Abstract:
There is provided a method for performing an intra-packet data service node (PDSN) hard handoff. The method is implemented by setting up a channel passing through a target base station controller (T-BSC), a source base station controller (S-BSC), a source packet control function (S-PCF) and a PDSN by establishing a channel link between the S-BSC and the T-BSC via a mobile station center (MSC) in an active packet session mode, performing the hard handoff between the S-BSC, the T-BSC and a mobile station (MS) and transmitting or receiving user packet data exchanged between the MS and the T-BSC through the established channel link to or from the PDSN in case the hard handoff is completed.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to synchronous IMT-2000 wireless packet communication networks; and, more particularly, to a method for performing a fast intra-packet data service node (PDSN) hard handoff, i.e., a hard handoff between packet control function units (PCFs) in the PDSN, without data loss via a mobile switching center (MSC) so as to provide high-speed/high-quality real-time data services without data loss in an active packet mode.  
         DESCRIPTION OF RELATED ART  
         [0002]    In conjunction with current integrated Internet protocol (IP) networks, an Internet protocol based wireless packet data network is standardized so as to provide Internet services and real-time VoIP services in a third generation synchronous IMT-2000 wireless access network.  
           [0003]    In particular, there exist technical problems of header compression and a handoff in implementing the current Internet protocol based wireless packet network and these problems should be solved to obtain satisfactory QoS.  
           [0004]    According to a standardization document IS-835 related to the third generation IMT-2000 synchronous wireless packet data network, as components constructing the wireless packet data network, there are a base station controller (BSC), a packet control function (PCF) unit, a packet data service node (PDSN), a mobile Internet protocol (IP) home agent (HA) and an authentication/authorization/accounting (AAA) unit.  
           [0005]    Referring to FIG. 1, there is illustrated a call-processing flow diagram showing an intra-PDSN hard handoff procedure defined in the IS-835 and IOS V4.x.  
           [0006]    When a message showing that a signal strength of a mobile station (MS)  101  became over a given signal strength threshold defined in a network and the MS  101  will convert to another access network identifier (ANID) is transmitted from the MS  101  to a source-BSC (S-BSC)  103 , the S-BSC  103  sends a Handoff Required message including a cell list within a domain of a target-BSC (T-BSC)  107  to an MSC  111  in step S 101  and actuates a T 7  timer. The Handoff Required message contains a previous ANID (PANID).  
           [0007]    The MSC  111  selects the T-BSC  107  having an available wireless channel from the cell list, adds the PANID and a hard handoff indicator to a Handoff Request message and transmits the Handoff Request message to the T-BSC  107  in step S 103 . Herein, the hard handoff indicator means a handoff type component representing a hard handoff. After receiving the Handoff Request message, the T-BSC  107  allocates appropriate idle wireless resources and transmits null traffic channel data on a forward traffic channel.  
           [0008]    To set up an A 8 -Connection, the T-BSC  107  provides an A 9 -Setup-A 8  message to a target-PCF (T-PCF)  109  and actuates a TA 8 -Setup timer in step S 105 . Herein, the A 8  is a user traffic path for BSC-PCF packet data services defined in the standardization document. The A 9  represents a signal path for the BSC-PCF packet data services defined in the standardization document. In step S 105 , a hard handoff indicator field in the A 9 -Setup-A 8  message is set to 1.  
           [0009]    After receiving the A 9 -Setup-A 8  message, the T-PCF  109  sets up the A 8 -Connection, transmits an A 9 -Connect-A 8  message the T-BSC  107  and actuates a Twaitho 9  timer in step S 107 . At this time, the T-BSC  107  and the T-PCF  109  do not receive packet data from a PDSN  121  and the PDSN  121  continuously sends forward packet data to the S-BSC  103  through an S-PCF  105 . Meanwhile, after receiving the A 9 -Connect-A 8  message, the T-BSC  107  stops an operation of the TA 8 -Setup timer.  
           [0010]    Since the hard handoff indicator field in the A 9 -Setup-A 8  message was set to 1, an A 10 /A 11  Connection is not established yet. The A 10  and A 11  represent traffic and signal paths for PCF-PDSN packet data services defined in the standardization document, respectively.  
           [0011]    Then, in step S 109 , the T-BSC  107  allows the MS  101  to be tuned to a corresponding wireless channel by transmitting a Handoff Request Ack message including appropriate wireless channel information to the MSC  111  and actuates a T 9  timer so as to wait for the signal receiving from the MS  101  through the corresponding wireless channel.  
