Abstract:
A method and system that each allow for communication between a first network and a second network. The first and second networks typically operate in accordance with different protocols and a user associated with the first network is typically connected to the second network. The method includes determining when a routing entity is associated with at least one of the networks. The method also includes using a gateway for traffic when the routing entity is associated with one of the network. Further, the method includes using tunnelling for the traffic when the routing entity is associated with the other of the networks.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method of communication between a first network and a second network.  
       BACKGROUND OF THE INVENTION  
       [0002]     A communication system can be seen as a facility that enables communication between two or more entities such as user equipment and/or other nodes associated with the system. The communication may comprise, for example, communication of voice, data, multi-media and so on.  
         [0003]     A communication system typically operates in accordance with a given standard or specification which sets out what the various elements of the system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely, user equipment or terminal is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters which should be used for the connection may also be defined. In other words, a specific set of “rules” on which the communication can be based needs to be defined to enable communication by means of the system.  
         [0004]     Communication systems providing wireless communication for user terminals or other nodes are known. An example of the wireless system is a cellular network. In cellular systems, a base transceiver station (BTS) or similar access entity serves mobile stations (MS) or similar user equipment (UE) via a wireless interface between the entities. The operation of the apparatus required for the communication can be controlled by one or several control entities. The various control entities may be interconnected. One or more gateway nodes may also be provided for connecting the network to another network, such as another cellular system or to a public switched telephone network (PSTN) and/or other communication networks such as internet protocol (IP) and/or other packet switched networks. The Session Initiation Protocol (SIP) is one of the communication protocols that can be used between user equipment and certain network elements.  
         [0005]     Various different standards have been suggested. For example, the third generation partnership project (3GPP) is defining a reference architecture, for example the universal mobile telecommunication system (UMTS). This UMTS core network is divided into three principal domains. These are the circuit switched domain, the packet switched domain and the Internet protocol multi-media (IM) domain. The IM domain makes sure that multi-media services are adequately managed. The IP Multimedia System (IMS) currently defined by 3GPP is described as supporting the protocol IPv6 (Internet protocol version 6) as defined in the Internet Engineering Task Force IETF standard http://www.ietf.org/html.charters/ipv6-charter.html and RFCs: RFC2460, RFC2461 and RFC3513. However, there are other reference architectures for 3G networks being proposed currently. For example, there exists the third generation partnership project 2 (3GPP2). This is a collaborative third generation telecommunications specification project. It comprises North American and Asian interests developing global specifications. 3GPP2 was born out of the International Telecommunication Union&#39;s (ITU) International Mobile Telecommunications (IMT-2000) initiative. Currently, with 3GPP2 networks, they can either support IPv4 or IPv6, that is the Internet Protocol version 4 or version 6. 3GPP2 standards allow IPv4 or IPv6 to be used in cdma2000 networks. If a 3GPP user roams to an IPv4 based 3GPP2 network, it is desirable that he should be able to access his home network, i.e. the IPv6 IMS via the 3GPP2 network. Accordingly, this would involve some IPv4/IPv6 inter working.  
         [0006]     In the document http://www.ietf.org/internet-drafts/draft-elmalki-sipping-3gpp-translator-00.txt, an IPv6-IPv4 translation mechanism for SIP based services in the third generation partnership project networks is described. This document is however concerned about the connection of a 3GPP IMS system supporting IPv6 with an IPv4 host for example on the Internet. This document does not address the issue of for example a 3GPP user accessing his home network when he roams to a network supporting a different version of the IP protocol.  
         [0007]     It is an aim of embodiments of the present invention to address or at least mitigate the above described problems.  
       SUMMARY OF THE INVENTION  
       [0008]     According to the first aspect of the invention there is provided a method of communication between a first network and a second network, said first and second networks operating in accordance with different protocols, wherein a user associated with said first network is connected to said second network, said method comprising the steps of determining if a routing entity is associated with the first or the second network; and using a gateway for traffic if said routing entity is associated with given one of said first and second networks and tunnelling for traffic if said routing entity is associated with the other of the first and second networks.  
