Abstract:
There is provided a method of supporting an interworking between a wireless local area network (WLAN) and a mobile communications network. The interworking is facilitated by an interworking function (IWF) disposed on a WLAN side of the interworking. The method comprises the step of connecting the WLAN to the mobile communications network by employing the IWF as an auxiliary radio network controller for the mobile communications network, in particular, a drift radio network controller (DRNC) in a UMTS network.

Description:
This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/US03/17096, filed May 30, 2003, which was published in accordance with PCT Article 21(2) on Dec. 18, 2003 in English and which claims the benefit of U.S. provisional patent application No. 60/386,638, filed Jun. 6, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to networks and, more particularly, to the utilization of an InterWorking Function (IWF) as a logical Radio Network Controller (RNC) for a hybrid coupling between a Wireless Local Area Network (WLAN) and a mobile communications network. 
     2. Background of the Invention 
     A number of different architectures may be employed in an interworking between a Wireless Local Area Network (WLAN) coverage area and mobile communications network technologies such as Universal Mobile Telecommunications System (UMTS). As is known, WLANs offer much higher access data rates than cellular mobile networks such as UMTS, but provide very limited coverage (typically up to 100 meters from the radio transmitter), while UMTS offers widespread coverage (ranging several hundred kilometers). Interworking may be provided between a WLAN hotspot and a mobile communications network such as UMTS to allow a user to utilize either the WLAN or the mobile communications network, or both, depending on the location of the user. The interworking between the WLAN and the mobile communications network may provide the user with roaming capability as the user moves between, and through, the coverage areas of the WLAN and the mobile communications network in order to efficiently use the capabilities of the access networks. However, it is typically the case that the user and control planes are not separate in such an interworking and, thus, the Quality of Service (QOS) negotiations, mobility, Authentication Authorization and Accounting (AAA) procedures of the UMTS are not re-used, resulting in expensive UMTS radio resources being tied up implementing these functions. 
     Accordingly, it would be desirable and highly advantageous to have a WLAN-UMTS interworking such that aids in separating the user and control planes such that the signaling still goes through the UMTS network but the data uses the WLAN radio resources. Such an interworking would provide the advantage that the QOS negotiations, mobility, AAA procedures of the UMTS are re-used while freeing up expensive UMTS radio resources. 
     SUMMARY OF THE INVENTION 
     The problems stated above, as well as other related problems of the prior art, are solved by the present invention, which is directed to the utilization of an InterWorking Function (IWF) as a logical Radio Network Controller (RNC) for a hybrid coupling between a Wireless Local Area Network (WLAN) and a mobile communications network. 
     According to an illustrative embodiment of the present invention, there is provided a method for supporting an interworking between a Wireless Local Area Network (WLAN) and a mobile communications network. The interworking is facilitated by an InterWorking Function (IWF) disposed on a WLAN side of the mobile communications network. The method comprises the step of connecting the WLAN to the mobile communications network by employing the IWF as a Drift Radio Network Controller (DRNC) for the mobile communications network. 
     According to another aspect of the present invention, there is provided an apparatus for supporting an interworking between a Wireless Local Area Network (WLAN) and a mobile communications network. The interworking is facilitated by an InterWorking Function (IWF) disposed on a WLAN side of the mobile communications network. The apparatus comprises means for connecting the WLAN to the mobile communications network using the IWF as a Drift Radio Network Controller (DRNC) for the mobile communications network. 
