Embed Size (px)
DESCRIPTION
gsm report
Citation preview
ABSTRACT
The report presents the GSM, the Global System for Mobile communications, is a digital cellular
communications system which has rapidly gained acceptance and market share worldwide, although it was
initially developed in a European context. In addition to digital transmission, GSM incorporates many advanced
services and features, including ISDN compatibility and worldwide roaming in other GSM networks. The
advanced services and architecture of GSM have made it a model for future third-generation cellular systems,
such as UMTS. This will give an overview of the services offered by GSM, the system architecture, the radio
transmission structure, and the signaling functional architecture.
The purpose of the latest technology expand is for the development of available system to fit the current
time flow, to simplify the procedure and beside that are harmless to consumer.. The purpose of developing
this system is to give more convenient to both side that will be using this system. SMS is the best medium
to give a short note. This technology used to complete the system development.
This project report includes all the details development of GSM which is the first step towards a true personal
communication system that will allow communication anywhere, anytime, and with anyone. The functional
architecture of GSM, employing intelligent networking principles, and its ideology, which provides enough
standardization to ensure compatibility, but still allows manufacturers and operators freedom, has been widely
adopted in the is the first step towards a true personal communication system that will allow communication
anywhere, anytime, and with anyone. The functional architecture of GSM, employing intelligent networking
principles, and its ideology, which provides enough standardization to ensure compatibility.
1
ACKNOWLEDGEMENT
I would like to heartfelt thanks to our worthy H.O.D. of E.C.E Dep’t. of C.E.C ,LANDRAN by
whose efforts I got a chance to have my Industrial Training at Telecommunication Consultants of
India Ltd. (TCIL), Mohali (Pb.) that would be very helpful in my future.
With profound sense of gratitude, I take it as a highly esteemed privilege in expressing sincere
thanks to our Sir Arvind Thakur for his technical guidance, sound advice, excellent supervision,
encouragement at every step which would help me in completing my entire course of training. I
am highly beholden to Mr. ASHOK RAYAT for his personal interest & affectionate behavior,
which is a source of great inspiration to me in completing my training. I am also thankful to staff
of TCIL, Mohali who always co-operate with me & ever ready to help me.
This is my strong realization that any academic study in engineering remains incomplete until it
is complemented with on site practical industrial training.
Amandeep Kaur
(7004040417)
2
CONTENTS
I. INTRODUCTION
II. COMPANY PROFILE
III. STUDY SCHEME
IV. SATELLITE COMMUNICATION
a. INTRODUCTION
b.DTH (DIRECT TO HOME)
c. HISTORY OF DTH
d. WORKING OF DTH
V. GSM NETWORK
a. DEFINITION
b. INTRODUCTION
c. ADVANTAGES
VI. OPEN SYSTEM INTERFACE OF GSM
a. NSS
b. BSS
c. NMS
VII. GSM NETWORK ELEMENTS
VIII. GSM NETWORK SPECIFICATIONS
a. RADIO CHANNELS
b. DUPLEX DISTANCE
c. ACCESS METHOD
d. GSM FRAME STRUCTURE
e. GSM LOGICAL CHANNELS
3
CHAPTER 1 INTRODUCTION
On 10th March 1978, Telecommunications Consultants India Ltd. (TCIL) was incorporated as a
wholly owned Govt. of India Company. The Company was set up with the objective of
extending a wide ranging telecom expertise available with DOT to friendly developing countries.
On August 1st, 1978, the company commenced its business. The Company has since then been
engaged in adopting world class communication & IT technologies for catering to the needs of
countries mainly in developing world. Year 2003-04 as Silver Jubilee Year of the successful
business achievements of the company. Company has established its credibility for having an
assured business in the field of new technology in Wireless Networks & in Information
Technology all over the world.
OBJECTIVES:
To provide world-class technology & Indian Expertise globally in all fields of Telecomm.
& Information & Technology.
To sustain, expand & excel in its operations in overseas/Indian markets by developing
proper marketing strategies.
To acquire State-of-the-Art technology on a continuing basis.
4
CHAPTER 1.1 COMPANY PROFILE
Company was incorporated in 1978 by Department of Telecommunications (DOT), Govt. of
India under aegis of Ministry of Communications – 9001:2000 certified public sector
undertaking. TCIL, a premier telecommunication consultancy & engineering company with a
strong base in information, headed by Minister of Communications & Information Technology.
There are also Ministers of State for Communications & information Technology.
DOT has its role in making, licensing & coordination matters relating to telegraphs, telephones,
wireless, data, facsimile & telemetric services & other like forms of communications. In
addition, DOT is responsible for frequently management in the field of radio communications in
close coordination with international bodies. It also enforces wireless regulatory measures for
wireless transmission by users in the country.
There are four PSUs under DOT. TCIL is one of them. Other being Bharat Sanchar Nigam Ltd.
(BSNL), Mahanagar Telephone Nigam Ltd., ITI.
GROWTH:
Started with a modest equity of 1 million Indian rupees (INR), TCIL has made rapid strides in
the two decades of its existence. Today it has a turn over of Rs. 5.90 billion INR during 2002-
2003 financial years. A net worth of over 3.80 billion INR, & has to its credit the rate distinction
of being adjudged “Excellent” based on MOU by the Govt. of India, for the eleventh consecutive
year. Maintaining consistently high standards of growth & performance, TCIL is today one of
the most prestigious Public Sector Enterprise of the Govt. of India.
INDUSTRY SEGMENTS:
TCIL has marked its presence by providing IT & Telecommunications services in the following
business sectors.
Government Departments
5
Telecom Services Providers
Defence
Oil & petroleum
Police
Aviation
Housing
Banking & Finance
Transportation
Power
IT SERVICES:
Turnkey Solutions to meet end-to-end customers requirements
Networking Solutions with total System Integration & Implementations
Project consultancy services from concept to commissioning
On-site Manpower Support
IT Training
THRUST AREAS:
Telecom operations Support Systems
Computer Hardware & Networking
Application Software Development
E-Governance & E-Commerce Networks
Network Security Services & Solutions
E-Education & Smart Schools
Customer Relationship Management (CRM) Solutions
Voice Over IP
FTTH Broad Band Networks
6
CHAPTER 1.2 STUDY SCHEME
In the whole of the six months industrial training period we have to study about the various
Telecom sectors which includes Principles of Networking, Principles of Digital Telecom,
Artificial Intelligence & remote communication, Telecommunication regulations & many more.
Following are the topics or fields which we have to cover in our whole of the training period.
Principles of Networking
Principles of Digital Telecomm.
Broadband Communication network
Wireless communication System
Switching & Transmission fundamentals
New generation Networks
Voice over IP
Geographical Information System
Artificial Intelligence & remote communication
Billing & customer care
Telecommunication regulations
Market & services
7
CHAPTER 1.3 SEMESTER SCHEME
TCIL-IT mainly provides the industrial training and one year diploma in Telecommunication.
Company basically follows the semester system scheme as given follows:
SEMESTER 1:
Principles of Networking
Principles of Digital Telecomm.
Broadband Communication network
Wireless communication System
SEMESTER 2:
Switching & Transmission fundamentals
New generation Networks
Voice over IP
Geographical Information System
Artificial Intelligence & remote communication
Billing & customer care
Telecommunication regulations
Market & services
8
CHAPTER 1.4 MISSION ‘n’ VISION
MISSION:
The mission statement of the company is to “To excel in providing Communication
Solutions in Telecommunication services sector globally”.
VISION:
“To excel in providing Communication Solutions globally by anticipating opportunities in
technology”.
9
CHAPTER 1.5 FUTURE SCOPE
There is a variety of careers available or future scope for telecommunications systems
professionals.
Telecommunications Career Paths
Telecommunications Systems Managers: Telecommunications systems managers
develop, modify, and monitor the various different telecommunications systems.
Telecommunications systems exist to gather and transmit data quickly, and enable users to
manage the functions of electronic equipment on their own. Telecommunications systems
managers have to keep up with the constantly improving and changing technology and
create plans to implement the latest technology on existing systems. Additionally, systems
managers coordinate and supervise the efforts of teams of engineers and systems analysts.
Telecommunications systems managers find the skills developed in pursuit of
telecommunications degrees applicable and necessary to appropriately address the
requirements of managing telecommunications systems.
Line Installers: Line installers are responsible for the installation of new lines, and they do
this by constructing utility poles, towers, and underground trenches to carry the wires and
cables necessary to operate communications equipment such as telephones and televisions.
After the construction phase is complete, line installers attach and mount cables to poles,
towers and other similar devices. In addition to these responsibilities, duties also include
setting up services for customers and installing home and business network equipment.
Much of this work requires intense physical labor as well as knowledge of
telecommunications technology.
10
Customer Service Representative: Customer service specialists and providers assist new and
existing telecommunications customers with various aspects of their accounts, including repair,
installation, billing, and selecting appropriate telecommunications services. Customer service
representatives communicate with customers in many different ways, including in person, over
the telephone, through written and e-mail correspondence by fax.
Often, a customer service specialist is the consumer's primary telephone and cable service
provider contact. Because this is true, customer service professionals must be friendly,
helpful, and able to understand the needs and concerns of consumers. Additionally,
successful customer service professionals employed in the telecommunications industry
benefit from an educational background specific to the industry.
Computer Software Engineers: Computer software engineers develop and build new
computer software technology. Such technology is often crucial to the innovation and growth
of telecommunications. This group of technology professionals works in a fast-paced
environment. They build, test, and design new software that enables consumers, businesses,
and other organizations with the means to utilize technological innovation.
Students interested in pursuing this path to telecommunications career opportunities should
have a strong background in engineering and computer science. Computer software engineers are
definitely on the cutting edge of innovation and are essential players in developing new
technology. Therefore, computer software engineers who are effectively able to communicate
and manage other technical professionals are considered strong candidates for
telecommunications management positions.
11
CHAPTER 1.6 TRAINEE & COMPANY DETAILS
Name of the Trainee : Amandeep Kaur
Mobile Number : +91-9872229221
Email ID : [email protected]
Company Name: -
TCIL-IT
(TELECOMMUNICATION CONSULTANTS OF INDIA LTD. - INFORMATION
TECHNOLOGY)
A GOVERNMENT OF INDIA ENTERPRISE
UNDER MINISTRY OF COMMUNICATION AND INFORMATION TECHNOLOGY, NEW
DELHI.
MANAGED BY ICSIL (INTELLIGENT COMMUNICATION SYSTEMS OF INDIA LTD)
& A JOINT VENTURE OF DSIIDC (DELHI STATE INDUSTRIAL INFRASTRUCTURE
DEVELOPMENT COROPRATION) & TCIL (TELECOMMUNICATION CONSULTANTS
OF INDIA LTD)
A GOVERNMENT OF INDIA ENTERPRISE.
ADDRESS
TCIL –IT, SCF 45, Phase 10, Mohali,
Email Id: [email protected]
Phone number:-0172-5090393, 9779750564
In-charge:-
Name :
Email :
Phone Number :
Company Head:-
Name : Mr.Ashok Rayat
Phone Number : 09779750564, 0172-5090393
12
CHAPTER 2 MOBILE COMMUNICATION
2.1: Basic concepts : A connection between two people − a caller and the called person − is the
basic service of all telephone networks. To provide this service, the network must be able to set
up and maintain a call, which involves a number of tasks: identifying the called person,
determining the location, routing the call, and ensuring that the connection is sustained as long as
the conversation lasts. After the transaction, the connection is terminated and (normally) the
calling user is charged for the service he has used.
In a fixed telephone network, providing and managing connections is a relatively easy process,
because telephones are connected by wires to the network and their location is permanent from
the networks’ point of view. In a mobile network, however, the establishment of a call is a far
more complex task, as the wireless (radio) connection enables the users to move at their own free
will − providing they stay within the network's service area. In practice, the network has to find
solutions to three problems before it can even set up a call:
13
In other words, the subscriber has to be located and identified to provide him/her with the
requested services. In order to understand how we are able to serve the subscribers, it is
necessary to identify the main interfaces, the subsystems and network elements in the GSM
network, as well as their functions.
From ancient to modern times, mankind has been looking for means of long distance
communications. For centuries, letters proofed to be the most reliable way to transmit
information. Fire, flags, horns, etc. were used to transmit information faster.
