Abstract:
A system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the system comprising: a first base transceiver station of which a mobile station subjected to the soft hand-off is under control before the soft hand-off; a second base transceiver station of which the mobile station is under control after the soft hand-off; a first base transceiver station controller which controls the first base transceiver station; and a second base transceiver station controller which controls the second base transceiver station; a physical channel which connects the first base transceiver station controller and the second base transceiver station controller; wherein a first upstream data packet is transmitted from the mobile station to a codec in the first base transceiver station controller via the first base transceiver station; wherein a second upstream data packet is transmitted from the mobile station to the codec via the second base transceiver station, the second base transceiver station controller, and the physical channel; wherein a first downstream data packet is transmitted from the codec to the mobile station via the first base transceiver station; and wherein a second down stream data packet is transmitted from the codec to the mobile station via the physical channel, the second base transceiver station controller, and the second base transceiver station.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers and particularly, to a system for performing a soft hand-off between CDMA (Code Division Multiple Access) base transceiver stations under control of different CDMA base transceiver station controllers. 
     2. Description of the Prior Art 
     In a conventional CDMA system, a soft hand-off system is generally used for performing a hand-off between base transceiver stations (hereinafter, referred to as BTS) under the same base transceiver station controller (hereinafter, referred to as BSC). However, either of a hard hand-off system or a soft hand-off system which is performed under control of a mobile-services switching center (hereinafter, referred to as MSC) is used for performing a hand-off between BTSs under control of different BSCs because, as shown in FIG. 6, BSCs  1401 ,  1501  in the conventional CDMA system have no header converter and the conventional CDMA system has no link used for soft hand-off between BSCs. 
     The hard hand-off system adopts a method of deleting a current path before establishing a new path because the hard hand-off system is not capable of establishing a plurality of paths at the same time. Therefore, the hard hand-off system has a disadvantage of a short break which deteriorates a quality of communication. 
     On the other hand, the soft hand-off system adopts a method of deleting a current path after establishing a new path because the soft hand-off system is capable of establishing a plurality of paths at the same time. Therefore, the soft hand-off system does not have a disadvantage of the short break. 
     However, when performing a conventional soft hand-off between BTSs under control of different BSCs, the MSC has to perform both an information management and path controls (or call-in connection controls) for BSCs, BTSs, and MSs under control of the MSC. Therefore, the MSC is burdened with an excessive load, and moreover, a delay time of a communication becomes long. Thus, when performing the conventional soft hand off between BTSs under control of different BSCs, a communication quality deteriorates. 
     SUMMARY OF THE INVENTION 
     In order to overcome the aforementioned disadvantages, the present invention has been made and accordingly, has an object to provide a system for performing a soft hand off between base transceiver stations under control of different base transceiver station controllers which do not deteriorate a communication quality. 
     According to an aspect of the present invention, there is provided a system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the system comprising: a first base transceiver station of which a mobile station subjected to the soft hand-off is under control before the soft hand-off; a second base transceiver station of which the mobile station is under control after the soft hand-off; a first base transceiver station controller which controls the first base transceiver station; a second base transceiver station controller which controls the second base transceiver station; and a physical channel which connects the first base transceiver station controller with the second base transceiver station controller; wherein a first upstream data packet is transmitted from the mobile station to a codec in the first base transceiver station controller via the first base transceiver station; wherein a second upstream data packet is transmitted from the mobile station to the codec via the second base transceiver station, the second base transceiver station controller, and the physical channel; wherein a first downstream data packet is transmitted from the codec to the mobile station via the first base transceiver station; and wherein a second down stream data packet is transmitted from the codec to the mobile station via the physical channel, the second base transceiver station controller, and the second base transceiver station. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the first base transceiver station controller may comprise a header converter which converts a header of the second upstream data packet which has been used to bring the second upstream data packet toward the first base transceiver station controller to another header which is used to bring the second upstream data packet toward the codec. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the header of the second upstream data packet before the conversion may comprise: an identifier of an interface connected with the physical channel; an identifier of a switch port connected with the physical channel via the interface; and an identifier of the second base transceiver station controller. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the header converter may perform the conversion when the header converter determines that the second upstream data packet comes from a non-local base transceiver station controller on the basis of the identifier of the second base transceiver station controller. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the header of the second upstream data packet after the conversion may comprise: an identifier of the codec; and an identifier of a switch port which is connected with the codec. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the second base transceiver station controller may comprise a header converter which converts a header of the second downstream data packet which has been used to bring the second downstream data packet toward the second base transceiver station controller to another header which is used to bring the second downstream data packet toward the mobile station. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the header of the second downstream data packet before the conversion may comprise: an identifier of an interface connected with the physical channel; an identifier of a switch port connected with the physical channel via the interface; and an identifier of the first base transceiver station controller. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the header converter may perform the conversion when the header converter determines that the second downstream data packet comes from a non-local base transceiver station controller on the basis of the identifier of first base transceiver station controller. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the header of the second downstream data packet after the conversion may comprise: an identifier of an interface connected with the second base transceiver station; and an identifier of a switch port connected with the second base transceiver station via the interface. 
     In the system for performing a soft hand-off between base transceiver stations under control of different base transceiver station controllers, the header of the second downstream data packet after the conversion may further comprise an identifier of the second base transceiver station. 
     These and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of the best mode embodiments thereof, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a conventional hand-off system between CDMA base transceiver station controllers; 
     FIG. 2 is a block diagram showing a soft hand-off system between CDMA base transceiver station controllers according to an embodiment of the present invention; 
     FIG. 3 is a block diagram showing the structure of a header converter according to the embodiment of the present invention; 
     FIG. 4 is a sequence diagram showing a soft hand-off method between CDMA base transceiver station controllers according to the embodiment of the present invention; 
     FIG. 5 is a schematic diagram showing formats of headers of upstream and downstream data packets before and after conversion according to the embodiment of the present invention; and 
     FIG. 6 is a schematic diagram showing a method for header conversion according to the embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred modes of embodiment according to the present invention will be described with reference to the accompanying drawings. 
     Referring to FIG. 2, there is shown MS  101 , BTS 1   201 , BTS 2   301 , BSC 1   401 , BSC 2   501 , and MSC  601 . BTS-INF 1   402  functions as an interface between BTS 1   201  and BSC 1   401 . BTS-INF 1   502  functions as an interface between BTS 2   301  and BSC 2   501 . 
