Abstract:
A method of providing access of a mobile terminal to an IP network includes establishing a security association between the mobile terminal and a first security gateway of a first router in said plurality of routers. The mobile terminal is provided access to the IP network via the first router, and the data exchanged between the mobile terminal and the first router is encapsulated by using the security association. The security association is made available to at least one second router having a second security gateway. The mobile terminal is provided access to the IP network via said the second router, and data exchanged between the mobile terminal and the second router is encapsulated by using the same security association. Establishing the security association includes assigning a Security Parameter Index that identifies univocally the first security gateway and the security association. Making the security association available to the second router includes making available to the second router the Security Parameter Index. The second router may thus have access to the security association either by requesting it from the first router or by identifying it in a set of security associations sent from the first router to a set of routers candidate to become the second router as result of the mobility of the mobile terminal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. National Phase Application under 35 U.S.C. §371 of International Application No. PCT/EP2008/003495, filed Apr. 30, 2008, which was published Under PCT Article 21(2), the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This disclosure relates to techniques for providing access in communication networks. Specifically, this disclosure relates to managing the mobility of data/voice communication terminals, with a view to providing integrated F/M (Fixed/Mobile) access to an Internet Protocol (IP) based network. Reference to this possible field of application is not however to be construed in a limiting sense of the scope of this disclosure. 
     DESCRIPTION OF THE RELATED ART 
     The problem of transferring communications from/to a mobile terminal from an access point/network to another has been already tackled in the past, and a number of solutions have been provided. 
     For instance, MIP (Mobile IP), as specified in IETF RFC3344 (see Perkins, C., “IP Mobility Support for IPv4”, IETF RFC-3344, August 2002) allows an IP terminal to move from an IP access sub-network to another, without solutions of continuity (i.e. without breaks or interruptions). 
     These solutions maintain activity of the IP access session as initially established, even when the terminal is no longer in the area of coverage of the home access router, by rerouting the traffic to the home node. 
     Document U.S. Pat. No. 7,028,183 describes a technique to support secure communication based on the IPSec protocol in a clustered or distributed architecture, i.e. a network architecture including a plurality of edge routers that process the Encapsulating Security Payload (ESP) and/or the Authentication Header (AH) of a Internet Protocol Security (IPSec) tunnel on behalf of a multiplicity of end nodes. This document also describes certain procedures for distributing Security Association (SA) parameters negotiated by the end node and installing them on a plurality of edge routers. In that way the end node may move in a seamless way through the net by maintaining secure communication, that is by maintaining the SA as originally established. This document also mentions the case of a wireless access network, where additional procedures can be used for propagating, upon request, the SA information among the edge routers, thus allowing seamless roaming of the end nodes. 
     Document US2002/0165990 A1 discloses an arrangement wherein mobility is related to functional entities such as “home agent” and “foreign agent” entities, i.e. a mechanism of the Mobile IP type. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The applicant has noted that, despite certain advantages, the arrangements described in the foregoing inevitably suffer from some basic drawbacks. 
     For instance, they may imply the necessity of rerouting the traffic to the node Home, and/or require a new installation phase of an IPSec session to effect a handover between different access routers. 
     Also, they may require the execution and the exchange of protocol messages among various edge routers and/or may always require reference to a centralized repository (associated to the cryptographic node that manages the initial set-up of the Security Association). 
     Additionally, in an actual Internet environment, it may be necessary for the terminal to change its IP address, which would result in the TCP/UDP (Transport Control Protocol/User Datagram Protocol) sessions previously established being dropped: this will happen because the sessions are identified (also) via the IP addresses of the end-points of communication. 
     The object of the invention is thus to provide an improved arrangement which, may be exempt from those drawbacks. 
     According to the present invention, that object is achieved by means of a method having the features set forth in the claims that follow. The invention also relates to a corresponding network as well as a related computer program product, loadable in the memory of at least one computer and including software code portions for performing the steps of the method of the invention when the product is run on a computer. As used herein, reference to such a computer program product is intended to be equivalent to reference to a computer-readable medium containing instructions for controlling a computer system to coordinate the performance of the method of the invention. Reference to “at least one computer” is evidently intended to highlight the possibility for the present invention to be implemented in a distributed/modular fashion. 
