An ISDN/MSISDN number shall identify each member of a CUG. A CUG shall be defined for one or more basic service groups. CUG members can have additional capabilities that allow them to originate calls outside the group, and/or to receive calls from outside the group. CUG members can have additional restrictions that prevent them from originating calls to other members of the CUG, or from receiving calls from other members of the CUG. CUG shall remain unaffected when members roam to PLMNs supporting CUG. Roaming subscribers must have the same CUG facilities on the roamed-to PLMN as on the Home PLMN. When roaming to networks not supporting CUG, the CUG restrictions must be enforced. (However, where possible, the CUG facilities should be supported, see subclause 1.4.10.) Each individual subscriber may be a member of a maximum of 10 CUGs.

The applicability of this Supplementary Service is defined in TS 22.004.

MSISDN: CUG member: CUG index: CUG Interlock Code (IC): preferential CUG: suppress preferential CUG: Incoming Access (IA): Outgoing Access (OA): suppress OA: Incoming Calls Barred Within A CUG (ICB): Outgoing Calls Barred Within A CUG (OCB): CUG calls:

The CUG Supplementary Service shall be provided after prior arrangement with the service provider. At provision subscription options should be selected by the served mobile subscriber. A user may be a member of several CUGs. The service provider defines the number of CUGs, up to the maximum stated in subclause 1.2.1, which can be allocated to an individual subscriber. The user shall choose one of the following subscription options for each basic service group applied to the CUG Supplementary Service. This subscription option may be provisioned on a per basic service group basis or for all basic services:

• CUG calls only;
• CUG with incoming access, i.e. can also receive calls, which are not subject to CUG restrictions;
• CUG with outgoing access, i.e. can also make calls, which are not subject to CUG restrictions;
• CUG with incoming and outgoing access, i.e. can also make and receive calls, which are not subject to CUG restrictions.

A user may subscribe to one of two additional restrictions applying for each particular CUG:

• incoming calls barred within a CUG;
• outgoing calls barred within a CUG.

The network shall provide a subscription option in order to enable the user to specify a preferential CUG, for each basic service group included in at least one of the CUG(s). The user can request that no preferential CUG exists, or that a particular one of her CUGs (or the only one if a single CUG applies) is used as a preferential CUG for the particular basic service group. If a user has the subscription option outgoing calls barred within a CUG, it is not allowed to specify that particular CUG as a preferential CUG. The subscription options are shown in Annex A1. The CUG indices shall be allocated by prior arrangement with the service provider. The choice of preferential CUG(s) shall be alterable only by service provider action upon request by the served user.

Withdrawal of the CUG Supplementary Service, membership of one or more CUGs, will be by the action of the service provider, at the request of the subscriber or CUG management, or for administrative reasons.

The CUG Supplementary Service will be activated by the service provider as a result of provision.

The CUG Supplementary Service will be deactivated by the service provider as a result of withdrawal.

Normal call setup procedures shall apply to calls with the CUG Supplementary Service.

A user having neither the restriction of incoming calls barred within a CUG, nor the restriction of outgoing calls barred within a CUG can make calls to, and receive calls from, members of those CUGs of which the user is a member. Upon receipt of a call setup attempt to or from a CUG subscriber the network shall check its validity in conjunction with the access capabilities subscribed to. On successful validation of a CUG call setup attempt the network shall attempt to establish the call to the required destination.

Upon receipt of a call setup attempt to or from a CUG subscriber, the network shall check its validity in conjunction with the access capabilities subscribed to. If an invalid request is received or the checks cannot be performed, then the network shall reject the call and return an appropriate indication to the calling user. The network shall prohibit a user with incoming calls barred within a CUG from receiving CUG calls from members of the same CUG. The network shall prohibit a user with outgoing calls barred within a CUG from making CUG calls within that CUG.

The HPLMN shall control handling of roaming, when a CUG subscriber is roaming into a network not supporting CUG, without relying on extra functionality in network entities not supporting CUG. For subscribers roaming in a PLMN not supporting CUG the following apply:

1. In the case of basic service groups not subject to CUG restrictions, incoming and outgoing calls shall be allowed as normal.
2. In the case of basic service groups subject to CUG restrictions and without incoming access, incoming calls shall not be allowed.
3. In the case of basic service groups subject to CUG restrictions and without outgoing access, outgoing calls shall not be allowed.
4. Normal incoming calls are allowed for basic service groups subject to CUG restrictions and for which the called user has incoming access allowed.
5. Outgoing calls are allowed for basic service groups subject to CUG restrictions and for which the user has outgoing access allowed.

Except for ACR, the following is valid:

• The call restriction Supplementary Services, when active and operative, takes precedence over the CUG restrictions.
• The activation of a call restriction Supplementary Service does not affect any current CUG call.
  For ACR, see TS 22.088.