Technical Improvements in the 19th century simplified long distance communications:
Telegraphy and later on telephony. Both techniques were wireline. In 1873, J. C. Maxwell laid
the foundation of the electro-magnetic theory by summarising empirical results in four equations,
which are still valid today. It would however be several decades before Marconi made economic
use of this theory by developing devices for wireless transmission of Morse signals (about 1895).
Already 6 years later, the first transatlantic wireless transmission of Morse signals took place.
Voice was transmitted the first time in 1906 (R. Fesseden), and one of the first radio broadcast
transmission 1909 in New York.
Figure: 2.2
14
The economically most successful wireless application in the first half of the 20th century was
radio broadcast. There is one transmitter, the so-called radio station. Information, such as news,
music, etc. is transmitted from the radio station to the receiver equipment, the radio device. This
type of one-way transmission is called simplex transmission. The transmission takes place only
in one direction, from the transmitter to the receiver.
The first commercial wireless car phone telephony service started in the late 1940 in St. Louise,
Missouri (USA). It was a car phone service, because at that time, the mobile phone equipment
was bulky and heavy. Actually, in the start-up, it filled the whole back of the car. But it was a
real full duplex transmission solution. In the 50ies, several vehicle radio systems were also
installed in Europe. These systems are nowadays called single cell systems. The user data
transmission takes place between the mobile phone and the base station (BS). A base station
transmits and receives user data. While a mobile phone is only responsible for its user’s data
transmission and reception, a base station is capable to handle the calls of several subscribers
simultaneously.
The transmission of user data from the base station to the mobile phone is called downlink (DL),
the transmission from the mobile phone to the base station uplink (UL) direction. The area,
where the wireless transmission between mobile phones and the base station can take place, is
the base stations supply conversation, a technical solution is required, where the information
flow can take place in two directions. This type of transmission is called duplex transmission.
Walky-talky was already available the early 30ies. This system already allowed a transmission of
user data in two directions, but there was a limitation: The users were not allowed to transmit at
the same time. In other words, you could only receive or transmit user information. This type of
transmission is therefore often called semi-duplex transmission. For telephony services, a
technical solutions is required, where subscribers have the impression, that they can speak
(transmit) and hear (receive) simultaneously. This type of transmission solution is regarded as
full duplex transmission. area, Single cell systems are quite limited. The more and more distant
the subscriber is from the base station, the lower the quality of the radio link. If the subscriber is
leaving the supply area of the cell, no communication is possible any more.
15
CHAPTER 3 INTRODUCTION TO GSM
3.1: INTRODUCTION:
The global System for Mobile Communications, GSM 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. GSM is designed to provide a comprehensive range of
services and features to the users not available on analogue cellular networks and in many cases
very much in advance of the old public switched telephone network (PSTN). In addition to
digital transmission, GSM incorporates many advanced services and features like worldwide
roaming in other GSM networks.
16
The idea of cell-based mobile radio systems appeared at Bell Laboratories (in USA) in the early
1970s. However, mobile cellular systems were not introduced for commercial use until the
1980s. During the early 1980s, analog cellular telephone systems experienced a very rapid
growth in Europe, particularly in Scandinavia and the United Kingdom, but also in France and
Germany. Each country developed its own system, which was incompatible with everyone else's
in equipment and operation. But in the beginnings of cellular systems, each country developed its
own system, which was an undesirable situation for the following reasons:
The equipment was limited to operate only within the boundaries of each country, which in a
unified Europe were increasingly unimportant.
The market for each mobile equipment was limited, so economies of scale, and the subsequent
savings, could not be realized.
In order to overcome these problems, the Conference of European Posts and
Telecommunications (CEPT) formed, in 1982, the Group Special Mobile (GSM) in order to
develop a pan-European mobile cellular radio system (the GSM acronym became later the
acronym for Global System for Mobile communications). The standardized system had to meet
certain criteria’s:
• Good subjective speech quality
• Support for international roaming
• Ability to support handheld terminals
• Support for range of new services and facilities
• Spectral efficiency
• Low mobile and base stations costs
• Compatibility with other systems such as Integrated Services Digital Network (ISDN)
3.2: GSM background:
At the beginning of the 1980s a problem was that the European countries were using many
different, incompatible mobile phone systems. These systems are referred to as 1G (first
17
generation) systems. In Europe, the most common 1G system was NMT (Nordic Mobile
Telephone) and TACS (Total Access Communications System). In the United States, as well as
in other American countries, AMPS (Advanced Mobile Phone System) was, and still is, a widely
established system.
With the passage of time, the need for telecommunication services was remarkably increased.
Due to this, CEPT (Conference Europeans des Posts At Telecommunications) founded a group to
specify a common mobile system for Western Europe. This group was named “Group Specials
Mobile” and the system name GSM arose.
This abbreviation has since been interpreted in other ways, but the most common expression
nowadays is Global System for Mobile communications. GSM is a 2G (second generation)
At the beginning of the 1990s, the lack of a common mobile system was seen to be a general,
worldwide problem. For this reason the GSM system has now spread also to the Eastern
European countries, Africa, Asia and Australia. The USA, South America in general, and Japan
has made a decision to adopt other types of mobile systems, which are not compatible with
GSM. However, in the USA the Personal Communication System (PCS) has been adopted,
which uses GSM technology with a few variations.
18
During the time the GSM system was being specified, national telecommunication markets were
deregulated. Requirements for openness and competition were built into the specifications as
follows:
There should be several network operators in each country. This would lead to
competition in tariffs and service provisioning and it would ensure the rapid expansion
of the GSM system. The prices of the equipment would fall and the users would find the
cost of calls reducing.
The GSM system must be an open system, meaning that it should contain well-defined
interfaces between different system parts. This enables the equipment from several
manufacturers to coexist and hence improves the cost efficiency of the system from the
operator's point of view.
GSM networks must be built without causing any major changes to the already existing
Public Switched Telephone Networks (PSTN).
In addition to the commercial demands, some other objectives were defined:
The system must be Pan European.
The system must maintain a good speech quality.
The system must use radio frequencies as efficiently as possible.
The system must have high/adequate capacity
The system must be ISDN compatible (Integrated Services Digital Network) and
compatible with other data communication specifications.
The system must maintain good security both for subscriber and transmitted information.
The following list highlights some important years in the short history of GSM:
1982: CEPT initiated a new cellular system. The European Commission (EC) issued a directive
that required member states to reserve frequencies in the 900 MHz band for GSM to allow for
roaming.
19
1986: CEPT tested eight experimental systems in Paris.
1987: Memorandum of Understanding (MoU). Allocation of the frequencies: - 890 - 915 MHz
uplink (from mobile to base station) - 935 - 960 MHz downlink (from base station to mobile)
1988: European Telecommunications Standard Institute (ETSI) was created. ETSI includes
members from administrations, industry, and user groups.
1989 :Final recommendations and specifications for GSM Phase 1.
1990: Validation systems implemented and the first GSM World Congress in Rome with 650
participants.
1991: First official call in the world with GSM on 1st July.
1992: World's first GSM network launched in Finland. New frequency allocation for GSM 1800
(DCS 1800). - 1710 - 1785 MHz (uplink) - 1805 - 1880 MHz (downlink)
1993: GSM demonstrated for the first time in Africa at Telkom '93 in Cape Town. Roaming
agreements between several operators.
1994: The first GSM network in Africa was launched in South Africa. The GSM. By December
1994 there were 69 GSM networks in operation.
1995: There were 117 GSM networks operating around the world. Fax, data, and SMS roaming
were implemented.
1996: By December there were 120 networks operating. The 8K SIM was launched in addition
to prepaid GSM SIM cards.
1998: HSCSD (High Speed Circuit Switched Data) trials in Singapore. Over 2 million GSM
1900 users in the USA and a total of 120 million GSM 900/1800/1900 users worldwide.
1999: The first mobile data call using GPRS (General Packet Radio Service) in a live network
was made. The first HSCSD (High Speed Circuit Switched Data) networks are launched.. The
3G mobile communications system UMTS was specified in December. It is based on the GSM
standards to allow a smooth evolution from the 2nd generation to the 3rd generation..
2000: The first GPRS network is launched.
20
2001: The Multimedia Messaging Service (MMS) was standardized. GSM 700 supported; UL:
747 – 762 MHz and DL: 777 – 792 MHz UMTS and GSM standardized at 3GPP; UMTS/GSM
Rel. 4 standardized
2002: UMTS/GSM Rel. 5 standardized (IMS) was standardized for GSM/GPRS and UMTS.
Smartphone are under development for GSM/GPRS and UMTS – to allow a wide range of
mobile services, such as mobile Internet, mobile gambling, enhanced LDAs, video messaging,
agnostic services, etc.
2003: First commercial starts of UMTS network operators in Europe.
21
CHAPTER 4 GSM NETWORK ELEMENTS
GSM stands for Global System for Mobile communication & is a globally accepted standard for
digital cellular communication. GSM is the name of a standardization group established in 1982
to create a common European mobile telephone standard that would formulate specifications for
a pan-European mobile cellular radio system operating at 900 MHz
It is estimated that many countries outside of Europe will join the GSM partnership. GSM
provides recommendations, not requirements. The GSM specifications define the functions and
interface requirements in detail but do not address the hardware. The reason for this is to limit
the designers as little as possible but still to make it possible for the operators to buy equipment
from different suppliers.
The GSM network is divided into three major systems:
Base Station Subsystem (BSS)
Network Switching Subsystem (NSS)
Network Management Subsystem (NMS)
The Network Switching Subsystem is responsible for switching, mobility management, and
traffic element, i.e. that here network elements such as exchanges and data bases can be found.
The exchanges are responsible for switching, while the data bases are used to keep track of the
current location of the subscriber and his mobile phone. Mobile subscribers can be anywhere
worldwide. This creates a challenge when there is a call since even in a mobile network a
subscriber’s location must be known before a call can be set up. There are millions of cells, were
the subscriber and his mobile phone can be located. The NSS databases serve to locate mobile
subscribers when needed.
22
The Base Station Subsystem is responsible for the link between a mobile phone and a network
exchange. The radio interface must contain many functions to enable mobile calls. For example
user data must be protected by ciphering of user data in the base station and the mobile phone.
The transmission must be reliable which invokes error protection methods. If a mobile subscriber
wants to make a call, physical resources must be allocated to the user in a controlled manner.
The tasks of the BSS can be summarized under the key terms Radio Resource Management
(RRM) and Radio Link Management (RLM). The Network Management System supports the
operator in remote network supervision. Fault, configuration, and performance management are
central tasks performed within the NMS.
4.1: Mobile Station (MS)
In GSM, the mobile phone is called Mobile Station (MS). The MS is a combination of terminal
equipment and subscriber data. The terminal equipment as such is called ME (Mobile
Equipment) and the subscriber's data is stored in a separate module called SIM (Subscriber
Identity Module).
Therefore, ME + SIM = MS.
From the user’s point of view, the SIM is certainly the best-known database used in a GSM
network. The SIM is a small memory device mounted on a card and contains user-specific
identification. The SIM card can be taken out of one mobile equipment and inserted into another.
In the GSM network, the SIM card identifies the user − just like a traveler uses a passport to
identify himself.
23
The SIM card contains the identification numbers of the user and a list of available networks.
The SIM card also contains tools needed for authentication and ciphering. Depending on the type
of the card, there is also storage space for messages, such as phone numbers. A home operator
issues a SIM card when the user joins the network by making a service subscription. The home
operator of the subscriber can be anywhere in the world, but for practical reasons the subscriber
chooses one of the operators in the country where he/she spends most of the time.
4.2: Network Switching Subsystem (NSS)
The Network Switching Subsystem (NSS) contains the network elements MSC, GMSC, VLR,
HLR, AC and EIR.
24
The main functions of NSS are:
Call control: This identifies the subscriber, establishes a call, and clears the connection after the
conversation is over.
Charging: This collects the charging information about a call (the numbers of the caller and the
called subscriber, the time and type of the transaction, etc.) and transfers it to the Billing Centre.
Mobility management: This maintains information about the subscriber's location.
Signaling: This applies to interfaces with the BSS and PSTN.
Subscriber data handling: This is the permanent data storage in the HLR and temporary
storage of relevant data in the VLR.
4.2.1: Mobile services Switching Centre (MSC)
The MSC is responsible for controlling calls in the mobile network. It identifies the origin and
destination of a call (mobile station or fixed telephone), as well as the type of a call.
