CA2263934A1 - Private multiplexing cellular network - Google Patents

Abstract

A private multiplexing cellular network for facilitating celllular communication for private mobile stations (MS's), public MS's, and hybrid MS's. The private multiplexing cellular network includes a multiplexing circuit coupled to its radio subsystem. The multiplexing circuit is in turn coupled to two A-interfaces: a private A-interface for coupling the private radio subsystem with the private Mobile Switching Center (MSC), and a public A-interface for coupling the private radio subsystem with the public MSC.
Intelligence is also provided with the multiplexing circuit to decide, based on a number of parameters, whether the public MSC or the private MSC should handle a given service request.

Description

?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/ 15213PRIVATE MULTIPLEXIN G CELLULAR NETWORKBACKGROUND OF THE INVENTIONThe present invention relates to apparatuses and methods for implementing mobilecommunication. More particularly, the present invention relates to a novel privatemultiplexing cellular network, as well as components therefor, that advantageously offerscellular coverage to private cellular phone sets, i.e., private mobile stations (MS's), publiccellular phone sets, i.e., public mobile stations (MS's), and hybrid private-public cellular phonesets, i.e., hybrid mobile stations (MS's) in a seamless manner. In accordance with one aspect ofthe present invention, the coverage area under control of the private radio subsystem can beused by private MS's (and hybrid MS's in certain prede?ned circumstances) as if it is part ofthe private network, and by the public MS's (and hybrid MS's in certain other prede?nedcircumstances) as if it is part of the public network.Mobile communication is known in the art. One limited form of mobile communicationinvolves prior art cordless phones. In the prior art cordless phone system, each cordless phoneset typically comprises a base unit and a cordless unit. The base unit, typically located insidea residence or a business office, is usually coupled physically by copper wires or ?ber opticsto the public switched telephone network (PSTN). To uniquely identi?es it in the publicnetwork, each cordless phone set is speci?cally associated with a telephone number.Further, each cordless phone’s base unit is speci?cally associated with its cordless unitand communicates therewith in a wireless manner. As long as a user of the prior art cordlessunit stays within the limited range of the associated base unit (under a quarter mile in mostcases due to technical limitations inherent in cordless technology), calls may be made to andfrom the public network in a wireless manner.However, the prior art cordless phone has some signi?cant disadvantages. Besides thelimited range, the prior art cordless technology is limited in the number of cordless units that abase unit can support. Typically one, no more than two, handset is provided per base unit inthe prior art cordless phone. Because of this limitation, a telephone service provider must stillrun wires, either along telephone poles or in trenches, to each residence or business to enabletelephone service, whether or not cordless. Therefore, although the cordless unit appears?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213mobile to the user, the network that is required to implement this service is still essentially awired telephone network. ‘Users’ demand for mobile communication services, as well as the increasing costs ofbuilding and maintaining a wired telephone infrastructure, has turned many service providers toother wireless technologies for answers. Among existing technologies, cellular technology hasemerged the clear leader in term of market penetration. In particular, cellular phone systemsusing a standard known as Global Systems for Mobile Communication (GSM) has steadilygained popularity among service providers as the system of choice for implementing cellularservice. The popularity of the GSM standard stems from its robustness and its ability tosupport a rich set of features such as world-wide roaming, phone mail, data services,supplemental services, and the like. Information regarding the GSM standard is widelyavailable in the public domain, some of which are cited in Appendix B herein.For illustration purposes, Fig. 1 illustrates a representative prior art public cellularcommunication system. For illustration purposes, a cellular communication system for usewith the Global Systems for Mobile Communication (GSM) protocol is shown in Fig. 1.Referring to Fig. 1, there are shown four mobile station units (MS), also known as cellularhandsets, 150, 152, 154, and 156, which communicate to an antenna subsystem 158. As isknown to those familiar with the GSM protocol, MS's 150-156 typically communicate withantenna subsystem 158 via a radio link (RL) protocol. As is known, the radio link (RL)protocol is a LAPD-M protocol at GSM layer 2 and is defined by standard GSM 08.58.Antenna subsystem 158 couples to transceiver units (TRX) 160 and 162 of basetransceiver station (BTS) unit 164 as shown. Each of TRX's 160-162 outputs bearer data,which may be 8 Kbits per second (Kbps) or 16 Kbps (GSM) time division multiplexed(TDM) data representing, for example, voice conversations, facsimile, digital data, and the like.A TRX also outputs signaling information which is packet information that is forwarded eitherto antenna subsystem 15 8 for transmitting to the MS's or to a base station control function(BCF) 166 for communicating with a base station controller (BSC) or a mobile servicesswitching center (MSC). The mobile services switching center (MSC) will be discussed laterherein.From the GSM point of view, each of MS's 150-156 contains hardware and softwarethat can handle from its end functions such as radio resources control (RR), mobilitymanagement (MM), call control (CC), short message service (SMS), and supplemental services(SS). Base control function (BCF) 166 is coupled to a transcoder-rate adapter unit (TRAU)-2-?1015202530CA 02263934 1999-02-23WO 98/09457 PCTIUS97/ 152137168 for switching between either 8 Kbps or 16 Kbps to 64 Kbps TDM data before beingpassed on to the BSC. A transcoder—rate adapter unit (TRAU) is used for performing rateadaptation, or voice transcoding, between MS units communicating at different rates.TRAU unit 168 is coupled to an E1 module 170 of BTS unit 164. El module 170represents the means by which BTS unit 164 can communicate with a base station controller(BSC) unit 172. In one embodiment, E1 module 170 represents a 2.048 Mbits signaling wiredinterface that is channelized into 64K bits channels. BCF 166 represents a CPU module thatruns the software to handle provisioning of the TRAU or E1 resources at the request of basestation controller (BSC) 172.In the prior art, BTS unit 164 is essentially a “dumb” subsystem that operatesresponsive to commands from BSC unit 172. For example, when BSC 172 ?rst powers up, itwill con?gure BTS unit 164 via a link 174 by down loading the configuration data across link174. Link 174 represents the terrestrial link that carries the TDM data between BTS unit 164and BSC unit 172, typically using an interface known as Abis.A BSC unit may have multiple El modules for communicating with multiple BTS’s.For example, BSC unit 172 is shown having 3 E1 modules 176, 178, or 180 for communicatingwith 3 or more BTS's. Furthermore, although BTS 164 shows only two transceiver units 160and 162 for illustration purposes, it should be understood that a typical BTS unit may haveany number of transceiver units.Functionally speaking, the job of BSC unit 172 is radio resource (RR) control. Itmanages certain requirements regarding the status and location of the mobile stations and detailsregarding how to communicate with the mobile stations in the appropriate modulation scheme.In this manner, BSC unit 172 helps to hide this level of detail from any components upstream,e.g., mobile services switching center (MSC) 182 or the public network that is upstream fromMSC 182. BSC unit 172 also handles power control. BSC unit 172 directs BTS unit 164 and atransceiver unit therein to increase or decrease its transmission power from a handset toimprove transmission quality.Furthermore, BSC unit 172 also monitors handset communication quality to prepare forpower handovers, e.g., when one of the handsets roams among the different areas controlled bydifferent BTS’s. When a hand-over is eminent, BSC unit 172 further initiates the hand-over.The intra-B SC hand-over of the prior art ensures that communication for a single circuitbetween a given mobile station and MSC unit 182 remains uninterrupted during handover.?1015202530CA 02263934 1999-02-23WO 98/09457 PCTIU S97/ 15213BSC unit 172 further includes processor 184 for handling the aforementioned radioresource control (RR), optional TRAU unit 186,iand an El module 190. El module 190provides the means through which BSC unit 172 can communicate with MSC unit 182.MSC unit 182 may communicate with any number of BSC unit 172 and includes,among other things, an El module 192, a processor 193, and a gateway MSC unit 194. GMSCunit 194 facilitates communication between the cellular communication system of Fig. 1 and theoutside world, e.g., the public network. GMSC 194 is coupled to a link 194 for communicatingwith the public network. As is known, the communication between MSC 182 and the publicnetwork may be performed via the E interface.As is also known to those familiar with the GSM speci?cation, MSC unit 182 furtherinclude circuits to handle mobility management (MM), call control (CC) short message service(SMS), and other supplemental services (SS). Optionally, MSC unit 182 performs some radioresource (RR) handling, e.g., inter BSC and inter MSC handovers. Inter BSC occurs when amobile station roams among the BSC’s. In this case, the radio resource control must be handledby the upstream MSC since a BSC would not know how to hand-over to another BSC whenthe mobile station roams from a BSC to another BSC.Although public cellular networks, such as that described in Fig. 1, satisfactorilyprovide cellular communication capabilities for large urban areas, there are drawbacks. Amongthe drawbacks discussed in connection with the aforementioned co-pending patent applicationS/N O8/43 5,709 are the inef?cient backhauling of bearer data charmels back to the public MSCfor cross—connecting, the indiscriminate use of rate adaptation resources (TRAU) for datachannels that do not necessarily require rate adaptation, and the fact that a functional publiccellular network may not be a cost-effective solution for geographically remote or applicationswhere the end-user wishes to retain a high degree of control over the addition or removal ofusers.In the aforementioned co-pending patent application S/N 08/435,709, there aredescribed methods and apparatuses for implementing various combinations of private cellularnetworks to address the aforementioned drawbacks of public cellular networks. Referring nowto Fig. 2A, there is shown a private cellular network 200, representing a private cellularnetwork of the type disclosed in co-pending patent application S/N 08/435,709. Privatecellular network 200 may be coupled to a public network 202 via a connection 204. Thecoupling between cPBX 200 and public network 202 may be accomplished, in oneembodiment, via an E1 interface which may represent a wired or a microwave link.