PRIORITY  
       [0001]     This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 2004-89039 entitled “Method and Apparatus for Transmitting SMS Message Between Mobile Communication Network and WLAN and System Using the Same,” filed in the Korean Intellectual Property Office on Nov. 3, 2004, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention:  
         [0003]     The present invention relates generally to a method and apparatus for providing Short Message Service (SMS) between heterogeneous networks. More particularly, the present invention relates to a method and apparatus for providing SMS in a cellular mobile communication network and an Internet Protocol (IP)-based Wireless Local Area Network (WLAN) which supports SMS, and a system using the same.  
         [0004]     1. Description of the Related Art:  
         [0005]     Conventional Mobile communication networks that provide voice service adopt multiple access schemes to identify users. The multiple access schemes include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). FDMA divides a given spectrum into channels and each user is allocated one frequency channel. TDMA allows a number of users to access a frequency channel by allocating unique time slots to each user within the channel. Unlike FDMA and TDMA, CDMA utilizes the same frequency band for a plurality of subscribers at the same time and a call for each subscriber is uniquely encoded and transmitted across the frequency band.  
         [0006]     The rapid development of communication technology has driven mobile communication networks to provide high-speed data service in addition to traditional voice service. High-speed data service enables multimedia service involving transmission of moving pictures as well as e-mail and still images. So-called 3rd generation mobile communication systems supporting both voice service and packet service include synchronous CDMA 2000  1×, 1×Evolution-Data Only (EVDO) capable of high-speed packet transmission, 1×Evolution-Data and Voice (EV-DV), and asynchronous Universal Mobile Telecommunication System (UMTS).  
         [0007]     Traditionally, voice service is provided over a circuit-switched network, such as the Public Switched Telephone Network (PSTN), and packet service over an IP network.  
         [0008]     While packet data service was originally provided through Personal Computer (PC) or wired networks, it is now available through WLAN, too. Hence, the packet data service can be received with a mobile terminal (MT), such as a cellular phone.  
         [0009]      FIG. 1  illustrates the configurations of a typical cellular mobile communication system and a typical WLAN in parallel.  
         [0010]     Referring to  FIG. 1 , an MT  130  includes a radio transmitter/receiver for providing a radio interface with a Base Transceiver Station (BTS)  100  by a predetermined radio protocol. The BTS  100  allocates radio resources to the MT  130  and receives data from the MT  130 . The MT  130  wirelessly accesses the BTS  100  within the coverage area of the BTS  100  (that is, cell) and transmits/receives voice and data to/from the BTS  100 . As the MT  130  is capable of accessing both a mobile communication network  106  and a WLAN  140 , it is called a Hybrid Access Terminal (HAT).  
         [0011]     One or more BTSs  100  are connected to a Base Station Controller (BSC)  102 . The BSC  102  manages and controls the BTSs  100 . It also takes charge of implementing overall functions associated with radio resource management. One or more BSCs  102  are connected to a Mobile Switching Center (MSC)  104 .  
         [0012]     The MSC  104  provides the functions of circuit switching between subscribers, call setup, call path setup, handoff, and roaming, in addition to those provided by a standard communication switch. The MSC  104  is connected to a PSTN  108 . It is also connected to a Signaling System  7  (SS 7 ) network  110  via a No.  7  interface, and thus connected to an SMS center (SMSC)  112  and a Home Location Register (HLR)  114  through the SS 7  network  110 .  
         [0013]     The SMSC  112  stores/transfers incoming/outgoing SMS messages, connects to a network, and connects to a service provider. The SMSC  112  is an independent node having a unique Signaling Point Code (SPC) in the SS 7  network  110 . The SMSC  112 , connected to the HLR  114  and the MSC  104 , locates a receiving mobile subscriber and transmits an SMS message to the mobile subscriber over a Public Land Mobile Network (PLMN).  
         [0014]     The HLR  114  is a database center for managing information about the status and statistics of mobile subscribers, including the current location information of the HAT  130  and service-related information. The HLR  114  is also connected to the SS 7  network  110 .  
