EP0923816A1

EP0923816A1 - Communication routing method by satellite in a network

Info

Publication number: EP0923816A1
Application number: EP98924403A
Authority: EP
Inventors: Antoine Totaro; Erick Flores; Jean Charpentier; Roland Thies
Original assignee: Alcatel CIT SA; Alcatel SA
Current assignee: Alcatel CIT SA; Alcatel Lucent SAS
Priority date: 1997-05-07
Filing date: 1998-05-07
Publication date: 1999-06-23
Also published as: FR2763188B1; WO1998051020A1; AU7661398A; US6259921B1; AU746322B2; CA2259470A1; FR2763188A1

Abstract

The invention concerns a method for routing a communication between a first terminal which is mobile (5) and a second terminal (4) in a global telecommunication network, the communication capable of being routed in the global network (a) at least partially via a satellite telecommunication network (1) using base stations with access to the satellites (2, 3), and (b) at least partially via an earth telecommunication network (PSTN) connected to said base stations (2, 3), each satellite (1) of the satellite communication network defining a total coverage covering a plurality of base stations, the total coverage defining a plurality of sub-coverage areas each associated with one respective base station (2,3). The method is characterised in that it comprises a step of updating the location of the first terminal (5) in a sub-coverage area associated with said plurality of base stations (2, 3) closest to said second terminal, so as to minimise the distance for routing said communication via said earth telecommunication network (PSTN).

Description

COMMUNICATION ROUTING METHOD IN A SATELLITE NETWORK

The present invention relates generally to a telecommunications network with mobiles by satellite. More particularly, the invention relates to such a network in which a communication established between a mobile terminal and another terminal, whether mobile or fixed, is conveyed in part through the terrestrial network (s) (s) ( s), such as PSTN or ISDN. Thus, according to known techniques, a communication established between two terminals, respectively mobile and fixed, is conveyed (1) - through a satellite or radio link, between the mobile terminal and a land base station (or Gateway), and (2) - through a land link between said base station and the fixed terminal. Similarly, a communication established between two mobile terminals is conveyed (1) - through a satellite or radio link, between one of the mobile terminals and a land base station (or Gateway), (2) - through a land link (PSTN) between said base station and another land base station, and finally (3) - through a satellite or radio link between the other land base station and the other mobile terminal.

The type of network concerned by the invention is a terminal mobility network. In such a network, on the one hand each mobile terminal has the capacity to access the network from different places while it is moving and, on the other hand, the network has the capacity to identify, locate and reach it. terminal. For this, the network stores location information of the terminal, this information being updated by a registration procedure, called location update.

According to the prior art, each mobile terminal accesses the terrestrial network through, on the one hand, a satellite and, on the other hand, the base station which is closest to it. In the remainder of the description, the term "Gateway" will be used to denote a set consisting of a base station and a Mobile Service Switch, or MSC in English literature for the Mobile Switching Center. The choice of the base station closest to the terminal to access the terrestrial network aims to minimize power losses in the link between the terminal and the earth base station via satellite.

The services offered by the satellite networks are superimposed on the already existing services delivered by the terrestrial networks. This results in a higher traffic load, which can be critical, in the terrestrial networks. In addition, access by each terminal to the terrestrial network through the base station closest to the terminal can induce a high cost of communication.

Patent application GB-A-2281014 describes a satellite telecommunications system in which the communication between a mobile terminal and a fixed terminal is routed through the base station, or Gateway, which offers the shortest routing path to through the PSTN terrestrial network. The solution proposed in this application thus reduces the traffic load in the PSTN terrestrial network. However, it does not solve the problem of the high cost of the communication which will be billed to the user.

