The 3GPP AAA Proxy in case of I-WLAN access as specified in TS 23.234 represents a AAA proxying and filtering function and resides in the visited 3GPP network. It is involved in access and service authentication and authorization procedures of a WLAN UE.
The Accounting Interworking Function that performs translation of the accounting signalling and parameters that are
understood by the IP-Edge into the credit management signalling and parameters that are understood by the OCS and
the OFCS is defined in BBF WT-300.
The AF is an element offering applications that require dynamic policy and/or charging control
over the IP-CAN user plane behaviour. The AF shall communicate with the PCRF to transfer dynamic session
information, required for PCRF decisions as well as to receive IP-CAN specific information and notifications about
IP-CAN bearer level events. One example of an AF is the P-CSCF of the IM CN subsystem.
When the User Data Convergence (UDC) architecture is applied, certain functional entities keep the application logic, but do not locally store user data permanently. Examples of such functional entities are HLR/HSS/AuC and Application Servers. These data-less functional entities are known in the UDC architecture as Application Front Ends. The application that is handled by an AFE determines the type of AFE, e.g. HLR-FE or HSS-FE.
The reference points between the Front Ends and the core and service layers are not affected by the UDC architecture. More information on Application Front Ends can be found in
The ANDSF (which is an optional element in the architecture) contains data management and control functionality
necessary to provide network discovery and selection assistance data as per operators' policy. The ANDSF is able to initiate data transfer to the UE, based on network triggers, and respond to requests from the UE. It provides functions such as inter-system mobility policy, access network discovery information.
The ANDSF in the subscriber's home operator network may interact with other databases such as the HSS user profile
information residing in subscriber's home operator network. Details of such interaction with these databases are not described in this Release of the specifications. For details on ANDSF, see TS 23.402.
An AS i.e., SIP Application Server, OSA Application Server, or CAMEL IM-SSF, offers value
added IM services and resides either in the user's home network or in a third party location. The third party could be a network or simply a stand-alone AS.
The OSA Application Server does not directly interact with the IMS network entities but through the
OSA Service Capability Servers (OSA SCS-s). Further information on OSA is provided in TS 22.127.
A SIP Application Server specified within 3GPP that supports IMS reference points (e.g. ISC, Sh, Ut), in
support of an application, is considered as part of the IM CN subsystem. Examples of such ASs are SCC
AS and TAS.
The AS (SIP Application Server and/or the OSA Service Capability Server and/or IM-SSF) can communicate with the
HSS. The Sh and Si interfaces are used for this purpose.
The Serving-CSCF to AS interface is used to provide services residing in an AS. Two cases were identified:
Serving-CSCF to an AS in Home Network.
Serving-CSCF to an AS in a trusted External Network (e.g., Third Party or Visited). The S-CSCF does not
provide authentication and security functionality for secure direct third party access to the IM Subsystem. The
OSA framework provides a standardized way for third party access to the IM Subsystem.
The Interrogating-CSCF to AS interface is used to forward SIP requests destined to a Public Service Identity hosted by the AS directly to that AS.
The AS to MRFC interfaces are:
Mr', used for session control;
Cr, used for media control.
The AS to MRB interface (Rc) is used by the AS to request that MRF resources with certain characteristics be assigned to a call.
An Application Server may influence and impact the SIP session on behalf of the services supported by the operator's network. An AS may host and execute services.
The ATCF is a function in the serving (visited if roaming) IMS network. It enables SRVCC Session Transfer
mechanisms in the serving network for a UE. The SCC AS can provide Session Transfer mechanisms in the serving
network, if an ATCF is present in the SIP registration path of the UE, as defined in TS 23.237.
The AuC can be considered a subset of the HSS that holds the following functionality for the CS Domain and PS
The AuC is associated with an HLR and stores an identity key for each mobile subscriber registered with the
associated HLR. This key is used to generate security data for each mobile subscriber:
data which are used for mutual authentication of the IMSI and the network;
a key used to check the integrity of the communication over the radio path between the mobile station and the
a key used to cipher communication over the radio path between the mobile station and the network.
The AuC communicates only with its associated HLR over a non-standardised interface denoted the H‑interface.
The HLR requests the data needed for authentication and ciphering from the AuC, stores
them and delivers them to the VLR and SGSN and MME which need them to perform the security functions for
a mobile station.