Abstract:
The present invention is related to a method and system for providing a wireless transmit/receive unit (WTRU) status, in providing real time services via a wireless local area network interworking with 3GPP systems. An entity such as a packet data gateway (PDG) in the 3GPP network stores and maintains the current state of the WTRU and updates the state of the WTRU when it changes. The WTRU signals a change in its state to the PDG. When the PDG receives a message from the 3GPP system directed to the WTRU, the PDG examines the status of the WTRU prior to forwarding the message to the WTRU.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. provisional application No. 60/576,753 filed Jun. 2, 2004, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention is related to wireless local area networks interworking with 3GPP systems. More particularly, the present invention is related to a method and system for improving the reliability of real time services initiated by an entity in a 3GPP network to an entity in a wireless local area network (WLAN) interworking with the 3GPP system.  
       BACKGROUND  
       [0003]     Wireless local area networks (WLANs) and other wireless communication systems have become popular because of their convenience and flexibility. As the deployment and use of these systems increases, much work is being done to establish standards by which various systems can interwork. One new wireless communication system being standardized is called the Third Generation Partnership Project (3GPP). In order for WLANs to interwork with 3GPP systems, (such systems also being known as I-WLANs), they must be able to operate under a plurality of different scenarios and support a variety of services.  
         [0004]     Most of the prior art in interworking WLAN systems with 3GPP communication systems relates to enabling a wireless transmit/receive unit (WTRU) operating on a WLAN to access a 3GPP network to which the WTRU user is a subscriber. The connection is established through a WLAN access gateway (WAG), to a packet data gateway (PDG), both of which are part of the 3GPP network. Once the connection is established, the WTRU on the I-WLAN can access services on the 3GPP system, including packet switched (PS) services.  
         [0005]     However, most of the work done has been to facilitate access by the WTRU of resources on the 3GPP system, without much consideration given to users on the 3GPP system who might want to access the WTRU. For example, Voice over Internet Protocol (VoIP) is one of the services that an I-WLAN WTRU can support, using session initiation protocol (SIP). Thus, a WTRU on an I-WLAN can establish a 3GPP connection and place a VoIP call to a device on the 3GPP system. However, a 3GPP device cannot easily place a call to the WTRU, even though connected to the 3GPP system. Current 3GPP specifications treat a WLAN as a black box, with little information being provided to the 3GPP system regarding the WTRU. The only available information is whether the WTRU has established the necessary tunnel to a packet data gateway (PDG) of a 3GPP network in order to receive a particular service.  
         [0006]     The PDG does not have access to any other information regarding the status of the WTRU; such as whether it is ON, whether it is in a SLEEP mode, or whether it is OFF or disconnected from the I-WLAN. This has negative consequences for users on the 3GPP network trying to communicate with the WTRU.  
         [0007]     For example, in the case of a terminated VoIP (SIP) call to the WTRU, a WTRU on the 3GPP system sends to the WTRU on the I-WLAN a SIP_INVITE message. The proxy call state control function (P-CSCF) on the 3GPP system forwards the SIP_INVITE message to the PDG for routing to the WTRU operating on the I-WLAN. If the WTRU is in a SLEEP state, the message will be delayed at the access point (AP) of the I-WLAN, to be delivered when the WTRU wakes up. If the delay in delivering the SIP_INVITE message is long enough, without any progress report from the P-CSCF back to the sender, the WTRU will be perceived as “NOT RESPONDING/NOT AVAILABLE” by the sender and the call will be dropped.  
         [0008]     Therefore, there is a need for providing information regarding the status of a WTRU to a PDG or any entity on a 3GPP network that is responsible for routing packet data to the WTRU.  
       SUMMARY  
       [0009]     The present invention is related to a method and system for providing a wireless transmit/receive unit (WTRU) status, in providing real time services via a wireless local area network interworking with 3GPP systems. The WTRU signals each change in its state to a packet data gateway (PDG) or other device in the 3GPP network. The PDG stores and maintains the current state of the WTRU and updates the state of the WTRU when it changes. When the PDG receives a message from a device on the 3GPP system directed to the WTRU, the PDG examines the state of the WTRU prior to forwarding the message to the WTRU. In the case that the WTRU is in an ASLEEP state, the message shall be stored and delivered when the WTRU wakes up. A paging mechanism may be used to inform the WTRU of a pending message. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will be understood from consideration of the drawings in which like elements are designated by like numerals, wherein:  
         [0011]      FIG. 1  is a diagram of a WTRU traveling from an interworking wireless local area network (I-WLAN) access network (AN) associated with the WTRU&#39;s home 3GPP network, to a different I-WLAN AN associated with a different 3GPP network, called a visited network.  