The MSC is responsible for several important tasks, such as the following.
Call control: MSC identifies the type of call, the destination, and the origin of a call. It also sets
up, supervises, and clears connections.
25
Initiation of paging: Paging is the process of locating a particular mobile station in case of a
mobile terminated call (a call to a mobile station).
Charging data collection: The MSC generates CDRs, Charging Data Records, which contain
information about the subscribers’ usage of the network.
4.2.2: Gateway Mobile services Switching Centre (GMSC)
The GMSC is responsible for the same tasks as the MSC, except for paging. It is needed in case
of mobile terminated calls. In fixed networks, a call is established to the local exchange, to which
the telephone is connected to. But in GSM, the MSC, which is serving the MS, changes with the
subscriber’s mobility. Therefore, in a mobile terminated call, the call is set up to a well defined
exchange in the subscriber’s home PLMN. This exchange is called GMSC. The GMSC than
interacts with a database called Home Location Register, which holds the information about the
MSC, which is currently serving the MS. The process of requesting location information from
the HLR is called HLR Interrogation. Given the information about the serving MSC, the GMSC
then continues the call establishment process. In many real life implementations, the MSC
functionality and the GMSC functionality are implemented in the same equipment, which is then
just called MSC. Many operators use GMSCs for breakout to external networks such as PSTNs.
4.2.3: Visitor Location Register (VLR)
In the Nokia implementation, Visitor Location Register (VLR) is integrated with the MSC
cabinet. VLR is a database which contains information about subscribers currently being in the
service area of the MSC/VLR, such as:
Identification numbers of the subscribers
Security information for authentication of the SIM card and for ciphering
Services that the subscriber can use
26
The VLR carries out location registrations and updates. When a mobile station comes to a new
MSC/VLR serving area, it must register itself in the VLR, in other words perform a location
update. Please note that a mobile subscriber must always be registered in a VLR in order to use
the services of the network. Also the mobile stations located in the own network is always
registered in a VLR.
The VLR database is temporary, in the sense that the data is held as long as the subscriber is
within its service area. It also contains the address to every subscriber's Home Location Register,
which is the next network element to be discussed.
4.2.4: Home Location Register (HLR)
HLR maintains a permanent register of the subscribers. For instance the subscriber identity
numbers and the subscribed services can be found here. In addition to the fixed data, the HLR
also keeps track of the current location of its customers. As you will see later, the GMSC asks for
routing information from the HLR if a call is to be set up to a mobile station (mobile terminated
call).
In the Nokia implementation, the two network elements, Authentication Centre (AC) and
Equipment Identity Register (EIR), are located in the Nokia DX200 HLR.
27
4.2.5: Authentication Centre (AC)
The Authentication Centre provides security information to the network, so that we can verify
the SIM cards (authentication between the mobile station and the VLR, and cipher the
information transmitted in the air interface (between the MS and the Base Transceiver Station)).
The Authentication Centre supports the VLR's work by issuing so-called authentication triplets
upon request.
4.2.6: Equipment Identity Register (EIR)
As for AC, the Equipment Identity Register is used for security reasons. But while the AC
provides information for verifying the SIM cards, the EIR is responsible for IMEI checking
(checking the validity of the mobile equipment). When this optional network element is in use,
the mobile station is requested to provide the International Mobile Equipment Identity (IMEI)
number. The EIR contains three lists:
Mobile equipment in the white list is allowed to operate normally.
If we suspect that mobile equipment is faulty, we can monitor the use of it. It is then
placed in the grey list.
28
If the mobile equipment is reported stolen, or it is otherwise not allowed to operate in the
network, it is placed in the black list.
Note that IMEI checking is an optional procedure, so it is up to the operator to define if and
when IMEI checking is performed. (Some operators do not even implement the EIR at all.)
4.3: Base Station Subsystem (BSS)
The Base Station Subsystem is responsible for managing the radio network, and it is controlled
by an MSC. Typically, one MSC contains several BSSs. A BSS itself may cover a considerably
large geographical area consisting of many cells (a cell refers to an area covered by one or more
frequency resources). The BSS consists of the following elements:
BSC Base Station Controller
BTS Base Transceiver Station
TRAU Tran coder and Rate Adaptation Unit (often referred to as TC (Tran coder))
4.3.1: Base Station Subsystem (BSS)
The Base Station Subsystem is responsible for managing the radio network, and it is controlled
by an MSC. Typically, one MSC contains several BSSs. A BSS itself may cover a considerably
large geographical area consisting of many cells (a cell refers to an area covered by one or more
frequency resources). The BSS consists of the following elements:
BSC Base Station Controller
BTS Base Transceiver Station
TRAU Tran coder and Rate Adaptation Unit (often referred to as TC (Tran coder))
29
Some of the most important BSS tasks are listed in the following:
Radio path control: In the GSM network, the Base Station Subsystem (BSS) is the part of the
network taking care of radio resources, that is, radio channel allocation and quality of the radio
connection.
Synchronization: The BSS uses hierarchical synchronization, which means that the MSC
synchronizes the BSC, and the BSC further synchronizes the BTSs associated with that particular
BSC. Inside the BSS, synchronization is controlled by the BSC. Synchronization is a critical
issue in the GSM network due to the nature of the information transferred. If the synchronization
chain is not working correctly, calls may be cut or the call quality may not be the best possible.
Ultimately, it may even be impossible to establish a call.
Air- and A-interface signaling: In order to establish a call, the MS must have a connection
through he the BSS.
Connection establishment between the MS and theNSS: The BSS is located between two
interfaces, the air- and the A-interface. The MS must have a connection through these two
30
interfaces before a call can be established. Generally speaking, this connection may be either a
signalling connection or a traffic (speech, data) connection.
Mobility management and speech transcending: BSS mobility management mainly covers the
different cases of handovers. These handovers and speech transcoding are explained in later
sections.Let us now have a closer look at each of the individual network elements (BSC, BTS,
and Transcoder). Base Station Controller (BSC)
The BSC is the central network element of the BSS and it controls the radio network. It has
several important tasks, some of which are presented in the following:
Connection establishment between the MS and the NSS: All calls to and from the MS are
connected through the switching functionality of the BSC.
Mobility management: The BSC is responsible for initiating the vast majority of all handovers,
and it makes the handover decision based on, among others, measurement reports sent by the MS
during a call.
Statistical raw data collection: Information from the Base Transceiver Stations, Transcoders,
and BSC are collected in the BSC and forwarded via the DCN (Data Communications Network)
to the NMS (Network Management Subsystem), where they are post-processed into statistical
views, from which the network quality and status is obtained.
31
Air- and A-interface signalling support;
In the A-interface, SS#7 (Common Channel Signalling System No. 7) is used as the signalling
language, while the environment in the air interface allows the usage of a protocol adapted from
ISDN standards, namely LAPDm (Link Access Protocol on the ISDN D Channel, modified
version). Between the Base Transceiver Station and the BSC (Abis interface), a more
standardized LAPD protocol is used. The BSC also enables the transparent signalling connection
needed between the MSC/VLR and the MS.
BTS and TRAU control: Inside the BSS, all the BTSs and TCs are connected to the BSC(s).
The BSC maintains the BTSs. In other words, the BSC is capable of separating (barring) a BTS
from the network and collecting alarm information. TRAUs are also maintained by the BSC, that
is, the BSC collects alarms related to the transcoders.
4.3.2: Base Transceiver Station (BTS)
The BTS is the network element responsible for maintaining the air interface and minimizing the
transmission problems (the air interface is very sensitive for disturbances). This task is
accomplished with the help of some 120 parameters. These parameters define exactly what kind
of BTS is in question and how MSs may "see" the network when moving in this BTS area. The
BTS parameters handle the following major items: what kind of handovers (when and why),
paging organization, radio power level control, and BTS identification. The BTS has several very
important tasks, some of which are presented in the following.
Air interface signaling:
A lot of both call and non-call related signaling must be performed in order for the system to
work. One example is that when the MS is switched on for the very first time, it needs to send
and receive a lot of information with the network (more precisely with the VLR) before we can
start to receive and make phone calls. Another example is the signaling required to set up both
mobile originated and mobile terminated calls. A third very important signaling in mobile
32
networks is the need to inform the MS when a handover is to be performed (and later when the
MS sends a message in the uplink direction telling the network that the handover is completed.
Later in this chapter, we will have a closer look at all of these different cases.
Ciphering: Both the BTS and the MS must be able to cipher and decipher information in order
to protect the transmitted speech and data in the air interface.
Speech processing: Speech processing refers to all the functions the BTS performs in order to
guarantee an error-free connection between the MS and the BTS. This includes tasks like speech
coding (digital to analogue in the downlink direction and vice versa), channel coding (for error
protection), interleaving (to enable a secure transmission), and burst formatting (adding
information to the coded speech / data in order to achieve a well-organized and safe
transmission).
Modulation and De-modulation
User data is represented with digital values 0 and 1. These bit values are used to change one of
the characteristics of an analogue radio signal in a predetermined way. By altering the
characteristic of a radio signal for every bit in the digital signal, we can "translate" an analogue
signal into a bit stream in the frequency domain. This technique is called modulation. In GSM,
Gaussian Minimum Shift Keying (GMSK), is applied. The base station can contain several
TRXs (Transceivers), each supporting one pair of frequencies for transmitting and receiving
33
information. The BTS also has one or more antennas, which are capable of transmitting and
receiving information to/from one or more TRXs. The antennas are either unidirectional or
sectaries’. It also has control functions for Operation and Maintenance (O&M), synchronization
and external alarms, etc.
4.3.3: Tran coder and Rate Adaptation Unit (TRAU)
In the air interface (between MS and BTS), the media carrying the traffic is a radio frequency.
To enable an efficient transmission of digital speech information over the air interface, the digital
speech signal is compressed. We must however also be able to communicate with and through
the fixed network, where the speech compression format is different. Somewhere between the
BTS and the fixed network, we therefore have to convert from one speech compression format to
another, and this is where the Trancoder comes in.
For transmission over the air interface, the speech signal is compressed by the mobile station to
13 kbit/s (Full Rate and Enhanced Full Rate), 5.6 kbit/s (Half Rate), or 12.2 kbit/s (Enhanced
Full Rate). A more modern speech codec is the AMR (Adaptive MultiMate Coding) which is
more flexible since it produces speech with bitrates similar to older solutions but adapted to link
conditions.
However, the standard bit rate for speech in the PSTN is 64 Kbits/s. The modulation technique is
called "Pulse Code Modulation" (PCM). This requires the GSM network to perform bit rate
adaptation of speech.
34
4.4: GSM Interfaces :
One of the main purposes behind the GSM specifications is to define several open interfaces,
which then limit certain parts of the GSM system. Because of this interface openness, the
operator maintaining the network may obtain different parts of the network from different GSM
network suppliers. When an interface is open, it also strictly defines what is happening through
the interface, and this in turn strictly defines what kind of actions/procedures/functions must be
implemented between the interfaces.
The GSM specifications define two truly open interfaces within the GSM network. The first one
is between the Mobile Station (MS) and the Base Station (BS). This open-air interface is called
Um. It is relatively easy to imagine the need for this interface to be open, as mobile phones of all
different brands must be able to communicate with GSM networks from all different suppliers.
The second interface is located between the Mobile services Switching Centre, MSC and the
Base Station Controller (BSC). This interface is called the “A-interface”. The system includes
more than the two defined interfaces, but especially the ones within the BSS not totally open.
35
Following are the specified interfaces:
Um: MS - BTS (air or radio interface)
A: MSC – BSC
Abis: BSC – BTS (proprietary interface)
Ater: BSC – TRAU (sometimes called Asub) (proprietary interface)
B: MSC – VLR
C: MSC – HLR
D: HLR – VLR
E: MSC – MSC
F: MSC – EIR
G: VLR - VLR.
36
4.5: Network Management Subsystem (NMS)
The Network Management Subsystem (NMS) is the third subsystem of the GSM network in
addition to the Network Switching Subsystem (NSS) and Base Station Subsystem (BSS), which
we have already discussed. The purpose of the NMS is to monitor various functions and
elements of the network.
The functions of the NMS can be divided into three categories:
Fault management
Configuration management
Performance management
These functions cover the whole of the GSM network elements from the level of individual
BTSs, up to MSCs and HLRs.
4.5.1: Fault management
The purpose of fault management is to ensure the smooth operation of the network and rapid
correction of any kind of problems that are detected. Fault management provides the network
operator with information about the current status of alarm events and maintains a history
database of alarms.
The alarms are stored in the NMS database and this database can be searched according to
criteria specified by the network operator.
37
4.5.2: Configuration management
The purpose of configuration management is to maintain up-to-date information about the
operation and configuration status of network elements. Specific configuration functions include
the management of the radio network, software and hardware management of the network
elements, time synchronization, and security operations.
4.5.3: Performance management: In performance management, the NMS collects
measurement data from individual network elements and stores it in a database. On the basis of
these data, the network operator is able to compare the actual performance of the network with
the planned performance and detect both good and bad performance areas within the network.
4.5.4: Services Provided by GSM:
Telecommunication services can be divided into Bearer Services, Teleservices, and
Supplementary Services. Call diversion, caller identification, encrypted speech, fax and error
protected data are a few examples of current and new services provided by the GSM.
38
Supplementary services are provided on top of teleservices or bearer services, and include
features such as caller identification, call forwarding, call waiting, multiparty conversations, and
barring of outgoing (international) calls, among others.
1 Teleservices:
A Teleservice utilizes the capabilities of a Bearer Service to transport data, defining which
capabilities are required and how they should be set up. The most basic Teleservice supported by
GSM is telephony. There is an emergency service, where the nearest emergency service provider
is notified by dialing three digits (similar to 911). The Telephony Teleservice and Emergency
Teleservice cover normal speech calls. These are both the fundamental services for making
ordinary telephone calls, but they are separated because of a special need for Emergency calls.
The ISDN, on which GSM is based, has a great deal of potential for other information and data
services. These are the videotext, telexes, and electronic mail services. The Videotext, Telexes
and Advanced Message Handling Teleservices provide these for in GSM. The last of these
covers the electronic mail requirements.
This Advanced Message Handling Teleservice (or the Electronic Mail Teleservice) is designed to
allow quite long messages. GSM has one more Teleservice that is designed for short, paging type
messages. This Teleservice, called Short Message Service (SMS), is by far the most widely used
and flexible. The SMS Teleservice was originally defined to utilize some spare signaling
capacity in GSM. However, it soon became apparent that SMS would become a key service in
differentiating GSM from any other cellular service. SMS is effectively an international paging
service, overlaid on top of the GSM network, with the capability to send, as well as receive,
messages.
2 Supplementary Services:
The supplementary services basically consist of call forwarding and call barring.
2.1 Call Forwarding: The Call Forwarding Supplementary Service is used to divert calls from
the original recipient to another number, and is normally set up by the subscriber himself. It can
39
be used by the subscriber to divert calls from the Mobile Station when the subscriber is not
available, and so to ensure that calls are not lost. A typical scenario would be a salesperson turns
off his mobile phone during a meeting with customers, but does not wish to lose potential sales
leads while he is unavailable.
2.2 Call Barring: The concept of barring certain types of calls might seem to be a
supplementary disservice rather than service. However, there are times when the subscriber is
not the actual user of the Mobile Station, and as a consequence may wish to limit its
functionality, so as to limit the charges incurred. Alternatively, if the subscriber and user are one
and the same, the Call Barring may be useful to stop calls being routed to international
destinations when they are routed. The reason for this is because it is expected that the roaming
subscriber will pay the charges incurred for international re-routing of calls. So, GSM devised
some flexible services that enable the subscriber to conditionally bar calls.
Newer GSM Services:
The newer GSM services were not all generally available by the GSM operators at the time of
writing and comprise:
Number Identification:
Calling Line Identification Presentation: This service deals with the presentation of the
calling party's telephone number. The concept is for this number to be presented, at the
start of the phone ringing, so that the called person can determine who is ringing prior to
answering. The person subscribing to the service receives the telephone number of the
calling party.
Calling Line Identification Restriction: A person not wishing their number to be
presented to others subscribes to this service. In the normal course of event, the
restriction service overrides the presentation service.
Connected Line Identification Presentation: This service is provided to give the
calling party the telephone number of the person to whom they are connected. This may
40
seem strange since the person making the call should know the number they dialed, but
there are situations (such as forwarding’s) where the number connected is not the number
dialed. The person subscribing to the service is the calling party.
Connected Line Identification Restriction: There are times when the person called
does not wish to have their number presented and so they would subscribe to this person.
Normally, this overrides the presentation service.
2 Multi-Party: This service is similar to a conference type service, in that several calls may be
connected with all parties talking to each other. However, there are enough differences, caused
by its application in the mobile environment, for it to be known by a different name.
3 Charging: This service was designed to give the subscriber an indication of the cost of the
services as they are used. Furthermore, those Service Providers who wish to offer rental services
to subscribers without their own Subscriber Identity Module (SIM) can also utilize this service in
a slightly different form.
4 Additional Information Transfer(User-to-User Signaling): This service allows the
subscriber to send and receive information to and from the person with whom they have an
active call. The amount of information is limited, but may include text (such as names and
addresses), and numbers (such as telephone numbers).
5 Call Offering (Call Transfer): The call transfer service allows the subscriber to transfer or
forward a call to another party. This party can be either another GSM Mobile Station or indeed, a
person on a different network. One of the difficulties with this service is the billing ramifications.
If A calls B, and B asks to be transferred to C, then it is not clear who should be charged for the
rest of the call (A, who initiated the call but is no longer a participant, or B, who asked for the
call transfer. To charge B is technically difficult.)
41
CHAPTER 5 GSM NETWORK SPECIFICATIONS
5.1: RADIO CHANNEL:
A mobile station communicates with a base station via a radio channel. A radio channel is a bi-
directional radio transmission path. Each radio channel has two distinct frequencies; one for
downlink and one for uplink.
Downlink is defined as the transmission path from the base station to the mobile station.
Uplink is defined as the transmission path from the mobile station to the base station.
The base station transmits on one frequency while the mobile station transmits on another
frequency. This creates a full duplex communication path. That is, simultaneous communication
in both directions.
GSM 900 GSM1800 GSM 1900
Uplink frequency
Downlink frequency
890-915
MHZ
935-960
MHZ
1710-1785 MHZ 1850-1910 MHZ
1805-1880 MHZ 1930-1990 MHZ
5.2: DUPLEX DISTANCE:
The distance between one uplink frequency and its corresponding downlink frequency is called
the duplex distance. The duplex distance varies for different frequency bands. For GSM 900
band it is 45MHz and for GSM 1800MHz its 80MHz.
42
5.3: CHANNEL CONCEPT:
The carrier separation is 200 KHz; this provides 124 carriers in GSM 900 band, 374 carriers in
GSM 1800 band and 299 carriers in GSM 1900 band. Since each carrier is shared by eight
mobile subscribers, the total numbers of channels are:
124*8=992 channels in GSM 900
374*8=2992 channels in GSM 1800
299*8=2392 channels in GSM 1900
Each of these channels, which is one time slot on a TIME DIVISION MULTIPLE ACCESS
frame, is called a physical channel. A variety of information is transmitted between the BTS and
the MS. There are different types of logical channels depending on the type of information being
transmitted. Each logical channel is used for a specific purpose, e.g. paging, call setup or speech.
These logical channels are mapped onto the physical channels.
5.4: TRANSMISSION RATE:
The transmission rate over the air is 270 k bit/s. This is true for GSM 900, GSM 1800 and GSM
1900. The amount of information transmitted over a radio channel over a period of time is
known as the transmission rate. Transmission rate is expressed in bits per second or bit/s.
5.5: ACCESS METHOD:
The Air Interface uses the Time Division Multiple Access (TDMA) technique to transmit and
receive traffic and signaling information between the BTS and MS. The TDMA technique is
used to divide each carrier into eight time slots. These time slots are then assigned to specific
users, allowing up to eight conversations to be handled simultaneously by the same carrier
.
43
5.6: GSM Frame structure
The information contained in one time slot on the TDMA frame is called a burst. There are five
different types of bursts:
NORMAL BURST (NB) used to carry information on traffic and control channels.
FREQUENCY CORRECTION BURST (FCB) used for frequency synchronization of the
mobile.
SYNCHRONIZATION BURST (SB) used for frame synchronization of the mobile
ACCESS BURST used for random access and handover access.
DUMMY BURST used when no other type of burst is to be sent.
44
The relationship between bursts and frames is shown in Figure. There are two types of
multiform. They are:
26-TDMA frame multiframe which is used to carry TCH, SACCH and FACCH
51-TDMA frame multiframe which is used to carry BCCH, CCCH, SDCCH and SACCH
A super frame consists of 51 or 26 multiframes and a hyper frame consists of 2048 super frames.
45
5.7: LOGICAL CHANNELS:
There are 12 logical channels in the system. Two are used for traffic, nine for control signaling
and one for message distribution.
Many types of logical channels each designed to carry a different message to or from an MS. All
information to and from an MS must be formatted correctly, so that the receiving device can
understand the meaning of different bits in the message. For example, as seen previously, in the
burst used to carry traffic, some bits represent the speech or data itself, while others are used as a
training sequence. There are several types of burst. The relationship between bursts and logical
channels is shown in the figure below.
46
Traffic Channels (TCH): There are two types of TCHs:
Full rate channel, Bm - used for full rate speech at 13kbps or data up to 9.6kbps
Half-rate channel, Lm - used for half rate speech at 6.5kbps or data up to 4.8kbps
CONTROL CHANNELS
There are three different groups of control channels with each group containing three different
logical channels.
Broadcast Channels (BCH) (Downlink Only)
Frequency Correction Channel (FCH) - used for frequency correction of MS
Synchronization Control Channel (SCH) – carries information about the TDMA frame
number and the BASE STATION IDENTITY CODE of the BTS
Broadcast Control Channel (BCH) - Broadcasts cell specific information to the MS
Common Control Channels (CCCH)
Paging Channel (PCH)- used on the downlink to page the MS
Random Access Channel (RACH) - used on the uplink by the MS to request allocation
of an SDCCH, either as a page response or an access at MS call origination/registration.
Access Grant Channel (AGCH) - used on the downlink to allocate an SDCCH or TCH
to an MS. An allocation to a TCH can be done in the case of an Immediate Assignment
on TCH.
Dedicated Control Channels (DCCH) (Uplink and Downlink)
Standalone Dedicated Control Channel (SDCCH) – used for system signalling during
call setup or registration, uplink and downlink, as well as the transmission of short text
messages in idle mode.
Slow Associated Control Channel (SACCH) - control channel associated with a TCH
or a SDCCH. Measurement Reports from the MS to the BTS are sent on the uplink (see
section on Measurement Reports). On the downlink the MS receives information from
47
the BTS on what transmitting power to use and also instructions on TIMING ADVANCE
(TA).The SACCH is also used for the transmission of short text messages in call
connected (busy) mode.
Fast Associated Control Channel (FACCH) - Control channel associated with a TCH.
Also referred to as FAST ASSOCIATED SIGNALLING, the FACCH works in stealing
mode. That is, 20 ms of speech is replaced by a control message. It is used during
handover as SACCH signalling is not fast enough. Used on uplink and downlink.
Cell Broadcast Channel (CBCH): This is used only on the downlink to carry SHORT
MESSAGE SERVICE CELL BROADCAST (SMSCB). CBCH uses the same physical
channel as the SDCCH
5.8: HANDOVER IN GSM:
In a mobile communications network, the subscriber can move around. How can we maintain the
connection in such cases? To understand this, we must study the process of handing over the
calls. Maintaining the traffic connection with a moving subscriber is made possible with the help
of the handover function. The basic concept is simple: when the subscriber moves from the
coverage area of one cell to another, a new connection with the target cell has to be set up and
the connection with the old cell has to be released. There are two reasons for performing a
handover:
Handover due to measurements occurs when the quality or the strength of the radio signal
falls below certain parameters specified in the BSC. The deterioration of the signal is
detected by the constant signal measurements carried out by both the mobile station and
the BTS. As a consequence, the connection is handed over to a cell with a stronger signal.
Handover due to traffic reasons occurs when the traffic capacity of a cell has reached its
maximum or is approaching it. In such a case, the mobile stations near the edges of the
cell may be handed over to neighboring cells with less traffic load.
The decision to perform a handover is always made by the BSC that is currently serving the
subscriber, except for the handover for traffic reasons. In the latter case the MSC makes the
48
decision. There are four different types of handover and the best way to analyze them is to follow
the subscriber as he moves:
Intra cell − Intra-BSC handover
The smallest of the handovers is the intra-cell handover where the subscriber is handed over to
another traffic channel (generally in another frequency) within the same cell. In this case, the
BSC controlling the cell makes the decision to perform handover.
Inter-cell − Intra-BSC handover
The subscriber moves from cell 1 to cell 2. In this case, the handover process is controlled by the
BSC. The traffic connection with cell 1 is released when the connection with cell 2 is set up
successfully.
Inter-cell − Inter-BSC handover
The subscriber moves from cell 2 to cell 3, which is served by another BSC. In this case, the
handover process is carried out by the MSC, but the decision to make the handover is still done
by the first BSC. The connection with the first BSC (and BTS) is released when the connection
with the new BSC (and BTS) is set up successfully.
49
Inter-MSC handover
The subscriber moves from a cell controlled by one MSC/VLR to a cell in the domain of another
MSC/VLR. This case is a bit more complicated. Considering that the first MSC/VLR is
connected to the GMSC via a link that passes through PSTN lines, it is evident that the second
MSC/VLR cannot take over the first one just like that.
The MSC/VLR currently serving the subscriber (also known as the anchor MSC) contacts the
target MSC/VLR and the traffic connection is transferred to the target MSC/VLR. As both MSCs
are part of the same network, the connection is established smoothly. It is important to notice,
however, that the target MSC and the source MSC are two telephone exchanges. The call can be
transferred between two exchanges only if there is a telephone number identifying the target
MSC.
50
Such a situation makes it necessary to generate a new number, the Handover Number (HON).
The generation and function of the HON are explained in the following.
The anchor MSC/VLR receives the handover information from the BSS. It recognizes that the
destination is within the domain of another MSC and sends a Handover Request to the target
MSC via the signaling network. The target MSC answers by generating a HON and sends it to
the anchor MSC/VLR, which performs a digit analysis in order to obtain the necessary routing
information. This information allows the serving MSC/VLR to connect the target MSC/VLR.
When the two MSCs are connected, the call is transferred to a new route.
In practice, the handover number is similar to the roaming number. The subscriber number
identifies the serving MSC and it is only in temporary use during the handover. Moreover, the
roaming number and the handover number have a similar purpose that is, connecting two MSCs.
The structure of the handover number is shown below:
HON = CC + NDC + SN
• CC = Country Code
51
• NDC = National Destination Code (of the serving network)
• SN = Subscriber Number
The call will not last forever and the connection has to be released sooner or later. To understand
the process of releasing the connection, we must consider a few things such as: Who pays for the
call, which exchange takes care of the charging operation, and where is the subscriber data
stored. This will be discussed in the next section, but before that, let us sum up the stages of
inter-MSC handover.
5.9: Security in the GSM network
Large efforts have been made to provide good security in the GSM network. In this section, we
will first discuss how an operator can ensure that all the SIM cards currently located in the
network are entitled to use the network (authentication). A second measure is to provide secure
transmission of speech and data in the Air Interface through ciphering. A third security feature is
to allocate temporary subscriber numbers. By doing so, we do not need to broadcast of the real
identity number so often.
5.9.1: Authentication principle
Authentication is a procedure used in checking the validity and integrity of subscriber data. With
the help of the authentication procedure the operator prevents the use of false SIMs in the
network. The authentication procedure is based on an identity key, Ki, which is issued to each
subscriber when his data is established in the HLR. The authentication procedure verifies that the
Ki is exactly the same on the subscriber side and on the network side.
Authentication is performed by the VLR at the beginning of every call establishment, location
update, and call termination (on the called subscriber side). In order to perform the
authentication, the VLR needs the basic authentication information. If the mobile station was
asked to broadcast its Ki, this would undermine the principle of authentication, because
identification data would be sent across the air.
52
The trick is to compare the Ki stored in the mobile with the one stored in the network without
actually having to transmit it over the radio Air Interface. The Ki is processed by a random
number with a “one-way” algorithm called A3 and the result of this processing is sent to the
network. Due to the type of the algorithm A3, it is easy to get the result on the basis of Ki and a
random number, but it is virtually impossible to get the Ki on the basis of the result and random
number (hence the name “one way” algorithm).
Since the security issue concerns confidentiality as well, the network uses more than one
algorithm. The algorithms are introduced in the following sections.
5.9.2: Security algorithms
The GSM system uses three algorithms for the purposes of authentication and ciphering. These
algorithms are A3, A5 and A8. A3 is used in authentication, A8 is used in generating a ciphering
key and A5 is used in ciphering.
53
Algorithms A3 and A8 are located in the SIM module and in the Authentication Centre (AC). A5
is located in the mobile station and in the BTS.
Before an operator starts to use the security functions, the mobile subscriber is created in the
Authentication Centre. The following information is required when creating the subscriber:
IMSI of the subscriber
Ki of the subscriber
Algorithm version used.
The same information is also stored in the mobile subscriber's SIM. The basic principle of GSM
security functions is to compare the data stored by the network with the data stored in the
subscriber’s SIM. The IMSI number is the unique identification of the mobile subscriber. Ki is
an key with a length of 32 hexadecimal digits. The algorithms A3 and A8 use these digits as a
basic value in authentication.
The Authentication Centre generates information that can be used for all the security purposes
during one transaction. This information is called an authentication triplet. The authentication
triplet consists of three numbers:
RAND
SRES
54
Kc.
RAND is a Random number,
SRES (Signed Response) is a result that the algorithm A3 produces on the basis of certain source
information, and Kc is a ciphering key that A8 generates on the basis of certain source
information basis of certain source information.
5.9.3:
Ciphering / speech encryption
Ciphering is used across the air interface to provide traffic and signaling encryption. When the
authentication procedure has been completed successfully, the BTS and the mobile station are
ready to start the ciphering procedure for further signaling and speech / data transmission.
The speech of the user, the TDMA frame number (Time Division Multiple Access) and the
ciphering key, Kc, are processed by the ciphering algorithm (A5), which produces the coded
speech signal.
55
5.10: Advantages of GSM
Due to the requirements set for the GSM system, many advantages will be achieved. These
advantages can be summarized as follows:
GSM uses radio frequencies efficiently, and due to the digital radio path, the system
tolerates more intercellular disturbances.
The average speech quality is better than in analogue systems.
Data transmission is supported throughout the GSM system
Speech is encrypted and subscriber information security is guaranteed
With ISDN compatibility, new services are offered
International roaming is technically possible within all countries using the GSM system
The large market increases competition and lowers the prices both for investments and
usage.
56
CHAPTER 6 CDMA (CODE DIVISION MULTIPLE ACCESS)
6.1: INTRODUCTION:
CDMA ( Code Division Multiple ACCESS): CDMA is a method in which users occupy the
same time and frequency allocations, and are channelized by unique assigned codes. The signals
are separated at the receiver by using a correlated that Access accepts only signal energy from
the desired channel. Undesired signals contribute only to the noise. A CDMA system uses
effective power control process.
6.2: Advantages:-
The main advantages of this technology are:
Fast Network deployment.
Reduced service interruptions
Low Maintenance & operational cost
Better system coverage flexibility
Higher capacity
Easy transition to mobile services.
6.3: Salient Features of CDMA
It is an advanced comm. Technology.
It has Anti-jam and security features.
Large capacity as compared to other Technology Like FDMA and TDMA.
It uses spread spectrum technology.
Better use of the multipath.
Frequency Reuse.
57
6.4: Frequency Bands: CDMA uses the frequency bands as given below:
CDMA 824- 849 MHz
869- 894 MHz
PCS 1850- 1910 MHz
1930- 1990 MHz
58
6.5: MULTIPLE ACCESS METHODS: In CDMA the multiple access techniques used are
given as follows:
Frequency Division Multiple Access (FDMA)
FDMA is a multiple access method in which users are assigned specific frequency bands. The
user has sole right of using the frequency band for the entire call duration.
Time Division Multiple Access (TDMA)
In TDMA an assigned frequency band shared among a few users. However, each user is allowed
to transmit in predetermined time slots. Hence, channelization of user is achieved through
separation in time.
59
6.6: SPREADING SPECTRUM:6.6: SPREADING SPECTRUM:
Shannon’s Equation
C= W Log (1+S/N)
Where C=Capacity (bps)
W=Bandwidth
S=Signal Power
N=Noise Power
Shannon’s Capacity Equation is basis for spread spectrum. System with large band width
can operate at very low SNR level & can provide acceptable data rate per user.
Therefore in CDMA
– All users uses same 1.25 MHz spectrum.
– Each user has unique Digital code identifier.
– Digital codes separate users to avoid interference.
6.6.1: SPREAD SPECTRUM TECHNIQUES: Mainly there are two types of spread spectrum
techniques are used in CDMA as given below:
Frequency Hopped Spread Spectrum:
Spreading can also be achieved by hopping the narrowband information signal over
a set of frequencies. The type of spreading can be classified as fast or slow
depending upon the rate of hopping to the rate of information.
Direct Sequence Spread Spectrum:
The information signal is inherently narrowband, on the order of less than 10KHz. The energy
from this narrowband signal is spread over a much larger bandwidth by multiplying the
60
information signal by a wideband spreading code. DSS technique is used in the IS-95 CDMA
cellular system.
Direct Sequence Spread using Walsh code
Consist of 64 orthogonal codes each 64 bits long
Spreads spectrum to 1.2288 M bps from 9.6 Kbps
Channel Capacity
C=W log (1+S/N)
6.6.2: Spread spectrum principle:
Originally spread spectrum radio technology was developed for military use to counter the
interference by hostile jamming. The broad spectrum of the transmitted signal gives rise to
“spread spectrum”. A spectrum signal is generated by modulating the radio frequency (RF)
signal with a code consisting of different pseudo random binary sequences, which is inherently
resistant to noisy signal environment.
A number of spread spectrum RF signals thus generated share the same frequency spectrum and
thus the entire bandwidth available in the band will be used by each of the users using same
frequency at the same time.
On the receive side only the signal energy with the selected binary sequence code is accepted and
information content is recovered. The other user signals, whose codes do not match contribute
only the noise and are not “de-spread” back in bandwidth. This transmission and reception of
signals differentiated by “codes” using the same frequency simultaneously by a number of users
is known as code Division Multiple Access (CDMA).
Techniques as opposed to conventional method of Frequency Division Multiple Access and
Time Division Multiple Access. In the fig. It has been tried to explain that how the base band
signal of 9.6 kbps is spread using a long pseudo-random Noise(PN) source to occupy entire
bandwidth of 1.25 Mhz. At the receiving end this signal will have interference from signals of
other users of the same cell, user different cells and interference from other noise sources. All
these signals get combined with the desired signal but using a correlator and correct PN code, the
original data can be reproduced back.
61
6.3: Spreading Codes:
CdmaOne systems use two types of code sequences:
• Orthogonal sequences (Walsh codes).
• Pseudorandom Noise (PN) sequences.
Long codes (242 =4400 Billion)
Short codes (215 =32768)
6.4: CDMA Channels: There is the following main CDMA channels used as given below.
These are of two types mainly i.e. Forward Link Channels and Reverse Link Channels as given
below:
62
Forward Link Channels
Pilot Channel
Sync Channel
Paging Channels
Traffic Channels
Reverse Link Channels
Access Channels
Traffic Channels
Pilot channel (W0)
The pilot is used by the subs unit to obtain initial system synchronization and to distinguish cell
sites. Every sector of every cell site has a unique pilot channel.
Transmitted constantly.
Allows the mobile to acquire the system.
Provides mobile with signal strength comparison.
Approximately 20% of the radiated power is in the pilot.
Has unique PN Offset (215 ) for each cell or sector.
Sync channel (W32):
Used during system Acquisition stage. Sync chl provides the subs unit with network information
related to cell site identification, pilot transmit power & cell site PN offset.
Used by mobile to synchronize with the system
Transmits sync message with
Pilot PN offset - System time
Long PN code - System ID
Network ID - Paging chl data rate
Tx at 1200 bps
63
PAGING CHLS (W1-W7):
On this chl base station can page the subs unit and it can send call set-up and traffic chl
assignment information.
Means of communication between base to mobile station.
Paging CHL data Rates can be 2.4,4.8 or 9.6 Kbps.
CDMA assignment has 7 paging CHLs.
Each paging CHL supports 180 pages per set.
Total pages/ CDMA RF chl = 1260
Provides mobile with
System Parameter message - Neighbour list
Access Parameter list - CDMA Channel list
Used by base station to :
Page mobile - Transmit overhead information
Assign mobile to traffic channel
Traffic Channels (W8-W31 & W33-W63):
The traffic chl carries the actual call. That is, the voice and control information between the subs
unit & base station.
TX up to 9.6kbps on rate set 1 and up to 14.4kbps on rate set 2.
Access CHLS:
Provides communication from Mobile to base station when mobile is not using traffic
Chl. The access chl is used for call origination & for response to pages, orders &
registration requests. It is paired with corresponding paging chl.
Each Access CHL uses long PN code.
Base station responds to transmission on a particular Access CHL.
64
Mobile responds to base station message by emitting on Access CHL.
Tx at 4800bps
6.5: Power control:
CDMA will not work without an effective power control, because of the near-far problem, fading
& varying path loss.
The system requires fast closed loop power control for Raleigh fading.
Requires wide dynamic range open loop power control to handle variations in path losses in
different locations.
There are basically two methods of power control in CDMA
Open loop power control: This is purely a mobile unit function. It gives open estimation.
This is done only during the initial stage as soon as the mobile is turned on.
Closed loop power control:This involves both, the Base station and the mobile unit and
gives the closed loop power correction.
Open loop power control:
An original estimate is made by the mobile. Mobile adjusts its Trans power according to changes
in its received power from the base station.
When the mobile is turned on, it locks on to the pilot, paging and synch channel.
There is no traffic channel assigned to the mobile and hence no closed loop.
The mobile Tx power will be inversely proportional to the pilot strength received.
Closed loop power control:
Base station provides rapid correction to the mobiles.
Compares with the threshold value.
Takes decision for increasing or decreasing the power.
65
Commands the mobile to adjust the output power accordingly.
After the traffic channel is assigned, the power control shifts to closed loop control
Reverse channel has got 16 power control groups of 1.25ms in one 20ms frame.
BTS receives the mobile receive power once every 1.25ms and BTS send Power control
bit in the 2nd next 1.25 ms cycle to increase(0) or decrease(1) the power by 1db.
6.6: Frequency Reuse:
In CDMA reuse patterns are not required. Subscriber in every cell can use the same frequency at
the same time. Subscriber is discriminated from another by the assignment of a unique code to
every conversation.
In GSM freq. Reuse pattern of 7 is used.
66
6.7: HANDOFFS IN CDMA: The following type of handoffs is mainly used in CDMA:
Softer handoff:
Multi sector hand off (Intra BTS)
Can have up to 3or 6 sectors involved (same cell)
Voice data is combined at cell and passed as one cell to BSC
Make before break
Soft handoff
Multi-cell Handoff (Inter BTS)
Can have up to 3 cells involved (same FA)
Each cell provides voice data to BSC
67
CHAPTER 7 INTRODUCTION TO GPRS
7.1: GPRS (2.7G):
General packet radio service (GPRS) is a packet oriented mobile data service available to users
of the 2G cellular communication systems global system for mobile communications (GSM), as
well as in the 3G systems. In 2G systems, GPRS provides data rates of 56-114 kbit/s GPRS data
transfer is typically charged per megabyte of traffic transferred, while data communication via
traditional circuit switching is billed per minute of connection time, independent of whether the
user actually is using the capacity or is in an idle state. GPRS is a best-effort packet switched
service, as opposed to circuit switching, where a certain quality of service (Quos) is guaranteed
during the connection for non-mobile users.
2G cellular systems combined with GPRS are often described as 2.5G, that is, a technology
between the second (2G) and third (3G) generations of mobile telephony. It provides moderate
speed data transfer, by using unused time division multiple access (TDMA) channels in, for
example, the GSM system. Originally there was some thought to extend GPRS to cover other
standards, but instead those networks are being converted to use the GSM standard, so that GSM
is the only kind of network where GPRS is in use. GPRS is integrated into GSM Release 97 and
newer releases. It was originally standardized by European Telecommunications Standards
Institute (ETSI), but now by the 3rd Generation Partnership Project (3GPP)
GPRS was developed as a GSM response to the earlier CDPD and i-mode packet switched
cellular technologies
68
7.2: GPRS NETWORK
7.3: GPRS ARCHITECTURE
GPRS COMPONENTS:
To ensure the interworking of the PLMN, PDN and the wireless networks (GSM or TDMA), two
new major components are required. These components are called GPRS Support Nodes. There
are two types of GPRS Support Nodes
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
69
Internet
X.25 Network
GSM NetworkWith GPRS CapabilityMS
7.4: SERVING GPRS SUPPORT MODE:
Service access point for the mobile station
Main functions
1. Mobility management
2. Registration
3. Authentication
Interacts with the mobile for
1. packet data flow
2. And related functions like compression and ciphering
3. Protocols like SNDCP(Sub-network dependent convergence protocol) and
LLC(logical link control)
70
RadiusServer
ChargingGateway
WAPServer
Mediation
Billing
MS
GGSN
GGSNSGSN
MSC
BSCPCU
PSTNGPRSNetwork
Intranet
Internet
4. GTP(Gateway tunneling protocol for GTP tunneling to other support nodes
An SGSN delivers packets to mobile stations within its service area. SGSNs send queries
to Home Location Registers (HLRs) to obtain profile data of GPRS subscribers.
SGSNs detect new GPRS mobile stations in a given service area; and, finally, SGSNs process
registration of new mobile subscribers and keep a record of their location inside a given service
area
GGSN: GATEWAY GPRS SUPPORT NODE:
GGSN connected to SGSN on one side and to outside world external networks such as
Internet and X.25
A gateway it functions as a wall for these external networks to protect the GPRS network
Data from external network, after verification of address forwarded to the SGSN
Routes packets received from the mobile to the correct network. Acts as a router
GGSNs are used as interfaces to external PDNs. GGSNs maintain routing information
that is necessary to tunnel the Protocol Data Units (PDUs) to the SGSNs that service
particular mobile stations.
Other functions include network and subscriber screening and address mapping. One or
more GGSNs may support multiple SGSNs.
BORDER GATEWAY
Interconnects different GPRS operators’ backbones
Facilitates GPRS roaming
Uses standard IP router technology
71
7.5: GPRS INTERFACES
The GPRS Interfaces are defined as follows
New interfaces. All of them known as G interfaces
Gb: BSS and SGSN carries traffic and signaling information between BSS of GSM and
GPRS
Gn: SGSN and SGSN/GGSN of same network. Data and signalling of for intra-system
functioning
Gd: SMS-GSMC/SMS-IWMSC and SGSN for better use of SMS services
Gp: between SGSN and GGSN of other public land mobile networks. Interface between
two GPRS networks. Security and routing
Gs: SGSN and MSC/VLR. Location data handling and paging requests through the MSC.
72
Gr: SGSN and HLR. Subscriber data can be accessed by the SGSN from the HLR
Gf: SGSN and EIR. Equipment information in EIR to SGSN
Gi: GGSN and external networks. Not a standard interface. Depends on the type of
network that is being connected to the GPRS network
7.6: GPRS LOGICAL CHANNELS:
PBCCH: Packet Broadcast Control Channel(DL)
• Broadcast system information specific to packet data
PCCCH; Packet Common Control Channel
• Contains logical channels for common control signalling
• PBCCH: Packet Broadcast Control Channel(DL)
• Broadcast system information specific to packet data
PDTCH: Packet Data Traffic Channel
• Channel temporarily used for data transfer
PACCH: Packet Associated Control Channel
• Used for signalling information transfer for a given mobile
PAGCH: Packet Access Grant Channel(DL)
• Notifies that mobile about resource assignment before actual packet transfer
PNCH: Packet Notification Channel(DL)
• Used for sending information to multiple mobile stations
PPCH: Packet Paging Channel(DL)
73
• Pages a mobile station before packet transfer begins
PRACH: Packet random Access Channel(UL)
• Used by the mobile station for initialization of the uplink packet transfer
7.7: Services offered
GPRS extends the GSM circuit switched data capabilities and makes the following services
possible:
"Always on" internet access
Multimedia messaging service (MMS)
Push to talk over cellular (Pock/PTT)
Instant messaging and presence—wireless village
Internet applications for smart devices through wireless application protocol (WAP)
Point-to-point (P2P) service: inter-networking with the Internet (IP)
If SMS over GPRS is used, an SMS transmission speed of about 30 SMS messages per minute
may be achieved. This is much faster than using the ordinary SMS over GSM, whose SMS
transmission speed is about 6 to 10 SMS messages per minute.
7.8: WORKING OF GPRS:
To lessen the impact of the delay in implementing 3rd generation wireless systems, General
Packet Radio Service (GPRS) is being introduced as an intermediate step to efficiently transport
high-speed data over the current Global Systems for Mobile Communications (GSM) and
TDMA-based wireless network infrastructures.
GPRS signalling and data traffic do not travel through the GSM network. The GSM network is
only used for table look up, in the Location Register data bases, to obtain GPRS user profile data.
GPRS uses 1 to 8 radio channel timeslots which can be shared by multiple users
74
It packetizes the user data and transports it over Public Land Mobile Networks (PLMN) using an
IP backbone. From there, it interfaces to other Public Data Networks (PDNs), including the
Internet.
As a result, GPRS has the ability to offer speeds of 14,400 bps to 115,000 bps, which allow for
comfortable Internet access using wireless devices. Because GPRS has a range of supported
bandwidths, it allows for short "busty" traffic, such as e-mail and web browsing, as well as large
volumes of data. In addition, because GPRS supports Quality of Service, service providers can
offer selective services to users.
Finally, because GPRS has fast connection setup, the user has the perception of being "always
on" for continuous operation.
7.9: PROTOCOLS SUPPORTED:
GPRS supports the following protocols:
Internet protocol (IP). In practice, mobile built-in browsers use IPv4 since IPv6 is not
yet popular.
Point-to-point protocol (PPP). In this mode PPP is often not supported by the mobile
phone operator but if the mobile is used as a modem to the connected computer, PPP is
used to tunnel IP to the phone. This allows an IP address to be assigned dynamically to
the mobile equipment.
X.25 connections: This is typically used for applications like wireless payment terminals,
although it has been removed from the standard. X.25 can still be supported over PPP, or
even over IP, but doing this requires either a network based router to perform
encapsulation or intelligence built in to the end-device/terminal; e.g., user equipment
(UE).
When TCP/IP is used, each phone can have one or more IP addresses allocated. GPRS will store
and forward the IP packets to the phone during cell handover (when you move from one cell to
75
another). TCP handles any packet loss (e.g. due to a radio noise induced pause) resulting in a
temporary throttling in transmission speed.
Coding schemes and speeds
The upload and download speeds that can be achieved in GPRS depend on a number of factors
such as:
the number of BTS TDMA time slots assigned by the operator
the maximum capability of the mobile device expressed as a GPRS multisport class
The channel encoding used summarized in the following table.
Coding
scheme
Speed
(k bit/s)
CS-1 8.0
CS-2 12.0
CS-3 14.4
CS-4 20.0
The least robust, but fastest, coding scheme (CS-4) is available near a base transceiver station
(BTS), while the most robust coding scheme (CS-1) is used when the mobile station (MS) is
further away from a BTS.
Using the CS-4 it is possible to achieve a user speed of 20.0 k bit/s per time slot. However, using
this scheme the cell coverage is 25% of normal. CS-1 can achieve a user speed of only 8.0 Kbit/s
per time slot, but has 98% of normal coverage. Newer network equipment can adapt the transfer
speed automatically depending on the mobile location.
In addition to GPRS, there are two other GSM technologies which deliver data services: circuit-
switched data (CSD) and high-speed circuit-switched data (HSCSD). In contrast to the shared
nature of GPRS, these instead establish a dedicated circuit (usually billed per minute). Some
applications such as video calling may prefer HSCSD, especially when there is a continuous
flow of data between the endpoints.
76
The following table summarizes some possible configurations of GPRS and circuit switched data
services.
Technology Download
(kbit/s) Upload (kbit/s)
TDMA Timeslots
allocated
CSD 9.6 9.6 1+1
HSCSD 28.8 14.4 2+1
HSCSD 43.2 14.4 3+1
GPRS 80.020.0 (Class 8 & 10 and
CS-4) 4+1
GPRS 60.0 40.0 (Class 10 and CS-4) 3+2
EGPRS
(EDGE)236.8
59.2 (Class 8, 10 and
MCS-9) 4+1
EGPRS
(EDGE)177.6
118.4 (Class 10 and
MCS-9) 3+2
7.10: MULTIPLE ACCESS TECHNIQUES:
The multiple access methods used in GSM with GPRS are based on frequency division duplex
(FDD) and TDMA. During a session, a user is assigned to one pair of up-link and down-link
frequency channels. This is combined with time domain statistical multiplexing; i.e., packet
mode communication, which makes it possible for several users to share the same frequency
channel. The packets have constant length, corresponding to a GSM time slot. The down-link
uses first-come first-served packet scheduling, while the up-link uses a scheme very similar to
reservation ALOHA (R-ALOHA). This means that slotted ALOHA (S-ALOHA) is used for
reservation inquiries during a contention phase, and then the actual data is transferred using
dynamic TDMA with first-come first-served scheduling
77
CHAPTER 8 INTRODUCTION TO UMTS
8.1: INTRODUCTION:
Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G)
mobile telecommunications technologies, which is also being developed into a 4G technology.
The first deployment of the UMTS is the release99 (R99) architecture. It is specified by 3GPP
and is part of the global ITU IMT-2000 standard. The most common form of UMTS uses W-
CDMA (IMT Direct Spread) as the underlying air interface but the system also covers TD-
CDMA and TD-SCDMA (both IMT CDMA TDD). Being a complete network system, UMTS
also covers the radio access network (UMTS Terrestrial Radio Access Network, or UTRAN) and
the core network (Mobile Application Part, or MAP), as well as authentication of users via
USIM cards (Subscriber Identity Module).
Unlike EDGE (IMT Single-Carrier, based on GSM) and CDMA2000 (IMT Multi-Carrier),
UMTS requires new base stations and new frequency allocations. However, it is closely related
to GSM/EDGE as it borrows and builds upon concepts from GSM. Further, most UMTS
handsets also support GSM, allowing seamless dual-mode operation. Therefore, UMTS is
sometimes marketed as 3GSM, emphasizing the close relationship with GSM and differentiating
it from competing technologies.
The name UMTS, introduced by ETSI, is usually used in Europe. Outside of Europe, the system
is also known by other names such as FOMA or W-CDMA In marketing, it is often just referred
to as 3G.
8.2: Features:
78
UMTS, using W-CDMA, supports maximum theoretical data transfer rates of 21 M bit/s (with
HSPA), although at the moment users in deployed networks can expect a transfer rate of up to
384 k bit/s for R99 handsets, and 7.2 M bit/s for HSDPA handsets in the downlink connection.
This is still much greater than the 9.6 k bit/s of a single GSM error-corrected circuit switched
data channel or multiple 9.6 k bit/s channels in HSCSD (14.4 k bit/s for CDMA One), and—in
competition to other network technologies such as CDMA2000, PHS or WLAN—offers access
to the World Wide Web and other data services on mobile devices.
Precursors to 3G are 2G mobile telephony systems, such as GSM, IS-95, PDC, CDMA PHS and
other 2G technologies deployed in different countries. In the case of GSM, there is an evolution
path from 2G, to GPRS, also known as 2.5G. GPRS supports a much better data rate (up to a
theoretical maximum of 140.8 Kbit/s, though typical rates are closer to 56 Kbit/s) and is coding
schemes. With EDGE the actual packet data rates can reach around 180 Kbit/s (effective). EDGE
systems are often referred as packet rather than connection oriented (circuit switched). It is
deployed in many places where GSM is used. E-GPRS, or EDGE, is a further evolution of GPRS
and is based on more modern "2.75G Systems".
Since 2006, UMTS networks in many countries have been or are in the process of being
upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G.
Currently, HSDPA enables downlink transfer speeds of up to 21 M bit/s. Work is also
progressing on improving the uplink transfer speed with the High-Speed Uplink Packet Access
(HSUPA). Longer term, the 3GPP Long Term Evolution project plans to move UMTS to 4G
speeds of 100 M bit/s down and 50 M bit/s up, using a next generation air interface technology
based upon Orthogonal frequency-division multiplexing.
The first national consumer UMTS networks launched in 2002 with a heavy emphasis on Telco-
provided mobile applications such as mobile TV and video calling. The high data speeds of
UMTS are now most often utilized for Internet access: experience in Japan and elsewhere has
shown that user demand for video calls is not high, and Telco-provided audio/video content has
declined in popularity in favor of high-speed access to the World Wide Web - either directly on a
handset or connected to a computer via Wi-Fi, Bluetooth, Infrared or USB.
79
8.3; Air interfaces
UMTS provides several different terrestrial air interfaces, called UMTS Terrestrial Radio Access
(UTRA). All air interface options are part of ITU's
8.4: Radio access network:
UMTS also specifies the UMTS Terrestrial Radio Access Network (UTRAN), which is
composed of multiple base stations, possibly using different terrestrial air interface standards and
frequency bands.
UMTS and GSM/EDGE can share a Core Network (CN), making UTRAN an alternative radio
access network to GERAN (GSM/EDGE RAN), and allowing (mostly) transparent switching
between the RANs according to available coverage and service needs. Because of that, UMTS'
and GSM/EDGE's radio access networks are sometimes collectively referred to as
UTRAN/GERAN.
UMTS networks are often combined with GSM/EDGE, the latter of which is also a part of IMT-
2000.
The UE (User Equipment) interface of the RAN (Radio Access Network) primarily consists of
RRC (Radio Resource Control), RLC (Radio Link Control) and MAC (Media Access Control)
protocols. RRC protocol handles connection establishment, measurements, radio bearer services,
and security and handover decisions. RLC protocol primarily divides into three Modes -
Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledge Mode (AM). The
functionality of AM entity resembles TCP operation where as UM operation resembles UDP
operation. In TM mode, data will be sent to lower layers without adding any header to SDU of
higher layers. MAC handles the scheduling of data on air interface depending on higher layer
(RRC) configured parameters.
Set of properties related to data transmission is called Radio Bearer (RB). This set of properties
will decide the maximum allowed data in a TTI (Transmission Time Interval). RB includes RLC
information and RB mapping. RB mapping decides the mapping between RB<->logical
80
channel<->transport channel. Signaling message will be send on Signaling Radio Bearers
(SRBs) and data packets (either CS or PS) will be sent on data RBs. RRC and NAS messages
will go on SRBs.
8.5: Spectrum allocation:
Over 130 licenses have already been awarded to operators worldwide (as of December 2004),
specifying W-CDMA radio access technology that builds on GSM. In Europe, the license
process occurred at the tail end of the technology bubble, and the auction mechanisms for
allocation set up in some countries resulted in some extremely high prices being paid for the
original 2100 MHz licenses, notably in the UK and Germany. In Germany, bidders paid a total
€50.8 billion for six licenses, two of which were subsequently abandoned and written off by their
purchasers (Mobilcom and the Sonora/Telephonic consortium). It has been suggested that these
huge license fees have the character of a very large tax paid on future income expected many
years down the road. In any event, the high prices paid put some European telecom operators
close to bankruptcy (most notably KPN). Over the last few years some operators have written off
some or all of the license costs. More recently, a carrier in Finland has begun using 900 MHz
UMTS in a shared arrangement with its surrounding 2G GSM base stations, a trend that is
expected to expand over Europe in the next 1–3 years.
The 2100 MHz UMTS spectrum allocated in Europe is already used in North America. The
1900 MHz range is used for 2G (PCS) services, and 2100 MHz range is used for satellite
communications. Regulators have, however, freed up some of the 2100 MHz range for 3G
services, together with the 1700 MHz for the uplink. UMTS operators in North America who
want to implement a European style 2100/1900 MHz system will have to share spectrum with
existing 2G services in the 1900 MHz band.
AT&T Wireless launched UMTS services in the United States by the end of 2004 strictly using
the existing 1900 MHz spectrum allocated for 2G PCS services. Cingular acquired AT&T
Wireless in 2004 and has since then launched UMTS in select US cities. Cingular renamed itself
81
AT&T and is rolling out some cities with a UMTS network at 850 MHz to enhance its existing
UMTS network at 1900 MHz and now offers subscribers a number of UMTS 850/1900 phones.
T-Mobile's rollout of UMTS in the US will focus on the 2100/1700 MHz bands.
In Canada, UMTS coverage is being provided on the 850 MHz band on the Rogers, Bell, and
TELUS networks. Recently, new providers Wind Mobile and Mobil city, have begun operations
in the 2100/1700 MHz bands and Quebecor and Shaw Communications are planning their own
launches in coming years.
In 2008, Australian Telco Telstra replaced its existing CDMA network with a national 3G
network, branded as Next, operating in the 850 MHz band. Telstra currently provides UMTS
service on this network, and also on the 2100 MHz UMTS network, through a co-ownership of
the owning and administrating company 3GIS. This company is also co-owned by Hutchison 3G
Australia, and this is the primary network used by their customers. Optus is currently rolling out
a 3G network operating on the 2100 MHz band in cities and most large towns, and the 900 MHz
band in regional areas. Vodafone is also building a 3G network using the 900 MHz band.
In India BSNL has started its 3G services since October 2009 beginning with the larger cities and
then expanding over to smaller cities. The 850 MHz and 900 MHz bands provide greater
coverage compared to equivalent 1700/1900/2100 MHz networks, and are best suited to regional
areas where greater distances separate subscriber and base station.
Carriers in South America are now also rolling out 850 MHz networks.
82
CHAPTER 9 INDUSTRIAL VISIT ON HLR
9.1: Home Location Register (HLR)
HLR maintains a permanent register of the subscribers. For instance the subscriber identity
numbers and the subscribed services can be found here. In addition to the fixed data, the HLR
also keeps track of the current location of its customers. As you will see later, the GMSC asks for
routing information from the HLR if a call is to be set up to a mobile station (mobile terminated
call). In the Nokia implementation, the two network elements, Authentication Centre (AC) and
Equipment Identity Register (EIR), are located in the Nokia DX200 HLR.
9.2: Data stored in HLR:
In HLR mainly stores the Permanent and the Temporary data in it, as shown follows:
Permanent data in HLR: The permanent data stored is changed only by Man-Machine (MM).
The following type of data is stored in HLR permanently:
IMSI,MS-ISDN number
Category of MS(whether pay phone or not)
Roaming Restriction( allowed or not)
Supplementary services like call forwarding.
Temporary data in HLR: The data changes from call to call& is dynamic. The temporary data
stored is as given below:
MSRN
RAND/SRES and Kc.
VLR address, MSC address.
83
Message waiting data used for SMS.
9.3: DX 200 HLR:
Once the architecture of the DX 200 MSC/VLR is understood, it becomes a relatively easy
matter to understand all the other DX 200 elements, because of the same architecture and the
presence of similar units in all the elements. The HLR is no exception. The figure below shows
the DX 200 HLR architecture and a brief explanation of HLR-specific units follows thereafter.
The maximum number of created subscribers in a DX 200 HLR is 300 000. A DX 200 HLR
supports 1 200 000 subscriber and its integrated AuC has a capacity of 2.4 million subscribers.
84
Functional units in the HLR:
It can be seen that there is only one signaling related unit in the HLR compared to the many in
MSC. This is because user traffic does not come to the HLR. The rest of the units and their
functions are exactly same as in the MSC. However, we see that there are three extra units in the
HLR that do not exist in the MSC. These are the database-related units. The HLRU (Home
Location Register Unit) is responsible for subscriber data management and mobility
management. The Authentication Unit (ACU) is responsible for the management of
authentication data. It generates authentication triplets and sends them to the VLR and the EIRU
(Equipment Identification Register Unit) handles the equipment identity and its checking.
9.4: HLR HARDWARE:
It is a central database where the permanent data storage takes place. Data of the subscriber
pertaining to the class of services allowed are permanently kept in the HLR data base.
Class of Services: STD, GPRS, ISD etc. are exclusively defined for each subscriber in the HLR
data base. These basic & other supplementary services like CFU, CF, CAW, CLIP, etc.
It is an important Network element (NE) in the GSM architecture. Any subscriber initiated
terminated service as well as location update involves the process of HLR & enquiry.
These special cases with the call flow scenario are explained with MML. Call begins with the
description of HLR hardware perspective where the type of different cards along with their
functions is defined. HLR comprises of 2 units:
Home Location Group cabinet (HLGC)
Home Location register Cabinet (HLRC)
The HLGC houses the main processing unit that controls the entire HLR unit.
85
The HLRC essentially maintains the database of subscribers related to class of services. This is
kept in HLRU functional unit. The data corresponds to subscribers handset entity is kept in ERU
functional unit and data related to subscribers ,SIM(IMSI), Ki related algorithm’s are kept in
AUC functional unit.
9.4.1: Following is the functional unit’s description of HOME LOCATION GROUP
CABINET (HLGC):-
1. PDFU [Power Distribution & Fuse Unit]:-
The PDFU distributes -48V / -60 V power from rectifier or batteries through the cartage
distribution table. The PDFU also contain fuses for these cables along with the alarm circuit for
input voltages. Power distribution has 2N redundancy
2. CLSU [Clock System Unit]:-
This consist of two sub units including clock and alarm copper unit.
The CLSU generates the clock signals necessary for synchronizing the functions of MSC and
transmit further them to CLBU unit. When use in hierarchical mode, the clock system unit is
synchronize from clock pulses from PSTL.
The CLSU field the timing signals to the units in HLGC cabinet. One CLSU unit can handle the
clock requirement up to 15 cartages.
3. GSW [Group Switch]:-
The GSW is the switching network of HLR and is located in the Home location Group switch
cabinet. It is controlled by the central memory and marker unit. The CMM together with group
switch carries out the necessary switching of signaling required in HLR. HLR group switch does
not handle the traffic data. The traffic data is switched by the MSC. The GSW switches the
signaling required for HLR enquiry.
It has 2n redundancy.
4. BDCU [Basic Data Communication Unit]:-
86
It contains communication link to the operation and maintenance network to the CSR to the
billing centre.
5. OMU [Operation and Maintenance Unit]:-
The OMU handles all centralized suppression and alarm recovery function and the connection
towards the user interface. This is computer unit with storage device and subunit. The OMU has
2n redundancy and also has storage device subunit
6. CMM [Central Memory and Marker]:-
It handles central memory and marker. It also handles the routing function of HLR. It also
contains all system configuration data files. It assists in the central functions of CCSU unit.
The marker control and supervises the group switch. It hunts for free circuits and is responsible
for establishing and realizing all connections.
The marker and group switch together made a switching identity. The central memory and
marker has 2n redundancy.
7. CCSU [Command Channel signaling Unit]:-
It handles CCS7 signaling. It also controls the PCM connections of the exchange and ET
(external terminal) is connected to BDCU (Basic Data Communication Unit). It has n+1
redundancy.
9.4.2: Following is the functional unit’s description of HLRC (Home Location Register
Cabinet):
1. PDFU [Power Distribution & Fused Unit]:-
It distributes -48/-60 volts of power from the rectifier or batteries to cartridge through
distribution cable. It also contains fuses & alarm circuits for incoming voltages.
It has 2n redundancy.
87
2. DBDU [Data Base Distribution unit]:-
It is responsible for distribution of the HLR/AUC data to correct HLR/AUC units. This unit has
dedicated storage device as sub unit. The HLR functional units that mange large data base are
equipped with dedicated storage devices. These are memory units having hard disk as storage
device. These acts as sub-units to OMU, DB units.
3. CLBU [Clock & Buffer Unit]:-
CLBU distributes the clock signal generated by CLSU to the units in the same cabinet. The
CLBU also collects the wired alarms from the unit whose functioning it handles.
4. EIRU [Equipment Identity Register Unit]:-
It has following types:
1. Equipment Main Unit (EMU)
2. Equipment Identity Register Unit (EIRU)
EMU contains the main data base for EIRU. Its responsibility is to manage the interface with the
CEIR (Central EIR)
EIRU performs verification of equipment identity & provides network with list of stolen/ faulty
equipment.
5. STU [Statistical unit]:-
It collects performance & measurement data from the network that are used in the operation sub
system part of the GSM. It has a storage device & 2n redundancy.
6. ET [External Terminal Interface]:-
It performs electrical signals synchronization & adaptation of external PCM lines i.e. produces
PCM frame structure.
7. HLR Unit:-
88
It controls subscriber data base & is used for modifying subscriber data. The HLR is also
responsible for call handling. It has a storage device as a sub-unit.
8. ACU [Authentication & Control Unit]:-
It is responsible for storing authentication data. The control unit provides authentication triplets:
SRES
RAND
Kc
For the user authentication & speech encryption.
9.5: Locating a subscriber:
• Telecommunication requires a point to point connection between the calling and the
called party. Such a connection in Mobile network is possible only when the network
knows the location of the subscriber. The network keeps track of the subscribers’ location
with the help of various databases, more precisely the SIM, the VLR, and the HLR. The
whole mobile network area is connected through an air interface to the Visitor Location
Register (VLR), which is integrated into the Mobile services Switching Centre (MSC).
• The HLR stores the basic data of the subscriber on a permanent basis. The only variable
information in the HLR is the current location of the subscriber (the VLR address). The
VLR address is needed, because the HLR needs to know from what MSC/VLR to ask for
routing information in case of a mobile terminated call (a call to the mobile station).
When the subscriber moves to another VLR area, its data is erased from the old VLR and
stored in the new VLR.
9.6: Location updation procedure:
The transaction that enables the network to keep track of the subscriber is called a
location update.
89
The mobile phone constantly receives information sent by the network. This information
includes identification (ID) of the VLR area in which the mobile is currently located. In
order to keep track of its location, the mobile stores the ID of the area in which it is
currently registered. Every time the network broadcasts the ID of the area, the mobile
compares this information to the area ID stored in its memory.
When the two IDs are no longer the same, the mobile sends the network a request, that is,
a registration inquiry to the area it has just entered.
This request can be performed to register in a new area logically under the currently used
VLR or it may be sent to a new VLR depending on situation.
9.7: Location updation registration:
90
Location registration takes place when a mobile station is turned on. This is also known
as IMSI Attach, because as soon as the MS is switched on, it informs the Visitor Location
Register (VLR) that it is now backing in service and is able to receive calls.
As a result of a successful registration, the network sends the MS two numbers that are
stored in the SIM (Subscriber Identity Module) card of the mobile station.
These two numbers are the Location Area Identity (LAI) and the Temporary Mobile
Subscriber Identity (TMSI). The network sends the LAI via the control channels of the
air interface.
The TMSI is used for security purposes, so that the IMSI of a subscriber does not have to
be transmitted over the Air Interface. The TMSI is a temporary identity, which regularly
gets changed.
9.8: The call setup procedure:
The PSTN exchange analyses the dialed number. The result of the analysis is the routing
information required for finding the mobile network (Public Land Mobile Network,
PLMN) in which the called subscriber has made his subscription. The PSTN identifies
the mobile network with the NDC, after which it accesses the mobile network via the
nearest Gateway Mobile services Switching Centre (GMSC).
The GMSC analyses the MSISDN in the same way as the PSTN exchange did. As a
result of the analysis, it obtains the HLR address to the HLR where the subscriber is
permanently registered. Notice that the GMSC itself does not have any information about
the location of the called subscriber. The subscriber’s location can only be determined by
the two databases, the HLR and the VLR. At this stage however, the GMSC only knows
the HLR address, so it sends a message (containing the MSISDN) to the HLR. In practice
this message is a request for locating the called subscriber in order to set up a call. This is
called an HLR Enquiry.
The HLR interrogates the MSC/VLR that is currently serving the called subscriber to
know the current status of the mobile station so as to avoid setting up a call to a
subscriber whose phone is switched off. Secondly, we need to have some sort of
91
information that enables the GMSC to route the call to the target MSC, wherever in the
world it may be.
In terms of routing the call, the serving MSC/VLR is the destination of the call. After
receiving the message from the HLR, the serving MSC/VLR generates a temporary
Mobile Station Roaming Number (MSRN) and associates it with the IMSI. The roaming
number is used to initiate the connection and it has the following structure:
The MSC/VLR sends the roaming number to the HLR. The HLR does not analyses the
roaming number, because the MSRN is used for traffic transactions only and the HLR
does not handle traffic, it is only a database that helps in locating subscribers and co-
ordinates call set-up. Therefore, the HLR simply forwards the MSRN to the GMSC that
originally initiated the process.
When the GMSC receives the message containing the MSRN, it analyses the message.
The roaming number identifies the location of the called subscriber, so the result of this
analysis is a routing process, which identifies the destination of the call - the serving
MSC/VLR.
The final phase of the routing process is taken care of by the serving MSC/VLR. In fact,
the serving MSC/VLR also has to receive the roaming number so that it knows that this
is not a new call, but one that is going to terminate here – that is, a call to which it has
already allocated an MSRN. By checking the VLR it recognizes the number, so it is then
able to trace the called subscriber.
Now the routing of the call is done to the destination MSC/VLR, and it is time for the
MSC to initiate the paging process on the radio interface part of GSM.
9.9: HOME LOCATION REGISTER COMMANDS
SUBSCRIBER CREATION
HGSUI:- It creates a subscriber accounting the HLR.
92
The complete command is as follows:-
HGSUI: MSISDN = <91 - - - - - - - - - ->, IMSI = <40453- - - - - - - - - - - >, Profile =1;
MSISDN to be created is mapped with the IMSI of the SIM on which the number has to be
serviced.
In this command, the profile of the subscriber services is also defined.
Profile = 1 for Pre Paid Subscribers
Profile = 2 for Post Paid Subscribers (VPN –Virtual Private N/W or CUG-Closed User
Group)
Profile = 0 for Post Paid Subscribers (Normal)
SUBSCRIBER DELETION
HGSUE:- It deletes the entire services of the subscriber MSISDN.
The complete command is as follows:-
HGSUI: MSISDN = <91 - - - - - - - - - ->;
; confirms the execution of the command
Now, this number and IMSI do not exist in the network and can be re-used i.e. allocated to
another subscriber.
VIEWING SUBSCRIBER DETAILS
HGSDP: MSISDN = <91 - - - - - - - - - ->, ALL;
OR
HGSDP: IMSI <40535 - - - - - - - - - ->, ALL;
TO VIEW THE STATUS ONLY, WE USE-
HGSDP: MSISDN = <91 - - - - - - - - - ->;
SIM SWAP
For shifting the number to a different SIM if old SIM is faulty
Command:-
93
HGICI: IMSI=<old IMSI>, NIMSI<new IMSI>;
RESET SIM
Command:-
HGIRI: IMSI = < IMSI to be reset>;
SUBSCRIBER MODIFICATION
Eg- Modifying TS22 parameter
HDSDC: MSISDN=<91--------->, SUD=TS22 – 0;
HDSDC: MSISDN=<91--------->, SUD=TS22 – 1;
HDSDC: MSISDN=<91--------->, ALL;
PARAMETERS LISTED UNER THIS COMMAND:-
94
NAM- Network Access Mode
For GPRS or data service
NAM 0 – Service Enabled
NAM 1 - Service Disabled
TS11 - Voice Telephony or speech
TS11-1 => Enabled
TS11-0 =>Disabled
TS 21 – Incoming SMS
TS 22 – Outgoing SMS
BS 3G-1 => 3G services Enabled
BS 21 to BS26 => 3G signaling
RSA- Service Area Restriction
RSA1- Total Restriction
RSA0- No Restriction
RSA2 - Only Home PLMN allowed
SUPPLEMENTARY SERVICES:-
S TYPE -> Profile of the user
S TYPE 1 – Prepaid, STYPE 2- Postpaid
OBO- Operator barring of outgoing services
OBO 1- All Barred
OBO2 – Only ISD barred
OBO 0 - All calls allowed
OBR- Operator barring of roaming service
95
OBR 0 –All roaming allowed
OBR 1 – Only local roaming allowed
CAW- Call waiting
CFU- Call forwarding unconditional
CFNRY- Call forwarding when no reply
CFNRC- Call forwarding when not reachable
CLIP- Caller line Identification parameter
CLIR- Caller line Identification restriction
PRBT & TICK75 – Ring Back tone
STYPE2 & OICK 22 – Post paid services
PDPCP- Packet Data protocol
For Prepaid subscriber GPRS service is defined by PDPCP
PDPCP2- For 2G
PDPCP3- For 3G
APN- Access point Network
EQOSID- Speeds for data services
20’s - 2G
30’s - 3G
96
97
98
