Mobile access for cordless terminal mobility

Background of the Invention

1) Field of the Invention

The present invention relates to a communication network including the capability of cordless terminal communications, and, more specifically, to a method and apparatus for making available to a cordless terminal the supplementary services subscribed to in the home local exchange regardless of the physical location of the cordless terminal, i.e., no matter which exchange it is communicating with.

2) Discussion of Related Art

Since the advent of mobile radiocommunication systems, demand for these services was beyond expectations. Thus, system designers constantly face the challenge of increasing system capacity without reducing call quality below consumers tolerance levels. This challenge has been met in various creative ways. For example, digital communication systems are expected to provide a three to sevenfold increase in capacity over the original analog systems.

Even with the popularity enjoyed by mobile communication systems in recent years, the legacy fixed communication networks continue to be the major carriers of communications. This resulted in the more recent development of hybrid communication systems, i.e., those which are a mixture of fixed and wireless technology. In hybrid communication systems, such as Personal Communication Systems (PCS), the coverage of a fixed network is supplemented by that of a wireless network to provide both additional capacity and mobility of portable terminals. In providing these benefits, however,

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PCT/SE95/01431 designers must confront the challenges which face the wireless industry as well as those known to fixed communication networks.

Wireless networks, for example cellular 5 networks, must cope with various situations not found in fixed networks, such as interference and roaming. Roaming occurs when a mobile unit which is being served by a home transmitting station, passes out of the geographic region covered by that station and into an area covered by another transmitting station. If the mobile unit is in the midst of a call or connection, then a handover is needed from the home transmitting station to the new serving station.

Thus a hybrid system having portable terminals which are supported via a radio link to one of a plurality of exchanges must also provide a solution for handing over calls or connections.

Another issue arises with respect to supplementary services which may be provided to subscribers using such mobile units. These supplementary services include, for example, call forwarding and call transferring, which have been prevalent in fixed communication networks for some time. Naturally, subscribers in newly developed hybrid systems will expect their portable units to provide the same functions as they enjoyed when using a fixed network or will resist the implementation of hybrid communications.

Several compatibility issues arise in hybrid systems which impact on a subscriber's ability to consistently receive supplementary services. Transmitting stations and/or exchanges which link portable terminals to the fixed part of the system can be made by different manufacturers. Different manufacturers may implement the same service in

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PCT/SE95/01431 different ways (due to lack of standardization) which may adversely impact a mobile terminal's ability to receive services at equipment other than its home equipment. Further, services for which a subscriber has paid and receives at a home station may not be even be available at a transmitting station and/or exchange to which the portable terminal finds itself connected after roaming. These variations will cause confusion and displeasure to consumers who have consistently received a particular set of supplementary services upon demand in the conventional fixed network only to experience unreliability in the hybrid network.

One potential solution to this dilemma is to provide a consistent environment for roaming mobile users in the hybrid system. If all of the equipment experienced by such users was identical, then supplementary services could be identically provided regardless of the subscriber's geographical location.

However, this option is not believed to be commercially feasible given the competitive environment in this industry.

A second solution might be to standardize the supplementary services and the ways in which these services are implemented so that even different manufacturers would produce equipment that would provide a consistent set of supplementary services to a roaming mobile. However, the standardization process of these services is unlikely to afford relief to the aforementioned problems for systems to be implemented in the near future.

The GSM, a standard used in parts of Europe for cellular communications, provides for service profiles to follow the subscriber to the exchange to which his or her equipment is connected after

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- 4 roaming. If, for example, a subscriber having access to call forwarding was to travel to an area served by an exchange other than the subscriber¹s home exchange, a description indicating that subscription 5 would also be forwarded to this exchange.

Summary of the Invention

According to exemplary embodiments of the present invention, conventional fixed networks can be extended using wireless technology in such a way that supplementary services to which a subscriber has subscribed (e.g., call forwarding, call transfer, path replacement, call completion, call offer, do not disturb services, message services, etc.) are provided to that subscriber even when that subscriber is connected to an exchange other than its home exchange. Moreover, this can be accomplished even when the home exchange and other exchanges are not compatible in terms of the types of services which they can support.