         [0009]     According to a second aspect of the invention there is provided a system comprising a first network and a second network, said first and second networks operating in accordance with different protocols, wherein a user associated with said first network is connected to said second network, a routing entity in one of said networks and a gateway, wherein said gateway is used for traffic if said routing entity is associated with given one of said first and second networks and tunnelling is used for traffic if said routing entity is associated with the other of the first and second networks.  
         [0010]     According to a third aspect of the invention there is provided a gateway between a first network and a second network, said first and second networks operating in accordance with different protocols, said gateway arranged so that when a user associated with said first network is connected to said second network, traffic associated with said user passes through said gateway, said gateway being arranged to modify said traffic. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]     For a better understanding of the present invention and as to how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings in which:  
         [0012]      FIG. 1  shows two networks in which embodiments of the present invention can be used;  
         [0013]      FIG. 2  shows a signalling flow in an embodiment of the invention; and  
         [0014]      FIG. 3  shows the roaming gateway of  FIG. 1 , in more detail. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0015]     It will be understood that in the following description the present invention is described with reference to particular non limiting examples from which the invention can best be understood. The invention, however, is not limited to such examples.  
         [0016]     It should be appreciated that the term “service” used in this document should be understood to broadly cover any service or goods which a user may desire, require or be provided with. The term also should be understood to cover the provision of complementary services. In particular, but not exclusively, the term service will be understood to include internet protocol multimedia services such as conferencing, voice and video telephony, gaming, rich call, presence, e-commerce and messaging.  
         [0017]     In preferred embodiments of the present invention, a user obtains access to a network via user equipment (UE). The user equipment, in embodiments of the present invention can be moved. Accordingly, the user equipment may be a laptop or notebook computer, mobile telephone, personal data assistant, organisers, or combinations of these entities.  
         [0018]     Embodiments of the present invention are described in the context of a 3GPP user, where the 3GPP network supports IPv6, roams to a 3GPP2 network which supports IPv4. However, it should be appreciated that the principal of embodiments of the present invention can be extended to the user of an IPv4 network roaming into an IPv6 network. Embodiments of the present invention also have broader application to any situation where a user from one network supporting one protocol roams into a different network supporting a different protocol. That protocol may be an internet protocol and different versions of that protocol. Alternatively, the protocol may be an internet protocol and a different protocol or both protocols may be different from the IP protocol.  
         [0019]     Reference will now be made to  FIG. 1  which shows two networks with which embodiments of the present invention can be implemented.  
         [0020]      FIG. 1  shows two networks  2  and  4 . Network  2  is the home network of the user equipment  6 . The user equipment  6  is in a visited network  4 . In the embodiment shown in  FIG. 1 , the home network  2  is a 3GPP IPv6 network and the visited network is a 3GPP2 network.  
         [0021]     The mobile station  6  is arranged to attach to the radio network (RN)  8 . The radio network  8  comprises the radio access network. The radio network  8  may comprise a base station or similar entity. The mobile station  6  will communicate via a wireless interface with the base station. The base station may be connected to a control element similar to a radio network controller in the 3GPP standard or the base station controller of the GSM standard. Alternatively, the control function may be incorporated with a base station type element.  
         [0022]     The radio network  8  is connected to a packet data serving node PDSN/FA (Foreign agent)  10 . This element  10  is provided in a core network of the visited network  4 . Also provided in the core network is a P-CSCF  12  (proxy-call state control function). Finally, also provided is a roaming gateway RGW  14 . The roaming gateway  14  is a new entity proposed by embodiments of the present invention. The PDSN provides packet switched communication.  
         [0023]     The core network of the visited network  4  may comprise a series of call state control functions (CSCFs) of which the proxy call state control function P-CSCF  12  is shown.  
         [0024]     In embodiments of the present invention, communications from the mobile station  6  to the radio network  8  are via the wireless interface. The radio network  8  is connected to the PDSN/FA  10 . The PDSN/FA is connected both to the RGW  14  and P-CSCF. The P-CSCF is connected to the RGW  14 .  
