Patent Publication Number: US-6993359-B1

Title: Method and apparatus for inter-cell handover in wireless networks using multiple protocols

Description:
CROSS REFERENCE 
   Title: METHOD AND APPARATUS FOR INTEGRATED WIRELESS COMMUNICATIONS IN PRIVATE AND PUBLIC NETWORK ENVIRONMENTS 
   Inventors: Ian Leslie Sayers, Paul Jan Long, Sheausong Yang 
   Application SC/File Ser. No. 09/188,856, now U.S. Pat. No. 6,539,237 
   Filing Date: Nov. 9, 1998 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a method and apparatus that provides for wireless calls in private network environments and in public network environments. More particularly, this invention relates to inter-cell handover in wireless networks. 
   Conventional Cellular Systems 
   Present day cellular mobile telephone systems provide for a large and increasing demand for mobile services. Cellular systems “reuse” frequency within a group of cells to provide wireless two-way radio frequency (RF) communication to large numbers of users. Each cell covers a small geographic area and collectively a group of adjacent cells covers a larger geographic region. Each cell has a fraction of the total amount of RF spectrum available to support cellular users. Cells are of different sizes (for example, macro-cell or micro-cell) and are generally fixed in capacity. The actual shapes and sizes of cells are complex functions of the terrain, the man-made environment, the quality of communication and the user capacity required. Cells are connected to each other via land lines or microwave links and to the public-switched telephone network (PSTN) through telephone switches that are adapted for mobile communication. The switches provide for the handover of users from cell to cell and thus typically from frequency to frequency as mobile users move between cells. 
   In conventional cellular systems, each cell has a base station with RF transmitters and RF receivers co-sited for transmitting and receiving communications to and from cellular users in the cell. The base station employs forward RF frequency bands (carriers) to transmit forward channel communications to users and employs reverse RF carriers to receive reverse channel communications from users in the cell. 
   The forward and reverse channel communications use separate frequency bands so that simultaneous transmissions in both directions are possible. This operation is referred to as frequency division duplex (FDD) signaling. In time division duplex (TDD) signaling, the forward and reverse channels take turns using the same frequency band. 
   The base station in addition to providing RF connectivity to users also provides connectivity to a Mobile Services Switching Center (MSC). In a typical cellular system, one or more MSCs will be used over the covered region. Each MSC can service a number of base stations and associated cells in the cellular system and supports switching operations for routing calls between other systems (such as the PSTN) and the cellular system or for routing calls within the cellular system. 
   Base stations are typically controlled from the MSC by means of a Base Station Controller (BSC). The BSC assigns RF carriers to support calls, coordinates the handover of mobile users between base stations, and monitors and reports on the status of base stations. The number of base stations controlled by a single MSC depends upon the traffic at each base station, the cost of interconnection between the MSC and the base stations, the topology of the service area and other similar factors. 
   A handover between base stations occurs, for example, when a mobile user travels from a first cell to an adjacent second cell. Handovers also occur to relieve the load on a base station that has exhausted its traffic-carrying capacity or where poor quality communication is occurring. The handover is a communication transfer for a particular user from the base station for the first cell to the base station for the second cell. During the handover in conventional cellular systems, there may be a transfer period of time during which the forward and reverse communications to the mobile user are severed with the base station for the first cell and are not established with the second cell. 
   In time division multiple access (TDMA) systems, multiple channels are defined using the same carrier. The separate channels each transmit discontinuously in bursts which are timed so as not to interfere with the other channels on that carrier. Typically, TDMA implementations also employ FDMA techniques. Carriers are reused from cell to cell in an FDMA scheme, and on each carrier, several channels are defined using TDMA methods. The Global System for Mobile Communications (GSM), PCS 1900, IS-136, and PDC standards are examples of TDMA methods in current use. 
   The present specification uses a GSM system for purposes of explanation but the present invention applies to any wireless system protocol. 
   GSM Cellular Systems 
   The GSM system architecture is described, for example, in detail by M. Mouly and M.-B. Pautet, The GSM System for Mobile Communications, 1992 and Mouly and M.-B. Pautet,  GSM Protocol Architecture: Radio Sub - system Signaling , IEEE 41st Vehicular Technology Conference, 1991. The following sections highlight some unique aspects of GSM systems. 
   The GSM system provides many advanced services, including: ISDN compatible supplementary services; Global roaming among GSM networks and other network types; advanced packet data services. The term ISDN includes narrow band (N-ISDN) and broad band (B-ISDN) where B-ISDN encompasses ATM and Frame Relay. 
   GSM System Architecture 
   There is a very comprehensive set of GSM Specifications which define the three major components of any GSM network, namely, the Mobile Station (MS), Base Station Sub-System (BSS) and the Network Sub-System (NSS). 
   Base Station Subsystem (BSS) 
   The Base Station Subsystem (BSS) is subdivided into two main entities, the Base Transceiver Station (BTS) and the Base Station Controller (BSC). The BTS includes the radio transceivers that define the radio cell and supports the radio (Um) interface link to the mobile station. The BTS further supports the defined channel coding, encryption and speech coding functions. The BTS interfaces to the BSC via the Abis-interface. 
   The Base Station Controller (BSC) manages the radio resources of multiple BTSs. The BSC controls all of the functions related to the radio network, including the allocation and release of radio resources and control of radio interface handovers. The BSC interfaces to the MSC via the A-interface. 
   Network Subsystem 
   The network subsystem (NSS) comprises four components these are, the Mobile Services Switching Center (MSC), Home Location Register (HLR), Visitor Location Register (VLR), Authentication Center (AUC) and the Equipment Identity Register (EIR). 
   The main part of the network subsystem (NSS) is provided by the Mobile Services Switching Center (MSC). The MSC provides the ability to track the mobile user, switch calls to/from the user to the PSTN/ISDN/PLMN (public land mobile network) and maintain contact with the mobile user via radio handovers. 
   The GSM PLMN (GSM public land mobile network) contains two database functions related to the mobility of the user these are the Home Location Register (HLR) and the Visited Location Register (VLR). 
   The Home Location Register (HLR) is used by the operator to maintain data on all their subscribers. The subscriber data includes both fixed data, such as International Mobile Subscriber Identity (IMSI), subscriber MSISDN number and selected supplementary services, and dynamic data such as whereabouts of the mobile user and current settings for any supplementary services. Whenever a mobile users roams into a new Visitor Location Register (VLR) area the HLR downloads the subscriber data to the VLR The HLR is also required to deal with mobile terminating calls by routing the call to the correct VLR for further processing. 
   The Visitor Location Register (VLR) is used as a local cache to store the subscriber data near the current location of the mobile user. Once the VLR has downloaded the subscriber data the mobile user can begin to use the services provided by the network. The process of downloading the user data and establishing a presence in a particular location is called roaming. 
   In order to prevent fraudulent use of the network, the GSM PLMN also contains two further databases the Authentication Center (AUC) and the Equipment Identity Register (EIR). 
   The Authentication Center (AUC) is a maintained in a secure environment since it contains the network authentication algorithms. The network uses this database to obtain data that is used to “challenge” the mobile user when they make an access to the network. The AUC uses two algorithms known as A3 and A8, which are also stored in the Subscriber Identity Module (SIM) of the user. The A3 algorithm is used to authenticate the user by the familiar challenge response mechanism. The A8 algorithm is used to generate the required key for the radio interface encryption algorithm know as A5. Generally the A3 and A8 algorithms are developed by the network operators. 
   The Equipment Identity Register (EIR) contains a list of all the valid International Mobile Equipment Identity (IMEI) values. Using the unique IMEI value associated with all mobiles it is possible to restrict the use of specific mobiles. This database is used to prevent the use of stolen or misbehaving mobile stations. 
   Operations and Maintenance 
   Associated with the BSS and NSS equipment are Operations and Maintenance Centers, OMC-R and OMC-S, respectively. The OMC-R and OMC-S provide the following standard operations and maintenance control functions for the GSM BSS and NSS: 
   Configuration Management 
   Fault management 
   Test Management 
   Performance Management 
   Security Management 
   Account Management 
   Other functions may be available depending upon the BSS or NSS manufacturer. In addition, the OMC-S may also be required to perform database or user management functions on the HLR and VLR. 
   Basic Services Provided by GSM 
   GSM was designed to be a feature rich mobile services with most services based upon ISDN principles. In basic terms the GSM provides a basic set of services which can be enhanced by the use of supplementary services. The Basic Services include:
         Speech, the most basic service   Short Message, a two way messaging service   Group 3 FAX, this services allows connection to Group 3 FAX machines   Cell Broadcast, this service allows messages to be broadcast to the mobile stations.       

   The Bearer Services include:
         Asynchronous Data 300-14400 bps, allows access to normal V-Series Modems   Synchronous Data 300-14400 bps, allows access to CSPDNs   General Packet Radio Services 9600-170000 bps, a packet services allowing seamless access to the internet.       

