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  Call Setup in a GSM Network : Setting up a call between two communication devices seems very quick and very simple operation,but when we look deeper in to this and analyse this then we can understand that a lot of operations are happening with in a short span of time. Before going deep in to this first i will give a brief introduction of various elements included in this process. 1.BTS-BTS stands for Base Transceiver Station.It is nothing but your Tower which radiates the signal to your mobile.It is the first player in this operation which always have a touch with the mobile. 2.BSC-BSC stands for Base Station Controller.It is a large unit which controls all the BTS(Towers).We can say that a number of BTS are controlled by a single BSC.There are so many BSCs present in an area depending on the number of users and all are inter connected. 3.MSC-MSC stands for Mobile Switching Center.It is responsible for switching the call to the called subscriber.A number of BSCs are connected to the MSC and it controls the BSC. 4.HLR-HLR stands for Home Location Register.It is the server which stores the details of the all the subscribers permanently. 5.VLR-VLR stands for Visitor Location Register.It is the server which stores the details of the all the visiting subscribers temporarly. All the above said units are interconnected and plays a vital role in call connection. Call Setup : 1.When a subscriber initiates a call by dialling a number in his mobile it directly send a request to the BTS which he comes under. 2.BTS there by sends the request to the BSC to which it is connected. 3.From the BSC the request is made to the MSC to which it is connected. 4.Then MSC sends a request to the HLR to check the information about the caller like account balance(if pre paid),live user,area of the caller etc. 5.After checking all the details the HLR sends a acknowlegement message to the MSC that the caller is O.K. to make a call or not. 6.If that message is O.K. the operation continues or else the MSC sends a NOT O.K. message to the BSC which has made the request and BSC to the BTS and BTS to the Mobile.At the next instance the call get disconnected.   7.If the message recieved by the MSC is O.K. then it again sends a request to the HLR to find the called party(the subscriber to whom call is made). 8.The called party and the caller may comes under the same MSC or different MSC.If both comes under the same MSC then the HLR finds the subsciber easily and informs the MSC that to which area the called party belongs.The MSC therefore establishes a air link between the both parties.Thus the call gets connected. 9.If both parties comes under different MSC then the HLR again search for the MSC to which the called party belongs and inform the same to the MSC of the caller.Thus the MSC of the caller establishes a air link between the both parties.Thus the call gets connected. After the call gets disconnected the Billing is made the Billing Server which is present in the HLR. Overview of The Universal Mobile Telecommunication System  (DRAFT, July 2002)   Table of Contents 1. 3G Systems 2. UMTS Services 3. UMTS Architecture 4. Core Network  5. Radio Access 6. User Equipment  1. 3G Systems  3G Systems are intended to provide a global mobility with wide range of services including telephony, paging, messaging, Internet and broadband data. International Telecommunication Union (ITU) started the process of defining the standard for third generation systems, referred to as International Mobile Telecommunications 2000 (IMT-2000). In Europe European Telecommunications Standards Institute (ETSI) was responsible of UMTS standardisation  process. In 1998 Third Generation Partnership Project (3GPP) was formed to continue the technical specification work. 3GPP has five main UMTS standardisation areas: Radio Access  Network, Core Network, Terminals, Services and System Aspects and GERAN. 3GPP Radio Access group is responsible of:    Radio Layer 1, 2 and 3 RR specification   Iub, Iur and Iu Interfaces   UTRAN Operation and Maintenance requirements   BTS radio performance specification   Conformance test specification for testing of radio aspects of base stations   Specifications for radio performance aspects from the system point of view 3GPP Core Network group is responsible of:   Mobility management, call connection control signalling between the user equipment and the core network.   Core network signalling between the core network nodes.   Definition of interworking functions between the core network and external networks.   Packet related issues.   Core network aspects of the lu interface and Operation and Maintenance requirements 3GPP Terminal group is responsible of:   Service capability protocols   Messaging   Services end-to-end interworking   USIM to Mobile Terminal interface   Model/framework for terminal interfaces and services (application) execution   Conformance test specifications of terminals, including radio aspects 3GPP Services and System Aspects group is responsible of:   Definition of services and feature requirements.   Development of service capabilities and service architecture for cellular, fixed and cordless applications.   Charging and Accounting   Network Management and Security Aspects   Definition, evolution, and maintenance of overall architecture. Third Generation Partnership Project 2 (3GPP) was formed for technical development of cdma2000 technology which is a member of IMT-2000 family. In February 1992 World Radio Conference allocated frequencies for UMTS use. Frequencies 1885 - 2025 and 2110 - 2200 MHz were identified for IMT-2000 use. See the UMTS Frequency page for more details. All 3G standards are still under constant development. In 1999 ETSI Standardisation finished for UMTS Phase 1 (Release '99, version 3) and next release is due December 2001. UMTS History page has a list of all major 3G and UMTS milestones. Most of the European countries and some countries round the world have already issued UMTS licenses either by beauty contest or auctions. 2. UMTS Services    UMTS offers teleservices (like speech or SMS) and bearer services, which provide the capability for information transfer between access points. It is possible to negotiate and renegotiate the characteristics of a bearer service at session or connection establishment and during ongoing session or connection. Both connection oriented and connectionless services are offered for Point-to-Point and Point-to-Multipoint communication. Bearer services have different QoS  parameters for maximum transfer delay, delay variation and bit error rate. Offered data rate targets are:   144 kbits/s satellite and rural outdoor   384 kbits/s urban outdoor   2048 kbits/s indoor and low range outdoor UMTS network services have different QoS classes for four types of traffic:   Conversational class (voice, video telephony, video gaming)   Streaming class (multimedia, video on demand, webcast)   Interactive class (web browsing, network gaming, database access)   Background class (email, SMS, downloading) UMTS will also have a Virtual Home Environment (VHE). It is a concept for personal service environment portability across network boundaries and between terminals. Personal service environment means that users are consistently presented with the same personalised features, User Interface customisation and services in whatever network or terminal, wherever the user may be located. UMTS also has improved network security and location  based services. 3. UMTS Architecture  A UMTS network consist of three interacting domains; Core Network (CN), UMTS Terrestrial Radio Access Network (UTRAN) and User Equipment (UE). The main function of the core network is to provide switching, routing and transit for user traffic. Core network also contains the databases and network management functions. The basic Core Network architecture for UMTS is based on GSM network with GPRS. All equipment has to be modified for UMTS operation and services. The UTRAN provides the air interface access method for User Equipment. Base Station is referred as Node-B and control equipment for   Node-B's is called Radio Network Controller (RNC). UMTS system  page has an example, how UMTS network could be build. It is necessary for a network to know the approximate location in order to be able to page user equipment. Here is the list of system areas from largest to smallest.   UMTS systems (including satellite)   Public Land Mobile Network (PLMN)   MSC/VLR or SGSN   Location Area   Routing Area (PS domain)
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