INTRODUCTION TO

CELLULAR SYSTEMS
A cellular system is a wireless communication network
that allows mobile devices to communicate with each
other and with fixed infrastructure, such as base stations or
cell towers. The term "cellular" refers to the division of
the coverage area into small geographic regions called
cells. Each cell is served by a base station, and the overall
system is designed to provide seamless communication as
a user moves from one cell to another.
components and concepts of a cellular system

⚫ Cellular Architecture:
⚫ The cellular network divides a geographic area into cells, each served by a base station or cell tower.
⚫ Cells are organized in a pattern to maximize coverage and capacity while minimizing interference.
⚫ Base Stations:
⚫ Base stations are radio transmitters/receivers mounted on cell towers or other structures.
⚫ They provide wireless connectivity to mobile devices within their respective cells.
⚫ Frequency Reuse:
⚫ Cellular systems use the same frequency band in different cells, but cells are far enough apart to minimize interference.
⚫ This concept allows for efficient spectrum utilization and increased network capacity.
⚫ Handoff/Handover:
⚫ Handoff refers to the process where a mobile device transitions from one cell to another while maintaining an ongoing communication session.
⚫ This ensures continuous connectivity as users move within the network.
⚫ Mobile Switching Center (MSC):
⚫ MSC is a central component that connects calls, manages handoffs, and oversees the overall operation of the cellular network.
⚫ Cellular Generations:
⚫ Cellular systems evolve through generations, with each generation bringing improvements in data rates, capacity, and technology.
⚫ Examples include 2G (GSM), 3G (UMTS), 4G (LTE), and 5G, each offering advancements in speed, latency, and connectivity.
⚫ Mobile Data Services:
⚫ Beyond voice calls, cellular systems support various data services such as SMS, MMS, and mobile internet access.
⚫ High-speed data services have become increasingly important, enabling applications like video streaming, online gaming, and real-time
communication.
⚫ Roaming:
⚫ Roaming allows users to maintain connectivity when moving between different cellular networks, often in different geographical locations or
countries.
⚫ Security:
⚫ Cellular systems incorporate various security measures to protect user data and communications, including encryption and authentication
protocols.
⚫ Emerging Technologies (5G and Beyond):
⚫ 5G, the fifth generation of cellular technology, introduces ultra-fast data rates, low latency, and massive device connectivity.
⚫ Ongoing research explores beyond 5G technologies to further enhance mobile communication capabilities.
Frequency Reuse
⚫ Frequency reuse is a concept used in wireless communication systems to maximize the utilization of the
available radio frequency spectrum. The idea is to divide a geographical area into smaller cells, and then
reuse the same set of frequencies in different cells, taking advantage of the fact that signals attenuate over
distance. This allows for efficient use of the limited frequency spectrum and increases the capacity of the
overall communication system.
⚫ There are two main types of frequency reuse:
⚫ Fixed Frequency Reuse:
⚫ In fixed frequency reuse, a predetermined set of frequencies is assigned to cells in such a way that the same
frequencies are used in cells that are sufficiently far apart to avoid interference.
⚫ The most common method is to use a regular pattern, such as a hexagonal grid, where each cell uses a
frequency that is not reused in its immediate neighboring cells. This pattern ensures that interference is
minimized.
⚫ Dynamic Frequency Reuse:
⚫ Dynamic frequency reuse allows for a more flexible allocation of frequencies based on real-time demand and
traffic conditions.
⚫ The idea is to dynamically adjust the frequency assignments according to the changing traffic patterns in
different cells. Cells experiencing high demand can be allocated additional frequencies, while cells with lower
demand can share frequencies more effectively.
⚫ Dynamic frequency reuse requires advanced algorithms and monitoring systems to optimize frequency
assignments in real-time.
Frequency Reuse
GSM SERVICES
⚫ Voice Services:
⚫ Mobile Originated Call (MOC): The ability to make calls from a mobile phone.
⚫ Mobile Terminated Call (MTC): Receiving calls on a mobile phone.
⚫ Short Message Service (SMS):
⚫ Point-to-Point Messaging: Sending text messages from one mobile device to another.
⚫ Broadcast Messaging: Sending a message to multiple recipients simultaneously.
⚫ Supplementary Services:
⚫ Call Waiting: Notifying a user of an incoming call while they are already on a call.
⚫ Call Hold/Retrieve: Placing an active call on hold and retrieving it later.
⚫ Call Forwarding: Redirecting incoming calls to another number.
⚫ Conference Calling: Connecting multiple parties in a single call.
⚫ Caller ID: Displaying the phone number of the calling party.
⚫ Data Services:
⚫ General Packet Radio Service (GPRS): Providing packet-switched data services for mobile communication.