     The claims are an integral part of the disclosure of the invention provided herein. 
     An embodiment of this disclosure is a network node, hereinafter referred to as an Integrated Access Router (IAR); such a node includes functional elements for controlling the access to an IP network and routing the data and voice traffic of mobile and fixed terminals. 
     In an embodiment, terminal mobility may be managed without solutions of continuity (i.e. any break) as the mobile terminal moves between different access points (APs), such as e.g. unlicensed radio technology APs (Bluetooth, WiFi 802.11, WiMAX) or 2G/3G radio technology APs (GERAN/UTRAN). IP-based voice calls or data communications may thus be transferred from a network to another in a manner which is fully transparent (seamless) to the user. 
     In an embodiment, the architecture of the IAR node may include an element with the role of Security Gateway (SGW); the standard functionalities for managing the IPSec protocol associated with that element may be implemented by resorting to arrangements which permit to maintain active, without interrupting the on-going session(s) of a terminal as the terminal moves from an access area to another, i.e. from an IAR access node to another. 
     In an embodiment, the arrangement disclosed herein is capable of managing the context related to a secure access session to the IP network as established by the mobile terminals. 
     In an embodiment, the arrangement disclosed herein is capable of managing in a seamless and substantially transparent way the transfer of a secure access connection to the IAR node as the terminal from an access node to another. A related re-configuration procedure may be largely independent of the underlying radio technology and may not require any change to the standard terminals. 
     In an embodiment, the arrangement disclosed herein is capable of notionally maintaining a steadily active access connection of a terminal to the same Security Gateway and an initial IAR node. 
     In an embodiment, the arrangement disclosed herein may be integrated with standard techniques for supporting mobility at the network layer. 
     In an embodiment, a tunneling mechanism based on the ESP IPSec protocol may be used to provide the access connection of the terminal to the IP network, so that access node termination may not necessarily take place on a given node (Home node, as in the case of conventional solutions such as e.g. Mobile IP, 2G/3G, etc.), but rather take advantage of a Security Gateway function distributed over the IAR access nodes of the provider. 
     In an embodiment, the tunnel encapsulation mechanism may lead to assigning an innermost address which kept fixed, irrespective of any changes in the access sub-network, thus playing the role of identifying the terminal in the sessions which are kept active during the terminal mobility. This makes it possible to avoid having to re-establish a new ESP IPSec session as the access node changes by moving also the session context, which is completely transparent to the mobile terminal. 
     In an embodiment, the arrangement disclosed herein based on the use of the ESP IPSec protocol may be integrated with a mechanism of managing IP mobility and secure network access based on routing techniques and particularly on the dynamic announcement of the host-specific prefixes assigned to the terminals by the access nodes visited thereby (these host-specific prefixes are currently referred to as “/32” prefixes in the Ipv4 protocol). 
     Various embodiments of the arrangement disclosed herein are adapted for managing network layer mobility in a scenario of fixed/mobile integration. This may apply in particular to the management of the mobility within a same administrative net domain (intra-domain), possibly involving the adoption of dynamic announcement of the host-specific prefixes (e.g. “/32” prefixes, IPv4) assigned to the terminals, in conjunction with the Security Association (SA) IPSec context being made available in a seamless manner to a plurality of access routers. 
     This disclosure foresees the possible use of certain procedures to manage in a simple and efficient way those operations involved in making the context available in a seamless manner to a plurality of edge routers. In an embodiment, this involves a mechanism of creating a structure and assigning an SPI identifier for the Security Association; the router will thus be able to immediately determine, by analysing a field in that identifier, the edge router (e.g. home IAR node) from which the context may be made available. 
     The disclosure herein provides a general integrated (fixed/mobile) access technique to an IP network which is adapted for use with a variety of possible access configurations and technologies. 
    
    
     
       BRIEF DESCRIPTION OF THE ANNEXED DRAWINGS 
       The invention will now be described, by way of example only, with reference to the enclosed figures of drawing, wherein: 
         FIG. 1  shows a typical multi-access network scenario; 
         FIGS. 2   a  to  2   c  show possible communication links; and 
         FIG. 3  shows an IPSec data packet. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following description, numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
     As mentioned in the foregoing, the arrangements disclosed herein are particularly suitable for a multi-access network scenario, such as shown in  FIG. 1 . 
