Call forwarding in a telecommunication system

Details Call forwarding in a telecommunication system Call forwarding in a telecommunication system

2000-03-16

2002-12-31

Le, Thanh Cong (Department: 2684)

Telecommunications

Radiotelephone system

Special service

C379S211020, C455S445000

Reexamination Certificate

active

06501948

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to set-up of forwarded calls in a system wherein closed user groups are defined.
BACKGROUND OF THE INVENTION
It is known in telecommunication systems to define closed user groups (CUG), e.g. defined by the staff of a company or by a certain circle of friends. The services of a closed user group may be different and e.g. cheaper than normal calls.
The use of a closed user group in a telecommunication system is described in the GSM 02.85 specification published by the ETSI (European Telecommunications Standards Institute). In accordance with the specification, a subscriber belonging to a closed user group may have various subscriber options defined for himself which tell what kinds of calls the subscriber may receive or make. These subscriber options are
1. CUG calls only; the subscriber may set up calls only with subscribers of his own CUG group,
2. Access for CUG and incoming calls; the subscriber may set up calls with subscribers of his own CUG group and also receive calls coming from outside his own CUG group (IA, Incoming Access),
3. Access for CUG and outgoing calls; the subscriber may set up calls with subscribers of his own CUG group and may also make calls going outside his own CUG group (OA, Outgoing Access), and
4. Access for CUG and outgoing and incoming calls; the subscriber may set up calls with subscribers of his own CUG group and may also make calls going outside his own CUG group and receive calls coming from outside his own CUG group (IA+O Å).
In addition, restrictions within the user group may be defined for he subscriber,
1. ICB, incoming calls barred within a CUG, and
2. OCB, outgoing calls barred within a CUG.
A subscriber may belong simultaneously to several closed user groups CUG, of which one may be selected as default group, which is used in the set-up of outgoing calls, unless otherwise mentioned for the individual call.
FIG. 1
shows storing of information relating to closed user groups in a home location register HLR. A copy of the information presented in the figure is also preserved in the subscribers visitor location register VLR. An international mobile subscriber identity IMSI functions as the key to the record. A list of the basic services to which the subscriber has a right is appended to the subscriber identity. Services are distinguished from each other with the aid of basic service group codes BSGC. To the services is connected information on the closed user group CUG to be primarily used when setting up a call as well as information on OA access of outgoing calls outside the group. In the example shown in the figure, such a user group is defined for primary use in connection with speech service T
11
for the subscriber, the CUG INDEX of which =1, and there is also access for outgoing calls going outside the group (OA=T). Correspondingly, in connection with fax service T
62
of group
3
, such a user group is used primarily, the CUG INDEX of which =2, and outgoing calls going outside the group are barred (OA=F). In connection with the PAD service (Packet Assembler/Disassembler) BA
6
to be used when connecting to packet data networks at a transmission rate of 9600 bits a second, such a user group is used primarily, the CUG INDEX of which =4, and outgoing calls going outside the group are barred (OA=F).
In addition to service information and primary CUGs relating to services, the visitor location register stores a description of network-specific CUG IC (CUG Interlock Code) group attributes which are used between subscriber-specific CUG INDEX group attributes and exchanges. In the example shown in the figure, the CUG INDEX
1
of the subscriber's user group corresponds to the network-specific CUG IC
101
symbol, while CUG INDEX
2
corresponds to CUG IC
12
, CUG INDEX
3
to CUG IC
1
and CUG INDEX
4
to CUG IC
14
.
FIG. 2
shows transmission of information relating to the use of a closed user group when setting up a call. In the example, a call is set up between two mobile stations MSA and MSB (MS=Mobile Station). According to the figure, the CUG user group which is to be used is distinguished between the calling mobile station MSA and the mobile switching centre MSC and a visitor location register VLR typically located in connection with the MSC, using subscriber-specific CUG INDEX information together with the subscriber identity. If in connection with the call set-up, the MSA does not separately state any CUG to be used, then that closed user group will be used which has been defined by the subscriber as the default group for this basic service. If no default group has been defined for the basic service and the subscriber does not in connection with the call set-up indicate any closed user group to be used, the call will be set up as a normal call, if the subscriber has given access to normal calls (OA).
Upon receiving the request for a call set-up, the MSC/VLR checks if the MSA has the right to set-up of the CUG call he requested. This is done with the aid of the CUG INDEX information obtained from the subscriber, with subscriber data stored in the visitor location register VLR and with a special authorisation function. The call set-up is continued, if it is found that the subscriber is so entitled.
A user group to be used in communication between mobile switching centres is identified within the user group's network by a CUG IC identifier performing unambiguous identification. in addition, in communication between exchanges the term OA is used, which tells whether the call is allowed to be an outgoing call going outside the CUG.
When setting up a call, the calling subscriber MSA's exchange MSC contacts the GMSCB gateway mobile services switching centre of subscriber B based on the MSISDN number (MSISDN=Mobile Subscriber ISDN) which identifies subscriber B. The GMSCB is a centre able to make SRI (Send Routing Information) enquiries to subscriber B's home location register HLRB. In the SRI, the GMSCB sends to the HLRB the IC(A) identifier of the CUG defined by subscriber A and information on access of outgoing calls going outside the group.
FIG. 3
shows the operation of home location register HLRB. The HLRB receives the SRI enquiry (step N
01
) and checks whether MSB belongs to the CUG defined by subscriber A by comparing the IC(B) group symbols of subscriber B with the IC(A) group data stated by subscriber A (step N
02
). If it is found that subscriber B belongs to the defined user group, then IC(A)∈{IC(B)} is true, and the operation proceeds to step N
03
, where it is checked whether MSB has barred incoming calls within the group (ICB). If calls within the group are allowed (ICB(B) is false), a further check is made in step N
04
to find out whether subscriber B has defined forwarding of the call. The call will be forwarded, if subscriber B has determined that his call is to be forwarded unconditionally to subscriber C (CFU, Call Forwarding Unconditional) or if HLR finds that the subscriber can not be reached and the subscriber has defined CFNRc (Call Forwarding on Not Reachable) to be made in such a case. If forwarding is not defined or the forwarding conditions are not met, the call set-up is continued as a CUG call (step N
05
). If the call is defined to be forwarded to a third subscriber (subscriber C), the CUG information (IC(A), OA(A)) is checked to find out whether forwarding of the call can be carried out (step N
20
).
If it is found in step N
02
that subscriber B does not belong to the user group (IC(A)∉{IC(B)}) defined by subscriber A, or in step N
03
that subscriber B has barred internal calls in the group, progress is made to steps N
11
and N
12
, where it is checked whether the call can be set up as a normal call. A check is made in step N
11
to find out whether subscriber A has allowed the call to go outside the group (OA(A)) and in step N
12
whether subscriber B has allowed access for calls coming from outside the group (IA(B)). If each condition is

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