   The following GSM supplementary services are currently available:
         Call Forwarding   Call Barring Services   Call Transfer   Conference Calling   Call Wait and Call Hold   Calling Line Identification   Call Completion to a Busy Subscriber       

   In private wireless networks, Mobile station access the network through the private base stations (P-BTS) using standard GSM protocols in the same way as they access the public wireless networks. But these private base stations are directly connected to a private LAN and employ Voice over IP technologies such as H.323 to route calls among Mobile station and between Mobile station and other PSTN and PBX terminals. In such private networks, typical inter-cell handover methods in a traditional public GSM network cannot be employed for handovers among private cells. Also, handovers between private cells and public cells requires new techniques for communication and handling between the MAP signaling based public cellular networks and voice over IP (VoIP) signaling based private cellular networks. 
   In accordance with the above background, it is the object of the present invention to provide wireless systems having the capability to have handover among cells in public and private networks. 
   SUMMARY OF THE INVENTION 
   The present invention is a communication system formed by a private wireless network that can be used with public wireless networks using a public wireless protocol, such as GSM, and typically includes public networks, such as PSTN, ISDN and the Internet, using a wired-packet protocol, such as IP. The private network also typically includes a local area network (LAN) and the private network typically connects to the public networks using a wired-packet protocol, such as IP. 
   In the present invention, the public and private wireless networks operate with the same public wireless protocol, such as GSM, and the private wireless network additionally operates with a wired-packet protocol, such as IP. In this environment, multiple wireless cells are present and inter-cell handovers employ multiple protocols including the wired-packet protocol. 
   The private wireless network uses private base stations (P-BTS) which include software for a wireless protocol, such as GSM, and include software for private network operation with a wired protocol, such as IP. 
   The communication system permits users to operate freely in both public and private wireless networks using standard mobile stations while achieving high private network data rates. The communication system typically uses normal wireless handsets or other mobile or fixed stations without need for any modifications. 
   The private base stations (P-BTS) in one embodiment are directly connected to a private LAN and thereby enable standard wireless stations to make and receive calls over the LAN. Also, the range of calls, using standard Internet protocols, extends between LANs and between different corporations over the Internet without requiring the support of a switch (e.g. MSC). The wireless stations can freely roam between the public wireless network and the private wireless network and a single telephone number can be assigned to a mobile station for use in both the public and the private wireless networks. 
   P-BTSs along with one or more gatekeepers and one or more gateways and a PLMN signaling Interworking Unit (IWU) together provide the same level of functionality to GSM Mobile station as does a GSM public wireless network (that includes a Network Subsystem and one or more Base Station Subsystems). 
   The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description in conjunction with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram representation of a communication system including a public wireless network, other public networks such as PSTN, ISDN and the Internet and including a private network. 
       FIG. 2  depicts further details of the private network in the communication system of FIG.  1 . 
       FIG. 4  depicts the architecture of a public land mobile network interworking unit (PLMN IWU) used in the private wireless network of FIG.  1  and  FIG. 2  to communicate with the public land mobile network (PLMN). 
       FIG. 3  depicts a coverage area serviced by both public (MSCs) and private (P-BTS) networks in which intercell handovers occur. 
       FIG. 5  depicts primary interface protocol stacks for wireless GSM base with added private network (P-BTS) software. 
       FIG. 6  depicts a call processing plane of software modules for IP-Based private wireless base stations (P-BTS). 
       FIG. 7  depicts a wireless system including a public wireless system and a private wireless system with a MS that moves throughout the wireless system to locations requiring different handover operations. 
       FIG. 8  depicts the call flows of a handover of an MS from the a private network P-BTS to a public network MSC/BSS via the PLMN IWU. 
       FIG. 9  depicts the call flows of a back handover (handback) of an MS from a public network MSC/BSS to a private network P-BTS via the PLMN IWU where the MS previously originated in the private network P-BTS. 
       FIG. 10  depicts the call flows of a subsequent handover of an MS via the PLMN IWU from one MSC/BSS to another MSC/BSS in the public network where the MS originated with a P-BTS in the private network. 
       FIG. 11  depicts the call flows of a handover of an MS from the public network MSC/BSS to a private network P-BTS via the PLMN IWU. 
       FIG. 12  depicts the call flows of a back handover (handback) of an MS from a private network P-BTS to a public network MSC/BSS via the PLMN IWU where the MS originated with the public network MSC/BSS. 
       FIG. 13  depicts the call flows of a handover of an MS via the PLMN IWU from an old target P-BTS in the private network to a new MSC/BSS in the public network where the MS originated with an old MSC/BSS in the public network. 
       FIG. 14  depicts the call flows of one method of implementing an anchor P-BTS to target P-BTS handover. 
       FIG. 15  depicts the handover call flows of a MS handover between an anchor P-BTS and a target P-BTS (Anchor-to-Target 1 ). 
       FIG. 16  depicts the anchor P-BTS handover internal call flows of the anchor P-BTS in the FIG. call flow (Anchor-to-Target 1 ). 
       FIG. 17  depicts a continuation of the anchor P-BTS handover internal call flows of  FIG. 16  (Anchor-to-Target 1 ). 
       FIG. 18  depicts the handover target P-BTS internal call flows of the target P-BTS in the  FIG. 15  call flow (Anchor-to-Target 1 ). 
       FIG. 19  depicts a continuation of the target P-BTS handover internal call flows of the  FIG. 18  call flow (Anchor-to-Target 1 ). 
       FIG. 20  depicts the back handover (handback) call flows of a MS subsequent back handover after a handover of the  FIG. 15  call flow between an anchor P-BTS and a target P-BTS (Target 1 -to-Anchor). 
       FIG. 21  depicts the anchor P-BTS back handover (handback) internal call flows of the anchor P-BTS in  FIG. 20  (Target 1 -to-Anchor). 
       FIG. 22  depicts a continuation of the anchor P-BTS back handover (handback) internal call flows of  FIG. 21  (Target 1 -to-Anchor). 
       FIG. 23  depicts the target P-BTS back handover (handback) internal call flows of the  FIG. 21  back handover (Target 1 -to-Anchor) and also depicts the target P-BTS handover to third where the handover is to a third target P-BTS (Target 1 -to-Target 2 ). 
       FIG. 24  depicts a continuation of the target P-BTS back handover (handback) internal call flows of  FIG. 23  (Target 1 -to-Anchor). 
       FIG. 25  depicts the handover to third call flows of a MS handover between an old target P-BTS and a new target P-BTS (Target 1 -to-target 2 ). 
       FIG. 26  depicts a continuation of the MS handover to third of  FIG. 25  (Target 1 -to-Target 2 ). 
       FIG. 27  depicts the anchor P-BTS handover internal call flows of the anchor P-BTS of the FIG. handover to third (Target 1 -to-Target 2 ). 
       FIG. 28  depicts a continuation of the anchor P-BTS handover internal call flows of  FIG. 27  handover to third (Target 1 -to-Target 2 ). 
       FIG. 29  depicts a continuation of the target P-BTS handover to third internal call flows where the initial internal call flows for the target P-BTS are the same as the handback call flows of  FIG. 23  (Target 1 -to-Target 2 ). 
   

