text: 1. Field of the Invention
  The present invention relates in general to telecommunications networks and more particularly to a private wireless network that is integrated with a public wireless network.
  2. Description of Related Art
  Recent advances in telecommunications technology have allowed a wide array of special telecommunication services to be made available to subscribers. Examples of such services include abbreviated dialing, which allows a subscriber to reach a party by dialing less than the entire telephone number of that party, call forwarding, in which calls directed to the subscriber may be forwarded to another line, terminating call screening, which allows the subscriber to specify certain times during which all or selected incoming calls are to be rejected, and originating call screening, in which calls to certain telephone numbers are barred. In general, enhanced telecommunications services (“services”) encompass those call features that do more than simply place or terminate telephone calls as dialed.
  To enable such services, telecommunications networks typically carry “signals,” as well as the voice or data comprising the conversation between the calling party and the called party. These signals monitor the status of the lines, indicate the arrival of incoming calls, and carry the information needed to route the voice or other data through the network. At one time, these signals were inband, i.e., the signals were transmitted through the same circuits as used for voice transmission. However, most telecommunications networks now use out-of-band signaling, i.e., the signals are transmitted over a signaling network separate from the circuit-switched network that carries voice and data. Thus, signals carried on the separate signaling network are used to control the switches in the circuit-switched network to set up and tear down the circuit between the calling party and called party. Currently, Signaling System 7 (“SS7”) is the most commonly used signaling system.
  In previous decades, the switches themselves provided the special telecommunications services. However, the switches had to have a great deal of “intelligence” built into them to accomplish this. In particular, a typical switch included a database of control information and call processing logic, in addition to switching capabilities. This approach was unwieldy because a telecommunications provider needed to update the software and databases on all of its many switches in order to update services or add new services throughout its telecommunications network. To complicate matters, the software needed to program switches from different vendors often differed greatly.
  To overcome these limitations, most telecommunications networks in the Unites States have adopted the advanced intelligent network (“AIN”) approach. The advent of AIN has improved matters in two ways. First, most of the control information and call processing logic, usually referred to as “service logic,” resides in a central network location, the service control point (“SCP”), instead of in the multitude of switches. Second, AIN provides a set of standardized messages between the switches and the SCP to allow for a variety of services. These standards are embodied in Bellcore's AIN Release 0.1 and AIN Release 0.2.
  The benefit of having the call control functions in a centralized SCP is that changes made at the SCP will apply to a large number of switches. This makes changing services and adding new services much easier and reduces the problem of differences in switches from different vendors. Moreover, the centralization at the SCP and the standardized message set allows an SCP to control a large number of switches, which are referred to as service switching points (“SSPs”) in AIN parlance, even those from different vendors. Indeed, in the AIN approach, the switches can be quite generic but still able to provide a variety of services. This is because, instead of the SSPs themselves having the necessary call processing logic, the SSPs signal the SCP for guidance at predefined “trigger points” in the call processing. The triggers can occur either when the SSP is attempting to originate a call or attempting to terminate a call. The query signal from the SSP passes a set of relevant parameters, in a predefined format, to the SCP. Such parameters can include the calling party's telephone number and the called party's telephone number, for example. When the SCP receives the query, it executes the appropriate service logic and consults the appropriate databases to obtain the information and instructions needed to provide the intelligent network service. The SCP then sends a response message to the SSP instructing it how to complete the call to provide the service.
  Because of the large number of SSPs and other network elements connected to the signaling network, the signaling network typically includes one or more signal transfer points (“STPs”) that route the signals through the signaling network. Thus, the signals between SSPs and other SSPs or the SCP are often routed through one or more STPs. When SS7 signaling is used, signals may be routed to specific network elements based on their point codes. Alternatively, signals may be routed using Global Title Translation (“GTT”), in which STPs route signals to their intended destinations without the need for point codes. In particular, when GTT is used, STPs route signals based on information contained in their payloads.
  Wireless telecommunications networks have also been developed on a similar model. In wireless networks, switching is performed by mobile switching centers (MSCs). Each MSC typically controls one or more base stations or base transceiver stations (BTSs), sometimes via one or more base station controllers (BSCs). Each BTS provides a wireless coverage area within which mobile stations can communicate with the BTS over an air interface. The mobile stations can be cellular or PCS telephones, or other devices. Different formats may be used for communicating over this air interface. At present, the most commonly used formats in the United States are Advanced Mobile Phone Service (AMPS), Time Division Multiple Access (TDMA), Global System for Mobile Communications (GSM), and Code Division Multiple Access (CDMA).
  Each mobile station typically has a “home” wireless network, in which a home location register (HLR) serves as a centralized repository of information about the mobile station. Typically, the HLR contains a service profile for the mobile station, the last reported location of the mobile station, and the current status of the mobile station, such as whether it is active or inactive. The service profile indicates which enhanced services the mobile station subscribes to.
  Mobile stations typically identify themselves to wireless networks using one or more types of identification numbers. Each mobile station typically has a 10-digit Mobile Identification Number (MIN). The MIN may be, but need not be, the same as the directory number that would be dialed to reach the mobile station. Thus, a mobile station may also have a Mobile Directory Number (MDN) different from its MIN. Each mobile station also typically has a unique 32-bit Electronic Serial Number (ESN).