     A multi-access network may include both mobile and fixed networks, such as e.g. Wireless Fidelity (WiFi), Worldwide Interoperability for Microwave Access (WiMAX), or 2G/3G networks, and Local Area Networks (LAN) connected over a Digital Subscriber Line (DSL) to the Internet. By way of example,  FIG. 1  shows a scenario comprising WiFi, WiMAX and 2G/3G networks with their associated access networks, which have access a common IP network, such as the Internet. 
     In the network architecture as considered herein, not only horizontal handoffs—such as a transfer of the communication of a mobile terminal MS 1  from an WiFi access point AP to another—but also handoffs between different networks—such as a transfer of the communication of a mobile terminal MS 2  from a WiMAX access point to 2G/3G access point (i.e. base station or Node B)—may occur. Moreover, such handoffs may involve a single operator (i.e. handover) or also different operators (i.e. roaming). 
     According to this disclosure, an ESP IPSec tunnel may be established to a Security Gateway (SGW), which may form part of an Integrated Access Router (IAR). Such IPSec tunnel may provide a homogeneous access model independent from the underlying network technologies, which may be completely different. Specifically, the IP connection over the local IAR/SGW node is maintained or re-established automatically during the movement of the mobile terminal and the procedure is completely transparent to the user/mobile terminal. 
     Those skilled in the art will appreciate that such an IPSec tunnel has also the advantage that communication over “vulnerable” radio technologies (e.g. WiFi) is protected against possible intrusion and/or interceptions. 
     Various embodiments as described herein have the ability to maintain end-to-end communication sessions during the movement of the terminal, even in the case of a movement between access nets with different IAR/SGW nodes. In this case mobility is usually designate as macro-mobility or network layer mobility. 
     In an embodiment, network layer mobility is supported through a management of the advertisement (announcement) mechanism of the terminal address. 
     For example a dynamic IP address pool may be defined and IP addresses may be assigned, which are “persistent” to a change of the routing area. In this case, if a terminal is not found in the area of coverage of the home access router, the specific addresses assigned to the mobile terminal are announced with the IP intra-domain routing protocols. Therefore, such addresses are “persistent” even though the address are assigned dynamically from the address pool, which is managed by the Home access node, because they are announced by the node that is currently responsible for the IP access of the terminal. 
     In an embodiment, this is achieved by announcing the host-specific (e.g. “/32”) prefix of the mobile terminal (i.e. the sub-net containing only the IP address of the mobile terminal) by the responsible access node, i.e. the visited access node when the terminal is not found in the Home access area. 
     The number of host-specific prefixes which have to be announced explicitly in the intra-domain routing protocol are typically less than a few thousands. This number may even be reduced by suitable network optimizations such as intervening in opportune way on the aggregation of addresses, the dimension of the IAR nodes and the access areas. 
     In an embodiment, the mechanism above is used in conjunction with the Mobile IP (MIP) protocol, which permits also a management of mobility on a network layer. 
       FIGS. 2   a  to  2   c  illustrate some examples of an IPSec tunnel set up with different access technologies. 
     Specifically,  FIG. 2   a  shows how an IPSec tunnel  60  may be established with a typical WiFi/WiMAX access network. 
     In such a network, the mobile terminal establishes a connection to an access point AP. The access point AP forwards then the traffic through a suitable access network AN to an Integrated Access Router (IAR), which e.g. allows in turn access to a public IP network. 
     Those skilled in the art will appreciate that the access network may be any communication network, such as e.g. Ethernet or fibre optics, including also wireless networks. Moreover, especially in the case of WiFi/WiMAX access points, the IAR may even be included in the AP, without requiring an extra access network. 
     In the exemplary embodiment shown, the IAR comprises hardware or software modules (Security Gateway) responsible for the establishment and management of a Security Association with the mobile terminal MS via the IPSec protocol. 
