Abstract:
The invention allows providing a fixed access point for a terminal device. One of multiple access points is assigned to serve as a fixed access point for a terminal device based on a received identifier of the terminal device. A notification about the assignment of the fixed access point is transmitted to at least one of the terminal device and a gateway node serving the terminal device. As a result, Mobile IP based handover between GPRS and WLAN will be seamless. Furthermore, the invention allows using a dedicated gateway for infected terminals to provide quarantined access to network services.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to telecommunications. In particular, the invention relates to providing a fixed access point for a terminal device communicating with a packet data network via a mobile access system. 
   2. Description of the Related Art 
   In recent years mobile access systems, i.e. systems which allow mobile access to packet switched data communication networks or packet data networks, have emerged. The access provided by mobile access systems is typically, although not necessarily, wireless. Wireless Local Area Network (WLAN or Wireless LAN) is an example of a mobile access system. A Wireless LAN allows a mobile user to connect to a packet data network through a wireless connection. A standard, IEEE 802.11, specifies the technologies for Wireless LANs. 
   Another example of a mobile access system is General Packet Radio Service (GPRS). GPRS also allows packet data transmission for mobile communication networks. GPRS is designed to support e.g. digital mobile telecommunication networks based on the Global System for Mobile Communications (GSM) standard. However, GPRS is not restricted to only GSM networks but supports also for example 3 rd  Generation Partnership Project (3GPP) based digital mobile telecommunication networks, or 3GPP systems for short. 
   Since the packet data networks typically utilize Internet Protocol (IP), Mobile Internet Protocol (Mobile IP) is typically utilized to provide mobility. Mobile IP is an extension to Internet Protocol aimed to provide mobility support for Internet Protocol. Using Mobile IP allows a terminal device to move from one link to another without changing its IP address (as seen by the layers above Internet Protocol) and yet be reachable by other terminal devices. Mobile IP is being developed by IETF (Internet Engineering Task Force) and full specifications may be obtained e.g. from http://www.ietf.org. 
   Mobile IP basically implements a forwarding system. When a mobile terminal device, or mobile node, is on its ‘home’ network, it functions normally. When it moves to a different network, data packets are forwarded from its home network to its new location. This allows normal hosts and routers that do not implement Mobile IP to continue to operate as if the mobile node had not moved. The router on the home network that is responsible for catching data packets intended for the mobile node and forwarding them to the mobile node when it is moving is called a home agent. The mobile node is assigned a permanent or semi-permanent IP address called a home address. When the mobile node is moving, it is also assigned a new, temporary address called a care-of address. The mobile node, being away from home, informs its home agent of its current care-of address with a process called registration after which the home agent will be able to forward the data packets addressed to the home address of the mobile node on to the care-of address of the mobile node. 
   Mobile access systems interface with packet data networks via access points. In other words, the access point is a network entity providing an interface via which a mobile access system may access a packet data network. For example, in the case of General Packet Radio Service, a network node called a Gateway GPRS Support Node (GGSN) typically comprises one or more access points serving as interfaces to external IP networks such as the Internet, other mobile service providers&#39; GPRS services, or enterprise intranets. In the case of Wireless LAN, a network node called Packet Data Gateway (PDG) typically comprises one or more access points serving as interfaces to packet data networks. In the case of GPRS, the interface is referred to as Gi interface, whereas in the case of Wireless LAN, the interface is referred to as Wi interface. It should be noted that the term ‘access point’ is sometimes used in prior art, particularly in relation to Wireless LAN, to refer to a base station to which a mobile terminal device connects over a radio link. However, herein the term ‘access point’ is strictly used to refer to the above described network entity providing an interface via which a mobile access system may access a packet data network. 
   A current object on the field of telecommunications is to enable interworking between various mobile access systems, such as between GPRS systems and Wireless LANs so that e.g. resources and services within a GPRS system may be accessed by Wireless LAN users and vice versa. As part of this object, it is intended to integrate access points associated with various mobile access systems into one network node. For example, it is intended to implement the functionalities of a Gateway GPRS Support Node, a Packet Data Gateway and a home agent in one network node. 
   However, while the integration of the functionalities of the Gateway GPRS Support Node, the Packet Data Gateway and the home agent into one network node facilitates interworking between various mobile access systems, it also creates further problems of its own. 