-4-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213Private cellular network 200 has suf?cient resources to perform switching andcommunication management among its private MS's without assistance from the publicnetwork. Advantageously, the mobility, roaming, and hand-off capabilities are handled by theresources within private cellular network 200 without the intervention of public network 202.Additional resources or features may thus be added to the private cellular network for thebene?t of owners of private MS's without requiring corresponding changes in the publicnetwork.Within private cellular network 200, shown are a cPBX subsystem 206, a BSCsubsystem 208 and BTS subsystem 210, and MS units 212 and 214. As will be discussedlater, cPBX subsystem 206, BSC subsystem 208 and BTS subsystem 210 represent theenhanced versions of the respective MSC, BSC and BTS of the prior art.MS units 212 and 214 represent standard cellular handsets which are GSM standardhandsets in the preferred embodiment. MS 212 and 214 communicate with BTS subsystem210 via an appropriate cellular interface such as the aforementioned radio link (RL) interface.The typical radius of operation between each MS unit and a BTS subsystem is in the range of2 to 3 Kilometers, which is substantially greater than the 200 meter range typically offered bythe prior art wireless WPBX. The additional range offered by the cellular cPBX of Fig. 2Arepresents a signi?cant advantage because it is dif?cult, as is well known to those skilled in thecommunication art, to scale up the distance offered by the prior art wireless bases and cordlesshandsets due to interference problems inherent in the prior art cordless technology.Each cPBX subsystem 206 is capable of coupling to more than one BSC subsystem208. BSC subsystem 208 communicates with cPBX subsystem 206 via link 216 using, forexample, an A interface. Similarly, each BSC subsystem 208 is capable of coupling to morethan one BTS subsystem 210. BTS subsystem 210 is coupled to BSC subsystem 208 via link218 utilizing, for example, Abis interface. Further, each BTS subsystem 210 is capable ofcoupling to a number of MS units, of which only two are shown. In this manner, privatecellular network 200 is organized in a hierarchy, the top of which is occupied by cPBXsubsystem 206. Depending on system con?guration, the cPBX con?guration shown in Fig. 2Acan handle as few as 7 simultaneous calls up to as many as 1,000 (correlating to up to 10,000MS's)It should be understood that the drawing of Fig. 2A is a functional representation andthat the different components of the private cellular network 200 may either be integrated toco-locate at the same location or on a single chassis or dispersed in a wide geographic area to-5-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213increase the domain of the private network. The ability to configure a physical chassis toperform individual BTS, BSC, or cPBX function, or any combination of these subsystems,represents a unique advantage of the private network disclosed in co—pending patentapplication S/N 08/435,709.As will be discussed later, the components of private cellular network 200 are designedsuch that they can be added or removed from private cellular network 200 in a modular fashion.In this manner, a scalable private cellular network may be realized, whose capabilities may beexpanded or shrunk as necessary to ?ll the need of a particular site.In the purely private network con?guration, each MS unit, e.g., MS units 212 and 214,is registered with and recognizable by cPBX subsystem 206. More particularly, theinformation associated with each MS unit is registered in a home location registry (HLR) incPBX subsystem 206. The registration of an MS unit with the HLR registry in cPBXsubsystem 206 permits that MS unit to be recognized as a private MS unit and to utilize theresources of private cellular network 200 for cellular communication. For example, a registeredMS unit may make calls via BTS subsystem 210, BSC subsystem 208, and cPBX subsystem206 to a telephone set in public network 202. Alternatively, MS unit 212, being an MS unitthat is registered with the HLR registry within cPBX subsystem 206 may make a local call toanother MS unit also registered with the HLR registry within cPBX subsystem 206, e.g., MSunit 214 via BTS subsystem 210. When an MS unit is registered with the HLR registry incPBX 206, it may also receive a call, whether from public network 202 or from another MSunit that is registered with the same HLR registry.In the purely private network configuration of Fig. 2A, a standard GSM handset that isnot registered with the HLR registry within cPBX subsystem 206 is deemed a non-nativehandset and cannot use the resources of private cellular network 200 to make or receive calls.Further, each of BTS subsystem 210, BSC subsystem 208, and cPBX subsystem 206 isfurnished with intelligent cross-connect capability. Consequently, the actual cross-connectthat builds the connection between the calling MS unit and the receiving MS unit may bedistributed down from cPBX subsystem 206, e.g. to BSC subsystem 208 or BTS subsystem210. For example, MS units 212 and 214 may be cross-connected at a lower level in thehierarchy, e.g., BTS subsystem 210, instead of at a higher level, e.g., at cPBX subsystem 206.If the call is made between MS units controlled by the same BSC subsystem, e.g., BSCsubsystem 208 but different BTS subsystems, the cross-connect switching may be performedat BSC subsystem 208 instead of at cPBX subsystem 206. In this manner, the channels-5-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/U S97/ 15213containing the bearer data between MS units do not always have to be backhauled all the wayto cPBX subsystem 206. IThe intelligence switch capability in the subsystems of private cellular network 200permits the entire network to handle more traffic by freeing up the bandwidth leading to cPBXsubsystem 206 if the required cross—connect between channels carrying bearer data could beperformed by a component further down the hierarchy.In the prior art public cellular systems, e.g., the public cellular system of Fig. 1, cross-connection among call paths is centralized at a central public mobile services switching center.In the prior art , all circuits between the BTS and MSC are rate-adapted, or TRAUed, beforethe MSC and all MSC cross connect functions are performed at 64 Kbps. This necessitatestwo TRAUing functions to be performed for calls between two 16 Kbps handsets controlledby the same MSC. In the private network of Fig. 2A, the TRAU is advantageously associatedwith the gateway to the public network, and need not be employed for calls internal to thenetwork. There is provided TRAU resource within the network, however, to accomplish rateadaptation when necessary, e.g. for calls between a 8 Kbps handset and a 16 Kbps handset.It is observed that GSM standard MS units in private cellular network 200 transmit andreceive data at a prede?ned rate, say 8 Kbps or 16 Kbps. Since the channels carrying bearerdata may be cross-connected by a subsystem within the inventive private cellular network 200instead of at the public MSC, it is often not necessary to TRAU the bearer data channels forcalls between MS units within the private cellular network 200. Consequently, the ability tocross-connect certain calls within the private network without TRAUing advantageouslyimproves communication quality and reduces the computational overhead associated withTRAUing.Fig. 2B shows in a symbolic format cPBX subsystem 206 of Fig. 2A. Within cPBXsubsystem 206, shown are a gateway MSC (GMSC) block 250, a registry 252 which containsboth the home location registry (HLR) and the visitor location registry (VLR registry), aprivate MSC block 254 and a cPBX block 256. GMSC block 250 represents the interface forcommunicating with the public network, e.g., public network 202 of Fig. 2A. Within GMSCblock 25 0, there is shown a public network interface 258 and a transcoder/rate adapter unit(TRAU) block 260. In one embodiment, public network interface 258 represents a trunkmodule which has been loaded with the appropriate software for communicating with thepublic network via standard interfaces such as ISDN, R2, and analog interfaces using inband orcommon analog signaling.?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213TRAU block 260 resides in GMSC block 250 to facilitate rate adaptation to build a callbetween an MS unit of the private cellular network and a telephone set in public network 202of Fig. 2A. Rate adaptation is necessary because a GSM MS unit and a public networktypically transmits and receives data at different rates. It is important to note that the presentinvention eliminates the TRAUing function whenever possible for calls that are switchedwithin the private cellular network, e.g., between MS units controlled by cPBX subsystem206. In contrast, prior art public cellular systems automatically provide TRAUing between theprior art BTS and the prior art MSC, either at the BTS, BSC, or between the BSC and theMSC.In the prior art wireless wPBX, a registry is not necessary since cordless phones areassociated with a particular base and do not roam from base to base. In contrast, a registry ispreferably provided in the private cellular network of Fig. 2A to provide mobility managementof the MS’s. Furthermore, the home location registry (HLR) and visitor location registry (VLRregistry) are preferably integrated in registry 252 of the private cellular network.Registry 252 of private cellular network 200 of Fig 2B serves, among others, to keeptrack of MS units that are authorized to use the resources of the private cellular network, thesubscriber data such as names, unique identi?cation information such as is kept in SubscriberIdenti?cation Module (SIM) for GSM handsets, telephone numbers associated with the MSunits, and the like. Subscriber information is kept track of because private cellular network 200must keep track of the MS units controlled by it as well as the subscribers on its network.PBX block 256 handles supplemental services (SS) that may be offered by privatecellular network 200. Furthermore, PBX block 256 handles the call control (CC) function,which includes the ability to intelligently understand the destination intended for the telephonenumber dialed. In one embodiment, the destination intended for the number dialed isdetermined in accordance to a numbering system. By way of example, extensions 2000 to 6000may indicate a destination MS unit inside private cellular network 200, while other numbersdialed may indicate calls that must be routed to telephone sets in the public network. PBXblock 256 may also contain circuits for performing functions typically expected of a PBXsystem such as call forwarding, call transfer, and the like.Private MSC block 254 handles mobility management (MM) and with the help of thePBX (256) radio resource (RR) management. The PBX 256 handles call processing (CC) andSupplemental Services (SS) via the MM session and assists with RR by forwarding calls?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213between cPBX's for handsets that have roamed into the coverage area of other cPBX’s or needto be handed over to another CPBX. ‘Switching decisions are made by the PBX 256. However, in some applications, privateMSC 254 may listen to messages sent across the MM session to decide whether or not itshould act as a BSC. When acting as a BSC, the PBX function is bypassed, the circuit crossconnect function to public MSC is made by the private MSC function.The intelligence within the private PBX block 256 may decide that switching may bemore efficiently performed at a BSC or BTS further down the hierarchy. In this case, there is asignaling connection between the MS units and the cPBX for CC and SS control via the privateMSC MM session. However, the switched voice/data path for the call will not traverse theCPBX, but will be cross connected by the BSC's and/or BTS's further down the hierarchy.Although the strictly private cellular network represents cost-effective and efficientcellular solutions for some markets, it has been recognized that strictly private cellular systemsthat do not make its radio subsystem resources to public MS's, i.e., MS units not speci?callyregistered with the home location registry of the private network, has some drawbacks incertain applications. For example, some private cellular networks may utilize the same cellularfrequency for operation as the public network. In this case, the fact that public MS's cannotutilize the radio resources of the private cellular network to make and receive calls whileroaming within the coverage area of the private cellular network means that there is a lapse or“hole” in coverage, from the perspective of the public MS users, while roaming.In other cases, the private cellular networks may be employed as temporary cellularnetworks to offer cellular service to geographical locations too remote or economicallyunrewarding to warrant the implementation of a full-scale public cellular network. In thesecases, it may be desirable to build into the private cellular network a migration path such thatwhen the public cellular network eventually grows and reaches the locations currently servicedby the private cellular network, the integration of the private radio subsystem resources intothe public network to offer cellular service to public cellular system customers would begradual and seamless for both the current private cellular system customers (who own privateMS's and are registered with the private HLR), and the public cellular system customers (whoown public MS's and are not known to the private HLR). Such gradual and seamless migrationpermits the use of the private radio subsystems by both the private and public MS's tooriginate and receive cellular services as the public network coverage area grows andencompasses the coverage area under control of the private radio subsystem. Advantageously,-9-?CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213the private MS's do not have to be replaced if and when the public network coverage areareaches the private network coverage area, and the public MS's do not have to suffer a lapse ofcoverage while being within the private network coverage area.These and other highly desirable features that overcome the disadvantages associatedwith traditional cordless phone systems as well as strictly private or public cellular systemsare realized by the novel private multiplexing cellular network, which is described in details inthe text of this speci?cation and its drawings.