     Header converter (hereinafter, referred to as HC)  404  is a feature of the present invention and converts a header of a packets such as a data packet and a control packet in response to an instruction by control processor (hereinafter, referred to as CP)  417 . HC  504  is similar to HC  404 . Switch (hereinafter, referred to as SW)  405  connects any arbitrary port with another arbitrary port. SW  505  is similar to SW  405 . 
     P 1    406  to P m    407 , P m+1    408  to P q    409 , and P q+1    410  are connection ports which connect SW  405  with other apparatus such as BTS 1   201 , BSC 2   501 , and MSC  601 . P 1    506  to P m    507 , P m+1    508  to P q    509 , and P q+1    510  are similar to P 1    406  to P m    407 , P m+1    408  to P q    409 , and P q+1    410 . 
     MUX 1   411  to MUXk  412  multiplex and demultiplex various data. MUX  511  to MUXk  512  are similar to MUX  411  to MUX  412 . CODEC 1   413  to CODECn  414  are coders/decoders which encode and decode communication data. CODEC 1   513  to CODECn  514  are similar to CODEC 1   413  to CODECn  414 . 
     CCHC  415  is a control channel controller which outputs and inputs control data between BTS 1   201  and BSC 1   401 . CCHC  515  is similar to CCHC  415 . 
     MSC-INF  416  connects BSC 1   401  with MSC  601 . MSC-INF  516  is similar to MSC-INF  416 . CP  417  controls the whole BSC 1   401 . CP  517  is similar to CP  417 . 
     Referring to FIG. 3, B-INF  701  is an interface with BTS-INF 1   402  (or  502 ) to BTS-INFm  403  (or  503 ). HD-CK (header checker)  702  extracts a header from a data packet or a control packet which is supplied from B-INF  701  and supplies the header to CTL (controller)  704 . HD-CK  702  also refers to a BSC-ID (BSC identifier) in the header to determine whether the packet containing the header is supplied from another BSC or a local BSC, and if the packet is supplied from another BSC, HD-CK  702  requests CTL  704  to perform a header conversion. HD-CK  702  supplies the packet without any modification to HD-C (header converter)  703 . 
     If CTL  704  requests HD-C  703  to perform a header conversion, HD-C  703  converts the header of a packet supplied from HD-CK  702  to a header supplied from CTL  704  to output the packet. If CTL  704  does not request HD-C  703  to perform a header conversion, HD-C  703  outputs a packet supplied from HD-CK  702  without a header conversion. 
     CTL  704  writes header conversion information supplied from CP  417  or  517  to Pre-TABLE  706  or Post-TABLE  707 . 
     If HD-CK  702  requests CTL  704  to perform a header conversion, CTL  704  searches pre-TABLE  706  for a header which is the same as the header supplied from HD-CK  702 , and if the search is successful, CTL  704  retrieves an post-conversion header which corresponds to the header which is searched for from Post-TABLE  707 . Then, CTL  704  requests HD-C  703  to perform a header conversion while supplying the retrieved header to HD-C  703 . 
     CTL  704  manages the information for correlating pre-conversion headers and post-conversion headers. The information is supplied from CP  417  or  517 . 
     Pre-TABLE  706  stores pre-conversion headers which are supplied from CP  417  or  517  via CTL  704 . Post-TABLE  707  stores post-conversion headers which are supplied from CP  417  or  517  via CTL  704 . 
     Next, the operation of this embodiment will be explained. 
     Referring to FIG. 2, it is assumed that MS  101  is communicating with a telephone or the like (not shown) via BTS 1   201  while using CODEC 1   413  in BSC 1   401 . On the communication lines are BTS-INF 1   402 , HC  404 , P 1    406 , SW  405 , P m+1    408 , and MUX 1   411 . 
     When MS  101  travels to enter a coverage area of BTS 2   301  which is under control of BSC 2   501  and MS  101  detects that the radio wave from BTS 2   301  becomes strong, MS  101  transmits a soft-hand-off request to BSC 1   401  via BTS 1   201 . When receiving the request, BSC 1   401  starts a control for establishing a communication path between MS  101  and CODEC 1   413  in BSC 1   401  via BTS 2   301  and BSC 2   501 . 
     Next, the above control will be explained with reference to FIGS. 2 and 4. 
     Referring to FIG. 4, CP  417  and CCHC 415  of BSC 1   401  (hereinafter, referred to as CP/CCHC of BSC 1   401 ) receive the soft hand-off request (SHO.REQ) from MS  101  via BTS 1   201  ( 802 ,  803  in FIG.  4 ). Then, CP/CCHC of BSC 1   401  transmits a connection request (hereinafter, referred to as CONN.REQ) to CP  517  and CCHC  515  of BSC 2   501  (hereinafter, referred to as CP/CCHC of BSC 2   501 ) via a physical link to confirm whether a physical link is established (or usable) between BSC 1   401  and BSC 2   504  ( 804 ,  805  in FIG.  4 ). Here, each physical link is a link connected by a cable. The number of physical links varies depending on the number of subscribers. 
