The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. The HLR is a database used for storage and management of subscriptions. The switching system includes the following functional elements − Home Location Register (HLR) The Network switching system (NSS), the main part of which is the Mobile Switching Center (MSC), performs the switching of calls between the mobile and other fixed or mobile network users, as well as the management of mobile services such as authentication. GSM - The Network Switching Subsystem (NSS) Time-delay measurements of received signals from the MS Providing an interface to the Operations and Maintenance Center for the BSS Performing traffic concentration to reduce the number of lines from the MSC It is a switching device that handles the radio resources. The function of the BSC is to allocate the necessary time slots between the BTS and the MSC. It controls the power transmission of the BSS and MS in its area. It assigns and releases frequencies and time slots for the MS. The BSC also translates the 13 Kbps voice channel used over the radio link to the standard 64 Kbps channel used by the Public Switched Telephone Network (PSDN) or ISDN. The BSC is the connection between the mobile and the MSC. It handles radio channel setup, frequency hopping, and handovers. The BSC manages the radio resources for one or more BTSs. Voice through full- or half-rate servicesĭecoding, decrypting, and equalizing received signals It also includes the following functions −Įncoding, encrypting, multiplexing, modulating, and feeding the RF signals to the antenna Each BTS has between 1 and 16 transceivers, depending on the density of users in the cell. Its transmitting power defines the size of a cell. A BTS is usually placed in the center of a cell. The BTS corresponds to the transceivers and antennas used in each cell of the network. In a large urban area, a large number of BTSs may be deployed. The BTS houses the radio transceivers that define a cell and handles the radio link protocols with the MS. A separate high-speed line (T1 or E1) is then connected from the BSS to the Mobile MSC. The BSS uses the Abis interface between the BTS and the BSC. A BSS may have one or more base stations. The radio components of a BSS may consist of four to seven or nine cells. The BTS and the BSC communicate across the specified Abis interface, enabling operations between components that are made by different suppliers. You need to insert the SIM card into another GSM cellular phone to receive calls at that phone, make calls from that phone, or receive other subscribed services. The SIM provides personal mobility so that the user can have access to all subscribed services irrespective of both the location of the terminal and the use of a specific terminal. We will discuss more about GMS services in GSM - User Services. High speed, circuit switched data at speeds up to 64 Kbps. General Packet Radio Services (GPRSs) using either an X.25 or IP based data transfer method at the speed up to 115 Kbps. X.25 packet switching through a synchronous or asynchronous dial-up connection to the PAD at speeds typically at 9.6 Kbps. The MS also provides access to the various data services available in a GSM network. Moreover, the mobile facilitates access to voice messaging systems. The MS also provides the receptor for SMS messages, enabling the user to toggle between the voice and data use. As such, other services are also provided, which include − It provides the air interface to the user in GSM networks. The MS consists of the physical equipment, such as the radio transceiver, display and digital signal processors, and the SIM card. The GSM network can be broadly divided into − These functions and interfaces are explained in this chapter. A GSM network comprises of many functional units.
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