-10-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213SUMMARY OF THE INVENTIONThe present invention relates, in one embodiment, to a private multiplexing cellularnetwork that advantageously facilitates cellular communication for private MS’s. Further, theinventive private multiplexing cellular network allows the public MSC’s to employ its privateradio resources to facilitate cellular communication for public MS’s in a seamless manner whilethose public MS’s are within the coverage area of the private multiplexing cellular network.Advantageously, the implementation of a private network does not thereby result in alapse or “hole” in cellular coverage for users of public MS’s. In fact, public MS users can relyon the private multiplexing cellular network to provide radio subsystem resources for cellularcommunication in areas where the public network coverage has yet to reach. Additionally, theseamless manner with which public MS’s employ the private radio subsystem resources tomake and receive calls represents an ef?cient built-in migration path for integrating the privatenetwork into the public network in the future. For private MS users, all advantages associatedwith a private cellular network still apply.In accordance with one aspect of the present invention, at least one BSC of the privatemultiplexing cellular network is coupled to a multiplexing circuit. The multiplexing circuit is inturned coupled to two A-interfaces: a private A-interface for communicating with the privateMSC and a public A-interface for communicating with the public MSC. Via the multiplexingcircuit, calls from within the private multiplexing cellular network coverage area may be built, ina multiplexed manner, to either the public MSC or the private MSC. Likewise, calls that arriveat the private network coverage area via either MSC may be routed, via the multiplexing circuit,to the destination MS within the private network coverage area.In accordance with yet another aspect of the invention, there is provided within themultiplexing circuit intelligence for deciding whether the public A-interface or the private A-interface should be employed for servicing a service request received from either the MS’swithin the private multiplexing cellular network coverage area or from one of the MSC’s.In accordance with yet another embodiment of the invention, the private multiplexingcellular network facilitates cellular communication for a class of novel mobile stations, knownherein as hybrid mobile stations (MS). A hybrid mobile station has two telephone numbersassociated with its Subscriber Identi?cation Module (SIM): a public telephone number which-11-?CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213is known to the public network, and a private telephone number, which is known to the privatemultiplexing cellular network. Since a hybrid MS is known to both networks, albeit viadifferent telephone numbers, a hybrid MS may be operated within both networks. Either ofthe public or private telephone numbers may be dialed, and the intelligence within themultiplexing circuit decides whether the public MSC or the private MSC should handle the calldepending on which number is dialed.These and other features of the present invention will be presented in more detail in thefollowing speci?cation of the invention, the ?gures, and the appended claims.-12-?10152025WO 98/09457CA 02263934 1999-02-23PCT/US97/15213BRIEF DESCRIPTION OF THE DRAWINGSAdditional advantages of the invention will become apparent upon reading the followingdetailed description and upon reference to the drawings, in which:Fig. 1 illustrates a representative prior art public cellular communication system.Figs. 2A and 2B illustrate a private cellular network.Fig. 3 illustrates, in accordance with one embodiment of the present invention, a privatemultiplexing cellular network.Fig. 4 illustrates, in accordance with once aspect of the present invention, the generalcall ?ow for handling an incoming call request from the public MSC.Fig. 5 illustrates, in accordance with one aspect of the present invention, a pending pagetable.Fig. 6 shows, in accordance with one embodiment of the present invention, a techniqueemployed by the multiplexing circuit for deciding whether the public A-interface or the privateA-interface should be employed in building in the SCCP connection to an MS.Fig. 7 illustrates, in accordance with one embodiment of the present invention, thegeneral call ?ow for handling an incoming call request from the private MSC.Fig. 8 illustrates, in accordance with one embodiment of the present invention, thegeneral call ?ow for handling an outgoing service request by an MS within the private coveragearea310.Fig. 9 illustrates, in accordance with one embodiment of the present invention, thegeneral call ?ow for handling inter-BSC handovers.To facilitate discussion, Fig. 10 illustrates, in accordance with one embodiment of thepresent invention, the different kinds of cells available in the public network and in the privatenetwork.-13-?CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213Fig. 1 1 illustrates, in accordance with one aspect of the present invention, a modifiedhandover table that includes data useful in handovers among cells.Fig. 12 illustrates, in accordance with one embodiment of the present invention, adecision matrix for deciding, based on the nature of the call currently in progress, whether aparticular potential destination cell may be validly employed for handover purposes.-14-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213DESCRIPTION OF THE PREFERRED EMBODIMENTAn invention is described for implementing a novel private multiplexing cellularnetwork. In the following description, numerous speci?c details are set forth in order toprovide a thorough understanding of the present invention. It will be obvious, however, to oneskilled in the art, that the present invention may be practiced without some or all of thespeci?c details. In other instances, well-known process steps have not been described in detailin order not to unnecessarily obscure the present invention.Fig. 3 illustrates, in accordance with one embodiment of the present invention, a privatemultiplexing cellular network 300, which is shown coupled to a public cellular network 302 anda PSTN network 304. Private multiplexing cellular network 300, which employs the GSMprotocol for cellular communication, has a coverage area shown in Fig. 3 as private coveragearea 310. Within private coverage area 310, private MS’s, such as private MS 308, mayemploy the private MSC and the private radio subsystem of private multiplexing cellularnetwork 300, which includes its private BSC’s and private BTS’s, to communicate in a cellularmanner to other MS’s in the private multiplexing cellular network 300, phone sets in PSTNnetwork 304, and MS’s in public cellular network 302 (via PSTN 304) in the manner expectedof a private cellular network. For further infonnation regarding the details and implementationof a private cellular network that can facilitate cellular communication for its private MS’s,reference may be made to the aforementioned patent application S/N 08/435,709.As the term is employed hereinafter, a private MS is an MS having a single telephonenumber associated with its Subscriber Identity Module (SIM), which telephone number is“known” to the private multiplexing cellular network 300 (but not known by public cellularnetwork 302). In other words, the SIM of a private MS is known to the HLR of the privatemultiplexing cellular network 300 (hereinafter “private HLR”) and the phone numberassociated with that SIM is associated with private MSC 312. Although Fig. 3 shows onlyone private BSC 314 and two private BTS’s 316 and 318 for illustration purposes, privatemultiplexing cellular network 300 may have any number of private BSC’s 314 and privateBTS’s, depending on needs.Cellular communication in public cellular network 302 is facilitated for the public MS’s,such as public MS 322, within public coverage area 311 via the public MSC 326 and the public-15-?1015202530CA 02263934 1999-02-23WO 98109457 PCT/US97/15213radio subsystem. A public MS, as the term is used herein, denotes an MS having a singletelephone number associated with its SIM. Further, the SIM of a public MS is known to theHLR associated with the public network (hereinafter “public HLR”) and the phone numberassociated with that SIM is associated with public MSC 326. A portion of the public radiosubsystem is shown in Fig. 3 as public Base Station Subsystem (BSS) 324. Public cellularnetworks are well known and are implemented in a variety of ways. Thus, details regardingtheir implementation will not be repeated here.Public coverage area 31 1 may overlap private coverage area 310, as shown in Fig. 3,when the private multiplexing cellular network 300 is implemented in a geographic location thatis surrounded by coverage areas under public network control. Alternatively, there may be nooverlap between private coverage area 310 and public coverage area 31 1, such as the case whenprivate multiplexing cellular network 300 is implemented in a geographic location that thepublic network has yet to reach.Private multiplexing cellular network 300 also supports a type of hybrid public-privateMS’s, referred herein as hybrid MS’s. In accordance with one aspect of the present invention,hybrid MS’s, such as hybrid MS 306 of Fig. 3, has two telephone numbers associated with itsSIM: a private telephone number known to private multiplexing cellular network 300 and apublic telephone number known to public cellular network 302. In other words, the SIM of ahybrid MS is known by both the private and public HLR. However, the telephone numberassociated with the SIM in the public HLR, i.e., the telephone number associated with thepublic MSC 326 (hereinafter “public telephone number”) differs from the telephone numberassociated with the SIM in the private HLR, i.e., the telephone number associated with theprivate MSC 312 (hereinafter “private telephone number”). Since hybrid MS’s are known toboth the private MSC and the public MSC, hybrid MS’s may employ either the private MSCor the public MSC to facilitate cellular communication.Since the private telephone number of a hybrid MS is known only within privatemultiplexing cellular network 300, any call that terminates at the hybrid MS when its privatenumber is dialed must be handled by private MSC 312 (as will be apparent to those skilled inthe art, the term “call,” “telephone call” or like terms are not intended to be limiting herein andare employed as short hand references to connections that may carry voice, data, fax, shortmessage, and the like). For outgoing service requests that originate from a hybrid MS, private-15-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/U S97/ 15213‘multiplexing cellular network 300 treats the outgoing service request as one originating from aprivate MS since the identity of the hybrid MS (e.g., its IMSI or TMSI) is known to theprivate multiplexing cellular network 300. In this manner, a hybrid MS, while being insideprivate coverage area 310, is treated as a private MS for outgoing service requests or forincoming service