⚫ Short Message Service (SMS): Apart from text messages, GSM also supports the transmission of small amounts of data via SMS.
⚫ Emergency Services:
⚫ Emergency Number Dialing (e.g., 911): Allowing users to dial emergency services quickly.
⚫ International Roaming:
⚫ Roaming Services: Allowing users to use their mobile phones in different countries.
⚫ SIM (Subscriber Identity Module):
⚫ SIM Card Services: GSM networks use SIM cards to store user information, including contacts and authentication data.
⚫ Security Features:
⚫ Encryption: Ensuring the security of voice and data transmissions.
⚫ Cell Broadcast:
⚫ Broadcast of Messages to Multiple Users: Broadcasting messages to multiple users in a specific geographical area.
⚫ Multimedia Messaging Service (MMS):
⚫ Sending Multimedia Content: Sending messages with multimedia content such as pictures, videos, and audio.
⚫ USSD (Unstructured Supplementary Service Data):
⚫ Interactive Services: Providing interactive services, such as checking account balance or activating services, through a text-based menu.
GSM ARCHITECTURE
⚫ GSM stands for Global System for Mobile Communications. It is a standard
developed for the digital cellular networks used in mobile phones. GSM was first
introduced in the 1980s as a replacement for the older analog mobile networks. It
set the foundation for the 2G (second generation) mobile communication system.
GSM architecture can be divided into three main components:
⚫ 1. Mobile Station (MS)
⚫ 2.Base Station Subsystem (BSS)
⚫ 3.Network Subsystem (NSS)
MOBILE STATION (MS)
⚫ The MS is the mobile device used by the end-user, such as a mobile phone or a
GSM-enabled device.
⚫ It consists of two main components: the Mobile Equipment (ME), which includes
the physical device like the phone or modem, and the Subscriber Identity Module
(SIM), which contains information specific to the user, such as the International
Mobile Subscriber Identity (IMSI).
BASE STATION SUBSYSTEM
(BSS)
⚫ The BSS is responsible for the radio communication with the
mobile device.
⚫ It comprises two main components: Base Transceiver Station
(BTS) and Base Station Controller (BSC).
⚫ Base Transceiver Station (BTS): This component is responsible
for handling the radio communication with the mobile device. It
manages the radio frequency functions, such as modulation,
demodulation, and transmission power control.
⚫ Base Station Controller (BSC): The BSC manages one or more
BTS units. It handles call setup, frequency hopping, handovers,
and other tasks related to radio resource management.
NETWORK SUBSYSTEM (NSS)
⚫ The NSS is responsible for the overall network operation and management.
⚫ It comprises three main components: Mobile Switching Center (MSC), Home Location Register (HLR),
and Visitor Location Register (VLR).
⚫ Mobile Switching Center (MSC): The MSC is the central component that performs the call switching
functions, connecting calls within the network or to external networks.
⚫ Home Location Register (HLR): The HLR is a database that stores subscriber information, including
subscriber profiles and current locations. It is a permanent database used for authentication and call routing.
⚫ Visitor Location Register (VLR): The VLR is a temporary database that stores information about
subscribers currently within the jurisdiction of the MSC that it serves. It communicates with the HLR to
obtain necessary information about the subscriber.
⚫ Authentication Center (AUC):
⚫ The AUC is responsible for providing authentication and encryption parameters to mobile devices (such as
mobile phones) and the network.
⚫ When a mobile device attempts to connect to the network, the AUC verifies the user's identity by
challenging the device to provide a valid authentication key. This process helps prevent unauthorized
access and protects against various security threats, including identity theft and eavesdropping.
⚫ Equipment Identity Register:- The EIR contributes to the overall security of the mobile network by
ensuring that only legitimate and approved mobile devices are allowed to connect. Unauthorized devices,
such as those with modified or fake IMEI (International Mobile Equipment Identity) numbers, can be
detected and blocked
GSM ARCHITECTURE
 GSM protocols
⚫ The GSM (Global System for Mobile Communications) protocol stack consists of seven layers, similar
to the OSI (Open Systems Interconnection) model. Here's an explanation of each layer in the GSM
protocol stack:
⚫ Physical Layer (Layer 1):
⚫ Function: This layer deals with the physical transmission of raw binary data over the air interface.
⚫ Key Elements: Radio waves, modulation, transmission power, frequency bands, and physical
connection interfaces (like cables).
⚫ Data Link Layer (Layer 2):
⚫ Function: Responsible for error detection and correction, as well as organizing bits into frames for
reliable transmission.
⚫ Key Elements: Frame structure, error detection mechanisms, synchronization, and Logical Link Control
(LLC).
⚫ Network Layer (Layer 3):
⚫ Function: Handles routing, addressing, and logical connections between network entities.
⚫ Key Elements: Network topology, addressing (e.g., Mobile Station ISDN (Integrated services Digital