         [0015]     With respect to WLAN  140 , HAT  141  wirelessly communicates with an Access Point (AP)  116  that is compliant with Institute of Electrical and Electronics Engineers (IEEE) 802.16-based Wireless Broadband Internet (WiBro), or IEEE 802.20. The AP  116  is connected to an Access Router (AR)  118  by a Session Initiation Protocol (SIP). As the HAT  141  is connected to the WLAN  140 , and can access the Internet  120  via WLAN  140 , the AR  118  processes all IP packets between the Internet  120  and the HAT  141 .  
         [0016]     Conventional mobile communication systems boast a wide range of services, relative to the WLAN, yet it suffers from low data rate and high price. By contrast, the WLAN delivers a large amount of data at high data rate with low cost to users, compared to the data service provided by the mobile communication system. Thus, the WLAN attracts more and more users. Despite these benefits, however, one of the challenges encountered with setting up a WLAN is limited service range and too narrow a frequency bandwidth to accommodate a large number of subscribers. Moreover, it is difficult to provide high-quality service with the WLAN because of its susceptibility to interference.  
         [0017]     Since the mobile communication network and the WLAN can each overcome the problems of the other, studies are made on interworking between them.  
         [0018]     As described above, the mobile communication network and the WLAN are based on independent standards. While a voice call is transferred between them, the SMS remains yet to be provided between them.  
         [0019]     Accordingly, a need exists for developing a method, apparatus, and system for providing an SMS between heterogeneous networks like the cellular network  106  and WLAN  140  because they work based on different protocols and different connection standards.  
       SUMMARY OF THE INVENTION  
       [0020]     An object of the present invention is to address at least the above problems and disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide a method and apparatus for providing an SMS between heterogeneous networks without a modification to existing systems, and a system using the same.  
         [0021]     Another object of the present invention is to provide a method and apparatus for providing an SMS between an MT in a mobile communication system and an MT in a WLAN, and a system using the same.  
         [0022]     The above exemplary objects are achieved by providing an apparatus and method for providing an SMS between a cellular mobile communication network and a WLAN, and a system using the same.  
         [0023]     According to one aspect of the present invention, in an SMGW for transmitting an SMS message from a transmitting MT connected to a mobile communication network to a receiving MT connected to a WLAN in a communication system, upon request of transmission of an SMS message from the transmitting MT, a first protocol processor signals the ID of the receiving MT. A first interface couples data between the mobile communication network and the first protocol processor. A subscriber information database stores information about the location of the receiving MT connected to the WLAN, the IDs of MTs in the mobile communication network and the WLAN, and IP addresses mapped to the IDs. A second protocol processor converts the IP address of the receiving MT to a URI of the receiving MT. A second interface couples data between the second protocol processor and the WLAN.  
         [0024]     According to another aspect of the present invention, in a method of transmitting an SMS message from a transmitting MT connected to a mobile communication network to a receiving MT connected to a WLAN in an SMGW, upon request of transmission of an SMS message from the transmitting MT, the ID of the receiving MT is signaled and an IP address corresponding to the ID of the receiving MT is detected. The IP address of the receiving MT is converted to a URI.  
         [0025]     According to a another aspect of the present invention, in an SMGW for transmitting an SMS message from a transmitting MT connected to a WLAN to a receiving MT connected to a mobile communication network in a communication system, upon request of transmission of an SMS message from the transmitting MT, a second protocol processor converts a URI of the receiving MT to an IP address of the receiving MT. A second interface couples data between the second protocol processor and the WLAN. A subscriber information database stores an ID of the receiving MT mapped to the IP address of the receiving MT. A first protocol processor signals the ID of the receiving MT. A first interface couples data between the mobile communication network and the first protocol processor.  
