAh  264  obtains authentication information from HSS  272 , as illustrated with arrow  203 . AAAh  264  may also obtain from HSS  272  other data for the user, which comprises, for example, an IMSI and an MSISDN. The user identities IMSI and MSISDN may be referred to as user data hereinafter. User data and authentication information is provided from AAAh  264  to AAAv  262 , as illustrated with arrow  204 . The user data and authentication information are further provided from AAAv  262  to VPN-GW  268 , as illustrated with arrow  205 . As part of ongoing IKEv2 authentication phase (IKE_AUTH) and the message exchange associated therewith, which illustrated with double-headed arrow  202 , VPN-GW  268  sends to client node  250  an IKEv2 authentication message. The IKEv2 authentication message has encapsulated within it an Encapsulated Authentication Protocol (EAP) authentication request message pertaining to, for example, EAP-SIM or EAP-AKA authentication methods. The EAP authentication request message comprises, for example, a random challenge (RAND) and may also comprise a network authentication token (AUTN) and a Message Authentication Code (MAC). In order to obtain successful authentication, client node  250  sends a proper response parameter (RES), calculated in client node  250  on the basis of information in the EAP authentication request, to VPN-GW  268  in an EAP authentication response message further encapsulated in an IKE_AUTH message, which is, once again part of message exchange illustrated with double-headed arrow  202 . Upon receiving the EAP authentication request message, VPN-GW  268  checks at least the given RES and finds it correct. Because the RES was correct, WPN-GW  268  sends an EAP success message encapsulated in an IKE_AUTH message to client node  250 . This message is also part of the message exchange illustrated with double headed arrow  202 . 
     At this point a PDP context is not opened in GGSN  266 . VPN-GW  268  sends a first authorization message comprising the user identities IMSI and MSISDN and the requested APN to GGSN  266 , as illustrated with arrow  206 . The first authorization request message may be sent, for example, using the GPRS Tunneling Protocol (GTP-C), the Radius protocol or the Diameter protocol. GGSN  266  sends a second authorization request message to control server  278  as illustrated with arrow  207 . The second authorization request message comprises the IMSI and MSISDN and the desired APN. Control server  278  checks from its database the authorization of the user to use the APN requested. If there is an authorization, control server  278  sends an authorization accepted message to GGSN  266 , as illustrated with arrow  208 . GGSN  266  allocates an IP address from the APN. The IP address allocation may also be performed by control server  278  or the address may already have been provided in message  208  to GGSN  266 . GGSN  266  sends the IP address to VPN-GW  268 , as illustrated with arrow  209 . The IP address is further provided from VPN-GW  268  to client node  250 , as illustrated with arrow  210 . 
     In one embodiment of the invention, the providing of the IP address to client node  250  is performed in an earlier phase when the authentication is still ongoing. The IP address may be provided in association with an extra IKE_AUTH message exchange between client  250  and VPN-GW  268 . 
     At time T 2 , client node  250  starts using the IP address obtained. Thereupon, client node  250  sends a session related packet to VPN-GW  268 . Upon receiving the packet VPN-GW  268  checks from its firewall rules whether the access point for the source IP address is allowed to communicate with the destination IP address indicated in the packet. If the firewall rules allow the packet, the packet is routed towards the destination by VPN-GW  268 . In  FIG. 2  there are shown four routes for packet traffic, namely route R 1  towards sub-network  140 , route R 2  towards sub-network  280 , route R 3  towards P-CSCF  274  and route R 4  towards MGW  276 . Based on routing rules, VPN-GW  268  sends the session signaling related packet over route R 3  to P-CSCF  274 . At some point in session signaling P-CSCF  274  sends a response signaling message comprised in a packet towards client node  250 . The response packet is processed in VPN-GW  268  so that is it subjected to firewall rule checking and routing process in a manner similar to packet sent by client node  250 . Finally the packet is assumed to be received to client node  250 . At a later time, a multimedia session is assumed to be established from client node  250  via VPN-GW  268  to a destination node, for example, network node  146 . The user plane for the session uses an IPSEC security association between client node  250  and VPN-GW  268 . The IP multimedia session goes on for a certain time. At time T 3  control server  278  detects that the prepaid account associated with the mobile subscriber for client node  250  has been exhausted. Therefore, control server  278  sends a session release request message GGSN  266 , as illustrated with arrow  211 . The session release request message is sent further by GGSN  266  to VPN-GW  268 , as illustrated with arrow  212 . In response to the release request VPN-GW  268  deletes the security association used by the ongoing IP multimedia session. Preferably, the user plane security association is deleted. 