Network “ set of communication standards to transmit data voice and signaling”)Number,
MSISDN(Mobile Station International Subscriber Directory Number ” We use to identify a phone
number”)), and routing protocols.
⚫ Transport Layer (Layer 4):
⚫ Function: Ensures end-to-end communication, segmentation, and reassembly of messages.
⚫ Key Elements: Segmentation, flow control, and error recovery.
 GSM protocols
⚫ Session Layer (Layer 5):
⚫ Function: Manages sessions or connections between applications on different devices.
⚫ Key Elements: Session establishment, maintenance, and termination.
⚫ Presentation Layer (Layer 6):
⚫ Function: Responsible for data translation, encryption, and compression to ensure
compatibility between different systems.
⚫ Key Elements: Data encryption, data compression, and data format conversion.
⚫ Application Layer (Layer 7):
⚫ Function: Provides network services directly to end-users or applications.
⚫ Key Elements: User interfaces, application protocols (e.g., Short Message Service or
SMS), and end-user services.
⚫ In the GSM context, the layers are often combined into three main groups:
⚫ Um (User Mobile) Interface (Air Interface): Combines Physical, Data Link, and part of
the Network Layer.
⚫ Abis Interface: Combines Network Layer (partially), Transport Layer, Session Layer, and
Presentation Layer.
⚫ A (Access) Interface: Encompasses the remaining part of the Network Layer, Transport Layer,
Session Layer, Presentation Layer, and the Application Layer.
GSM protocols architecture
GSM protocols
⚫ Layer 1 − The physical layer. It 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, (Integrated Services
Digital Network)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 − GSM signalling protocol’s third layer is divided into three
sublayers −
⚫ Radio Resource Management (RR),
⚫ Mobility Management (MM), and
⚫ Connection Management (CM).
GSM protocols architecture
OSI REFERENCE MODEL
GSM Connection Establishment
⚫ The Global System for Mobile Communications (GSM) is a widely used standard for mobile
communication. The process of GSM connection establishment involves several steps to ensure a secure and
reliable connection between a mobile device and the GSM network. Here is an overview of the key steps in
GSM connection establishment:
⚫ Powering On the Mobile Device:
⚫ When you turn on your mobile device, it goes through an initialization process, and the GSM module within the device is activated.
⚫ Registration with the Network:
⚫ The mobile device searches for available GSM networks and registers with the network that provides the strongest signal. This
process is known as cell selection and cell reselection.
⚫ Authentication:
⚫ After registering with the network, the mobile device undergoes a process of authentication. The SIM card in the device and the
network authenticate each other to ensure that the device is authorized to use the network.
⚫ Ciphering:
⚫ Once authentication is successful, ciphering (encryption) is activated to secure the communication between the mobile device and
the network. This helps prevent unauthorized access to the user's communication.
⚫ Location Update:
⚫ The mobile device periodically updates its location with the network. This information is crucial for call routing and other
network-related functions.
⚫ Call Setup:
⚫ When a user initiates a call, the mobile device sends a request to the network to set up the call. The network determines the
appropriate resources and establishes the connection.
⚫ Handover (Optional):
⚫ During an ongoing call, if the mobile device moves from one cell to another, a handover may occur. Handover ensures that the call
remains connected as the device transitions between different cells.
⚫ Call Release:
⚫ When the call is complete or terminated, the mobile device and the network release the allocated resources, and the connection is
terminated.
GSM CONNECTION
ESTABLISHMENT TYPES
In GSM (Global System for Mobile Communications), there are several types of connections that can be established to facilitate various
communication services. Here are the primary GSM connection establishment types:
⚫ Mobile-Originated Call (MOC):
⚫ This type of connection is initiated by the mobile station (MS), i.e., the mobile phone user. When a user dials a phone number and
initiates a call, the GSM network goes through the process of call setup to establish a connection with the called party.
⚫ Mobile-Terminated Call (MTC):
⚫ In this scenario, the call is initiated by someone else to the mobile user. When an incoming call is received, the GSM network
establishes a connection to the mobile station to allow the user to answer the call.
⚫ In the context of telecommunications, "Mobile-Terminated Call" (MTC) refers to a call that is terminated at the mobile device. In
other words, it is a call that is received by the mobile user. The term "terminated" here does not imply the end of the call but
rather indicates that the call is reaching its destination, which is the mobile device.
⚫ So, in the case of an MTC, "terminated" means that the call is being received by the mobile user, allowing them to answer and
engage in the conversation