     These and other aspects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments, which is to be read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a communication structure  100  to which the present invention may be applied, according to an illustrative embodiment of the present invention; 
         FIG. 2  is a diagram illustrating the steps involved in moving a User Equipment (UE) from a Universal Mobile Telecommunications System (UMTS) to a Wireless Local Area Network (WLAN) data plane, according to an illustrative embodiment of the present invention; 
         FIG. 3  is a diagram illustrating the protocol stack from User Equipment (UE) to a Universal Mobile Telecommunications System (UTMS) Radio Network Controller (RNC) for a user plane, according to an illustrative embodiment of the present invention; and 
         FIG. 4  is a diagram illustrating the protocol stack from a WLAN Access Point (AP)—InterWorking Function (IWF) side to a Universal Mobile Telecommunications System (UTMS) Radio Network Controller (RNC) for the control plane, according to an illustrative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to the utilization of an InterWorking Function (IWF) as a logical Radio Network Controller (RNC) for a hybrid coupling between a Wireless Local Area Network (WLAN) and a mobile communications network. In a preferred embodiment of the present invention, the coupling is between a WLAN and a third generation ( 3 G) Universal Mobile Telecommunications System (UMTS). However, it is to be appreciated that the present invention is not limited to UMTS (with respect to the mobile communications network that is coupled to the WLAN) and, thus, any other type of a mobile communications network may also be employed in a coupling with the WLAN while maintaining the spirit and scope of the present invention. Some of the many types of other mobile communications networks include those employing, e.g., Code Division Multiple Access (CDMA) 2000, General Packet Radio Service (GPRS), and so forth. 
     With respect to the preferred embodiment of the present invention that involves a coupling between a WLAN and a UMTS, the present invention allows the high spectrum cost and low data rates of UMTS to be complemented by the unlicensed band, high data rate but small coverage area of WLANs. The present invention essentially uses the user plane interface to connect the WLAN to the UMTS network over the lur interface and uses the UMTS network to carry the signaling or control plane. 
     It is to be understood that the present invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. Preferably, the present invention is implemented as a combination of hardware and software. Moreover, the software is preferably implemented as an application program tangibly embodied on a program storage device. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU), a random access memory (RAM), and input/output (I/O) interface(s). The computer platform also includes an operating system and microinstruction code. The various processes and functions described herein may either be part of the microinstruction code or part of the application program (or a combination thereof that is executed via the operating system. In addition, various other peripheral devices may be connected to the computer platform such as an additional data storage device and a printing device. 
     It is to be further understood that, because some of the constituent system components and method steps depicted in the accompanying Figures are preferably implemented in software, the actual connections between the system components (or the process steps) may differ depending upon the manner in which the present invention is programmed. Given the teachings herein, one of ordinary skill in the related art will be able to contemplate these and similar implementations or configurations of the present invention. 
       FIG. 1  is a block diagram illustrating a communication structure  100  to which the present invention may be applied, according to an illustrative embodiment of the present invention. A description will now be given with respect to  FIG. 1  of a UMTS-WLAN interworking that employs an InterWorking Function (IWF) as a logical Drift Radio Network Controller (DRNC) for the UMTS, according to an illustrative embodiment of the present invention. The WLAN may be, but is not limited to, a WLAN according to the Institute of Electrical and Electronics Engineers (IEEE) specification 802.11 or to the European Telecommunications Standards Institute (ETSI) High Performance Radio Local Area Network Type 2 (HIPERLAN2). 
     The communication structure includes an InterWorking Function (IWF) as a logical Radio Network Controller (RNC) (and hence reference numeral  105  shall be interchangeably used herein to represent the IWF and the logical RNC, as they are one and the same for the purposes of the present invention), a WLAN Access Point (AP)  110 , a User Equipment (UE)  120 , a UMTS Node B  125 , a UMTS RNC  130 , a Serving General Packet Radio Service (GPRS) Support Node (SGSN)  135 , a Gateway General Packet Radio Service (GPRS) Support Node (GGSN)  140 , the Internet  145 , a Home Location Register (HLR)  150 , a Mobile Switching Center (MSC)  155 , and a Public Switched Telephone Network (PSTN)  160 . 
