MCA - Mobile Computing

Issues in mobile computing:

1.      Network Issues

2.      Design Issues

3.      Security Issues

4.      Usability Issues

5.      System Issues

Security issues involved in mobile computing

Main article: Mobile security

Mobile security or mobile phone security has become increasingly important in mobile computing. It is of particular concern as it relates to the security of personal information now stored on the smartphone.
More and more users and businesses use smartphones as communication tools but also as a means of planning and organizing their work and private life. Within companies, these technologies are causing profound changes in the organization of information systems and therefore they have become the source of new risks. Indeed, smartphones collect and compile an increasing amount of sensitive information to which access must be controlled to protect the privacy of the user and the intellectual property of the company.
All smartphones, as computers, are preferred targets of attacks. These attacks exploit weaknesses related to smartphones that can come from means of communication like SMS, MMS, wifi networks, and GSM. There are also attacks that exploit software vulnerabilities from both the web browser and operating system. Finally, there are forms of malicious software that rely on the weak knowledge of average users.
Different security counter-measures are being developed and applied to smartphones, from security in different layers of software to the dissemination of information to end users. There are good practices to be observed at all levels, from design to use, through the development of operating systems, software layers, and downloadable apps.

Wireless telephony:

wireless-Atermdescribingacomputernetworkwhere thereisnophysicalconnection(eithercoppercableorfibre optics)betweensenderandreceiver,butinsteadtheyare connectedbyradio. Applicationsforwirelessnetworksincludemulti-party teleconferencing,distributedworksessions,personaldigitalassistants,andelectronicnewspapers.Theyinclude thetransmissionofvoice,video,images,anddata,each traffictypewithpossiblydifferingbandwidthand quality-of-servicerequirements.Thewirelessnetwork componentsofacompletesource-destinationpathrequires considerationofmobility,hand-off,andvarying transmissionandbandwidthconditions.Thewired/wireless networkcombinationprovidesaseverebandwidthmismatch,as wellasvastlydifferenterrorconditions.Theprocessing capabilityoffixedvs.mobileterminalsmaybeexpectedto differsignificantly.Thisthenleadstosuchissuestobe addressedinthisenvironmentasadmissioncontrol, capacityassignmentandhand-offcontrolinthewireless domain,flowanderrorcontroloverthecompleteend-to-end path,dynamicbandwidthcontroltoaccommodatebandwidth mismatchand/orvaryingprocessingcapability.

Or

Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor.
The most common wireless technologies use radio. With radio waves distances can be short, such as a few meters for television or as far as thousands or even millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones.
Somewhat less common methods of achieving wireless communications includes the use of other electromagnetic wireless technologies, such as light, magnetic, or electric fields or the use of sound.

GSM Architecture:

A GSM network consists of several functional entities whose functions and interfaces are defined. The GSM network can be divided into following broad parts.

• The Mobile Station(MS)
• The Base Station Subsystem (BSS)
• The Network Switching Subsystem (NSS)
• The Operation Support Subsystem(OSS)

Following is the simple architecture diagram of GSM Network.

The added components of the GSM architecture include the functions of the databases and messaging systems:

• Home Location Register (HLR)
• Visitor Location Register (VLR)
• Equipment Identity Register (EIR)
• Authentication Center (AuC)
• SMS Serving Center (SMS SC)
• Gateway MSC (GMSC)
• Chargeback Center (CBC)
• Transcoder and Adaptation Unit (TRAU)

Following is the diagram of GSM Netwrokalongwith added elements.

The MS and the BSS communicate across the Um interface, also known as the air interface or radio link. The BSS communicates with the Network Service Switching center across the A interface.

GSM network areas:

In a GSM network, the following areas are defined:

• Cell: Cell is the basic service area: one BTS covers one cell. Each cell is given a Cell Global Identity (CGI), a number that uniquely identifies the cell.
• Location Area: A group of cells form a Location Area. This is the area that is paged when a subscriber gets an incoming call. Each Location Area is assigned a Location Area Identity (LAI). Each Location Area is served by one or more BSCs.
• MSC/VLR Service Area: The area covered by one MSC is called the MSC/VLR service area.
• PLMN: The area covered by one network operator is called PLMN. A PLMN can contain one or more MSCs.

