Patent Publication Number: US-2003227940-A1

Title: Method for connecting a terminal over an access network to the core part of a radio communication network and corresponding gateway

Description:
[0001] The invention is based on a priority application EP 02 360 165.1 which is hereby incorporated by reference.  
       FIELD OF THE INVENTION  
       [0002] The present invention relates to access networks and more precisely to a method for connecting a terminal over an access network to the core part of a radio communication network.  
       BACKGROUND OF THE INVENTION  
       [0003] Known in the art is a terminal supporting simultaneously GSM and DECT protocol stacks. At home, the terminal can use the DECT standard on the air interface to establish a telephone call, the call being further routed in the PSTN. On the move, the terminal will use the GSM network to establish a communication. Such terminals provide a fixed/mobile convergence since the appropriate communication network is automatically chosen depending on the availability of a communication over the DECT interface.  
       [0004] This solution presents the drawback that the terminal should be addressed over different phone numbers depending on the used radio access network (GSM or DECT air interface). Moreover, the different services proposed to the terminal depend on the network. Furthermore, no handover is available between the different access networks since no central entity accessible by both access networks contains the user profile to control handover. Consequently, the terminal has to reinitialize completely the activated sessions when changing of access network.  
       [0005] A particular object of the present invention is to provide a method for unifying the services proposed to a terminal able to establish a communication over different access networks.  
       [0006] Another object of the invention is to provide a gateway between an access network and the core network of a radio communication network to perform the above mentioned method.  
       SUMMARY OF THE INVENTION  
       [0007] These objects, and others that appear below, are achieved by a method for connecting a terminal over an access network, herein called remote access network, to a core part of a radio communication network, said radio communication network comprising said core network and a dedicated radio access network different from said remote access network, said method comprising the steps of:  
       [0008] interfacing over a gateway said remote access network to an entity of said core network, said entity being an element of said core network at the interface between said core network and another communication network;  
       [0009] performing at said gateway a protocol stack translation for mapping protocols used in said remote access network to protocols used in said entity of said core network;  
       [0010] controlling the connection over said remote access network by said core network.  
       [0011] These objects are further achieved by a gateway between an access network herein called remote access network, and an entity of a core network of a radio communication network, said radio communication network comprising said core network and a dedicated radio access network different from said remote access network, said entity being an element of said core network at the interface between said core network and another communication network, said gateway comprising:  
       [0012] means for performing a protocol stack translation between a communication protocol stack used in said remote access network and said communication protocols used in said entity of said core network;  
       [0013] means for receiving control information from said core network destined to a terminal connectable to said core network over said remote access network.  
       [0014] These objects are further achieved by an entity belonging to a core network of a radio communication network said entity being an element of said core network at the interface between said core network of said radio communication network and another communication network, said entity comprising means for communicating with a first radio access network, herein called dedicated radio access network and means for communicating with a second access network, herein called remote access network, different from said dedicated radio access network over a gateway.  
       [0015] These objects are further achieved by an entity belonging to a core network of a radio communication network, said entity being an element of said core network which would be contacted for establishing a connection with a terminal over a dedicated radio access network, said entity comprising:  
       [0016] means for receiving at least signalling data from a second entity, said second entity being an element of said core network at the interface between said core network and another communication network, said signalling data being related to a connection initiated by a mobile terminal over a second access network, herein called remote access network, different from said dedicated radio access network, a gateway, and over said second entity.  
       [0017] According to the present invention, a unique core network controls the communications to and from a terminal whatever the used access network. A protocol translation between the access network and the core network is ensured by a gateway located at the interface between the access network and an element of the core network at the interface between the core network of this radio communication network and another radio communication network.  
       [0018] The method according to the present invention presents the advantage to provide unified services over all available interfaces of the terminal.  
       [0019] Another advantage of the present invention is to enable an access over the remote access network from an area where no radio coverage is available for using the dedicated radio access network. For example, if the terminal is located in a GSM/GPRS only area, it will continue to be able to access to UMTS services through the fixed remote access network with the same rates.  
