Module 2_ GSM Mobile services.pptx

Module 2:
GSM Mobile services
CSC603.1: To identify basic concepts and principles in
computing, cellular architecture.

INSTRUCTIONS
All are instructed to maintain discipline throughout the
lecture.
If any student has any query, “raise hand”
At the end of the session,give your attendance on cymsys.
Rizvi College of
Start-up & Incubation

CONTENTS
● GSM Mobile services
○ System Architecture
○ Radio interface
○ Protocols
○ Localization and
Calling
○ Handover
○ Security (A3, A5 &
A8)
● GPRS system and protocol
architecture
● UTRAN, UMTS core network
● Improvements on Core
Network

Cellular System Infrastructure
● Early wireless systems had a high-power transmitter, covering the entire service area.
● This required a very huge amount of power and was not suitable for many practical reasons.
● The cellular system replaced a large zone with a number of smaller hexagonal cells with a single BS
(base station) covering a fraction of the area.

● In a cellular structure, a MS (mobile station) needs to communicate with the BS of
the cell where the MS is currently located and the BS acts as a gateway to the rest
of the world.
● Therefore, to provide a link, the MS needs to be in the area of one of the cells (and
hence a BS) so that mobility of the MS can be supported.
● Several base stations are connected through hard-wires and are controlled by a BS
controller (BSC), which in turn is connected to a mobile switching center (MSC).
● Several mobile switching centers are interconnected to a PSTN (public switched
telephone network) and the ATM (asynchronous transfer mode) backbone. To
provide a better perspective of wireless communication technology, simplified
system infrastructure for cellular system is shown in the figure:

● A BS consists of a base transceiver system (BTS) and a BSC. Both tower and antenna are a part of the
BTS, while all associated electronics are contained in the BSC.
● The HLR (home location register) and VLR (visitor location register) are two sets of pointers that
support mobility and enable the use of the same telephone numbers worldwide.
● The AUC (authentication center) unit provides authentication and encryption parameters that verify
the user's identity and ensure the confidentiality of each cell.
● The EIR (equipment identity register) is a database that information about identity of mobile
equipment. Both AUC and EIR can be implemented as individual stand-alone units or as a combined
AUC/EIR unit.
● The HLR is located at the MSC where MS is initially registered and is the initial home location for
billing and access information.
● In simple words, any incoming call, based on the calling number, is directed to the HLR of the home
MS where the MS is registered. The HLR then points to the VLR of the MSC where the MS is
currently located.

● The VLR contains information about all MS visiting that particular MSC and
hence points to the HLR of the visiting MSs for exchanging related
information about the MS.
● Such a pointer allows calls to be routed or rerouted to the MS, wherever it is
located. In cellular systems, a reverse direction pointer is needed that allows
traversal of many control signals back and forth between the HLR and VLR
such bidirectional HLR-VLR pointers help in carrying out various
functionalities.

Cellular Networks: Recap
• Radio Spectrum
– Spectrum = media used by wireless, a.k.a ‘Air Interface’
– Each network is assigned radio spectrum
– Spectrum assigned to users for data channels
– Spectrum may be licensed by international agreement
• Cellular Concept
– Divide the spectrum by physical area, i.e. ‘cell’
– Spectrum Reuse through non-interfering cells
– Can be split on many levels
• Picocells, Microcells, Macrocells, Satellite cells

The cellular system: cell structure
• Channel allocation: Implements space division multiplexing (SDM) –
frequency reuse
– base station covers a certain transmission area (cell)
– Cellular concept: channel reuse across the network prevents interference, improves the
likelihood of a good signal in each cell
• Mobile stations communicate only via the base station
• Advantages of cell structures
– higher capacity, higher number of users
– less transmission power needed
– more robust, decentralized
– base station deals with interference, transmission area etc. locally
• Problems
– Expensive
– fixed network needed for the base stations
– handover (changing from one cell to another) necessary
– interference with other cells
f4
f3
f5
f1
f2
f3
f6
f7
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f4
f5
f1

Cellular Networks
• Operation
– Initialisation: when handset is turned on it selects a
channel and connects to the switch
– Paging: switch must locate a mobile by broadcasting
requests from base stations
– Handoff: switches must be able to move calls between cells
when mobile moves
– Blocking/Dropping: calls may be blocked or dropped if
conditions in a cell change
– Interworking: calls may be placed to other networks or may
allow users to roam into other networks