           [0012]    The MSC  111  prepares a call switching from the S-BSC  103  to the T-BSC  107  and delivers a Handoff Command message including the wireless channel information provided from the T-BSC  107  to the S-BSC  103  in step S 111 . After then, the S-BSC  103  terminates an operation of the T 7  timer.  
           [0013]    The S-PCF  105  receives an A 9 -Air Link (AL) Disconnected message from the S-BSC  103  and, then, stops packet data transmission to the S-BSC  103  in step S 113 . After transmitting the A 9 -AL Disconnected message, the S-BSC  103  actuates a Tald 9  timer.  
           [0014]    In step S 115 , the S-PCF  105  sends an A 9 -AL Disconnected Ack message to the S-BSC  103  and the S-BSC  103  terminates an operation of the Tald 9  timer.  
           [0015]    In step S 117 , the S-BSC  103  transmits a general handoff direction message (GHDM) or a universal handoff direction message (UHDM) to the MS  101  and actuates a Twaitho timer so as to allow the MS  101  to return to the S-BSC  103 .  
           [0016]    The MS  101  provides the S-BSC  103  with an MS Ack Order message as a response to the GHDM or UHDM in step S 119 .  
           [0017]    In step S 121 , the S-BSC  103  transmits a Handoff Commenced message to the MSC  111  so as to notify that the MS  101  is instructed to move to a channel of the T-BSC  107  and actuates a T 306  timer to wait for transmission of a Clear Command message from the MSC  111 . The Handoff Commenced message is transmitted after an operation of the Twaitho timer is terminated.  
           [0018]    If the MS  101  completes the hard handoff procedure by obtaining synchronization through the use of a backward communication channel frame or preamble data, the MS  101  transmits a Handoff Completion message to the T-BSC  107  in step S 123  and the T-BSC  107  which received the Handoff Completion message transmits a BSC Ack Order message to the MS  101  in step S 125 .  
           [0019]    Further, in step S 127 , the T-BSC  107 , which received the Handoff Completion message from the MS  101 , provides the T-PCF  109  with an A 9 -AL Connected message including the PANID. The T-BSC  107  terminates an operation of the Twaitho 9  timer and the T-PCF  109  actuates a Talc 9  timer.  
           [0020]    The T-PCF  109 , which received the A 9 -AL Connected message, establishes an A 10 /A 11  link and the PDSN  121  releases an A 10 /A 11  link established with the S-PCF  105  in step S 129 .  
           [0021]    Then, the T-PCF  109  transmits an A 9 -AL Connected Ack message to the T-BSC  107  as a response to the A 9 -AL Connected message and terminates an operation of the Talc 9  timer in step S 131 .  
           [0022]    After the T-BSC  107  detects that the MS  101  is connected to the T-BSC  107 , the T-BSC  107  transmits a Handoff Complete message to the MSC  111  so as to notify that the hard handoff is successfully performed for the MS  101  and terminates an operation of the T 9  timer in step S 133 .  
           [0023]    In step S 135 , the MSC  111  supplies a Clear Command message to the S-BSC  105 . The S-BSC  105  terminates an operation of the T 306  timer and the MSC  111  actuates a T 315  timer.  
           [0024]    The S-BSC  103  sends an A 9 -Release-A 8  message to the S-PCF  105  so as to release the A 8 -Connection and actuates a Trel 9  timer in step S 137 .  
           [0025]    The S-PCF  105  releases the A 8 -Connection and sends an A 9 -Release-A 8  Complete message to the S-BSC  103  in step S 139 . The S-BSC  103  terminates an operation of the Trel 9  timer.  
           [0026]    Finally, the S-BSC  103  transmits a Clear Complete message to the MSC  111  and completes the intra-PDSN hard handoff procedure in step S 141 .  
           [0027]    As described above, according to the intra-PDSN hard handoff procedure of the prior art, during the steps S 111  to S 129  being performed, the data transmitted from the PDSN  121  are not delivered to users, i.e., the MS  101 . Moreover, since there exists an A 8  and A 10  connection time, a time delay occurs.  
           [0028]    Therefore, in order to prevent data loss due to the time delay, there need regular doses of buffers in a node. However, although there are prepared the buffers, in case a size of data stored in the buffers exceeds the capacity of the buffers, there inevitably occurs a severe problem of causing the data loss.  
           [0029]    That is, there is a problem that the existing intra-PDSN hard handoff performing method employed in the third generation IMT-2000 synchronous packet data network is improper to processing the packet data requiring fast transmission without data loss, i.e., real-time services.  