   DETAILED DESCRIPTION 
   Communication System—FIG.  1  and  FIG. 2   
   In  FIG. 1 , the communication system  10  includes a public wireless network  15 , public networks  8  (such as PSTN, ISDN and the Internet) and private networks  14 . The public wireless network  15  includes the ability to communicate, in a conventional manner, with conventional wireless mobile stations  4 . The private networks  14  function to communicate with the conventional mobile stations (MS)  4  and provide additional private network capabilities not provided by the public wireless network  15 . 
   The public wireless network  15  of  FIG. 1 , sometimes called the public land mobile network (PLMN), includes the mobile stations (MS)  4 , Base Station Sub-System (BSS)  5  and the Network Sub-System (NSS)  6 . The Base Station Subsystem (BSS)  5  is composed of the Base Transceiver Stations (BTSs)  12  and the Base Station Controller (BSC)  16 . Each of the BTSs  12  includes a radio transceiver that defines the radio boundary of a cell  11  and handles the radio (Um) interface protocols with the mobile stations  4 . 
   The cells  11  in the wireless public network  15  of  FIG. 1  each exist over a different area and together the cells  11  collectively exist over a larger area designated as a region  111 . Each cell  11  in the region  111  uses frequencies or other properties that are isolated from the frequencies or other properties of other cells in the region. When mobile stations  4  travel from one of the cells  11  to another one of the cells  11 , a handover occurs. 
   The private networks  14  of  FIG. 1  include private base stations (P-BTSs)  27  within the private wireless networks  22  for communications with mobile stations  4  located within the domain of the private networks  14 . The private base stations (P-BTSs)  27  function in private regions formed of private cells (see private cells  411  of  FIG. 3 ) within the domain of the private networks  14  of FIG.  1 . The private cells  411  typically cover a portion of the area covered by one or more of the cells  11  of the public wireless network  15  of FIG.  1 . Typically, the allocation of frequency spectrum in different public and private regions is under governmental control and frequency spectrum is allocated to different entities in different regions and different countries. The owner of the rights to particular frequencies in a region, including regions for public wireless network  15  and private wireless networks  22 , controls the allocation of frequencies among public cells  11  of FIG.  1  and the private cells  411  (see FIG.  3 ). 
   The Base Station Controller (BSC)  16  manages the radio resources of one or more BTSs  12  across an Abis interface. The BSC  16  controls the radio network, including allocation of radio time slots and frequencies to mobile stations  4 , release of resources, interpretation of measurement results and control of radio interface handovers. The BSC  16  interfaces to the NSS  6  via an A-interface to MSC  17 .The Network Subsystem (NSS)  6  includes the Mobile Services Switching Center (MSC)  17  that provides, in a conventional system, the functions required to switch calls to/from the mobile stations  4  and the fixed public networks  8  (including PSTN and ISDN). In addition, the MSC  17  also provides the functions needed to track and maintain communication with mobile stations  4  and these functions include registration, authentication, location updating, MSC handovers, and call routing to roaming mobile stations  4 . The GSM/TDMA/CDMA cellular system employs a Home Location Register (HLR)  19  and a Visitor Location Register (VLR)  13 , an Authentication Center (AUC) secure database  2  and an Equipment Identity Register (EIR)  3 . The Operations and Maintenance Center includes the OMC-R  7  and the OMC-S  9 . 
   In  FIG. 1 , private networks  14  include the private wireless networks  22  (including private wireless networks  22 - 1 , . . . ,  22 -W as shown in FIG.  2 ), private wired networks  24 , including local area networks (LANs,  24 - 1 , . . . ,  24 -L, as shown in FIG.  2 ), and connection units  29  (including connection units  29 - 1 , . . . ,  29 -I as shown in FIG.  2 ). The private networks  14  can include wide area networks (WAN) and any other type of network presently or hereafter available. As shown in  FIG. 2 , the connection units  29  of  FIG. 1  include, in one embodiment, hubs  23  for interconnecting the private wireless networks  22  and the LANs  24  and for connecting the private networks  14  to the public networks  8 . As shown in  FIG. 2 , a typical hub  23  connects to a router  33  that directs calls among the public network facilities including the ISDN  28 , the PSTN  26 , the Internet  25  and the private networks  14 . The private networks  14  use the same protocol as the Internet  25  and connects directly without need for a separate gateway. The connection units  29  include, as shown in  FIG. 2 , gateways  42 - 1 ,  42 - 2 , . . . ,  42 -G for connecting the ISDN  28  and the PSTN  26  which use different protocols than the private networks  14 . 
   In FIG.  1 ,the private wireless networks  22  include the wireless capabilities of the public wireless network  15  of FIG.  1 . In addition, the private wireless networks  14  are suitable for operating with advanced technologies that are not generally available publicly. Current advanced technologies operate with rates of 384 kb/s and are approaching rates of 2 Mb/s for W-CDMA. In  FIG. 1 , wireless communications between the public BTSs  12  and mobile stations  4  operate with a wireless protocol such as GSM/TDMA/CDMA. In  FIG. 1 , wireless communications between the private P-BTSs  27  and mobile stations  4  for convenience and compatibility operate with the same wireless protocol (such as GSM/TDMA/CDMA) as used by the public BTSs  12  in the public wireless network  15 . 
   In  FIG. 1 , the private wired networks  24  are typically local area networks (LANs) operating with a wired-packet protocol such as IP. 
   The private wireless networks  22  in  FIG. 1  do not require the internal support of a circuit switch from the public networks and therefore, the private networks  14  in the  FIG. 1  system can easily expand to accommodate new user requirements under control of the owners of the private networks  14 . 
   In the private networks  14  of  FIG. 1 , the mobile stations  4  are typically unmodified, conventional wireless mobile station handsets like those widely used in conventional public wireless networks and therefore the mobile stations  4  can freely move between the public wireless network  15  of FIG.  1  and the private wireless networks  22  of  FIG. 1  without restriction. Because of this free movement capability, only a single number is required for each mobile station  4  for both private wireless network communications and for public wireless network communications. 
   The private wireless networks  22  of  FIG. 1  have P-BTSs  27  with corresponding private cells (P cells)  411  (see  FIG. 3 ) in the private wireless domain. The public wireless network  15  of  FIG. 1  has BTSs  12  with corresponding public cells  11  in the public wireless domain. The allocation of frequencies among the public wireless network cells and the private network cells is determined by agreement of the owners of the public wireless network  15  and the private networks  14 . 
   The private wireless networks  22  of  FIG. 1  each have an interworking unit (IWU)  39  that facilitates the inter working of different protocols that coact in processing calls from one wireless network to another. The private wireless networks  22  of  FIG. 1  have gatekeepers  41  that function to correlate addresses that are for the same mobile stations but which are presented in different protocols. 
   Interconnected Public Wireless Network and Private Wireless Network— FIG. 2   
   In  FIG. 2 , private networks  14  include private networks  14 - 1 , . . . ,  14 -N. Private network  14 - 1  is typical and includes the private wireless networks  22  (including private wireless networks  22 - 1 , . . . ,  22 -W), local area networks (LANs)  24  (including LANs  24 - 1 , . . . ,  24 -L), and connection units  29  (including connection units  29 - 1 , . . . ,  29 -I). The private networks  14  can include wide area networks (WAN) and any other type of network presently or hereafter available. The connection unit  29  includes a hub  23  for interconnecting the private wireless networks  22  and the LANs  24  and for connecting the private network  14 - 1  to the public networks  8 . The hub  23  connects to the router  33  that directs calls among the public network facilities including the ISDN  28 , . . . , PSTN  26  and the Internet  24  and the private networks  14 . The private networks  14  use the same protocol as the Internet  25  and connect directly without need for a separate gateway. The connection unit  29  includes gateways  42 - 1 , . . . ,  42 -G for connecting the ISDN  28 , . . . , PSTN  26  which use different protocols than the private networks  14 . 
   In  FIG. 2 , the private wireless networks  22  include the wireless capabilities of the public wireless network  15  of FIG.  1 . In  FIG. 2 , wireless communications between the private P-BTSs  27  and mobile stations  4  for convenience and comparability operate with the same wireless protocol (such as GSM) as used by the public BTSs  12  in the public wireless network  15 . 
   In  FIG. 2 , the local area networks (LANs)  24  are private wired networks operating with a wired-packet protocol such as IP. LAN  24 - 1  is typical and includes, for example, a server  25  and LAN terminals  21  (including terminals  21 - 1 , . . . ,  21 -T). Terminals  21 - 1 , . . . ,  21 -T communicate with each other and with the public networks  8  through connection unit  29  using the wired-packet protocol. 
   In  FIG. 2 , the P-BTSs  27 - 1 , . . . ,  27 -P are associated with protocol converters  28 - 1 , . . . ,  28 -P, respectively, that connect P-BTSs  27 - 1 , . . . ,  27 -P to connection unit  23  using the private network protocol used by the LANs  24  and the router  23 . Therefore, the mobile stations  4  communicating through the P-BTSs  27  in the private networks  14  have access to the terminals  21  in LANs  24  and have access to the public networks  8 . 
   In  FIG. 2 , the wireless P-BTS  27  directly connect the mobile stations  4  through router  33  to other facilities in private networks  14  and thereby permit, for example, the mobile stations  4  to send and receive calls to and from the terminals  21  in the LAN networks  24 . Furthermore, the range of calls from and to mobile stations  4  in the private wireless network  22 , using standard Internet protocols (IP), extends over the Internet in public networks  8  to any Internet facility such as different LANs and different corporations in different regions or countries. 
   The private wireless networks  22  in  FIG. 2  do not require the internal support of a circuit switch (for example, an MSC) from the public networks and therefore, the private networks  14  in the  FIG. 2  system can easily grow to accommodate new user requirements under control of the owners of the private networks  14 . 
   In the private networks  14  of  FIG. 2 , the mobile stations  4  are typically unmodified, conventional wireless mobile station handsets like those widely used in conventional public wireless networks and therefore the mobile stations  4  can freely move between the public wireless network  15  of FIG.  1  and the private wireless networks  22  of  FIG. 2  without restriction. Because of this free movement capability, only a single number is required for each mobile station  4  for both private wireless network communications and for public wireless network communications. 
   The private wireless networks  22  of  FIG. 2  have P-BTSs  27 - 1 , . . . ,  27 -P which operate in the private cells  411  (See FIG.  3 ). The allocation of frequencies among the public wireless network cells  11  and the private network cells  411  is determined by agreement of the owners of the public wireless network and the private networks  14 . 
   In order to allow users to roam freely between the public wireless network  15  and private wireless networks  22 , a PLMN interworking unit (PLMN IWU)  39 - 1  is provided. The PLMN IWU  39 - 1  connects to the Private Wireless Networks, Gatekeeper  41  and the PLMN  15 . The PLMN TWU  39 - 1  can be connected to the H.323 Gatekeeper database  43  by a number of means, however in this example, the IWU is connected via an IP link. The PLMN IWU  39 - 1  is connected to the PLMN via a Signaling System 7 (SS7) link that is running Message Transfer Part (MTP), Signaling Connection Control Part (SCCP), Transactions Control Application Part (TCAP) and the Mobile Application Part (MAP). The PLMN IWU  39 - 1  converts between the signaling protocols found in the Private Network  22 - 1  which are based upon IP and the PLMN which is based up SS7. 
