Mobile Computing

Mobile Computing : December-2009

Que. 1 Attempt following. A] Explain benefits of wireless n/w.

Benefits of Wireless Networks Companies can realize the following benefits by implementing wireless networks: � � � � � Mobility Ease of installation in difficult-to-wire area Reduced installation time Increased reliability Long-term cost saving

1) Mobility User mobility indicates constant physical movement of the person and their network appliance. Many jobs require workers to be mobile, such as inventory clerks, healthcare workers, policemen, emergency care specialists, and so on. Wire line networks require a physical tether between the user's workstation and the network's resources, which makes access to these resources impossible while roaming about the building or elsewhere. As an analogy, consider talking on a wired phone having a cord connecting the handset to the telephone base station. You can utilize the phone only within the length of its cord. With a wireless cellular phone, however, you can walk freely within your office, home, or even talk to someone while driving a car. Wireless networking offers mobility to its users much like the wireless phone, providing a constant connection to information on the network. This connection can be extremely useful if you are at a customer's site discussing a new product, delivering emergency care to a crash victim, or in a hotel room sending and receiving e-mail. You cannot become mobile unless you eliminate the- wire through the use of wireless networking.

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Mobile Computing : December-20092) Ease of installation in difficult-to-wire area

The implementation of wireless networks offers many tangible cost savings when performing installations in difficult-to-wire areas. If rivers, freeways, or other obstacles separate buildings you

want to connect a wireless MAN solution may be much more economical than installing physical cable or leasing communications circuits such as Tl service or 56 Kbps lines. Some organizations spend hundreds, thousands, or even millions of dollars to install physical links with nearby facilities. If you are facing this type of installation, consider wireless networking as an alternative. The deployment of wireless networking in these situations costs thousands of dollars, but will result in a definite cost savings in the long run.

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3) Reduced Installation Time The installation of cabling is often a time-consuming activity. For LANs, installers must pull twisted-pair wires above the ceiling and drop cables through walls to network outlets that they must affix to the wall. These tasks can take days or weeks, depending on the size of the installation. The installation of optical fiber between buildings within the same geographical area consists of digging trenches to lay the fiber or pulling the fiber through an existing conduit. You might need weeks or possibly months to receive right-of-way approvals and dig through ground and asphalt. The deployment of wireless LANs, MANs, or WANs, greatly reduces the need for cable installation, making the network available for use much sooner. Thus, many countries lacking a network infrastructure have turned to wireless networking as a method of providing connectivity among computers without the expense and time associated with installing physical media. Increased Reliability A problem inherent to wired networks is the downtime due to cable faults. Moisture erodes metallic conductors. These imperfect cable splices can cause signal reflections that result in unexplainable errors. The accidental cutting of cables can also bring a network down quickly. Water intrusion can also damage communications lines during storms. These problems interfere with the users' ability to utilize network resources, causing havoc for network managers. The advantage of wireless networking, then, is experiencing fewer problems because less cable is used. 4) Long-Term Cost Savings Companies reorganize, resulting in the movement of people, new floor plans, office partitions, and other renovations. These changes often require recabling the network, incurring both labor and material costs. In some cases, the re-cabling costs of organizational changes are substantial, especially with large enterprise networks. A reorganization rate of 15% each year can

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Mobile Computing : December-2009result in yearly reconfiguration expenses as high as $250,000 for networks having 6,000 interconnected devices. The advantage of wireless networking is again based on the lack of cable you can move the network connection by simply relocating an employee's PC. B] Explain Block diagram of Satellite Earth Station.

Earth Station: Satellite communication system consists of a number of earth stations interconnected through a single relay repeater called satellite. At transmitting earth station: base band signal modulates intermediate carrier frequency. Modulated signal is up-converted using local oscillator to microwave frequency band (for C band, it is 6 GHz). The RF signal is amplified in a high power amplifier (HPA) and transmitted to the satellite repeater through transmitting antenna. Frequency used for this transmission is called up-link frequency. Signal is received through satellite antenna and it is amplified and converted to down-link frequencies and then amplified and transmitted back to the earth through transmit satellite antenna. Frequencies used for transmitting signals from satellite to earth station are called down-link frequencies. Earth, station receives this signal (transmitted from satellite) through antenna, is amplified first by sensitive low noise amplifier (LNA) and then down converted and then demodulated to receive the baseband signal. Satellite Earth Station There are mainly three types of earth station depending upon capacity channels transmission.