GSM: Overview
• GSM
– formerly: Groupe Spéciale Mobile (founded 1982)
– now: Global System for Mobile Communication
– Pan-European standard (ETSI, European Telecommunications Standardisation
Institute)
– Aim : to replace the incompatible analog system
– simultaneous introduction of essential services in three phases (1991, 1994, 1996) by
the European telecommunication administrations
□ seamless roaming within Europe possible
• Today many providers all over the world use GSM
(219 countries in Asia, Africa, Europe, Australia, America)
– more than 4,2 billion subscribers in more than 700 networks
– more than 75% of all digital mobile phones use GSM
– over 29 billion SMS in Germany in 2008, (> 10% of the revenues for many operators)
[be aware: these are only rough numbers…]
– See e.g. www.gsmworld.com/newsroom/market-data/index.htm

Characteristics of GSM Standard
• Fully digital system using 900,1800 MHz frequency band
(in US 1900 MHz).
• TDMA over radio carriers(200 KHz carrier spacing.
• User/terminal authentication for fraud control.
• Encryption of speech and data transmission over the radio
path.
• Full international roaming capability.
• Low speed data services (upto 9.6 Kb/s).
• Compatibility with ISDN.
• Support of Short Message Service (SMS).

Advantages of GSM over Analog system
• Capacity increases
• Reduced RF transmission power and longer battery
life.
• International roaming capability.
• Better security against fraud (through
terminal validation and user authentication).
• Encryption capability for information security
and privacy.
• Compatibility with ISDN, leading to wider range
of services

Performance characteristics of GSM (wrt. analog sys.)
• Communication
– mobile, wireless communication; support for voice and data services
• Total mobility
– international access, chip-card enables use of access points of different providers
• Worldwide connectivity
– one number, the network handles localization
• High capacity
– better frequency efficiency, smaller cells, more customers per cell
• High transmission quality
– high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g.,
from cars, trains)
• Security functions
– access control, authentication via chip-card and PIN

Disadvantages of GSM
• There is no perfect system!!
– no end-to-end encryption of user data
– no full ISDN bandwidth of 64 kbit/s to the user
• reduced concentration while driving
• electromagnetic radiation
• abuse of private data possible
• roaming profiles accessible
• high complexity of the system
• several incompatibilities within the GSM
standards

GSM Specifications-1
• RF Spectrum
GSM 900
Mobile to BTS (uplink):
890-915 Mhz
BTS to Mobile(downlink):935-960 Mhz
Bandwidth : 2* 25 Mhz
GSM 1800
Mobile to BTS (uplink): 1710-1785 Mhz BTS to
Mobile(downlink) 1805-1880 Mhz Bandwidth : 2* 75
Mhz

GSM Specification-II
• Carrier Separation
• Duplex Distance
• No. of RF carriers
• Access Method
: 200 Khz
: 45 Mhz
: 124
: TDMA/FDMA
• Modulation Method : GMSK (Gaussian Minimum Shift Keying – PSK)
• Modulation data rate : 270.833 Kbps

Global System for Mobile Communications (GSM)
The GSM framework is made up of three primary linked subsystems.
They are as follows:
1) Base station subsystem (BSS)
2) Network and switching subsystems
3) Operation support subsystem (OSS).
Through specific network interfaces, the subsystems communicated with one another
and with the users.

Global System for Mobile Communications (GSM)

Interface in Global System for Mobile Communications (GSM)

Interface in Global System for Mobile Communications (GSM)
● The interface that links a BTS to a BSC is known as the Abis interface.
● GSM has standardised the Abis interface for all manufacturers, which transfers traffic and
maintenance data.
● BTS and BSC equipment from the same vendor might be used to minimise small differences.
● Physically, the BSCs are interconnected to the MSC through dedicated/leased lines or a
microwave link.
● The A interface, which is specified within GSM, is the interface between a BSC and an MSC.
● The A-interface employs the signalling correction control portion (SCCP) of the SS7 protocol.
● It allows for communication between the MSC and the BSS, as well as network
communications between individual subscribers and the MSC.

GSM PROTOCOLS
GSM architecture is a layered model that is designed to allow communications between two different systems. The
lower layers assure the services of the upper-layer protocols. Each layer passes suitable notifications to ensure the
transmitted data has been formatted, transmitted, and received accurately.
MS Protocols:
The signaling protocol in GSM is structured into three general layers, depending on the interface.
Layer 1: The physical layer, which uses the channel structures over the air interface.
Layer 2: The data-link layer. Across the Um interface, the data-link layer is a modified version of the Link access protocol for
the D channel (LAP-D) protocol used in ISDN, called Link access protocol on the Dm channel (LAP-Dm). Across the A
interface, the Message Transfer Part (MTP), Layer 2 of SS7 is used.
Layer 3: The third layer of the GSM signaling protocol is divided into three sublayers:
1. Radio Resource management (RR)
2. Mobility Management (MM) and
3. Connection Management (CM).