     Such a Security Gateway SGW may be implemented on the IAR node through one or more specialized modules, which manage the traffic of the IPSec tunnels. Such modules may be integrated in the IAR by means of one or more router interfaces mounted in expansion slots typically available in an IAR. In this case traffic coming from the line interfaces of the router and destined to the SGW unit(s) may be routed internally by the IAR node, exploiting the internal switching fabric. Additionally, such hardware modules may be controlled by one or more software or hardware components on the IAR node. 
     In an embodiment, the Security Gateway SGW may be implemented on the IAR node as an additional software module. This implementation may be suitable if performance requirements for the elaboration of the IPSec protocol are not particularly elevated. 
     Those skilled in the art will appreciate that also mixed software/hardware implementation may be used. For example, additional software components may be required if the additional hardware modules or the IAR node (e.g. the network processor or the forwarding engine) are only able to elaborate the IPSec protocol in native way. Such SGW modules and the IPSec procedures are well known in the art, rendering a more detailed description herein unnecessary. 
     Preferably, the ESP protocol of the IPSec suite may be used, as this allows modifying the origin address in the external header of the tunnel without invalidating the session. Moreover, ESP may be used in the tunnel mode, which allows complete encapsulation of IP application packets of the mobile terminal. 
     In order to access the IAR node, and more specifically the Security Gateway SGW, an IP connection is established, and consequently an IP address, designated in the following as IP L , is assigned to the mobile terminal. Such an IP address may be fixed or dynamically assigned to ensure enough connectivity to contact the IP address of the SGW. For that purpose the IP address IP L  may also be only a local IP address, which per se has no connectivity to the public IP network. 
     In the example shown in  FIG. 2   a , the IP address IP L  is assigned directly by the AP, which supports layer 3 functions. 
     Subsequently, the mobile terminal is able to contact the IP address associated to the SGW and establish the IPSec Tunnel  60 . 
       FIG. 2   b  shows an analogous configuration at the example of a possible 2G/3G communication link, wherein the AP represents the base-station and the traffic of the mobile terminal passes typically through a Gateway GPRS Serving/Support Node (GGSN). In this case the IP address IP L  may be assigned by the GGSN node. 
       FIG. 2   c  shows a further example, wherein both the AP and the GGSN support only layer 2 functions. In such a case the IP address IP L  may be assigned by the IAR node. For this purpose a Point-to-Point Protocol (PPP) session may be established, such as a PPP link between the mobile terminal and the IAR node. 
     In the above examples, the IP address is assigned dynamically and, consequently, a movement of the mobile terminal to another access point may cause a re-assignment of a new IP address IP L . 
     Those skilled in the art will appreciate that any communication link and access network may be used in order to establish a data connection between the mobile terminal and the SGW node. Moreover, any IP assignment mechanism may be used in the case of an IP connection between the mobile terminal and the SGW node. 
     Subsequent to the assignment of the IP address IP L , the mobile station MS contacts the Security Gateway (SGW) and starts the usual procedures for establishing an ESP IPSec tunnel  60 . During such operation the mobile station MS may receive also a second IP address IP MS , which has access to the public IP network. 
     According to this disclosure, the IP address IP MS  will remain unchanged even after a possible handoff resulting e.g. from a movement of the mobile station. Therefore, the IP address IP MS  may be used to identity the mobile terminal on a network layer. 
     At the end of the IPSec tunnel setup process, the SGW memorizes the information related to the IPSec session in a database, designated Security Association Database (SAD) and Security Policy Database (SPD). The elements of the aforesaid database related to the IPSec session may be identified through a Security Parameter Index (SPI) assigned to the same session. According to the IPSec protocol, the parameter SPI is comprised of a 32-bit field assigned in arbitrary way by the SGW node. 
     In the exemplary embodiments described in the following, the SA (i.e. the IPSec tunnel) is maintained active (always-on) in a way which is substantially transparent to the mobile terminal, even if the IAR node (and the associated SGW) may change. This means that the SGW nodes which are distributed in the network behave as a single “virtual” Security Gateway. 
     This is achieved by associating to the different SGW, according to a routing principle commonly known as “anycast”, the same IP address IP Any     —     SGW . 