         [0026]     According to another aspect of the present invention, in a method of transmitting an SMS message from a transmitting MT connected to a WLAN to a receiving MT connected to a mobile communication network in an SMGW, upon request of transmission of an SMS message from the transmitting MT, a URI of the receiving MT is converted to an IP address of the receiving MT. An ID of the receiving MT mapped to the IP address of the receiving MT is detected and the SMS message is transmitted to the receiving MT according to the ID of the receiving MT.  
         [0027]     According to another aspect of the present invention, in a system for transmitting an SMS message from a transmitting MT connected to a mobile communication network to a receiving MT connected to a WLAN, an SMSC receives an SMS request message from the transmitting MT, asks an HLR about the location of the receiving MT, and transmits an SMS delivery point-to-point message to an SMGW that can transmit an SMS message originating from the transmitting MT to the receiving MT. The HLR receives the SMS request message from the SMSC and transmits the SMS request message to the SMGW according to the location of the receiving MT. The SMGW receives the SMS request message from the HLTR, transmits a response message for the SMS request message to the SMSC, and transmits the SMS message to the receiving MT according to the SMS delivery point-to-point message received from the SMSC.  
         [0028]     According to another aspect of the present invention, in a system for transmitting an SMS message from a transmitting MT connected to a WLAN to a receiving MT connected to a mobile communication network, upon request of transmission of an SMS message from the transmitting MT, an SMGW transmits an SMS delivery point-to-point message to an SMSC that can transmit the SMS message to the receiving MT. The SMSC receives an SMS delivery point-to-point message from the SMGW, asks an HLR about the location of the receiving MT, and transmits the SMS message to the receiving MT when the receiving MT is located.  
         [0029]     According to another aspect of the present invention, in a method of transmitting an SMS message from a transmitting MT connected to a mobile communication network to a receiving MT connected to a WLAN, upon request of transmission of an SMS message from the transmitting MT, an SMSC asks an HLR about the location of the receiving MT. The HLR searches an internal database and transmits an SMS request message to an SMGW that can transmit the SMS message to the receiving MT, if the receiving MT is connected to the WLAN. The SMGW transmits the SMS request message to the SMSC, if the receiving MT is within the coverage area of the SMGW. The SMSC transmits an SMS delivery point-to-point message including an ID of the receiving MT to the SMGW. The SMGW transmits the SMS message to the receiving MT.  
         [0030]     According to another aspect of the present invention, in a method of transmitting an SMS message from a transmitting MT connected to a WLAN to a receiving MT connected to a mobile communication network, upon request of transmission of an SMS message from the transmitting MT, an SMGW transmits an SMS delivery point-to-point message to an SMSC. The SMSC transmits an SMS request message to an HLR to ask about the location of the receiving MT. The HLR detects the location of the receiving MT and transmits the SMS request message to an MSC. The MSC transmits an SMS response message to the HLR. The HLR transmits the SMS response message to the SMSC. The SMSC transmits the SMS message to the receiving MT. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     The above and other exemplary objects, features and advantages of the present invention will become more apparent from the following detailed description of certain exemplary embodiments with reference to the accompanying drawings, in which:  
         [0032]      FIG. 1  illustrates the configurations of existing cellular mobile communication system and WLAN;  
         [0033]      FIG. 2  illustrates a network configuration for providing the SMS between a mobile communication network and a WLAN according to an exemplary embodiment of the present invention;  
         [0034]      FIG. 3  is a block diagram of a Short Message GateWay (SMGW) further provided according to an exemplary embodiment of the present invention;  
         [0035]      FIG. 4  is a diagram illustrating signal flow for registering the location of an MT connected to the WLAN according to an exemplary embodiment of the present invention;  
         [0036]      FIG. 5  is a diagram illustrating signal flow for an operation for transmitting an SMS message from an MT connected to the cellular mobile communication network to an MT connected to the WLAN according to an exemplary embodiment of the present invention;  
         [0037]      FIG. 6  is a diagram illustrating signal flow for an operation for transmitting an SMS message from the MT connected to the WLAN to the MT connected to the cellular mobile communication network according to an exemplary embodiment of the present invention; and  
         [0038]      FIG. 7  is a flowchart illustrating an operation for transmitting a received IP packet from an AR to an AP according to an exemplary embodiment of the present invention. 