⚫ Mobile-Originated SMS (MOSMS):

⚫ Mobile-originated Short Message Service (SMS) refers to text messages sent by the mobile user. When a user composes and sends
an SMS, the GSM network is involved in establishing the connection to deliver the message.
⚫ Mobile-Terminated SMS (MTSMS):
⚫ Mobile-terminated SMS refers to text messages sent to the mobile user. When someone sends an SMS to a mobile user, the GSM
network facilitates the delivery of the message to the recipient's mobile station.
⚫ Mobile-Originated Packet Data (MO-PD):
⚫ With the advent of GPRS (General Packet Radio Service) and later technologies like EDGE (Enhanced Data rates for GSM
Evolution), mobile users can initiate packet data connections. These connections are used for data services such as internet browsing
or email.
⚫ Mobile-Terminated Packet Data (MT-PD):
⚫ Packet data connections can also be initiated by external entities, such as servers or other mobile users, to send data to the mobile
station.
⚫ Supplementary Services:
⚫ GSM supports various supplementary services like call waiting, call forwarding, conference calling, and others. The establishment
of connections related to these services involves specific signaling procedures within the GSM network.
Mobile-Originated Call (MOC)
Mobile-Terminated Call (MTC)
GSM CALL FLOW
Random Access Channel Channel Assignment Module

Access Grant Channel

Standalone Dedicated Control

Channel

Traffic Control
Channel
GSM Frequency Allocation
⚫ GSM Frequency Allocation.
⚫ GSM (Global System for Mobile Communications) is a standard developed to ensure
compatibility and interoperability for mobile communications. GSM operates in various
frequency bands, and the frequency allocation depends on the region and country. The primary
frequency bands for GSM are:
⚫ GSM 900 MHz Band:
⚫ Uplink (Mobile to Base Station): 890-915 MHz
⚫ Downlink (Base Station to Mobile): 935-960 MHz
⚫ DCS(Digital Cellular System) 1800 MHz Band (GSM 1800 MHz or GSM 1.8 GHz):
⚫ Uplink: 1710-1785 MHz
⚫ Downlink: 1805-1880 MHz
⚫ PCS (Personal Communications Service)1900 MHz Band (GSM 1900MHz or GSM 1.9 GHz):
⚫ Uplink: 1850-1910 MHz
⚫ Downlink: 1930-1990 MHz
⚫ These frequency bands are divided into carrier frequencies, and each carrier frequency is further
divided into timeslots to allow multiple users to share the same frequency channel through
Time Division Multiple Access (TDMA). GSM uses a combination of Frequency Division
Multiple Access (FDMA) and TDMA to maximize the utilization of available frequency
spectrum.
GSM Routing
GSM (Global System for Mobile Communications) routing refers to the process of directing voice and data
traffic within a GSM network. GSM is a standard for mobile communication used by a majority of the
world's mobile phones. The network consists of various components, and routing plays a crucial role in
ensuring that calls and data are efficiently and accurately directed to their intended destinations.
⚫ Here are some key aspects of GSM routing:
⚫ Base Station Subsystem (BSS): The BSS is responsible for the radio communication with mobile devices. It
includes Base Transceiver Stations (BTS) and Base Station Controllers (BSC). The BSS manages the radio
resources and helps in routing calls between mobile devices.
⚫ Mobile Switching Center (MSC): The MSC is a core component of the GSM network that performs the
task of call routing and mobility management. It connects calls, handles signaling, and manages the handover
of mobile devices between different cells.
⚫ Home Location Register (HLR): The HLR is a database that stores subscriber information and details
about their current location in the network. When a call is initiated, the HLR is consulted to determine the
current location of the called party.
⚫ Visitor Location Register (VLR): The VLR is a temporary database that stores information about
subscribers who are currently within the jurisdiction of the MSC served by the VLR. It helps in the routing
of calls within the visited area.
⚫ Gateway Mobile Switching Center (GMSC): The GMSC is responsible for routing calls to other networks.
When a call is made to a subscriber in a different network, the GMSC connects to the appropriate MSC in
that network.
⚫ Intelligent Network (IN): IN is a set of network components and protocols that enable the delivery of
value-added services, such as call forwarding, call waiting, and prepaid billing. IN plays a role in the routing
of calls based on these additional services.
GSM Mobility Management
GSM (Global System for Mobile Communications) Mobility Management is a crucial aspect of cellular networks that ensures seamless
communication for mobile devices as they move across different geographical areas. Mobility management allows a mobile user to
maintain connectivity and access services while on the move. Here are the key components of GSM Mobility Management:
⚫ Location Area (LA):
⚫ GSM networks are divided into Location Areas, which consist of multiple cells. A Location Area is a group of cells that are grouped together
logically. When a mobile device moves from one cell to another within the same Location Area, there is no need to update the network about the

change in location . (SS7 Signaling System 7) signaling protocols .

