Release of remaining activities in VPLMNs

Details Release of remaining activities in VPLMNs Release of remaining activities in VPLMNs

1998-10-15

2002-05-14

Hunter, Daniel (Department: 2684)

Telecommunications

Radiotelephone system

Zoned or cellular telephone system

C455S412100, C455S550100

Reexamination Certificate

active

06389283

ABSTRACT:

BACKGROUND
The Global System for Mobile communication (GSM) describes a European standard for radiocommunication utilized by the corresponding Public Land Mobile Networks (PLMNs) in the region and in many other countries, which standard is intended to provide uniformity so that users can access radiocommunication systems throughout Europe and many other countries with minimal equipment compatibility problems. In addition to lower level details such as modulation, frame formats, etc., the GSM standard also specifies standard higher level activities which can be performed within the system. There are many such activities which may be associated with a particular subscriber in the GSM network including call related events such as call set-up, and call termination. Other types of subscriber activities include invocation of call related and call independent supplementary services such as call hold, call waiting, call transfer, and call forwarding. Based upon roaming agreements between the different mobile network operators, mobile subscribers belonging to a specific (home) PLMN, referred to herein as an HPLMN, can make use of their subscribed services and facilities while roaming on other PLMNs, referred to as the visited PLMN (VPLMN).
FIG. 1
illustrates the network architecture used in GSM systems. Home location register (HLR)
115
stores data relating to subscribers including, for example, current location of the subscriber equipment, directory number (MSISDN), radio number plan identification (e.g., International Mobile Subscriber Identity (IMSI)), supplementary service profiles and teleservice profiles. Visitor location register (VLR)
120
manages data associated with subscribers which are currently situated within its area of responsibility, e.g., those mobiles which have roamed into its service area. Authentication Center (AUC)
145
works in close association with HLR
115
, wherein AUC
145
provides the information to authenticate all calls in order to guard against possible fraud, stolen subscriber cards or unpaid bills.
When mobile unit
150
, a subscriber of HPLMN
101
, tries to invoke a subscriber activity while in PLMN
102
, VLR
120
requests a “triplet” of information from HLR
115
in order to determine whether mobile unit
150
is authorized to use the particular service. The “triplet” consists of a random number (RAND), a signed response (SRES) and a key cipher (Kc), which are generated by AUC
145
. The “triplet” of information is requested by HLR
115
and stored therein. The “triplet” of information is transmitted to VLR
120
from HLR
115
in response to a specific request from VLR
120
, e.g., during location updating. VLR
120
transmits the RAND to mobile unit
150
. In response mobile unit
150
performs a calculation based upon the RAND in order to determine a SRES which is transmitted to VLR
120
. VLR
120
compares the SRES received from HLR
115
and the SRES received from mobile unit
150
. If the SRESs match then VLR
120
determines that mobile unit
150
is authorized. HLR
115
updates its database to indicate that mobile unit
150
is located in VLR
120
.
When mobile unit
150
moves from PLMN
102
to PLMN
190
, mobile unit
150
recognizes the change and sends a location updating message to the new VLR (not shown) in PLMN
190
. The new VLR informs HLR
115
of the new location of mobile unit
150
. HLR
115
then sends a Cancel Location message to previously visited VLR
120
, located in PLMN
102
, to indicate that mobile unit
150
is no longer present in the area served by PLMN
102
. HLR
115
sends an insert subscriber data (ISD) message to the new VLR which provides the new VLR with the relevant subscriber data.
This architecture supports simultaneous activities in different VLRs in case of subscriber movement. In addition, activities on different gateway mobile switching centers (GMSCs) may be maintained simultaneously in certain service scenarios. One scenario in which there are simultaneous subscriber activities is support for optimal routing, a network feature which enables the calls directed to a mobile subscriber to be routed directly to the mobile subscriber's actual location, or to her forwarded-to destination (instead of via the HPLMN or in the case of Late Call Forwarding via the VPLMN). For instance, in an exemplary optimal routing scenario, an HLR may receive Send Routing Information (SRI) messages from more than one GMSC. The PLMN associated with a GMSC in an optimal routing scenario is referred to as an interrogating PLMN (IPLMN). The IPLMN interrogates the HPLMN of a called party in order to determine the whereabouts of that party. The interested reader may refer to GSM standard documents numbered 02.79 and 03.79 for more details of the optimal routing feature.
Allowing simultaneous subscriber activities in GSM make certain fraud scenarios very difficult to control by the network operator due to the fact that a legitimate subscriber may invoke several subscriber activities in a single network or in different networks. It is possible for a subscriber to enter an area served by a particular MSC/VLR while still having subscriber activities which are ongoing in a VLR associated with a previously visited MSC/VLR area which the subscriber has left. For instance, referring again to
FIG. 1
, mobile unit
150
may initiate a call forwarding service in GMSC
170
while located in the area served by PLMN
102
. Mobile unit
150
may then move into the area served by PLMN
190
and invoke another call service, without canceling the call forwarding service activated while mobile unit
150
was located in the area served by PLMN
102
. Therefore, mobile unit
150
will have activities in both PLMN
102
and PLMN
190
which appear to an operator of a PLMN as fraudulent subscriber activity.
An HPLMN may control fraudulent subscriber activity using an Immediate Service Termination (IST) command to terminate the fraudulent activity.
FIG. 2
illustrates the implementation of the IST command. In step
205
, the HPLMN changes the subscriber's entry in the HLR, e.g. by removing the subscribers subscription, in order to prevent the subscriber from resuming activities in the HPLMN and VPLMN after the invocation of the IST command. In step
210
, the HPLMN sends a Mobile Application Part (MAP) Cancel Location command to the VLR in order to prevent the resumption of activity by the subscriber within the VPLMN without the need to reference the HPLMN. In step
215
, the HPLMN sends an IST command to the VPLMN. In step
220
, the VPLMN confirms receipt and comprehension of the IST command. In step
225
, the VPLMN terminates all activities of the subscriber which were indicated by the IST command. In step
230
, the VPLMN sends confirmation to the HPLMN that all activities have been terminated.
As stated above, a subscriber may have remaining activities in PLMNs where the subscriber is no longer located. In order for the IST command to be truly effective, all subscriber activity should be terminated. Hence, there is a need for the HLR to track subscriber activity not only in the current VPLMN, but also in all PLMNs in which the subscriber has remaining activities. There are several proposed solutions which attempt to address this issue.
One solution is based upon custom applications for mobile network enhanced logic (CAMEL). CAMEL provides international intelligent network services for the GSM. CAMEL can be used to terminate all originated, terminated and forwarded calls of a subscriber, provided there is a control relationship between the CAMEL server in the HPLMN and the MSC controlling the call or forwarding leg. Using CAMEL requires the service control point (gsmSCP) to control all ongoing calls. As the amount of subscribers who are using CAMEL increases, the capacity required of the gsmSCP and the service switching point (gsmSSP) likewise increase which leads to a greater expense in monitoring the remaining activities. Normally, when a subscriber has been removed from the HLR it shall be communicated to the SCP to start th

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