   In  FIG. 2 , the gatekeeper  41  includes a local database (see data base  43  in  FIG. 3 ) which communicates via IP providing local user authentication, a local client for communicating with a remote protocol gateway (gateway  42  provides remote IP-to-SS7 conversion) through cell router  34 , and a local interface module which communicates over IP to the PLMN IWU  39 - 1 . 
   The interworking unit (IWU)  39 , when the IWU is a Public Land Mobile Network Interworking Unit (PLMN IWU), provides a link between the domain of the private wireless network  22  and the domain of the public wireless network (PLMN)  15 . In a preferred embodiment, the signaling for the private wireless network  22  operates in the IP domain and signaling for the public wireless network  15  operates in the SS7 domain. In such an embodiment, the PLMN IWU  39 - 1  contains, in one embodiment, two independent software stacks, one for the private IP domain and one for the public SS7 domain. 
   In  FIG. 2 , the P-BTSs  27  are in the private wireless network  22  of FIG.  1  and FIG.  2 . In this embodiment, each P-BTS  27  contains the required protocol stacks to perform the functions of the wireless control signaling from the mobile station  4  and the H.323 endpoint, gatekeeper  41  or gateway  42 . In this embodiment, the H.323 endpoint can be a PC based terminal  21  (see  FIG. 2 ) or another mobile station  4 . The gatekeeper  41  provides the functions necessary to control the “terminals” within the H.323 domain and, in this embodiment, “terminals” include GSM mobile stations  4 . 
   The H.323 gatekeeper  41  provides the functions required to register the mobile stations  4  (equivalent to Location Updating), permit access to the network, translation of called numbers and routing of calls, if required. These functions are largely equivalent to those normally found in the MSC  17  or HLR  19  (see  FIG. 1 ) of a public wireless network  15 . The gatekeeper functions only need to exist in one P-BTS  27  of the P-BTS  27 - 1 , . . . , P-BTS  27 -P within the H.323 zone of FIG.  2 . In one embodiment, a tone and announcement module in gatekeeper  41  handles the actual generation of the various tone and announcement used according to the Call Control based on different call handling situations. Tone and Announcement are usually played towards the “far-end” LAN direction while only a tone is played toward the local MS direction. 
   In order to support the full range of wireless functions, the functions of a standard H.323 gatekeeper are augmented. The redesign includes the addition of a Local User Database (LUDB)  6 — 6  (See  FIG. 6 ) to control the mobile station and provide Supplementary Services (SS) functionality. The gatekeeper database contents are transferred to the serving P-BTS when the mobile station  4  registers (that is, Location Updating has taken place) on a P-BTS. For example, if a mobile station  4  has registered on P-BTS  27 - 1  in FIG.  2  and the user data of mobile station  4  is stored with the gatekeeper  41  supported by P-BTS  27 - 3 , then the relevant contents of the user database in P-BTS  27 - 3  are transferred to P-BTS  27 - 1  when the registration takes place. Any updates or alterations to the data by interaction of mobile station  4  are reflected back to the main gatekeeper database  7 - 3  stored in the gatekeeper  41 . This approach reduces the amount of call control signaling that is required within a LAN and provides redundancy for increased reliability. 
   In order to provide external PSTN or public wireless network interconnection, an H.323 gateway  42  is provided in FIG.  2 . The gateway  42  is part of the normal VoIP LAN-PSTN operation. The gateway  42  provides line interface and transcoding functions that allow the voice and data traffic to be sent to existing networks (for example, PSTN, ISDN, B-ISDN, PBX). 
   An additional function required of a P-BTS  27  when used in a LAN environment of  FIG. 2  is the ability to control the handover of mobile stations  4  between different P-BTSs  27  as mobile stations  4  move around within the LAN zone serviced by the private networks  14  of FIG.  2 . The handover decision is made internally within each P-BTS  27 , only the signaling necessary to command a handover needs to go between the P-BTSs  27 . 
   In  FIG. 2 , the Multi-Conference Unit (MCU)  45  is used to bridge the old P-BTS and the target P-BTS in embodiments of TDMA systems where the bridge is used during the handover procedure as explained in detail in the  FIG. 14  call flow description. It is also used to bridge the anchor P-BTS and the target P-BTS in embodiments of CDMA and W-CDMA systems where the bridge is used both during the handover procedure as well as after the completion of the handover procedure. 
   Signaling Links and Traffic Links between Private and Public Wireless Networks— FIG. 3   
     FIG. 3  provides a detailed view of a private wireless network  22 , having a PLMN IWU  39 , interconnected between the public wireless network (PLMN)  15  and private wireless network  22 . The private wireless network  22  includes a plurality of P-BTS  27 , including P-BTS  27 - 1 , . . . ,  27 -P, each associated with a corresponding private cell  411 , including the private cells  411 - 1 , . . . ,  411 -P, respectively. The public wireless network  15  includes an MSC  17  and a BSS  5  associated with the public cell  11 . The public cell  11  typically covers a larger area than the private cells  411  and typically the private cells  411  are within the operating region of the public cell  11 . Each of the public and private cells include mobile stations  4 , for example, mobile station  4 - 1  is typical of the mobile stations serviced by P-BTS  27 - 1  in the private wireless network  22  and mobile station  4 -P is typical of the mobile stations serviced by P-BTS  27 -P in the private wireless network  22 . The mobile station  4 - 15  is typical of the mobile stations serviced by BSS  5  in the public wireless network  15 . 
   In  FIG. 3 , the PLMN IWU  39 - 1  is interconnected to the public HLR  19  and MSC  17  of the public wireless network (PLMN)  15  via signaling links (shown as broken lines in FIG.  3 ). In the embodiment described, these signaling links use the SS7 protocol. The PLMN IWU  39 - 1  also connects to the gatekeeper  41  that includes the H.323 database  43  via a signaling link that uses the IP protocol. In the embodiment described, the PLMN IWU  39 - 1  connection to the gatekeeper  41  only carries signaling information, however, in other embodiments, it may carry voice or other related signaling traffic. 
   While the PLMN IWU  39 - 1  has been shown as a single entity located in the private wireless network  22 , the PLMN IWU  39 - 1  can also be located in the public wireless network  15  (shown with broken lines as  39 - 1 ′) as a single entity or can be distributed in parts at various different locations. The links between the PLMN IWU  39 - 1  and other components are implemented as a function of where the PLMN IWU  39 - 1  or its parts are located. In  FIG. 3 , the PLMN IWU  39 - 1  is located as a single entity in the private wireless network  22  and the links from the PLMN IWU  39 - 1  with the MSC  17  and HLR  19  exist in different forms. In one form, the links are leased lines or other direct connections. In another embodiment, the connections between the PLMN IWU  39 - 1  and the PLMN  15  are indirect through, for example, the cell router  34 . 
   In  FIG. 3 , the public wireless network (PLMN)  15  includes the gatekeeper  41  that connects to a connection unit  29 . The connection unit  29  includes means for interconnecting a mobile station  4 , for example, mobile station  4 - 1  serviced by P-BTS  27 - 1  in the private wireless networks  22  to another mobile station  4 , for example, mobile station  4 -P serviced by P-BTS  27 -P in the private wireless network  22 . Also, the connection unit  29  includes means for interconnecting a mobile station  4 , for example, mobile station  4 - 1  serviced by P-BTS  27 - 1  in the private wireless networks  22  to another mobile station  4 , for example, mobile station  41 - 15  serviced by the BSS  5  in the public wireless network  15 . When such connections involve different signaling protocols, each of the protocols are abstracted to the protocol (for example, H.323) database  43 . 
   The connection unit  29  can use any convenient switching or routing apparatus for directing calls from one mobile station to another. For example, in one embodiment described, the cell router  34  in connection unit  29  is an IP router that uses IP addresses for routing calls among the P_BTSs  27  or for routing calls through H.323 gateway  42  to the public wireless network  15 . In another example, the cell router  34  includes an ATM or other switch that switches calls among mobile stations  4  located in any of the cells including public cell  11  and private cells  411 - 1 , . . . ,  411 -P. 
   The gatekeeper  41  enables protocol independent cell routing using cell router  34  with information from address correlation database  43 . Gatekeeper  41  includes a lookup table which correlates identifiers in different protocols. The different protocols include, for example, IP addresses, MSRN numbers, and virtual circuit identifiers (VCI). The correlation performed in gatekeeper  41  using database  43  enables any embodiment of cell router  34  to correlate identifiers from different protocols. Byway of example, the router  34  in different embodiments is implemented as an IP router, a frame relay switch, or an ATM switch. In each of the se embodiments, ceU router  34  functions to switch and/or route mobile traffic to and from mobile stations  4 . 
   The switching role of a conventional MSC  17 , such as shown in  FIG. 1 , is fulfilled by packet or cell routing hardware included within cell router  34 . In operation, for example, when a mobile station  4  in  FIG. 3  requests a path through the network, the gatekeeper  41  maps an MSRN number to an appropriate IP address in the case of an IP router. In operation, for another example, when a mobile station  4  in  FIG. 3  requests a path through the network, the gatekeeper  41  maps a VCI address to an appropriate IP address in the case of an ATM switch and further the gatekeeper  41  maps an MSRN number to the appropriate IP address. Similar mappings are effected for any IP, frame, ATM switch or other routing or switching mechanism. The IP, MSRN, VCI or other identifier mapping occurs in the gatekeeper  41  and hence operation is independent of any particular embodiment of router  34 . Also, the particular routing mechanism employed for switching calls among cells is external to the private wireless network  22 . The private wireless network  22  is able to operate with any protocol that may exist or may be defined. 
   Public (MSCs) and Private (P-BTS) Networks— FIG. 4   
     FIG. 4  depicts public coverage areas  151 - 1  and  151 - 2  serviced by public MSCs  17 - 1  and  17 - 2 , respectively, within PLMN and private coverage areas  411 - 1 ,  411 - 2  and  411 - 3  serviced by private P-BTS  27 - 1 ,  27 - 2  and  27 - 3 , respectively, in a private wireless network  22 . Intercell handovers occur between the public MSCs and the private P-BTSs using the H.323 Gateway  27 - 2  and the PLMN IWU  39 - 1  in the private wireless network  22 . 
   Protocol Stacks for Signaling— FIG. 5   
   In a GSM example of the present invention, the  FIG. 1  public wireless network  15  includes conventional GSM base station software that does not provide support for call control or connection to the private wired protocol (Internet Protocol) that is used in the private networks  14  of FIG.  1  and FIG.  2 . Accordingly, the conventional GSM base station software requires protocol interfaces to facilitate inter-operation of the wireless protocol and the wired-packet protocol. For convenience, the protocol interfaces, namely protocol interfaces  28 - 1 , . . . ,  28 -P, are located with the P-BTSs  27 - 1 , . . . ,  27 -P in a private wireless networks  14  of FIG.  2 . 
   To support the architecture, the standard GSM stack i s modified by the P-Network Software  32  as shown in the FIG.  5 . In  FIG. 5 , the components  31 - 1 ′ and  31 - 2 ′ are equivalent to the standard components of a GSM stack. As can be seen from  FIG. 5 , in addition to the private Wireless Air Interface requirements and the H.323 Terminal Equipment requirements, the LAN based P-BTS  27  also provides the following functionality:
         Interworking between the two Call Control Functions—private wireless and LAN based.   Private Wireless Mobility Management (since there is no BSC or MSC in the standard GSM stack).       