     UMTS Node B  125  includes a transceiver for communicating with UE  120  via the air interface. UMTS Node B  125  performs various front end functions for providing communications between UE  120  and UMTS RNC  130 . UMTS RNC  130  performs the management of the radio interface and interfaces with SGSN  135 . SGSN  135  provides the interface between UTRAN  165  and the packet switched network, and performs a role similar to that of MSC  155  in the circuit switched portion. SGSN  135  performs mobility management and session management support. Communications structure  100  may comprise a plurality of UTRAN  165  coupled to SGNS  135 . GGSN  140  interconnects the public land mobile network (PLMN) to any other packet data network (PDN), for example, the Internet. GGSN  140  may be viewed as an IP router that performs such functions as address mapping and tunneling. There is generally one GGSN  140  for the PLMN. MSC  155  routes calls in the circuit switched network and is connected to PTSN  160 . HLR  150  is a database that administers the subscriber related data. It contains information such as, the services to which the subscriber is entitled, and the location of the area in which the subscriber is currently registered. The information of a subscriber can be retrieved using either the subscriber&#39;s unique international mobile subscriber identity number (IMSI) or Mobile Station International ISDN number (MSISDN). 
     The UE  120  communicates with a UMTS Terrestrial Radio Access Network (UTRAN)  165 , the latter including the Node B  125  and the RNC  130 . The UTRAN  165 , in turn, is connected to a Core Network (CN)  170  that includes the SGSN  135  (packet based services), the MSC  155  (circuit based services) and the GGSN  140  (gateway to other Public Land Mobile Networks (PLMNs)). The UMTS network may include a plurality of UTRAN  165  coupled to CN  170 . An lu interface connects the UTRAN  165  to the CN  170 . The UMTS network may include a plurality of UTRANs  165  coupled to CN  170 . 
     Inside the UTRAN  165 , RNCs corresponding to radio network subsystems are connected together through an lur interface  175 . The lu and lur interfaces are logical interfaces. The lur interface  175  can be conveyed over a direct physical connection between RNCs ( 105  &amp;  130 ) or virtual networks using any suitable transport network. For each connection between User Equipment (UE)  120  and the UTRAN  165 , one RNC is the Serving RNC (SRNC) responsible for the resources of its set of cells. When required, a Drift RNC (DRNC) supports the SRNC by providing radio resources as shown in  FIG. 2  below. The role of an RNC (Serving or Drift) is on a per connection basis between a UE and the UTRAN  165 . 
     A number of Access Points (APs) (e.g., WLAN AP  110 ) are tied back to the InterWorking Function (IWF)  105  that, in turn, is connected to the UMTS. The interworking function  105  may be embodied within a separate hardware coupled to the access points, or as a portion of the access point, and include various software modules and hardware necessary to implement the desired functions. As shown in  FIG. 1 , according to the present invention, the IWF  105  implements the lur user plane interface between itself  105  and the RNC  130  and acts as a DRNC (drift RNC) for the UMTS network. 
     The coupling employed herein is referred to as “hybrid coupling”, since the tight and loose coupling definitions of the European Telecommunications Standards Institute (ETSI) do not describe the coupling employed by the present invention where the signaling and user planes are split between the UMTS and the WLAN. The splitting of the signaling and user planes aids in keeping the WLAN gateway (i.e., the IWF) simple, as the WLAN gateway only needs to carry the user plane while the complex control plane reuses the UMTS. For Packet Switched (PS) services, the data plane takes the majority of radio resources. By diverting the data part to the WLAN in hotspots, considerable radio resources are conserved and can now be used for other users and other services, while the UE retains the connection with the CN  170 . 
       FIG. 2  is a diagram illustrating the steps involved in moving a User Equipment (UE) from a Universal Mobile Telecommunications System (UMTS) to a Wireless Local Area Network (WLAN) data plane, according to an illustrative embodiment of the present invention. The steps depicted in  FIG. 2  correspond to signaling between a UE, a UMTS Serving Radio Network Controller (SRNC), and a WLAN InterWorking Function (IWF) employed as a Drift RNC (DRNC). In the example of  FIG. 2  as well as the following examples, the UE, SRNC, and WLAN IWF shall hereinafter be respectively represented by UE  120 , RNC  130 , and IWF  105  shown in  FIG. 1 . 