These and other features of the present invention can be achieved by, for example, routing calls to a subscriber which has roamed into an area served by another exchange back through the home exchange. In this way, a subscriber will always have access to the services of that exchange regardless of the current geographic location of that subscriber's equipment.

According to one exemplary embodiment of the present invention, both a signalling connection and a call bearing connection are established between the visited exchange and the home exchange. According to another exemplary embodiment of the present invention, a signalling connection is established between the visited exchange and the home exchange, but the visited exchange retains the call connection.

Brief Description of the Drawings

The invention will now be described with reference to the drawing figures in 5 which:

Figure 1 is a functional block diagram of the architecture of a Personal Communications Service (PCS);

Figure 2 is a functional block diagram illustrating the location updating of a roaming Cordless Terminal Mobile (CTM) subscriber;

Figure 3 is a functional block diagram illustrating a first step in establishing a call which terminates a CTM subscriber;

Figure 4 is a functional block diagram illustrating a second step in establishing a call which terminates at a CTM subscriber;

Figure 5 is a functional block diagram illustrating a first step in establishing a call which originates at a CTM subscriber;

Figure 6 is a functional block diagram illustrating a second step in establishing a call which originates at a CTM subscriber;

Figure 7(a) through Figure 7(c) are exemplary flowcharts in accordance with the present invention;

Figure 8 is a functional block diagram illustrating an alternate embodiment for establishing a call which terminates at a CTM subscriber.

Detail Description of Preferred Embodiments

Figure 1 illustrates an exemplary PCS embodiment of the present invention which is provided here as an initial reference for describing the various connections which will be used in subsequent embodiments. PSTN/ISDN 10 represents a fixed network over which connections or calls are made. TCAP (Transaction Capacity Application Part) 11 handles

7- \

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- 6 exchange of protocol data units using general standardized protocol functions (to provide common and general system for the transfer of information between two nodes). SCP refers to service control point and provides the network with Intelligent

Network Service Logic. The Home Data Base (HDB) 13 stores information which identifies the current location of subscribers and supplies any requesting exchange in the network with this location information. It is also where the associated parameters of a cordless transmitter or a subscriber are stored. As will be later described, HDB 13 can be co-located with home local exchange 17 or can be located centrally. AUTH 14 is a repository for authentication data which can be used to authenticate accesses to the system.

The Visited Local Exchange (VLE) 15 is the exchange or switch that serves the location being visited by the subscriber. Although not illustrated in the Figures, those skilled in the art will readily appreciate that there will be many such visited local exchanges to which a portable terminal may be connected, but just one is illustrated to simplify the Figures. Each visited local exchange 15 has one or more base stations, called here Radio Fixed Parts (RFP), 16 connected thereto for providing the wireless transmissions for the hybrid network.

The Home Local Exchange (HLE) 17 is the exchange which has direct access to the HDB for a particular

CTM subscriber, provides the subscriber with CTM service, and which may also have at least one RFP 18 connected thereto. As will be described in more detail below, the home local exchange 17 continues to be involved in connections associated with its subscribers even when portable terminals 19 of those

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- 7 subscribers have roamed into other areas, e.g., an area served by visited local exchange 15.

Having described the major functional blocks of Figure 1, a description of the various connections illustrated by lines therebetween will now be undertaken. Portable terminals, e.g., cordless telephones such as element 19, are connected to the hybrid system over an air interface denoted by line 20. Communication over an air interface can be accomplished using any one of a number of known access techniques, such as DECT or CT2, which specify the format for wireless data communications. Those skilled in the art will readily appreciate that the selection of a particular access technique will be dictated by various design considerations such as frequency reuse, regional geography and service capabilities.

The radio fixed parts 16 and 18 are connected to their respective exchanges 15 and 17 by a link (which can be a wire link, a fiber optic link, a microwave link, etc.) using, for example, an ISDN access protocol known as DSS1. In the exemplary embodiment, the ISDN access protocol is altered. The first and second levels of the protocol (dealing with physical/electrical signal interaction and synchronization, respectively) are not so altered that the present invention can be used without substantial modification of preexisting hardware. However, only part of the third level is interpreted by the visited local exchange 15 in contrast to preexisting systems. The part of the third level which is interpreted by the visited local exchange 15 deals with directing the signal to the network. The portion of the protocol not interpreted by the visited local exchange 15 is interpreted by the home

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PCT/SE95/01431 local exchange 17 for providing other services, including the supplemental services such as call forwarding, making transmission through the visited local exchange 15 transparent. To illustrate this difference, the protocol is marked DSS1+ in the figures.