   The Call Processing Plane Software Modules are significantly more complicated than those found in a normal public BTS and are defined in FIG.  6 . 
   Call Processing Plane Software Modules for IP-Based P-BTS— FIG. 6   
   In  FIG. 6 , the software modules for the call processing plane include modules, indicated in  FIG. 6  by cross-hatched ovals, used for inter-cell handover operation of P-BTSs  27  as follows:
         Call Control Module—The module  6 - 1  is responsible for the “call feature control” function for the mobile station, including both basic Call Control (CC) as well as Call Related Supplementary Services (CRSS). The module  6 - 1  includes the handover (HO) control for controlling the handover of MSs.   Mobility Management Module—The module  6 - 3  is responsible for handling the Mobility Management Function of the mobile station, including location update and handover control/co-ordination This function was originally located in the private wireless MSC and is fulfilled in the IP-based P-BTS. It also provides the ability to find a terminating mobile station and the ability to handle the call when the mobile station moves from one P-BTS to another P-BTS.   System Control Module—The module  6 - 4  is responsible for the End-Point registration, Administration, and status reporting in LAN. This entity is the “end-point” function and does not cover the gatekeeper functions which may be resident on the same P-BTS as well.   Local User Database Module (LUDB)—The module  6 - 6  maintains a copy of user data for each of the mobile stations that is registered on the current P-BTS. The data is stored in local memory as a “cache.” Any changes to the local copy will be “written-back” to the domain user database automatically. All the other modules who need the user data to operate interact with the Local User Database module for the data interrogation. The Local User Database Module will interact with the Domain User Database Module when necessary and does it in a way that is transparent to all the other modules in the P-BTS.   RIL 3 -CC Encoder/Decoder Module—The module  6 - 7  is responsible for encoding and decoding the GSM Radio Interface Layer  3  Call Control messages.   RIL 3 -MM Encoder/Decoder Module—The module  6 - 8  is responsible for encoding and decoding the GSM Radio Interface Layer  3  Mobility Management messages.   H.225.0 RAS Encoder/Decoder Module—The module  6 - 9  is responsible for encoding and decoding the H.225.0 Registration Administration and Status (RAS) messages. This module is shared between Call Processing Plane and the gatekeeper Plane.   H.225.0 CC Encoder/Decoder Module—The module  6 - 10  is responsible for encoding and decoding the H.225.0 Call Control messages. The H.225.0 Call Control Message is based on ISDN Q.931 Message Set.   H.245 Encoder/Decoder Module—The module  6 - 11  is responsible for encoding and decoding the H.245 messages. The H.245 specification defines a set of messages for controlling the allocation and management of the logical channels for multimedia applications.   RRM Module—The module  6 - 12  is responsible for the entire Radio Resource Management functionality that is normally split between the BTS and the BSC in the traditional architecture. The RRM Module will directly interface with the Call Control Module for radio resource functions, such as channel set-up, paging, etc.   RIL3 Message Delivery Module—The module  6 - 13  is responsible for looking into the protocol discriminator field in the layer- 3  message header to determine which module has to process this message. The delivery of the CC message will now be sent to the RIL 3 -CC Encoder/Decoder Module, and the MM message to the RIL 3 -MM Encoder/Decoder Module.   SMSCB Controller Module—The SMS-CB module  6 - 15  is used to keep track of the functionality of receiving and distributing the SMS CB messages that are to be broadcast by all or part of the P-BTSs within the current H.323 Zone.   Frequency Hopping Control Module—The module  6 - 16  controls the frequency of communications for the target mobile station.   RIL 3 RR Encoder/DecoderModule—The module  6 - 17  decodes and encodes the RIL 3 -RR messages to and from the BTS internal RR message formats. The formats of the RIL 3 -RR messages are specified in the GSM Technical Specification 04.08 along with the RIL 3 -MM, RIL 3 -CC, RIL 3 -SS, and RIL 3 -SMS messages specifications. This module provides the encoding and decoding of the RIL 3 -RR message which is required for the P-BTS.   BTS Power Control Module—The module  6 - 18  is responsible for providing the P-BTS power control (down-link) both statically and dynamically. The P-BTS Power Control Module takes the Mobile Uplink Measurement Data that is sent from a mobile, that is in dedicated mode, and compiled to provide the best power adjustment strategy for the given mobile. The goal is to maintain the P-BTS power in the optimal level so that the signal strength and signal quality for the down-link signal is within the private wireless quality guideline without causing excessive interference to the adjacent cell sites that are using the same or adjacent frequencies.   MS Power Control Module—The module  6 - 19  interfaces with the Channel Encoding and Decoding to add/retrieve the power control information into/out-off the header fields of the Layer  1  messages. The retrieval of the Mobile&#39;s up-link power level and the encoding of the command to instruct Mobile Station to increase/decrease the output power should be separated from the intelligence of performing sliding window algorithm over Mobile&#39;s power level and making decision to increase or decrease the MS power level.   BTS Measurement Report Module—The module  6 - 20  interfaces with GSM burst processing components to obtain the P-BTS measurement of the Mobile uplink signal. Specifically, the Automatic Gain Control and Demodulator for uplink power-level, and the Channel decoding unit for signal quality. Depending on the actual hardware architecture the input may come from more than just the three components identified above.   Timing Advance Module—The module  6 - 21  interfaces with the Burst Format function and retrieves the burst delay information for the Mobile, and then interfaces with the Channel Encoding and Decoding to add the Mobile timing advance information into the layer- 1  header field. The Timing Advance Module can be treated as part of the Traffic Channel Processing Domain or as part of the Call Processing Domain. It autonomously monitors the delay of the arriving burst and instructs the burst formatting function to encode the amount of timing-advance that the mobile station needs to do in order to let the burst arrive within the burst envelope that the BTS is expected.   LAPDn Module—The module  6 - 22  interfaces the message delivery to the channel coding/decoding.       

