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Digital notes on Wireless Networks and Mobile Computing for B.Tech III Year - II Sem students at Malla Reddy College of Engineering & Technology. The course covers topics such as network topologies, cellular communications, WLAN, GSM, mobile computing, medium access control, mobile IP network layer, and more. The document also discusses the characteristics of communication devices and applications of mobile computing.
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(Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – ‗A‘ Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Hakimpet), Secunderabad – 500100, Telangana State, INDIA.
III Year B.Tech IT – II Sem L T /P/D C 4 -/-/- 3 (R15A0432) WIRELESS NETWORKS AND MOBILE COMPUTING (Open Elective-IV)
Objectives: The main objective of this course is to provide the students with the
competences required for understanding and using the communications component of an universal communications environment.
UNIT- Introduction to Network topologies and cellular communications.
HIPERLAN : protocol Architecture. WLAN : Infrared vs radio transmission ,infrastructure and ad hoc
networks, IEEE 802.11. GSM : Mobile services, System architecture, Radio interface, Protocols, Localization and calling, Handover, Security, and New data services.
Mobile computing: Introduction to MC, novel Applications, Limitations and architecture.
UNIT- (Wireless) Medium Access Control : Motivation for a specialized MAC
(Hidden and exposed terminals, Near and far terminals), SDMA, FDMA, TDMA, CDMA.MAC protocols for GSM , collision Avoidance
(MACA, MACAW) protocols Mobile IP Network Layer : IP Mobile IP Network layers, packet delivery and handover management, location management registration,
tunneling and encapsulation, Route optimizations, Dynamic Host Configuration Protocol (DHCP).
S. No (^) Unit Topic Page no
(^1) I Introduction to MC^5
(^2) I Mobile services^8
(^3) II SDMA^40
(^4) II Mobile IP^56
Dynamic Host Configuration Protocol 71
(^6) III Indirect TCP^79
(^7) III Database^ Hoarding^88
classification of new data delivery mechanisms (^110)
(^9) IV selective tuning^116
(^10) V MANET^127
(^11) V Bluetooth^168
Wireless Networks & Mobile Computing R15A
Unit-
Introduction to Mobile Computing
The rapidly expanding technology of cellular communication, wireless LANs, and satellite services will make information accessible anywhere and at any time. Regardless of size, most mobile computers will be equipped with a wireless connection to the fixed part of the network, and, perhaps, to other mobile computers. The resulting computing environment, which is often referred to as mobile or nomadic computing , no longer requires users to maintain a fixed and universally known position in the network and enables almost unrestricted mobility. Mobility and portability will create an entire new class of applications and, possibly, new massive markets combining personal computing and consumer electronics.
Mobile Computing is an umbrella term used to describe technologies that enable people to access network services anyplace, anytime, and anywhere.
A communication device can exhibit any one of the following characteristics: Fixed and wired : This configuration describes the typical desktop computer in an office. Neither weight nor power consumption of the devices allow for mobile usage. The devices use fixed networks for performance reasons.
Mobile and wired : MaŶLJ of todaLJ͛s laptops fall iŶto this ĐategoƌLJ; useƌs carry the laptop from one hotel to the next , reconnecting to the ĐoŵpaŶLJ͛s network via the telephone network and a modem.
Fixed and wireless : This mode is used for installing networks, e.g., in historical buildings to avoid damage by installing wires, or at trade shows to ensure fast network setup.
Mobile and wireless : This is the most interesting case. No cable restricts the user, who can roam between different wireless networks.
In many fields of work, the ability to keep on the move is vital in order to utilise time efficiently. The importance of Mobile Computers has been highlighted in many fields of which a few are described below: a. Vehicles: Music, news, road conditions, weather reports, and other broadcast information are received via digital audio broadcasting (DAB) with 1.5 Mbit/s. For personal communication, a universal mobile telecommunications system (UMTS) phone might be available offering voice and data connectivity with 384 kbit/s. The current position of the car is determined via the global positioning system (GPS). Cars driving in the same area
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be triggered, but the police and ambulance service will be informed via an emergency call to a service provider. Buses, trucks, and trains are already transmitting maintenance and logistic information to their home base, which helps to improve organization (fleet management), and saves time and money.