     When CP/CCHC of BSC 2   501  receives the CONN.REQ, if the physical link is established (or usable), CP/CCHC of BSC 2   501  transmits a connection acknowledge (hereinafter, referred to as CONN.ACK) to CP/CCHC of BSC 1   401  ( 806 ,  807  in FIG. 4) via a physical link . When CP/CCHC of BSC  1   401  receives the CONN.ACK, it determines that a physical link between BSC 1   401  and BSC 2   501  for soft hand-off is usable. 
     Next, CP/CCHC of BSC 1   401  transmits a channel assignment request (hereinafter, referred to as CH_ASS.REQ) for establishing a communication channel between MS  101  and CODEC 1   413  via BTS 2   301  and BSC 2   501  to CP/CCHC of BSC 2   501  ( 808 ,  809  in FIG. 4) via a physical link. 
     Next, CP/CCHC of BSC 2   501  transfers the CH_ASS.REQ to BTS 2   301  ( 810  in FIG.  4 ). When CP/CCHC of BSC 2   501  receives a channel assignment acknowledge (hereinafter, referred to as CH_ASS.ACK) from BTS  301  ( 811  in FIG.  4 ), CP/CCHC of BSC 2   501  transfers the CH_ASS.ACK to CP/CCHC of BSC 1   401  ( 812 ,  813  in FIG. 4) via a physical link. At this time, CP/CCHC of BSC 1   401  determines that a communication channel between MS  101  and CODEC 1   413  via BTS 2   301  and BSC 2   501  is able to be established. 
     After transferring the CH_ASS.ACK, CP/CCHC of BSC 2   501  transmits a header conversion table write request (hereinafter, referred to as HC_TABLE_WR.REQ) to HC  504  in order to set header conversion information for the communication channel ( 814  in FIG.  4 ). HC  504  writes header  1503  in FIG. 5 to Pre-TABLE  706  and header  1504  in FIG. 5 to Post TABLE  707 . 
     After normally setting the header conversion information, HC  504  transmits a header conversion table write acknowledge (HC_TABLE_WR.ACK) to CP/CCHC of BSC 2   501  ( 815  in FIG.  4 ). 
     Similarly, After receiving the CH_ASS.ACK, CP/CCHC of BSC 1   401  transmits a HC_TABLE_WR.REQ to HC  404  in order to set header conversion information for the communication channel ( 816  in FIG.  4 ). HC  404  writes header  1501  in FIG. 5 to Pre-TABLE  706  and header  1502  in FIG. 5 to Post TABLE  707 . 
     After normally setting the header conversion information, HC  404  transmits a HC_TABLE_WR.ACK to CP/CCHC of BSC 1   401  ( 817  in FIG.  4 ). 
     After completing the setting of the header conversion information, CP/CCHC of BSC 1   401  transmits a soft hand-off acknowledge (SHO.ACK) to MS  101  via BTS 1   201  to permit MS  101  to start a communication via BTS 2   301  ( 818 ,  819  in FIG.  4 ). 
     After receiving the SHO.ACK, MS  101  starts a communication on the established communication channel via BTS 2   301  ( 820  in FIG.  4 ). 
     The above-explained control realizes simultaneous communications (or soft hand-off state) between MS  101  and CODEC 1   413  via BTS 1   201  under control of BSC 1   401  and via BTS 2   301  under control BSC 2   501 . 
     Here, it is necessary not only to establish a physical link for soft hand-off between BSC 1   401  and BSC 2   501  but also to perform header conversions to realize the above-explained control. 
     The header conversions are performed in HCs  404  and  504  on the basis of the header conversion information which CPs  417  and  517  set to HCs  404  and  504 , respectively. Referring to FIG. 4, the header conversions are performed in places marked with ∘, that is, in places represented by  829  to  834 . 
     In FIG. 4, header conversions  829  to  832  are performed before the header conversion information is dynamically set. Header conversions  829  to  832  do not use a communication channel but a control channel. 
     The control channel does not vary depending on each call as a communication channel but is fixed. Therefore, the header conversion information for the control channel is prestored in CP  417  in BSC 1   401  and CP  517  in BSC 2   501 . 
     Therefore, when BSC 1   401  and BSC 2   501  are reset, CP  417  and  517  automatically set the header conversion information for the control channel to HC  404  and  504 , respectively. Thus, the CONN.REQ, the CONN.ACK, the CH_ASS.REQ, and the CH_ASS.ACK are able to be transmitted between BSC 1   401  and BSC 2   501  with header conversions. 
     On the other hand, because a communication channel varies depending on a situations with respect to idles of CODECs at the time when an MS requests a soft hand-off, CP  417  and  517  set header conversion information to HC  404  and  504  every time a MS requests a soft hand-off, respectively. 