   One of these problems relates to handovers between GPRS and WLAN not being seamless. This problem is illustrated in  FIGS. 1   a - 1   b .  FIGS. 1   a - 1   b  disclose a packet data network  101 , a first gateway  102 , a second gateway  103 , a GPRS mobile access system  104 , a WLAN mobile access system  105 , a terminal device  106 , a first home agent  107 , a first WLAN access point  108 , a first GPRS access point  109 , a second home agent  110 , a second WLAN access point  111  and a second GPRS access point  112 .  FIG. 1   a  illustrates a situation before a handover, whereas  FIG. 1   b  illustrates the situation after the handover. As illustrated by arrow  113  in  FIG. 1   a , the terminal device  106  has GPRS access to the packet data network  101  via the GPRS mobile access system  104  and the first GPRS access point  109  at the first gateway  102 . Furthermore, the terminal device  106  has registered itself with the first home agent  107  at the first gateway  102 . Therefore, all the IP traffic to and from the terminal device  106  will be routed via the first home agent  107  at the first gateway  102 , as illustrated by arrow  113 . 
   A need may arise for the terminal device  106  to switch its mobile access from GPRS to WLAN. For example, the terminal device  106  may move to an area where GPRS reception is unacceptably poor but where WLAN reception is acceptable. The problem with prior art in such a situation is the randomness of the selection of the subsequent access point. When the terminal device  106  wants to create a WLAN or GPRS connection, it uses an Access Point Name (APN) to specify to which external packet data network it requires to establish a connection. In the example of  FIGS. 1   a - 1   b , the terminal device  106  uses an Access Point Name specifying the packet data network  101 . When, as is often the case in real life implementations, there are multiple suitable access points corresponding to the specified Access Point Name, a Domain Name System server selects one of the multiple suitable access points. The selection by the Domain Name System server is typically random, due to e.g. load balancing issues. The Domain Name System server may utilize e.g. round robin in selecting the access point. 
   Therefore, in our example, the second WLAN access point  111  at the second gateway  103  will be selected by chance during the handover from GPRS to WLAN. Yet, at the same time, the IP traffic will still need to be routed via the first home agent  107  at the first gateway  102  since that is the home agent the terminal device  106  registered itself with. The result is illustrated in  FIG. 1   b . All the IP traffic to and from the terminal device  106  will be routed via both the second gateway  103  and the first gateway  102 , as illustrated by arrow  114 . 
   Obviously, in order to optimize routing it would have been desirable to be able to specifically select the first WLAN access point  108  which is located in the same gateway  102  as the home agent  107  used. However, due to the random nature of the prior art access point selection by the Domain Name System server, this is not possible. As a result, Mobile IP based handover between GPRS and WLAN is not seamless. 
   Yet another problem associated with prior art relates to isolating mobile terminal devices infected with viruses and other malicious software. As the mobile terminal devices are getting more software capabilities, they are also becoming more vulnerable to viruses. If a network can detect a misbehaving mobile terminal device, it should be able to either disconnect the terminal device from the network or it should be able to make sure that the misbehaving terminal device is not causing any additional damage to other terminal devices and network elements. In the latter case, one way is to use a dedicated gateway for infected terminals to provide quarantined access to services. However, since in prior art the Domain Name System server randomly selects the gateway, the terminal device access cannot be anchored to any dedicated gateway. 
   Therefore, the object of the present invention is to alleviate the problems described above and to introduce a mechanism that allows providing a fixed access point for a terminal device. 
   SUMMARY OF THE INVENTION 
   A first aspect of the present invention is a method of providing a fixed access point for a terminal device. An identifier of a terminal device is received. One of multiple access points is assigned to serve as a fixed access point for the terminal device based on the received identifier of the terminal device, wherein each of the multiple access points is arranged to interface at least one of multiple mobile access systems with a packet data network. A notification about the assignment of the fixed access point is transmitted to at least one of the terminal device and a gateway node serving the terminal device. It is to be understood that the term ‘fixed’ in relation to an access point is herein used to disclose the access point being permanent over multiple subsequent sessions and over handovers between various mobile access systems. 