b. Emergencies : An ambulance with a high-quality wireless connection to a hospital can carry vital information about injured persons to the hospital from the scene of the accident. All the necessary steps for this particular type of accident can be prepared and specialists can be consulted for an early diagnosis. Wireless networks are the only means of communication in the case of natural disasters such as hurricanes or earthquakes. In the worst cases, only decentralized, wireless ad-hoc networks survive.
c. Business : Managers can use mobile computers say, critical presentations to major customers. They can access the latest market share information. At a small recess, they can revise the presentation to take advantage of this information. They can communicate with the office about possible new offers and call meetings for discussing responds to the new proposals. Therefore, mobile computers can leverage competitive advantages. A travelling salesman today needs instant access to the company‘s database: to ensure that files on his or her laptop reflect the current situation, to enable the company to keep track of all activities of their travelling employees, to keep databases consistent etc. With wireless access, the laptop can be turned into a true mobile office, but efficient and powerful synchronization mechanisms are needed to ensure data consistency.
d. Credit Card Verification : At Point of Sale (POS) terminals in shops and supermarkets, when customers use credit cards for transactions, the intercommunication required between the bank central computer and the POS terminal, in order to effect verification of the card usage, can take place quickly and securely over cellular channels using a mobile computer unit. This can speed up the transaction process and relieve congestion at the POS terminals.
e. Replacement of Wired Networks : wireless networks can also be used to replace wired networks, e.g., remote sensors, for tradeshows, or in historic buildings. Due to economic reasons, it is often impossible to wire remote sensors for weather forecasts, earthquake detection, or to provide environmental information. Wireless connections, e.g., via satellite, can help in this situation. Other examples for wireless networks are computers, sensors, or information displays in historical buildings, where excess cabling may destroy valuable walls or floors.
f. Infotainment : wireless networks can provide up-to-date information at any appropriate location. The travel guide might tell you something about the history of a building (knowing via GPS, contact to a local base station, or triangulation where you are) downloading information about a concert in the building at the same evening via a local wireless network. Another growing field of wireless network applications lies in entertainment and games to enable, e.g., ad-hoc gaming networks as soon as people
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meet to play together. Limitations of Mobile Computing Resource constraints: Battery
Interference: Radio transmission cannot be protected against interference using shielding and result in higher loss rates for transmitted data or higher bit error rates respectively
Bandwidth: Although they are continuously increasing, transmission rates are still very low for wireless devices compared to desktop systems. Researchers look for more efficient communication protocols with low overhead.
Dynamic changes in communication environment: variations in signal power within a region, thus link delays and connection losses
Network Issues: discovery of the connection-service to destination and connection stability
Security constraints: Not only can portable devices be stolen more easily, but the radio interface is also prone to the dangers of eavesdropping. Wireless access must always include encryption, authentication, and other security mechanisms that must be efficient and simple to use.
A simplified reference model The figure shows the protocol stack implemented in the system according to the reference model. End-systems , such as the PDA and computer in the example, need a full protocol stack comprising the application layer, transport layer, network layer, data link layer, and physical layer. Applications on the end-systems communicate with each other using the lower layer services. Intermediate systems , such as the interworking unit, do not necessarily need all of the layers.
A Simplified Reference Model
Ring Topology ● In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network. ● To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses. Star Topology ● Many home networks use the star topology. A star network features a central connection point called a "hub node" that may be a network hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet. ● Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.) Tree Topology
● A tree topology joins multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the root of a tree of devices. This bus/star hybrid approach supports future expansion of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone. Mesh Topology
● Mesh topology introduces the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing. ● A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others. Summary ● Topology remains an important part of network design theory. You can probably build a home or small business computer network without understanding the difference between a bus design and a star design, but becoming familiar with the standard topologies gives you a better understanding of important networking concepts like hubs, broadcasts, and routes.
Cellular Communications: Mobile Technology ● Mobile phone or cellular technology is widely used and is based upon the concept of frequency re-use by the application on a series of coverage cells. ● Mobile phone or cellular telecommunications technology has been in widespread use since the early 1980s. ● Since its first introduction, its use has increased very rapidly to the extent that a major portion of the global population has access to the technology. ● From developed nation to growing nation, mobile phone or cellular communications technology has been installed in all countries around the globe.
● The cellular telecommunications industry has been a major driver in the growth of the radio and electronics industries.
