Patent Publication Number: US-2006002351-A1

Title: IP address assignment in a telecommunications network using the protocol for carrying authentication for network access (PANA)

Description:
PRIORITY STATEMENT UNDER 35 U.S.C. S.119(e) &amp; 37 C.F.R. S.1.78  
      This non-provisional patent application claims priority based upon the prior U.S. provisional patent application entitled “QSA: PPP Free Operation”, application No. 60/584,160, filed Jul. 01, 2004, in the name of Lila MADOUR. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method and system for assigning an IP address to a Mobile Node (MN).  
      2. Description of the Related Art  
      CDMA2000, also known as IMT-CDMA Multi-Carrier or IS-95, is a Code-Division Multiple Access (CDMA) version of the IMT-2000 standard developed by the International Telecommunication Union (ITU). The CDMA2000 standard is a third-generation (3G) mobile wireless technology allowing mobile nodes (e.g. mobile stations, wireless PDAs, etc) to access IP-based high-speed voice and data traffic over the CDMA-based cellular network. CDMA2000 can support mobile data communications at speeds ranging from 144 Kbps to 2 Mbps.  
      In order to fully recognize the advantages of the present invention, a short description of some technical concepts associated with CDMA2000 IP-based cellular telecommunications networks is required. A typical CDMA2000 network comprises a number of nodes including a plurality of Mobile Nodes (MNs), a plurality of Base Stations (BSs), one or more Packet Control Functions (PCFs) and one or more Packet Data Serving Nodes (PDSNs), or their equivalent. The BSs may be connected to the PCF, which is an entity in the CDMA2000 Radio Access Network (RAN) that controls the transmission of data packets between the BSs and the PDSN. The PCF is in turn connected with the PDSN.  
      In a CDMA2000 network, the PDSN provides access to the Internet, intranets and applications servers for MNs utilizing the CDMA2000 RAN. Acting as an access gateway, the PDSN provides simple IP and mobile IP access, Foreign Agent (FA) support, and packet transport for virtual private networking. It may also act as a client for an Authorization, Authentication, and Accounting server (AAA) and provides the MNs with a gateway to the IP network.  
      The AAA server of a CDMA2000 network intelligently controls access to network resources, enforces policies, audits the usage, and provides the information necessary to bill for the services accessed by the MNs. These combined processes are essential for effective network management and security.  
      In CDMA2000 networks, the Point-to-Point Protocol (PPP) is used for setting up data session between the MNs and the serving PDSN. PPP is a protocol for communication between two nodes using a serial interface. PPP uses the Internet Protocol (IP) and thus it is sometimes considered a member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection (OSI) reference model, PPP provides layer 2 (data-link layer) service. Essentially, it packages a computer&#39;s TCP/IP packets and forwards them to a server where they can actually be put on the Internet. The use of PPP in CDMA2000 networks is defined in the Internet Engineering Task Force (IETF) Request for Comments (RFC) 1661, which is herein included by reference in its entirety, as a link layer protocol between the MN and the PDSN for the establishment of packet data sessions. In CDMA2000 networks, four types of packet data sessions may be established using PPP: Simple IPv4, Mobile IPv4, Simple IPv6 and Mobile IPv6, on which work in still in progress.  
      Recently, the 3G Partnership Project 2 (3GPP2) has accepted a work item that proposes elimination of PPP from the CDMA2000 packet data system and its replacement with an IP level signaling for at least the following motivations:  
      PPP is a very old technology mainly designed for wire-line dial-up services and 3GPP2 is considering upgrading to a better-suited protocol;  
      High-Level Data Link Control (HDLC) like framing is a processor intensive task: according to a study made by Qualcomm Inc. for broadcast multicast service, HDLC-like framing is 62 times more computational intensive compared to packet based framing, which has been adopted as an option to support broadcast/multicast service in 3GPP2. The MN and the PDSN utilize a processor intensive procedure whereby they parse received data on an octet-by-octet basis for HDLC flags to determine higher layer packet boundaries. This operation could be rather performed at a hardware level. However, this requires the platform hardware to support HDLC, which is not the case with current PDSNs; and  
      PPP is based on peer-to-peer negotiation, which may cause high call setup delay times. According to a recent benchmark, the average PPP call setup time is about 2.5 seconds, which is inappropriate for most applications used in CDMA2000 networks.  