The invention aims to remedy this drawback by providing a method of routing communication as well as terminals and base station for the implementation of this particularly advantageous method. To this end, a method of routing a communication between a first terminal which is mobile and a second terminal in a global telecommunications network, said communication being able to be routed in the global network (a) - at least in part through a satellite telecommunications network using base stations, and (b) - at least in part through a terrestrial telecommunications network connected to the base stations, said communication being routed through a base station minimizing the distance from routing of said communication through said terrestrial telecommunications network, is characterized according to the invention in that it comprises, before an establishment of said communication, a step of updating the location of the first terminal in the coverage associated with the station basic minimizing the distance of communication through the land telecommunications network tre, said updated location being different from a current location of said first terminal. This step is contrary to the conventional location update procedure since the location update will be carried out in a base station coverage which is not the coverage in which the terminal receives a maximum power signal. This is a "forced" location update.

The cost of the communication billed to the user, with regard to the terrestrial network, which is calculated according to the location information previously updated in a "forced" manner, thus takes into account the routing path real communication through the PSTN. Another advantage of updating the location information before establishing the call is to allow the reception of another call, to avoid the loss of information transmitted to the user, whose location has not been update, etc ...

In addition, communication is routed, whenever possible, mainly through satellite links, thus avoiding overload of the terrestrial network and lower cost of communication. The latter advantage comes from the fact that a satellite network infrastructure has a lower cost than a terrestrial network infrastructure. According to a first embodiment, the first terminal is a calling terminal, and the location update of said first terminal is carried out in the sub-coverage of the base station closest to said second terminal which is a called terminal. A mobile terminal for implementing this embodiment includes means for storing association information associating with each of a plurality of called number prefixes, which are a function of call areas, station identification information base, and means for updating the location in an identified base station.

According to a second embodiment, the first terminal is a called terminal, and the location update of this first terminal is carried out in the base station closest to the second terminal which is a calling terminal. A master base station for implementing this embodiment then comprises means sensitive to location information received from the base station nearest to the second terminal to produce location update trigger information which is sent to the base station which is associated with the sub-coverage to which the called terminal belongs, which retransmits said update triggering information of location to the first terminal so that the latter performs a location update in the sub-coverage of the base station closest to the second terminal.

Other characteristics and advantages of the present invention will appear more clearly on reading the description which follows, with reference to the corresponding appended drawings in which:

- Figure 1 shows a schematic representation of a satellite network in which a method according to the invention is implemented; - Figure 2 is a schematic block diagram of a terminal for the implementation of the invention; and

- Figure 3 is a block diagram of a master base station for the implementation of the invention.

In the following description, reference is made to the elementary notions of terminal mobility in a telecommunications network as well as to a practical implementation which refers to the terminology and Recommendations GS M (Global System for Mobile communication) of ETSI, the content of these Recommendations, and in particular those relating to Mobility Management (MM) being included by reference in this request. Nevertheless, the invention can be applied to any “global” mobility network of terminals using in combination a satellite network and a terrestrial network, such as ISDN or PSTN, etc. for the routing of communications. It is assumed, by way of example, that access to the terrestrial network uses GSM type procedures.

With reference to FIG. 1, a telecommunications network for implementing the invention comprises a terrestrial network, of the PSTN or ISDN type, to which base stations 2, 3 and 6 are attached, providing access to a network by satellite 1. The base stations access the PSTN terrestrial network through switches 20, 30. Couples 3 and 30 as well as 2 and 20 constitute gateways. When a mobile terminal 5 is involved in a communication, either to receive a communication from a fixed terminal 4 or mobile, or to establish a communication with a fixed terminal 4 or mobile, the satellite network 1 is used. Base stations 2 and 3 then provide access between the network terrestrial and satellite network. As will appear in more detail later, the base station 6 is a master base station. The satellite network typically includes several satellites, each of them 1 defining a total coverage covering a plurality of base stations 2 and 3, this total coverage defining a plurality of under-coverings each associated with a respective one of the base stations. 2 -and 3. Using a technique such as Multiple Access to Frequency Divison, Multiple Access to Space Divison or even Multiple Access to Code Divison or other, each base station associated with a satellite is allocated only a part of the total data exchange capacity with the satellite 1. Typically, the satellite network accesses, via the base stations 2, 3, databases (not shown) for locating the mobile terminals 5. These bases of data store location information of each mobile terminal 5, each mobile terminal updating such databases as it travels s. According to the invention, in order to minimize, or even make zero, the routing distance, through the terrestrial network, of a communication established between a first mobile terminal and a second terminal, fixed or mobile, provision is made for step of updating the location of the first terminal in the sub-coverage of the base station which is closest to the second terminal.