⚫ Cell Update:
⚫ When a mobile device moves from one Location Area to another, it needs to perform a Cell Update. The mobile device informs the network
about its new location by updating the relevant location information, such as the new cell and Location Area. This process ensures that the
network can route calls and messages to the mobile device correctly.
⚫ Location Update:
⚫ A Location Update occurs when a mobile device enters a new Location Area. The device sends a Location Update message to the network,
providing information about its new location. This update is necessary to keep the network informed about the current location of the mobile
device.
⚫ GSM Registration:
⚫ Mobile devices need to register with the GSM network when they are powered on or when they enter a new network area. Registration involves
identifying the mobile device to the network and updating its location information.
⚫ Authentication and Security:
⚫ GSM networks employ authentication and encryption mechanisms to ensure the security of communication between the mobile device and the
network. The mobile device must be authenticated before it can access network services.
⚫ Handover:
⚫ Handover, also known as handoff, occurs when a mobile device moves from one cell to another while in the middle of a call. The network
seamlessly transfers the call from the current cell to the new cell without interrupting the call quality.
⚫ Roaming:
⚫ Roaming enables a mobile device to use network services outside its home network. When a mobile device roams into a foreign network, the
visited network communicates with the home network to ensure service continuity for the roaming subscriber.
⚫ Routing and Paging: (When someone tries to reach a mobile user, the network initiates a paging procedure to locate and alert the intended recipient)
⚫ The network must know the location of a mobile device to route calls and messages to it. Paging is the process by which the network locates a
mobile device when there is an incoming call or message.
GSM Security
⚫ GSM (Global System for Mobile Communications) is a widely used standard for cellular networks. It is the technology used for 2G and
3G mobile phone systems. While GSM has been a prevalent and successful technology, it does have some security vulnerabilities. Here
are some key aspects of GSM security:
⚫ Encryption:
⚫ A5 Algorithms: GSM initially used the A5/1 (symmetric cipher used for encrypting over- the-air transmissions in the GSM standar ) d.

encryption algorithm, which was later supplemented by A5/2. A5/1, however, has been found to be vulnerable to certain attacks, and A5/2 is
considered even weaker. In response, A5/3, a stronger encryption algorithm, was introduced in 3G networks.
⚫ Authentication:
⚫ SIM Cards: Subscriber Identity Module (SIM) cards are used for user authentication. The SIM card contains a secret key that is used to
authenticate the user to the network (0x8FE8A2CD7F5B9D1C2E3A4F6B5C7D8E9F). However, there have been instances of attacks on SIM
cards, such as the "SIM card cloning" technique.
⚫ Man-in-the-Middle Attacks:
⚫ Interception: GSM communications can be intercepted by attackers using devices known as IMSI (International Mobile Subscriber Identity)
catchers or "Stingrays”. (These are devices used for mobile phone tracking and interception) These devices mimic legitimate cell towers, tricking
mobile devices into connecting to them. Once connected, the attacker can intercept and eavesdrop on communications.
⚫ Location Tracking:
⚫ Triangulation: The location of a GSM device can be determined through triangulation using multiple cell towers. While this is a standard and
legitimate practice for network management, it raises privacy concerns, as an attacker could potentially exploit this for tracking purposes.
⚫ SMS Interception:
⚫ Vulnerability to SMS Interception: SMS messages sent over GSM networks are not encrypted, and they can be intercepted using various
techniques. This lack of encryption makes SMS communication vulnerable to eavesdropping.
⚫ Denial of Service (DoS) Attacks:
⚫ Jamming: GSM networks can be vulnerable to jamming attacks, where an attacker floods the network with interference, disrupting
communication between mobile devices and the network.
⚫ Weaknesses in Implementation:
⚫ Implementation Flaws: The security of GSM also depends on the implementation of the technology by mobile operators. Weaknesses in the
implementation of protocols and standards can introduce vulnerabilities.
⚫ Evolution and Improvements:
⚫ 3G and 4G Security: While 2G GSM networks had certain vulnerabilities, later generations of mobile networks, such as 3G and 4G, have
introduced improvements in terms of encryption and security protocols. 4G networks, in particular, have enhanced security features.
⚫ Future Concerns:
⚫ 5G Security: With the deployment of 5G networks, new security challenges and considerations emerge. While 5G incorporates advanced
security features, the increased complexity and connectivity also bring new potential vulnerabilities that need to be addressed.
GSM Security architecture