     
    
       [0039]     Throughout the drawings, like reference numbers should be understood to refer to like elements, features, and structures.  
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0040]     The matters exemplified in this description are provided to assist in a comprehensive understanding of various exemplary embodiments of the present invention disclosed with reference to the accompanying figures. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the exemplary embodiments described herein can be made without departing from the scope and spirit of the claimed invention. Descriptions of well-known functions and constructions are omitted for clarity and conciseness.  
         [0041]      FIG. 2  illustrates a network configuration for providing the SMS between a mobile communication network and a WLAN according to an exemplary embodiment of the present invention.  
         [0042]     Exemplary aspects of the present invention are based on the premise that the HATs  130  and  141  are single-mode terminals that can access a cellular mobile communication system or a WLAN alone, or dual-mode ones that can access both. The cellular mobile communication system is compliant with the CDMA 2000  1× standards, and the WLAN is compliant with IEEE 802.11-based Wi-Fi, IEEE 802.16-based WiBro, or IEEE 802.20. The mobile communication system and the WLAN already have their protocols. Hereinbelow, the WLAN protocol standards will be represented as IEEE 802.11 or 802.16 and any system conforming to these WLAN protocol standards is called a WLAN system.  
         [0043]     Referring to  FIG. 2 , the HAT  130  capable of selectively accessing the WLAN or the cellular network is connected to the cellular network  106  and thus operates in CDMA 2000  1×. The HAT  141  connected to the WLAN operates according to IEEE  802 . 11  or  802 . 16 . The HAT  130  is connected to the MSC  104  through the BTS  100  and the BSC  102  that form a radio access network in the mobile communication system. The BTS  100  handles radio access protocols regarding the HAT  130  in the cellular network  106 . The MSC  104  interfaces between HATs or between a HAT and the PSTN.  
         [0044]     The MSC  104  is connected to the SMSC  112  and the HLR  114  through the SS 7  network  110 . The SMSC  112  stores and transfers the SMS messages for SMS subscribers. The HLR  114  stores and manages the service profiles and location registration information of users connected to the cellular network. In accordance with an exemplary embodiment of the present invention, an SMGW  214  is further provided, which is connected to the cellular network  106  through the SS 7  network  110  and to the WLAN  140  through the IP network  120 .  
         [0045]      FIG. 3  is a block diagram of the SMGW  214  according to an exemplary embodiment of the present invention. The SMGW  214  has a plurality of function blocks for active communications between the heterogeneous networks.  
         [0046]     Referring to  FIG. 3 , the SMGW  214  includes a subscriber information database (DB)  300  for storing information about SMS subscribers, for example, the Mobile Identity Numbers (MINs) of HATs used in their telephone network and mobile communication network, IP addresses mapped to the MINs, and the locations of HATs connected to the WLAN  140 . In accordance with one exemplary embodiment of the present invention, the cellular network  106  communicates with the SMGW  214  through an Interim Standard (IS)- 41  protocol processor  302  and the IP network  120  communicates with the SMGW  214  through an SIP protocol processor  304 .  
         [0047]     The IS- 41  protocol processor  302  communicates with the MSC  104  or the HLR  114  connected to the SS 7  network  110  through a No.  7  interface  306 . The SIP protocol processor  304  communicates with the AR  118  connected to the IP network  120  through an IP network interface  308 . The IS- 41  protocol processor  302  operates in compliance with protocols preset with the HLR  114  and the MSC  104  to locate the HAT  130  within the cellular network  106  and transmit/receive SMS messages to/from the HAT  130 . The SIP protocol processor  304  handles a protocol preset to receive location registration information from the HAT  141  within the WLAN  140  and transmit/receive SMS messages to/from the HAT  141 .  
