Source: {"pile_set_name": "USPTO Backgrounds"}

1. Field of the Invention
The present invention relates to cellular communication systems, and more particularly, to a method and apparatus for the routing of auxiliary communication services, such as voice mail, within such a system.
2. History of the Prior Art
Broadly speaking, the present invention involves an interrelationship between two telephone technologies, namely, cellular radio telephony and voice mail systems. The general state of the art of each of these technologies is discussed briefly below.
Cellular radio communications is, perhaps, the fastest growing field in the world-wide telecommunications industry. Although cellular radio communication systems comprise only a small fraction of the telecommunications systems presently in operation, it is widely believed that this fraction will steadily increase and will represent a major portion of the entire telecommunications market in the not too distant future. This belief is grounded in the inherent limitations of conventional telephone communications networks which rely primarily on wire technology to connect subscribers within the network. A standard household or office telephone, for example, is connected to a wall outlet, or phone jack, by a telephone cord of a certain maximum length Similarly, wires connect the telephone outlet with a local switching office of the telephone company. A telephone user's movement is thus restricted not only by the length of the telephone cord, but also by the availability of an operative telephone outlet, i.e. an outlet which has been connected with the local switching office. Indeed, the genesis of cellular radio systems can be attributed, in large part, to the desire to overcome these restrictions and to afford the telephone user the freedom to move about or to travel away from his home or office without sacrificing his ability to communicate effectively with others.
In a typical cellular radio system, the user, or the user s vehicle, carries a relatively small, wireless device which communicates with a base station and connects the user to a mobile switching center or exchange. The exchange facilitates communications between the user, other mobile stations in the system and landline parties in the public switched telephone network ("PSTN"). The interconnection of mobile telephone users ("mobile subscribers") with the PSTN requires that each mobile subscriber in the system be made available to anyone who has a telephone, whether fixed or mobile. Hence, the problem of locating a mobile subscriber moving from one area to another (a "roaming subscriber") within a wide geographic area has become of primary importance. A known solution to this problem is based on the concept of mobile registration.
Mobile registration is the process by which a mobile telephone unit becomes listed as being present in the service area of one of the mobile exchanges in a mobile telephone service network. In accordance with one early solution to the problem of locating roaming mobiles, as each mobile telephone unit enters a new area within the network, it transmits a unique identity signal which is detected by the mobile exchange associated with that area. This exchange records an indication of the presence of the mobile subscriber in its memory and then informs all of the other exchanges of the presence of the mobile within its coverage area at that particular moment. When the mobile subscriber crosses over into another area, the exchange associated with that area, upon receiving an identity signal from the mobile telephone unit, will record an indication of the mobile subscriber's presence there and then transmit the identity to all of the other exchanges together with its own identity signal, for the purpose of updating the mobile subscriber's position.
In other known solutions, a mobile subscriber s identity and position messages are sent by each exchange, whose respective areas are crossed by such mobile subscriber, to a specific center. Any exchange in the mobile network which contacts this center may receive all the information necessary for locating and making a connection to the mobile subscriber. This solution eliminates the need to advise one or more of the other mobile exchanges each time a mobile subscriber enters a new area without making or receiving a call there and thereby reduces the amount of mobile subscriber location data that must be processed by each of the mobile exchanges within the network.
In some systems, the aforementioned center may be a common national center such as that used in the mobile telephone location system disclosed in U.S. Pat. No. 4,700,374 issued to Bini. In other systems, the center may be the exchange to which a mobile subscriber is assigned ("home exchange") or it may be a home location register ("HLR") which stores the location information of mobile subscribers. In such other systems, the mobile subscriber may preregister in an area other than the normal service and billing area ("home area") for service to be provided in the other area ("visited area") by the exchange associated with the visited area ("visited exchange"). When a roaming subscriber arrives in the visited area, the mobile subscriber is qualified to make telephone calls from there and calls which are received in the mobile subscriber's home area are forwarded to the visited area for transmission to the mobile subscriber.