Two different variants must nevertheless be adopted respectively depending on whether the mobile terminal 5 is a calling terminal and a called terminal. These two variants will now be studied successively.

A / Mobile Terminal 5 is a calling terminal.

Reference is made to Figures 1 and 2 to describe this first variant. The mobile terminal 5 is initially registered in a database as being located in the sub-coverage associated with the base station 2 and supported by this base station 2, this base station 2 being the most basic base station. close to the terminal 5. With a view to initiating a call to establish a communication with a remote terminal, for example a fixed terminal 4, the user of the mobile terminal 5 enters the number called on the keyboard 50 of his terminal 5. The format of this phone number includes successively a country code prefix CC (Country Code), an area code prefix NDC (National Destination Code) and a subscriber number SN (Subscriber Number). According to the invention, the mobile terminal 5 further comprises a memory 51 which stores association information which associates with each of a plurality of prefixes of number called CC and NDC, which are a function of call areas, GW base station identification information. The base station identified GW as a function of the prefix information CC and NDC is the base station 3 which is closest to the called terminal, which is assumed to be the fixed terminal 4 in FIG. 2. This association memory 51 can be charged initially, before the sale of the mobile terminal 5, according to the geographic position of the base stations 2, 3 and the prefixes CC and NDC associated with the geographic areas covered by these base stations. It can also be updated, for example by radio, according to the evolution of the network, the addition of new base stations, the modification of the numbering plan, etc. From this information GW identification of base station 3, the mobile terminal 5 deduces therefrom, if necessary, the resource, or channel, specific to be used to access this base station. The specific resource to be used can be a particular frequency in FDMA, an orthogonal code in CDMA, etc. Depending on this information, the mobile terminal 5 transmits, to the base station 3, through a transmission unit / reception 52, a UP location update message. This message is received by the base station 3 which registers the mobile terminal 5 in a database associated with it. This "forced" update of the location of the mobile 5 in the sub-coverage associated with the base station 3 then offers the possibility for the terminal 5 to then use this base station 3 to establish a communication. The term "forced" is used here to highlight an important characteristic of the invention according to which, unlike conventional procedures of the GSM type in which the terminal always registers in the base station closest to it, the terminal is part of the base station which offers a minimization of the communication routing distance through the terrestrial telecommunications network PSTN or ISDN. It can therefore occur a location update of the first terminal in the coverage associated with the base station minimizing the routing distance of the communication through the terrestrial telecommunications network, said updated location being different from a current location of said first terminal

Note that in the above description, only the CC prefix or the NDC prefix can be used instead of the two CC and NDC prefixes.

After registering, by updating the location in the coverage area of the base station 3, the terminal 5 thus establishes a communication with the terminal 4, via the satellite 1 and the base station 3 using the links L1 and L3, according to a conventional procedure. As a result, the routing of communication through the terrestrial network is very significantly reduced.

At the end of the communication, the mobile terminal 5 automatically re-registers as belonging to the coverage area of the original base station 2. For this, a memory space is provided in the terminal for storing identification data of this base station 2. In practice, this memory space as well as the memory 51 can be located either in a memory of the terminal or else in a smart card, of SIM card type (Subscriber Identity Module).

B / Mobile Terminal 5 is a terminal called.

Reference is now made to Figures 1 and 3 to explain this second variant of the invention. In this variant, it is assumed that the calling terminal is terminal 4, the mobile terminal 5 being the called terminal.

