WO1999003292A1

WO1999003292A1 - System for automatic roaming in a private microcellular network

Info

Publication number: WO1999003292A1
Application number: PCT/IB1998/001132
Authority: WO
Inventors: Jonathan M. Crowther; Kwok Kuen Kwong; Huey-Sheng Ma; Scott Larribeau
Original assignee: Nortel Networks Corporation
Priority date: 1997-07-11
Filing date: 1998-07-10
Publication date: 1999-01-21
Also published as: AR013645A1; AU8237498A

Abstract

A method and apparatus for automatic roaming in a private microcellular network is described. The invention allows a roaming mobile subscriber to automatically receive at a visited site calls placed to a home site. A mobility user database (MUD) stores mobile identification information concerning the mobile subscriber, and a home site identifier associated with the mobile subscriber. The MUD provides the home side identifier in response to a query specifying the corresponding mobile identification information. The mobile identification information may be the mobile identification number (MIN) of the subscriber. Assignment of the MIN to the subscriber is not under control of the network. When the mobile subscriber roams to the visited site, the visited site queries the MUD with the mobile identification information. The MUD, which is responsive to queries from a number of sites, responds with the home site identifier of the subscriber. The visited site assigns a forwarding number to the mobile subscriber, and sends a forwarding instruction to the home site identified by the home site identifier. The home site associates the mobile subscriber with a home number assigned by the telephone system. Upon receiving the forwarding instruction, the home site also associates the home number with the forwarding number so that calls directed to the home number are forwarded to the forwarding number of the subscriber.

Description

SYSTEM FOR AUTOMATIC ROAMING IN A PRIVATE MICROCELLULAR NETWORK

BACKGROUND Field of Invention

The present invention relates to the field of cellular telephony, and in particular to private cellular telephone systems.

Description of the Related Art

The number of cellular telephone users in the United States and abroad has increased dramatically in the past decade. Most cellular customers subscribe to a public cellular service provider, known as a "cellco." In more recent years, network communications companies have recognized the need to tailor public network functions to the requirements of individual businesses. For example, Internet companies have begun to exploit the market for corporate-based Intranet solutions. Similarly, cellular networking companies have developed microcellular networks in which a private network is set up to link communications within and among one or more business sites. The base stations serving the private microcells are typically located in corporate offices and coupled to the PBXs of the business. When the mobile subscriber roams into the business site, the phone registers with the private network and then emulates a desk phone that is served by the PBX. When the mobile is registered with the private network, it is no longer under the jurisdiction of the public cellco, and therefore is not charged cellco telephone rates. Private cellular networks have been developed by Northern Telecom

Limited, the assignee of the present invention. See, for example, U.S. Patent No. 4,771,448, issued to Koohgoli, et al, and U.S. Patent No. 5,537,610, issued to Mauger, et al, both patents assigned to Northern Telecom. Also refer to U.S. Patent No. 5,235,632, issued to Raith. These and all other references herein are incorporated by reference herein.

The forwarding of calls to roaming subscribers can be handled in different ways. The visited site may assign the roaming subscriber a temporary directory number for use in the foreign service area. The visited site provides this temporary forwarding number to the subscriber's home site. Thus, calls placed to the roaming subscriber's regular number at his home site are forwarded to the temporary number at the visited site. In order to transfer the forwarding number from the visited site to the home site, the visited site must have knowledge of the mobile subscriber's home site location. This information may be provided by the mobile subscriber by embedding a home site identifier number within the subscriber's mobile identification number (MIN), which is assigned to the mobile unit upon subscription to the cellco. The subscriber provides the MIN to the visited site upon registration. This approach requires segregation of the mobile identification numbers according to their home sites. •^'

The 700 Follow Me Roaming service employs a centralized 700 number database. All roaming subscribers are assigned a phone number beginning with a three-digit 700 prefix. Whenever such a mobile unit powers up to register with the visited site, it provides its phone number to the visited site. In response, the visited site provides the phone's location to the centralized 700 database. When another phone dials the roaming subscriber, the Follow Me Roaming system looks up the current location of the mobile unit in the centralized database, and forwards the call to the visited site. One disadvantage of the Follow Me Roaming system is that the centralized 700 database must be referred to for each call. For a further discussion of roaming, please refer to U.S. Patent No. 4,901,340, issued to Parker, et al., and U.S. Patent No. 5,440,613, issued to Fuentes. SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for automatic roaming in a private microcellular network. The invention allows a roaming mobile subscriber to automatically receive at a visited site calls placed to a home site. A mobility user database (MUD) stores mobile identification information concerning the mobile subscriber, and a home site identifier associated with the mobile subscriber. The MUD provides the home site identifier in response to a query specifying the corresponding mobile identification information. The mobile identification information may be the mobile identification number (MIN) of the subscriber. Assignment of the MIN to the subscriber is not under control of the network.