     Upon identifying a UE  120  that is attached to a node B that, in turn, is close to a WLAN coverage area, the UTRAN  165  requests that the UE  120  obtain a performance measure (e.g., Bit Error Rate (BER)) on the WLAN and to forward a measurement report corresponding to the performance measure to the UTRAN  165  (step  205 ). Accordingly, the performance measure on the WLAN is obtained by the UE  120 , and the measurement report is forwarded from the UE  120  to the UTRAN  165  (step  207 ). If the performance measure is greater than a pre-determined threshold, then the SRNC  130  can utilize the WLAN IWF  105  as a DRNC as illustrated in  FIG. 1  and in steps  215  through  245  that follow. The UE  120  will process this new radio (WLAN) link but remain camped to the cell that belongs to the SRNC  130 . 
     If a radio link is to be set up in a node-B (not shown) that is controlled by an RNC (not shown) other than the SRNC  130 , then a request to establish the radio link is sent from the SRNC  130  to the DRNC (i.e., the IWF)  105  (step  215 ). That is, the SRNC  130  requests that the DRNC (IWF)  105  establish a Radio Link through a RADIO-LINK SETUP request. The request is made using an RNSAP message. The RNSAP message includes QoS parameters and the type of Dedicated/Common Transport Channel to be used. 
     According to the QoS parameters, the requested service may be assigned a type of service by the IWF  105  based on a mapping between UMTS QoS classes and WLAN QoS parameters (if the WLAN supports QoS), as well as a WLAN physical layer and Media Access Control (MAC) layer parameters (step  220 ). 
     Typically, Call Admission Control (CAC) is always performed in the SRNC  130 . However, if an lur (hereinafter lur  175  depicted in  FIG. 1 ) is to be used (as in this example), then CAC is performed within the DRNC, i.e., the IWF  105  (step  225 ), as well as resource allocation being performed within the DRNC, i.e., the IWF  105  (step  228 ). The CAC may be performed and resources allocated by the IWF  105  according to pre-established criteria (which may be static and/or dynamic). The criteria may include, but is not limited to, the following: type of service assigned by the IWF  105  and the type of Dedicated/Common Transport Channel requested by the SRNC  130 ; WLAN resources available in the AP  110  to which the UE  120  shall attach. Moreover, allocation and pre-emption of Radio Links in the IWF  105  when a RADIO LINK SETUP request comes from the SRNC can follow procedures that use an allocation/retention priority QoS attribute. 
     Acknowledgement is sent back to the SRNC  130  according to the result of the CAC (step  230 ). The acknowledgement is sent using an RNSAP message. Layer 1 (L1) and the MAC layer are configured accordingly in the WLAN AP  110  (step  235 ). 
     The SRNC  130  establishes the transport bearer over the lur  175  (using, e.g., Access Link Control Application Protocol (ALCAP)) (step  240 ). The SRNC  130  then sends an ACTIVE SET UPDATE message to the UE  120  in order to signal a new active radio link having designated data and control paths (step  245 ). The data path is UE  120  &lt;-&gt;IWF  105  &lt;-&gt;RNC &lt;-&gt;SGSN  135  &lt;-&gt;GGSN  140  and the control path is UE  120  &lt;-&gt;Node B  125  &lt;-&gt;RNC  130  &lt;-&gt;SGSN  135  &lt;-&gt;GGSN  140  (as in UMTS) as illustrated in  FIG. 1 . The UMTS data bearers, if in existence, shall be released when no more data activity is seen on the UMTS data channels (step  250 ). 
       FIG. 3  is a diagram illustrating the protocol stack from User Equipment (UE) to a Universal Mobile Telecommunications System (UTMS) Radio Network Controller (RNC) for a user plane, according to an illustrative embodiment of the present invention. 
     A UE protocol stack  31 - 0  includes a Wideband Code Division Multiple Access (WCDMA) layer portion  310   a , a WLAN Physical (PHY) layer portion  310   b , a MAC layer portion  310   c , a Radio Link Control (RLC) layer portion  310   d , a Packet Data Convergence Protocol (PDCP) layer portion  310   e , a WLAN MAC/Logical Link Controller (LLC) layer portion  310   f , an Internet Protocol (IP) layer  310   g , a Transmission Control Protocol (TCP)/User Datagram Protocol (UDP) layer  310   h , and an applications layer  310   i.    