requests via its private telephone number. To elaborate, an IMSI(International Mobile Subscriber Identi?er) represents the identi?er that is uniquely associatedwith a SIM. A Temporary Mobile Subscriber Identi?er (TMSI) represents a temporaryidenti?er that may be used in place of the IMSI to identify an MS during a call.However, the public telephone number of a hybrid MS is known in public cellularnetwork 302. This allows a hybrid MS to be treated as a public MS for incoming servicerequests that terminate on it. In other words, the service request to a hybrid MS via its publictelephone number may be handled by public MSC 326 within any coverage area available tothe public MS’s. This includes, for example, public coverage area 31 1 under control of thepublic radio subsystem of public network 302. For outgoing service requests, a hybrid MS istreated as a public MS while within public coverage area 311, and its outgoing service requestsmay be handled by public MSC 326.Unlike the strictly private cellular network disclosed in co-pending patent applicationS/N 08/435,709, which does not permit MS’s that are not registered with the private cellularnetwork, i.e., with the private HLR, to employ the resources of the private cellular network tomake or receive calls, the inventive private multiplexing cellular network 300 advantageouslyallows those MS’s to seamlessly employ the private radio subsystem of the privatemultiplexing cellular network 300 (and the public MSC) to perform cellular communicationwhen they roam within private coverage area 310. In this manner, the existence of the privatemultiplexing cellular network does not result in a “hole” in the public network coverage forusers of public MS’s.To permit public MS’s to utilize the private radio resources, i.e., the private BSC’s andthe private BTS’s of the private network, to facilitate cellular communication, there isprovided, in accordance with one aspect of the present invention, a multiplexer circuit 330 forcoupling the private radio subsystem to both private MSC 312 and public MSC 326.Multiplexer circuit 330 is coupled to two A-interfaces: public A-interface 329 forcommunicating with public MSC 326 and private A-interface 327 for communicating with-17-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213private MSC 312. When appropriately multiplexed, the private radio subsystem appears topublic MS owners and public MSC 326 as a seamless part of the public cellular network.Multiplexing circuit 330 may be implemented using any suitable technology, including forexample discrete logic, ASICS, processor logic, or even analog circuits. In one embodiment,multiplexing circuit 330 may be implemented via software using, for example, two differentdrivers to communicate with the public MSC and the private MSC.Via the multiplexing circuit, a public MS may seamlessly make and receive calls usingpublic MSC 326 and the private radio subsystem when it roams within private coverage area310. An incoming service request to a hybrid MS via the public telephone number of thehybrid MS may be handled by public MSC 326 (since it knows the public telephone numberof the hybrid MS), using either the public radio subsystem or the private radio subsystemdepending on the location of the destination hybrid MS. In the above scenarios, public MSC326 obtains its knowledge regarding whether a public MS or a hybrid MS is within privatecoverage area 310 via location updates from those MS’s.For calls to and from private MS’s, outgoing calls from hybrid MS’s when they arewithin private coverage area 310, or incoming calls to a hybrid MS using the private telephonenumber, multiplexer circuit 330 permits those calls to be handled by the combination of privateradio subsystem/private MSC 312. In this manner, multiplexing circuit 330 multiplexesincoming and outgoing calls to and from MS’s within private coverage area 310 so that theappropriate MSC would handle the call. The appropriate MSC may represent either privateMSC 312 or public MSC 326, depending on whether the call is incoming or outgoing, whetherthe MS involved is public, private, or hybrid, and if the latter, whether the public telephonenumber or the private telephone number is dialed.In the embodiment, multiplexing circuit 330 is co-resident with private BSC 314. Inanother embodiment, multiplexing circuit 330 may in fact, be co-resident with private MSC312 or may represent a stand-alone unit interfacing with private BSC 314, private MSC 312,and public MSC 326. Further, although there may be provided a multiplexing circuit withevery private BSC of the private multiplexing cellular network to enable every private BSC todirectly couple, in a multiplexed manner, with either the public MSC or the private MSC, suchan arrangement is not required. In one embodiment, only some private BSC’s are providedwith a direct connection to a multiplexing circuit, and other private BSC’s may access the-18-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/U S97/ 15213desired MSC (public or private) via the private BSC that is coupled to the multiplexing circuit.Alternatively, multiple BSC’s may be coupled to a single or a few multiplexing circuits,permitting the BSC’s to gain access to the public and private network in a multiplexed manner.For outgoing calls from an MS within private coverage area 310, MS’s with an identity,(e.g., IMSI or TMSI) known to private multiplexing cellular network 300 (whether a hybridMS or a private MS) are preferably handled by private MSC 312. Outgoing calls from an MShaving an identity associated with a SIM not associated with the private HLR are understoodto be outgoing calls from public MS’s that have roamed into private coverage area 310 and arehandled by public MSC 326 using the radio subsystem resources of private multiplexingcellular network 300, i.e., via private BSC 314 and the private BTS’s of Fig. 3.In Fig. 4 and the ?gures that follow, the discussion is made with reference to a privatemultiplexing cellular network 300 wherein multiplexing circuit 330 is co-resident with privateBSC 314. However, the implementation of a private multiplexing cellular network 300 whereinmultiplexing circuit 330 is external to private BSC 314 (or associated with private MSC 312)should be apparent to those skilled in the art given this disclosure. In both of these latter cases,the switching of traf?c channels and packet information between the private BSC and theMSC’s across the A-interfaces may employ well—known facilities of the SS7. Theseimplementations may further include additional messages between the BSC and themultiplexing circuit in order to query the content of the Pending Page Table (discussed later inHg5)Fig. 4 illustrates, in accordance with one aspect of the present invention, the general call?ow for handling an incoming service request from the public network, e.g., public cellularnetwork 302 of Fig. 3, via public MSC 326. The service request may represent a request forany type of communication service to the destination MS, including SMS (short messageservice) or a regular call (fax, voice, or data). In Fig. 4, the destination MS for the servicerequest through public MSC 326 is chosen to be public MS 332 to simplify the discussionalthough it should be noted that the destination MS may also be a hybrid MS that is calledusing its public telephone number. To further simplify the illustration task, drawing elementshaving a like number perform analogous functions in the ?gures herein.In Fig. 4, a Page Request message 402 is sent from public MSC 326 to private BSC314. The Page Request message 402 is ?rst received by multiplexing circuit 330 (on private‘ -19-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213IBSC 314 in this example) from public MSC 326. Page Request message 402 is sent frompublic MSC 326 if the destination phone number is one that is associated with public MSC326, i.e., either the destination phone is a public MS, or the destination phone is a hybrid MS,e.g., hybrid MS 306, and the public telephone number of the hybrid MS is dialed. Public MSC326 knows that the Page Request message 402 should be sent to private BSC 314 since itknows, from the location updates from the public and hybrid MS’s, that the MS associatedwith the dialed telephone number is currently within the coverage area of the privatemultiplexing cellular network, e.g., private multiplexing cellular network 300.Page Request 402 includes an identi?cation of the destination MS, e.g., the IMSI orTMSI of the MS being paged by public MSC 326. Once Page Request message 402 is receivedby multiplexing circuit 330, both the identi?cation of the destination MS (the destination IMSI(or TMSI)) and an A—interface identi?cation (public or private) are stored in a Pending PageTable. The storage operation is represented symbolically in Fig. 4 by block 404. Oneimplementation of the Pending Page Table is shown in Fig. 5.In Fig. 5, each pending page request for an MS believed to be within private coveragearea 310 is stored in an entry of Pending Page Table 500. As mentioned earlier, each entry ofPending Page Table 500 preferably includes the identity of the MS being paged (preferablyidenti?ed by its IMSI or TMSI), and the identity of the interface through which the pagerequest, e.g., Page Request message 402 of Fig. 4, is sent. In one embodiment, the knowledgeregarding the identity of the A-interface through which the Page Request message is sent(private or public) is derived from the fact that the Page Request message is received fromeither the public A-interface (e.g., A-interface 329 of Fig. 3) or the private A-interface (e.g., A-interface 327).Entries are preferably kept in Pending Page Table 500 until the page is completed ordeemed unsuccessful by the paging BSC or BSC’s. For example, once the SCCP connectionhas been made between the appropriate MSC (either the private MSC or the public MSC), andthe MS being paged, the pending page entry in Pending Page Table 500 is removed therefrom.In one embodiment, race conditions that may occur while paging hybrid MS’s areadvantageously avoided through the use of Pending Page Table 500. Race conditions may existsince hybrid MS’s have two telephone numbers, a private telephone number and a publictelephone number, and both of those telephone numbers may be simultaneously dialed, thereby-20-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/U S97/ 15213causing the hybrid MS to be paged by both the private MSC and the public MSC. In oneembodiment, if a destination MS already has its ‘identity (IMSI or TMSI) stored in PendingPage Table 500, a subsequent page for that destination MS will be dropped and simply doesnot have its identity entered into Pending Page Table 500. Of course, while a destination MS isbusy, a subsequent page for that destination MS may be handled using any conventionaltechnique.Since the private radio subsystem, which comprises the private BSC’s and privateBTS’s of private multiplexing cellular network 300, appears from the perspective of publicMSC 326 as part of the public network, paging requests from public MSC 326 may bereceived seamlessly by private BSC 314.Private BSC 314 pages public MS 332 (via private BTS 318) using the Page message406. Thereafter public MS 332, acting as an MS authorized to use the private radio subsystemof private multiplexing cellular network 300, proceeds to establish communication with publicMSC 326. In one embodiment, public MS 332 issues a Charmel Request message 410 toprivate BTS 318 on a random access charmel to request a charmel for communication. Sinceprivate BSC 314 is the entity that actually assigns the channel, this Channel Request message410 is forwarded from private BTS 318 to private BSC 314 via the Channel Required message412. Subsequently, private BSC 314 then assigns a channel via the Channel Activate message414. In one embodiment, private BSC 314 assigns a dedicated signaling channel (e.g., aStandalone Dedicated Control Channel or “SDCCH” channel) for signaling purposes since it isunknown at this point what kind of connection is desired (voice, data, fax, or SMS). On thechannel assigned by Channel Activate message 414, control information to and from public MS332 may be communicated.Upon receiving Channel Activate message 414, private BTS 318 then replies to privateBSC 314 with a Channel Activate Acknowledge message 416. Via the Immediate Assignmessage 418, private BSC 314 requests that