# Calling line identification presentation (CLIP)

The CLIP service provides the calling party's address information to the called party. This information consists of:

- The calling party's national (ISDN) number

- The country code, and other international call information (if any)

- (Optional) Subaddress information, if provided by the calling user

This service is available under many variants, including Q.SIG.

## CLIP under non-Q.SIG variants

Under most non-Q.SIG variants, the service is generally available to the called user (no subscription is required).

The CLIP service is activated and deactivated by the service provider. When the service is activated, the network automatically invokes the service in the call setup phase. The application need not perform any special activation or invocation operations to use the service.

The calling user can present address information to the network in the ACU_CONN_RQ primitive. If the calling user does not include address information in the primitive, the network fills in the information by default.

To specify address information, the calling user uses the following macros:

Macro | Description
--- | ---
Acu_conn_rq_a_calling_nb | Pointer to buffer containing calling number.
Acu_conn_rq_calling_nb_size | Size of buffer containing calling number.
Acu_conn_rq_a_calling_nb_sub | Pointer to buffer containing calling subaddress.
Acu_conn_rq_calling_nb_sub_size | Size of buffer containing calling subaddress.
Acu_conn_rq_calling_nb_plan | Calling number plan.
Acu_conn_rq_calling_nb_pres | Calling number presentation.
Acu_conn_rq_calling_nb_type | Calling number type.
Acu_conn_rq_calling_nb_sub_odd_even | Called subaddress odd/even.
Acu_conn_rq_calling_nb_sub_type | Calling subaddress number type.

The Acu_conn_rq_calling_nb_pres macro determines if this information is to be made available to the called user. If the calling user sets Acu_conn_rq_calling_nb_pres to N_PRES_ALLOWED, the called user can access this information. If the calling user sets Acu_conn_rq_calling_nb_pres to N_PRES_RESTRICTED, the network invokes the Connected line identification presentation (COLP) service, and blocks this information from the called user.

The called user receives the address information in the ACU_CONN_IN primitive. To access this information, the called user uses the following macros:

Macro | Description
--- | ---
Acu_conn_rq_a_calling_nb | Pointer to buffer containing calling number.
Acu_conn_rq_calling_nb_size | Size of buffer containing calling number.
Acu_conn_rq_a_calling_nb_sub | Pointer to buffer containing calling subaddress.
Acu_conn_rq_calling_nb_sub_size | Size of buffer containing calling subaddress.
Acu_conn_rq_calling_nb_plan | Calling number plan.
Acu_conn_rq_calling_nb_pres | Calling number presentation.
Acu_conn_rq_calling_nb_screen | Calling number screening indicator.
Acu_conn_rq_calling_nb_type | Calling number type.
Acu_conn_rq_calling_nb_sub_odd_even | Called subaddress odd/even.
Acu_conn_rq_calling_nb_sub_type | Calling subaddress number type.

The Acu_conn_in_calling_nb_screen macro indicates the result of the network's screening of the address information. Screening is the process by which the network checks that the address information provided by the calling user is acceptable to the network. Possible values for this macro are:

Value | Meaning
--- | ---
N_SCREEN_USER_PASSED | The number was successfully screened.
N_SCREEN_USER_FAILED | The number was not acceptable to the network.
N_SCREEN_NETWORK_PROVIDED | The number was provided by the network (the calling user did not provide the information directly).
N_SCREEN_USER_PROVIDED | No screening took place.

## CLIP under the Q.SIG variant

The Q.SIG application has the role of network. As a provider of the CLIP service, the application is responsible for the following:

- Determining whether the calling party address information is to be presented to the called user, depending upon the presentation setting

- Sending the calling party address information to the called user

- Screening the calling party address information and providing the screening result in the primitive sent to the called user

If the application cannot verify the calling party address information (that is, if the screening result is N_SCREEN_NETWORK_PROVIDED or N_SCREEN_USER_PROVIDED), it can include the default access number for the calling user interface in the message sent to the called user. This information is stored in the following macros:

Macro | Description
--- | ---
Acu_conn_rq_a_calling_nb2 | Order to buffer containing second calling number.
Acu_conn_rq_calling_nb2_size | Size of buffer containing second calling number.
Acu_conn_rq_calling_nb2_pres | Presentation of second calling number.
Acu_conn_rq_calling_nb2_screen | Screen indicator of second calling number.
Acu_conn_rq_calling_nb2_type | Type of second calling number.

## CLIP and call forwarding services

When a call has been diverted or deflected, and the diverted-to user has been provided with the CLIP service, the diverted-to user receives the address information of the calling user, unless the calling user has subscribed to the CLIR service.