Qualification of a mobile subscriber in a visited area may be automatically performed when the roaming subscriber appears in the visited area and the mobile station is switched on, e.g. when the user initiates a first telephone call. The roaming mobile subscriber automatically transmits its identification number to the visited exchange and requests roamer service. If the roaming subscriber is a visitor from a cooperating exchange, the visited exchange provides service to the roaming subscriber by allocating a temporary roamer number to it. The visited exchange also notifies the roaming subscriber's home exchange of the roaming subscriber s location in the coverage area of the visited exchange. The roaming subscriber s identification number is then entered into a list of roamers so that incoming calls to the home exchange of the roaming subscriber are forwarded to the visited exchange where the roaming subscriber is then located.
With this overview of cellular radio technology in mind, the other parent technology of the present invention, i.e., the rendition of auxiliary communication services such as voice mail, fax mail, video mail, teletex or other services will now be briefly discussed. While it should be understood that the invention contemplates the routing of various auxiliary communication services within a cellular network, the most presently common of such services, voice mail, will be used hereinafter as exemplary of the principles of the present invention. Voice mail, as is commonly understood in the art, refers to an automatic answering and message storing and forwarding system which allows a caller to leave a stored message for a specific telephone extension or to forward a message to an intended recipient. The voice mail system in essence, offers two distinct features: call answering and message forwarding. The call answering feature is typically invoked when a caller directly dials a telephone number or requests to be connected to a specific extension which is found to be busy, inoperative, nonanswering, etc. The unavailability of the called party results in the telephone call being redirected to the voice mail system call answering feature. At this juncture the call is routed to a voice mail receiving station and the caller is greeted by a prerecorded announcement message or a live telephone operator and prompted to leave a message which is stored in a "voice mailbox" assigned to the called party.
While the call answering feature of a voice mail system is geared to the convenience of the message recipient, the message forwarding feature is geared towards aiding the message originator. The message forwarding feature may be involved, for example, when a message originator calls the voice mail system by dialing an access code using a telephone station set touch-tone pad. The message originator designates one or more message recipients, who are also served by the telephone switching system, by dialing their station or directory numbers, and then dictates a voice message for delivery by the voice mail system to the designated message recipients. The voice mail system records the dialed directory numbers and places the message in the voice mailbox assigned to each of the designated message recipients. Each of the message recipients may then access the voice mail system to listen to the message, save the message for subsequent action, delete it, append comments and route the message to other message recipients, or reply and return a message to the message originator.
Several voice mail systems are commercially available. While such systems vary in features and capacity, all share, as a common core of functions, the ability to store messages for later retrieval by system users. Each user is assigned a voice mailbox and may retrieve his messages by accessing the system and then identifying his voice mailbox. In general, anyone having knowledge of the telephone numbers for the system, may leave messages, but only users having a voice mailbox may retrieve messages. To retrieve messages a user of a typical voice mail system accesses the system over the telephone lines and, after identifying himself by mailbox number, and possibly a password, hears a recorded message produced by the system advising him of the status of his mailbox, e.g., number of messages waiting, etc. The user may then listen to brief prerecorded portions of each message, commonly referred to as "headers" which further describe the message, for example, by identifying the originator. The user may then decide whether or not to listen to each message.
The desirability of providing voice mail services to mobile radiotelephone system subscribers has not been lost on cellular system operators. The economic incentives for incorporating a voice mail system into a cellular radio network are, at least, twofold. First, the cellular operator can charge each participating mobile subscriber a monthly fee for voice mail services. Second, the ability of a mobile subscriber to retrieve messages left in his absence increases the likelihood that the mobile subscriber will, after listening to a particular message, call the message originator and thereby generate additional revenues for the cellular system operator.
The use of voice mail systems in cellular radio networks has developed in line with the growth of cellular radio communications generally. Initially, a single mobile switching center in each of several large metropolitan cities provided communications services to mobile subscribers in the local area. The national cellular radio landscape, at this stage of development, consisted of dispersed pockets or islands of cellular radio networks with little or no roaming therebetween. Where desired, a voice mail