GSM PROTOCOLS
The MS to BTS Protocols:
The RR layer oversees the establishment of a link, both radio and fixed, between the MS and the MSC. The main functional
components involved are the MS, the BSS, and the MSC. The RR layer is concerned with the management of an RR-
session, which is the time that a mobile is in dedicated mode, as well as the configuration of radio channels, including the
allocation of dedicated channels.
The MM layer is built on top of the RR layer and handles the functions that arise from the mobility of the subscriber, as well
as the authentication and security aspects. Location management is concerned with the procedures that enable the system
to know the current location of a powered-on MS so that incoming call routing can be completed.
The CM layer is responsible for CC, supplementary service management, and Short Message Service (SMS) management.
Each of these may be considered as a separate sub-layer within the CM layer. Other functions of the CC sub-layer include
call establishment, selection of the type of service (including alternating between services during a call), and call release.

GSM PROTOCOLS
BSC Protocols:
After the information is passed from the BTS to the BSC, a different set of interfaces is used. The Abis interface is used
between the BTS and BSC. At this level, the radio resources at the lower portion of Layer 3 are changed from the RR to the
Base Transceiver Station Management (BTSM). The BTS management layer is a relay function at the BTS to the BSC.
The RR protocols are responsible for the allocation and reallocation of traffic channels between the MS and the BTS. These
services include controlling the initial access to the system, paging for MT calls, thehandover of calls between cell sites,
power control, and call termination. The RR protocols provide the procedures for the use, allocation, reallocation, and
release of the GSM channels. The BSC still has some radio resource management in place for the frequency coordination,
frequency allocation, and the management of the overall network layer for the Layer 2 interfaces.
From the BSC, the relay is using SS7 protocols so the MTP 1-3 is used as the underlying architecture, and the BSS mobile
application part or the direct application part is used to communicate from the BSC to the MSC.

GSM PROTOCOLS
MSC Protocols:
At the MSC, the information is mapped across the A interface to the MTP Layers 1 through 3 from the BSC. Here, the
equivalent set of radio resources is called the BSS MAP. The BSS MAP/DTAP and the MM and CM are at the upper layers of
Layer 3 protocols. This completes the relay process. Through the control-signaling network, the MSCs interact to locate and
connect to users throughout the network. Location registers are included in the MSC databases to assist in the role of
determining how and whether connections are to be made to roaming users.
Each user of a GSM MS is assigned a HLR that is used to contain the user's location and subscribed services. A separate
register, the VLR, is used to track the location of a user. As the users roam out of the area covered by the HLR, the MS
notifies a new VLR of its whereabouts. The VLR in turn uses the control network (which happens to be based on SS7) to
signal the HLR of the MS's new location. Through this information, MT calls can be routed to the user by the location
information contained in the user's HLR.

Security in GSM
Security algorithms should be

Security in GSM - Access Control

Security in GSM- Authentication and Encryption

Security in GSM- Authentication

Security in GSM- Authentication
Steps in Authentication

General Packet Radio Service (GPRS)
● GPRS is a packet-switched radio service, established to provide higher data
rate compared to GSM.
● GSM focuses on voice service while GPRS concentrate on data transmission.
● GPRS is an extension to GSM, so it does not require special hardware, instead
it requires only software installations and can provide service on same
wireless network.
● GPRS also guarantee reliability and good QoS with the help of its protocol
stack.

General Packet Radio Service (GPRS)

Characteristics of GPRS
Packet switching operation:
● GPRS technology works with packet switching technique and is quite
advantageous compared to GSM which works on circuit switching technique.
● Packet switching is more efficient and can maximum utilize available capacity
of system as well it also allows high commonality in internet techniques.

Always-on connection:
● As GPRS works with packet switching technique, and in packet switching
charges are on the base of amount of data carried as it uses service provider’s
capacity.
● While in circuit switching technique, charges are calculated on the base of
time for which circuit is used or for the time of call.

Speed:
The main reason to establish GPRS is to provide higher data rate over GSM.
GPRS can provide data rate upto 172 kbps, which is quite higher compared to
GSM

Support more applications:
Always on characteristics and packet switching along with higher data rate allows
GPRS to work with many new applications.
One of the greatest advancement in GPRS is Blackberry form of PDA and mobile.