      However, there is no other existing IETF-based protocol that provides all the capabilities of PPP, i.e. link layer negotiation, header compression negotiation, IP address configuration, packet data session termination, and link layer echo test. Other protocols have recently been identified as IP access based protocols that may represent an alternative to PPP, but each one lacks one or more of the capabilities of PPP.  
      Recently, the IETF has considered using the Protocol for Carrying Authentication for Network Access (PANA) as one of these possible replacements for PPP for setting up data sessions in CDMA2000 networks. PANA involves two entities, a PANA Authentication Client (PAC) in the MN and a PANA Authentication Agent (PAA) in the PDSN, or connected thereto. An Enforcement point (EP) is just an Access Router that provides per packet enforcement policies applied on the inbound and outbound traffic of the MN, although in some case the EP may be implemented in the PDSN itself. PANA, as defined today in the IETF draft, is limited to carry Extensible Authentication Protocol (EAP) authentication between the PAC and the AAA through the PAA. Any EAP method can be transported, including the methods that allow bootstrapping for other protocols in the access network for encryption and data integrity, if so required by the operator.  
      It is known that in most cases access networks require some form of authentication in order to prevent unauthorized usage. In the absence of physical security (and sometimes in addition to it), a higher layer (L2+) access authentication mechanism is needed. Depending on the deployment scenarios, a number of features are expected from the authentication mechanism. For example, support for various authentication methods (e.g., MD5, TLS, SIM, etc.), network roaming, network service provider discovery and selection, separate authentication for access (L1+L2) service provider and Internet Service Provider (ISP, L3), etc. In the absence of a link-layer authentication mechanism that can satisfy these needs, operators are forced to either use non-standard ad-hoc solutions at layers above the link, insert additional shim layers for authentication, or misuse some of the existing protocols in ways that were not intended by design. PANA is proposed to be developed to fill this gap by defining a standard network-layer access authentication protocol. As a network-layer access authentication protocol, PANA can be used over any link-layer that supports IP.  
      PPP-based authentication could provide some of the required functionality. But using PPP only for authentication is not a good choice, as it incurs additional messaging during the connection setup and extra per-packet processing, and it forces the network topology to a point-to-point model. There is now an interest in the CDMA2000 community to remove PPP from some of the existing architectures and deployments.  
      The goal of PANA is to define a protocol that allows clients, such as MNs of a CDMA2000 network, to authenticate themselves to the access network using IP protocols. Such a protocol would allow a client to interact with a AAA infrastructure to gain access without needing to understand the particular AAA infrastructure protocols that are in use at the site. It would also allow such interactions to take place without a link-layer specific mechanism. PANA would be applicable to both multi-access and point-to-point links. It would provide support for various authentication methods, dynamic service provider selection, and roaming clients. Mobile IPv4 developed its own protocols for performing PANA-like functions (e.g., MN-Foreign Agent (FA) interaction). Mobile IPv6 does not have the equivalent of an FA that would allow the access/visited network to authenticate the MN before allowing access. The PAA can perform the authentication function attributed to the FA in Mobile IPv4, in Mobile IPv6 networks. Work is currently being performed with PANA with the assumption that a PAC is already configured with an IP address before using PANA. This IP address will provide limited reachability to the PAC until it is authenticated with the PAA. Upon successful authentication, the PAC is granted broader network access possibly by either a new IP address assignment, or by enforcement points changing filtering rules for the same IP address.  
      Conclusively, PANA is being developed into an IP-based protocol that allows a device to authenticate itself with the network (and to a PAA in particular) in order to be granted network access. In order to better understand the use of PANA, a short explanation of the PANA usual terminology may be appropriate:  
      PANA Session:  
      A PANA session begins with the initial handshake between the PANA Client (PaC) and the PANA Authentication Agent (PAA), and terminates by an authentication failure, a timeout, or an explicit termination message. A fixed session identifier is maintained throughout a session. A session cannot be shared across multiple physical network interfaces. A distinct PANA session is associated with the device identifiers of PAC and PAA.  
      Session Identifier:  
      This identifier is used to uniquely identify a PANA session on the PAA and PAC. It includes an identifier of the PAA, therefore it cannot be shared across multiple PAAs. It is included in PANA messages to bind the message to a specific PANA session. This bi-directional identifier is allocated by the PAA following the initial handshake and freed when the session terminates.  
      PANA Security Association:  
      A PANA security association is a relationship between the PAC and PAA, formed by the sharing of cryptographic keying material and associated context. Security associations are duplex. That is, one security association is needed to protect the bi-directional traffic between the PAC and the PAA.  
