Page 452 - 5G Basics - Core Network Aspects

1 Core network aspects

The AP function sends a registration request by initiating a call request to the fixed network. In the
registration procedure, the AP function acts as a "proxy" for the MS PAM function and provides,
together with the SRF, the means to transfer information related to authentication between the MS
PAM function and the PAM-SCF.

When an AP function receives a deregistration request from a MS PAM function or when it detects
that a terminal is no longer accessible via the AP (e.g., has moved out of range, has been turned off,
etc.), the AP function frees the terminal identifier or subscriber number allocated to the terminal
and sends a deregistration request by initiating a call request to the fixed network.
• Originating call handling
When an AP function receives a call request from a MS PAM function via the air interface, it checks
the PSTN/ISDN access line status. If a line is free, the AP function initiates a call request to the
PSTN/ISDN containing the terminal identifier or the subscriber number corresponding to the
terminal. If there is no line available, the AP function sends a rejection to the MS PAM function to
allow the MS PAM function to automatically select and establish the call through the mobile network
radio access if available.
• Terminating call handling

When an AP function receives a terminating call request from the PSTN/ISDN for a mobile terminal,
the AP function recognizes the terminal to be connected by using the terminal identifier (in case a
PSTN line is used) or the subscriber number (in case an ISDN line is used) and completes the call to
the terminal with the CLI to be presented via the air interface to the MS PAM function.
7.2.3 CCF/SSF

The CCF establishes, manipulates and releases calls/connections. The CCF provides trigger mechanisms to
access IN functionality (e.g., passes events to the SSF).

The SSF extends the logic of the CCF to include recognition of service control triggers and to interact with the
PAM-SCF. The SSF manages signalling between the CCF and the SCF and it modifies call/connection
processing functions (in the CCF) as required to process requests for IN provided service usage under the
control of the PAM-SCF. The CCF/SSF interacts with the SRF for bearer channel establishment between the
SRF and the AP function under the control of PAM-SCF.
The PAM service trigger is handled in SSF as follows:
• When a PAM user requests registration/deregistration/originating call at an AP, the AP initiates a
call which invokes an IN trigger based on a prescribed number plan (the SAC of the PAM service) at
the SSF so that interaction with a PAM-SCF is initiated.
• A terminating call to a PAM user served with a fixed PAM service number invokes an IN trigger at
the SSF based on a prescribed number plan which comprises part of the digits of the fixed PAM
service number.
• For a terminating call to a PAM user served with a MSISDN, the PAM-SSF invokes an IN trigger based
on the terminating service subscription downloaded in CCF (MSC/VLR) from the HLR/AuC (HSS).

The CCF/SSF sets up the bearer connection between the AP function and the SRF function under the control
of the PAM-SCF to exchange the registration/deregistration/originating call parameters between the AP
function and the SRF in-band.
In originating and terminating call, the SSF executes the instruction from the PAM-SCF for the call processing
with updated parameters including the CLI as follows:
• In originating call, the SSF updates the CLI to represent the registered PAM user using fixed PAM
service number or MSISDN as opposed to the CLI of the AP upon the instruction from the PAM-SCF.
• In terminating call, in case a PSTN analogue access line is used, the SSF updates the CLI to indicate
the PAM user to be connected via updating the original CLI with additional terminal identifier
information upon the instruction from the PAM-SCF.

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