     According to this disclosure the network operator may manage the SA associated to the mobile terminal in an appropriate manner in order to avoid that the mobile terminal has to re-establish the IPSec tunnel. For example, the SA may be transferred to or reproduced (i.e. duplicated) on the new SGW: this operation may be performed on request or in a predictive manner. 
     The following is a description of an exemplary way of making SA available to a new SGW by transfer or replication. 
     As explained in the foregoing, the mobile station MS may receive two IP addresses (IP L  and IP MS ) and establish a SA with the SGW associated to the Home IAR node. In such case the IP packets sent by the mobile station MS to a generic destination having the IP address IP DEST  will have IP MS  and IP DEST  as the source address and the destination address, respectively. According to the ESP IPSec protocol the packet will be encapsulated having IP L  and IP Any     —     SGW , respectively, in the external header. 
       FIG. 3  shows in that respect an exemplary encapsulation scheme for the packets transmitted on the ESP IPSec Tunnel between the MS and the SGW. 
     Specifically, such an encapsulation scheme might be used to transmit a data packet comprising an IP header  30  having as source address IP MS  and as destination address IP DEST , and the payload  40 . This data packet is then encapsulated by encrypting the payload  40  and encapsulating the data packet in a new IP packet. This is achieved by adding an external IP header  10  having as source address IP L  and as destination address IP Any     —     SGW , and the mentioned Security Parameter Index SPI which forms part of the ESP IPSec Header  20 . In the example shown, the SPI value has a dedicated field for the security gateway identification “SGW ID” and a dedicated field for the security association identification “SA ID”. According to the IPSec specification such an encapsulated data packet might also have an EPS trailer  50 . 
     If the mobile station MS moves now to a new AP, the mobile station may receive a new IP address IP L , designated in the following IP L     —     NEW . However, this IP address is only used for the communication over the IPSec tunnel and not for the communication with the public IP network. 
     In the simplest case, the IAR node, which receives the traffic from the MS over the new AP is again the Home IAR node. Consequently the packets are received and processed by the same SGW that has initially established the SA. 
     Conversely, if the terminal has moved to an AP served by a different IAR node, designated in the following IAR VISITED , the traffic transmitted by the MS will be received by a different SGW having the same IP address IP Any     —     SGW . This procedure is completely transparent to mobile station MS. 
     The new SGW begins therefore to receive packets coming from the mobile terminal connected to the new IAR node. As mentioned in the foregoing, the IPSec communication will contain again the SPI field as pointer to the SA database. 
     In order to maintain the pre-existing IPSec session the parameters of the related SA are communicated (i.e. made available) to the new SGW VISITED . 
     For this purpose, the new SGW VISITED  may request a transfer or replication of the SA from the SGW Home . Alternatively, the new SGW VISITED  may already contain a copy of the SA that has been replicated previously on candidate SGW due to a predictive strategy. 
     In an embodiment, this mechanism is optimized by assigning suitable SPI values, which identify the SA. 
     According to the IPSec protocol, the SPI value is assigned in an arbitrary way and is of local validity only. Nevertheless, the SPI values may be selected in a suitable way, which may identify univocally the SA established by different terminals with the SGWs of the network. This can be achieved by assigning SPI values which have global validity at least within the same network domain. For example, the 32 bits of the SPI string may be structured in order to contain a dedicated space for identifying the SGW Home  node (i.e. the node which has assigned the SA to the mobile terminal). 
     According to this criterion, other SGW nodes are therefore able to determine if the SPI belongs to their own identification spaces. If the SPI has been assigned by the same SGW node (i.e. the SGW HOME  node), the value is used to seek the relative SA in the database containing the “local” SA. Conversely, if the SGW determines that the SPI has been assigned by another node, the SGW node searches the SA in the database related to terminals connected to the net as “Visited”. If this search fails, the SGW establishes that the terminal is implicitly starting a handover and requests, through opportune procedures, the SA for the session related to the MS from the SGW HOME  node, which can be identified by the SPI value. 
     In an embodiment, the SGW node may memorize also the IP address IP MS  assigned to the terminal. The IP address IP MS  may then also be sent to the new SGW VISITED  during the transfer or replication of the SA. 