         [0048]     In operation, when the HAT  130  transmits an SMS message to the HAT  141 , the IS- 41  protocol processor  302  provides the MIN information of the receiving HAT  141  to the subscriber information DB  300 .  
         [0049]     The subscriber information DB  300  outputs the IP address of the HAT  141  corresponding to the MIN information to the SIP protocol processor  304 . The SIP protocol processor  304  converts the IP address to a Uniform Resource Identifier (URI), the ID of the HAT  141  in the IP network  120 .  
         [0050]     Meanwhile, when the HAT  141  originates an SMS message to the HAT  130 , the SIP protocol processor  304  converts the URI of the HAT  141  received from the IP network  120  to an IP address and outputs the IP address to the subscriber information DB  300 . The subscriber information DB  300  provides the MIN of the HAT  141  corresponding to the IP address to the IS- 41  protocol processor  302 .  
         [0051]     SMS messages can be exchanged between different MTs within the cellular network in the existing SMS procedure. Therefore, a description will be made of exchanging SMS messages between the HAT  141  connected to the WLAN  140  and the HAT  130  connected to the cellular network  106 , or between the HAT  141  connected to the WLAN, and an associated system.  
         [0052]     If the HAT  141  is to receive an SMS message from the cellular network  106 , it must register its location in order to notify the cellular network  106  of the location. The location registration will be described with reference to  FIG. 4 .  
         [0053]      FIG. 4  is a diagram illustrating signal flow for registration of the HAT  2  within the WLAN  140  according to an exemplary embodiment of the present invention.  
         [0054]     Referring to  FIG. 4 , when the HAT  141  moves to the WLAN  140  or is initially power-on within the WLAN  140 , it establishes the SIP to the SMGW  214 . In step  401 , the HAT  141  transmits a REGISTER message to the AP  116  to register its location.  
         [0055]     The AP  116  transmits the REGISTER message to the SMGW  214  through the AR  118  in step  403 . In step  405 , the SMGW  214  stores the IP address and MIN of the HAT  141  included in the REGISTER message in the subscriber information DB  300  and transmits to the HLR  114  a REGISTRATION NOTIFICATION (REGNOT) message notifying the connection of the HAT  141  to the WLAN  140 .  
         [0056]     The HLR  114  recognizes that the HAT  141  has been connected to the WLAN  140  from the received REGNOT message. The HLR  114  then stores the received location information of the HAT  141  and transmits a REGISTRAITON NOTIFICATION RESPONSE (regnot) message to the SMGW  214  in step  407 .  
         [0057]     The SMGW  214  transmits a  200  OK message as a response for the registration request of the HAT  141  to the AP  116  through the AR  118  in step  409 . The AP  116  transmits the  200  OK message to the HAT  141  in step  411 . Thus, the location registration is completed.  
         [0058]     For the HAT  130  within the cellular network  106  to transmit an SMS message to the HAT  141  that has registered its location to the SMGW  214  and the HLR  114  in the above procedure, the following procedure is performed.  
         [0059]      FIG. 5  is a diagram illustrating signal flow for an operation for transmitting an SMS message from the HAT  130  within the cellular network  106  to the HAT  141  within the WLAN  140  according to an exemplary embodiment of the present invention.  
         [0060]     Before describing  FIG. 5 , it is assumed that the HAT  130  works according to IS- 2000 , an extension of the CDMA radio access standard, IS- 95 . The MSC  104  and the SMGW  214  communicate based on IS- 41  and the SMGW  214  and the HAT  141  communicate by the SIP.  
         [0061]     Referring to  FIG. 5 , to transmit an SMS message, the HAT  130  is allocated radio resources, including a Traffic Channel (TCH), by the BSC  102  and the MSC  104  in the cellular network  106  in step  501 . After successful setup of radio resources, the HAT  130  transmits to the MSC  104  an SMS-Mobile Originated (SMS-MO) message including the contents of an SMS message destined for the HAT  141  in step  503 .  