The various connections provide the protocol for allowing the visited local exchange 15 and the home local exchange 17 to function in the cooperative manner described below. These protocols are termed herein MAAP (Mobile Access Application Part) protocols. MAAP-LC is a subset of this protocol which includes messages which allow the HDB 13 to keep track of and pass information on regarding, the location of an home local exchange's subscribers.

This subset of protocol commands can be implemented, for example, in a manner similar to that of the GSM MAP protocols which support mobility. For reference to GSM MAP protocols, the interested reader is referred to a document entitled GSM 9.02 Version 2 Draft, June 1992, Part III, pp. 173-226.

The MAAP-CC subset relates to call control, i.e., shifting control between the visited local exchange 15 and home local exchange 17, and can be implemented, for example, in a manner similar to that of GSM MAP commands which support inter-exchange handover. This connection provides a signalling link between the visited local exchange 15 and the home local exchange 17 as will be described in more detail below. Lastly, the MAAP-AC subset of protocols relates to commands used to empower the visited local exchange to optionally authenticate a portable terminal 19 at access.

The INAP (Intelligent Network Application Part) connections provide intelligence to the network such

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- 9 as 800 number service or premium rate service. The ISUP/TUP/MFC connection between the visited local exchange 15 and home local exchange 17 is the call bearing connection which routes the call therebetween. Having described an exemplary communication system according to the present invention, the ways in which these elements provide various functions will now be presented.

Location updating will first be described with 10 respect to Figure 2. In order for the system to handle movement of a portable terminal from one service area to another, it is necessary for the new exchange to be alerted by the mobile of its presence. This process is commonly known as registration and will be performed in a manner based upon the particular access technology used for the air interface 20, e.g., DECT or CT2. When portable terminal 19 roams into a new location, e.g., an area serviced by visited local exchange 15, it sends a notification of its presence via the air interface 20 to the visited local exchange 15.

At this time, the visited local exchange 15 can optionally perform a terminal authentication procedure, for example using some combination of the portable terminal's identification number, electronic serial number and a counter, by using the MAAP-LC protocol and the MAAP-AC protocols. The visited local exchange 15 will then notify the HDB 13 about the new location and request the previous visited local exchange, or, if none, the home local exchange 17, to de-register the mobile terminal 19. Next, HDB 13 confirms registration with the visited local exchange 15.

According to one exemplary embodiment, the HDB

13 also sends the address of the home local exchange

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- 10 17 which supports the subscriber of the mobile terminal 19 with services to the visited local exchange 15 along with the confirmation of registration. Alternatively, the address of the home local exchange 17 associated with that subscriber can be maintained at the HDB 13 for access as needed by the visited local exchange 15. This address can be used by visited local exchange 15 to establish signalling links and/or route calls through home local exchange 17.

When a telephone call arrives at the home local exchange 17 from the fixed network 10 from, for example, unit 24, that is to be connected to a roaming subscriber, the home local exchange 17 sends a request to the HDB 13 to obtain the subscriber's location by using the MAAP-LC protocol unless the subscriber's location (i.e., visited local exchange's address) was previously returned to the home local exchange 17. The HDB 13 then returns the address of the visited local exchange 15 that the subscriber is presently visiting. The home local exchange 17 establishes a MAAP-CC session (i.e., a signalling connection) to visited local exchange 15, and notifies visited local exchange 15 about the call.

The visited local exchange 15 then returns a routing number, e.g., a directory telephone number expressed as an E.164 number, to the home local exchange 17. The home local exchange 17 establishes an ordinary, call-bearing connection to the visited local exchange 15. When the connection is completed, the visited local exchange 15 pages the subscriber's mobile terminal 19 and through-connects the answer to the home local exchange 17. The home local exchange 17 now has access to both the call and the control signals, e.g., depressed keystrokes, and can

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- 11 therefore execute any subsequent service that the subscriber may request as if the portable terminal 19 was directly connected to one of its own radio fixed parts (e.g., RFP 18).