When the mobile subscriber roams to the visited site, the visited site queries the MUD with the mobile identification information. The MUD, which is responsive to queries from a number of sites, responds with the home site identifier of the subscriber. The visited site assigns a forwarding number to the mobile subscriber, and sends a forwarding instruction to the home site identified by the home site identifier. The home site associates the mobile subscriber with a home number assigned by the telephone system. Upon receiving the forwarding instruction, the home site also associates the home number with the forwarding number so that calls directed to the home number are forwarded to the forwarding number of the subscriber.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a private microcellular network of the present invention.

Figure 2 illustrates a home location register according to the present invention.

Figure 3 is a call blueprint illustrating the operation of the present invention when the mobile subscriber roams between sites in the private network.

Figure 4 illustrates the mobility user database (MUD) of the present invention. Figure 5 illustrates a visitor location register according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and apparatus for automatic roaming in a private microcellular network. In the following description, numerous details are set forth in order to enable a thorough understanding of the present invention. However, it will be understood by those of ordinary skill in the art that these specific details are not required in order to practice the invention. Further, well-known elements, devices, process steps and the like are not set forth in detail in order to avoid obscuring the present invention. Finally, please note that the term "circuitry" as used herein refers to any hardware, software and/or firmware for performing the functions described herein.

Figure 1 illustrates a private microcellular network of the present invention. In this example, the system includes first, second and third private branch exchanges (PBXs) 100, 102, 104, respectively. Each PBX may be implemented with a MERIDIAN Ml (Northern Telecom trademark) or similar private branch exchange. Each PBX controls telephone switching within an associated private, e.g., corporate, site. Desk phones 106 at the corporate site are connected by wire to the associated PBX. The PBX is also coupled to the public switched telephone network (PSTN) 108 that is geographically local to the PBX. The location of each corporate site PBX is indicated by a private number prefix (PNP). In this example, each desk phone 106 connected to a PBX is assigned a private telephone number comprising the private number prefix followed by a four-digit directory number (DN). This private phone number is assigned by the private network operator.

As in conventional private networks, a telephone at one site may reach another telephone at the same or another site by dialing the private phone number of the called telephone. For example, a caller at private number 655-5145 may dial the private number 444-0505 to reach another party within the private network at a different site. The call is communicated over a private line connecting the two corporate sites. The line may be in the form of an ISDN connection, for example. Because the calls are placed over the private network, they avoid public phone charges.

The desk phones 106 at the private sites may also communicate over the PSTN 108. Through an agreement with the public phone company, the private phones may, for example, retain the four-digit directory number as the last four digits. However, the private number prefix is typically replaced by a public number prefix. By dialing the public telephone number (the public number prefix followed by the directory number), an outside caller can directly place a call to a phone within the private network through the PSTN 108. The public telephone number is otherwise known in the art as the direct inward dial number (DID).

Each PBX also supports cellular telephone communications through one or more base stations 110 connected to the PBX. Each base station 110 defines a cell area. The cells at each private corporate site are referred to as microcells, to be contrasted with the macrocells of the public cellco network. To handle registration at each site and roaming among sites, each PBX includes a home location register (HLR) 112 and a visitor location register (VLR) 114. The HLR 112 is a database that contains subscription information, service activation information and current location information for mobile subscribers having the PBX connected to the HLR as their home site. The HLR 112 also contains subscriber verification information. Further information concerning the HLR may be found in U.S. Patent No. 5,537,594 issued to Maidenhead, et al., and assigned to Northern Telecom, incorporated by reference herein. The VLR 114 is a database that contains information concerning mobile units that have roamed to the PBX associated with the VLR. Assume that the mobile subscriber 116 powers-up within its home site.

The subscriber will attempt to register with the home site PBX 100. The PBX 100 determines that the subscriber unit is at its home site by examining its HLR, as shown in Figure 2. (The first row represents the HLR entries for one subscriber when the subscriber is at its home site. The second row represents the HLR when the subscriber is roaming.) The HLR includes entries for storing unique identifiers for the mobile, including without limitation a mobile identification number (MIN) and an electronic serial number (ESN) or other identifiers as defined by the private cellular system. The home site of a mobile unit is defined as the site having the HLR in which the MIN of the mobile unit is entered. The MIN is assigned to the mobile unit by the public cellco upon subscription to the cellco. The ESN is programmed into the mobile unit upon manufacture. In many instances, the private network operator has no control over the assignment of the MIN and ESN to the cellular telephone.