         [0062]     In step  505 , the MSC  104  generates an SMS Delivery Point-to-Point (SMDPP) message including the MINs of the HAT  130  and the HAT  141  and provides the SMDPP message with the contents of the SMS message to the SMSC  112 .  
         [0063]     The SMSC  112  transmits an smdpp message (smdpp[ACK]) as a response message for the SMDPP message to the MSC  104  in step  507 . In step  509 , the MSC  104  transmits an SMS-ACK message for the SMS message originated from the HAT  130  to the HAT  130  through the BSC  102 . Thus, the HAT  130  knows that the SMS message has been successfully transmitted to the SMSC  112 .  
         [0064]     In step  511 , the SMSC  112  transmits an SMSREQ message (SMREQ[MIN]) to the HLR  114  to ask about the location of the SMGW  214  to which the HAT  141  belongs using the MIN of the HAT  141  included in the SMDPP message and thus to locate the HAT  141 .  
         [0065]     The HLR  114  searches for the location information of the HAT  141  using the called number (that is, MIN) of the HAT  141  and transmits the SMSREQ message (SMSREQ[MIN]) to the SMGW  214  using the searched location information in step  513 .  
         [0066]     The SMGW  214  detects the IP address of the HAT  141  using the MIN included in the SMSREQ message and transmits to the HLR  114  an SMS request response message (smsreq[SMSADDR]) as a response message for the SMSREQ message, including an SMS address (SMSADDR) being the routing address of an SMS processing device, required to receive the SMS message from the HAT  130  in step  515 .  
         [0067]     In step  517 , the HLR  114  detects the location information of the SMSC  112  to which the HAT  130  belongs using the SMSADDR and transmits the SMS request response message(smsreq[SMSADDR]) as a response message for the SMSREQ message to the SMSC  112 .  
         [0068]     In step  519 , the SMSC  112  generates an SMDPP message (SMDPP[MIN]) using the SMSADR and transmits the SMDPP message with the SMS message to the SMGW  214 .  
         [0069]     The SMGW  214  detects the IP address of the HAT  141  by searching for the location information of the HAT  141  based on the SMDPP message in step  521 . The SMGW  214  converts the IP address of a URI used in the IP network, equivalent to the MIN of the HAT  141 . Then the SMGW  214  generates a MESSAGE message (MESSAGE[URI, SMS]), including the SMS message and transmits it to the HAT  141  within the WLAN  140  using the URI in step  521 .  
         [0070]     In step  523 , the HAT  141  generates a  200  OK message to the SMGW  214 . Thus, the SMGW  214  transmits an smdpp message (smdpp[ACK]) as a response message for the SMDPP[MIN] message to the SMSC  112  in step  525 , thereby completing the SMS message transmission.  
         [0071]     Now a description will be made of an operation for transmitting an SMS message from the HAT  141  within the WLAN  140  to the HAT  130  within the cellular network  106  with reference to  FIG. 6 .  
         [0072]     Referring to  FIG. 6 , upon request for transmission of an SMS message from the user, the HAT  141  transmits to the SMGW  214  a MESSAGE message (MESSAGE[URI, SMS]), including the MIN of the receiving HAT  130 , the SMS message, and the URI of the transmitting HAT  141  in step  601 .  
         [0073]     The SMGW  214  generates an SMDPP message (SMDPP[MIN]) including the SMS message and the MIN of the HAT  130  and transmits it to the SMSC  112  in step  603 . In step  605 , the SMSC  112  transmits an SMSREQ message (SMSREQ[MIN]) including the MIN of the HAT to the receiving HLR  114  to obtain the MSC  104  to which the HAT  130  belongs to.  
         [0074]     The HLR  114  searches for the location information of the receiving HAT  130  and transmits the SMSREQ message (SMSREQ[MIN]) to the MSC  104  in step  607 .  
         [0075]     In step  609 , the MSC  104  transmits to the HLR  114  an smsreq message (smsreq[SMSADDR]) as a response message for the SMSREQ[MIN] message including the SMSADDR of the HAT  130  required to transmit the SMS message to the HAT  130 . In step  611 , the HLR  114  transmits the received smsreq message including the SMSADDR to the SMSC  112 .  
