Developing OSA-based Applications over the Interworking WLAN and Cellular Network Environment

Transcription

1 Developing OSA-based s over the Interworking WLAN and Cellular Network Environment Chung-Ming Huang, Tz-Heng Hsu, and Chih-Wen Chao Laboratory of Multimedia Mobile Networking Department of Computer Science and Information Engineering National Cheng Kung University Taiwan,R.O.C. huangcm@locust.csie.ncku.edu.tw ABSTRACT Open Service Architecture (OSA) is a framework that aims at building various kinds of services on the top of G cellular networks. OSA/Parlay provides APIs for application developers to access the network functions like authentication and authorization of mobile users. OSA/Parlay provides necessary openness and flexibility for application development in the G cellular networks. In this paper, we proposed an OSA-based service platform simulating environment for interworking WLAN and G cellular networks. The main contribution of this paper is to overcome the problems of user mobility in the interworking WLAN and G cellular networks. A new location update scheme is proposed to obtain mobile users locations and status information over the interworking WLAN and cellular networks. The corresponding system functions and modules are verified by developing a simple OSA-based application in the proposed simulating environment. Keywords Open Service Architecture (OSA), Parlay APIs, Interworking WLAN and G cellular network, Location Update.. INTRODUCTION The G cellular network is expected to be capable of supporting a wide range of services by adopting standard specifications that are proposed by IETF, international, or industry organizations. With the coming presence of G and the increased percentage of data services, the need for opening services has become more and more urgent. As a result, in the context of GPP s Open Service Architecture (OSA) specification, the specified APIs have been designed to simplify and speed up service creation and deployment for G mobile networks while at the same time preserving the network s integrity. G cellular networks will be toward to IP-based networks and will, hopefully, to be integrated with WLAN data networks [, ]. In such a heterogeneous networking environment, the integrity issues of control and transmission protocols will be a critical problem. A typical interoperability issue is location services. For ex- This research is supported by the National Science Council of the Republic of China (Taiwan) under the grant No. NSC 9-9-E , Computer Communication Laboratory (CCL) under the grant No. T-9008-, Industrial Technology Research Institute (ITRI), Republic of China (Taiwan). Copyright is held by the author/owner(s).. ample, a user may want to query location information of his friends or family members over the interworking WLAN and G cellular networks. In order to provide integrated service over interworking WLAN and G cellular networks, a new simulating environment should be designed for helping service providers to develop OSA/Parlay-based applications over the interworking WLAN and G cellular networks. In this paper, a new simulating environment which can allow developers to test and evaluate applications for interworking WLAN and cellular networks is proposed. The aim of our work is to explore the service platform and its applications development in interworking WLAN and G cellular networks. Using OSA/Parlay APIs, operators and rd party service providers can conveniently create their services. However, telecommunication and data communication are different stories. How to develop an application that can use OSA/Parlay Service Capability Features (SCFs) in interworking WLAN and G cellular networks environment becomes a key issue in such a heterogeneous networking environment. Through the procedures of developing applications that use OSA/Parlay services, e.g., location service, instant message service, and presence service, we can find the integrity problems of developing telecom service and data communication service in interworking WLAN and cellular networks. As a result, our experience can provide telecom application developers and service providers some guidance to create their services in future interworking WLAN and G cellular networks more effectively. The remaining part of this paper is organized as follows: Section introduces related works for interworking WLAN and cellular networks. Section describes the proposed simulating architecture for interworking WLAN and cellular networks. Session introduced a new location update scheme to obtain mobile users locations and status information over the interworking WLAN and cellular networks. Section gives a simple OSA-based application that is developed using the proposed simulating environment. Section has the conclusion remarks.. RELATED WORKS Developing OSA-based applications over interworking WLAN and cellular networks is not trivial because of the characteristics of the WLAN and cellular networks,. In this Section, we give a brief survey of the approaches for interworking WLAN and cellular networks. G cellular data networks, such as Universal Mobile Telecommunication System (UMTS) or General Packet Radio Service (GPRS), provide wide area coverage but only support low data rates. However, the low data rates are not sufficient for many data intensive