private BTS 318 moves public MS 332 to thecharmel assigned (which may be the SDCCH channel in one embodiment). The ImmediateAssign message is further forwarded by private BTS 318 to public MS 332 as shown in Fig. 4.After public MS 332 moves to the channel indicated by Immediate Assign message 418,public MS 332 responds with a Set Asynchronous Balance Mode (SABM) message 440,which represents a LAPD—M message requesting a link layer association to establish LAPD—M' -21-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/U S97/ 15213connection via the SABM message 440. Private BTS 318 acknowledges the receipt of theSABM message 440 with a Unnumbered Acknowledged (UA) message 437.On top of the SABM message 440, a Service Request via the Complete Layer 3 (“ComL3”) message may be piggybacked, which includes the identity of the destination MS, e.g., theIMSI or TMSI of public MS 332 in the illustration of Fig. 4. The Service Request piggybackedon the SABM message 440 is then forwarded from private BTS 318 to private BSC 314 via theEstablish Indication message 439.When private BSC 314 receives the identity of the MS that responded to the pagerequest, e.g., from public MS 332 in this example, multiplexing circuit 330 compares thereceived identity (either IMSI or TMSI) against entries in Pending Page Table 500 of Fig. 5 tomatch up the Page Request and Page Response. The comparison step is representedsymbolically in Fig. 4 by logic block 441. If the identity of the MS indicated by the ServiceRequest message (piggybacked on SABM message 440) matches one of the pending entries inPending Page Table 500, the associated A-interface identity (private or public), which is storedearlier in block 404, is then employed to allow the BSC 314 to establish the SCCP connectionwith the MSC through which the Page Request message was originally sent. Fig. 6 discusses indetail later herein one technique for determining which MSC should be involved in the buildingof the SCCP connection.Note that for incoming calls to MS’s within private coverage area 310, it may not benecessary to check with the private HLR of private multiplexing cellular network 300 todetermine which interface (private or public) should be employed to service the call request.For further information regarding the private HLR, reference may be made to, for example, theabove referenced co-pending patent application S/N 08/435,709.By storing in block 404 the identity of the destination telephone (using its TMSI orIMSI) and the identity of the interface through which the Page Request is sent, it is possible tomatch up (at a later time in block 441) the MS that issues the Service Request message(piggybacked on the SABM Page Response) with the earlier Page Request message to allowprivate BSC 314 to send messages from private BSC 314 back out the same A-interfacethrough which the Page Request message is originally sent. Via this technique, the SCCPconnection can advantageously be made from the destination MS identi?ed by the Page-22-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/ 15213Request message 402 to the correct MSC through which the Page Request is originally sentwhen the destination MS unit responds to the Page Request message.In the context of Fig. 4, since the Page Request message 402 was sent through publicMSC 326, multiplexing circuit 330 understands after consulting Pending Page Table 500 thatthe SCCP connection needs to be built from the public A-interface 329 to the destination MS.The COM L3 message 442 is therefore sent from private BSC 314 to public MSC 326 toestablish the SCCP connection between those two entities. Once the SCCP connection isestablished, all subsequent messages between public MSC 326 and public MS 332 are routedthrough the SCCP connection. The messages may employ, for example, DTAP (direct transferapplication part) within the radio subsystem.The BSC, e.g., private BSC 314 of Fig. 4, will become involved again only when theMSC with which the SCCP connection is made wants to reassign the channel or disconnect thecall. For example, during reassignment, the BSC needs to know which A-interface is employedfor the call so the channel assignment messages from the controlling MSC can be properlyinterpreted. For example, when public MS 332 moves from a location area controlled by oneBSC to a location area controlled by another BSC (irrespective whether those BSC’s arecontrolled by private multiplexing cellular network 300 or public cellular network 302), thecontrolling public MSC 326 needs to participate in the inter-BSC handover. In oneembodiment, the information about which A-interface being used is associated with the callcontrol information stored for this connection in private BSC 314 so that channel assignmentmay be appropriately performed via the correct A-interface.Note that in Fig. 4, the private MSC is not employed in the establishment of the SCCPconnection (and subsequent building of the call via the established SCCP connection) betweenthe public MSC and the private radio subsystem of private multiplexing cellular network 300.In this manner, cellular communication between the public MSC can be seamless irrespectivewhether the radio resource that handles the communication belongs to the private multiplexingcellular network or the public network.Fig. 6 shows, in accordance with one embodiment of the present invention, thetechnique employed by multiplexing circuit 330 for deciding whether the public A-interface orthe private A-interface should be employed in handling a service request. In block 602, it isascertained whether the service request received by the multiplexing circuit is an MS--23-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213terminated call (i.e., an incoming service request) and whether the identity of the MS to bechecked (identi?ed by its IMSI or TMSI) exists in Pending Page Table 500.For an incoming service request, i.e., a request to an MS within private coverage area310, the MS identity to be checked in block 602 represents the identity of the destination MS.As discussed in connection with Fig. 4, the identity of the destination MS may be obtainedfrom, for example, the Page Request message from the MSC. For an outgoing service request,i.e., a service request that originates from an MS within private coverage area 310, the MSidentity to be checked in block 602 represents the identity of the originating MS. The identityof the originating MS may be obtained from, for example, the Channel Request message whenan MS wishes to request a channel to begin communicating with the private radio subsystem.If the service request represents an MS-terminated call and the MS identity to bechecked in block 602 matches one of the entries in Pending Page Table 500, the MS to bechecked represents an MS responding to an early Page Request message, e.g., Page Request 402of Fig. 4. In this case, the method proceeds to step 604 to ascertain whether the original PageRequest message that the MS is responding to arrived earlier via the public A-interface or theprivate-A interface. The identity of the A-interface through which the Page Request messagearrived was stored earlier in Pending Page Table 500, along with the identity (IMSI/TMSI) ofthe MS identified by the Page Request message.If the earlier Page Request message arrived via the private A-interface, the private A-interface is then employed to establish the SCCP connection between the private MSC and theMS whose identity is checked in Fig. 6 (as shown in step 606). On the other hand, if thepublic A-interface was the interface through which the Page Request message was sent earlier,the public A-interface would then be employed to establish the SCCP connection between thepublic MSC and the MS (as shown in step 608).If it is ascertained in step 602 that the service request is not an MS-terminated servicerequest, the outgoing, MS-originated service request may represent a request from an MSwithin the private coverage area to perform a location update, to make a call, or to send a shortmessage. In this case, the method proceeds to step 640 wherein it is ascertained whether theoutgoing service request represents a location update. If yes, the method proceeds to step 642to service the location update.-24-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213In step 642, it is then ascertained whether the MS that issues the location updateservice request represents a purely private MS (i.e., not a hybrid MS) that sent an IMSI. Inthis case, the private A—interface is employed for the location update from the private MS tothe private MSC (step 644). If the MS sent an TMSI (for the purpose of this example,assume that a private MS never issues a TMSI) or if the IMSI is not known to the privatenetwork or if the MS that originates the service request is a hybrid MS, the MS that requeststhe location update can be assumed to be a public MS or a hybrid MS, and the public A-interface is employed for the location update (step 646).Note that location updates from hybrid MS’s are made to the public MSC, therebyallowing the public network to keep track of hybrid MS’s. In this manner, calls to hybridMS’s using their public telephone numbers may be handled by the public MSC. On the otherhand, calls to hybrid MS’s using their private telephone numbers require, in this embodiment,that the entire private network be paged (since the private MSC does not participate inlocation updates by hybrid MS’s). Even then, however, the paging operation is not anexpensive operation, particularly since private networks tend to be small.If it is ascertained in step 640 that the outgoing service request is not a location update,the method proceeds to step 650 to begin servicing this outgoing service request. In step 650,it is ascertained whether the TMSI was sent. If the TMSI was received in connection with theoutgoing service request, the IMSI is then requested in steps 652, 654, and 656 from the MSissuing the outgoing service request. The IMSI is desirable since the IMSI may be employedby the multiplexing circuit to ascertain whether this IMSI is known to the private network (i.e.,belonging to a SIM'that is associated with either a purely private MS or a hybrid MS). Oncethe IMSI is obtained (either directly from the outgoing service request or from steps652/654/656), it is then ascertained in step 658 whether the IMSI is associated with a SIMknown in the private multiplexing cellular network (i.e., either a purely private MS or a hybridMS).In one embodiment, the IMSI is compared against entries in the private HLR (in step658) to ascertain whether this IMSI is associated with a private MS SIM, a hybrid SIM, orwith a public MS SIM. In another embodiment, the private HLR downloads to themultiplexing circuit in advance the list of IMSI’s that are known to the private network. When-25-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/ 15213a check of step 658 is required, the checking can be done locally within the multiplexing circuitwithout wasting network bandwidth to check the HLR.If the MS that issues the outgoing service request is a purely private MS or a hybridMS (ascertained in step 658), the private A-interface is employed for servicing the outgoingservice request. In other words, the private MSC is employed to handle outgoing servicerequests for MS’s that are private or hybrid. On the other hand, if the MS that issues theoutgoing service request is a public MS (ascertained in step 65 8), the public A-interface is thenemployed for servicing the outgoing service request.Fig. 7 illustrates, in accordance with one embodiment of the present invention, the stepsinvolved when multiplexing circuit 330 handles a Page Request from private MSC 312 andfacilitating the building of an SCCP connection between private MSC 3 l2to the MS beingpaged. Although private MS 306 is employed in Fig. 7 as the destination MS for ease ofillustration, the Page Request message, when sent by the private MSC, represents a PageRequest for an MS that is either a private MS or a hybrid MS but the private telephonenumber is dialed.Referring now to Fig. 7, a Page Request message 700 is sent from private MSC 312 toprivate BSC 314 for a destination MS. The private MSC may wish to page an MS to initiateany type of cellular communication service, including SMS (short message service) or forregular calls (fax, voice, or data). The Page Request Message 402 is ?rst received bymultiplexer circuit 330 (on private BSC 314 in this example). In block 702, the identity of thedestination MS, along with the identity of the A-interface through which the Page Requestmessage 700 is sent (the private A-interface in the case of Fig. 7) is stored. In one embodiment,the identities of both the paged MS and the A-interface (public or private) are stored in anentry in Pending Page Table 500 of Fig. 5.Private BSC 314 then pages private MS 306 via Page message 704. Thereafter, privateMS 306 proceeds to establish a SCCP connection with private MSC 312. In one embodiment,these messages include Channel Request message 706, Channel Required message 708, ChannelActivate message 710, Channel Activate Acknowledge 712, Immediate Assign 714 (which isforwarded via BTS 316 directly from private BSC 314 to private MS 306, SABM message716, and Establish Indication (718). These messages have been discussed in detail earlier inconnection with Fig. 4.