   A second aspect of the present invention is a system of providing a fixed access point for a terminal device. The system comprises a terminal device, a packet data network and multiple mobile access systems. The system further comprises multiple network nodes, each of which network nodes comprises at least one access point, each access point arranged to interface at least one of the mobile access systems with the packet data network. At least one of the multiple network nodes further comprises a fixed access point assigner arranged to assign one of the access points to serve as a fixed access point for the terminal device based on a received identifier of the terminal device. At least one of the multiple network nodes further comprises a notification transmitter arranged to transmit to at least one of the terminal device and a gateway node serving the terminal device a notification about the assignment of the fixed access point. 
   A third aspect of the present invention is a network node. The network node comprises at least one access point arranged to interface at least one of multiple mobile access systems with a packet data network. The network node further comprises a fixed access point assigner arranged to assign one of the at least one access point comprised in the network node and another access point comprised in another network node to serve as a fixed access point for a terminal device, based on a received identifier of the terminal device. The network node further comprises a notification transmitter arranged to transmit to at least one of the terminal device and a gateway node serving the terminal device a notification about the assignment of the fixed access point. 
   A fourth aspect of the present invention is a computer program embodied on a computer readable medium for providing a fixed access point for a terminal device. The computer program controls a data-processing device to perform the steps of: 
   receiving an identifier of a terminal device, 
   assigning one of multiple access points to serve as a fixed access point for the terminal device based on the received identifier of the terminal device, wherein each of the multiple access points is arranged to interface at least one of multiple mobile access systems with a packet data network, and 
   transmitting, to at least one of the terminal device and a gateway node serving the terminal device, a notification about the assignment of the fixed access point. 
   A fifth aspect of the present invention is a network node which comprises at least one access point means for interfacing at least one of multiple mobile access systems with a packet data network. The network node further comprises a fixed access point assigning means for assigning one of the at least one access point means comprised in the network node and another access point means comprised in another network node to serve as a fixed access point means for a terminal device, based on a received identifier of the terminal device. The network node further comprises a notification transmitting means for transmitting to at least one of the terminal device and a gateway node serving the terminal device a notification about the assignment of the fixed access point means. 
   A sixth aspect of the present invention is a gateway node serving a terminal device. The gateway node comprises a notification receiver arranged to receive a notification about assignment of one of multiple access points to serve as a fixed access point for the terminal device, wherein each of the multiple access points is arranged to interface at least one of multiple mobile access systems with a packet data network. The gateway node further comprises a forwarder arranged to forward data traffic from the terminal device to the fixed access point in response to the received notification. 
   A seventh aspect of the present invention is a terminal device. The terminal device comprises a notification receiver arranged to receive a notification about assignment of one of multiple access points to serve as a fixed access point for the terminal device, wherein each of the multiple access points is arranged to interface at least one of multiple mobile access systems with a packet data network. The terminal device further comprises a transmitter arranged to transmit data traffic from the terminal device to the fixed access point in response to the received notification. 
   In an embodiment of the invention, the identifier of the terminal device is received in a request to forward data traffic from the terminal device to a network node comprising the fixed access point in order to test software disposed in the network node. 
   In an embodiment of the invention, the identifier of the terminal device is received in a message about the terminal device being infected. It is to be understood that the term ‘infected’ is herein used to disclose infection by malicious software, such as e.g. viruses, trojans, and worms. 
   In an embodiment of the invention, an access point comprised in a network node arranged to quarantine infected terminal devices is assigned to serve as the fixed access point for the terminal device. 
   In an embodiment of the invention, the identifier of the terminal device is received in a request by the terminal device to access the packet data network via one of the multiple mobile access systems. 
   In an embodiment of the invention, before assigning the fixed access point, one of the multiple access points is assigned to serve as an arbitrary access point for the terminal device. Then, a session initiation request comprising the identifier of the terminal device is sent to the assigned arbitrary access point. The session initiation request is forwarded from the assigned arbitrary access point to the assigned fixed access point, and the requested session is initiated with the assigned fixed access point in response to receiving the forwarded session initiation request. 
   In an embodiment of the invention, the notification about the assignment of the fixed access point is transmitted in a session initiation response to at least one of the terminal device and the gateway node serving the terminal device. 
   In an embodiment of the invention, the notification about the assignment of the fixed access point is transmitted via the assigned arbitrary access point to at least one of the terminal device and the gateway node serving the terminal device. 