   CSU Module—The module  6 - 29  is a circuit switching unit that controls the switching of calls. This module provides software based routing mechanism for routing RTP (Real Time Protocol) based packet voice data between the GSM time slots (traffic only) and VoIP data ports. This module provides the abstraction of “port.” Different ports can be connected either duplex or simplex. It can also connect two GSM time slots together or two VoIP ports together to allow loop-back connection on both interfaces. 
   HO RTP Library—The module  6 - 27  is a handover library for the transport layer. This module handles the management of the RTP ports dedicated to the handover from/to a P-BTS. RTP/RTCP is the H.323 based transport protocol used for virtual connections over IP for the transportation of voice packets. 
   VB Link Library—The module  6 - 28  a link library that provides an underlying transport mechanism for the signaling exchange between the P-BTS and the GateKeeper. It is based on TCP over IP protocol. 
   Handover Operation With P-BTS— FIG. 7   
     FIG. 7  depicts a wireless system including a public wireless system  15  and a private wireless system  22  with a MS  4 - 1  that moves throughout the wireless system to locations indicated by  4 - 1   1 ,  4 - 1   2 ,  4 - 1   3 ,  4 - 1   4  and  4 - 1   5  and to alternate locations  4 - 1   3′   4 - 1   4′ .  FIG. 7  also depicts MS  4 - 2  that moves throughout the wireless system to locations indicated by  4 - 2   1 ,  4 - 2   2  and  4 - 2   3  and to alternate location  4 - 2   3′ . As the MS  4 - 1  and  4 - 2  move to different locations, different handover operations occur.  FIG. 7  is used to depict examples of handover operations as mobile stations  4 - 1  and  4 - 2  move about in the wireless system coverage areas. 
   In  FIG. 7 , the wireless system includes wireless P-BTS  27 - 1 ,  27 - 2  and  27 - 3  in the private wireless network  22  and standard MSCs  17 - 1 ,  17 - 2  and BSSs  5 - 1 ,  5 - 2 , respectively, in a public wireless network (PLMN)  15 . The coverage area of MSC  17 - 1  is indicated as  151 - 1  and the coverage area of MSC  17 - 2  is indicated as  151 - 2 . The coverage areas of the wireless P-BTS  27 - 1 ,  27 - 2  and  27 - 3  are schematically represented by the hexagons  411 - 1 ,  411 - 2  and  411 - 3 , respectively. The relative sizes of the coverage areas is not intended to be represented in  FIG. 7  since typically, the PLMN coverage areas  151 - 1  and  151 - 2  will be larger than the coverage areas  411 - 1 ,  411 - 2  and  411 - 3  of the private wireless network  22 . The private wireless network  22  includes the H.323 gateway  42  and the PLMN IWU  39 . 
   In one example, mobile station  4 - 1  is initially at a location indicated by  4 - 1   1  in the coverage area  411 - 1  serviced by the P-BTS  27 - 1 . Then, the mobile station  4 - 1  moves from the location indicated by  4 - 1   1  in the coverage area  411 - 1  to the coverage area  411 - 2  at location  4 - 1   2  serviced by the P-BTS  27 - 2  and a private-to-private handover procedure represented by arrow  41 - 1  occurs handing over from P-BTS  27 - 1  to P-BTS  27 - 2 . Then, the mobile station  4 - 1  moves back from the location indicated by  4 - 1   2  in the coverage area  411 - 2  to the location  4 - 1   3  in the coverage area  411 - 1  serviced by the P-BTS  27 - 1  and a back handover (private-to-private handback) procedure represented by arrow  41 - 2  occurs handing back to P-BTS  27 - 1 . This example demonstrates a private-to-private handover followed by a private-to-private handback. 
   In another example, the mobile station  4 - 1  moves from the location indicated by  4 - 1   3  in the coverage area  411 - 1  to the location  4 - 1   4  in the coverage area  151 - 1  serviced by the MSC  17 - 1  and the BSS  5 - 1  and a private-to-public handover procedure represented by arrow  41 - 3  occurs handing over to BSS  5 - 1 . Then, the mobile station  4 - 1  moves back from the location indicated by  4 - 1   4  in the coverage area  151 - 1  to the location  4 - 1   5  in the coverage area  411 - 1  serviced by the P-BTS  27 - 1  and a back handover (public-to-private handback) procedure represented by arrow  414  occurs handing back to P-BTS  27 - 1 . This example demonstrates a private-to-public handover followed by a public-to-private handback. 
   In another example, the operation starts the same as in the first example where mobile station  4 - 1  is initially at a location indicated by  4 - 1   1  in the coverage area  411 - 1  serviced by the P-BTS  27 - 1 . Then, the mobile station  4 - 1  moves from the location indicated by  4 - 1   1  in the coverage area  411 - 1  to the coverage area  411 - 2  at location  4 - 1   2  serviced by the P-BTS  27 - 2  and a private-to-private handover procedure represented by arrow  41 - 1  occurs handing over from P-BTS  27 - 1  to P-BTS  27 - 2 . Then, the mobile station  4 - 1  moves from the location indicated by  4 - 1   2  in the coverage area  411 - 2  to the coverage area  411 - 3  at location  4 - 1   3′  serviced by the P-BTS  27 - 3  and a private-to-private handover to third procedure represented by arrow  41 - 2 ′ occurs handing over to P-BTS  27 - 3 . This example demonstrates a private-to-private handover followed by a private-to-private handover to third. 
   In another example, the operation starts in location  4 - 1   3  in the coverage area  411 - 1  serviced by the P-BTS  27 - 1 . The mobile station  4 - 1  moves from the location indicated by  4 - 1   3  in the coverage area  411 - 1  to the location  4 - 1   4  in the coverage area  151 - 1  serviced by the MSC  17 - 1  and the BSS  5 - 1  and a private-to-public handover procedure represented by arrow  41 - 3  occurs handing over to BSS  5 - 1 . Then, the mobile station  4 - 1  moves from the location indicated by  4 - 1   4  in the coverage area  151 - 1  to the location  4 - 1   4′  in the coverage area  151 - 2  serviced by the MSC  17 - 2  and the BSS  5 - 21  and a public-to-public handover to third procedure represented by arrow  41 - 4 ′ occurs handing over to BSS  5 - 2 . This example demonstrates a private-to-public handover followed by a public-to-public handover to third. 
   In a further example, mobile station  4 - 2  is initially at a location indicated by  4 - 2   1  in the coverage area  151 - 2  serviced by the MSC/BSS ( 17 - 2 / 5 - 2 ). Then, the mobile station  4 - 2  moves from the location indicated by  4 - 2   1  in the coverage area  151 - 2  to the coverage area  411 - 3  at location  4 - 2   2  serviced by the P-BTS  27 - 3  and a public-to-private handover procedure represented by arrow  40 - 1  occurs handing over from MSC/BSS ( 17 - 2 / 5 - 2 ) to P-BTS  27 - 3 . Then, the mobile station  4 - 2  moves back from the location indicated by  4 - 2   2  in the coverage area  411 - 3  to the location  4 - 2   3  in the coverage area  151 - 2  serviced by the MSC/BSS ( 17 - 2 / 5 - 2 ) and a back handover (private-to-public handback) procedure represented by arrow  40 - 2  occurs handing back to MSC/BSS ( 17 - 2 / 5 - 2 ). This example demonstrates a public-to-private handover followed by a private-to-public handback. 
   In a still further example, mobile station  4 - 2  is initially at the location indicated by  4 - 2   1  in the coverage area  151 - 2  serviced by the MSC/BSS ( 17 - 2 / 5 - 2 ). Then, the mobile station  4 - 2  moves from the location indicated by  4 - 2 , in the coverage area  151 - 2  to the coverage area  411 - 3  at location  4 - 2   2  serviced by the P-BTS  27 - 3  and a public-to-private handover procedure represented by arrow  40 - 1  occurs handing over from MSC/BSS ( 17 - 2 / 5 - 2 ) to P-BTS  27 - 3 . Then, the mobile station  4 - 2  moves from the location indicated by  4 - 2   2  in the coverage area  411 - 3  to the location  4 - 2   3′  in the coverage area  151 - 1  serviced by the MSC/B SS ( 17 - 1 / 5 - 1 ) and a private-to-public handover to third procedure represented by arrow  40 - 2 ′ occurs handing over to MSC/BSS ( 17 - 1 / 5 - 1 ). This example demonstrates a public-to-private handover followed by a private-to-public handover to third. 
   Public Network and Private Network Operations—FIG.  8 -FIG.  13 . 
   Operations that involve both the PLMN public wireless networks  15  of FIG.  7  and the private wireless network  22  of  FIG. 7 , for example, are represented in the call flows of FIG.  8  through FIG.  13 . 
     FIG. 8  depicts the call flows of a handover of an MS from the a private network P-BTS to a public network MSC/B SS via the PLMN IWU. In  FIG. 7 , for example, MS  4 - 1  moving from location  4 - 1   3  to location  4 - 1   4  is handed over via  41 - 3  from the private network P-BTS  27 - 1  to the public network MSC/BSS ( 17 - 1 / 5 - 1 ) via the PLMN IWU  39 . 
     FIG. 9  depicts the call flows of a back handover (handback) of an MS from a public network MSC/BSS to a private network P-BTS via the PLMN IWU where the MS previously originated in the private network P-BTS. In  FIG. 7 , for example, MS  4 - 1  moving from location  4 - 1   3  to location  4 - 1   4  is handed back via  41 - 4  from the public network MSC/BSS ( 17 - 1 / 5 - 1 ) to the private network P-BTS  27 - 1  via the PLMN IWU  39 . 
     FIG. 10  depicts the call flows of a subsequent handover of an MS via the PLMN IWU from one MSC/BSS to another MSC/BSS in the public network where the MS originated with a P-BTS in the private network. In  FIG. 7 , for example, MS  4 - 1  moving from location  4 - 1   4  to location  4 - 1   5′  is handed over via  41 - 4 ′ from the public network MSC/BSS ( 17 - 1 / 5 - 1 ) to public network MSC/BSS ( 17 - 2 / 5 - 2 ) via the PLMN IWU  39 . 
     FIG. 11  depicts the call flows of a handover of an MS from the public network MSC/BSS to a private network P-BTS via the PLMN IWU. In  FIG. 7 , for example, MS  4 - 2  moving from location  4 - 2   1  to location  4 - 2   2  is handed over via  40 - 1  from the public network MSC/BSS ( 17 - 2 / 5 - 2 ) to the private network P-BTS  27 - 3  via the PLMN IWU  39 . 
     FIG. 12  depicts the call flows of a back handover (handback) of an MS from a private network P-BTS to a public network MSC/BSS via the PLMN IWU where the MS originated with the public network MSC/BSS. In  FIG. 7 , for example, MS  4 - 2  moving from location  4 - 2   2  to location  4 - 2   3  is handed back via  40 - 2  from the private network P-BTS  27 - 3  to the public network MSC/BSS ( 17 - 2 / 5 - 2 ) via the PLMN IWU  39 . 
     FIG. 13  depicts the call flows of a handover of an MS via the PLMN IWU from an old target P-BTS in the private network to a new MSC/BSS in the public network where the MS originated with an old MSC/BSS in the public network. In  FIG. 7 , for example, MS  4 - 2  moving from location  4 - 2   2  to location  4 - 2   3′  is handed over via  40 - 2 ′ from the private network P-BTS  27 - 3  to the public network MSC/BSS ( 17 - 1 / 5 - 1 ) via the PLMN IWU  39 . 
   Anchor and Target Private Network Handover Operations—FIG.  14 -FIG.  19 . 
   Operations that involve handovers from an anchor P-BTS to a target P-BTS (Anchor-to-Target 1 ) in the private wireless network  22  of  FIG. 7 , for example, are represented in the call flows of FIG.  14  through FIG.  28 . 
     FIG. 14  depicts the call flows of one method of implementing an anchor P-BTS to target P-BTS private-to-private handover (Anchor-to-Target 1 ). In  FIG. 7 , for example, mobile station  4 - 1  is initially at a location indicated by  4 - 1   1  in the coverage area  411 - 1  serviced by the anchor P-BTS  27 - 1 . Then, the mobile station  4 - 1  moves from the location indicated by  4 - 1   1  in the coverage area  411 - 1  to the coverage area  411 - 2  at location  4 - 1   2  serviced by the target P-BTS  27 - 2  (Target 1 ) and a private-to-private handover procedure represented by arrow  41 - 1  occurs handing over from anchor P-BTS  27 - 1  to target P-BTS  27 - 2 . 
   In order to provide continuous coverage within the private domain (Intranet), it is necessary to be able to perform at least intra-domain and inter-domain handovers. In order to simplify the implementation of the network, the P-BTS performs the handover candidate calculations on the measurement data being sent by the mobile station. Once a handover candidate has been identified and the decision made, then the process to begin the handover needs to be started. There are two methods used to facilitate the handover process. One method uses the conference facilities of H.323 and the resources of the gatekeeper  41  and multi-conference unit (MCU)  45  to bridge the old P-BTS and the target P-BTS. Another method uses the multicast options of the Intranet to send the uplink and downlink IP packets to both the old and new P-BTSs. In either case, the target P-BTS enables the new radio interface, prepares to take over the mobile station Call Control state machine and establishes the necessary routing to access the network. Once the new radio channel has been established, the terminal is instructed to move to the new P-BTS and the old P-BTS resources are released. If each P-BTS used a different LAI, then location updating (registration) is automatically performed when the call terminates. In performing the handover as shown In  FIG. 14 , the following phases are undertaken:
         Phase  1 : Once the handover algorithm has determined that a handover is required then the transport addresses of the new base station must be determined. The new base station address is determined by making use of the RAS Location Request with the BTS ID as the addressed party. When appropriate this operation is extended to include the locations of BTSs within the Public GSM network.   Phase  2 : If the gatekeeper knows the transport addresses of the Target BTS (EP 3 ) then it is returned in the Location Confirm (LCF) message. At this point the Old BTS (EP 1 ) must request the resources from the Target BTS. The resource request is performed by adding a new “Non-Standard Message” to the H.323 repertoire. This new message requests the resources from the Target BTS. This message may also include call control information appropriate to this mobile station. In addition, to speed up the location updating process, it may also include the Old BTSs copy of the user data.    In the case of a handover to the Public network then the “Non-Standard Message” would have to be sent to the gateway and converted into the appropriate Handover message for the public network. The gateway would also have to start handling the call for the Old BTS.   Phase  3 : When the Target BTS receives the request for the resources, if they are available then it will respond with a confirmation and a multicast address to be used by the Old BTS.   Phase  4 : Upon receiving the confirmation the Old BTS begins to establish a conference between the destination BTS (EP 2 ) or Fixed Terminal and the Target BTS. Once the multicast distributed conference has been established the Old BTS can instruct the mobile station to handover to the Target BTS.   Phase  5 : The Handover Command is sent to the mobile station which will then begin to access the Target BTS on the indicated timeslot. Once the mobile station is established on the Target BTS an End Session message is sent to the Old BTS to release the resources from the BTS. The Call Control is now located on the Target BTS.       