           [0030]    Specifically, since the hard handoff performing method defined in the third generation synchronous IMT-2000 wireless packet network cannot provide fast and seamless real-time services since there is the time delay when the handoff is performed in the active mode, it is difficult to provide real-time audio/video packet data services such as VoIP.  
         SUMMARY OF THE INVENTION  
         [0031]    It is, therefore, a primary object of the present invention to provide an intra-PDSN hard handoff performing method capable of providing a fast intra-packet data service without data loss by establishing a link between BSCs via an MSC in case of an active packet session mode in a third generation synchronous IMT-2000 wireless packet communication network.  
           [0032]    In accordance with the present invention, there is provided a method for performing an intra-packet data service node (PDSN) hard handoff, comprising the steps of: setting up a channel passing through a target base station controller (T-BSC), a source base station controller (S-BSC), a source packet control function (S-PCF) and a PDSN by establishing a channel link between the S-BSC and the T-BSC via a mobile station center (MSC) in an active packet session mode; performing the hard handoff between the S-BSC, the T-BSC and a mobile station (MS); and transmitting or receiving user packet data exchanged between the MS and the T-BSC through the established channel link to or from the PDSN in case the hard handoff is completed.  
           [0033]    In accordance with the present invention, it is possible to perform a packet hard handoff without packet data loss by reducing a time delay caused in a handoff procedure performed during a packet data session of an active mode in an intra-PDSN.  
           [0034]    In particular, in case it is impossible to directly establish a link between a T-BSC and an S-BSC measuring a power strength of a wireless signal transmitted from an MS in the active mode, the hard handoff is performed by establishing a link between the S-BSC and an MSC by transmitting a circuit identification code (CIC) of the S-BSC when the S-BSC sends a Handoff Required message to the MSC and, meanwhile, establishing a link between the T-BSC and the MSC by transmitting a CIC of the MSC when the MSC sends a Handoff Request message to the T-BSC.  
           [0035]    Therefore, during performing the hard handoff procedure in the active mode, the S-BSC can continuously maintain a link with an S-PCF as an anchor and transmit packets to the MS.  
           [0036]    Furthermore, when the inventive hard handoff procedure is completed, by establishing a link between the T-BSC, a T-PCF and the PDSN after being converted to a dormant mode, it is possible to provide packet data services in a next active mode without data loss and time delay due to the link establishment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]    The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0038]    [0038]FIG. 1 provides a call-processing flow diagram showing an intra-PDSN hard handoff procedure defined in IS-835 and IOS V4.x;  
         [0039]    [0039]FIG. 2 describes a call-processing flow diagram representing an intra-PDSN hard handoff procedure in accordance with the present invention;  
         [0040]    [0040]FIG. 3 is a conceptual diagram depicting a link established between BSCs via an MSC when performing an intra-PDSN hard handoff in an active mode in accordance with the present invention; and  
         [0041]    [0041]FIG. 4 illustrates a conceptual diagram showing a flow of packet data transmitted through a link established between an S-BSC and a T-BSC via an MSC when performing an intra-PDSN hard handoff in an active mode in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]    Hereinafter, with reference to the accompanying drawings, some preferred embodiments of the present invention would be explained in detail. Hereinafter, when assigning reference numerals to components constructing each drawing, same components are represented by an identical reference numeral although they are shown in different drawings.  
         [0043]    Referring to FIG. 2, there is illustrated a procedure rapidly supporting an intra-PDSN hard handoff without data loss by establishing a link between BSCs via an MSC in an active mode of a synchronous IMT-2000 wireless packet network. FIG. 2 describes a call-processing flow diagram representing the intra-PDSN hard handoff procedure in accordance with the present invention.  
         [0044]    When a message showing that a signal strength of a mobile station (MS)  101  became over a given signal strength threshold defined in a network and the MS  101  will convert to another access network identifier (ANID) is transmitted from the MS  101  to a S-BSC  103 , the S-BSC  103  sends a Handoff Required message including a cell list within a domain of a T-BSC  107  to an MSC  111  in step S 201  and actuates a T 7  timer. The Handoff Required message contains a previous ANID (PANID).  
         [0045]    Further, the Vandoff Required message includes a circuit identification code (CIC) value delivering call resources of the S-BSC  103  as an extender.  
         [0046]    The MSC  111  selects the T-BSC  107  having an available wireless channel from the cell list, adds the PANID and a hard handoff indicator to a Handoff Request message and transmits the Handoff Request message to the T-BSC  107  in step S 203 . The Handoff Request message contains a CIC value therein.  