       FIG. 3  is a block diagram illustrating a single gateway node communication system in one embodiment of the invention. 
     In  FIG. 3  there is no GGSN but all policy signaling is relayed via VPN-GW  268  and control server  278 . At time T 1  client node  250  initiates the establishing of a security association towards VPN-GW  268 . The security association initiation (IKE_SA_INIT) is illustrated with double-headed arrow  301 . Thereupon, the IKEv2 authentication phase (IKE_AUTH) is commenced. Client node  250  sends an IKEv2 authentication message to VPN-GW  268 , as part of authentication phase messaging illustrated with double-headed arrow  302 . The IKEv2 authentication message provides the identity of the current user of client node  250  and the name of the access point desired by the user. The identity of the user is expressed as a Network Access Identifier (NAI). Upon obtaining the NAI in VPN-GW  268 , the NAI is provided by VPN-GW  268  to AAAh  264  via AAAv  262  (not shown). The correct AAAh is found using the mobile country code and mobile network code provided as part of the NAI. On the basis of the user identity in NAI, AAAh  264  obtains authentication information from HSS  272 , as illustrated with arrow  303 . The authentication information may comprise a number of GSM authentication triplets or a number of UMTS AKA authentication vectors. AAAh  264  may also obtain from HSS  272  other data for the user, which comprises, for example, an IMSI and an MSISDN. The user identities IMSI and MSISDN may be referred to as user data hereinafter. User data and authentication information is provided from AAAh  264  to AAAV  262 , as illustrated with arrow  304 . The user data and authentication information are further provided from AAAv  262  to VPN-GW  268 , as illustrated with arrow  305 . Thereupon, the authentication is performed between client node  250  and VPN-GW  268 . The continued authentication procedure between VPN-GW  268  and client node  250  is comprised in the messaging illustrated with double-headed arrow  302 . The authentication procedure uses IKEv2 authentication phase (IKE_AUTH) messages, which have encapsulated in them Encapsulated Authentication Protocol (EAP) message pertaining to, for example, EAP-SIM or EAP-AKA authentication methods. The EAP challenge and response authentication procedures are performed. Successful authentication of client node  250  is followed by and EAP success message from VPN-GW  268  to client node  250 . 
     Thereupon, VPN-GW  268  sends an authorization request message to control server  278  as illustrated with arrow  306 . The authorization request message comprises APN desired by client node  250  and user data identifying the user of client node  250 , for example the IMSI or the MSISDN of the user. If the user is authorized to use the APN, control server  278  sends an authorization accept message VPN-GW  268  as illustrated with arrow  307 . The IP address for client node  250  may be obtained from control server  278  or from another node interfaced by VPN-GW  268 . Anyway, the IP address allocated from the access point identified by the APN is provided from VPN-GW  268  to client node  250 , as illustrated with arrow  308 . The message  308  may be comprised in the IKEv2 authentication phase. 
     In one embodiment of the invention, the IP address may also be provided in an informational IKEv2 message only after complete IKEv2 authentication phase. In one embodiment of the invention, the sending of authorization request to control server  278  may be sent during authentication messaging process illustrated with double-headed arrow  305 . 
     At time T 2  client node  250  starts establishing an IP multimedia session towards destination terminal. The IP multimedia session is established via for example session initiation protocol signaling, which is conveyed via VPN-GW  268  to P-CSCF  274  and from there onwards to other call state control functions that are not shown. The IP multimedia session is assumed to reach a two-way communication state, for example, a speed state. The IP multimedia session is also made known control server  278  (messaging not shown). 