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(1) Main (2) Primary (3) Remote 1. Main earth station uses full bandwidth of transponder. One transponder has bandwidth of 36 MHz which can transmit maximum of 1920 channels. 2. Primary earth station can transmit minimum of 300 channels. 3. Remote earth station can transmit only few channels. Generally 2 or 3 channels or even sometime single channel. Only SCPS or MSPC circuits are working with remote station. Different parameters for different earth stations are given in Table

Site Selection for Earth Station: Once a network has been planned and cities and towns have been identified, a search has to start for site selection of earth station. Following are

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Mobile Computing : December-2009important factors to be considered for selection of the site for an earth station. 1) Since the earth station transmits 6 GHz and receives 4 GHz; all stations including earth stations operating in these bands must be properly shielded to avoid mutual radio interference. 2) For up-link and down-link, microwave frequencies are used;. Station should be away from terrestrial microwave link working with these frequencies so that interference can be avoided. 3) Land should either be rock or a soil but should afford the means of obtaining a good earth ground. 4) The site should have good access to a main highway and also be near to electric power distribution for reliable electric power. 5) Site should reasonably near the telecommunication switching center to minimize the length of the interconnecting link from earth station. 6) The site should be away from any electro-magnetic source. 7) Accommodation for staff, educational and other facilities, should be available.

C] �

Explain call processing in GSM. Mobile Originated Call

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Initially when the user enters the called number and presses the send key. The MS establishes a signaling connection to the BSS on a radio channel. This may involve authentication and ciphering. Once this has been established the call setup procedures will take place according to the sequence shown in Fig. 1) The MS sends the dialed number indicating service requested to the MSC (via BSS) 2) The MSC checks from the VLR if the MS is allowed the requested Service. If so, MSC asks the BSS to allocate necessary resources for the call. 3) If the call‟s allowed, the MSC routes the call to GMSC. 4) The GMSC routes the call to the Local Exchange of called user. 5) The LE alerts (applies ringing) the called terminal. 6) Answer back (ring back tone) from the called terminal to LE 7) Answer back signal is routed back to the MS through the serving MSC which also completes the speech path to the MS. � Mobile Terminated Call

The sequence shown in Figure relates to a call originating in the PSTN and terminating at an MS in a GSM network.

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1) The PSTN user dials the .MSISDN of the called user in GSM. 2) The LE routes the call to the GMSG of the called GSM user. 3) The GMSC uses the dialed MSISDN to determine the serving HLR for the GSM user and interrogates it to attain the required routing number. 4) The HLR requests the current serving VLR for the called MS for a MSRN (MS Roaming Number) so that the call can be routed to the correct MSC. 5) The VLR passes the MSRN to the HLR. 6) The HLR passes the MSRN to the GMSC. 7) Using the MSRN, the GMSC routes the call to the serving MSC. 8) The MSC interrogates the VLR for the current Location Area Identity (LAI) for the MS. 9) The VLR provides the current location (LAI) for the MS. 10) The MSC pages the MS via the appropriate BSS. The MS responds to the page and sets up the necessary signaling links. 11) When the BSS has established the necessary radio links, the MSC is in formed and the call is delivered to the MS. 12) When the MS answers the calf, the connection is completed to the calling PSTN user.

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Que. 2

Explain Logical Architecture of Wireless N/W.

A logical architecture defines the network's protocols-rules by which two entities communicate. People observe protocols every day. Individuals participating in a business meeting, for example, interchange their ideas and concerns while they avoid talking at the same time. They also rephrase a message if no one understands it. Doing so ensures a well-managed and effective means of communication. Likewise, PCs, Servers, routers, and other active devices must conform to very strict rules to facilitate the proper coordination and transformation. One popular standard logical architecture is the 7-layer Open System Interconnection (OSI) Reference Model, developed by the International Standards Organization (ISO). OSI specifies a complete set of network functions, grouped into layers. Fig. 3.2 illustrates the OSI Reference Model. The OSI layers provide the following network functionality:

Layer 7 Application layer Establishes communications with other users and provides services such as file transfer and e-mail to the end users of the network. Layer 6 Presentation Layer

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Mobile Computing : December-2009Negotiates data transfer syntax for the application layer and performs translations between different data types, if necessary. Layer 5 Session Layer Establishes, manages, and terminates sessions between applications. Layer A Transport layer Provides mechanisms for the establishment, maintenance, and orderly termination of virtual circuits, while shielding the higher layers from the network implementation details. Layer 3 Network layer Provides the routing of packets from source to destination. Layer 2 Data Link layer Ensures synchronization and error control between two entities. Layer 1 Physical layer Provides the transmission of bits through a communication channel by defining electrical, mechanical, and procedural specifications. B] 1] Explain following MS

�

Mobile Station consist of two units Mobile Hand set is one of the most complicated GSM devices. It provides user the access to the Network.