     In an embodiment, the SGW VISITED  node determines the IP address IP MS  directly from the encapsulated data packet received from the mobile terminal. In this case the SGW VISITED  node uses the transferred or replicated SA to decode the encapsulated data packets, which contains in the IP header  30  also the IP address IP MS  of the mobile terminal. 
     Once the necessary information has been inserted in the database, the SGW VISITED , knowing the IP address representing the network identity of the mobile terminal, is able to forward correctly the traffic to the MS. 
     In an embodiment, the IAR node announces this IP address as a host-specific (e.g. “/32”) prefix, namely the subnet containing only the IP address IP MS  with the intra-domain routing protocol in order to guarantee the correct routing of the traffic from the network toward the MS. This allows also the on-going application sessions to be maintained by re-directing the traffic to MS through the IAR VISITED  node rather than through the IAR HOME  node. 
     In fact, the announcement of the host-specific prefix may be effected only starting from the IAR VISITED  node, while for the node IAR HOME  it is typically sufficient to announce only the sub-net of the IP pool from which the IP address IP MS  has been assigned. Those skilled in the art will appreciate that usually explicit host-specific routes prevail over any sub-net routes (i.e. rule of the longest prefix matching). 
     Accordingly, when the mobile terminal moves from an IAR VISITED  to another IAR VISITED , the first IAR node will eliminate the announcement of the host-specific prefix of MS, while a new announcement will be started by the second node. For this purpose, the new IAR node may notify (e.g. when the SA context is activated on the SGW of the new IAR) a handover of the mobile terminal to the preceding IAR node. 
     In order to identify the address of the preceding IAR node such information is stored in the context of the MS managed by the IAR HOME  node. For this purpose, every IAR Visited  node, which establishes communication with a mobile terminal, will communicate such information to the IAR HOME  node. 
     Instead of using the announcement of a host-specific (e.g. “/32”) prefix, an embodiment may foresee the usage of the Mobile IP protocol in order to manage mobility. In this case, the IAR VISITED  node performs the role of a “Foreign Agent” and the IAR HOME  node the role of “Home Agent” as specified in the MIP architecture. 
     In an embodiment, the two techniques may be used in combination. For example, the host-specific prefix announcing mechanism is used by default and the MIP technique is used if the number of host-specific prefixes announced exceeds a predetermined threshold. 
     As mentioned previously, an embodiment may use a “predictive” strategy. In this case, the information of active contexts, or rather the SA and related additional information (e.g. the related IP address IP MS  if stored in the database) are replicated and installed in advance in the database of the SGW serving adjacent routing areas. Such nodes are in fact possible candidates for a handover operation from the current IAR node. 
     The candidate IAR nodes may e.g. be derived from network planning information, which are usually available to the IAR or SGW nodes, which are therefore able to replicate in a proactive manner the context and related information. 
     In an embodiment, the candidate IAR/SGW nodes that receive a replica of the information of the context, are those nodes which serve radio access areas in “contiguity” of the area currently visited by the mobile terminal. A “contiguity” existing between two areas means that their radio coverage areas overlaps partially or entirely (for instance in the case of a WiFi hot-spot inside a 2G/3G radio cells). 
     Using a predictive strategy guarantees at the moment of a handover that the mobile terminal MS will already find on the new node the necessary information for managing correctly the related traffic. 
     In an embodiment, the new IAR/SGW node will then inform the old IAR/SGW node that context information may be deleted. For example, the old IAR/SGW node may inform the previous candidate nodes (i.e. those having received previously replicates of the context information) to delete the replicas/duplicates. The new IAR/SGW node will then identify new candidate nodes and transmit a replica of the context to them. 
     Disconnection of a mobile terminal from the network may occur explicitly or implicitly. 
     In the former case, the mobile station MS will notify the SGW with a “Context Release” message. The node SGW receiving such message will cancel the partnership context to such terminal and, if the node does not coincide with the IAR HOME  node, it may notify in turn the IAR HOME  node that it can remove also the original context. 