Integrated Services Digital Network

public data network

Serving GPRS Support Node
(SGSN)
⚫ SGSN stands for Serving GPRS Support Node, which is a critical component in a mobile network
infrastructure. It plays a key role in the packet-switched domain of GSM (Global System for Mobile
Communications) and UMTS (Universal Mobile Telecommunications System) networks. Here are some key
points about SGSN:
⚫ Functionality: The SGSN is responsible for managing and controlling the data sessions for mobile devices
within its coverage area. It handles the packet-switched data traffic, such as internet browsing, email, and
other data services.
⚫ Location Tracking: SGSN is involved in tracking the location of mobile devices within the network. It
helps in maintaining the mobility of devices as they move across different cells and tracking their current
location.
⚫ Session Management: SGSN establishes and maintains the data sessions for mobile devices, ensuring that
the devices can send and receive data efficiently. It also handles the activation and deactivation of packet
data connections.
⚫ Security: SGSN plays a crucial role in ensuring the security of data transmissions over the network. It
implements various security protocols and mechanisms to protect user data and privacy.
⚫ Interworking: SGSN facilitates the interworking between the mobile network and external packet data
networks, such as the internet. It ensures that data can flow seamlessly between the mobile network and
external networks.
⚫ Handover Support: SGSN is involved in the handover process, which allows a mobile device to smoothly
transition from one cell to another without interrupting the ongoing data session.
⚫ GPRS Tunneling Protocol (GTP): SGSN uses the GTP to establish and maintain tunnels for data
transmission between different network elements, such as between SGSNs or between SGSN and the
Gateway GPRS Support Node (GGSN).
⚫ Integration with Other Network Elements: SGSN works in conjunction with other network elements,
including the GGSN, Home Location Register (HLR), and Mobile Switching Center (MSC), to provide
comprehensive mobile services.
GPRS (GENERAL PACKET RADIO
SERVICE)
⚫ GPRS stands for General Packet Radio Service. It is a mobile data service that enables the sending and receiving of data over mobile networks.
GPRS is part of the GSM (Global System for Mobile Communications) standard and is used for 2G and 2.5G mobile communication networks.
⚫ GPRS is a packet-switched technology, meaning that data is broken down into packets before transmission. This is in contrast to
circuit-switched networks, where a dedicated communication path is established for the entire duration of the call. Packet-switching allows for
more efficient use of network resources and enables simultaneous voice and data transmission.
⚫ Mobile Station (MS):
⚫ The mobile station refers to the user's device, such as a mobile phone or a data terminal.
⚫ Base Station Subsystem (BSS):
⚫ Base Transceiver Station (BTS): The BTS is responsible for the radio communication with the mobile station. It manages the radio frequency
resources and handles the radio interface protocols.
⚫ Base Station Controller (BSC): The BSC controls multiple BTS units. It manages the handovers, frequency hopping, and other tasks related to
radio resource management.
⚫ Network Switching Subsystem (NSS):
⚫ Mobile Switching Center (MSC): The MSC is the central component responsible for call processing, handovers, and connection to the public
switched telephone network (PSTN).
⚫ Gateway MSC (GMSC): The GMSC is responsible for routing incoming calls to the appropriate MSC.
⚫ Home Location Register (HLR): The HLR is a database that stores subscriber information and location information. It is consulted to determine
the subscriber's location when a call or data session is initiated.
⚫ Visitor Location Register (VLR): The VLR is a temporary database that stores information about subscribers currently within the jurisdiction of
the MSC to which it is associated.
⚫ GPRS Support Nodes (GSN):
⚫ Serving GPRS Support Node (SGSN): The SGSN is responsible for the delivery of data packets from and to the mobile stations within its
service area. It keeps track of the location of the mobile station and manages the mobility and authentication functions.
⚫ Gateway GPRS Support Node (GGSN): The GGSN is responsible for interfacing between the GPRS network and external packet data
networks, such as the Internet or corporate intranets. It performs IP address assignment and is the point where user data enters or exits the GPRS
network.
⚫ Operation and Maintenance Center (OMC):
⚫ The OMC is responsible for network operation, maintenance, and management.
GATEWAY GPRS Support Node (GGSN)
⚫ The GGSN serves as a gateway between the GPRS network and external
packet-switched networks, such as the Internet or private corporate intranets. Its
primary function is to route data packets from mobile devices within the GPRS
network to the appropriate destination on external networks and vice versa.
⚫ Key functions of the GGSN include:
⚫ Packet Routing: The GGSN is responsible for routing and forwarding IP (Internet Protocol)
packets between the mobile devices within the GPRS/3G network and external networks. It
acts as a gateway between the mobile network and the internet.
⚫ IP Address Allocation: The GGSN assigns IP addresses to mobile devices within the network.
This is essential for establishing communication between the mobile device and external
networks.
⚫ Authentication and Charging: The GGSN plays a role in the authentication of mobile devices
trying to access the network. It also assists in charging and billing procedures, helping to keep
track of the data usage by individual users.
⚫ Quality of Service (QoS) Management: The GGSN is involved in managing the quality of
service for data traffic. It ensures that different types of data traffic (e.g., voice, video, internet
browsing) receive appropriate priority and resources based on QoS parameters.
⚫ Tunneling and Encapsulation: The GGSN uses tunneling and encapsulation techniques to
securely transmit data between the mobile device and external networks. It establishes tunnels
for data transmission, maintaining the integrity and security of the communication.
⚫ Interworking with External Networks: The GGSN interfaces with external networks, such as
the internet or private corporate networks. It acts as a bridge, allowing mobile devices to
communicate with services and resources outside the mobile network.
 GPRS
GPRS is a packet-switched technology, meaning that data is broken down into packets before
transmission. This is in contrast to circuit-switched networks, where a dedicated
communication path is established for the entire duration of the call. Packet-switching allows
for more efficient use of network resources and enables simultaneous voice and data
transmission.
Key features of GPRS include:
⚫ Packet Switching: Unlike traditional circuit-switched networks, GPRS uses packet-switching
technology. This means that data is broken down into packets, which can be sent separately and
reassembled at the destination. Packet switching is more efficient for transmitting data because
it only uses network resources when data is actually being transmitted.
⚫ Always-On Connection: GPRS provides an "always-on" connection, allowing users to stay
connected to the internet or other data services without the need to establish a new connection
for each data session. This is in contrast to older technologies where a connection had to be
established and disconnected for each data transfer.
⚫ Increased Data Transfer Rates: GPRS offers higher data transfer rates compared to
traditional GSM, making it suitable for applications such as web browsing, email, and other
data-intensive services.
⚫ Compatibility: GPRS is designed to work with existing GSM networks, making it a relatively
straightforward upgrade for mobile operators. It operates in the 2G (second-generation) mobile
network spectrum.
⚫ Global Availability: GPRS is widely used globally and has become a standard feature on
many mobile networks around the world.
GPRS Architecture
Authentication of GPRS
user
Data compression
Registration of mobile device in
network

