Using two SIM cards with same MSISDN number

Details Using two SIM cards with same MSISDN number Using two SIM cards with same MSISDN number

1999-05-26

2002-04-02

Hunter, Daniel (Department: 2684)

Telecommunications

Radiotelephone system

Zoned or cellular telephone system

C455S558000, C455S432300, C455S550100, C455S551000

Reexamination Certificate

active

06366777

ABSTRACT:

This application is the national phase of international application PCT/FI97/00714 filed Nov. 24, 1997 which designated the U.S.
FIELD OF THE INVENTION
The invention relates to a method and equipment for using two SIM cards with the same MSISDN number in a mobile communication system.
BACKGROUND OF THE INVENTION
In order to illustrate the invention, but in no way to restrict it, the invention is described within a GSM system (Global System for Mobile Communications) and using its terminology. As shown in
FIG. 1
, the structure of the GSM network consists of two main parts: a Base Station Subsystem (BSS) and a Network Subsystem (NSS). The BSS and mobile stations MS communicate via radio connections. In the BSS, each cell is served by a Base Transceiver Station (BTS). A group of base transceiver stations BTS is connected to a Base Station Controller (BSC), the function of which is to control the radio frequencies and channels used by the base transceiver station BTS. The base station controllers BSC are connected to a Mobile Switching Centre (MSC). The function of the mobile switching centre is to switch calls involving at least one mobile station MS. Some MSCs are coupled to other data communication networks, such as a Public Integrated Services Network (PISN), and they comprise switching functions for processing calls to and from these networks. These mobile switching centres are called Gateway Mobile Switching Centres (GMSC or Gateway MSC).
The GSM system has two types of databases for routing calls. Network subscriber data are stored, permanently or semi-permanently, at a Home Location Register (HLR). These data include, for instance, information about those services the subscriber has access to and the subscriber's current location. The other register type is a Visitor Location Register (VLR). It is usually connected to a single mobile switching centre MSC, but it can also serve several centres. The Visitor Location Register is commonly integrated in the mobile switching centre MSC. An integrated network element such as this is briefly called a VMSC (Visitor MSC). When the mobile station MS is active (it has registered in the network and can initiate or receive a call), the majority of the subscriber data concerning the mobile station MS in the Home Location Register HLR is loaded (copied) into the Visitor Location Register VLR of the mobile switching centre MSC in whose area the mobile station MS is located.
Base stations BTS continuously broadcast information about themselves and their environment. The information comprises e.g. a location area identifier, base station identifier, base station type and what is known as adjacent cell information. When a mobile station MS is locked to the base station of a specific cell, it also monitors the transmission quality of the base stations indicated by the adjacent cell information sent by the base station BTS, and changes over to one of these base stations if the coverage of the current base station degrades. A cellular radio network usually knows the location of a mobile station with the accuracy of what is known as a Location Area (LA). A location area usually includes a suitable number of predefined cells and their base stations. Location area data, for instance a Location Area Index (LAI), sent by a base station informs the mobile station of the location area that the base station BTS belongs to. When the mobile station MS changes cells within the same location area, location updating to the cellular radio network is not needed. But when the mobile station changes over to a new base station and notices on the basis of the location area data—for instance the LAI—that the location area changes, the mobile station initiates location updating by sending a location update request to the cellular radio network. As a result of this location update request the network stores the new location area of the mobile station in its subscriber registers. The location updating in the GSM system given as an example is described e.g. in Mouly-Pautet, “
The GSM System for Mobile Communications
”, particularly chapter 7.1.4, and in the ETSI recommendation “GSM 03.12, Location Registration Procedures DCS, ETSI/PT 12”.
FIG. 2
illustrates signalling relating to location updating. In
FIG. 2
it is assumed, similarly as in the GSM system, that a mobile subscriber's MSISDN identifier (Mobile Subscriber ISDN) is not used on the radio path. Instead, an IMSI identifier (International Mobile Subscriber Identity) or a TMSI identifier (Temporary Mobile Subscriber Identity) is used in order to protect the subscriber's identity. In step
2
-
1
the mobile station MS sends a location update request Loc_Update_Req, which proceeds (via the base station BTS and the base station controller BSC) to the mobile switching centre MSC. In step
2
-
2
the mobile switching centre MSC sends a location update command to the visitor location register VLR, which performs the update in step
2
-
3
. In step
2
-
4
the visitor location register VLR sends an acknowledgement to the mobile switching centre MSC to the effect that the location updating has been performed, the MSC forwarding the acknowledgement Loc_Update_Ack to the mobile station MS in step
2
-
5
.
The IMSI (or the TMSI) and the mobile subscriber's MSISDN are associated with each other in the home location register HLR in a way described for instance in Mouly-Pautet, “
The GSM System for Mobile Communications
”, particularly chapter 8.1.1.3. To sum up, the home location register maintains a conversion table or file associating a specific MSISDN number with a specific IMSI number. Table T in
FIG. 3
represents this table.
FIG. 3
illustrates the set-up of a call terminating at a mobile station MS in a GSM mobile communication system. If the mobile station MS given in
FIG. 1
is not located within the area of its own home location register, the parts in
FIG. 2
correspond to those in
FIG. 1
, with the home location register HLR and the visitor location register VLR being, however, connected to different mobile switching centres MSC. In step
3
-
1
the call arrives at the Gateway Mobile Switching Centre (GMSC), which in step
3
-
2
defines, on the basis of the directory number MSISDN of the called subscriber, the subscriber's home location register HLR and sends it an inquiry concerning routing information. Information indicating the visitor location register VLR in the area of which the subscriber is located has been updated to the subscriber's home location register HLR in connection with location updating. In step
3
-
3
, on the basis of this information, the home location register HLR sends a request Provide Roaming Number to the visitor location register VLR. The mobile subscriber's IMSI is also sent to the visitor location register VLR in this request. In step
3
-
4
the VLR stores the data it has received and reserves a Mobile Station Roaming Number (MSRN). In step
3
-
5
the VLR sends the roaming number MSRN it has reserved to the home location register HLR, which in step
3
-
6
transmits it to the centre GMSC which inquired the routing information. A roaming number domain is defined in such a way that a call is always routed to that mobile switching centre MSC whose visitor location register VLR has reserved the roaming number concerned. On the basis of the roaming number MSRN, the gateway mobile switching centre GMSC can thus route the call forward by sending in step
3
-
7
an initial address message to the mobile switching centre MSC indicated by the roaming number MSRN. In this example the mobile switching centre MSC concludes from the roaming number MSRN that the call will terminate in the area of its own centre. In step
3
-
8
the mobile switching centre MSC inquires of its own visitor location register VLR the called subscriber's information for setting up the call. In a normal case the visitor location register VLR returns in step
3
-
9
the information needed for setting up the call. Arrows
3
-
10
and
3
-
11
describe this process.
In the ex

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