     An IWF (employed herein as a DRNC) protocol stack  320  includes a WLAN PHY layer portion  320   a , an ATM layer portion  320   b , an Asynchronous Transfer Mode Adaptation Layer 2 (AAL2) portion  320   c , a UDP/IP layer portion  320   d , a MAC layer portion  320   e , an RLC layer portion  320   f , a PDCP layer portion  320   g , and a WLAN MAC/LLC layer portion  320   h.    
     An RNC protocol stack  330  includes an ATM layer portion  330   a , an AAL2 portion  330   b , a UDP/IP layer portion  330   c , a Layer 1 portion  330   d , a Layer 2 portion  330   e , a MAC layer portion  330   f , an IP layer portion  330   g , an RLC layer portion  330   h , a UDP layer portion  330   i , a General Packet Radio Service Tunneling Protocol User (GTP-U) portion  330   j , and a PDCP portion  330   k.    
       FIG. 4  is a diagram illustrating the protocol stack from a WLAN Access Point (AP)—InterWorking Function (IWF) side to a Universal Mobile Telecommunications System (UTMS) Radio Network Controller (RNC) for the control plane, according to an illustrative embodiment of the present invention. In the illustrative embodiment of  FIG. 4 , the IWF communicates with the UMTS over a lur interface as a logical Drift Radio Network Controller (DRNC). 
     An AP-IWF (logical RNC) protocol stack  410  includes a WLAN PHY layer portion  410   a , an ATM layer portion  410   b , an Asynchronous Transfer Mode Adaptation Layer 5 (AAL5) portion  410   c , a UDP/IP layer portion  410   d , a WLAN MAC/LLC layer portion  410   e , a Simple Transmission Control Protocol (SCTP) layer portion  410   f , an MTP3 User Adaptation Layer (M3UA) portion  4109 , a Signaling Connection Control Part (SCCP) layer portion  410   h , an IP layer portion  410   i , a Radio Network Subsystem Application Part (RNSAP) layer portion  410   j , a Transmission Control Protocol layer  410   k , and a signaling applications layer  410   l.    
     An RNC protocol stack  420  includes a first ATM layer portion  420   a , a second ATM layer portion  420   b , a first AAL5 portion  420   c , a second AAL5 portion  420   d , a first UDP/IP layer portion  420   e , a second UDP/IP layer portion  420   f , a first SCTP layer portion  420   g , a second SCTP layer portion  420   h , a first M3UA layer portion  420   i , a second M3UA layer portion  420   j , a first SCCP layer portion  420   k , a second SCCP layer portion  420   l , a first RNSAP layer portion  420   m , and a second RNSAP layer portion  420   n.    
     A description will now be given of some of the many advantages of the present invention. One such advantage is that the QOS negotiations, mobility, addressing and AAA procedures of the UMTS are re-used; this helps keep the WLAN gateway (IWF) simple, as the IWF only carries the user plane while the complex control plane reuses the UMTS system. For PS services, the data plane consumes the majority of radio resources. Thus, by diverting the data part to the WLAN in hotspots, considerable expensive UMTS radio resources can be saved and/or used for other users and/or other services while the UE retains the connection with the CN. Another advantage is that the present invention allows all the cellular operators to share the WLAN in hot spots as long as the lur interface is available with each operator. Yet another advantage is that the UMTS operator can use existing WLAN deployment instead of deploying his own WLANs in hotspots. Still another advantage is that the UMTS operator provides one point of attachment (GGSN) to give access to both the UMTS and the WLAN networks. A further advantage of the present invention is scalability, as an RNC can be attached to up to seven DRNCs. Moreover, another advantage of the present invention is that no modifications to the existing UMTS network nodes are required for interworking. 
     Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.