   In an embodiment of the invention, the session initiation request is forwarded from the assigned arbitrary access point to the assigned fixed access point via an Internet Protocol tunnel. Furthermore, the notification about the assignment of the fixed access point is first transmitted via the Internet Protocol tunnel until the assigned arbitrary access point from which the notification is further transmitted to at least one of the terminal device and the gateway node serving the terminal device. 
   In an embodiment of the invention, the identifier of the terminal device is bound to an address of one of the multiple access points. Furthermore, the one of the multiple access points to the address of which the received identifier of the terminal device is bound, is assigned to serve as the fixed access point. 
   In an embodiment of the invention, the identifier of the terminal device is bound to an address of an access point comprised in a network node which further comprises a home agent associated with the terminal device. 
   In an embodiment of the invention, a network node comprising a home agent associated with the terminal device is searched for, and, if the network node is found, an access point comprised in the found network node is assigned to serve as the fixed access point. 
   The invention allows providing a fixed access point for a terminal device as opposed to the randomly changing access point of the prior art. As a result, Mobile IP based handover between GPRS and WLAN will be seamless. As another result, the present invention allows using a dedicated gateway for infected terminals to provide quarantined access to network services. As yet another result, the present invention facilitates testing software, e.g. a new software release, disposed in such a ‘live’ network node which comprises at least one access point, by allowing e.g. a network operator to define a restricted group of test terminal devices which alone are initially allowed to utilize the network node and the at least one network node comprised in it. 

   
     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: 
       FIGS. 1   a - 1   b  illustrate prior art Mobile IP based handover between GPRS and WLAN, 
       FIG. 2  is a flow diagram illustrating a method according to an embodiment of the present invention, and 
       FIG. 3  is a block diagram illustrating a system according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 2  illustrates an embodiment of the method of the present invention relating to providing a fixed access point for a terminal device, wherein each of multiple access points is arranged to interface at least one of multiple mobile access systems with a packet data network. 
   First, terminal device  220  initiates a procedure to access a packet data network via one of the multiple mobile access systems available, step  201 . In case of GPRS and WLAN, this procedure is referred to as ‘Access, Authentication and Authorization (AAA)’. In the embodiment of the present invention illustrated in  FIG. 2 , the terminal device  220  sends the request to a serving gateway  230 , step  202 . In case of GPRS, the serving gateway  230  may be e.g. a Serving GPRS Support Node (SGSN) which is a prior art network node typically delivering packets to and from GPRS enabled terminal devices within its service area. In case of WLAN, the serving gateway  230  may be e.g. a WLAN Access Controller. However, it should be noted that some implementations of mobile access systems may not utilize any serving gateway. The request sent by the terminal device  220  comprises an identifier of the terminal device  220  which is subsequently received by the serving gateway  230 . The identifier of the terminal device  220  may be e.g. a Mobile Subscriber Integrated Services Digital Network (MSISDN) number of the subscriber associated with the terminal device  220 . Alternatively, the identifier of the terminal device  220  may be e.g. an International Mobile Subscriber Identity (IMSI) of the subscriber associated with the terminal device  220 . In case of GPRS, the request sent by the terminal device  220  to the serving gateway  230  may be e.g. an ‘Activate PDP Context Request’ message. In case of WLAN, the request sent by the terminal device  220  to the serving gateway  230  may be e.g. a policy equivalent to the ‘Activate PDP Context Request’ message. 
   In the embodiment of the present invention illustrated in  FIG. 2 , having received the identifier of the terminal device  220 , the serving gateway  230  sends a query message to a Domain Name System server  240  at step  203 . As per prior art, the Domain Name System server  240  assigns one of available access points to serve as an arbitrary access point for the terminal device  220 . In the embodiment of the present invention illustrated in  FIG. 2 , the assigned arbitrary access point is the access point  251  comprised in a first gateway  250 . The Domain Name System server  240  sends a response message to the serving gateway  230 , step  204 . The response message may include e.g. an Internet Protocol address of the assigned arbitrary access point  251 . 
   Next, at step  205 , a session initiation request is sent from the serving gateway  230  to the first gateway  250  comprising the assigned arbitrary access point  251 . In case of GPRS, the session initiation request sent by the serving gateway  230  to the first gateway  250  may be e.g. a ‘Create PDP Context Request’ message. In any case, the session initiation request sent by the serving gateway  230  to the first gateway  250  comprises the identifier of the terminal device  220 . At step  206 , in accordance with the present invention, one of the available access points is assigned to serve as a fixed access point by utilizing new and inventive software and/or hardware (not illustrated in  FIG. 2 ) arranged in connection with the first gateway  250 . 
