28-07-2014, 03:57 PM
CALL ROUTING IN CELLULAR SYSTEMS
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ABSTRACT
The seminar report mainly covers the aspect of the cellular system. Starting with the basics and a brief overview of the Wireless Communication Technology, the project report extends of the concept and GSM Technology also covering the concept of 2G. The project report discusses the architecture and layout of the PSTN and Telephony system. Covering the brief topics and terminology of GSM, presentation extends to Subsciber Identity Module (SIM). The authentication process and call setup process will also be discussed. Various algorithms in the Authentication process will be briefed. Also a Call Setup Flowchart; indicating the various steps and conditions will be covered.
: WIRELESS COMMUNICATION
Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor.
The most common wireless technologies use electromagnetic wireless telecommunications, such as radio. With radio waves distances can be short, such as a few metres for television remote control, or as far as thousands or even millions of kilometres for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones.
Less common methods of achieving wireless communications include the use of light, sound, magnetic, or electric fields.
Introduction
The Global System for Mobile communications is a digital cellular communications system. It was developed in order to create a common European mobile telephone standard but it has been rapidly accepted worldwide.
5 GSM Frequencies
GSM networks operate in a number of different frequency ranges. Most 2G networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including Canada and the United States) use the 850 MHz and the 1900 MHz bands because the 900 and 1800 MHz frequency bands were readily allocated. Most 3G GSM networks in Europe operate in the 2100 MHz frequency band. GSM 900 uses 890-915 MHz to send information from the mobile station to the base station (uplink) and 935-960 MHz for the other direction (downlink), providing 124 RF channels (channel numbers 1 to 124) spaced at 200KHz. Duplex spacing of 45MHz is used. In some countries the GSM 900 band has been extended to cover a larger frequency range. This extended GSM, known as E-GSM, uses 880-915 MHz (uplink) and 925-960 (downlink), adding 50 channels to the original GSM 900 band. Time division multiplexing is used to allow eight full rate or sixteen half rate speech channels per radio frequency channel.
Selective cells
It is not always useful to define a cell with a full coverage of 360 degrees. In some cases, cells with a particular shape and coverage are needed. These cells are called selective cells. Typical examples of selective cells are the cells that may be located at the entrances of tunnels where coverage of 360 degrees is not needed. In this case, a selective cell with coverage of 120 degrees is used.
Umbrella cells
A freeway crossing very small cells produces an important number of handovers among the different small neighbouring cells. In order to solve this problem, the concept of umbrella cells is introduced. An umbrella cell covers several micro cells. The power level inside an umbrella cell is increased comparing to the power levels used in the micro cells that form the umbrella cell. When the speed of the mobile is too high, the mobile is handed off to the umbrella cell. The mobile will then stay longer in the same cell (in this case the umbrella cell). This will reduce the number of handovers and the work of the network.
CALL PROCESSING
In telephony, call control refers to the software within a telephone switch that supplies its central function. Call control decodes addressing information and routes telephone calls from one end point to another. It also creates the features that can be used to adapt standard switch operation to the needs of users. These are called supplementary services and are commonly invoked by a Vertical service code. Examples include "Call Waiting", "Call Forward on Busy" etc.
Call control software, because of its central place in the operation of the telephone network, is marked by both complexity and reliability. Call control systems will typically require many thousands of person years in development. They will contain millions of lines of high level code. However they must and do meet reliability requirements that specify switch down time of only a few minutes in forty years.
The required functionality and reliability of call control is a major challenge for Voice over IP (VoIP) systems. VoIP systems are based on Internet standards and technology which have not previously attempted to satisfy such complex and demanding requirements as those that specify call control.
An alternative name often used is call processing.
The user dials the telephone number, presses the send or talk key, and the mobile phone sends a call setup request message to the mobile phone network via the nearest mobile phone base transceiver station (BTS). The call setup request message is handled next by the Mobile Switching Centre, which checks the subscriber's record held in the Visitor Location Register to see if the outgoing call is allowed. If so, the MSC then routes the call in the same way that a telephone exchange does in a fixed network.