MS:

The MS consists of the physical equipment, such as the radio transceiver, display and digital signal processors, and the SIM card. It provides the air interface to the user in GSM networks. As such, other services are also provided, which include:

• Voice teleservices
• Data bearer services
• The features' supplementary services

The MS Functions:

The MS also provides the receptor for SMS messages, enabling the user to toggle between the voice and data use. Moreover, the mobile facilitates access to voice.messaging systems. The MS also provides access to the various data services available in a GSM network. These data services include:

• X.25 packet switching through a synchronous or asynchronous dialup connection to the PAD at speeds typically at 9.6 Kbps.
• General Packet Radio Services (GPRSs) using either an X.25. or IP.based data transfer method at speeds up to 115 Kbps
• High.speed, circuit.switched data at speeds up to 64 Kbps

We will discuss more about GMS services in GSM - User Services.

What is SIM?

The SIM provides personal mobility so that the user can have access to all subscribed services irrespective of both the location of the terminal and the use of a specific terminal. You need to insert the SIM card into another GSM cellular phone to receive calls at that phone, make calls from that phone, or receive other subscribed services.

The BSS is composed of two parts:

• The Base Transceiver Station (BTS)
• The Base Station Controller (BSC)

The BTS and the BSC communicate across the specified Abis interface, enabling operations between components that are made by different suppliers. The radio components of a BSS may consist of four to seven or nine cells. A BSS may have one or more base stations. The BSS uses the Abis interface between the BTS and the BSC. A separate high-speed line (T1 or E1) is then connected from the BSS to the Mobile MSC.

The Base Transceiver Station (BTS):

The BTS houses the radio transceivers that define a cell and handles the radio link protocols with the MS. In a large urban area, a large number of BTSs may be deployed.

The BTS corresponds to the transceivers and antennas used in each cell of the network. A BTS is usually placed in the center of a cell. Its transmitting power defines the size of a cell. Each BTS has between 1 and 16 transceivers, depending on the density of users in the cell. Each BTS serves a single cell. It also includes the following functions:

• Encoding, encrypting, multiplexing, modulating, and feeding the RF signals to the antenna.
• Transcoding and rate adaptation
• Time and frequency synchronizing
• Voice through full- or half-rate services
• Decoding, decrypting, and equalizing received signals
• Random access detection
• Timing advances
• Uplink channel measurements

The Base Station Controller (BSC):

The BSC manages the radio resources for one or more BTSs. It handles radio channel setup, frequency hopping, and handovers. The BSC is the connection between the mobile and the MSC. The BSC also translates the 13 Kbps voice channel used over the radio link to the standard 64 Kbps channel used by the Public Switched Telephone Network (PSDN) or ISDN.

It assigns and releases frequencies and time slots for the MS. The BSC also handles intercell handover. It controls the power transmission of the BSS and MS in its area. The function of the BSC is to allocate the necessary time slots between the BTS and the MSC. It is a switching device that handles the radio resources. Additional functions include:

• Control of frequency hopping
• Performing traffic concentration to reduce the number of lines from the MSC
• Providing an interface to the Operations and Maintenance Center for the BSS
• Reallocation of frequencies among BTSs
• Time and frequency synchronization
• Power management
• Time-delay measurements of received signals from the MS

·         The Network switching system (NSS), the main part of which is the Mobile Switching Center (MSC), performs the switching of calls between the mobile and other fixed or mobile network users, as well as the management of mobile services such as authentication.

·        

·         The switching system includes the following functional elements.

·         Home Location Register (HLR)

·         The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription in the form of SIM then all the information about this subscription is registered in the HLR of that operator.