2 applications. Wireless Local Area Networks (WLANs) support higher speed data, but cover only small areas. WLAN networks will provide wireless data coverage by means of hot spot deployments. A cellular-wlan interworking architecture can combine their benefits []. A cellular-wlan interworking architecture integrating wide-area cellular data service and high bandwidth WLAN networking service in hotspot locations is gaining significant popularity. In the interworking architecture, a mobile terminal has the ability to access high bandwidth services at the WLAN coverage, while access cellular network at other places. Mobile operators must provide a seamless user experience between the WLAN and cellular networks. Such an interworking architecture combines the benefits of WLAN and cellular technologies. Two general interworking solutions specified by the European Telecommunications Standardization Institute (ETSI) are () the tight coupling and () the loose coupling approach. Tight Coupling is an approach integrating the WLAN into a G network. A WLAN network can connect to the G core network and act like radio access network. The data over WLAN will pass through the G core network before arriving the external PDNs. The benefit of this approach is the reuse of the G infrastructure, such as bill systems, subscriber databases, and other core network resources. However, this approach will be highly specific to the G technology used and difficult to analyse, define and standardize. A WLAN is deployed as an access network complementary to the G network in the loose coupling approach. The WLAN makes use of the subscriber s database in the G core network but has no data interface to the G core network. It means that the data over WLAN will reach the external PDNs directly instead of passing through the G core network using the loose coupling solution. The benefit of this approach is avoiding any impact on the Serving GPRS Support Node (SGSN) and GPRS Support Node (GGSN) nodes. Moreover, the loose coupling approach allows many different network operators to be able to operate in the same market. For example, one network operator can offer G subscription service and the other one can offer WLAN subscription service.. SYSTEM ARCHITECTURE Figure depicts the abstract system architecture of the service platform simulating environment. In the proposed simulating environment, developers can use OSA/Parlay APIs to develop and evaluate OSA-based applications. The OSA-based applications invoke the services provided by the OSA/Parlay gateway. The interworking part of WLAN and cellular networks is simulated in the proposed environment. Some extensions should be made to achieve interworking WLAN and cellular networks. Extensions can be conventiently integrated by making use of highly reusable components in the simulating environment. The proposed simulating environment consists of the following major components: () status server, () instant message gateway (IMG), () SIP server/proxy, () Wireless Access (), () Wireless Access Point (AP), () User Equipment (UE), (7) Home Subscriber (HSS)/Home Location Register (), (8) Visited Location Register (VLR), (9) Mobile-Switching Center (C), and (0) Base Station (BS). A UE can be a standard handset or mobile device that is equipped with a WLAN card and a GPRS/UMTS card. WLAN and GPRS/UMTS dual-mode mobile devices are now available. By communicating with a WLAN Access Point (AP), the UE can access Internet services through a gateway named WLAN Access (). In the proposed simulating environment, we assume that the UE can monitor the broadcast-control channel and initiate a location update when the UE moves into another base station (BS) or access point WLAN and G Cellular Interworking Network Simulating Environment HSS VLR AP UE Status Instant Message SIP / Proxy Protocol Protocol OSA/ PARLAY Simulator Parlay Framework SCF to FW OSA/PARLAY API Mobility SCF Other SCFs Figure : The abstract system architecture of the service platform simulating environment. (AP). A WLAN Access () in WLAN plays the role as the C in cellular networks. A UE sends an update request as well as either the International Mobile Subscriber Identity (II) or the Temporary Mobile Subscriber Identity (TI) to the new VLR via the new C in cellular networks. The new VLR then allocates and sends a Mobile Station Roaming Number (RN) to the that keeps the most current location. The location and status servers provide services to the underlying telecommunication networks. The simulating environment of interworking WLAN and cellular networks can provide users and BTS locations while an OSA/Parley application is running. In the proposed simulating environment, an instant message gateway (IMG) serves as a key to send messages between the WLAN network and the cellular network. The IMG has the ability to send messages to an instant message server (ICQ, N server) and provides the interface to communicate between