The mobile terminal 19 accesses the network by sending a service request (e.g., a SETUP message) to the appropriate visited local exchange via the air interface, as illustrated in Figure 5. visited local exchange 15 then establishes a signalling connection (using MAAP-CC) to the home local exchange 17 and transfers the service request to the home local exchange 17.

When the home local exchange 17 has analyzed the request it sends a routing number to the visited local exchange 15 and requests the visited local exchange 15 to extend the call bearing-connection to the home local exchange 17. The visited local exchange 15 may use any available trunk signalling system that fulfills the requested transmission medium requirement (TMR) to extend the connection.

The home local exchange 17 now has access to both the call and the signalling connection and can therefore offer the portable terminal 19 any service as if the portable terminal was using one of the home local exchange's own RFPs. Figure 6 illustrates that an ordinary telephone call to a subscriber can be connected anywhere in the fixed network 10.

Figures 7(a) through 7(c) are flowcharts of an exemplary embodiment of the invention. Figure 7(a) begins at step 70 with a portable terminal registering with a visited local exchange whose transmission range or service area it has roamed into. Thereafter, at step 71, the identity of the portable terminal 19 unit might be authenticated as an optional step. The HDB 13, which tracks the

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- 12 locations of the portable terminal, is notified as to the portable terminal's new location at step 72 through registration of the portable terminal. In turn, the home data base 13 can optionally notify the home local exchange 17 of the mobile terminal's new location, as illustrated at step 73. To avoid potential confusion, the presence of the portable terminal is de-registered from either the home local exchange 17 or another visited local exchange the service area range of which the portable terminal has left, as shown at step 74. The home local exchange's address may then be sent to the new visited local exchange so that the new visited local exchange can direct a portable terminal initiated connection to the correct address, as shown in step 75.

Alternatively, the visited local exchange 15 can request this address from the HDB 13 as needed.

With reference to Figure 7(b), the procedure for call set-up from a terminal 24 connected to the home local exchange 17 to a portable terminal 19 located in a service area of a visited local exchange 15 is shown beginning at step 76. At step 77, the address of the visited local exchange 15 is obtained from the HDB 13 if not previously communicated to the home local exchange 17. Then at step 78 a MAAP-CC link is established between the home local exchange 17 and the visited local exchange 15. At step 79 the routing or telephone directory number is transmitted to the home local exchange 17 so that the visited local exchange 15 can receive the call. At block 80, the call is then connected to the visited local exchange 15. Subsequently, visited local exchange 15 pages the portable terminal 19 at step 81 and the call is put through to the home local exchange 17 at block 82. Since the home local exchange 17 now has

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- 13 both the signalling (MAAP-CC) and call connection, it can subsequently execute supplementary services as shown by block 83.

Figure 7(c) depicts an exemplary embodiment of 5 the present invention wherein a call originates at the portable terminal 19. Therein the initial block 84 shows that a call-setup message is sent to visited local exchange 15 via RFP 16. The next step 85 establishes a MAAP-CC link between visited local exchange 15 and home local exchange 17. At block 86, a request is sent to the home local exchange 17 for a transfer of service over the MAAP-CC link. After this, a routing number from the portable terminal is sent to the visited local exchange 15. Then the call connection can be extended to the home local exchange

17. Once again, the home local exchange 17 can now provide the supplementary services to the portable terminal 19 based upon the subscriber profiles stored therein as if the portable terminal 19 was connected through RFP 18 instead of RFP 19.

Having described exemplary systems and methods for providing the capability to route calls back through a subscriber's home exchange to take advantage of the stability afforded thereby with respect to that subscriber's services, an example will now be provided in which such a service is actually invoked to complete the discussion. The following example uses the call completion-busy subscriber service, however those skilled in the art will recognize that other services can be implemented according to the present invention in a similar manner. Rather than duplicate Figures, reference is made to the elements and connections in Figure 3.