·         Mobile Services Switching Center (MSC)

·         The central component of the Network Subsystem is the MSC. The MSC performs the switching of calls between the mobile and other fixed or mobile network users, as well as the management of mobile services such as such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber. It also performs such functions as toll ticketing, network interfacing, common channel signaling, and others. Every MSC is identified by a unique ID.

·         Visitor Location Register (VLR)

·         The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time.

·         Authentication Center (AUC)

·         The Authentication Center is a protected database that stores a copy of the secret key stored in each subscriber's SIM card, which is used for authentication and ciphering of the radio channel. The AUC protects network operators from different types of fraud found in today's cellular world.

·         Equipment Identity Register (EIR)

·         The Equipment Identity Register (EIR) is a database that contains a list of all valid mobile equipment on the network, where its International Mobile Equipment Identity (IMEI) identifies each MS. An IMEI is marked as invalid if it has been reported stolen or is not type approved.

The operations and maintenance center (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS).

Here are some of the OMC functions:

• Administration and commercial operation (subscription, end terminals, charging and statistics).
• Security Management.
• Network configuration, Operation and Performance Management.
• Maintenance Tasks.

GSM Air interface:

In mobile or wireless communication, the air interface is the radio-based communication link between the mobile station and the active base station. In GSM/UMTS, the various UTRA standards are air interfaces, and are also (but not exclusively) referred to as "access modes".

In the OSI model, the air interface comprises layers 1 and 2 of the mobile communications system, establishing a point-to-point link between the mobile station and the base station.

Radio Transmission

Logical Channels

Messages

Radio Transmission

Logical Channels

Messages

Terminal

Base Station

Layer 1 Bits

Layer 2 Packets

Layer 3 Messages

Mobility and Location Management

The ability to change locations while connected to the network creates a dynamic computing environment. This means that data which is static for stationary computing becomes dynamic for mobile computing. An example is that a stationary computer is permanently attached to the nearest server while mobile computers need a mechanism to determine which server to use.

As people move, their mobile computers will use different network addresses. The networking used today has to be changed to deal with dynamically changing addresses. If we, for example, look at how the Internet Protocol (IP) is designed for fixed computing, a host IP is bound with its network address so moving to a new location means that it needs a new IP name.
There are a few questions that must be answered when looking at a location management scheme. What happens when a mobile user changes location? Who should know about the change? How can you contact a mobile host? Should you search the whole network or does anyone know about the mobile users moves?
A few basic mechanisms to determine a mobile computer's current location has been discussed to modify the IP-based protocols. We will look at four of them in this article; broadcast, central services, home base and forwarding pointers.
Selective Broadcast
With this method a message is sent to all network cells asking the mobile computer to reply with its current address. This scheme may be too expensive in large networks. However, if the mobile computer is known to be in one of a few cells a message is sent out to the selected cells. A disadvantage with selective broadcast is that it can only be used when we have enough information about current location.
Central Services
The current address for each mobile user is kept in a centralized database. When a mobile computer changes its address it also updates the central database by sending a message containing its new address.

Channel Structure:

Wireless LAN:

Wireless local area networks (WLANs) based on the Wi-Fi (wireless fidelity) standards are one of today's fastest growing technologies in businesses, schools, and homes, for good reasons. They provide mobile access to the Internet and to enterprise networks so users can remain connected away from their desks. These networks can be up and running quickly when there is no available wired Ethernet infrastructure. They can be made to work with a minimum of effort without relying on specialized corporate installers.
Design goals for wireless LANs
global, seamless operation
low power for battery use
no special permissions or licenses needed to use the LAN
robust transmission technology
simplified spontaneous cooperation at meetings
easy to use for everyone, simple management
protection of investment in wired networks
security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation)
transparency concerning applications and higher layer protocols, but also location awareness if necessary.