In accordance with the procedures for handling incoming calls as defined by the GS M Recommendations, the routing of the incoming call is carried out by the PSTN terrestrial network on the incoming MSC, called GMSC. The MSC (Mobile Switching Center) function, as defined by the GSM Recommendations, handles call handling and routing for mobiles. In the diagram of FIG. 1, an MSC 30 is associated, or integrated, with the base station 3 to form a gateway. This MSC 30, in response to the reception of an establishment request received from the terminal 4, and as a result of exchange with an HLR (Home Location Register) managing the mobile called 5, receives location information from the mobile, called LAI (Location Area Identifier). As a result of receiving this LAI, the MSC 30 checks whether the coverage area associated with this LAI is under its responsibility. For this, the MSC 30 includes a verification program. If this is the case, the call is established immediately through the base station 3. Otherwise, this LAI information is returned, via the satellite 1, to the so-called master base station 6, which manages it. of the network by exchange of messages with the base stations 2 and 3. As shown in FIG. 3, this master base station 6 comprises a transmitter / receiver 60 as well as a correspondence table 61 between the information LAI and the gateway (3.30) or (2.20) in charge of mobiles in the coverage area associated with this LAI. The master base station 6 is sensitive to the location information LAI received from the base station 3 closest to the terminal 4 to produce location update trigger information which is transmitted, via the satellite 1 , to base station 2 which is associated with the sub-coverage to which the terminal called 5 belongs. This base station 2 then retransmits location update trigger information intended for terminal 5 so that the latter performs a location update in the undercoverage of the base station 3 which is closest to the terminal 4. Thus, the terminal 5 registers in a "forced" manner in the coverage area of the station basic 3. The communication routing distance through the terrestrial network is then reduced.

It should be noted that in the particular case for which both the called and calling terminals are mobile terminals, only one of the procedures described above must be applied. For example, only the procedure described in B / applies. For this, the calling mobile terminal comprises means for detecting, as a function of the prefix of the number called, that the called terminal is a mobile terminal. In this case, said calling terminal does not implement the procedure described in A /, by deactivating the means for updating the location in a base station. The called mobile terminal implements the procedure described in B /.

Claims

CLAIMS:

1 - Method for routing a communication between a first terminal which is mobile (5) and a second terminal (4) in a global telecommunications network, said communication being able to be routed in said global network (a) - at least in partly through a satellite telecommunications network (1) using satellite access base stations (2, 3), and (b) - at least partly through a terrestrial telecommunications network (PSTN) connected to said stations base (2, 3), said communication being routed through a base station minimizing the distance of routing of said communication through said terrestrial telecommunications network, characterized in that it comprises, before establishment of said communication, a step of updating the location of the first terminal in the coverage associated with the base station minimizing the distance for routing the communication through the network of terrestrial telecommunications, said updated location being different from a current location of said first terminal.

2 - Method according to claim 1, characterized in that the first terminal (5) is a calling terminal, and by a location update of said first terminal (5) in the coverage of the base station (3) the closer to said second terminal (4) which is a called terminal.

3 - Method according to claim 1, characterized in that the first terminal (5) is a called terminal, and by a location update of said first terminal (5) in the coverage of the base station (3) the closer to said second terminal (4) which is a calling terminal.

4 - Mobile terminal for implementing the method according to claim 2, characterized in that it comprises means (51) for storing association information associating with each of a plurality of prefixes with called number (CC , ND), which are a function of call areas, base station identification information (GW), and means for updating the location in an identified base station.

5 - Terminal according to claim 4, characterized in that said means for storing are located in a smart card. 6 - Mobile terminal according to claim 4 or 5, characterized in that that it comprises means for detecting, as a function of the number prefix called, that the called terminal is a mobile terminal, and means for deactivating said location updating means accordingly. 7 - Base station for implementing the method according to claim 3, characterized in that it comprises means sensitive to location information received from the base station (3) closest to said second terminal (4) to produce location update trigger information which is sent to the base station (2) which is associated with the coverage to which said first terminal (5) belongs, which base station (2 ) retransmits said location update trigger information intended for the first terminal (5) so that the latter performs a location update in the coverage of the base station (3) closest to said second terminal ( 4).