     At time T 3 , the prepaid account for the use of client node  250  is exhausted and therefore control server  278  sends a session release request message to VPN-GW  268  as illustrated with arrow  309 . In response to the session release request VPN-GW  268  deletes the security association carrying at least the user plane packets for the IP multimedia session. In one embodiment of the invention all security associations established between client node  250  VPN-GW  268  are deleted. 
       FIG. 4  is a block diagram illustrating the distribution of session control node information in one embodiment of the invention. 
     In  FIG. 4  there is a VPN-GW  268  which communicates with a GGSN  266 . There is also transmitted user plane packet traffic between VPN-GW  268  and GGSN  266 . In  FIG. 4  GGSN  266  is used to provide the P-CSCF address for P-CSCF  274  to client node  250 . At time T 1  client node  250  wishes to establish an IPSEC security association between client node  250  and VPN-GW  268 . VPN-GW  268  authenticates client node  250  in a manner similar to  FIGS. 2 and 3 . The initiation of security association establishment between client node  250  and VPN-GW  268  is illustrated with double-headed arrow  401 . The IKEv2 authentication phase is started, as illustrated with double-headed arrow  402 . Client node  250  provides user identity for it&#39;s user to VPN-GW  268 . A NAI is sent from VPN-GW  268  to AAAh  264  via AAAv  262 . The authentication information and user identity information from HSS  272  are provided back to VPN-GW  268  via the reverse path, as illustrated with arrows  403 ,  404  and  405 . EAP authentication challenge and response messaging is performed over between client node  250  and VPN-GW  268  as part of IKEv2 authentication phase. 
     Thereupon, VPN-GW  268  starts PDP context establishment to GGSN  266 , as illustrated with arrow  406 . Beforehand GGSN  266  has been configured with configuration information comprising, for example, the address for P-CSCF  274 . As the create PDP context request message  406  arrives at GGSN  266 , it is responded by GGSN  266  with create PDP context request accept message, as illustrated with arrow  407 . To the create PDP context request accept message or any other GTP-C protocol message GGSN  266  adds a protocol configuration option, which comprises the P-CSCF address. As the create PDP context request accept message is received in VPN-GW  268 , the P-CSCF address and other similar configuration option fields are extracted by VPN-GW  268 . VPN-GW  268  provides the IP address to client node  250  in an IKEv2 authentication related message illustrated with arrow  408 , to which it adds a configuration payload, which further comprises the P-CSCF address. Thereupon, client node  250  may start establishing a SIP session via P-CSCF  274  further towards IP multimedia subsystem  270 . 
       FIG. 5A  is a flow chart illustrating a first part of a method for the transmitting of signaling plane information in one embodiment of the invention. 
     At step  500 , an association establishment is started between a client node and a first network node. In one embodiment of the invention the first network node is a virtual private network gateway comprising firewall functionality and a router functionality. 
     At step  502 , authentication data is obtained to the first network node from an authentication server using an identity provided by the client node at step  500 . In one embodiment of the invention the authentication server is an authentication authorization and accounting server that is an AAA server. An AAA server may contact another AAA server in the client&#39;s home network. An AAA server may obtain authentication information from an external source such as an authentication center within a GSM network. User identity and user data is obtained to the first network node from the authentication server. The user identity may comprise, for example, an IMSI or an MSISDN. The user data may comprise an access point name provided from the client node. 
     At step  504 , the client node authentication is continued. 
     At step  506 , the user identity and user data is provided from the first network node to the second network node. In one embodiment of the invention, the second network node is a GGSN. 
     At the step  508 , the user is authorized in the second network node. In one embodiment of the invention, the authorization comprises the user&#39;s right to obtain an IP address from a certain access point. In one embodiment of the invention, the authorization is checked from a further third network node, which is, for example, an LDAP directory server, a Radius server or an IP multimedia register comprising user authorization information pertaining to different services and access points. 