     Next, the route of a data packet when a soft hand off between BSCs  401  and  501  is performed will be explained with reference to FIGS. 2,  4 , and  5 . 
     As a result of the above-explained control, MS  101  is in a state of a soft hand-off (or a state of a simultaneous communication) between BSC 1   401  and BSC 2   501 . 
     First, an upstream communication from MS  101  to CODEC 1   413  via BTS 2   301  and BSC 2   501  will be explained. 
     Header information described in a header of an upstream data packet which is transmitted from MS  101  to BSC 2   501  is as represented by reference  1501  in FIG.  5 . Header  1501  is added to the upstream data packet in BTS 2   301 . 
     The upstream data packet is transmitted to BTS-INF 1   502  without using header information  1501 . 
     Because BTS-INFs are mere interfaces (or data relay apparatuses), BTS-INFs do not perform monitoring/discrimination with respect to data packets and merely receive data packets to transmit them. Therefore, BTS-INF 1   502  receives the upstream data packet to transmit it to HC  504 . 
     In general, HCs  404  and  504  determines whether a BSC-ID described in a header of an upstream packet is of a local BSC or of another (or non-local) BSC and if the BSC-ID is of local BSC, HCs  404  and  504  do not convert the header and merely transfers the upstream packet to a port which corresponds to a BTS-INF from which the upstream packet comes. The port which corresponds to a certain BTS-INF is determined uniquely because one or more BTS-INF corresponds to a single port. Therefore, HC  504  does not perform a header conversion and transmits the upstream data packet without any modification to P 1    506 . 
     SW  505  switches the upstream data packet to P m  in accordance with the description of “P m ”  1506  in header  1501 . The upstream data packet outputted from P m  is transmitted to HC  504  again. 
     In general, HCs  404  and  504  do not perform monitoring/discrimination for a downstream packet and merely transmits a data packet received from a port to a BTS-INF which is designated by a description with respect to BTS-INF in a header. Therefore, HC  504  does not perform discrimination of BSC-ID  1505  of the upstream data packet (but temporarily a downstream data packet) and transmits the downstream data packet to BTS-INFm  503  in accordance with description of “BTS-INF m ”  1507  in header  1501 . 
     The upstream data packet transmitted from BTS-INF m    503  reaches HC  404  via BTS-INF m    403 . 
     In general, HCs  404  and  504  determines whether a BSC-ID described in a header of an upstream packet is of a local BSC or of another (or non-local) BSC and if the BSC-ID is of another (or non-local) BSC, HCs  404  and  504  convert the header and transfers the upstream packet to a port which corresponds to a BTS-INF from which the upstream packet comes. Therefore, HC  404  refers to BSC-ID  1505  and determines that the upstream data packet comes from BSC 2   501 . Then, HC  404  converts header  1501  of the upstream data packet to header  1502  using the information in CTL  704 , Pre-TABLE  706 , and Post-TABLE  707  designated by HC_TABLE_WR.REQ  816 . This conversion is represented by reference  833  in FIG.  4 . 
     HC  404  transmits the converted upstream data packet to P m    407  which corresponds to BTS-INFm  403 . SW  405  switches the converted upstream data packet to P m+1  in accordance with the description of “P m+1 ”  1508  in header  1502 . 
     The converted upstream data packet outputted from P m+1  is supplied to MUX 1   411 . MUX 1   411  transmits the converted upstream data packet to CODEC 1   413  in accordance with the description of “CODEC 1 ”  1509  in header  1502 . 
     CH-IDs  1510 ,  1511 ,  1512 , and  1513  are channel identifiers for discrimination as to whether the packet is a data packet, a control packet, or a broadcast packet. 
     As to an upstream communication from MS  101  to CODEC 1   413  via BTS 1   201 , header  1502  is added to an upstream data packet in BTS 1   201 . 
     Next, a downstream communication from CODEC 1   413  to MS  101  via BSC 2   501  and BTS 2   301  will be explained. 
     Header information described in a header of a downstream data packet which is transmitted from CODEC 1   413  is as represented by reference  1503  in FIG.  5 . The downstream data packet is transmitted to P m    407  in accordance with the description of “P m ”  1514  and BTS-INFm  403  in accordance with the description of “BTS-INFm”  1515  and reaches HC  504 . 
     HC  504  converts header  1503  of the downstream data packet (but temporarily a upstream data packet) to header  1504  using the information in CTL  704 , Pre-TABLE  706 , and Post-TABLE  707  designated by HC_TABLE_WR.REQ  814  because there is a description of “BSC 1 ”  1516  as BSC-ID indicating that the downstream data packet (but temporally an upstream data packet) comes from another (or non-local) BSC. This conversion is represented by reference  834  in FIG.  4 . 
