Core UMTS Network Elements

The following section sets out the elements of the GSM/UMTS core network, and some of the reasoning behind it. Figure 36 shows how these core elements fit together and how they fit into the overall system picture. However Figure 36 is not a true physical representation of the core network, nor does it show all the interfaces. As the core network has not been standardized there still exist other possibilities for bundling different functions into physical network elements.

Figure 36 UMTS Core Network Elements
(Adapted from Ericsson Document EN/LZT 123 5374 R1B)

MSC Server
The MSC Server handles control layer functions related to circuit mode communication services at the UTRAN and PSTN/ISDN borders and performs among others the following functions:

• Media gateway control

• ISDN services control

• Mobility management

• Authentication

• Charging data collection/output

• Services switching function (5SF)

• Internet dial-in services (RAS)

• Element management
   

In addition to these functions the MSC Server also houses the interworking and gateway functionality necessary to act as an SMS-IWMSC and SMS-GMSC for the Short Message Service.
 

Serving GPRS Support Node Server (SGSN Server)
The SGSN Server handles control layer functions related to packet mode communication services at the border between UTRAN and the basic core network and performs among others the following functions:

• Media gateway control

• Session management

• Mobility management

• Authentication

• Charging control

• Relaying of SMS

• Element management

Media Gateway (MGW)
The MGW handles transport and user plane functions for both packet and circuit mode communication at the borders between networks/network segments. These lower layer functions primarily concern the user data handling and includes e.g.:

• Media processing (speech coding. conference call bridging etc)

• Media generation (tones etc)

• Setup/release of user data bearers

• Provision of traffic/charging info for packet mode communication

• Security management

• Routing and switching QoS management

• Element management
   

Most MGW resources are shared between packet and circuit communication services or can easily be re-configured from one communication mode to the other. This offers a very cost efficient and flexible solution for managing future changes in the circuit and packet mode traffic balance.

Gateway GPRS Support Node (GGSN)
The GGSN constitutes the tunnel end-point for the GPRS specific GTP-tunnel for packet mode communication and is situated on the border between the basic UMTS core network and the ISP-POP”. The GGSN is (indirectly) selected by the end-user at setup of the PDP-context. From an addressing point of view the GGSN represents the point of presence for ‘logged on’ end-users, i.e. end-users with an established PDP-context. Addresses can be dynamically assigned (fetched from an external server or a pool of own addresses) or statically assigned (fetched from the HLR). In order to fulfill its role in the network the GGSN performs the following functions among others:

• Tunnel management

• IP-address management

• Charging data collection/output

• Security management

• Packet filtering

• Packet routing/tunneling

• QoS management

• Element management

Optionally, a GGSN may also include certain non-GPRS specific functions such as a Foreign Agent (FA).
 

Home Location Register (HLR)
The Home Location Register is a network database for mobile telecommunications. The HLR holds all mobile specific subscriber data and contains a number of functions for managing these data, controlling services and enabling subscribers to access and receive their services when roaming within and outside their home PLMN. The HLR communicates with the GSNs, MSCs and
other network element via the MAP-protocol.
 

The Authentication Centre (AUC)
The Authentication Centre (AUC) contains functions for secure storage of individual subscriber identifiers and keys. AUC also includes algorithms necessary for generating authentication and ciphering data based on the subscriber keys. The authentication and ciphering data, provided by the AUC upon request, are used by different network elements to protect the network, users and operators against unauthorized use of the system.

Service Control Point (SCP)
The SCP is a part of the IN concept and contains the service logic and its execution environment. The SCP works in close co-operation with the service switching functions in the MSCs and provides IN-services such as Virtual Private Network (VPN), Number Portability etc.
 

Flexible Number Register (FNR)
The FNR accommodates translation functions necessary to de-couple end-user identities from the actual network databases holding end-user data. These translation functions are essential in order to be able to e.g.:

Easily reconfigure some of the network databases, e.g. as a result of a growing number of end-users.
Allow end-users to keep their identities when changing from one administration to another.
 

Equipment Identity Register (EIR)
The Equipment Identity Register is a network database holding status information on mobile station equipment. The EIR is interrogated by means of the MAPprotocol from e.g. network elements providing access into the PLMN (MSC and
SGSN servers), in order to ensure that the mobile station equipment is not blacklisted for any reason.

Cost Control Node (CCN)
The Cost Control Node is a central part of the 3G charging environment. CCN contains centralized rating functions and constitutes the charging determination point for services provided to subscribers at both into and inter PLMN roaming.
CCN also handles credit limits for accumulated subscriber charges. These on-line charging mechanism are used for provision of features such as credit control (e.g. pre-paid), user cost information (advice of charge), fraud control etc.

CCN receives traffic information on-line and off-line from the different traffic handling/service nodes and instructs these nodes to proceed with the calls/services according to the outcome of the operator defined cost control analyses. CCN also has the ability to receive CDR’s deriving from the Serving network providing near-real-time revenue charging.
 

Billing Gateway (BGw)
The Billing Gateway is a key component for the off-line (CDR based) charging in UMTS. The BGw collects information from the different traffic handling/service nodes (GSN, MSC. SMS-C. voice mail, application servers. etc) and forwards it to the operator’s administrative systems for off-line billing, accounting. traffic analyses and similar functions. The BGw also acts as an intermediate storage and pre-processor for formatting the CDR-information into the specific formats used by the operator.

The BGw also provides an interface to CCN and can be used to relay information for online charging from the traffic handling/service nodes not having direct interfaces to CCN.

BGw also acts as an accounting/settlement broker by providing the ability to distribute CDR’s from the Serving network to the Home environment BGw or CCN in near real time.