         [0076]     The SMSC  112  generates an SMDPP message (SMDPP[MIN]) including the MIN of the HAT  130  and the SMS message using the SMSADDR and transmits it to the MSC  104  in step  613 . The MSC  104  then determines whether radio resources have been allocated to the HAT  130 .  
         [0077]     If the radio resources have not been allocated to the HAT  130  yet, the BSC  102  transmits a PAGE message (PAGE(SMS)) to the HAT  130  in step  615 . In step  617 , the HAT  130  returns a PAGE RESPONSE message to the BSC  102 .  
         [0078]     The BSC  102  and the MSC  104  allocate radio resources including a TCH to the HAT  130  in step  619 .  
         [0079]     If the radio resources have already been allocated to the HAT  130 , steps  615 ,  617  and  619  need not be performed.  
         [0080]     In step  621 , the MSC  104  transmits an SMS-Mobile Terminated (SMS-MT) message including the SMS message to the HAT  130  using the allocated radio resources.  
         [0081]     The HAT  130  transmits an SMS-ACK message to the MSC  104  in step  623 , and the MSC  104  transmits an smdpp message (smdpp[ACK]) as a response message for the SMDPP message in step  613  to the SMSC  112  in step  625 .  
         [0082]     The SMSC  112  transmits an smdpp message (smdpp[ACK]) as a response message for the SMDPP message in step  603  to the transmitting SMGW  214  in step  627 . In step  629 , the SMGW 214  transmits a  200  OK message to the HAT  141 , as a response for the SMS request.  
         [0083]     In the case where the AR  118  in the IP network receives an IP packet from an external network such as the cellular network, the AR  118  transmits the IP packet to the AP  116  to which a receiving HAT belongs, in the following procedure.  
         [0084]      FIG. 7  is a flowchart illustrating an operation for transmitting a received IP packet from the AR  118  to the AP  116  according to an exemplary embodiment of the present invention.  
         [0085]     Referring to  FIG. 7 , the AR  118  determines whether an IP packet has been received from an external IP network in step  700 . Upon receipt of an IP packet from the external IP network, the AR  118  analyzes the header of the IP packet in step  702 . The AR  118  reads the Medium Access Control (MAC) address of a receiving HAT from the IP header in step  704 .  
         [0086]     In step  706 , the AR  118  determines whether the receiving HAT is a HAT registered to the AR  118 . If it is not, the AR  118  discards the IP packet in step  714 .  
         [0087]     If the receiving HAT was registered to the AR  118 , the AR  118  detects the AP  116  connected to the receiving HAT in step  708  and detects an AR port connected to the AP  116  in step  710 . The AR  118  then transmits the IP packet to the AR  116  through the AR port in step  712 .  
         [0088]     As described above, certain exemplary embodiments of the present invention enable an SMS service between a cellular mobile communication network and a WLAN and thus provide mobility between the heterogeneous networks to users.  
         [0089]     In addition, since an SMGW is further defined without any modification to the existing network configurations, the number of components to be added to provide the SMS between heterogeneous networks may be minimized and mobile service and WLAN providers can provide the SMS more easily.  
         [0090]     While the present invention has been particularly shown and described with reference to certain exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.
A method and system for providing a short message service (SMS) between a cellular mobile communication network and an IEEE 802.11 WLAN are provided. To provide the SMS between the mobile communication network and the WLAN, a short message gateway (SMGW) is further provided between existing SS 7 network and IP network. A mobile terminal (MT) connected to the cellular network is allocated radio resources by a base transceiver station (BTS). One or more BTSs are connected to a mobile switching center (MSC) through a base station controller (BSC). The MSC is connected to an SMS center (SMSC), a home location register (HLR), and the SMGW through the SS 7 network. An MT connected to the WLAN is wirelessly connected to an access point (AP) and one or more APs are connected to the IP network and the SMGW through an access router (AR).