         [0012]      FIG. 2A  is a diagram of a connection between a WTRU in an I-WLAN AN, and a call state control function (CSCF) which provides subscriber services in a 3GPP home network.  
         [0013]      FIG. 2B  is a diagram of a connection between a WTRU in an I-WLAN AN and a CSCF, wherein the state of the UE is maintained in a AAA server.  
         [0014]      FIG. 3  is a diagram of the different states of the WTRU stored, and the actions prompting a change of the stored state.  
         [0015]      FIG. 4  is a timing diagram of an attempted Voice over IP (VoIP) call from a CSCF in a 3GPP network to a WTRU in a I-WLAN, in which the WTRU is in an ASLEEP state and the call is dropped.  
         [0016]      FIG. 5  is a timing diagram of a WTRU in an I-WLAN updating its state from ON to ASLEEP, after which a user in a 3GPP network attempts a VOIP call to the WTRU and is informed of the WTRU&#39;s state.  
         [0017]      FIG. 6  is a timing diagram in which the WTRU wakes from the ASLEEP state and the PDG updates the WTRU state to WTRU_ON, after which the CSCF completes a VoIP call to the WTRU. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     Hereinafter, a wireless transmit/receive unit (WTRU) includes but is not limited to a mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless local area network (I-WLAN) interworking with a third generation partnership project (3GPP) network. Hereinafter, a user equipment (UE) includes but is not limited to a mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a 3GPP network interworking with an I-WLAN. Hereinafter, an access point (AP) includes but is not limited to a Node-B, site controller, base station or any other type of interfacing device in a WLAN environment.  
         [0019]      FIG. 1  shows a WTRU  10  traveling from an area served by a first I-WLAN AN ( 12 ) to an area served by a second I-WLAN AN ( 14 ). The WTRU ( 10 ) is able to access packet switched (PS) services from a 3GPP network via an I-WLAN AN. The user typically wants to ultimately connect to his own 3GPP home network ( 16 ) to which he is a subscriber. The first I-WLAN ( 12 ) is associated by a roaming agreement with the 3GPP home network ( 16 ), and the WTRU ( 10 ) can connect to the 3GPP home network ( 16 ) through the first I-WLAN ( 12 ). The second I-WLAN ( 14 ) is not associated with the user&#39;s 3GPP home network, but can provide 3GPP PS services from the user&#39;s home network through a 3GPP visited network ( 18 ). Authentication, authorization and accounting (AAA) are provided by an AAA server (not shown) via mechanisms well known to those skilled in the art.  
         [0020]      FIG. 2A  shows a packet switched connection with a WTRU  10 , through an I-WLAN AN  12 , through a 3GPP network  20  to a call state control function (CSCF)  26  located therein. The 3GPP network  20  can be a home network, or a combination of a home network and a visited network. A WLAN Access Gateway (WAG)  22 , and a Packet Data Gateway (PDG)  24 , including a proxy-call state control function (P-CSCF), are shown in the 3GPP network  20 . An access point (AP)  28  is shown in the I-WLAN. The WTRU  10  establishes a connection to the 3GPP network  20  via the AP  28 , the WAG  22  and the PDG  24 . All packet data directed between the 3GPP network  20  and the WTRU  10  are transmitted via the PDG  24  and the WAG  22  in the 3GPP network  20  and the AP  28  in the I-WLAN  12 .  
         [0021]     The WAG  22  generates charging information and forwards it to the AAA server for accounting purposes, and enforces routing of packets through the PDG  24 . The PDG  24  maintains and updates routing information for the WTRU  10 , and routes the packet data directed to it after performing address translation and mapping. According to the present invention, the PDG  24  also stores and maintains the state of the WTRU  10 , and updates the state of the WTRU  10  whenever it changes. Although in a first embodiment the state of the WTRU  10  is stored and maintained in the PDG  24 , the state of the WTRU  10  could be stored and maintained at another location, such as in a AAA server  25 , as shown in  FIG. 2B  in a second embodiment.  
         [0022]     Communications regarding the state of the WTRU  10  are transmitted via signaling, such as by internet protocol (IP), between the WTRU  10  and the PDG  24 . The AP  28  communicates with wireless devices, such as WTRU  10 , via an air interface, and connects them to the wired network. There are many other functions performed by the WAG  22 , the PDG  24  and the AP  28  that are well known to those skilled in the art but are not relevant to the present invention. Accordingly, those functions will not be described in detail hereinafter.  