application server and instant message service providers. The OSA-based application services provided by the proposed simulating environment can be classified in four OSA/Parlay service capability features (SCFs): (i) mobility SCF, (ii) terminal SCF, (iii) presence and availability management SCF, and (iv) generic messaging SCF. For each SCF, various applications can be developed using the proposed simulating environment for evaluating and testing OSA/Parlay-based applications over the interworking WLAN and cellular network. The integrity issues of user mobility in the interworking WLAN and G cellular networks give challenges for the proposed simulating environment. One critical issue is how to obtain mobile users locations and status information over the interworking WLAN and cellular environment. A user may want to query location information of his friends or family members over the interworking WLAN and G cellular networks. In order to provide location service over interworking WLAN and G cellular networks, a new simulating environment should be designed for helping developer to query location of mobile users over interworking WLAN and G cellular networks. In Session, a new location update scheme is proposed to obtain mobile users locations and status information over the interworking WLAN and cellular networks. An OSA/Parlay application is not part of the proposed simulating environment. However, the developer can use the proposed simulating environment to develop OSA/Parlay applications. In order to help the developers to develop OSA/Parlay applications, we use Ericsson Mobile Positioning Center Emulator (MPC Emulator) as the auxiliary tool to cooperate with our proposed simulating environment. For validating the proposed simulating environment, a SCF to OSA/PARLAY API OSA-based s

3 C VLR VLR C VLR VLR LA LA LA LA Figure : The registration message flow of GSM location update (Case ). Figure : The registration message flow of GSM location update (Case ). simple application is developed and introduced in Section.. LOCATION AND STATUS TRACKING OVER WLAN AND CELLULAR NETWORK According to the OSA/Parlay specification, location and status services have been defined for cellular networks []. However, such services over the interworking WLAN and cellular environment are not discussed. How to obtain mobile users locations and status information over the interworking WLAN and cellular environment is still an open question. In the proposed simulating environment, we try to solve this problem by proposing a new location update scheme over the interworking WLAN and cellular environment. In the proposed scheme, the mobile users locations and status information can be obtained. Consequently, the OSA-based application developers can request location and status services which are either in WLAN or in cellular network. In the proposed scheme, the basic location unit is defined as the coverage of a Location Area (LA) or an Access Point (AP). In order to get the user location information in the interworking WLAN and cellular network, the WLAN Access () in WLAN acts as the C in cellular network. The C in a cellular network uses the Integrated Services Digital Network (ISDN) number as the unique identifier for identifying the location where the UE resides. The WLAN Access () is given a set of special sequence numbers, which are used to distinguish them with the ISDN numbers of Cs in cellular networks. For example, we take numbers from to as the C identities in cellular networks and the numbers grater than as the s ISDN numbers in the WLAN network. Hence, if the number that one gets is , one can identify that the user is in the WLAN network. The registration message flow of location update over the interworking WLAN and cellular network within the simulating environment is depicted as follows. Case : sage provides the capability to exchange information between applications using noncircuit-related signaling. This message includes (i) Address of the C, (ii) TI of the, (iii) previous location area identification (LAI), (iv) Target LAI, and (v) other related information lists used in the GSM standard.. VLR notices that the previous LA and the target LA are connected to the same C. It updates the LAI field of the VLR record, and then responses to the C with an acknowledgment.. C sends an acknowledgment to the Case :. sends a location update request message to through AP.. forwards the location update request to VLR using the TCAP message, MAP UPDATE LOCATION AREA.. VLR notices that the previous C and the target are connected to the same VLR. The VLR updates LAI and C fields of the VLR record, and obtains the address of the from s II. The VLR sends the MAP UPDATE LOCATION message to. The message includes (i) II of the, (ii) address of the target, (iii) address of the target VLR, and (iv) other related information listed in the GSM standard.. can identify the s record using the received II. The C number field of the record is updated. An acknowledgment is sent to the VLR.. VLR sends an acknowledgment to.. sends an acknowledgment to. sends a location update request message to the C through the BTS. This message includes (i) address of the previously visited LA, (ii) address of the previously visited C, and (iii) address of the previously visited VLR.. C forwards the location update request to the VLR using a Transaction Capabilities Part (TCAP) message, MAP UPDATE LOCATION AREA. The TCAP mes- Case :. The location update request is sent from to VLR. Since the moves from VLR to VLR, the target VLR does not have a VLR record of the and the II of the is not known. The target VLR obtains the address of the previous VLR from the MAP UPDATE LOCATION AREA