       [0020] Another advantage of the present invention is to enable an access to the core network of the radio communication network over the remote access network from a area having a radio coverage from a foreign operator. In this configuration no rooming agreement is necessary if the remote access network is used. Hence, the foreign operator radio access network needs not to be used. Moreover the costs for accessing the radio communication network over the remote access network are cheaper than the costs that would be required for using the radio access network of the foreign operator.  
       [0021] Another advantage of the invention is to provide services controlled by the core access network making the best of the functionality of all available access networks to communicate with a predefined terminal. Possible services are selection of the most appropriate access network according to access network profiles stored in the core network, hand-over procedure between the different access networks, macro-diversity over the different possible access networks since a unique core network will process the data from all access networks.  
       [0022] Further advantageous features of the invention are defined in the dependent claims. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023] Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment given by way of non-limiting illustrations, and from the accompanying drawings, in which:  
     [0024]FIG. 1 shows a system supporting the method according to the present invention;  
     [0025]FIG. 2 shows an example of protocol stack at a gateway according to the present invention between a remote access network and a core network. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0026]FIG. 1 shows a system where the method according to the present invention can be implemented. The system comprises a core network  10 , a first access network, herein called dedicated radio access network  11 , a second access network, herein called remote access network  12 , and a mobile terminal  13 .  
     [0027] Core network  10  and dedicated radio access network  11  are preferably part of a known cellular radio communication network for example GSM/GPRS or UMTS.  
     [0028] Remote access network  12  uses, in this embodiment of the invention, a PSTN network accessible by terminal  13  over a wireless interface as transport network. Such interfaces may be Bluetooth based, infrared based or an interface compatible with DECT standard.  
     [0029] Remote access network  12  is preferably a PSTN  122  for circuit switched data or the PSTN interconnected with the Internet  123  for packet switched data. Terminal  13  can connect to remote access network  12  over a local node or a local area network  121  using for example the Bluetooth technology.  
     [0030] In the framework of the invention, other possible types of access networks may be envisaged such as a wireless LAN based on Ethernet or on ADSL. Remote access network may also be a fixed access network for example a fixed LAN based on Ethernet, terminal  13  being physically connected to the LAN or connectable over a short range wireless interface to a local node of said fixed LAN.  
     [0031] It will be clear for a person skilled in the art how to transpose the present invention to such types of remote access networks.  
     [0032] Core network  10  comprises at least one mobile switching center MSC  101  for handling circuit switched traffic received from dedicated radio access network  11  and at least one Serving GPRS Support Node SGSN  102  for handling packet switched traffic received from dedicated radio access network  11 . Further core network  10  comprises at least one Gateway MSC (GMSC)  103  for handling circuit switched traffic and at least one Gateway GPRS Support Node (GGSN)  104 . GMSC  103  and GGSN  104  are interface between core network  10  and external communication networks such as fixed PSTN or Internet.  
     [0033] Core network  10  could in a restricted embodiment of the invention support only circuit switched or only packet switched traffic.  
     [0034] MSC  101 , SGSN  102 , GMSC  103  and GGSN  104  are preferably related to GSM/GPRS and UMTS core network, they can be mapped to equivalent entities if another type of core network is considered.  
     [0035] Core network  10  and more precisely MSC  101  and SGSN  102  are connected over predefined interfaces to dedicated radio access network  11 . If dedicated radio access network  11  is an UMTS Terrestrial Radio Access Network (UTRAN), the interfaces to the core network being respectively standardized lu CS and lu PS interfaces.  
     [0036] Dedicated radio access network  11  comprises a radio network controller RNC  111  and Node Bs  112  serving terminals  13  under their range.  
     [0037] Terminal  13  can according to the present invention get connected to core network  10  either over dedicated radio access network  11  or over remote access network  12 .  
     [0038] If connecting to core network  10  over remote access network  12 , terminal  13  can preferably connect over a local node  121 , using for example the Bluetooth technology. Local node  121  ensures the translation of the protocol used over the air interface to the protocols used in the remote access network  12 . In another embodiment of the present invention entity  121  may also be a private local area network. This embodiment enables it to increase the number of terminals type which can connect to the remote access network  12  even if they do not support the same technology as remote access network  12 . In another embodiment of the present invention entities  141 ,  142  may also be linked to entity  121  by a private network. This embodiment enables it to offer secured services linking private company LAN or MAN networks with the radio communication network.  