      PANA Client (PAC):  
      The client side of the protocol that resides in the host device, which is responsible for providing the credentials to prove its identity for network, access authorization.  
      Device Identifier (DI):  
      The identifier used by the network as a handle to control and police the network access of a client. Depending on the access technology, this identifier might contain any of IP address, link-layer address, switch port number, etc of a connected device.  
      PANA Authentication Agent (PAA):  
      The protocol entity in the access network side whose responsibility is to verify the credentials provided by a PANA client and grant network access service to the device associated with the client and identified by a DI. Note the authentication and authorization procedure can, according to the EAP model, be also offloaded to the backend AAA infrastructure.  
      Enforcement Point (EP):  
      A node on the access network where per-packet enforcement policies (i.e., filters) are applied on the inbound and outbound traffic of client devices. Information such as the DI and (optionally) cryptographic keys are provided by the PAA per client for constructing filters on the EP.  
      Network Access Provider (NAP):  
      A service provider that provides physical and link-layer connectivity to an access network it manages.  
      AAA-Key:  
      A key derived by the EAP peer and EAP server and transported to the authenticator.  
      In its current form, PANA lacks capabilities for insuring a proper alternative to PPP for the setup of data session in CDMA2000 networks. For example, PANA does not define mechanisms and functions currently provided by PPP, such as IP address configuration, security, and header compression mechanisms. Consequently, PANA as defined in IETF today is not sufficient, and additional capabilities, are required to convert it from just a transport mechanism for EAP packets into a suitable IP access protocol.  
      Although the industry is resolved to get rid of PPP for MN IP address allocation, and use a PANA-based solution instead, no optimized PANA signalling has been proposed so far. At best, a current PANA proposal has been described, wherein the MN acquires and IP address using DHCP (Dynamic Host Configuration Protocol) subsequent and on top of the initial PANA session setup, which adds to the session setup delays. Conclusively, so far no actual call scenarios have been proposed for the optimally using PANA as a means for authenticating a CDMA2000 terminal and assigning an IP address to that terminal.  
      Accordingly, it should be readily appreciated that in order to overcome the deficiencies and shortcomings of the existing solutions, it would be advantageous to have a method and system for efficiently providing and IP address to a CDMA2000 mobile terminal. The present invention provides such a method and system.  
     SUMMARY OF THE INVENTION  
      In one aspect, the present invention is a method for assigning an IP address to a Mobile Node (MN) in a telecommunications network, the method comprising the steps of:  
      receiving at a packet data switching node a first Protocol for Carrying Authentication for Network Access (PANA) message from the MN, the PANA message comprising an indication that the MN is requesting an IP address;  
      responsive to the first PANA message, sending from the packet data switching node to the MN a second PANA message comprising an IP address for the MN.  
      In another aspect, the present invention is a packet data switching node for assigning an IP address to a Mobile Node (MN) in a telecommunications network, the packet data switching node comprising:  
      a Protocol for Carrying Authentication for Network Access (PANA) Authentication Agent (PAA) module receiving a first PANA message from the MN, the PANA message comprising an indication that the MN is requesting an IP address;  
      wherein responsive to the first PANA message, the PAA sends to the MN a second PANA message comprising an IP address for the MN. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more detailed understanding of the invention, for further objects and advantages thereof, reference can now be made to the following description, taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is an exemplary nodal operation and signal flow diagram representing a CDMA2000 telecommunications network implementing the preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The innovative teachings of the present invention will be described with particular reference to various exemplary embodiments. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses of the innovative teachings of the invention. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed aspects of the present invention. Moreover, some statements may apply to some inventive features but not to others. In the drawings, like or similar elements are designated with identical reference numerals throughout the several views.  
      In order to alleviate the use of Point-to-Point Protocol (PPP) in Code Division Multiple Access 2000 (CDMA2000) networks, the present invention proposes to replace PPP by an IP based protocol for packet data access and Mobile Node (MN) configuration. More precisely, the invention relies on using the Protocol for Carrying Authentication for Network Access (PANA), with added enhancements and functionalities, in order to assign an IP address to an MN that registers with the CDMA2000 network.  
      To use PANA, a PANA client (PAC) in the MN and a PANA Authentication Agent (PAA) in the serving Packet Data Serving Node (PDSN) are typically required. According to the invention, the PAC and the PAA first establish a PANA session, where the MN is authenticated and authorized. Currently PANA does not support the assignment of an IP address to a requesting MN since, at the present moment, IETF suggests using the Dynamic Host Configuration Protocol (DHCP) for the MN&#39;s configuration. However, using DHCP creates heavy signaling on the network&#39;s resources, which induces delays in the establishment of an IP data session.  
