ARCHITECTURE OVERVIEW OF (UMTS) :
The UMTS system consists of a number of logical network elements connected through open interfaces or access points. Functionally these elements are grouped into the Radio Access Network (RAN, UMTS Terrestrial RAN – UTRAN) and the Core Network (CN). The UTRAN handles all radio –related functionally, Radio Resource and Mobility Management (RRM and MM). Whereas, the CN is responsible for switching and routing calls and data connection to external networks at the same time as managing session and mobility information, Communication and Mobility (CM and MM). The system is completed by the User Equipment (UE) or 3G terminal, which interfaces with the user and the radio interface. The high-level architecture is shown in the figure below.
The collection of at least one logical network element of each type defines a UMTS Public Land Mobile Network (PLMN). The UMTS PLMN is a fully featured and operational network, either on its own together with the other sub-networks, that provides land mobile telecommunication services to the public. Each PLMN, typically established and operated by a signal operator, is connected to the other types of networks, such as Integrated Services Digital Network (ISDN), Public Switched Telephone Network (PSTN), Internet, and so on.
UMTS Radio Access Network:
UTRAN is subdivided into individual Radio Network Controller (RNC). Within a RNS, is connected to a set of Node B elements, each of which can server one or several cells. UTRAN is located between two new open interfaces, Uu and Iu. The Uu interface is a WCDMA radio interface through which the UE accesses the fixed part of the system. Iu connects the UTRAN to the CN. The main task of UTRAN is to create and maintain Radio Access Bearers (RABs) for communication between User Equipment (UE) and the core Network (CN). With RAB THE CN elements are given an illusion of a fixed communication path to the UE. While in GPRS/EDGE networks the logical link is defined between UE and SGSN, so called Radio Access Bearers (RABs) are defined between UE and the UTRAN. Hence, the locations of several functions have been shifted from the SGSN which is part of the GPRS CN to the Radio Network Controller (RNC) in UTRAN. A 3rd Generation Serving GPRS Support Node (3G-SGSN) no longer comprises logical link management functions.
Node B:
Node B is the physical unit for radio transmission-reception in cells. Depending on sectoring (Omni sectored cells), one or more cells may be served by a Node B. Node B connects with the UE via the WCDMA Uu radio interface and with the RCN via the lub asynchronous transfer mode (ATM)- based interface. The main task of Node B is to perform the air interface Layer1 processing (transfer information from transport to physical channels) although it also participates in some basic Radio Resources Management (RRM) operation. However, RNC is where the radio resources are managed.
Radio Network controller:
The Radio Network Controller (RNC) is the switching and controlling element of the UTRAN located between the lub and lu interface. It also has a third interface called lur for inter-RNS connections. The RNS interfaces the CN for both Packet-Switched and Circuit- Switched service domains and also terminates the Radio Resource Control (RRC) protocol that defines the message and procedures between the mobile and UTRAN. The whole functionally of a RNC can be grouped into two parts, UTRAN Radio Resource Management (RRM) and control functions. The RRM is a collection of algorithms used to guarantee the stability of the radio path and the QOS of radio connection by efficient sharing and managing of the radio resources. The UTRAN control functions include all of the functions related to setup, maintenance and release of Radio Bearers including the support functions for the RRM algorithms.
3G MSC:
The MSC is an exchange which performs all the switching and signaling functions for MSs / UEs located in a geographical area. The MSC area is sub-divided into so-called Location Areas LA.
3G SGSN:
The serving GPRS Support Node SGSN is responsible to provide service for all activated MS / UE in a certain geographical area, the so-called SGSN service area. The SGSN service area is subdivided into different Routing Area RA (a sub-set of the Location Area LA). A Routing Area consists of one several cells.
- Keeps track of the location of an individual MS / UE and stores it location (the Routing Area).
- It is responsible for the MS / UE Mobility Management (Location Updates, Attach, Paging…)
- Performs security functions and access control.
- Collecting charging data or billing data & forwarding to CGF (Ga).
- Inter-working PLMN – PDN (Gi).
- Screening –Filtering.
- Storing routing information (current SGSN).
- Requesting location information from HLR.
- Routing packets-SGSN (GN).
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