[attachment=66342]
ABSTRACT
The seminar report mainly covers the aspect of the cellular system. Starting with the basics and a brief overview of the Wireless Communication Technology, the project report extends of the concept and GSM Technology also covering the concept of 2G. The project report discusses the architecture and layout of the PSTN and Telephony system. Covering the brief topics and terminology of GSM, presentation extends to Subsciber Identity Module (SIM). The authentication process and call setup process will also be discussed. Various algorithms in the Authentication process will be briefed. Also a Call Setup Flowchart; indicating the various steps and conditions will be covered.
: WIRELESS COMMUNICATION
Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor.
The most common wireless technologies use electromagnetic wireless telecommunications, such as radio. With radio waves distances can be short, such as a few metres for television remote control, or as far as thousands or even millions of kilometres for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones.
Less common methods of achieving wireless communications include the use of light, sound, magnetic, or electric fields.
Introduction
The Global System for Mobile communications is a digital cellular communications system. It was developed in order to create a common European mobile telephone standard but it has been rapidly accepted worldwide.
5 GSM Frequencies
GSM networks operate in a number of different frequency ranges. Most 2G networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including Canada and the United States) use the 850 MHz and the 1900 MHz bands because the 900 and 1800 MHz frequency bands were readily allocated. Most 3G GSM networks in Europe operate in the 2100 MHz frequency band. GSM 900 uses 890-915 MHz to send information from the mobile station to the base station (uplink) and 935-960 MHz for the other direction (downlink), providing 124 RF channels (channel numbers 1 to 124) spaced at 200KHz. Duplex spacing of 45MHz is used. In some countries the GSM 900 band has been extended to cover a larger frequency range. This extended GSM, known as E-GSM, uses 880-915 MHz (uplink) and 925-960 (downlink), adding 50 channels to the original GSM 900 band. Time division multiplexing is used to allow eight full rate or sixteen half rate speech channels per radio frequency channel.
Selective cells
It is not always useful to define a cell with a full coverage of 360 degrees. In some cases, cells with a particular shape and coverage are needed. These cells are called selective cells. Typical examples of selective cells are the cells that may be located at the entrances of tunnels where coverage of 360 degrees is not needed. In this case, a selective cell with coverage of 120 degrees is used.
Umbrella cells
A freeway crossing very small cells produces an important number of handovers among the different small neighbouring cells. In order to solve this problem, the concept of umbrella cells is introduced. An umbrella cell covers several micro cells. The power level inside an umbrella cell is increased comparing to the power levels used in the micro cells that form the umbrella cell. When the speed of the mobile is too high, the mobile is handed off to the umbrella cell. The mobile will then stay longer in the same cell (in this case the umbrella cell). This will reduce the number of handovers and the work of the network.
CALL PROCESSING
In telephony, call control refers to the software within a telephone switch that supplies its central function. Call control decodes addressing information and routes telephone calls from one end point to another. It also creates the features that can be used to adapt standard switch operation to the needs of users. These are called supplementary services and are commonly invoked by a Vertical service code. Examples include "Call Waiting", "Call Forward on Busy" etc.
Call control software, because of its central place in the operation of the telephone network, is marked by both complexity and reliability. Call control systems will typically require many thousands of person years in development. They will contain millions of lines of high level code. However they must and do meet reliability requirements that specify switch down time of only a few minutes in forty years.
The required functionality and reliability of call control is a major challenge for Voice over IP (VoIP) systems. VoIP systems are based on Internet standards and technology which have not previously attempted to satisfy such complex and demanding requirements as those that specify call control.
An alternative name often used is call processing.
The user dials the telephone number, presses the send or talk key, and the mobile phone sends a call setup request message to the mobile phone network via the nearest mobile phone base transceiver station (BTS). The call setup request message is handled next by the Mobile Switching Centre, which checks the subscriber's record held in the Visitor Location Register to see if the outgoing call is allowed. If so, the MSC then routes the call in the same way that a telephone exchange does in a fixed network.