         [0025]     It should be appreciated that the media path, that is the data traffic from the mobile station goes to the radio network  8  to the PDSN/FA  10  to the RGW and vice versa. The signalling traffic (such as SIP) flows from the MS to the radio network  8  to the PDSN/FA  10  to the P-CSCF  12  and from there to RGW  14 . The connection between the P-CSCF  12  and the RGW  14  may operate in accordance with the session initiation protocol SIP.  
         [0026]     SIP is specified (in RFC 3261) by the Internet Engineering Task Force (IETF). SIP is an application layer signalling protocol for starting, changing and ending user sessions as well as for sending and receiving transactions. A session, may for example, be a two way telephone call or multi-way conference session or connection between a user and an application server (AS). The establishment of these sessions enables a user to be provided with the above mentioned services.  
         [0027]     The relevant elements of the home network  2  will now be described. The S-CSCF (Serving-CSCF)  16  is provided which has a connection to a HSS  18  (home subscriber server). The HSS has information related to the user&#39;s subscription information such as the services for which the user is permitted to obtain. The mobile station  20  is in the 3GPP network and using SIP. The IMS session is being established between mobile station  6  that is in the 3GPP2 network and the mobile station  20  in the 3GPP network. This is accomplished as a result of the RGW  14 .  
         [0028]     The roaming gateway node provides all the necessary inter working functionalities for a 3GPP roaming user. The RGW is required only when the P-CSCF is located in the visited network. If the P-CSCF resides in the home network then a tunnelling technique can be used to carry IPv6 traffic over IPv4 from the mobile station.  
         [0029]     In embodiments of the present invention, it is assumed that the mobile roaming user&#39;s mobile station supports the following: dual IP stack (IPv4 and IPv6). In other words, the mobile station itself is capable of supporting IPv4 and IPv6. It is also assumed that the mobile station  6  supports both the 3GPP and 3GPP2 air interfaces. Finally, it is assumed that the mobile station supports the USIM (universal subscribe identity module) requirements of the 3GPP specifications and R-UIM (removable-user identity module) required by the 3GPP2 specifications.  
         [0030]     In the embodiment shown in  FIG. 1  and described in relation to  FIGS. 2 and 3 , the scenario where a 3GPP user is roaming in a 3GPP2 network is described. However, embodiments of the present invention are equally applicable where a 3GPP 2 user is roaming in a 3GPP network.  
         [0031]     For a 3GPP user roaming in a 3GPP2 network, the RGW has to be in the 3GPP2 network and it has to be configured with the 3GPP IMS contact information. The same is true for a 3GPP2 user roaming in a 3GPP network, the RGW would be located in the 3GPP network with equivalent configuration, ie the 3GPP2 IMS information.  
         [0032]     Signalling and media traffic will be protocol and address translated by the RGW. Signalling and media paths are shown in  FIG. 1 .  
         [0033]     Reference will now be made to  FIG. 3  which shows the roaming gateway of  FIG. 1  in more detail. As mentioned, the interface between the P-CSCF and the RGW uses SIP. If the roaming user initiates a message and the destination is an IPv6 address, then the message would be forwarded by the PDSN/FA to the RGW  14 . Terminating messages for the roaming user will reach the RGW first in the visited network before they are modified and delivered to the mobile station  6 .  
         [0034]     The RGW  14  has a number of functional entities. There is a gateway manager  30 . This is the point of entry to the roaming gateway  14 . The gateway manager communicates with other internal entities in order to do address mapping, protocol translation or SIP message handling. The gateway manager is therefore connected to an address allocation and mapping handler  32 , a protocol translator  34  and a signalling message handler  36 . The address allocation and mapping handler is connected to an address mapping table  38 . The address mapping table  38  is also connected to the signalling message handler  36 . An IPv6 address pool  40  is provided which is connected again to the address allocation and mapping handler  32 .  