Development of cellular communications ● Although cellular communications are now accepted into everyday life, it took many years for their development to occur. ● Although the basic concepts for cellular communications technology were proposed in the 1940s it was not until the mid-1980s that the radio technology and systems were deployed to enable widespread availability. ● Usage of the cellular communications systems grew rapidly and as an example it was estimated that within the United Kingdom more calls were made using mobile phones than wired devices by 2011. ● Another example of the growth of cellular telecommunications systems occurred in 2004 when the GSMA announced at Mobile World Congress in February 2004 that there were more than 1 billion GSM mobile subscribers – it had taken 12 years since the first network was launched. By comparison it had taken over 100 years for the same figure to be reached for wired telephone connections. ● Then by 2015 more than 7 billion mobile subscriptions (for all technologies) were active. This is a major feat when it is realized that the global population was just over 7 billion. This meant that many people had more than one subscription, although market penetration was obviously very significant. cellular communications concepts ● As the name indicates, cellular telecommunications technology is based around the concept of using a large number of base stations each covering a small area or cell. With each base station communicating with a reasonable number of users, it means that the whole system can accommodate a huge number of connections, and the levels of frequency use are good. ● A cellular communications system has a number of different areas, each of which performs a different function. The main areas detailed below are the main ones that are normally referred to when discussing cellular communications systems. Each of these areas can often be split much further into different entities. Mobile handset or user equipment, UE: The user equipment or mobile phone is the element of a mobile communications system that the user sees. It connects to the network and enables the user to access voice and data services. The user equipment could also be a dongle used for accessing data on a laptop, or it could also be a modem on another form of device – for example cellular communications is starting to be used for Internet of Things, IoT applications and as a result it could be attached to a smart meter to automatically send meter readings or it could be used for any one of a host of other applications. HIPERLAN ● HIPERLAN is a European family of standards on digital high speed wireless communication in the 5.15-5.3 GHz and the 17.1-17.3 GHz spectrum developed by ETSI. The committee responsible for HIPERLAN is RES-10 which has been working on the standard since November 1991. ● The standard serves to ensure the possible interoperability of different manufacturers' wireless communications equipment that operate in this spectrum. The HIPERLAN standard only describes a common air interface including the physical layer for wireless
transparent and non-transparent, synchronous or asynchronous data transmission. Transparent bearer services only use the functions of the physical layer (layer 1) to transmit data. Data transmission has a constant delay and throughput if no transmission errors occur. Transmission quality can be improved with the use of forward error correction (FEC) , which codes redundancy into the data stream and helps to reconstruct the original data in case of transmission errors. Transparent bearer services do not try to recover lost data in case of, for example, shadowing or interruptions due to handover. Non-transparent
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bearer services use protocols of layers two and three to implement error correction and flow control. These services use the transparent bearer services, adding a radio link protocol (RLP). This protocol comprises mechanisms of high-level data link control (HDLC) , and special selective-reject mechanisms to trigger retransmission of erroneous data. Using transparent and non-transparent services, GSM specifies several bearer services for interworking with PSTN, ISDN, and packet switched public data networks (PSPDN) like X.25, which is available worldwide. Data transmission can be full-duplex, synchronous with data rates of 1.2, 2.4, 4.8, and 9.6 kbit/s or full-duplex, asynchronous from 300 to 9,600 bit/s.
Tele services : GSM mainly focuses on voice-oriented tele services. These comprise encrypted voice transmission, message services, and basic data communication with terminals as known from the PSTN or ISDN (e.g., fax). The primary goal of GSM was the provision of high-quality digital voice transmission. Special codecs (coder/decoder) are used for voice transmission, while other codecs are used for the transmission of analog data for communication with traditional computer modems used in, e.g., fax machines. Another service offered by GSM is the emergency number (eg 911, 999). This service is mandatory for all providers and free of charge. This connection also has the highest priority, possibly pre-empting other connections, and will automatically be set up with the closest emergency center. A useful service for very simple message transfer is the short message service (SMS) , which offers transmission of messages of up to 160 characters. Sending and receiving of SMS is possible during data or voice transmission. It can be used for ―serious‖ applications such as displaying road conditions, e-mail headers or stock quotes, but it can also transfer logos, ring tones, horoscopes and love letters. The successor of SMS, the enhanced message service (EMS) , offers a larger message size, formatted text, and the transmission of animated pictures, small images and ring tones in a standardized way. But with MMS, EMS was hardly used. MMS offers the transmission of larger pictures (GIF, JPG, WBMP), short video clips etc. and comes with mobile phones that integrate small cameras. Another non-voice tele service is group 3 fax , which is available worldwide. In this service, fax data is transmitted as digital data over the analog telephone network according to the ITU-T standards T.4 and T.30 using modems.