     [0039] According to the present invention, remote access network  12  is connected to core network  10  over a gateway  141 ,  142 . If remote access network supports circuit switched traffic, a specific gateway  141  for circuit switched traffic will handle the connection. If remote access network supports packet switched traffic, a specific gateway  142  for packet switched traffic will handle the connection. Gateway  141 ,  142  ensures the protocol stack translation between the communication protocols used in remote access network  12  and the protocols used in core network  10  (i.e. protocols defined in the UMTS standard). The protocol stack translation will be explained in more details below.  
     [0040] Gateway  141  resp.  142  are according to the present invention connected to GMSC  103  resp. to GGSN  104  i.e. to entities of the core network  10  at the interface between the core network of said radio communication network and the core network of another communication network.  
     [0041] In a preferred embodiment of the present invention, at least the signalling data of the call, received at GMSC  103 , resp. to GGSN  104  according to the present invention, are forwarded from GMSC  103 , resp. to GGSN  104  to MSC  101  resp. to SGSN  102 . These entities  101 ,  102  are usually controlling the call establishment for normal calls from terminal  13  over dedicated radio access network  11 . Then, forwarding the signaling data from GMSC  103 , resp. to GGSN  104  to MSC  101  resp. to SGSN  102  presents the advantage to reuse the same call establishment procedure as for normal calls over dedicated radio access network  11 . The forwarding of signaling data between GMSC  103 , resp. to GGSN  104  and MSC  101  resp. to SGSN  102  can be implemented using well known tunneling mechanisms.  
     [0042] Usually, several instance of MSCs  101 , resp. SGSNs  102  are under the control of a single GMSC  103 , resp. GGSN  104 . According to a preferred embodiment of the present invention, the appropriate instance of MSC  101  resp SGSN  102  is selected either according to geographical information from terminal  13  or according to observation by GMSC  103  resp GGSN  104  of the instance MSC  101 , resp. SGSN  102  used previously by terminal  13 . Alternatively, it will be clear to a person skilled in the art that a fixed MSC  101  resp SGSN  102  may be associated to GSMC  103  resp GGSN  104 .  
     [0043] Preferably, only the signaling data are forwarded from GMSC  103 , resp. to GGSN  104  to MSC  101  resp. to SGSN  102 , the user data remaining at GMSC  103 , resp. to GGSN  104  during the processing of signaling data at MSC  101  resp. to SGSN  102 .  
     [0044] However, if macrodiversity has to be performed at MSC  101  resp. to SGSN  102 , signaling data as well as user data have to be forwarded from GMSC  103 , resp. to GGSN  104  to MSC  101  resp. to SGSN  102 . Indeed the macrodiversity procedure will combine the user data received over dedicated radio access network  11  and user data received over access network  12  and GMSC  103 , resp. to GGSN  104 .  
     [0045] As a consequence, no matter if a call to/from terminal  13  is performed over dedicated radio access network  11  or over access network  12 , the call is controlled by the same entity, preferably MSC  101 , resp. SGSN  102  in core network  10 . The same services and functionality are available for the call no matter which access network  11  or  12  is used since the same user profile is used for providing these services.  
     [0046] The fact that gateways  141 ,  142  are interfaces to GMSC  103  or GGSN  104  presents the advantage that a connection can still be established over remote access network  12  to GMSC  103  or GGSN  104  even if no radio coverage is available for terminal  13  to get connected over MSC  101  or SGSN  102 . Then, the terminal  13  can be provided with the services of core network  10  whatever the radio coverage of dedicated radio access network  11 .  
     [0047] The access over remote access network  12  to GSMC  103  or GGSN  104  is also advantageous when terminal  13  is abroad i.e. not in the area covered by the dedicated radio access network of his usual operator but possibly by another operator having roaming agreements with the operator of the radio communication network. Instead of using the expensive roaming functionality, terminal  13  may advantageously connect to core network GMSC  103  or GGSN  104  of his usual operator over remote access network  12 .  
     [0048] Since a single central entity in core network  10 , preferably MSC  101  resp. to SGSN  102  as adressed above, controls the call over both access networks  11  and  12 , unified services can be provided to terminal  13  independently on the used access network  11 ,  12 .  
     [0049] Example for such services are:  
     [0050] Choice of the most appropriate access network. A feature possible with the network structure according to the invention is to select the used access network according to user requirements.  
     [0051] For this purpose, an entity in core network  10  should stored information concerning the capabilities of both access network  11 ,  12  in term of QoS and throughput: information on the maximum data throughput and on the quality of service may be stored by both access networks  11 , 12  in the core network  10  for example at MSC  101  or SGSN  102 .  
     [0052] Upon connection request from terminal  13  indicating a requested quality of service or a requested throughput, core network  10  or preferably MSC  101  or SGSN  102  may check which of the access network  11 ,  12  is the best adapted to fulfill these conditions and transmit this information to terminal  13  in order it gets connected over the best adapted access network  11 ,  12 . Preferably, MSC  101  or SGSN  102  can manage several simultaneous calls to or from terminal  13  over different access networks.  
     [0053] In a possible embodiment of the present invention, the connection request phase may use remote access network  12  while the data exchange phase will use the best appropriate access network as identified in the core network.  
     [0054] This feature is preferably carried out with standard Inter System change procedures between terminal  13  and core network  10  using common location management procedures.  
     [0055] Handover between two access networks. The core network can be informed of the possibility to start an handover. As a consequence, terminal  13  currently communicating over an access network  11 ,  12  will change the used access network  11 ,  12 . This notification is made by means of core network signaling to terminal  13 .  
     [0056] For this purpose MSC  101 , or SGSN  102  should be able to distinguish information received from the different radio access networks  11 ,  12 . A possible solution could be to manage different links, one for data coming from remote access network  12  and one for data coming from dedicated radio access network  11 .  
     [0057] Macro-diversity. This consists in sending/receiving simultaneously the same data over both radio access networks  11 ,  12  and combining them at reception. Macrodiversity can be implemented in the uplink (terminal to network direction) for this purpose terminal  13  should support simultaneous communication over several communication stacks. Macro diversity can as well be implemented in the downlink (network to terminal direction) for this purpose terminal  13  should comprise means for combining information received from core network  10  over remote access network  12  and over dedicated radio access network  11 .  
     [0058] At network side, SGSN  102  or MSC  101  should be equipped means for reconstructing data received in macrodiversity. Such means are known in the art and usually implemented in Radio Network controllers of UMTS network. Implementing such means in GMSC  103  or GGSN  104  can be performed without problem by a man skilled in the art according to the teachings of the present invention.  
     [0059] Nevertheless it is also possible, in another embodiment of the present invention to perform call establishment control as well as macrodiversity at GMSC  103 , resp. to GGSN  104 . In this case the forwarding of signaling or user data from GMSC  103 , resp. to GGSN  104  to MSC  101  resp. to SGSN  102  will no more be necessary. However modifications will be required at GMSC  103 , resp. to GGSN  104  to have them support call establishment or macrodiversity.  
     [0060]FIG. 2 shows an example of a protocol stack according to the present invention at gateway  142  for packet switched traffic. Moreover, FIG. 2 shows the protocol stack at terminal  13 , at ISP router  122 , the protocol stacks at GGSN  104  and finally the protocol stack at an application server with which terminal  13  communicates.  
     [0061] It will be clear for a person skilled in the art that the protocol stack can be adapted to a gateway  141  between the remote access network  12  and GMSC  103  in case of circuit switched traffic.  
     [0062] Moreover, FIG. 2 describes the protocol translation for the user plane i.e. the user data. Similarly, a protocol encapsulation is to be performed for the signaling plane between terminal  13  and the gateway  142  until entity  104 . Preferably, the core network signaling is further tunneled from GGSN  104  to entity SGSN  102  (comprising core network signaling). The protocol encapsulation for the signaling plane will not be further described but can be deduced without difficulty from the standardized signaling protocol in the UMTS network and from the above described protocol translation for the user plane.  
     [0063] The protocol stack at terminal  13  is characteristic of access network  12 . In this embodiment, access network  12  is a PSTN interconnected to Internet. The protocol stack at terminal  13  comprises following lower layers  20  according to the ISO OSI layer model.  