-25-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213The identity of the destination MS (IMSI or TMSI) that responds with Page Responsemessage 716 is then checked in block 720 of Fig. 17 against the pending Page Requests to ensurethat the SCCP connection is correctly built between private MSC 312 and the paged MS. Fig.6 discusses one technique for performing such an identity check. If the identity of the MS thatsends the Page Response message 716 matches one of the entries in Pending Page Table 500,multiplexing circuit 330 will then ascertain, using the matched entry, the identity of the A-interface (whether private or public) through which the Page Request for this destination MSarrives.The SCCP connection may then be built to the appropriate MSC (private MSC 312 inthe case of Fig. 7). Messages involved in the completion of the SCCP connection includes theCOM L3 message 722 from private BSC 314 to private MSC 312. Once the SCCP connectionis established, all subsequent messages between private MSC 312 and private MS 306 may berouted through this SCCP connection.Again, note that it may not be necessary to access the private HLR to ensure that theSCCP connection is built between the correct MSC and the destination MS. Further, when thePage Request message arrives through private MSC 312, the public MSC is not involved, asshown in Fig. 7, in the building of the SCCP connection and the subsequent building of any callpaths necessary to service the incoming call request. Advantageously, cellular communicationappears seamless from the perspective of the private MS users and hybrid MS users.Furthermore, since the private MSC handles the calls for private MS’s and incoming calls forhybrid MS’s, advantages associated with a purely private cellular network (i.e., ef?cient cross-connecting, intelligent TRAUing, avoidance of public network charges) are still retained forthese callsFig. 8 illustrates the steps taken by multiplexing circuit 330 to handle an outgoingservice request initiated by an MS within the private coverage area 310. As will be discussedin detail later herein, when the service request originates from a private MS or a hybrid MS,i.e., MS’s that are known in private multiplexing cellular network 300, the SCCP connection isbuilt from the originating MS to the private MSC to allow the private MSC to handle theoutgoing call. On the other hand, if the service request originates from an MS whose identity isunknown by private multiplexing cellular network 300, e.g., the originating MS is a public MS,-27-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/U S97/ 15213the SCCP connection is built from the MS with the unknown identity (IMSI) to the publicMSC to allow the public MSC to handle the outgoing call attempt.As shown in Fig. 8, an MS initiates an outgoing service request by issuing a channelrequest message 800. Messages 800, 802, 804, 806, 808, 810, 811, and 812 represent somerelevant messages required to establish communication between an MS and a private BSC.These messages are similar to those discussed in connection with Fig. 4 and are not repeatedhere for simplicity of illustration.In block 814, the identity of the originating MS, which identity (IMSI or TMSI) isincluded in the Service Request message piggybacked on the Establish Indication message 812,is checked by multiplexing circuit 330 of Fig. 3. Fig. 6 discloses a technique for checking theidentity of the originating MS for the purpose of routing the SCCP connection to theappropriate MSC. If the originating MS represents an MS known in private multiplexingcellular network 300 (i.e., a private MS or a hybrid MS), the SCCP connection is made toprivate MSC 312 via multiplexing circuit 330. Messages that may be employed to establishthis SCCP connection are shown in block 850 of Fig. 8.On the other hand, if the identity of the originating MS indicates that the originatingMS is not known in private multiplexing cellular network 300, the SCCP connection is thenmade between the originating MS and public MSC 326 (using the messages in block 860 of Fig.8).In one embodiment, the steps involved in checking the identity of the originating MS inprivate multiplexing cellular network 300 involves simply sending a proprietary MS ID Checkrequest to the private HLR and receiving a proprietary response therefrom. In block 850 ofFig. 8, the SCCP connection is built between the originating MS and the private MSC 312. Tofacilitate the building of the SCCP connection, a Com L3 Message 816 is sent between privateBSC 314 and private MSC 312.In block 860 of Fig. 8, the SCCP connection is alternatively built between theoriginating MS and the public MSC 326 (the Com L3 Message is sent between private BSC3 l4and public MSC 326 in step 820). After the SCCP connection is made between theoriginating MS and the appropriate MSC, all subsequent messages ?ow through this SCCPconnection. From the private BTS 316 or private BSC 314 point of view, the SCCP and the-28-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213identity of the A-interface (public or private) are then known. This data may be employedsubsequently to request circuit on the A interface to fully service the service request.Fig. 9 illustrates the general call ?ow for performing handover between a private BSCand a public BSC when the public MS wants to roam from the coverage area of a private BSCinto the coverage area of a public BSC. The discussion of Fig. 9 is made with reference to thenetwork illustration of Fig. 3, and reference may be made thereto to improve understanding.Handover preparation by a BSC includes, for a particular connection, a determination ofvalid destination cell(s) from the set of potential destination cells reported by the MS. In theprivate muliplexing cellular network 300, the BSC’s are required to differentiate the validdestination cells for MS handovers based on whether the MS is associated with a public MSCconnection or a private MSC connection. For example, a public connection, i.e., a connectionvia public MSC 326, may regard cells that are on either side of public/private cell boundary 390as proper destination cells for the purpose of handover. On the other hand, a privateconnection, i.e., a connection via private MSC 312, may not regard potential destination cellsthat are under control of public BSS 324 as proper destination cells for handover purposes.Preferably, private BSC 314 requests all MS’s to report on all possible neighbor cells, includingthose associated with public BSS 324. It is the job of private BSC 314 to ascertain which ofthose potential destination cells may be employed for handover given a particular connection(public or private).Note that since public BSC 324 only has to handle connections for the public MSC,public BSS 324 does not have to be modi?ed, e.g., does not have to be endowed with theintelligence for eliminating potential destination cells in the manner required of private BSC314. It simply needs to be recon?gured to be aware of the neighbor cells on the private side ofprivate/public cell boundary 390.Private BSC 314 then sends an HO Required message 902 to the controlling publicMSC 326. The HO Required message includes information regarding the cell to be handed overto. Public MSC 312 ascertains the BSC that controls the destination cell. For the purpose ofthe present discussion, public BSC 324 is assumed to be the destination BSC, i.e., the BSC thatcontrols the destination cell. Thus, public MSC 326 sends a Handover Request message 904 topublic BSC 324 to inform destination public BSC 324 that a handover is imminent.-29-?1015202530CA 02263934 1999-02-23WO 98/09457 PCTIU S97/ 15213Public BS 324 then acknowledges the HO Request message 902 via the HO RequestAcknowledge message 906. Public MSC 326 then sends a Handover Command message 908(a)to private BSC 314, which passes the received HO Command message 908(a) directly to publicMS 332 (as HO Command message 908(b)). The HO Command 908(b) message directs publicMS 332 to handover by telling public MS 332 the frequency to move to, the new frequency tolisten to, and the like (this information was included in H0 Request Acknowledge message 906from destination public BSC 324 to public MSC 326).Public MS 332 then communicates directly with public BSC 324 (i.e., the newdestination BSC that controls the destination cell) via the HO Access message 910. PublicBSC 324 then sends an HO Detect message 912 to public MSC 326 to inform public MSC 326that public BSC 324 and public 332 have successfully communicated. Further, public MS 332also sends an HO Complete message 914(a) to public BSC 324, which is passed on to publicMSC 326 as HO Complete message 9l4(b). The HO Complete messages 914(a) and 914(b)indicate to public MSC 326 that handover is completed and public BSC 324 is now handlingthe radio resource for public MS 332.Private BSC 314, representing the BSC that no longer handles the call for public MS332, then receives a Clear Command message 916 from public MSC 326, which directs privateBSC 314 to clear the SCCP connection between private BSC 314 and public MSC 326. Afterthe SCCP connection is cleared, private BSC 314 acknowledges that the SCCP connection isclear via the Clear Complete message 918.Although Fig. 9 illustrates in detail only the situation when a public MS wishes tohandover from a private BSC to a public BSC, handover may be accomplished from a privateBSC to another private BSC via messages similar to those shown in Fig. 9 except that theprivate MSC handles the handover. Handover between a public BSC to a private BSC isperformed in a manner similar to that shown in Fig. 9 and is not repeated here. Further, if thehandover is from a public BSC to a public BSC or from a private BSC to a private BSC (viapublic MSC 326), the handover may be accomplished using a GSM standard technique.Note that in Fig. 9, handover is performed between network nodes below the MSClevel. In other words, once an MS has its call handled by an MSC in the private world, aprivate MSC then handles the handover. Alternatively, once a call is handled by an MSC inthe public network, a public MSC may then handle the handover. There is no handover from a-30-?1015202530CA 02263934 1999-02-23WO 98109457 PCT/US97/15213public MSC to a private MSC, or vice versa. If a public MS begins its call within publiccoverage area 311 and moves into private coverage area 310, for example, handover may occurbetween the public radio subsystem and the private radio subsystem. All the while, however,the public MSC continues to handle the mobility management function for the call. Further,although public MS 332 is chosen in Fig. 9 to simplify illustration, handover is also performedfor hybrid MS’s that are called using their public telephone numbers.Further, handover among interconnected private MSC’s is also available. For furtherinformation regarding one technique for performing handover among interconnected privateMSC’s, reference may be made to the above referenced patent application S/N 08/435,709.Handover among interconnected public MSC’s may be accomplished using a conventionalGSM technique.In accordance with another aspect of the present invention, if private coverage area 310and public coverage area 311 overlap, an MS such as public MS 332 or hybrid MS 306 may beinstructed to give preference to either private coverage area 310 or public coverage area 31 1. Aroaming hybrid MS can choose to lock onto the private network (via location updates) to availits user of