Packet control
Unit

Public Land Mobile Integrated Services Digital Network

Here's why the SGSN is connected to the MSC
⚫ Coordination of Services: In a mobile network, users can use both
circuit-switched services (like voice calls) and packet-switched services (like
data sessions) simultaneously. The SGSN is responsible for packet-switched
services, while the MSC handles circuit-switched services. To provide a
seamless experience for users engaging in both types of services, there needs to
be coordination and communication between the SGSN and MSC.
⚫ Mobility Management: The SGSN is responsible for managing the mobility of
users in the packet-switched domain. When a user moves between different
SGSNs, there needs to be coordination with the MSC to ensure that
circuit-switched services are appropriately handled as the user roams within the
network.
⚫ Location Update: When a user engages in packet-switched services, the SGSN
updates the location information for that user. This updated information is often
shared with the MSC to keep it informed of the user's location in the
packet-switched domain.
⚫ Handover Scenarios: In scenarios where a user is engaged in a voice call
(circuit-switched) and then initiates a data session (packet-switched), handover
procedures may be required. The SGSN and MSC need to coordinate to manage
the transition between these different types of services.
UMTS (Universal Mobile Telecommunications System)

⚫ UMTS, which stands for Universal Mobile Telecommunications System, is a third-generation

(3G) mobile communication technology that evolved from GSM (Global System for Mobile
Communications). UMTS is designed to provide high-speed data and multimedia services
along with traditional voice communication. The architecture of UMTS is divided into several
key components:
⚫ User Equipment (UE):

⚫ The UE, also known as the mobile station or handset, is the device used by the end-user
for communication. It can support various services such as voice, data, and multimedia.

⚫ Utran (UMTS Terrestrial Radio Access Network):

⚫ Utran is the radio access network of UMTS and is responsible for establishing and
maintaining the air interface connections with the UE. It consists of two main elements:
⚫ NodeB (Node B): The NodeB is the base station in UMTS that communicates directly with the UE
over the air interface. It is responsible for radio transmission and reception.
⚫ RNC (Radio Network Controller): The RNC controls multiple NodeBs and is responsible for
tasks such as handovers, radio resource management, and encryption.
UMTS (Universal Mobile Telecommunications System)

⚫ Core Network (CN):

⚫ The Core Network is the backbone of the UMTS architecture and provides various services such as
call control, mobility management, and packet routing. It includes several key components:
⚫ MSC (Mobile Switching Center): The MSC is responsible for call routing and switching, similar to its
role in GSM.
⚫ SGSN (Serving GPRS Support Node): The SGSN handles packet-switched data services and is
responsible for mobility management within the UMTS network.
⚫ GGSN (Gateway GPRS Support Node): The GGSN interfaces with external packet-switched networks,
such as the internet, and is responsible for IP address assignment and packet routing.
⚫ Home Environment (HE):
⚫ The Home Environment includes the HLR (Home Location Register) and the AuC (Authentication
Center). The HLR stores subscriber information and provides services such as call routing and
subscriber authentication. The AuC is responsible for generating and verifying security information.
⚫ Authentication and Key Agreement (AKA):
⚫ AKA is a security mechanism used in UMTS to authenticate the user and establish a secure
connection. It involves the generation and exchange of authentication and encryption keys between
the UE, the HLR, and the AuC.
⚫ UE and UTRAN Interfaces:
⚫ The interfaces between various components of the UMTS architecture facilitate communication and
data exchange. Key interfaces include Iu (interface between RNC and CN), Iub (interface between
NodeB and RNC), and Iur (interface between RNCs).
UMTS (Universal Mobile Telecommunications System)
Architecture
UMTS Terrestrial Radio Access
Network