   In order to accommodate different handover cases, the P-BTS determines via the BTS ID whether Synchronized or Non-synchronized handover is to be used. 
   It should be noted that this procedure is equally applicable to both Private and Public mobile stations. This procedure also forms the basis for any scheme which requires handover to/from the Public GSM network. 
     FIG. 15  depicts the call flows of a second method of implementing the handover call flows of a MS private-to-private handover between an anchor P-BTS and a target P-BTS (Anchor-to-Target 1 ). In  FIG. 7 , for example, mobile station  4 - 1  is initially at a location indicated by  4 - 1   1  in the coverage area  411 - 1  serviced by the anchor P-BTS  27 - 1 . Then, the mobile station  4 - 1  moves from the location indicated by  4 - 1   1  in the coverage area  411 - 1  to the coverage area  411 - 2  at location  4 - 1   2  serviced by the target P-BTS  27 - 2  (Target 1 ) and a private-to-private handover procedure represented by arrow  41 - 1  occurs handing over from anchor P-BTS  27 - 1  to target P-BTS  27 - 2 . In this second method of a private-to-private handover, the first phase is the same as that described for the first method. The “IP Address Request” from the anchor P-BTS to the gatekeeper used in the call flow is essentially equivalent to a Location Request. In the second phase, after receiving the target P-BTS&#39;s IP Address from the gatekeeper, the anchor P-BTS assigns an RTP Port for handover connection (Far End HO RTP Port) and then requests resources from the target P-BTS through a “Perform Handover” message. In the third phase, the target sends a confirmation (Ack.) if resources are available. Local resources assigned include a new radio channel as well as an RTP Port for handover connection (Mob End HO RTP Port). Target P-BTS also completes its side of the two-way handover traffic connection between the two handover RTP Ports and also completes a two-way connection between its handover RTP port and the locally assigned radio (GSM) port. In the fourth phase, when the confirmation is received, the anchor P-BTS commands the mobile station to the new radio channel, completes its side of the two-way handover traffic connection between the two handover RTP Ports and also makes a one-way connection from the far end (remote) port to its handover RTP Port. Note that this far end (remote) port can be a radio (GSM) port or an RTP port. In the final fifth phase, when the mobile station successfully completes access to the target P-BTS over the new radio channel, a Handover Success message is sent to the anchor P-BTS. The anchor P-BTS then releases the old radio channel resources and completes the two-way connection between the far end (remote) port and its handover RTP Port. 
     FIG. 16  depicts the anchor P-BTS handover internal call flows of the anchor P-BTS in the  FIG. 15  call flow (Anchor-to-Target 1 ). 
     FIG. 17  depicts a continuation of the anchor P-BTS handover internal call flows of  FIG. 16  (Anchor-to-Target 1 ). 
     FIG. 18  depicts the handover target P-BTS internal call flows of the target P-BTS in the  FIG. 15  call flow (Anchor-to-Target 1 ). 
     FIG. 19  depicts a continuation of the target P-BTS handover internal call flows of the  FIG. 18  call flow (Anchor-to-Target 1 ). 
   Anchor and Target Private Network Back Handover Operations—FIG.  20 -FIG.  24 . 
   Operations that involve back handovers (handbacks) from a target P-BTS to an anchor P-BTS (Target 1 -to-Anchor) in the private wireless network  22  of  FIG. 7 , for example, are represented in the call flows of FIG.  20  through FIG.  22 . 
     FIG. 20  depicts the back handover (private-to-private handback) call flows of a MS subsequent back handover after a handover of the  FIG. 15  call flow between an anchor P-BTS and a target P-BTS (Target 1 -to-Anchor). In the  FIG. 7  example, the mobile station  4 - 1  moves back from the location indicated by  4 - 1   2  in the coverage area  411 - 2  serviced by the target P-BTS  27 - 2  to the location  4 - 1   3  in the coverage area  411 - 1  serviced by the anchor P-BTS  27 - 1  and a back handover (private-to-private handback) procedure (Target 1 -to-Anchor) represented by arrow  41 - 2  occurs handing back to anchor P-BTS  27 - 1 . In the back handover (private-to-private handback) implementation, when a handback is required, the target P-BTS knows the anchor P-BTS address. In the first phase, the target P-BTS requests resources from the anchor P-BTS through a “Perform Handback” message. In the second phase, the anchor P-BTS sends a confirmation (Ack.) if resources are available. Local resources assigned include a new radio channel. The anchor P-BTS also completes a one-way connection from the far end (remote) port to the newly assigned radio (GSM) port. In the third phase, when the confirmation is received, the target P-BTS commands the mobile station to the new radio channel. In the final fourth phase, when the mobile station successfully completes access to the anchor P-BTS over the new radio channel, the anchor P-BTS completes the two-way connection between the far end (remote) port and the newly assigned radio (GSM) port and also sends a Handover Success message to the target P-BTS. The target P-BTS then releases the old radio channel resources. Both anchor and the target P-BTS also break the Handover RTP connection between them which is no longer required and also release their respective handover RTP Ports of that connection. 
     FIG. 21  depicts the anchor P-BTS back handover (handback) internal call flows of the anchor P-BTS in the  FIG. 20  back handover (Target 1 -to-Anchor). 
     FIG. 22  depicts a continuation of the anchor P-BTS back handover internal call flows of  FIG. 21  (Target 1 -to-Anchor). 
     FIG. 23  depicts the target P-BTS back handover (handback) internal call flows of the of the target P-BTS in the  FIG. 20  back handover (Target 1 -to-Anchor). 
     FIG. 24  depicts a continuation of the target P-BTS back handover (handback) internal call flows of the  FIG. 23  (Target 1 -to-anchor). 
   Anchor and Target Private Handover to Third P-BTS Operations—FIG.  25 - FIG. 29 , 
   Operations that involve private-to-private handovers from a target P-BTS to a third P-BTS (Target 1 -to-Target 2 ) in the private wireless network  22  of  FIG. 7 , for example, are represented in the call flows of FIG.  25  through FIG.  29 . 
     FIG. 25  depicts the handover to third call flows of a MS handover between an old target P-BTS and a new target P-BTS (Target 1 -to-Target 2 ). In the  FIG. 7  example, the operation started with an Anchor-to-Target 1  handover where mobile station  4 - 1  was initially at a location indicated by  4 - 1   1  in the coverage area  411 - 1  serviced by the anchor P-BTS  27 - 1 . Then, the mobile station  4 - 1  moved from the location indicated by  4 - 1   1  in the coverage area  411 - 1  to the coverage area  411 - 2  at location  4 - 1   2  serviced by the target P-BTS  27 - 2  (Target 1 ) and an Anchor-to-Target 1  handover procedure represented by arrow  41 - 1  occurred handing over from anchor P-BTS  27 - 1  to target 1  P-BTS  27 - 2 . Then, the mobile station  4 - 1  moves from the location indicated by  4 - 1   2  in the coverage area  411 - 2  to the coverage area  411 - 3  at location  4 - 1   3′  serviced by the target P-BTS  27 - 3  (Target 2 ) and a Target 1 -to-Target 2  handover to third procedure represented by arrow  41 - 2 ′ occurs handing over to P-BTS  27 - 3  (Target 2 ). This example demonstrates a private-to-private handover followed by a public-to-private handover to third. In the handover to third (private-to-private handover followed by a private-to-private handover to a third BTS) implementation, when a handover to a third P-BTS is required, in the first phase, the old target P-BTS requests for resources from the anchor P-BTS through a “Perform Handback” message including the name of the new target P-BTS. In the second phase, the anchor requests and gets the IP address for the new target P-BTS from the gatekeeper. In the third phase, the anchor assigns a new Handover RTP Port (new Far End HO RTP Port) and requests resources from the new target P-BTS through a “Perform Handover” message. In the fourth phase, the new target sends a confirmation (Ack.) if resources are available. Local resources assigned include a new radio channel as well as an RTP Port for handover connection (new Mob End HO RTP Port). The new target P-BTS also completes its side of the two-way handover traffic connection between its handover RTP Port and the new handover RTP Port on the anchor and also completes a two-way connection between its handover RTP port and the locally assigned radio (GSM) port. In the fifth phase, the anchor P-BTS completes its side of the two-way handover traffic connection between its new handover RTP Port and the handover RTP Port on the new target P-BTS and also completes a one-way connection from the far end (remote) port to the newly assigned handover RTP Port and sends a confirmation (Ack.) back to the old target P-BTS. In the sixth phase, when the confirmation is received, the old target P-BTS commands the mobile station to the new radio channel. In the seventh phase, when the mobile station successfully completes access to the new target P-BTS over the new radio channel, a Handover Success message is sent to the anchor P-BTS. In the final eighth phase, the anchor P-BTS in turn sends a Handover Success message to the old target P-BTS and also completes the two-way connection between the far end (remote) port and the newly assigned handover RTP Port. The old target P-BTS then releases the old radio channel resources. Both the anchor P-BTS and the old target P-BTS also break the Handover RTP connection between them which is no longer required and also release their respective handover RTP Ports of that connection. 
     FIG. 26  depicts a continuation of the MS handover to third of  FIG. 25  (Target 1 -to-Target 2 ). 
     FIG. 27  depicts the anchor P-BTS handover internal call flows of the anchor P-BTS of the  FIG. 25  handover to third (Target 1 -to-Target 2 ). 
     FIG. 28  depicts a continuation of the anchor P-BTS handover internal call flows of  FIG. 27  handover to third (Target 1 -to-Target 2 ). 
     FIG. 29  depicts a continuation of the target P-BTS handover to third internal call flows where the initial internal call flows for the target P-BTS are the same as the handback call flows of  FIG. 23  (Target 1 -to-Target 2 ). 
   Further and Other Embodiments 
   The handover method is also applied to CDMA systems using soft handover. In these systems, the breaking of the link between the old P-BTS and the radio interface will not occur. A bridging circuit of MCU  45  of  FIG. 2  is inserted between the old P-BTS, the new P-BTS, and the remote (other) endpoint. This method is used to select the best signal from each P-BTS. Furthermore, it may be required to support multiple (more than two) P-BTSs communicating simultaneously with the mobile station. In this case, one radio link is set up with each of the se P-BTSs and the bridge is also set up so that it includes all these P-BTSs and the remote (other) endpoint. 
   GLOSSARY 
   The following abbreviations are used in the drawings: 
   