the advantages associated with the private network (e. g., lower calling costs).Alternatively, a roaming hybrid MS can choose to lock onto the public network if soinstructed. Advantageously, the preference setting minimizes the number of times an MS unithops from private coverage area 3 l0'to public coverage area 311 and vice versa.In some applications it may be desirable to limit the private network resources used bypublic MS’s so as to preserve a minimum level of access for private and/or hybrid MS’s in theprivate network cells in which public MS usage is permitted. By way of example, up to 20%of the radio bandwidth associated with these cells may be allocated to public MS’s while atleast 80% of the radio bandwidth resources should be allocated to private and/or hybrid MSunits. Of course, the bandwidth reserved for private and/or hybrid MS’s may be widely variedto meet the needs of a particular system.Other priority resource allocation schemes may be used as well. By way of example,public MS’s may be allowed to access any unused resources with the caveat that they may be"bumped" when resources they are using are subsequently required by private and/or hybridMS’s requesting access. Alternatively, public MS’s may be permitted access any time thereare available resources or available resources exceed a designated threshold. By way of further-31-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/ 15213example, schemes that consider the location of the public MS within the private network, thetraf?c on the resources would actually be used by the public MS, etc. may also be employed.The ability to govern the sharing of resources between private and/or hybrid MS’s and publicMS’s ensures that the private and/or hybrid MS’s will not be unduly denied access to theresources of the private network by an excessive in?ux of calls involving public MS’s and/orcalls involving hybrid MS’s using its public telephone number.In another aspect of the present invention, a handover control table in the BSC, whichincludes data regarding neighbor cell relationship, preferably includes information to indicatewhether the handover is allowed for a public connection, a private connection, or both. In oneembodiment, this information may exist as a ?ag in the neighbor cell relationship entry of thetable. By arbitrarily setting the value of this ?ag for a set of neighbor cell relationship entries,the boundary of the expansion of the public network into the private network may bearbitrarily restricted to a portion of the private network if desired. In this manner, a portion ofthe private network may remain strictly private, if such is desired.By way of example, Fig. 10 illustrates a plurality of cells 1002-1118 wherein cells1002-1006 are purely private cells (i.e., only calls handled by the private MSC are allowed),cells 1008-1012 are cells that could handle both private and public calls (i.e., cells labeled as“both” in Fig. 10 and can handle calls through either the private MSC or the public MSC), andcells 1014-1018 are cells that handle only public calls (i.e., calls controlled by the public MSC).The location of line 1020 relative to the public and private networks is determined by the sizeof the private network, with cells to the left of line 1020 belonging to the private network andcells to the right of line 1020 belonging to the public network. Cells in the private network arecontrolled either by the private MSC or by the public MSC via the multiplexing circuitdisclosed herein. Cells in the public network are controlled by the public MSC. Line 1022,which separate the purely private cells from cells that could handle both private and publiccalls can be arbitrarily placed anywhere within the private network by appropriately taggingeach cell with a ?ag as mentioned earlier.Fig. 11 illustrates, in one embodiment, a handover table 1102 suitable for use inascertaining whether a potential destination cell for the purpose of handover for a given call canin fact be employed. Each entry of handover table 1102 includes a Designated Type ?eld.The Designated Type ?eld indicates whether this cell is designated, via an appropriate ?ag, a-32-?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213purely private cell, a cell that could handle both private and public calls, or a public cell. Forexample, cell 1002 of Fig. 10 is shown in handover table 1102 as a purely private cell. Cell1008 of Fig. 10 is shown in handover table 1102 as a cell that could handle both private andpublic calls (labeled as “both” in Fig. 11). Likewise, cell 1010 is a cell that could handle bothprivate and public calls. Cell 1014 of Fig. 10 is shown in handover table 1102 as a public cell,i.e., belonging to the public network.Fig. 12 shows, in one embodiment, a decision matrix for determining whether, for aparticular type of call, handover to a potential destination cell may be accomplished. Ifhandover is desired, the handover table, e.g., handover table 1102 of Fig. 11, is first consultedto determine whether that potential destination cell is designated public, both, or private. Thisinformation is then employed, in combination with the call type information (public or privatecall) for the call associated with the handover attempt, in the decision matrix of Fig. 12 todetermine whether a potential destination cell is appropriate for the call, thereby allowinghandover to proceed. In one embodiment, the call type information, i.e., information regardingwhich MSC (public or private) currently controlling the call, is included in the call controlblock.In Fig. 12, boxes 1204 and 1208 represent non-allowable combinations. For example, apublic cell cannot accept a private call (box 1208). Analogously, a private cell cannot accept apublic call (box 1204).In box 1202, if the call type is public and the destination cell type is also public, thenhandover is allowed. As mentioned earlier, a public call is a call that is handled by the publicMSC, and may either be a call to/from a public MS, a call from a hybrid MS while outside theprivate network, or a call to a hybrid MS using its public telephone number. In box 1210, ifthe call type is private and the destination cell type is also private, then handover is allowed.A private call is a call to/from a private MS, a call from a hybrid MS while inside the privatenetwork, or a call to a hybrid MS using its private telephone number. If the potentialdestination cell is cell that could handle both private and public calls then either a private call ora public call may be handed over to it (box 1206 and 1212).Note that the presence of purely private cells, e.g., cells 1002-1006 of Fig. 10, mayresult in a “hole” in cellular coverage for public MS users. This is because a public MS, whileinside the private network, may lock on to a purely private cell to initiate its service request if' -33-?101520CA 02263934 1999-02-23WO 98/09457 PCT/U S97/ 15213this purely private cell has the strongest signal. Unless a solution is developed to resolve thisproblem, the service request from the public MS will be denied by the private MSC, i.e., theentity that controls the purely private cell of this example.One potential solution involves con?guring all cells of the private network to work withthe multiplexing circuit (thereby eliminating all purely private cells). Another potentialsolution involves purely private cells performing a directed retry for that public MS, which isessentially a handover from the purely private cell which receives the service request from thepublic MS to a cell that could handle a public MS. The cell that could handle a public MS mayrepresent either a public cell or a cell that could handle both public and private calls (labeled“both” in Fig. 10). If the directed retry is successful, the service request may proceed via thisnew cell and the public MSC. If the directed retry attempt fails or if there are no neighboringcells capable of handling a public MS, the attempted call associated with the public MS may bedropped altogether.As is apparent from the above discussion, not all cells of the private network need to becon?gured to work with the multiplexing circuit. The ability to allow some cells to remainpurely private allows the private network to be ?exibly configured and represents an optionfor reducing costsAlthough the foregoing invention has been described in some detail for purposes ofclarity of understanding, it will be apparent that certain changes and modi?cations may bepracticed within the scope of the appended claims. Given this disclosure, it will be apparent tothose of ordinary skills in the art that combinations and substitutions may be made withoutdeparting from the scope and the spirit of the present invention. Consequently, the scope ofthe invention is not limited to the speci?c examples given herein but is set forth in theappended claims.-34-?1015202530WO 98/09457Abis:ACM:ANM:BCF:BSC:BSS:BTS:CACB:CAS:CC:CCPU:CO:cPBX:DSP:GMSC:GSM:CAS HLR:IAM:IMSI:IPN:ISDN:IWF:LAPD-M:MM:MS:MSCOMC:PSTN:PBX:CA 02263934 1999-02-23PCT/US97/15213APPENDIX AGLOSSARY OF TERMS AND ABBREVIATIONSProtocol stack between a BTS and a BSCAddress Complete MessageAnswer MessageBase Station Control FunctionBase station ControllerBase Station SubsystemBase Transceiver StationCellular Adjunct Control BlockPrivate multiplexing cellular networkCall Control ManagementCellular CPUCentral Of?cecellular Private Branch ExchangeDigital Signal ProcessingGateway for MSCGlobal Systems for Mobile CommunicationHome Location RegistryInitial Address MessageInternational Mobile Subscriber Identi?erInterface to Public NetworkIntegrated Services Digital NetworkInnerWorking FunctionsLink Access Protocol on the Dm (control) charmelMobility ManagementMobile StationsMobile-Services Switching CenterOperation and Management CenterPublic Switched Telephone NetworkPrivate branch exchange-35-?10W0 98I09457RF:RL:RR :SCCP:SMS :SS:TDM data:TRAU:TRX:VLR:VME:wPBX:CA 02263934 1999-02-23module Radio Frequency module 4Radio LinkRadio Resource ManagementSignaling Connection Control PartShort Message ServicesSupplemental ServicesTime Division Multiplexed DataTranscoder-Rate Adapter UnitTransceiverVisitor Location RegistryAn industry standard bus for interconnecting componentswired PBX-36-PCT/US97/152 13?1015202530CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213APPENDIX BThe present disclosure is written for ease of understanding by those of skill in the art.For others, the following documents, incorporated herein by reference for all purposes,may be reviewed for additional information.Mouly, Michel & Pautet, Marie-Bernadette, "The GSM System for MobileCommunications", Mouly, Michel & Pautet, Marie-Bernadette, 1992.European Telecommunications Standards Institute, "European digital cellulartelecommunications system (Phase 2); Mobile radio interface signaling layer 3 Generalaspects (GSM 04.07)", 1994, Valbonne - France.I!European Telecommunications Standards Institute, European digitaltelecommunications system (Phase 2); Mobile radio interface layer 3 speci?cation(GSM 04.08 2" , 1994, Valbonne - France.European Telecommunications Standards Institute, "European digital cellulartelecommunications system (Phase 2); Mobile-services Switching Centre - Base StationSystem (MSC - BBS) interface Layer 3 speci?cation (GSM 08.08)" , 1994, Valbonne -France.European Telecommunications Standards Institute, "European digital cellulartelecommunications system (Phase 2); Signaling transport mechanism speci?cation forthe Base Station System - Mobile-services Switching Centre (BBS - MSC) interface(GSM 08.06)" , 1994, Valbonne - France.-37-?1015CA 02263934 1999-02-23WO 98/09457 PCT/US97/15213European Telecommunications Standards Institute, "European digital cellulartelecommunications system (Phase 2); Base Station Controller - Base TransceiverStation (BSC - BTS) interface Layer 3 speci?cation (GSM 08.58)" , 1994, Valbonne -France.European Telecommunications Standards Institute, "European digital cellulartelecommunications system (Phase 2); Mobile Application Part (MAP) speci?cation(GSM 09.02)" , 1994, Valbonne - France.European Telecommunications Standards Institute, "European digital cellulartelecommunications system (Phase 2); Signaling requirements on internetworkingbetween the Integrated Services Digital Network (ISDN) or Public Switched TelephoneNetwork (PSTN) and the Public Land Mobile Network (PLMN) (GSM 09.03)", 1994,Valbonne - France.-33-