Integrated Services Digital

Network
Public Switched Telephone Network

Packet Data Network

Radio Network
Controller
 handover
⚫ Handover (also known as handoff) refers to the process of transferring an ongoing communication session from one
network connection to another without interrupting or dropping the session. This is a crucial functionality in the
context of mobile devices, as users move between different areas or cells served by different base stations or access
points. The primary goal of handover is to maintain continuous and seamless connectivity for users.
⚫ There are several types of handovers in mobile computing:
⚫ Vertical Handover (VHO): In VHO, the handover occurs between different types of networks, such as moving from
a Wi-Fi network to a cellular network or vice versa. For example, a mobile device might switch from a Wi-Fi
connection at home to a cellular network when leaving the house.
⚫ Horizontal Handover (HHO): HHO involves handovers within the same type of network. For instance, a mobile
device may transition from one cell to another within the same cellular network.
⚫ Soft Handover: Soft handover involves the simultaneous connection to multiple cells or access points before
completely severing the connection with the initial one. This approach helps ensure a smooth transition without a
noticeable disruption in service.
⚫ Hard Handover: In contrast, hard handover involves disconnecting from one network before establishing a
connection with another. There may be a brief interruption in service during a hard handover.
⚫ The handover process typically involves the following steps:
⚫ Detection: The mobile device or network infrastructure detects a change in signal strength, quality, or other
parameters that may necessitate a handover.
⚫ Decision: Based on the detected conditions, a decision is made to initiate a handover. This decision can be made by
the mobile device itself (mobile-initiated) or by the network (network-initiated).
⚫ Preparation: Necessary preparations are made to establish the connection with the target network. This may involve
authentication, authorization, and other setup procedures.
⚫ Execution: The actual handover occurs, and the communication session is transferred to the new network.
⚫ Confirmation: The success of the handover is confirmed, and the communication session continues on the new
network.
⚫ Efficient handover mechanisms are crucial for providing uninterrupted service, maintaining call quality, and
optimizing resource utilization in mobile communication systems. Different wireless technologies and protocols,
such as GSM, CDMA, LTE, and Wi-Fi, have their own handover procedures and standards to ensure seamless
mobility.
Handover architecture
Soft and hard Handover
Security
Security in mobile computing is a critical aspect due to the widespread use of mobile devices such as smartphones and
tablets. These devices often store sensitive information and connect to various networks, making them vulnerable to
security threats. Here are some key considerations for ensuring security in mobile computing:
⚫ Device Security:
⚫ Screen Locks and Passwords: Encourage users to use strong passwords or PINs to secure their devices.
⚫ Biometric Authentication: Utilize fingerprint recognition, facial recognition, or other biometric authentication methods for an
added layer of security.
⚫ Remote Wipe and Lock: Enable the ability to remotely wipe or lock a device in case it is lost or stolen.
⚫ Data Encryption:
⚫ Full Disk Encryption: Encrypt the entire device to protect data stored on it.
⚫ Communication Encryption: Use secure communication protocols (e.g., HTTPS, VPNs) to encrypt data during transmission.
⚫ App Security:
⚫ App Permissions: Regularly review and limit app permissions to minimize the risk of unauthorized access to sensitive data.
⚫ App Source: Download apps only from official app stores to reduce the risk of malware.
⚫ Operating System Updates:
⚫ Regularly update the mobile operating system to patch vulnerabilities and improve overall security.
⚫ Mobile Device Management (MDM):
⚫ Implement MDM solutions to centrally manage and enforce security policies on mobile devices.
⚫ Monitor and control access to corporate resources from mobile devices.
⚫ Network Security:
⚫ Secure Wi-Fi Connections: Avoid connecting to unsecured Wi-Fi networks, and use virtual private networks (VPNs) when
accessing sensitive information over public networks.
⚫ Firewalls: Implement firewalls to monitor and control network traffic.
⚫ .
Authentication and Authorization
⚫ Implement strong authentication mechanisms, such as
multi-factor authentication, to enhance access control.
⚫ Define and enforce access policies based on user roles and
responsibilities.
⚫ Secure Data Storage and Transmission:
⚫ Store sensitive data securely and ensure that data transmission
between the device and servers is encrypted.
⚫ Incident Response Plan:
⚫ Develop and regularly update an incident response plan to
address security incidents promptly.
⚫ Privacy Policies:
⚫ Clearly communicate privacy policies to users and ensure
compliance with data protection regulations.