   In an embodiment, the first gateway  250  selects one of the available access points to serve as a fixed access point. The first gateway  250  may select e.g. an access point comprised in a network node which also comprises a home agent (not illustrated in  FIG. 2 ) associated with the terminal device  220  in order to avoid the above described handover related problems of prior art. In another embodiment, the first gateway  250  selects an access point comprised in a network node arranged to quarantine infected terminal devices if the identifier of the terminal device  220  was received in a message about the terminal device  220  being infected. In an embodiment, the first gateway  250  binds the address, e.g. an Internet Protocol address, of the selected access point and the identifier of the terminal device  220  to each other. In an embodiment, the binding information may be stored in a data base  260 . Therefore, while assigning the fixed access point, the first gateway  250  may search the database  260  in case previously stored binding information related to the identifier of the terminal device  220  were to be found, steps  207 - 208 . If previously stored binding information related to the identifier of the terminal device  220  were found at the data base  260 , the first gateway  250  would assign the access point indicated by the binding information to serve as the fixed access point. In this manner, the assigned access point will be ‘fixed’ since the same access point will be assigned over multiple subsequent sessions and over handovers between various mobile access systems, as opposed to randomly assigned access points of prior art. If the terminal device  220  gets infected, the binding information in the data base  260  may be updated to indicate e.g. an access point comprised in a network node arranged to quarantine infected terminal devices. 
   In another embodiment, rather than storing the binding information in a data base, the binding information may be configured at the first gateway  250  in such a way that a same identifier of the terminal device  220  results in a same address of the fixed access point. For example, the binding may be defined as a hash function from the identifier of the terminal device  220  to the address of the fixed access point. Furthermore, a list of terminals under quarantine may be maintained. That is, a list containing exceptions to the binding defined by the hash function may be maintained. 
   In yet another embodiment, the data base  260  may contain information about which home agents are associated with which terminal devices. In this embodiment, the first gateway  250  may query the data base  260 , steps  207 - 208 , to find an access point in a network node which also comprises the home agent associated with the terminal device  220 . 
   In the embodiment of the present invention illustrated in  FIG. 2 , an access point  271  comprised in a second gateway  270  is assigned to serve as the fixed access point. 
   At step  209 , the session initiation request is forwarded from the first gateway  250  to the second gateway  270  comprising the assigned fixed access point  271 . An Internet Protocol tunnel may be established for this purpose between the first gateway  250  and the second gateway  270 . In case of GPRS, e.g. GPRS Tunneling Protocol (GTP) may be used for establishing the tunnel, whereas in case of WLAN, e.g. Internet Key Exchange mobility extensions (MOBIKE) may be utilized for this purpose. At step  210 , the requested session is initiated at the second gateway  270 . Having initiated the requested session, a session initiation response is sent, step  211 , first from the second gateway  270  to the first gateway  250 , and then onwards from the first gateway  250  to the serving gateway  230 , step  212 . If the Internet Protocol tunnel was established between the first gateway  250  and the second gateway  270  for step  209 , the established tunnel may be used also for step  211 . In case of GPRS, the session initiation response may be e.g. a ‘Create PDP Context Response’ message. The serving gateway  230  may also inform the terminal device  220  about the assignment of the fixed access point  271 , step  213 . Thereafter, data traffic associated with the initiated session will be routed via the assigned fixed access point  271 , steps  214 - 215 . 
     FIG. 3  illustrates an embodiment of the system of the present invention relating to providing a fixed access point for a terminal device. 
   The system disclosed in  FIG. 3  comprises a terminal device  340 , a packet data network  300  and a GPRS mobile access system  310  as well as a WLAN mobile access system  320 . The system disclosed in  FIG. 3  further comprises two gateway network nodes  350  and  360 . The first gateway network node  350  comprises a first GPRS access point  353  and a first WLAN access point  352 . The second gateway network node  360  comprises a second GPRS access point  363  and a second WLAN access point  362 . The GPRS access points  353  and  363  are arranged to interface the GPRS mobile access system  310  with the packet data network  300 , whereas the WLAN access points  352  and  362  are arranged to interface the WLAN mobile access system  320  with the packet data network  300 . The first gateway network node  350  further comprises a first home agent  351 . The second gateway network node  360  further comprises a second home agent  361 . The system disclosed in  FIG. 3  further comprises a database  370  and a domain name server  380 . 