     At the step  510 , an address is provided from the second network node to the client node. In one embodiment of the invention, the address is an IP address. In one embodiment of the invention the IP address is provided in an IKE version 2 informational message in a configuration payload parameter. In one embodiment of the invention, the IP address is provided in an IKEv2 authentication message. 
     At the step  512 , the client node sends a signaling packet toward a session control node. In one embodiment of the invention the signaling packet is an IP packet comprising a session initiation protocol message. The session control node may for example a proxy call state control function pertaining to IP multimedia subsystem. 
     At the step  514 , the first network node performs firewall filtering and packet routing for the aforementioned packet. 
     At the step  516 , the session control node provides a response signaling to the client node. The method continues at the step  518  also labeled with letter A. 
       FIG. 5B  is a flow chart illustrating a second part of a method for the transmitting of signaling plane information in one embodiment of the invention. 
     At the step  518 , a second network node detects a session release condition. The session release condition may have been indicated from the third network node. The third network node for example supervises prepaid account exhaustion. 
     At the step  520 , the second network node requests session release form the first network node. 
     At the step  522 , the first network node requests secure association deletion from the client node. In one embodiment of the invention the security association carries the user plane packets pertaining to the multimedia session to be released. 
       FIG. 6  is a block diagram illustrating a network node in one embodiment of the invention. The network node acts as, for example, a VPN gateway as illustrated in  FIGS. 2 ,  3  and  4 . 
     In  FIG. 6  there is illustrated a network node  600 . Network node  600  comprises at least one processor, for example, processor  610 , at least one secondary memory, for example secondary memory  620  and at least one primary memory, for example, primary memory  630 . Network node  600  may also comprise any number of other processors and any number secondary memory units. There may also be other primary memories with separate address spaces. Network node  600  comprises also a network interface  640 . The network interface may, for example, be a cellular radio interface, a Wireless Local Area Network (WLAN) interface, a local area network interface or a wide area network interface. The network interface is used to communicate to the Internet or locally to at least one computer. 
     Processor  610  or at least one similarly configured processor within network node  600  executes a number of software entities stored at least partly in primary memory  630 . Primary memory  630  comprises a communication entity  632 , a filtering entity  634 , a routing entity  636  and an authentication entity  638 . Communication entity  632  communicates with remote network nodes for enabling them to communicate with other entities within network node  600 . Communication entity  632  comprises, for example, the Internet Protocol (IP) protocol stack, the IP stack together with the Diameter protocol, the Radius protocol or any successor protocol thereof. Authentication entity  638  communicates with an authentication server via communication entity  632 . Authentication entity may authenticate a client node, for example, using the IKEv2 protocol and at least one EAP authentication method such as EAP-SIM or EAP-AKA. Filtering entity  634  takes care of packet filtering and passing functions according to filtering rules. The filtering rules may be stored to secondary memory  620 . The filtering rules may be updated based on information obtained from communication entity  632 . 
     The entities within network node  600  such as communication entity  632 , filtering entity  634 , routing entity  636  and authentication entity  638  may be implemented in a variety of ways. They may be implemented as processes executed under the native operating system of the network node or the network node. The entities may be implemented as separate processes or threads or so that a number of different entities are implemented by means of one process or thread. A process or a thread may be the instance of a program block comprising a number of routines, that is, for example, procedures and functions. The entities may be implemented as separate computer programs or as a single computer program comprising several modules, libraries, routines or functions implementing the entities. The program blocks are stored on at least one computer readable medium such as, for example, a memory circuit, a memory card, a holographic memory, magnetic or optic disk. Some entities may be implemented as program modules linked to another entity. The entities in  FIG. 6  may also be stored in separate memories and executed by separate processors, which communicate, for example, via a message bus or an internal network within the network node. An example of such a message bus is the Peripheral Component Interconnect (PCI) bus. The internal network may be, for example, a local area network. The entities may also be partly or entirely implemented as hardware, such as ASICS or FPGAs. An entity may be a software component or a combination of software components. 
     It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.