The mobile unit 116, upon entering the home site coverage area, sends to the home site PBX 100 a registration request including its MIN and ESN. The home site PBX 100 compares the received MIN and ESN to the corresponding entries in its HLR 112 to determine whether the mobile unit 116 is permitted to register with the private network. If so, the home site PBX 100 returns a registration acknowledge signal to the mobile subscriber unit, thereby completing registration. Further description of the registration process may be found in

Lawrence Wong, et al., U.S. Patent Application Serial No. , entitled Method and Apparatus for Switching Between Public Macrocellular Telephone System and Private Microcellular Telephone System, assigned to the assignee of the present invention and filed concurrently herewith. That application is incorporated by reference herein.

In the HLR 112, the mobile subscriber 116, as identified by its MIN and ESN, is associated with a private directory number (DN). As explained above, the DN is a four-digit direct dial number assigned by the private network operator. With this association, the mobile unit is granted all the same privileges as the desk phone 106 having the same DN at the home site. These privileges or call features are specified in the user profile entry of the HLR. Based upon this association, when the desk phone receives an incoming call, the mobile unit having the MIN corresponding to the desk phone's DN will ring and receive the call as if it were a desk phone. Conversely, the mobile unit can place outgoing calls as if it were the corresponding desk phone. In other words, the mobile unit can dial other desk phones or mobile units throughout the private network using the private telephone numbers comprising the PNP/DN combination.

Figure 3 illustrates the operation of the present invention when the mobile unit roams between sites in the private network. Within the coverage area of the visited site, the mobile unit issues a registration request REGREQ, including its MIN and ESN, as before. In response, the visited site PBX 102 uses those parameters to check its HLR 112 to determine whether the visited site is the home site of the mobile unit. Because this is not the case in this example, there is no match in the HLR of the visited site. Accordingly, the visited site PBX 102 sends a FINDHOME query, along with the received MIN, across the private network to a private site that includes a mobility user database (MUD) 118 of the present invention. The MUD 118 may reside at any site, including without limitation the home site or the currently visited site. The MUD need not reside at a site having cellular capability. The MUD 118, shown in Figure 4, associates the MINs of all mobile units authorized to roam the system with their corresponding home site identifiers (PNPs). Individual MINs or ranges of MINs can be mapped to a home site identifier. In response to the received MIN of the FINDHOME command, the MUD 118 returns the corresponding home site ID. In this example, the MIN 415- 555-6964 is shown as being assigned to the home site 655. Accordingly, the PBX 104 that is home to the MUD 118 returns the PNP 655 along with the MIN back to the visited site PBX 102, as indicated by the signal HOME (MIN, PNP), as shown in Figure 3.

The MUD information may also be distributed over a network of MUDs. For example, each MUD may serve a group of sites. To respond to the

FINDHOME query, each MUD that is unable to respond to the query can pass it on to another MUD until the query is answered or all MUDs have been queried.

Return of the PNP from the MUD 118 indicates that the mobile unit 116 is an authorized member of the private network, and has roaming privileges. In response to the PNP, the visited site PBX 102 assigns a four-digit temporary local direct number (TLDN) to the MIN ofthe mobile unit. The TLDN is selected from a pool of TLDNs, which do not correspond to physical desk phones at the visited site. This assignment is shown in the VLR 114 of Figure 5. The PNP ofthe visited site, e.g., 444, combined with the TLDN, e.g., 0001, forms a temporary private number now corresponding to the MIN ofthe mobile unit. The VLR also stores a cell identification number identifying the microcell ofthe visited site in which the mobile unit currently resides. Further, the VLR stores the user profile associated with each DN.

Referring to Figure 3, the visited PBX 102 sends a registration notification signal REGNOT to the home site PBX 100 specifying the MIN, PNP and TLDN. The home site PBX 100 stores the received PNP and TLDN as a forwarding number in the HLR entry corresponding to the MIN, as shown in Figure 2. In one embodiment, REGNOT may also instruct the home site PBX 100 to prevent incoming calls from reaching the mobile's corresponding desk phone, so that only the mobile may receive such calls. Tn response to REGNOT, the home site PBX 100 may return a signal regnot to the visited site 102 along with the MIN to indicate that the set up ofthe forwarding feature at the home site has been completed. The REGNOT signal also transmits the user profile ofthe mobile from the home site to the visited site. If the mobile unit 116 had roamed not from the home site but from another visited site, then the home site would send a registration cancellation signal REGCANC to the previously visited site along with the MIN. This action deregisters the mobile unit from the previously visited PBX. In other words, the previously visited PBX clears the MIN from its VLR. The currently visited PBX sends a registration acknowledge (REGACK) message to the phone to indicate that it is now fully registered at the currently visited PBX. The previously visited PBX also sends a message regcanc to the home PBX along with the MIN to indicate that cancellation has taken place. After such cancellation, the TLDN assigned to the mobile is released for later reuse. As an option, the visited site can cancel registration ofthe phone at the visited site by sending a REGCANC signal to the home site. This typically occurs if the visited site detects no activity by the mobile for a period of time, e.g., 12 hours ("aging"), or polls the mobile and determines that it is no longer at the visited site.