         [0047]    In step S 205 , the T-BSC  107  establishes an ATM-based link channel via the MSC  111  between the S-BSC  103  and the T-BSC  107  by allocating appropriate idle wireless resources as receiving the Handoff Request message. Meanwhile, a PDSN  121  continuously transmits forward packet data to the S-BSC  103  through an S-PCF  105 .  
         [0048]    Moreover, the T-BSC  107  transfers null traffic channel data to the MS  101  through a forward traffic channel.  
         [0049]    Then, in step S 207 , the T-BSC  107  allows the MS  101  to be tuned to a corresponding wireless channel by transmitting a Handoff Request Ack message including appropriate wireless channel information to the MSC  111  and actuates a T 9  timer so as to wait for the signal receiving from the MS  101  through the corresponding wireless channel.  
         [0050]    In accordance with the present invention, although the hard handoff is performed in the active mode, there is not set up an A 8 /A 9  Connection between the T-BSC  107  and a T-PCF  109  and the A 8 /A 9  Connection will be set up in a dormant mode as described herein below.  
         [0051]    The MSC  111 , which received the Handoff Request Ack message, prepares a call switching from the S-BSC  105  to the T-BSC  107  and sends a Handoff Command message including the wireless channel information provided from the T-BSC  107  to the S-BSC  103  in step S 209 . Then, the S-BSC  103  terminates an operation of the T 7  timer.  
         [0052]    In step S 211 , the S-BSC  103  transmits a general handoff direction message (GHDM) or a universal handoff direction message (UHDM) to the MS  101  and actuates a Twaitho timer so as to allow the MS  101  to return to the S-BSC  103 .  
         [0053]    The MS  101  provides the S-BSC  103  with an MS Ack Order message as a response to the GHDM or UHDM in step S 213 .  
         [0054]    In step S 215 , the S-BSC  103  sends a Handoff Commenced message to the MSC  111  so as to notify that the MS  101  is instructed to move to a channel of the T-BSC  107 . The Handoff Commenced message is transmitted after an operation of the Twaitho timer is terminated.  
         [0055]    If the MS  101  completes the hard handoff procedure by obtaining synchronization through the use of a backward communication channel frame or preamble data, the MS  101  transmits a Handoff Completion message to the T-BSC  107  in step S 217  and the T-BSC  107  which received the Handoff Completion message transmits a BSC Ack Order message to the MS  101  in step S 219 .  
         [0056]    In step S 221 , after the T-BSC  107 , which received the Handoff Completion message, detects that the MS  101  is connected to the T-BSC  107 , the T-BSC  107  transmits a Handoff Complete message to the MSC  111  so as to notify that the hard handoff is successfully performed for the MS  101  and terminates an operation of the T 9  timer.  
         [0057]    After then, user packet data transmitted from the MS  101  are delivered to the S-BSC  103  via the T-BSC  107  and the MSC  111 . At this time, the S-BSC  103  exists as an anchor and continuously transmits packet data to an opposite node of the wireless packet data network through the S-PCF  105  and the PDSN  121  until the active mode is converted to the dormant mode. Likewise, the packet data arrived at the MS  101  from the opposite node are delivered in an order of the PDSN  121 , the S-PCF  105 , the S-BSC  103 , the MSC  111  and the T-BSC  107  in step S 223 .  
         [0058]    Therefore, since the S-BSC  103  plays a role of the anchor, there is no need to re-establish the A 8 /A 9  Connection between the T-BSC  107  and the T-PCF  109  and the A 10 /A 11  Connection between the T-PCF  109  and the PDSN  121 , respectively.  
         [0059]    As a result, it is possible to prevent a time delay required in establishing a link in the conventional handoff scheme.  
         [0060]    Referring to FIG. 3, there is shown a conceptual diagram depicting a link established between BSCs via an MSC when performing the intra-PDSN hard handoff in the active mode in accordance with the present invention. FIG. 4 illustrates a conceptual diagram showing a flow of packet data transmitted through a link established between an S-BSC and a T-BSC via an MSC when performing the intra-PDSN hard handoff in the active mode in accordance with the present invention. In FIG. 4, reference numerals  1  to  9  represent a flow of data packets before the handoff and reference numerals  10  and  11  describe a flow of data packets after the handoff.  
         [0061]    As illustrated in FIGS.  2  to  4 , since there is already established a channel link between the S-BSC  103  and the T-BSC  107  via the MSC  111  and the S-BSC  103  is determined as an anchor although the hard handoff of the intra-PDSN is executed in the active mode by performing the above handoff procedure in accordance with the present invention, it is possible to transmit the packet data to the wireless packet data network through the S-PCF  105  and the PDSN  121  by the channel link to the S-BSC  103  established via the MSC  111  even though packet data are exchanged through a wireless link established between the MS  101  and the T-BSC  107  by executing the hard handoff.  