     Implicit disconnection may occur e.g. when no activity takes place for a mobile terminal over a predetermined period of time. In this case, the node IAR VISITED  may remove the mobile station&#39;s context, also notifying the IAR HOME  node for a cancellation of the original context. For example this may occur when a timer responsive to user&#39;s traffic or “Keepalive” packets, expires. 
     A periodic exchange of “Keepalive” packets between the terminal and the net (e.g. the anycast address IP Any     —     SGW ) may be preferable in order to maintain the sessions with mobile terminals active. This allows the mobile terminal to remain connected even in the absence of traffic, or to activate the routing and SA context when a “silent” terminal moves to a new IAR node. 
     In the latter case, the presence of Keepalive traffic in the IPSec tunnel will allow the terminal to hook to the new SGW, which activates the associated SA context in order to guarantee a correct delivery of IP packets from the network to the mobile station. 
     Conversely, lack of receipt of a certain number of consecutive Keepalive packets from a mobile terminal may cause an interruption of the connection and a cancellation of the relative contexts. 
     In the following some exemplary procedures are described for the management of the sessions of the mobile terminals in the case of “persistent” IP addresses (i.e. using a “/32” prefix announcing mechanism). 
     Activation of a Secure Context for an Access to the Network of the Provider 
     The mobile station MS (not yet connected to the network) connect to an access node AP with layer 3 functions and, after being authenticated, receives a valid IP address IP L , which may also be a private IP address according to RFC1918. 
     The MS connects to the any cast address IP Any     —     SGW  of the Security Gateway SGW of the operator. Such connection is terminated on the SGW of the “nearest” IAR node (e.g. based on the internal network routing protocol). Such IAR node assumes the role of the IAR HOME  node for MS. 
     The MS is registered on SGW HOME  node, and the MS and the SGW HOME  node activate a Security Association SA through the IPSec protocol and create the ESP IPSec tunnel. Subsequently, the SGW HOME  node assigns the IP address IP MS  to the mobile terminal from an IP pool, which is announced in the intra-domain routing protocol of the operator. Additionally, the SGW HOME  node assigns a 32-bit Security Parameter Index SPI, which holds in a first field a number identifying the SGW HOME  node and in a second field a number that identifies in univocal way the SA. 
     The MS is now able to activate a session on the IP network, wherein the application traffic is encapsulated in the IPSec tunnel with the SGS having the IP address IP Any     —     SGW  (see e.g.  FIG. 3 ). In turn, the IAR HOME  node will verify the correctness of the SA in the Security Database and route the traffic to the IP address IP MS  of the mobile terminal over the ESP tunnel ESP. Moreover, the MS and the SGW HOME  node exchange periodically Keepalive packets in the same tunnel. 
     Handover from IAR HOME  to IAR VISITED    
     When the MS moves away from the routing area of the IAR HOME  node to a routing area of a different IAR node, the MS connects to a new AP and, after being re-authenticated, receives a new valid IP address IP L     —     NEW . 
     The MS transmits the application traffic or Keepalive packets with the new address IP L     —     NEW  through the SA to the IP address IP Any     —     SGW . Such traffic will be routed by the access network toward the SGW of the IAR VISITED  node, which is responsible for the routing area to which the MS has moved. 
     When the SGW VISITED  node receives the packets from MS, it identifies such terminal through the SPI field, and requests the secure SA context from the IAR HOME  node. Alternatively the IAR VISITED  node may already have such context if a proactive replication of the contexts has been activated. 
     The IAR VISITED  node registers its identity as the node responsible for the communication of the MS, and stores its address as additional information for the session context at the IAR HOME  node. Alternatively, the IAR HOME  node may record such address at the moment of a request of the SA information from the IAR VISITED  node. 
     At this moment the IAR VISITED  node has the SA context information available and is able to forward the traffic to the destination network. 
     The IAR VISITED  node announces also the IP address IP MS  of the MS as “/32” (i.e. host-specific) prefix in the intra-domain routing protocols of the network in order to allow correct routing of the traffic from the network toward the mobile terminal. 
     Handover from IAR VISITED     —     Old  to IAR VISITED     —     New    
     The MS may move from the routing area of an IAR VISITED  node, denoted in the following IAR VISITED     —     Old , to a routing area of a new IAR VISITED  node, designated in the following as IAR VISITED     —     New . In this case, the MS connects to a new AP and, after being re-authenticated, receives a new IP address IP L     —     NEW . 