     
       
         
             
             
           
             
                 
             
           
          
             
               Ack 
               Acknowledge 
             
             
               ACM 
               (ISUP) Address Complete Message 
             
             
               Act. 
               Activation 
             
             
               ANM 
               (ISUP) Answer Message 
             
             
               BSS 
               Base Station Subsystem 
             
             
               CC 
               Call Control 
             
             
               Chann. 
               Channel 
             
             
               CI 
               Cell Identifier 
             
             
               CID 
               Call Identifier 
             
             
               Cmd 
               Command 
             
             
               Comp 
               Complete 
             
             
               Conn. 
               Connect 
             
             
               CPN 
               Called Party Number 
             
             
               CRV 
               Call Reference Value 
             
             
               CSU 
               Circuit Switching Unit 
             
             
               Det 
               Detect 
             
             
               DSP 
               Digital Signal Processing 
             
             
               EP 
               (H.323) End Point 
             
             
               Est 
               Establishment 
             
             
               Hand 
               Handover 
             
             
               HO 
               Handover 
             
             
               HON 
               Handover Number 
             
             
               IAM 
               (ISUP) Initial Address Message 
             
             
               IWU 
               Interworking Unit 
             
             
               LAC 
               Location Area Code 
             
             
               LUDB 
               Local User DataBase 
             
             
               MAP 
               Mobile Application Part 
             
             
               MC 
               (H.323) Multi-Point Control Entity 
             
             
               MCU 
               (H.323) Multi-Point Control Unit 
             
             
               MM 
               Mobility Management 
             
             
               Mob 
               Mobile 
             
             
               MS 
               Mobile Station 
             
             
               MSC 
               Mobile Switching Center 
             
             
               Msg. 
               Message 
             
             
               OAM 
               Operations, Administration, and Maintenance 
             
             
               PLMN 
               Public Land Mobile Network 
             
             
               RAS 
               (H.323) Registration, Administration, and Status Protocol 
             
             
               REL 
               (ISUP) Release Message 
             
             
               Rel. 
               Release 
             
             
               Req 
               Request 
             
             
               RF 
               Radio Frequency 
             
             
               RLC 
               (ISUP) Release Complete Message 
             
             
               RR 
               Radio Resource Management 
             
             
               Rsp. 
               Response 
             
             
               RTCP 
               Real-Time Transport Control Protocol 
             
             
               RTP 
               Real-Time Transport Protocol 
             
             
               TCAP 
               (SS7) Transaction Capability Application Part 
             
             
               TCH 
               Traffic Channel 
             
             
               TSAP 
               (H.323) Transport Layer Service Access Point 
             
             
               VB Link 
               ViperBase (Gatekeeper) Link 
             
             
                 
             
          
         
       
     
   
   While the invention has been particularly shown and described with reference to preferred embodiments thereof it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention.