Gsm Introduction
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GSM Introduction
History Of GSM
In the early 1980s, many countries in Europe witnessed a rapid expansion of analog cellular telephone systems. However, each country developed its own system, and interoperability across borders became a limiting factor. In 1982, the Conference of European Post and Tele communications (CEPT), established a working group called the Groupe Spécial Mobile (GSM). The task of GSM is to define a new standard for mobile communications in the 900 MHz range using digital technology. 2
History Of GSM contd..,
1986 Field tests were held in Paris to select which digital transmission technology to use. The choice was Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA). 1987 A combination of TDMA and FDMA was selected as the transmission technology for GSM. Operators from 12 countries signed a Memorandum of Understanding committing themselves to introducing GSM by 1991. 3
History Of GSM contd..,
1988 CEPT began producing GSM specifications for a phased implementation. Another five countries signed the MoU. 1989 European Telecommunication Standards Institute (ETSI) took over responsibility for GSM specification. 4
History Of GSM contd..,
1990 Phase 1 specifications were frozen to allow manufacturers to develop network equipment. 1991 The GSM standard was released. An addition was made to the MoU allowing countries outside CEPT to sign. The year 1991 also saw the definition of the first derivative of GSM, GSM 1800 or DCS 1800, which more or less translates the GSM system in to the 1800MHz frequency band. 5
History Of GSM contd..,
The meaning of acronym GSM was changed to Global System for Mobile communications the same year. 1992 Phase 1 specifications were completed. First commercial Phase 1 GSM networks were launched. The first international roaming agreement was established between Telecom Finland and Vodafone in UK. 6
GSM SPECIFICATIONS
GSM was designed to be platformindependent. The GSM specifications do not specify the actual hardware requirements, but instead specify the network functions and interfaces in detail. This allows hardware designers to be creative in how they provide the actual functionality, but at the same time makes it possible for operators to buy equipment from different suppliers. 7
GSM PHASES
In the late 1980s, the groups involved in developing the GSM standard realized that within the given time-frame they could not complete the specifications for the entire range of GSM services and features as originally planned. Because of this, it was decided that GSM would be released in phases with phase 1 consisting of a limited set of services and features. 8
GSM frequency Ranges
For GSM 900 system 890-915 MHz is uplink range (MS transmit) 935-960 MHz is downlink range (MS receive) Bandwidth is 25 MHz.
9
For GSM 1800 system 1710-1785 MHz is uplink frequency range (MS transmit) 1805-1880 MHz is downlink frequency range (MS receive) Bandwidth is 75 MHz
10
System Architecture of GSM
GSM makes use of Cellular Structure The basic idea of cellular network is to partition the available frequency range – allocate only part of frequency spectrum to BTS – keep the range of base station small to reuse the frequency. One more important aspect of network planning is to reduce interference between different base stations. 11
Overview of GSM architectureSubsystems
Mobile Station – MS Subscriber Identity Module –SIM Base transceiver station (BTS) Base station controller (BSC) Transcoding rate and adaptation unit (TRAU) Mobile services switching center (MSC) Home location register (HLR), Visitor location register (VLR) Equipment identity register (EIR). Together, th ey form a p ubl ic la nd mobi le
12
GSM Network Architecture
13
GSM Architecture contd..,
MS – Mobile Station GSM-PLMN contains as many MSs as possible, available in various styles and power classes. In particular, the handheld and portable stations need to be distinguished. SIM-Subscriber Identity Module Identity of the subscriber =/= Identity of the mobile equipment. SIM provides portability to the subscriber. 14
GSM Architecture contd..,
SIM determines the directory number and the calls billed to a subscriber. SIM is a database on the user side. It consists of a chip, which the user must insert into the GSM telephone before it can be used. SIM communicates directly with the VLR and indirectly with the HLR. 15
GSM Architecture contd..,
BTS - Base Transceiver Station A large number of BTSs take care of the radio-related tasks and provide the connectivity between the network and the mobile station via the Air-interface. BSC- Base Station Controller The BTSs of an area are connected to the BSC via an interface called the Abis-interface. 16
GSM Architecture contd..,
BSC takes care of all the central functions and the control of the subsystem, referred to as the base station subsystem (BSS). The BSS comprises the BSC itself and the connected BTSs.
17
GSM Architecture contd..,
TR AU (T rans coding Ra te an d Ad ap tat io n Unit ): One of the most important aspects of mobile network is the effectiveness with which it uses the available frequency resources. Effectiveness addresses how many calls can be made by using a certain bandwidth which in turn translates in to -Necessity to compress data, at least over the Air-interface. Information compression is performed in both the MS and the TRAU.
18
GSM Architecture contd.., MSC (Mobi le Sw it ching Cent er)
MSC is similar to wireline Digital exchange A large number of BSCs are connected to the MSC via the A-interface. Major tasks of an MSC is: Routing of incoming and outgoing calls
19
GSM Architecture contd..,
HLR (Hom e Loc atio n Re gi st er) : A repository that stores the data of a large number of subscribers. An HLR can be regarded as a large database that administers the data of literally hundreds of thousands of subscribers. Every PLMN requires at least one HLR. 20
VLR (Visitor Location Register)
The Visitor Location Register (VLR) is a database containing information about all MSs that currently are located in the MSC service area. The VLR contains temporary subscriber information needed by the MSC to provide service for visiting subscribers. VLR is always integrated with MSC in a GSM network. The VLR can be seen as a distributed HLR. 21
VLR contd..,
VLR area = MSC area When a Mobile Station (MS) roams into a new MSC service area, the VLR connected to that MSC requests data about the MS from the HLR and stores it. When the MS makes a call, the VLR already has the information needed for call set-up. So in this way the no of queries made to HLR is reduced and there by reducing the load. 22
EIR (Eq uip me nt Ide nti ty Regi st er) GSM terminal equipment unique identifier is International mobile equipment identity (IMEI). EIR keeps track of IMEI of all the subscribers.
23
Signaling and Payload
Intercommunication between nodes and databases. Different signaling protocols between different subsystems. Out of Band signaling. 24
PCM
The A/D conversion is performed by using a process called Pulse Code Modulation (PCM). PCM involves three main steps: Sampling Quantization Coding
25
Step1: Sampling
Sampling involves measuring the analog signal at specific time intervals.
The accuracy of describing the analog signal in digital terms depends on how often the analog signal is sampled. This is expressed as the sampling frequency.
26
Step2: Quantization
The next step is to give each sample a value. For this reason, the amplitude of the signal at the time of sampling is measured and approximated to one of a finite set of values.
27
Step 3: Coding
Coding involves converting the quantized values into binary. Every value is represented by a binary code.
28
Pulse Code Modulation -PCM Pulse code modulation (PCM) is the worldwide process for transmission of digital signals. PCM is used to transmit both signaling data and payload. PCM is categorized into hierarchies, depending on the transmission rate.
29
Consider a 2Mbps PCM link be partitioned in 32 independent channels of 64kbps each One 64-Kbps time slot out of a 2-Mbps PCM link typically is used for signaling data A call setup consumes about 1 to 2 Kbps. 30
Block diagram of MOBILE Station
31
Subscriber Identity Module (SIM)
SIM is a microchip Except for emergency calls, a GSM mobile phone cannot be used without the SIM. In GSM terminology, the term MS refers to the combination of a SIM and an ME.
32
SIM
33
SIM contd..,
The SIM stores three types of subscriber related information: Fixed data stored before the subscription is sold: e.g. IMSI, authentication key and security algorithms Temporary network data: e.g. the location area of the subscriber and forbidden PLMNs Service data: e.g. language preference etc.., 34
SIM contd..,
A SIM contains information for GSM network operations. This information can be related to the mobile subscriber, GSM services or PLMN. The data storage requirements of a SIM are divided into two categories: mandatory and optional. 35
SIM as Database
The major task of a SIM is to store data. The SIM has an area of non-volatile memory which is used to store information specific to a particular subscriber and this includes the subscriber’s unique international mobile subscriber identity (IMSI) number. This number is used to identify each individual subscriber within the GSM network. 36
SIM contd..,
The SIM will also contain the subscriber’s secret authentication key, Ki, the authentication algorithm, A3, and the cipher key generation algorithm, A8. The language preference indicator is also located in the SIM and this is used to indicate the language to be used on the MS screen. The items described above are mandatory and must be present in any SIM that conforms to the GSM specifications. 37
SIM contd..,
The SIM may also contain a number of optional items which will include the subscriber’s abbreviated dialling numbers. The SIM may also contain a list of the last number(s) that the subscriber has dialled and an area of storage for the subscriber’s short messages. Inserting an SIM card into an ME effectively personalises the equipment to the particular subscriber. 38
Info stored on SIM – Administrative data PIN
Mandatory /changeable
Personal identification number; requested at every powerup (PIN or PIN2
PUK
Mandatory /fixed value
PIN unblocking key; required to unlock a SIM
SIM service table
Mandatory /fixed value
List of the optional functionality of the SIM
Last dialed number
Optional /changeable
Redial
Charging meter
Optional /changeable
Charges and time increments can be set
Language
Mandatory /changeable
Determines the language for prompts by the mobile station 39
Security related data Algorithm A3 and A8
Mandatory /fixed value Required for authentication and to determine Kc
Key Ki
Mandatory /fixed value Individual value; known only on SIM and the HLR
Key Kc
Mandatory /fixed value Result of A8, Ki, and random number (RAND)
CKSN
Optional /changeable value
Ciphering key sequence number 40
Subscriber Data IMSI
Mandatory /fixed value International mobile subscriber identity
MSISDN
Optional /fixed value
Mobile subscriber ISDN; directory number of a subscriber
41
Roaming Data TMSI
Mandatory / changeable value
Temporary mobile subscriber identity
LAI
Mandatory /changeable value
Location area information
Network color codes (NCCs) of restricted PLMNs
Mandatory /changeable
Maximum of 4 PLMNs can be entered on a SIM after unsuccessful location update; cause “PLMN not allowed.” Oldest entry deleted when more than 4 restricted PLMNs are found.
NCCs of preferred PLMNs
Optional / changeable
What PLMN should the MS select, if there is more than one to choose from and the home PLMN is not available?
42
PLMN data NCC, mobile country code (MCC), and mobile network code (MNC) of the home PLMN
Mandatory /Fixed
Network identifier
Absolute radio frequency channel numbers (ARFCNs) of home PLMN
Mandatory /Fixed
Frequencies for which the home PLMN is licensed.
43
Mobile Station characteristics
Technical Marvel
Falling Prices Availability of different devices Interaction with BTS Channel negotiation ,modulation/demodulation and coding/decoding functionality Efficient use of battery power Communicates directly with MSC and VLR as well via MM (mobility management) and CC (call control)
44
Mobile Station Classes
Different types of MSs have different output power capabilities and therefore different ranges. Hand-held phones generally have a lower output power and consequently a shorter range than a vehicle-mounted phone. According to GSM specifications, MSs are categorized into five classes according to MS output power. 45
MS Power Classes
46
Mobile Station Classes contd..,
The location of the MS also affects the received power of the transmitted signal. An MS located at the top of a high building has a greater range than one that is located at or below ground level.
47
History Of GSM
In the early 1980s, many countries in Europe witnessed a rapid expansion of analog cellular telephone systems. However, each country developed its own system, and interoperability across borders became a limiting factor. In 1982, the Conference of European Post and Tele communications (CEPT), established a working group called the Groupe Spécial Mobile (GSM). The task of GSM is to define a new standard for mobile communications in the 900 MHz range using digital technology. 2
History Of GSM contd..,
1986 Field tests were held in Paris to select which digital transmission technology to use. The choice was Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA). 1987 A combination of TDMA and FDMA was selected as the transmission technology for GSM. Operators from 12 countries signed a Memorandum of Understanding committing themselves to introducing GSM by 1991. 3
History Of GSM contd..,
1988 CEPT began producing GSM specifications for a phased implementation. Another five countries signed the MoU. 1989 European Telecommunication Standards Institute (ETSI) took over responsibility for GSM specification. 4
History Of GSM contd..,
1990 Phase 1 specifications were frozen to allow manufacturers to develop network equipment. 1991 The GSM standard was released. An addition was made to the MoU allowing countries outside CEPT to sign. The year 1991 also saw the definition of the first derivative of GSM, GSM 1800 or DCS 1800, which more or less translates the GSM system in to the 1800MHz frequency band. 5
History Of GSM contd..,
The meaning of acronym GSM was changed to Global System for Mobile communications the same year. 1992 Phase 1 specifications were completed. First commercial Phase 1 GSM networks were launched. The first international roaming agreement was established between Telecom Finland and Vodafone in UK. 6
GSM SPECIFICATIONS
GSM was designed to be platformindependent. The GSM specifications do not specify the actual hardware requirements, but instead specify the network functions and interfaces in detail. This allows hardware designers to be creative in how they provide the actual functionality, but at the same time makes it possible for operators to buy equipment from different suppliers. 7
GSM PHASES
In the late 1980s, the groups involved in developing the GSM standard realized that within the given time-frame they could not complete the specifications for the entire range of GSM services and features as originally planned. Because of this, it was decided that GSM would be released in phases with phase 1 consisting of a limited set of services and features. 8
GSM frequency Ranges
For GSM 900 system 890-915 MHz is uplink range (MS transmit) 935-960 MHz is downlink range (MS receive) Bandwidth is 25 MHz.
9
For GSM 1800 system 1710-1785 MHz is uplink frequency range (MS transmit) 1805-1880 MHz is downlink frequency range (MS receive) Bandwidth is 75 MHz
10
System Architecture of GSM
GSM makes use of Cellular Structure The basic idea of cellular network is to partition the available frequency range – allocate only part of frequency spectrum to BTS – keep the range of base station small to reuse the frequency. One more important aspect of network planning is to reduce interference between different base stations. 11
Overview of GSM architectureSubsystems
Mobile Station – MS Subscriber Identity Module –SIM Base transceiver station (BTS) Base station controller (BSC) Transcoding rate and adaptation unit (TRAU) Mobile services switching center (MSC) Home location register (HLR), Visitor location register (VLR) Equipment identity register (EIR). Together, th ey form a p ubl ic la nd mobi le
12
GSM Network Architecture
13
GSM Architecture contd..,
MS – Mobile Station GSM-PLMN contains as many MSs as possible, available in various styles and power classes. In particular, the handheld and portable stations need to be distinguished. SIM-Subscriber Identity Module Identity of the subscriber =/= Identity of the mobile equipment. SIM provides portability to the subscriber. 14
GSM Architecture contd..,
SIM determines the directory number and the calls billed to a subscriber. SIM is a database on the user side. It consists of a chip, which the user must insert into the GSM telephone before it can be used. SIM communicates directly with the VLR and indirectly with the HLR. 15
GSM Architecture contd..,
BTS - Base Transceiver Station A large number of BTSs take care of the radio-related tasks and provide the connectivity between the network and the mobile station via the Air-interface. BSC- Base Station Controller The BTSs of an area are connected to the BSC via an interface called the Abis-interface. 16
GSM Architecture contd..,
BSC takes care of all the central functions and the control of the subsystem, referred to as the base station subsystem (BSS). The BSS comprises the BSC itself and the connected BTSs.
17
GSM Architecture contd..,
TR AU (T rans coding Ra te an d Ad ap tat io n Unit ): One of the most important aspects of mobile network is the effectiveness with which it uses the available frequency resources. Effectiveness addresses how many calls can be made by using a certain bandwidth which in turn translates in to -Necessity to compress data, at least over the Air-interface. Information compression is performed in both the MS and the TRAU.
18
GSM Architecture contd.., MSC (Mobi le Sw it ching Cent er)
MSC is similar to wireline Digital exchange A large number of BSCs are connected to the MSC via the A-interface. Major tasks of an MSC is: Routing of incoming and outgoing calls
19
GSM Architecture contd..,
HLR (Hom e Loc atio n Re gi st er) : A repository that stores the data of a large number of subscribers. An HLR can be regarded as a large database that administers the data of literally hundreds of thousands of subscribers. Every PLMN requires at least one HLR. 20
VLR (Visitor Location Register)
The Visitor Location Register (VLR) is a database containing information about all MSs that currently are located in the MSC service area. The VLR contains temporary subscriber information needed by the MSC to provide service for visiting subscribers. VLR is always integrated with MSC in a GSM network. The VLR can be seen as a distributed HLR. 21
VLR contd..,
VLR area = MSC area When a Mobile Station (MS) roams into a new MSC service area, the VLR connected to that MSC requests data about the MS from the HLR and stores it. When the MS makes a call, the VLR already has the information needed for call set-up. So in this way the no of queries made to HLR is reduced and there by reducing the load. 22
EIR (Eq uip me nt Ide nti ty Regi st er) GSM terminal equipment unique identifier is International mobile equipment identity (IMEI). EIR keeps track of IMEI of all the subscribers.
23
Signaling and Payload
Intercommunication between nodes and databases. Different signaling protocols between different subsystems. Out of Band signaling. 24
PCM
The A/D conversion is performed by using a process called Pulse Code Modulation (PCM). PCM involves three main steps: Sampling Quantization Coding
25
Step1: Sampling
Sampling involves measuring the analog signal at specific time intervals.
The accuracy of describing the analog signal in digital terms depends on how often the analog signal is sampled. This is expressed as the sampling frequency.
26
Step2: Quantization
The next step is to give each sample a value. For this reason, the amplitude of the signal at the time of sampling is measured and approximated to one of a finite set of values.
27
Step 3: Coding
Coding involves converting the quantized values into binary. Every value is represented by a binary code.
28
Pulse Code Modulation -PCM Pulse code modulation (PCM) is the worldwide process for transmission of digital signals. PCM is used to transmit both signaling data and payload. PCM is categorized into hierarchies, depending on the transmission rate.