     With the new IP address IP L     —     NEW , the MS transmits its application traffic or Keepalive packets through the SA to the IP address IP Any     —     SGW . Such traffic will reach the SGW (i.e. SGW VISITED     —     New ) of the IAR VISITED     —     New  node. 
     When the SGW VISITED     —     New  node receives the packets from MS, it identifies the terminal through the SPI field, and requests the secure SA context from the IAR HOME  node. Alternatively the IAR VISITED  node may already have such context if a proactive replication of the contexts has been activated. In any case, the SGW VISITED     —     New  node receives also the identity of the IAR VISITED     —     Old  node which was responsible for the MS. 
     The IAR VISITED     —     New  node registers its identity in the context of the MS at the IAR HOME  node or the update is performed directly by the IAR HOME  node at the moment of a request from the IAR VISITED  node. 
     The IAR VISITED     —     New  node has the SA context information available and is able to forward the traffic to the destination network. 
     The IAR VISITED     —     New  node notifies the IAR VISITED     —     Old  node that it is now responsible for the MS and that it has to deactivate the announcement of the “/32” prefix of the MS and that it may delete the SA context information. 
     The IAR VISITED     —     NEW  node announces also the IP address IP MS  of the MS as host-specific “/32” prefix in the intra-domain routing protocols of the network in order to allow correct routing of the traffic from the network toward the mobile terminal. 
     Handover from IAR VISITED  to IAR HOME    
     The MS may move again in the routing area of the IAR HOME  node. In this case, the MS connects to a new AP and, after being re-authenticated, receives a new IP address IP L     —     NEW . 
     The MS transmits its application traffic or Keepalive packets now with the new IP address IP L     —     NEW  through the SA to the IP address IP Any     —     SGW . Such traffic will reach the SGW (i.e. SGW HOME ) of the IAR HOME  node. 
     When the SGW HOME  node receives the packets from MS, it identifies the terminal through the SPI field, recognizes its own role as IAR HOME  node and activates the secure SA context present in its database. 
     Moreover, the IAR HOME  node notifies the preceding IAR VISITED  node that it has to deactivate the announcement of the host-specific prefix of the MS and that it may delete the SA context information. Additionally, the IAR HOME  node may also cancel the information on the identity of the IAR VISITED  node in the context of MS in its database. 
     Finally, the IAR HOME  node is again able to forward the respective traffic to the MS. 
     Handover within a Same Routing Area 
     If a MS moves and connects to a new AP that belongs to the same routing area (i.e. the same IAR node), it may receive, after being re-authenticated, a new IP address IP L     —     NEW . 
     The MS now transmits its application traffic or Keepalive packets with the new IP address IP L     —     NEW  through the SA to the IP address IP Any     —     SGW . Such traffic will still reach the same IAR node, which controls the routing area in which the MS moves. 
     When the SGW HOME  node receives the packets from MS, it identifies the terminal through the SPI field, and recognizes that is already has the secure SA context present in its database. 
     The IAR node is therefore able to continue to forward the respective traffic to the MS. 
     Explicit Deactivation of the Secure Access Context 
     The MS sends of “Context Release” message to the IAR node to which it is currently connected. 
     The IAR node receives this message and cancels the SA context of the MS in its database. In case the IAR node is not the IAR HOME  home node, it will deactivate the announcement of the host-specific prefix and notify the deactivation also to the IAR HOME  node that will handle in turn the cancellation of the original context. 
     Implicit Deactivation of the Secure Access Context 
     In the absence of consumer traffic or Keepalive packets and at a given Timeout associated with the MS, the IAR node will cancel the SA context of the MS in its database. In case the IAR node is not the IAR HOME  home node, it will deactivate the announcement of the hot-specific prefix and notify the deactivation also to the IAR HOME  node that will handle in turn the cancellation of the original context. 
     Without prejudice to the underlying principles of the invention, the details and the embodiments may vary, even appreciably, with reference to what has been described by way of example only, without departing from the scope of the invention as defined by the annexed claims.