   In accordance with the present invention, the first gateway network node  350  further comprises a first fixed access point assigner  354  arranged to assign one of the access points  352 ,  353 ,  362 ,  363  to serve as a fixed access point for the terminal device  340  based on a received identifier of the terminal device  340 . The first gateway network node  350  further comprises a first notification transmitter  355  arranged to transmit to at least one of the terminal device  340  and a gateway node (not illustrated in FIG.  3 ) serving the terminal device  340  a notification about the assignment of the fixed access point. 
   Correspondingly, the second gateway network node  360  further comprises a second fixed access point assigner  364  arranged to assign one of the access points  352 ,  353 ,  362 ,  363  to serve as a fixed access point for the terminal device  340  based on a received identifier of the terminal device  340 . The second gateway network node  360  further comprises a second notification transmitter  365  arranged to transmit to at least one of the terminal device  340  and a gateway node (not illustrated in  FIG. 3 ) serving the terminal device  340  a notification about the assignment of the fixed access point. 
   In an embodiment, at least one of the first fixed access point assigner  354  and the second fixed access point assigner  364  is further arranged to assign such an access point to serve as the fixed access point which is comprised in a network node arranged to quarantine infected terminal devices, in response to the identifier of the terminal device received in a message about the terminal device being infected. In an embodiment, at least one of the first fixed access point assigner  354  and the second fixed access point assigner  364  is further arranged to assign one of the access points to serve as the fixed access point in response to the identifier of the terminal device  340  received in a request by the terminal device  340  to access the packet data network  300  via one of the mobile access systems  310  and  320 . 
   In the embodiment of the present invention illustrated in  FIG. 3 , the domain name server  380  is arranged to assign one of the access points  352 ,  353 ,  362 ,  363  to serve as an arbitrary access point for the terminal device  340 . 
   Further in the embodiment of the present invention illustrated in  FIG. 3 , at least one of the first fixed access point assigner  354  and the second fixed access point assigner  364  is further arranged to bind the identifier of the terminal device  340  to an address of one of the access points  352 ,  353 ,  362 ,  363 . The identifier of the terminal device  340  may be bound to e.g. an address of an access point comprised in a network node which comprises a home agent associated with the terminal device  340 . For example, if the first home agent  351  is associated with the terminal device  340  and the terminal device  340  is requesting GPRS access, the address of the first GPRS access point  353  may be bound to the identifier of the terminal device  340 . Correspondingly, if the second home agent  361  is associated with the terminal device  340  and the terminal device  340  is requesting WLAN access, the address of the second WLAN access point  362  may be bound to the identifier of the terminal device  340 . The binding may stored in data base  370 . 
   Further in the embodiment of the present invention illustrated in  FIG. 3 , the GPRS mobile access system  310  comprises a gateway node  311  serving the terminal device  340 . The serving gateway node  311  comprises a notification receiver  312  arranged to receive the notification about the assignment of one of the access points to serve as the fixed access point for the terminal device  340 . The serving gateway node  311  further comprises a forwarder  313  arranged to forward data traffic from the terminal device  340  to the fixed access point in response to the received notification. 
   Further in the embodiment of the present invention illustrated in  FIG. 3 , the terminal device  340  comprises a notification receiver  341  arranged to receive the notification about the assignment of one of the access points to serve as the fixed access point for the terminal device  340 . The terminal device  340  further comprises a transmitter  342  arranged to transmit data traffic from the terminal device  340  to the fixed access point in response to the received notification. 
   It should be noted that even though  FIG. 3  describes both the notification receiver  312  disposed in the serving gateway node  311  and the notification receiver  341  disposed in the terminal device  340 , both of them may not be needed. Typically, if an embodiment utilizes a serving gateway, then this serving gateway will comprise a notification receiver in which case another notification receiver disposed in a terminal device will not be needed. Correspondingly, even though  FIG. 3  describes both the forwarder  313  disposed in the serving gateway node  311  and the transmitter  342  disposed in the terminal device  340 , both of them may not be needed. Typically, if an embodiment utilizes a serving gateway, then this serving gateway will comprise a forwarder in which case a transmitter disposed in a terminal device will not be needed. 
   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.