Advantages
very flexible within the reception area
Ad-hoc networks without previous planning possible(almost) no wiring difficulties (e.g. historic buildings, firewalls)
more robust against disasters like, e.g., earthquakes, fire -or users pulling a plug

Disadvantages
Typically very low bandwidth compared to wired networks (1-10 Mbit/s) due to shared medium
many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE 802.11n)
products have to follow many national restrictions if working wireless, it takes a very long time to establish global solutions like, e.g., IMT-2000
Threats to WLAN Environment: - All wireless computer systems face security threats that can compromise its systems and services. Unlike the wired network, the intruder does not need physical access in order to pose the following security threats:
Eavesdropping
Tampering
Unauthorized access and spoofing
Denial of Service

IEEE 802.11: WIRELESS LAN

by Dinesh Thakur

Wireless communication is one of the fastest growing technologies these days. Wireless LANs are commonly found in office buildings, college campuses, and in many public areas.

IEEE 802.11 standard provides wireless communication with the use of infrared or radio waves.

802.11 Architecture

The 802.11architecture defines two types of services and three different types of stations

802.11 Services

The two types of services are

1. Basic services set (BSS)

2. Extended Service Set (ESS)

1. Basic Services Set (BSS)

• The basic services set contain stationary or mobile wireless stations and a central base station called access point (AP).

• The use of access point is optional.

• If the access point is not present, it is known as stand-alone network. Such a

BSS cannot send data to other BSSs. This type of architecture is known as adhoc architecture.

• The BSS in which an access point is present is known as an infrastructure network.

                             

2. Extend Service Set (ESS)

• An extended service set is created by joining two or more basic service sets (BSS) having access points (APs).

                                

• These extended networks are created by joining the access points of basic services sets through a wired LAN known as distribution system.

• The distribution system can be any IEET LAN.

• There are two types of stations in ESS:

(i) Mobile stations: These are normal stations inside a BSS.

(ii) Stationary stations: These are AP stations that are part of a wired LAN.

• Communication between two stations in two different BSS usually occurs via two APs.

• A mobile station can belong to more than one BSS at the same time.

802.11 Station Types

IEEE 802.11 defines three types of stations on the basis of their mobility in wireless LAN. These are:

1. No-transition Mobility

2. BSS-transition Mobility

3. ESS-transition Mobility

1. No-transition .Mobility: These types of stations are either stationary i.e. immovable or move only inside a BSS.

2. BSS-transition mobility: These types of stations can move from one BSS to another but the movement is limited inside an ESS.

3. ESS-transition mobility: These types of stations can move from one ESS to another. The communication mayor may not be continuous when a station moves from one ESS to another ESS.

GSM :

GSM (Global System for Mobile communication) is a digital mobile telephony system that is widely used in Europe and other parts of the world. GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephony technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1800 MHz frequency band.

GSM (Global System for Mobile communications) is an open, digital cellular technology used for transmitting mobile voice and data services. GSM differs from first generation wireless systems in that it uses digital technology and Time Division Multiple Access (TDMA) transmission methods.

GSM is a circuit-switched system that divides each 200kHz channel into eight 25kHz time-slots..GSM supports data transfer speeds of up to 9.6 kbit/s, allowing the transmission of basic data services such as SMS (Short Message Service). Another major benefit is its international roaming capability, allowing users to access the same services when travelling abroad as at home. This gives consumers seamless and same number connectivity in more than 210 countries. GSM satellite roaming has also extended service access to areas where terrestrial coverage is not available.

Global System for Mobile Communications. The first European digital standard, developed to establish cellular compatibility throughout Europe. It's success has spread to all parts of the world and over 80 GSM networks are now operational.

CDMA:

Short for Code-Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems, such as GSM, that use TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence.
CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.
CDMA is a military technology first used during World War II by English allies to foil German attempts at jamming transmissions. The allies decided to transmit over several frequencies, instead of one, making it difficult for the Germans to pick up the complete signal. Because Qualcomm created communications chips for CDMA technology, it was privy to the classified information. Once the information became public, Qualcomm claimed patents on the technology and became the first to commercialize it.