  When an MSC needs to find information about a mobile station, such as where it is located or what services it subscribes to, it queries the HLR corresponding to that mobile station. Thus, to inquire about a mobile station that is roaming, i.e., operating on a network other than its home network, the MSC queries an HLR that is outside of its network. Typically, these queries are routed to the appropriate HLR based on the mobile station's MIN and/or MDN. For example, the MSC may reference internal translation tables to determine which HLR to query for which MINs and/or MDNs. Alternatively, STPs may route queries to the appropriate HLR using GTT, based on either MIN or MDN.
  In a manner analogous to the AIN approach used in wireline networks, an MSC may also query a Wireless Intelligent Network (WIN) SCP for call processing instructions, in the course of either originating a call from or terminating a call to the mobile station. Such queries can arise from trigger points set by the mobile station's service profile that the MSC downloaded from the mobile station's HLR. Moreover, an MSC uses such queries to obtain the call processing instructions needed to provide enhanced telecommunications services to the mobile station. In response to such queries, the WIN SCP will typically execute the appropriate service logic and consult the mobile station's service profile to formulate the call processing instructions that the WIN SCP then sends to the MSC.
  The Telecommunications Industry Association/Electronics Industry Association (TIA/EIA) has developed a number of interim standards that specify how this signaling between MSCs, HLRs, WIN SCPs, and other network elements, should occur. In particular, most wireless networks in the United States use one of the revisions of TIA/EIA Interim Standard 41 (“IS-41”). The IS-41 signaling is typically run as an application on another signaling system, such as SS7. A recent revision of this Interim Standard, ANSI-41 Rev. D, which was published in July, 1997, is fully incorporated herein by reference. Furthermore, extensions to ANSI-41D or WIN triggers and WIN call processing are included in Interim Standard IS-771, which was published July, 1999, and is fully incorporated herein by reference.
  In addition to public wireline and wireless networks, businesses and other organizations (collectively referred to herein as “enterprises”) have been using private telecommunications networks for many years. Such networks are “private” in that the subscribers are typically limited to employees of, or other individuals associated with, the enterprise. For example, many enterprises have used private wireline switching systems, such as private branch exchanges (PBXs), to switch calls to and from telephones in the enterprise's office area. Such private telecommunications networks advantageously allow an enterprise greater control over its telecommunications system and enable the enterprise to customize the telecommunications it provides to its subscribers. For example, the enterprise can set up an abbreviated dialing plan for the private network, in which the subscriber telephones can reach one another by dialing an abbreviated digit string. In another typical service, calls to subscriber telephones that are not answered are sent to a voice mail system.
  Private telecommunications networks have also been provided with wireless capability. In particular, there have been developed various wireless office telephone systems (“WOTS”) that provide for wireless communication a, typically, limited geographic area, such as a building or campus. See, e.g., Lawrence Hart, et al., “Cellular and PCS: The Big Picture,” p. 183-232 (1997). However, many such WOTS systems require specialized telephones, so that a standard cellular or PCS telephone that can be used in a public wireless network may not work in a given WOTS system. With many people routinely carrying a cellular or PCS telephone, requiring a different telephone to be used at work is a substantial inconvenience.
  To overcome this disadvantage, some wireless office systems have been developed in accordance with the TIA's IS-94 specifications. The IS-94 specifications allow the same handsets to be used in both private cellular systems, e.g., wireless office systems, and public cellular systems. However, IS-94 is not designed to handoff calls between the private and public cellular systems. The lack of handoff capability is a significant disadvantage. In particular, if a user moves out of the limited coverage area of the wireless office system during the course of a call, the call may be dropped.
  Some wireless office systems, however, have some limited ability to allow users to move between the private and public cellular networks during the course of a call. An example is the ROAMEO in-building wireless telephone system that is sold by AG Communication Systems, headquartered in Phoenix, Ariz. The ROAMEO system is provided as an adjunct to a company's existing PBX, Centrex, or key system and allows standard wireless telephones to act as wireless extensions of the existing office desktop telephones. If a user originates a call in the public wireless network and then moves into the building served by the ROAMEO system during the course of the call, the call will continue using the public wireless network (provided the signal from the public wireless network is able to penetrate into the building). Moreover, once the call is ended, the telephone is automatically registered on the ROAMEO system. However, if a call is originated within the coverage area of the ROAMEO system, it may be dropped if the telephone leaves the ROAMEO coverage area.
  Widergen, et al., U.S. Pat. No. 5,890,064 discloses a wireless office system that is said to be integrated into both a private telephony network and a public cellular system. Certain of the disclosed embodiments are said to support handover of ongoing calls between cells of the wireless office system and the public cellular system. The wireless office system includes a wireless office gateway and a radio access network to provide wireless communications to corporate mobile terminal, which are part of a corporate group of terminals of the private telephony network. The public cellular system includes an HLR/SCP, which, in turn, includes a home location register (HLR) and a Service Controller Function (SCF). The SCF can store a user profile for each subscriber. The wireless office system communicates with the HLR to provide mobility management for the corporate mobile terminals and communicates with the SCF to provide intelligent network services for the corporate mobile terminals.
  A disadvantage with this configuration, however, is that many users may already have a cellular telephone for personal use and may be disadvantaged by having to use a separate “corporate mobile terminal” for business. In particular, it would be advantageous for many users to have one mobile telephone that could be used for both personal and business calls. Moreover, with respect to enhanced telecommunications services, a user may desire a different set of services for personal calls than for business calls. However, the Widergen approach of using the HLR/SCP to serve the corporate mobile terminals in both the private and public networks does not facilitate the application of separate business and personal services.