4 Service Database VLR 7 8 VLR Status OSA/Parlay IP Network Web C LA LA GPRS/G SGSN / HSS GGSN CSCF S/ Instant Messages WLAN Access WLAN Instant Message Figure : The registration message flow of GSM location update (Case ). message. It sends the message MAP SEND IDENTIFICATION to the previous VLR. Details concerning this message can be found in the GSM standard. Basically, the message provides TI of the that is used by the previous VLR to retrieve the corresponding II in the database.. The II is then sent back to the target VLR with an acknowledgment.. VLR creates a VLR record for the and sends a registration message to update the location information in.. updates the record of the. An acknowledgment is sent back to VLR.. VLR generates a new TI and sends it to the. 7. informs the previous VLR to delete the out-of-date record of the. 8. An acknowledgement is sent from VLR to. Once the application server receives a request from a user, it can make a request to the OSA/Parlay gateway via OSA/Parlay APIs. The OSA/Parlay gateway can fetch the information from the underlying WLAN and cellular network environment. In the proposed simulating environment, the OSA/Parlay gateway can communicate with the status server and the. The status server is responsible for managing the user status information which indicates that a user is reachable, non-reachable, or busy. and VLR are responsible for managing the user location information.. CASE STUDY To illustrate the usage of our OSA-based service platform simulating environment, an application called FriendFinder is developed using the OSA/Parlay APIs. FriendFinder is an application that offers specific location information regarding the location of friends or family members. FriendFinder can deliver user s location and status information via an S or a WAP gateway. Moreover, map information can also be sent to the requester using the Multimedia Messaging Service (M). Once the location of a friend or a family member is located, users can sent S or instant messages to chat with each other via the instant message gateway (IMG). Figure depicts the abstract system architecture of the FriendFinder application over the interworking WLAN and cellular networks. Figure : The abstract system architecture of the FriendFinder application. FriendFinder provides two operation scenarios for mobile users to query the locations of friends or family members: web browsing and S messages. The interfaces at the OSA/Parlay application side, including IpAppUserLocation, IpAppUserStatus, and IpAppUI, are simplified to one IpAppLogic interface. Message flows for retrieving user s location and status information via web browsing and S messages over the interworking WLAN and cellular networks are depicted as follows. Query location via web browsing This scenario shows how a user in WLAN can query locations of friends or family members via web browsing. A web service is implemented to handle the request from the user and the result from the FriendFinder application. Figure depicts the sequence diagram for querying location via the web interface over the interworking WLAN and cellular networks. In Figure, a user can use the browser to make a request of querying the location of a specific friend. The web server forwards this request to the FriendFinder application. After receiving the request, the FriendFinder application invokes the statusreportreq method on the OSA/Parlay gateway to retrieve the user status of a friend. The statusreportreq method invocation is mapped onto a Mobile Part (MAP) protocol dialogue. The Mobile Part (MAP) protocol is a signaling protocol for cellular networks []. After retrieving the user status, the FriendFinder application invokes the extendedlocaionreportreq method on the OSA/Parlay gateway to query the location of his friend. Since the does not store the LAI information of the Mobile Terminal, the requests the corresponding VLR to get the LAI information. After the FriendFinder application receives the result, it forwards the result to the web server. Then, the web server makes a response to the requested mobile user in the form of geographic graphic. Query location via S messages This scenario shows how a user in the cellular network can query locations of friends or family members via S messages. A user in the cellular network can send S messages to trigger the notification of the FriendFinder application. The result can be sent back to the user via S or M. Figure 7 depicts the sequence diagram for querying locations via the S interface over the interworking WLAN and cellular networks.