     HC  504  transmits the converted downstream data packet to P m    507  which corresponds to BTS-INFm  503 . SW  505  switches the converted downstream data packet to P 1  in accordance with the description of “P 1 ”  1517  in header  1504 . 
     The converted downstream data packet is supplied to HC  504  again. HC  504  does not convert the header of the converted downstream data packet and transmits the converted downstream data packet to BTS-INF 1   502  in accordance with the description of “BTS-INF 1 ”  1518 . Then the converted downstream data packet is transmitted to MS  101  via BTS 2   301 . 
     As to an downstream communication from CODEC 1   413  to MS  101  via BTS 1   201 , a header in which “P 1 ”, “BTS-INF 1 ”, “BTS 1 ” and “CH-ID” are described is added to a downstream data packet from the first. 
     Next, the method for converting a header will be explained with reference to FIGS. 3 and 6. 
     In FIG. 6, the header before conversion is represented by A 5  and the header after conversion is represented by B 5 . 
     A packet received by BTS-INF is supplied to B-INF  701 . B-INF  701  supplies the packet without any modification to HD-CK  702 . 
     HD-CK  702  extracts header A 5  from the packet to supply the extracted header A 5  to CTL  704  as shown in FIG.  6 . 
     Next, HD-CK  702  refers to a BSC-ID in the extracted header A 5 . If the BSC-ID is of another (or non-local) BSC, HD-CK  702  requests CTL  704  to perform a header conversion. On the other hand, if the BSC-ID is of a local BSC, HD-CK  702  does not request CTL  704  to perform a header conversion. 
     When requested to perform the header conversion, CTL  704  searches Pre-TABLE  706  for header A 5 . Pre-TABLE  706  stores various headers which CP  417  or  517  designate as headers subjected to header conversions. The storing such headers to Pre-TABLE  706  is performed by CTL  704  in accordance with an instruction by CP  417  or  517 . 
     If Pre-TABLE  706  has been stored header A 5 , CTL  704  retrieves post-conversion header B 5  which corresponds to header A 5  from Post-TABLE  707 . Post-TABLE  707  stores various headers which CP  417  or  517  designate as headers after conversions. The storing such headers to Post TABLE  707  is performed by CTL  704  in accordance with an instruction by CP  417  or  517 . 
     Correlation between headers stored in Pre-TABLE  706  and headers stored in Post-TABLE  707  is held by CTL  704 . Such correlation is designated by HC_TABLE_WR.REQ  816  or  814  from CP  417  or  517 . 
     CTL  704  supplies the retrieved header B 5  to HD-C  703  while requesting HD-C  703  to perform a header conversion. 
     When requested to perform a header conversion, HD-C  703  replaces original header AS to header B 5  which is supplied from CTL  704  to supply the converted packet to SW-INF  705 . 
     SW-INF  705  transmits the converted packet externally. 
     In the above embodiment, a header is modified to newly include an area exclusive for a BSC-ID used for determining whether to perform a header conversion. However, such an exclusive area is not a must. Alternatively, unused values of a CH-ID may be used for identifying BSC. For example, if valid values of a CH-ID consisting of 3 bits are 00H to 02H as shown below, the values of a CH-ID which may be used for identifying a BSC are 03H to 07H. The use of CH-ID for identifying a BSC may prevent change of the header format. 
     
       
         
               
               
             
           
               
                   
               
               
                 CH-ID 
                 type of channel 
               
               
                   
               
             
             
               
                 00H 
                 broadcast channel 
               
               
                 01H 
                 data channel 
               
               
                 02H 
                 control channel 
               
               
                 03H - 07H 
                 not used 
               
               
                   
               
             
          
         
       
     
     In the above embodiment, a new physical link is established between BSCs for a soft hand-off between BSCs. Alternatively, a link between a BSC and a MSC may realize soft hand-off between BSCs without newly establishing a physical link between BSCs. 
     Although the present invention has been shown and explained with respect to the best mode embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.