29
Consider a 2Mbps PCM link be partitioned in 32 independent channels of 64kbps each One 64-Kbps time slot out of a 2-Mbps PCM link typically is used for signaling data A call setup consumes about 1 to 2 Kbps. 30
Block diagram of MOBILE Station
31
Subscriber Identity Module (SIM)
SIM is a microchip Except for emergency calls, a GSM mobile phone cannot be used without the SIM. In GSM terminology, the term MS refers to the combination of a SIM and an ME.
32
SIM
33
SIM contd..,
The SIM stores three types of subscriber related information: Fixed data stored before the subscription is sold: e.g. IMSI, authentication key and security algorithms Temporary network data: e.g. the location area of the subscriber and forbidden PLMNs Service data: e.g. language preference etc.., 34
SIM contd..,
A SIM contains information for GSM network operations. This information can be related to the mobile subscriber, GSM services or PLMN. The data storage requirements of a SIM are divided into two categories: mandatory and optional. 35
SIM as Database
The major task of a SIM is to store data. The SIM has an area of non-volatile memory which is used to store information specific to a particular subscriber and this includes the subscriber’s unique international mobile subscriber identity (IMSI) number. This number is used to identify each individual subscriber within the GSM network. 36
SIM contd..,
The SIM will also contain the subscriber’s secret authentication key, Ki, the authentication algorithm, A3, and the cipher key generation algorithm, A8. The language preference indicator is also located in the SIM and this is used to indicate the language to be used on the MS screen. The items described above are mandatory and must be present in any SIM that conforms to the GSM specifications. 37
SIM contd..,
The SIM may also contain a number of optional items which will include the subscriber’s abbreviated dialling numbers. The SIM may also contain a list of the last number(s) that the subscriber has dialled and an area of storage for the subscriber’s short messages. Inserting an SIM card into an ME effectively personalises the equipment to the particular subscriber. 38
Info stored on SIM – Administrative data PIN
Mandatory /changeable
Personal identification number; requested at every powerup (PIN or PIN2
PUK
Mandatory /fixed value
PIN unblocking key; required to unlock a SIM
SIM service table
Mandatory /fixed value
List of the optional functionality of the SIM
Last dialed number
Optional /changeable
Redial
Charging meter
Optional /changeable
Charges and time increments can be set
Language
Mandatory /changeable
Determines the language for prompts by the mobile station 39
Security related data Algorithm A3 and A8
Mandatory /fixed value Required for authentication and to determine Kc
Key Ki
Mandatory /fixed value Individual value; known only on SIM and the HLR
Key Kc
Mandatory /fixed value Result of A8, Ki, and random number (RAND)
CKSN
Optional /changeable value
Ciphering key sequence number 40
Subscriber Data IMSI
Mandatory /fixed value International mobile subscriber identity
MSISDN
Optional /fixed value
Mobile subscriber ISDN; directory number of a subscriber
41
Roaming Data TMSI
Mandatory / changeable value
Temporary mobile subscriber identity
LAI
Mandatory /changeable value
Location area information
Network color codes (NCCs) of restricted PLMNs
Mandatory /changeable
Maximum of 4 PLMNs can be entered on a SIM after unsuccessful location update; cause “PLMN not allowed.” Oldest entry deleted when more than 4 restricted PLMNs are found.
NCCs of preferred PLMNs
Optional / changeable
What PLMN should the MS select, if there is more than one to choose from and the home PLMN is not available?
42
PLMN data NCC, mobile country code (MCC), and mobile network code (MNC) of the home PLMN
Mandatory /Fixed
Network identifier
Absolute radio frequency channel numbers (ARFCNs) of home PLMN
Mandatory /Fixed
Frequencies for which the home PLMN is licensed.
43
Mobile Station characteristics
Technical Marvel
Falling Prices Availability of different devices Interaction with BTS Channel negotiation ,modulation/demodulation and coding/decoding functionality Efficient use of battery power Communicates directly with MSC and VLR as well via MM (mobility management) and CC (call control)
44
Mobile Station Classes
Different types of MSs have different output power capabilities and therefore different ranges. Hand-held phones generally have a lower output power and consequently a shorter range than a vehicle-mounted phone. According to GSM specifications, MSs are categorized into five classes according to MS output power. 45
MS Power Classes
46
Mobile Station Classes contd..,
The location of the MS also affects the received power of the transmitted signal. An MS located at the top of a high building has a greater range than one that is located at or below ground level.
47
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