         [0023]     Referring to  FIG. 3 , a state diagram  30  of the state of the WTRU  10  as maintained at the PDG  24  in accordance with the present invention is shown. The state diagram  30  indicates three WTRU states which are defined as follows:  
         [0024]     1. WTRU_ON ( 32 )—The WTRU is powered on, is attached to an AP in the I-WLAN, and has established an IP tunnel with the PDG in a 3GPP network.  
         [0025]     2. WTRU_ASLEEP ( 34 )—The WTRU is powered on but has entered sleep mode. The tunnel with the I-WLAN is still ON.  
         [0026]     3. WTRU_OFF ( 36 )—The WTRU is currently powered off, or is detached from the AP, or the IP tunnel to the 3GPP PDG has simply been taken down.  
         [0027]     It should be noted that although only three states are set forth in  FIG. 3 , the present invention is not limited to these three states. Those of skill in the art should realize that other states could be added in the future. It is only important that the state of WTRU  10  is stored and maintained in the 3GPP network.  
         [0028]     The events internal relative to the WTRU  10  which trigger the sending of an update message in order to update of its state to the PDG  24  are also shown in  FIG. 3  as:  
         [0029]     1. WTRU_ATTACH ( 31 )—The WTRU  10  is on and is connected to an AP  28 , and has just set up an IP tunnel to the PDG  24  on the 3GPP network  20 . The PDG  24  stores the state of the WTRU with an initial value of WTRU_ON ( 32 ).  
         [0030]     2. WTRU_DETACH ( 33 )—The WTRU  10  is about to disconnect from the AP  28 , or is simply about to take down the IP tunnel to the PDG  24 , for example, in response to a user command. The WTRU  10  sends a message indicating its imminent action to the PDG  24 , and the state of the WTRU  10  stored at the PDG  24  is updated by the PDG  24  to WTRU_OFF  36 .  
         [0031]     3. WTRU_PWR_DN ( 39 )—The WTRU  10  is about to power down, for example, in response to a user command. The WTRU sends a message indicating its imminent action to the PDG  24 , and the state of the WTRU  10  stored at the PDG  24  is updated by the PDG  24  to WTRU_OFF  36 .  
         [0032]     4. WTRU_SLEEP ( 35 )—The WTRU  10  is about to enter sleep mode, either in response to a user command or by timeout (i.e., the maximum permissible time without communication between the WTRU  10  and the AP  28  has been exceeded), but the WTRU  10  will still be associated with the IP tunnel to the PDG  24 . The WTRU  10  sends a message indicating its imminent action to the PDG  24 , and the state of the WTRt  10  stored at the PDG  24  is updated by the PDG to WTRU_ASLEEP  34 .  
         [0033]     5. WTRU_WAKE ( 37 )—The WTRU  10  has just ended sleep mode and is actively communicating with an AP  28 , and the IP tunnel to the PDG  24  is still active. The WTRU  10  sends a message indicating its action to the PDG  24 , and the state of the WTRU  10  stored at the PDG  24  is updated by the PDG  24  to WTRU_ON  32 .  
         [0034]     One event which is not internal to the WTRU  10 , but which is internal to the PDG  24 , can also trigger an update of the state of the WTRU  10  at the PDG  24 :  
         [0035]     6. TOUT ( 38 )—The maximum permissible time without communication from the WTRU  10  has been exceeded, as indicated by a timer in the PDG  24 . The state of the WTRU  10  stored at the PDG  24  is updated by the PDG  24  to WTRU_OFF  36 .  
         [0036]     In the case of terminated traffic to a WTRU  10  from the 3GPP network  20  with which the PDG  24  is associated, the PDG  24  examines the state of the WTRU  10  prior to attempting to deliver the traffic to the WTRU  10 . In the case that the WTRU  10  is in the WTRU_ASLEEP  34  state, the traffic is stored by the PDG  24  and delivered when the state of the WTRU  10  changes to WTRU_ON  32 . The PDG  24  also sends a message  52  to the device that originated the traffic, indicating that the WTRU  10  is asleep. In a second embodiment, the PDG  24  can also use a paging mechanism to inform the WTRU  10  of pending traffic.  