     [0064] Layer 1/2: PPP (Point to Point Protocol)/L1  
     [0065] Layer 3: IP  
     [0066] Layer 4: TCP/UDP  
     [0067] On the top of the layers related to access network  12 , a layer  21  supports a tunneling protocol. This tunneling protocol may be the GPRS Tunneling Protocol (GTP-U&amp;C) or any equivalent tunneling protocol such as for example mobile IP tunneling for user plane plus a connection with GGSN using the GGSN IP address for the signaling plane. This tunneling encapsulates IP packets generated at layer  22 , the IP packets contain application data generated at layer  23 . Application data may be user data as well as signaling data. Moreover other ISO OSI layer 3 protocol data units may replace the IP packets.  
     [0068] ISP router  122  comprises two parallel layers stacks with a relay layer on the top of them for operating a protocol translation between the low layer used in the PSTN (PPP/L1, IP, TCP/UDP) and the ones used in the Internet (L1/L2/IP, TCP/UDP), ISP router may also offer firewall functions.  
     [0069] Gateway  142  comprises two parallel layers stacks with a relay layer on the top of them for operating a protocol translation between the ISP router side and the GGSN side.  
     [0070] Layer 1: L1/L2  
     [0071] Layer 2: IP  
     [0072] Layer 3: TCP/UDP.  
     [0073] Layer 4/5: layers  25  i.e. tunneling protocol corresponding to GPRS Tunneling protocol (GTP U&amp;C).  
     [0074] Layer 1 L1/L2 and Layer 4/5 may be different at Gateway  142  and at GGSN  104  (Indeed Gateway  142  is usually located at ISP provider while GGSN  104  is owned by the mobile operator).  
     [0075] GGSN  104  comprises also two parallel protocol stacks with a relay layer on the top of them for performing protocol translation between the radio communication network on the one hand and an application server on the other hand. Following layers are implemented:  
     [0076] Radio communication network side (referenced as Ge interface on FIG. 2)  
     [0077] Layer 1/Layer 2: L1/L2 of the internet network  
     [0078] Layer 3: IP  
     [0079] Application server side (referenced as Gi interface on FIG. 2):  
     [0080] Layer 1/Layer 2: L1/L2 of the internet network  
     [0081] Layer 3: IP  
     [0082] The protocol stack at application server will not be detailed further as it is not part of the present invention.  
     [0083] According to the present invention, the gateway  141  respectively 142 functionality may be incorporated in a stand alone module external to the GMSC  103  respectively GGSN  104  and owned preferably by the internet service provider. In another embodiment, the gateway functionality can be directly incorporated in the GMSC  103  respectively GGSN  104  and owned preferably by the radio communication operator. In another embodiment, the gateway functionality incorporated in the GMSC  103  respectively GGSN  104  and linked to remote access network  12  by a private WAN to have a secured access (no traffic through Internet).  
     [0084] In a prefered embodiment of the present invention where at least the signaling data of a call initiated by terminal  13  are forwarded from GMSC  103 , resp. to GGSN  104  to MSC  101  resp. to SGSN  102 , MSC  101  resp. to SGSN  102  and GMSC  103 , resp. to GGSN  104  must be modified according to the present invention to comprise means for tunelling at least signalling data from/to mobile terminal  13 , the signalling data being related to a connection initiated by mobile terminal  13  over access network  12 , different from dedicated radio access network  1 , over gateway  141 , resp  142 , and finally over GMSC  103 , resp. GGSN  104 .  
     [0085] MSC  101  resp SGSN  102  further preferably comprise means for selecting between remote access network  12  and dedicated radio access network  11  for communicating with a terminal  13  and means for performing macrodiversity by combining data received from/sent over remote access network  12  with data received from/sent over dedicated radio access network  11 .  
     [0086] To summarize the present invention provides unified services to a terminal no matter how (over dedicated access network  11  or over remote access network  12 ) it gets connected to the core network  10  of a radio communication network. Terminal  13  can use, with both connection types, the same bookmarks, the same agenda, the same address book . . . At network side, the services offered over both access networks are handled centrally in core network  10 .  
     [0087] The present invention presents also the advantage to use the radio resources of dedicated radio access network only for real mobility situation. Indeed each time access over the fixed remote access network is possible a handover will be performed. This will also contribute to optimize the indoors communication quality and decrease the power consumption of the terminal.