         [0035]     The address allocation and mapping handler  32  is arranged to pick an IPv6 address. This occurs when the user registers to the IMS. The IPv6 address is selected from the IPv6 address pool  40 . The address allocation and mapping handler will then map the selected IPv6 address to the roaming user&#39;s IPv4 address. This entity is also responsible for swapping addresses back and forth in the transport layer.  
         [0036]     The protocol translator  34  provides protocol translation between IPv4 and IPv6  
         [0037]     The signalling message handler  36  is arranged to receive SIP signalling messages from the gateway manager  30 . The source/destination address, contact address and any IP address in the SDP (session description protocol) are modified according to the mapping entry found in the mapping table  38 .  
         [0038]     When a user sends a REGISTER (SIP message), an IPv6 address is allocated and a mapping entry is added to this table. The entry is removed when the roaming user deregisters from IMS.  
         [0039]     The RGW needs to assign the MS an IPv6 address at the RGW and create a mapping between this assigned IPv6 address and the IPv4 address of the MS. The RGW is responsible for assigning IPv6 addresses to a number of mobile stations. Additionally the IPv6 address is released at the expiry of the SIP Registration lifetime. The IPv6 address assigned to an MS at the RGW is transient and hence it is drawn from a pool of IPv6 addresses. DHCPv6 (Dynamic Host Configuration Protocol) is a solution for managing a pool of IPv6 addresses. A lease period is assigned to each IPv6 address that is allocated to a MS by the RGW. This lease period would be equivalent of the SIP Registration lifetime. The address would be returned to the pool (for use by another MS) at the end of the lease period if it is not renewed. Hence DHCPv6 is one possible means of managing the IPv6 address pool. Note that the RGW could implement a proprietary scheme wherein it could manage its own IPv6 address pool without using a standardized solution like DHCPv 6 .  
         [0040]     Reference is now made to  FIG. 2  which illustrates the signalling flow during IMS registration using the RGW  14 .  
         [0041]     When the user wants to register to his home IMS, the mobile station  6  sends in step S 1  a REGISTER message to the P-CSCF  12 . The IPv4 P-CSCF in the visited network will forward the message to the RGW  14  since it does not know how to handle an IPv6 destination address. Thus, in step S 2 , the REGISTER message is forwarded by the P-CSCF  12  to the RGW  14 . In step S 3 , the RGW  14  allocates an address from the IPv6 address pool, i.e. an IPv6 address and maps it to the mobile station&#39;s IPv4 address. The mapping will be added as a mapping entry to the mapping table. The source and contact addresses of the REGISTER message are now modified to the mapped IPv6 address in the transport and application levels.  
         [0042]     In step S 4 , the modified register message is sent to the S-CSCF  16  in the user&#39;s home network. The S-CSCF  16  sends in step S 5  a 200 OK message to the RGW  14 . 200 OK is an SIP message and effectively is an acknowledgement. In step S 6 , the RGW will map the IPv6 address used in the 200 OK message received from the S-CSCF  16  to obtain the corresponding IPv4 address. This is done using the mapping table entry and is done on the transport and application levels. Thus, in step S 7  a modified 200 OK message is sent from the RGW  14  to the P-CSCF  12 . In other words, the address information in the 200 OK message now contains the corresponding IPv4 address.  
         [0043]     In step S 8  a 200 OK message is sent from P-CSCF  12  to the 3GPP mobile station. This is the same as the message sent in step S 7 .  
         [0044]     It should be appreciated that all SIP messages will be handled by the RGW in a similar way. Thus, SIP messages such as INVITE, 200 OK, REGISTER etc. which contain IP addresses will be modified by the gateway. If the message is going from the mobile station to its home network, the IPv6 address will be substituted for the IPv4 address. On the other hand, if the message is coming from the mobile station, the IPv4 address will be substituted by the IPv6 address.  
         [0045]     Embodiments of the present invention are advantageous in that it does not impose any new requirements and new protocols on the mobile terminals. Thus, no new protocols need to be standardised.