         [0037]      FIG. 4  illustrates a CSCF  26  on a 3GPP system  20  attempting to place a voice-over-IP (VoIP) call to a WTRU  10  on an I-WLAN AN, in which the WTRU  10  is in the WTRU_ASLEEP  34  state, without the benefit of the present invention. In this case, it is assumed that the WTRU  10  has an established tunnel to a PDG  24  on the 3GPP system and the WTRU  10  is in the WTRU_ASLEEP  34  state. The 3GPP network  20  is aware of the tunnel, but has no information regarding the state of the WTRU  10 . The CSCF  26  sends a session initiation protocol (SIP) INVITE message  40  to the WTRU  10  via a Proxy Call State Control Function (P-CSCF) within the PDG  24 . The P-CSCF within the PDG  24  forwards the SIP_INVITE message  40  to the PDG  24  for routing to the WTRU  10 , and the PDG  24  forwards it to the WAG  22 , and thence to the AP  28  in the I-WLAN AN  12  with which the WTRU  10  is associated. Since the WTRU  10  is in the WTRU_ASLEEP  34  state, the message will be stored at the AP  28  until the WTRU  10  wakes up. The delay in delivering the SIP_INVITE message  40 , without any progress report from the P-CSCF back to the sender, will be interpreted as the WTRU “NOT RESPONDING/NOT AVAILABLE” by the sender, and the call will be dropped.  
         [0038]      FIG. 5  illustrates a similar scenario in which a CSCF  26  on a 3GPP system  20  attempting to place a voice-over-IP (VoIP) call to a WTRU  10  on an I-WLAN AN  12 , in which the WTRU  10  is in the WTRU_ASLEEP  34  state and in which the present invention is used. In this case, it is also assumed that the WTRU  10  has again established a tunnel to a PDG  24  on the 3GPP system  20  and the WTRU  10  is about to enter the WTRU_ASLEEP  34  state. The WTRU  10  sends a WTRU_SLEEP message  50  to the AP  28  which forwards the message  50  to PDG  24  via the WAG  22 .  
         [0039]     Upon receipt of the WTRU_SLEEP message  50 , the PDG  24  changes the stored state of the WTRU  10  to WTRU_ASLEEP  34 . The 3GPP network  20  is now aware of the tunnel, and also has information regarding the state of the WTRU  10 . Accordingly, when the CSCF  26  sends an SIP_INVITE message  40  to the WTRU  10  via a P-CSCF in the PDG  24 , the P-CSCF forwards the SIP_INVITE message  40  to the PDG  24  for routing to the WTRU  10 , and the PDG  24  checks the state of the WTRU  10  before attempting to forward the SIP_INVITE message  40  to the WTRU  10 . Since the state of the WTRU  10  stored at the PDG  24  is the WTRU_ASLEEP  34  state, the message is not forwarded. The PDG  24  sends a message  52  to the CSCF  26  indicating the WTRU  10  is in the WTRU_ASLEEP  34  state, and the SIP_INVITE message  40  is stored at the PDG  24  until the WTRU  10  wakes up. The CSCF  26  can decide whether to wait for the WTRU  10  to wake up, and if so, the call will not be dropped. The PDG  24  can use a paging-like mechanism to inform the WTRU  10  of a pending message.  
         [0040]      FIG. 6  illustrates a CSCF  26  on a 3GPP system  20  placing a voice-over-IP (VoIP) call to a WTRU  10  on an I-WLAN AN  12  which was in the WTRU_ASLEEP  34  state and woke up, in which the present invention is used. In this case, the WTRU  10  has an active tunnel to the PDG  24  on the 3GPP system and is in the WTRU_ASLEEP  34  state. When the WTRU  10  wakes up, it sends to the PDG  24  a WTRU_WAKE message  60  via the AP  28  and the WAG  22 . The PDG  24  receives the WTRU_WAKE message  60  and changes the stored state of the WTRU to the WTRU_ON  32  state. The 3GPP network  20  is now aware of the tunnel, and also has information regarding the WTRU_ON  32  state of the WTRU  10 .  
         [0041]     The CSCF  26  sends a SIP_INVITE message  40  to the WTRU  10  via a P-CSCF in the PDG  24 . The P-CSCF forwards the SIP_INVITE message  40  to the PDG  24  for routing to the WTRU  10 , and the PDG  24  checks the state of the WTRU  10  before attempting to forward the SIP_INVITE message  40  to the WTRU  10 . Since the state of the WTRU  10  stored at the PDG is WTRU_ON  32  state, the SIP_INVITE message  40  is forwarded. The SIP_INVITE message  40  is passed through the WAG  22  and the AP  28  to the WTRU  10 . The WTRU  10  responds by sending a SIP_ACK message  62  to the CSCF  26 , which is forward through the AP  28 , the WAG  22  and the PDG  24  to the CSCF  26 , and the VoIP session is thereby established.  
         [0042]     Although the features and elements of the present invention are described in the preferred embodiments in particular combinations using VoIP, 3GPP, PDG and AAA server, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention, and using other communication services, standards and devices.