5 Web WebInterface locationrequest IpAppLogic OSA/Parlay IpUserLocation IpUserStatus statusreportreq statusreportres extendedlocationreportreq CellularNetwork StatusServe VLR MAP AnyTimeInterrogationRe q MAP AnyTimeInterrogationRe s MAP AnyTimeInterrogationRe s querylaireq querylaires OSA/Parlay Cellular Network IpAppLogic IpUIManager IpUserLocation IpUserStatus IpUI Status VLR C MT enablenotification MAP AnyTiemModification InsertSubscriberData MO S Attempt CAP InitialDPS reporteventnotification statusreportreq MAP AnyTimeInterrogationRes statusreportres extendedlocationreportreq querylaireq locationresponse extendedlocationreportres extendedlocationreportres creatui sendinforeq new MAP AnyTimeInterrogationRes querylaires Figure : The message flow for querying locations via the web interface. In Figure 7, the FriendFinder application registers its call back interface to enable system notifications in the cellular network. The FriendFinder application registers its interest in certain S events. When a user sends a S message to a specific service number, the FriendFinder application will be notified. Meanwhile, the reporteventnotification method on the OSA/Parlay gateway will be triggered. With the data stored in the reporteventnotification method, the FriendFinder application can get the information about the request for querying location of a specific user. The FriendFinder application invokes statusreportreq and extendedlocationreportreq methods to retrieve the user status and user location of the user who is being queried. After receiving the result, the FriendFinder application sends the result to the mobile user who queries friend s location information via S messages. Using the User Interaction interface (IpUI) of the OSA/Parlay APIs, the sendinforeq method on the OSA/Parlay gateway is mapped onto the MAP SendRoutinginfoForSM message to obtain the serving C from. Then, the MAP MTForwardShortMessage message is sent to the serving C for forwarding S messages. Finally, the mobile user receives an S message with his friend s status and location information. The above two scenarios illustrate how the OSA interfaces, including User Location, User status, and User Interaction, can be called to create an application. The illustrated case study shows the procedures of mapping OSA/Parlay APIs to the MAP or CAP protocol in order to communicate with the WLAN and cellular network components.. CONCLUSION In this paper, we have proposed an OSA-based service platform simulating environment for the interworking WLAN and G cellular networks. In the proposed simulating environment, an UE can access Internet services through a gateway named WLAN Access (). A WLAN Access () in WLAN plays the role as the C in the cellular network. A UE sends an update request as well as either the International Mobile Subscriber Identity (II) or the Temporary Mobile Subscriber Iden- sendinfores MAP SendRoutingInfoForSMreq MAP SendRoutingInfoForSMconf MAP MTForwardShortMessage MAP MTForwardSMConf Send S Figure 7: The message flow for querying location via S messages. tity (TI) to the new VLR via the new C in the cellular network. The new VLR then allocates and sends a Mobile Station Roaming Number (RN) to the that keeps the current location information. The main contribution of this paper is to overcome the problems of user mobility in the interworking WLAN and G cellular network. A new location update scheme is proposed to obtain mobile users locations and status information over the interworking WLAN and cellular networks. The corresponding system functions and modules are verified by developing a simple OSA-based application in the proposed simulating environment. 7. REFERENCES [] J. Ala-Laurila, J. Mikkonen, and J. Rinnemaa, Wireless LAN Access Network Architecture for Mobile Operators, IEEE Communications Magazine, VOL. 9, NO., pp. 8 89, November 00. [] H. Honkasalo, K. Pehkonen, M. Niemi, and A. Leino, WCDMA and WLAN for G and Beyond, IEEE Wireless Communications, pp. 8, April 00. [] A. Salkintzis, C. Fors, and R. Pazhyannur, WLAN-GPRS Integration for Next-Generation Mobile Data Networks, IEEE Wireless Communications, VOL. 9, NO., pp., October 00. [] M. Yates and I. Boyd, The Parlay Network API Specification, BT Technology Journal, VOL. 8, NO., pp. 7, April 000. [] rd Generation Partnership Project, Mobile Part (MAP) specification; GPP TS 9.00 V.8.0, 00.