         [0062]    Accordingly, since the process for establishing the A 8 /A 9 /A 10 /A 11  Connection between the T-BSC  107 , the T-PCF  109  and the PDSN  121  is omitted, the time delay due to the hard handoff is substantially reduced and, thus, it is possible to provide seamless fast packet data services.  
         [0063]    The process for setting up the A 8 /A 9 /A 10 /A 11  Connection between the T-BSC  107 , the T-PCF  109  and the PDSN  121  is performed in the dormant mode described herein below.  
         [0064]    As depicted in FIG. 2, after the T-BSC  107  detects that there is no packet data provided from the MS  101  or the S-BSC  103  anymore by actuating a timer, the active mode is converted to the dormant mode. Then, in order to set up the A 8 -Connection with the T-PCF  109 , an A 9 -Setup-A 8  message is transmitted to the T-PCF  109  and a TA 8 -Setup timer is actuated in step S 105 .  
         [0065]    The T-PCF  109 , which received the A 9 -Setup-A 8  message, sets up the A 8 -Connection and, then, provides an A 9 -Connect-A 8  message to the T-BSC  107  in step S 107 . Meanwhile, the T-BSC  107 , which received the A 9 -Connect-A 8  message, stops an operation of the TA 8 -Setup timer.  
         [0066]    Furthermore, there is established an A 10 /A 11  Connection between the T-PCF  109  and the PDSN  121  in step S 225 . As a result, the A 8 /A 9 /A 10 /A 11  Connection is set up between the MS  101 , the T-BSC  107 , the T-PCF  109  and the PDSN  121 .  
         [0067]    Then, in step S 135 , the MSC  111  supplies a Clear Command message to the S-BSC  105  and the MSC  111  actuates a T 315  timer.  
         [0068]    The S-BSC  103  transmits an A 9 -Release-A 8  message to the S-PCF  105  so as to release the A 8 -Connection with the S-PCF  105  and actuates a Trel 9  timer in step S 137 .  
         [0069]    The S-PCF  105  releases the A 8 -Connection and generates an A 9 -Release-A 8  Complete message as a response in step S 139 . The S-BSC  103  terminates an operation of the Trel 9  timer.  
         [0070]    Then, the A 10  Connection between the S-PCF  105  and the PDSN  121  is released and its state is updated in step S 227 .  
         [0071]    Finally, the S-BSC  103  provides the MSC  111  with a Clear Complete message to thereby terminate the Intra-PDSN hard handoff procedure in step S 141 .  
         [0072]    According to the hard handoff procedure in accordance with the present invention, a CIC is used as an extender when the S-BSC  103  transmits the Handoff Required message to the MSC  111  in the active mode and transmitted when the MSC  111  sends the Handoff Request message to the T-BSC  107  to thereby establish a link between BSCs via the MSC  111 , so that the hard handoff procedure can support the hard handoff by using the communication between the BSCs.  
         [0073]    When the handoff occurs, packet data transmitted from the MS  101  to the T-BSC  107  are provided to the S-BSC  103  through a channel link established by the CIC and transmitted to the wireless packet data network through the S-PCF  105  and the PDSN  121 .  
         [0074]    Herein, the S-BSC  103  plays a role of the anchor in the active mode to thereby allow the packet data passing through the T-BSC  107  to go through not the T-PCF  109  but the S-BSC  103  although the handoff occurs, so that the time delay due to the A 8 /A 9 /A 10 /A 11  Connection between the MS  101 , the T-BSC  107 , the T-PCF  109  and the PDSN  121  is reduced.  
         [0075]    After executing the handoff, the anchor state of the S-BSC  103  is released in the dormant mode.  
         [0076]    After the handoff, when the MS  101  existing at the cell domain of the T-BSC  107  is converted to the dormant mode, by setting up the A 8 /A 9  Connection between the T-BSC  107  and the T-PCF  109  and the A 10 /A 11  Connection between the T-PCF  109  and the PDSN  121 , there is no need to newly establish the A 8 /A 9 /A 10 /A 11  Connection when the dormant mode is converted to the active mode again. As a result, it is possible to reduce the time delay caused by the link establishment.  
         [0077]    Accordingly, compared to the prior art, the present invention can provide the packet data services without a break and data loss.  
         [0078]    As described above, the inventive handoff performing method can support the handoff without a break by performing the fast hard handoff in the packet wireless communication network.  
         [0079]    Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.