Therein, suppose that terminal 24 places a call to the portable terminal 19 through the fixed network

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- 14 10. The home local exchange 17 analyzes this number and since calls are routed via the home local exchange 15, the home local exchange 15 detects that the portable is busy.

Consider that the subscriber of terminal 24 has subscribed to the call completion/busy subscriber service. In this case, the user of unit 24 may invoke this service by, for example, depressing the appropriate keys. If invoked, home local exchange 17 will monitor the portable terminal's original call via the signalling (MAAP-CC) link. When the portable terminal 19 is free, i.e, an on-hook signal is generated, this signal is passed back to the home local exchange 17 via the signalling link. The home local exchange 17 recognizes that it has been monitoring this portable terminal and notifies unit 24 that the call can now be completed.

The previous exemplary embodiments have related to systems and methods wherein both the signalling and call-bearing connections are routed back through the home local exchange 17. However, there may be situations in which it is desirable to maintain callbearing responsibilities in the visited local exchange 15 and make only a signalling connection with the home local exchange 17. For· example, it may be the case that the service to be invoked by the subscriber will involve transferring the call to another user whose equipment is proximate the visited local exchange 15. Exemplary embodiments in accordance with this aspect of the present invention will now be described.

First, a call originating from the portable terminal will be described. As in previous embodiments, the portable terminal accesses the network by sending a request for connection to the

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- 15 nearest exchange (visited local exchange 15) via the air interface. The visited local exchange 15 analyses the number and establishes a signalling link to the home local exchange 17. The home local exchange 17 analyzes the dialled number, for example using an external database, to determine what the number would be if dialled in the visited local exchange 15. This number is then sent back to the visited local exchange 17 in order to extend the call-bearing connection.

The visited local exchange 15 uses any available trunk signalling system that fulfills the requested TMR (transmission medium requirement) when extending the connection to the dialed number. It also monitors the call and sends progress information (ringing, answer) back to the home local exchange 17 via the signalling link. Note that according to this exemplary embodiment the home local exchange 17 only has access to the signalling link rather than both the signalling link and the call-bearing connection. Instead, the call-bearing connection is optimized to travel, for example, a shortest path between the visited local exchange 15 and the called subscriber in the fixed network.

For connections which terminate at the portable terminal when it is connected to the visited local exchange 15, the operation of this system can, for example, be as follows. When the portable terminal roams into the area served by the visited local exchange 15, it sends a notification to the visited local exchange 15 about its presence. The visited local exchange 15 in turn notifies the portable terminal's the home data base 13 about the subscriber's whereabouts. To this point, the operation is similar to that described above with

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- 16 respect to the embodiment of Figure 2. Now reference is made to Figure 8.

When a call arrives to, for example, a gateway local exchange (GLE) 26 that is bound for the roaming subscriber, that exchange sets up a signalling link (MAAP-CC connection) to the home local exchange 17 requesting further directives. The home local exchange 17 sets up a call to the visited local exchange 15 requesting it to locate the portable terminal 19. The visited local exchange 15 pages the portable terminal and, if this is successful, an

E.164 number (routing or telephone number) is returned to the home local exchange 17 that enables it to establish a signalling connection to the portable mobile through the visited local exchange

15.

Next, the home local exchange 17 sends the received number to the exchange serving the calling equipment which uses that information to establish the call-bearing connection in an optimal manner,

e.g., shortest path, to the portable terminal. Note that this frequently means that the call-bearing connection will not be directed through the home local exchange 17.

Having described the basic connection premise whereby a signalling connection and a call-bearing connection are separately established, the way in which services can be invoked according to this embodiment will now be discussed. When a service request is received, the home local exchange 17 requests the visited local exchange 15 and the exchange serving the other connected party to change the call-bearing connection such that it passes through the home local exchange 17 by providing appropriate numbers (e.g., E.164 numbers) for this

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- 17 routing. In this way, the home local exchange 17 again possess both the signalling connection and the call-bearing connection so that services can be implemented by the home local exchange 17 and the consumer transparently experiences those services in a stable manner.

The invention described herein includes variations thereof. The described embodiment is to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes within the meaning and range of equivalency of the claim recitations are intended to be embraced therein.