      As opposed to the prior art, the current invention is directed at defining a method for providing an IP address to the MN though the use of PANA. For this purpose, a request for such an IP address has to be sent from the MN to the PDSN. Currently, PANA does not support such functionality. To alleviate this problem, the current invention proposes to include an indication that an IP address is requested into a PANA Start-Answer message sent from the MN to the serving PDSN. Such an indication may comprise, for example, an IP address with a blank value set to 0.0.0.0. Upon receipt of the message with the indication, the PDSN recognizes the blank IP address received from the MN as a request for a new IP address, and responsive thereto, authenticates the MN. If the authentication is successful, the PDSN further assigns an IP address from its pool of IP addresses to the requesting MN. The assigned IP address is then returned to the MN in a PANA Bind-Request message.  
      Reference is now made to  FIG. 1 , which is an exemplary nodal operation and signal flow diagram representing a CDMA2000 telecommunications network  100  implementing the preferred embodiment of the present invention. Shown in  FIG. 1 , is first a CDMA2000 MN  102  that implements a PAC module  103 , which is provided CDMA2000 radio coverage by a Base Station (BS, not shown for simplicity purposes), which is further connected to a CDMA2000 serving PDSN  106  that comprises a PAA module  107  and an Enforcement Point (EP) module  109 . Finally, the PDSN  107  is connected to an Authentication, Authorization, and Accounting (AAA) server  108  responsible for the authentication and authorization of the MNs served by the PDSN  106 .  
      According to the invention, the process starts in action  120  where a PANA discovery method is performed in order to discover a PAA for use by the MN  102 . The discovery phase  120  may be performed using a PANA multicast PAA Discovery message sent from the PAA  107  of the PDSN  106  to the PAC  103  of the MN  102 , or alternatively using a link layer indication that a new PAC is connected.  
      Once the discovery phase  120  is completed, the PAA  107  of the PDSN  106  sends to the PAC  103  of the MN  102  a PANA Start Request message  140  with parameters to indicate the beginning of the authentication phase and it includes a sequence number used to track the PANA messages that are exchanged. Responsive to the message  140 , the PAC  103  of the MN  102  responds with a PANA Start Answer message  144  comprising an indication  145  that the MN  102  requests the assignment of an IP address from the PDSN  106 . For example, the indication  145  may comprise a blank (NIL) IP address which value is composed of zeros (e.g. 0.0.0.0). The PDSN  106  receives the message  144  with the indication  145  requesting a new IP address and responsive thereto, before assigning the new IP address, starts an authentication  147  for the MN. Such authentication  147  may take various forms, as preferred by the operator of the network  100 . For example, the PDSN  106  may use an EAP-based (Extensible Authentication Protocol) authentication method that enables key exchange to allow other protocols to be bootstrapped for securing the data traffic between the PDSN  106  and the MN  102  when CDMA2000 link layer encryption is not used. EAP-AKA (Authentication Key Agreement Protocol) could be used to generate a master session key, which is then sent to the PDSN in the case where the EP (Enforcement Point) is implemented within the PDSN, like in the present example.  
      The exemplary authentication  147  of the MN  102  with the network  100  may comprise first, a PDSN request message  148  for the user identity of the MN terminal  102 , that may comprise a PANA Auth-Request message, which includes parameters  150  indicative of the requested MN identity. The PAC  103  of the MN  102  responds to message  150  with a PANA Auth-Answer message  152  comprising the terminal identity  153  (e.g., the terminal Network Access Identifier (NAI) of the MN  102 ). Upon receipt of the MN&#39;s identity in message  152 , the PDSN  106  sends to the MA server  108  a RADIUS Access-Request message  156  containing an EAP packet  150  with the MN&#39;s identity  153 . The home AAA server  108  receives the message  156 , decides that EAP-AKA authentication is suitable based on the user profile associated with the MN&#39;s identity  153 , and generates a random value RAND  159  and AUTN value  161  based on a Shared Secret Key (SSK) MN-AAA, which is part of the user profile stored in the AAA  108 , and also based on a sequence number, also stored in the AAA, and which is used for AKA authentication vector generation, action  158 . The AAA server  108  sends back to the PDSN  106  a RADIUS Access-Challenge message  160  that comprises EAP-AKA Challenge information  162 , i.e. the RAND  159 , the AUTN  161 , and a MAC attribute  163  to protect the integrity of the EAP message. The RADIUS message  160  is received by the PDSN  106 , which extracts the EAP-AKA challenge information  162  from the RADIUS message, and sends it further to the MN  102  in a PANA Auth-Request message  164 .  