Through the association ofthe MIN with the temporary forwarding number in the HLR, the roaming mobile unit will receive all calls placed to the desk phone home number 655-5145 (PNP/DN). Both calls from within the private network and outside calls directed to the corresponding public number of the desk phone will be forwarded to 444-0001 through the HLR at the home site. Conversely, the mobile unit can place outgoing calls as if it were the desk phone 106 residing at the home site. Standard techniques for setting up calls between a PBX and a mobile within the PBX's cell coverage area may be employed.

Based on the foregoing, it can be seen that the present invention can be employed with standard mobile units having MINs over which the private network operator has no control. In other words, the present invention does not require that the MINs themselves specify the home site ofthe mobile subscriber. Rather, that function is handled by the MUD 118. More generally, the invention is not dependent on the cellular standard employed by the subscriber, provided that the standard can uniquely identify the mobile, and this identification information (whether or not a MIN) is provided by the mobile to the visited site during registration.

Further, unlike the 700 Follow Me Roaming system, the present invention requires referral to a centralized database only upon registration ofthe phone at the visited site, and not for every phone call. According to the invention, the forwarding number is maintained at the home site after roaming registration, thereby avoiding the step of referral to a centralized database for each call.

Although the invention has been described in conjunction with particular embodiments, it will be appreciated that various modifications and alterations may be made by those skilled in the art without departing from the spirit and scope of the invention. The invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the amended claims.

Claims

CLAIMSWhat is claimed is:

1. A mobility user database (MUD) comprising: a MUD mobile identification information entry for storing mobile identification information concerning a mobile subscriber; and a MUD home site entry for storing a home site identifier associated with the mobile subscriber; wherein the MUD provides a home site identifier in response to a query specifying the corresponding mobile identification information.

2. The MUD of claim 1, wherein the home site identifier indicates a home site to which forwarding information should be sent.

3. The MUD of claim 1, wherein the MUD is responsive to queries from a plurality of sites.

4. The MUD of claim 1 , wherein the MUD is part of a telephone network comprising a visitor location register (VLR) having: a VLR mobile identification information entry for storing the mobile identification information; a VLR home site identifier entry for storing the home site identifier associated with the mobile subscriber; and a forwarding number entry for storing a forwarding number assigned to the mobile identification information.

5. The MUD of claim 1 , wherein the MUD is part of a telephone network comprising a visited site for associating a forwarding number with the mobile identification information, and for sending a forwarding instruction specifying the forwarding number to the home site.

6. The MUD of claim 5, wherein the network includes a home site having a home location register for storing the forwarding number and for associating the mobile identification information with a home number assigned by the telephone system.

7. The MUD of claim 1 , wherein the MUD is part of a telephone network including a home site and the mobile identification information is a mobile identification number (MIN), and assignment ofthe MIN to the subscriber is not under the control ofthe telephone network.

8. A method for enabling a roaming mobile subscriber of a telephone network to automatically receive at a visited site calls placed to a home site, the method comprising the steps of: the visited site querying a database for a home site identifier ofthe subscriber, wherein the database is responsive to queries from a plurality of sites; the database returning the home site identifier in response to the query; and the visited site sending a forwarding number to the home site identified by the home site identifier, wherein the forwarding number is a number at the visited site to which calls to the mobile subscriber are forwarded.

9. The method of claim 8, further comprising the step ofthe home site associating the subscriber with a home number assigned by the telephone network, wherein calls to the home number are forwarded to the forwarding number.

10. The method of claim 8, the querying step comprising the step of sending to the database mobile identification information concerning the subscriber.

11. The method of claim 10, wherein the mobile identification information is a mobile identification number (MIN), and assignment ofthe MIN to the subscriber is not under the control ofthe telephone network.

12. A communications network comprising: a mobility user database (MUD) for associating a home site identifier with mobile identification information concerning a mobile subscriber, wherein the MUD is responsive to queries from a plurality of sites in the network; a home site ofthe mobile subscriber for associating the mobile identification information with a home number assigned by the network; and a visited site for querying the MUD to obtain the home site identifier ofthe subscriber, and for sending a forwarding instruction to the home site instructing the home site to forward to the subscriber at the visited site calls placed to the home number.

13. The network of claim 12, wherein the mobile identification information is a mobile identification number (MIN), and assignment ofthe MIN to the subscriber is not under the control ofthe network.