CAPEX and OPEX:
● Capital Expenditure (CAPEX) and Operational Expenditure (OPEX) are important
for GPRS as they are concerned with finance.
● As GPRS is an upgradation to GSM and mostly in the form of Software upgrade,
so it does not require dedicated networks and other resources.
● GPRS can easily operate and maintain remotely.
● Hence the capital expenditure for GPRS is not as high as newly setup network.
● Simultaneously, operational expenditure is also very low, as operators don’t have
to maintain networks separately it
● can be handled and managed remotely.
● Also the base – station infrastructure will be same so it will not affect OPEX

Quality of Service (QoS):
● GPRS guarantees good Quality of Service (QoS) based on high, normal and
low service precedence, reliability class and delay class of the transmission
and user data throughput.
● Reliability class is used for greater error tolerance, error-detection and error-
correction.
● While delay class is used for channel access delay, coding for error correction
and transfer delay in GPRS network.

Security:
● GPRS provides various security services like authentication, user identity
confidentiality, user information confidentiality and access control

GPRS System Architecture
GPRS system architecture contains 2 new elements, i.e., GSN (GPRS Support Nodes),
which are also known as routers, and SGSN (Serving GPRS Support Nodes).
GPRS architecture includes following important components:
● MS
● BSS
● GGSN
● SGSN
● MSC
● HLR / GR
● VLR
● EIR
● Interfaces

● Mobile Station (MS) comprises of users’ hardware and software to interact with GPRS
network.
● Base Station Subsystem (BSS) is responsible to maintain radio connection with MS and
coding / decoding of voice.
● Every BSS of network is controlled by Base Station Controller (BSC).
● BSS is connected with MS via Um interface.
● All GSNs are integrated with GSM architecture and new interfaces have been defined in GPRS
architecture.
● Gateway GPRS Support Node (GGSN) is an interworking component between external packet
data network (PDN) and GPRS network.
● GGSN maintains GPRS user’s routing information and also performs address conversions.
● GGSN is connected with PDN via Gi interface and transfer information in terms of packets via
Gn interface.
● SGSN is connected with MS and BSS via Gb interface while it is connected with other SGSN
through Gn interface.

● SGSN request Home Location Register (HLR) or GPRS Register (GR) to track
location of individual MS and collecting billing information.
● SGSN can request to Equipment Identity Register (EIR) for identification and
authentication related tasks.
● SGSN can also request to Visitor Location Register (VLR) via Mobile
Switching Center (MSC) for bilingual
● information if MS is not available in HLR.
● As displayed in figure , information in packet data format is transferred from
external network to MS via GGSN, SGSN and BSS respectively.
● In GPRS architecture, MSC is used for signaling process

GPRS Protocol Architecture
● As per the architecture stack, all data inside GPRS backbone is transferred
through GPRS Tunneling Protocol (GTP).
● GTP uses both protocols, either TCP – for reliable communication or UDP –
for non-reliable communication.
● Generally, TCP is used for transferring X.25 packets while UDP is used for IP
packets.
● To adapt different characteristics of underlying layers networks, Subnetwork
Dependent Convergence Protocol (SNDPC) is used between SGSN and MS.
● LLC protocol is used for higher reliability during packet transfer between
SGSN and MS.
● To provide routing and Quality of Service (QoS) related information, Base
Station Subsystem GPRS Protocol (BSSGP) is used between SGSN and BSS.

GPRS Protocol Architecture
● But BSSGP does not perform error-correction and it works on top of a frame
relay (FR) network.
● At last to transfer data to MS via Um interface, Radio Link Protocol (RLC) is
used.
● RLC provides a reliable link, while the MAC controls access with signaling
procedures for the radio channel and the mapping of LLC frames onto the
GSM physical channels

Features of GPRS
GPRS includes following important features:
● Short Message Service (SMS):
○ SMS is a special-purpose protocol designed for text message communication. SMS contains
upto 160 characters to transfer text message.
● Enhanced Message Service (EMS):
○ Enhanced Message Service offers larger message size compared to SMS, which contains 760
characters in single transaction of data transfer.
● Multimedia Message Service (MMS):
○ Multimedia Message Service allows transmission of multimedia contents like JPG, GIF and
short videos.
● Wireless Application Protocol (WAP):
○ Wireless Application Protocol is a special purpose communication protocol used for mobile
browsers.

Module 2_ GSM Mobile services.pptx

Module 2_ GSM Mobile services.pptx

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Module 2_ GSM Mobile services.pptx