Supplementary services : In addition to tele and bearer services, GSM providers can supplementary services. these services offer various enhancements for the standard telephony service, and may vary from provider to provider. Typical services are user identification , call redirection , or forwarding of ongoing calls, barring of incoming/outgoing calls, Advice of Charge (AoC) etc. Standard ISDN features such as closed user groups and multiparty communication may be available.
GSM Architecture
A GSM system consists of three subsystems, the radio sub system (RSS), the network and switching subsystem (NSS), and the operation subsystem (OSS).
the connection between the RSS and the NSS via the A interface (solid lines) and the connection to the OSS via the O interface (dashed lines).
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Base station subsystem (BSS): A GSM network comprises many BSSs, each controlled by a base station controller (BSC). The BSS performs all functions necessary to maintain radio connections to an MS, coding/decoding of voice, and rate adaptation to/from the wireless network part. Besides a BSC, the BSS contains several BTSs.
Base station controllers (BSC): The BSC provides all the control functions and physical links between the MSC and BTS. It is a high capacity switch that provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in BTS. A number of BSC‘s are served by and MSC.
Base transceiver station (BTS): The BTS handles the radio interface to the mobile station. A BTS can form a radio cell or, using sectorized antennas, several and is connected to MS via the Um interface , and to the BSC via the Abis interface. The Um interface contains all the mechanisms necessary for wireless transmission (TDMA, FDMA etc.)The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network. A group of BTS‘s are controlled by an BSC.
Operation and Support system : The operations and maintenance center (OMC) is connected to all equipment in the switching system and to the BSC. Implementation of OMC is called operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional and local operational and maintenance activities that are required for a GSM network. OSS provides a network overview and allows engineers to monitor, diagnose and troubleshoot every aspect of the GSM network. The mobile station (MS) consists of the mobile equipment (the terminal) and a smart card called the Subscriber Identity Module (SIM). The SIM provides personal mobility, so that the user can have access to subscribed services irrespective of a specific terminal. By inserting the SIM card into another GSM terminal, the user is able to receive calls at that terminal, make calls from that terminal, and receive other subscribed services.
The mobile equipment is uniquely identified by the International Mobile Equipment Identity (IMEI). The SIM card contains the International Mobile Subscriber Identity (IMSI) used to identify the subscriber to the system, a secret key for authentication, and other information. The IMEI and the IMSI are independent, thereby allowing personal mobility. The SIM card may be protected against unauthorized use by a password or personal identity number.
Radio Interface
The most interesting interface in a GSM system is Um, the radio interface, as it comprises various multiplexing and media access mechanisms. GSM implements SDMA using cells with BTS and assigns an MS to a BTS.
Logical channels and frame hierarchy Two types of channels, namely physical channels and logical channels are present. Physical channel: channel defined by specifying both, a carrier frequency and a TDMA
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timeslot number. Logic channel: logical channels are multiplexed into the physical channels. Each logic channel performs a specific task. Consequently the data of a logical channel is transmitted in the corresponding timeslots of the physical channel. During this process, logical channels can occupy a part of the physical channel or even the entire channel.
Each of the frequency carriers is divided into frames of 8 timeslots of approximately is 4.615ms (577 s)s x 8 = 4.615 ms). The bits per timeslot and frame duration yield a gross bit rate of about 271kbps per TDMA frame. TDMA frames are grouped into two types of multiframes: 26-frame multiframe (4.615ms x 26 = 120 ms) comprising of 26 TDMA frames. This multiframe is used to carry traffic channels and their associated control channels. 51-frame multiframe (4.615ms x 51 235.4 ms) comprising 51 TDMA frames. This multiframe is exclusively used for control channels. The multiframe structure is further multiplexed into a single superframe of duration of 6.12sec. This means a superframe consists of
^ ^ 51 multiframes of 26 frames. 26 multiframes of 51 frames. The last multiplexing level of the frame hierarchy, consisting of 2048 superframes ( TDMA frames), is a hyperframe. This long time period is needed to support the GSM data encryption mechanisms. The frame hierarchy is shown below:
GSMFrameHierarchy