Claims (21)

WHAT IS CLAIMED IS:

1. A private cellular communication system having a private mobile services switching center and a base station controller, said base station controller being configured to facilitate cellular communication for a plurality of private mobile stations and a plurality of public mobile stations associated with a public network having a public mobile services switching center, comprising:
a multiplexing circuit coupled to said base station controller, said multiplexing circuit including a first interface circuit for coupling to said private mobile services switching center and a second interface circuit for coupling to said public mobile services switching center, said multiplexing circuit being configured to multiplex incoming and outgoing calls between said base station controller and one of saidprivate mobile services switching center and said public mobile services switching center, wherein a call from one of said public mobile stations is handled through said public mobile services switching center and said base station controller via said multiplexing circuit when said one of said public mobile station is within a location area controlled by said base station controller, a call to one of said private mobile stations is handled through said private mobile services switching center and said base station controller via said multiplexing circuit when said one of said private mobile station is within a location area controlled by said base station controller.

2. The private cellular communication system of claim 1 wherein said base station controller is further configured to facilitate cellular communication for a plurality of hybrid mobile stations, each one of said hybrid mobile stations having a public telephone number and a private telephone number different from said public telephone number, a call to a given one of said hybrid mobile stations, when called using said public telephone number, is handled through said public mobile services switching center and said base station controller via said multiplexing circuit, a call to said given one of said hybrid mobile stations, when called using said private telephone number, is handled through said private mobile services switching center and said base station controller via said multiplexing circuit.

3. The private cellular communication system of claim 2 wherein a call from said given one of said hybrid mobile stations, when made from within said location area controlled by said base station controller, is handled by said private mobile services switching center through said multiplexing circuit.

4. The private cellular communication system of claim 3 wherein a call from said given one of said hybrid mobile stations, when made from within a location area controlled by said public network, is handled by said public services switching center without involving said multiplexing circuit.

5. The private cellular communication system of claim 2 wherein a call from said given one of said hybrid mobile stations, when made from within a location area controlled by said public network, is handled by said public services switching center without involving said multiplexing circuit.

6. The private cellular communication system of claim 1 wherein said base station controller is further configured to facilitate cellular communication for a plurality of hybrid mobile stations, each one of said hybrid mobile stations having a public telephone number and a private telephone number different from said public telephone number, a call to a given one of said hybrid mobile stations, when called using said public telephone number, is handled through said public mobile services switching center and said base station controller via said multiplexing circuit.

7. The private cellular communication system of claim 1 wherein said base station controller is further configured to facilitate cellular communication for a plurality of hybrid mobile stations, each one of said hybrid mobile stations having a public telephone number and a private telephone number different from said public telephone number, a call to said given one of said hybrid mobile stations, when called using said private telephone number, is handled through said private mobile services switching center and said base station controller via said multiplexing circuit.

8. The private cellular communication system of claim 1 wherein said first interface circuit implements a private A interface and said second interface circuit implements a public A interface.

9. A private cellular communication system having a private mobile services switching center and a base station controller, said base station controller being configured to facilitate cellular communication for a hybrid mobile station having a pubic telephone number and a private telephone number, said public telephone number being known to a public mobile services switching center in a public network, said private telephone number being known to said private mobile services switching center, comprising:
a multiplexing circuit coupled to said base station controller, said multiplexing circuit including a first interface circuit for coupling to said private mobile services switching center and a second interface circuit for coupling to said public mobile services switching center, said multiplexing circuit being configured to multiplex incoming and outgoing calls between said base station controller and one of said private mobile services switching center and said public mobile services switching center, wherein a call from said hybrid mobile station, when made from within said location area controlled by said base station controller, is handled by said private mobile services switching center through said multiplexing circuit.

10. The private cellular communication system of claim 9 wherein a call from said hybrid mobile station, when made from within a location area controlled by said public network, is handled by said public services switching center without involving said multiplexing circuit.

11. The private cellular communication system of claim 10 wherein a call to said hybrid mobile station, when called using said public telephone number, is handled through said public mobile services switching center and said base station controller via said multiplexing circuit.

12. The private cellular communication system of claim 9 wherein a call to said hybrid mobile station, when called using said public telephone number, is handled through said public mobile services switching center and said base station controller via said multiplexing circuit.

13. The private cellular communication system of claim 12 wherein a call to said hybrid mobile station, when called using said private telephone number, is handled through said private mobile services switching center and said base station controller via said multiplexing circuit.

14. The private cellular communication system of claim 9 wherein a call to said hybrid mobile station, when called using said private telephone number, is handled through said private mobile services switching center and said base station controller via said multiplexing circuit.

15. The private cellular communication system of claim 9 wherein said first interface circuit implements a private A interface and said second interface circuit implements a public A interface.

16. A multiplexing circuit configured for use in a private cellular communication system having a private mobile services switching center and a base station controller, said base station controller being configured to facilitate cellular communication for a hybrid mobile station having a pubic telephone number and a private telephone number, said public telephone number being known to a public mobile services switching center in a public network, said private telephone number being known to said private mobile services switching center, comprising:
a first interface circuit configured for coupling to said private mobile services switching center; and a second interface circuit configured for coupling to said public mobile services switching center, said multiplexing circuit being configured to multiplex incoming and outgoing calls between said base station controller and one of said private mobile services switching center and said public mobile services switching center, wherein a call from said hybrid mobile station, when made from within said location area controlled by said-base station controller, is multiplexed by said multiplexing circuit through said first interface circuit to said private mobile services switching center.

17. The multiplexing circuit of claim 16 wherein a call to said hybrid mobile station, when called using said public telephone number, is multiplexed by said multiplexing circuit from said public mobile services switching center to said base station controller via said second interface circuit.

18. The multiplexing circuit of claim 17 wherein a call to said hybrid mobile station, when called using said private telephone number, is multiplexed by saidmultiplexing circuit from said private mobile services switching center to said base station controller via said first interface circuit.

19. The multiplexing circuit of claim 16 wherein a call to said hybrid mobile station, when called using said private telephone number, is multiplexed by saidmultiplexing circuit from said private mobile services switching center to said base station controller via said first interface circuit.

20. The multiplexing circuit of claim 1 wherein said first interface circuit implements a private A interface and said second interface circuit implements a public A interface.

21. The multiplexing circuit of claim 16 wherein a call from a mobile station not registered with said private mobile switching center while within said location area controlled by said base station controller is multiplexed by said multiplexing circuit from said base station controller to said public services switching center through said second interface circuit.