      The MN  102  verifies the AUTN  161  and the AT_MAC attribute  163 , action  166 , and if the verification is successful, it generates a response RES attribute  169  that is sent to the PDSN  106  via a PANA Auth-Answer message  168 . The purpose of the RES attribute  169  is to allow the home AAA server  108  to authenticate the peer, since the MAC attribute  169  protects the integrity of the EAP packet. The PDSN  106  receives the message  168  and forwards this response (i.e. the AKA Challenge information  170  with the RES attribute  169 ) via a RADIUS Access-Request message  172  to the AAA server  108 .  
      The home AAA  108  checks the AKA challenge information  170  received in message  172 . If the authentication is successful, the AAA server  108  sends a RADIUS Access-Accept message  176  transporting an EAP-Success parameter  178 , which informs the PDSN  106  that the MN  102  is successfully authenticated. The AAA server  108  also generates a Pairwise Master Key (PMK)  179  by using, for example, the first 32 bytes of a master key generated based on the user identity, CK (Cipher Key) and IK (integrity Key), which are session keys generated for the session using the SSK (Shared Secret Key). The AAA  108  sends the PMK parameter  179  to the PDSN  106  in the same message  176 . Upon receipt of message  176 , the PDSN  106  stores the PMK  179  and uses it to generate an IKE pre-shared key for subsequent IKE exchange.  
      The PDSN  106 , which is informed in message  176  of the successful authentication of the MN  102 , now assigns (selects) an IP address  181  for the MN  102 , action  177 , which may comprise the selection of an available IP address from the PDSN&#39;s pool of available IP addresses. The PDSN  106  then sends a PANA Bind request message  180  comprising i) the indication  178  informing the MN  102  of the successful authentication, and ii) the IP address  181  that is assigned to the MN  102 .  
      In action  182 , the MN  102  also generates the PMK upon receiving the EAP-Success message  180  and the IKE pre-shared key, and also installs the assigned IP address  181 .  
      Following successful authentication  147 , the PDSN  106  and the MN  102  each has a PMK, which they use to generate the IKE pre-shared key using, for example, the following algorithm: 
          IKE Pre-shared Key=HMAC-SHA-1 (PMK, “IKE-preshared key”|Session ID|Key-ID|EP-address).        

      Session ID: The value as defined in the PANA protocol and identifies a particular session of a client.  
      Key-ID: This identifies the PMK within a given PANA session. During the lifetime of the PANA session, there could be multiple EAP re-authentications. As EAP re-authentication changes the PMK, key-ID is used to identify the right PMK.  
      EP address: This is the IP address of the EP (assumed to be collocated with the PDSN) with which IKE key exchange is being performed.  
      IKE (v1 or v2) is then exchanged and IPsec SAs are established between the MS and the EP (PDSN).  
      Finally, in action  184 , the MN  102  answers to the PDSN  106  with a PANA Bind Answer message that informs the PDSN of the success of the authentication, and in action  186  packet data communication may take place between the MN  102  which now has an assigned IP address, and the PDSN  106 .  
      Therefore, with the present invention it becomes possible to optimize the packet data session setup time for the user and acquire an IP address during the PANA session exchange.  
      Based upon the foregoing, it should now be apparent to those of ordinary skills in the art that the present invention provides an advantageous solution, which offers considerable signalling optimization compared to using DHCP for acquiring an IP address after the PANA session establishment is completed. Although the system and method of the present invention have been described in particular reference to CDMA2000, it should be realized upon reference hereto that the innovative teachings contained herein are not necessarily limited thereto and may be implemented advantageously with any other access technology that uses PANA as an access interface It is believed that the operation and construction of the present invention will be apparent from the foregoing description. For example, the invention can also be implemented in General Packet Radio Service or Universal Mobile Telephone Service (GPRS/UMTS) networks, and in such a case, the PDSN  106  shown in  FIG. 1  would be rather a Serving GPRS Support Node (SGSN) or a Gateway GPRS Support Node (GGSN). Such nodes, are designates generically in the following claims as packet data switching nodes. While the method and system shown and described have been characterized as being preferred, it will be readily apparent that various changes and modifications could be made therein without departing from the scope of the invention as defined by the claims set forth hereinbelow.  
      Although several preferred embodiments of the method and system of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.