�

Subscriber Identity Module SIM is a removable module goes into the SIM has unique number called international" Mobile Subscriber Identity (IMSI). It has built in Microcomputer & memory into it.

2]

BSC

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Mobile Computing : December-2009� � BSC controls several BTSs. BSC manages channel allocation & Handover of calls from one BTS to another BTS. � � BSC is connected to MSC via A interface. Transmission rate on A I/f is 2 Mbps (G.703). � Interface between BSC & BTS is called A'bis I/f. � BSC has database for all of its BTS's parameters. � 3] � � � � � � BSC provides path fromS to MSC. MSC MSC is heart of the entire network connecting fixed line network to Mobile network. MSC manages all call related functions and Billing information. MSC is connected to HLR & VLR for subscriber identification & routing incoming calls. MSC capacity is in terms of no of subscribers. MSC is connected to BSC at one end and Fixed Line network on other end. Call Detail Record (CDR) is generated for each & every call in the MSC.

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4] � � � � � � � � �

BTS BTS has a set of Transceivers to talk to MS. One BTS covers one or more than one cell. Capacity of BTS depends on no of Transceivers. BTS is connected to BSC via A'bis interface. Transmission rate on A‟bis is 2 Mbps (G.703). Interface between MS & BTS is called Air I/F. Transmission rate on Air interface is 13 Kbps. BTS controls RF parameters of MS. Each TRx has 8 TDMA channels to carry Voice & signaling

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Que. 2 Attempt following: A] Explain Handover in GSM Cellular systems require handover procedures, as single cells do not cover the whole service area, but, e.g., only up to 35 km around each antenna. The smaller the cell size and the faster the movement of a mobile station through the cells (up to 250 km/h for GSM), the more handovers of ongoing calls are required. However, a handover should not cause a cut-off, also called call drop. There are two basic reasons for a handover (about 40 have been identified in the standard): � The mobile station moves out of the range of a BTS or a certain antenna of a BTS respectively. Thus, the received signal level becomes lower continuously until it falls underneath the minimal requirements for communication. Or the error rate may grow due to interference, the distance to the BTS may be too high (max. 35 km) etc. all these effects may diminish the quality of the radio link and make radio transmission impossible in the near future. � The wired infrastructure (MSC, BSC) may decide that the traffic in one cell is too high and shift some MS to other cells with a lower load (If possible). Thus, handover may be due to load balancing. Fig. shows four possible handover scenarios in GSM: � Intra-cell handover: Within a cell, narrow-band interference could make transmission at a certain frequency impossible. The BSC could then decide to change the carrier frequency (scenario 1). � Inter-cell, intra-BSC handover: This is a typical handover scenario. The mobile station moves from one cell to another, but stays within the control of the same BSC. The BSC then performs a handover, assigns a new radio channel in the new cell and releases the old one (scenario 2). � Inter-BSC, intra-MSC handover: As a BSC only controls a limitedPage 14

Mobile Computing : December-2009number of cells; GSM also has to perform handovers between cells controlled by different BSCs. This handover then has to be controlled by the MSC (scenario 3). This situation is also shown in Figure. � Inter MSC handover: Finally, a handover could be required between two cells belonging to different MSCs. Now both MSCs perform the handover together (scenario 4). In order to provide all information necessary for a handover due to a weak link, MS and BTS both perform periodic measurements of the downlink and uplink quality respectively. (Link quality comprises signal level and bit error rate.) Measurement reports are sent by the MS about every half-second "and contain the quality of the current link used for transmission as well as the quality of certain channels in neighboring cells (the BCCHs).

B]

Explain GPRS In early 2000, only a small portion of GSM subscribers used data

services, because existing GSM systems do not support easy access, high data rate, and attractive prices. GSM operators must offer better services to stimulate the demand. The solution is the General Packet Radio Service (GPRS). GPRS reuses the existing GSM infrastructure to provide end-to-endPage 15

Mobile Computing : December-2009packet-switched services. GPRS standardization was initiated by ETSI/SMG in 1994. The main set of GPRS specifications was approved by SMG #25 in 1997, and was completed in 1999. GPRS products were developed in 1999, and service deployment has begun. The GPRS core network has' also been developed for IS-136 TDMA systems, and is anticipated to evolve as the core network for the third-generation mobile systems as well. To accommodate GPRS, new radio channels are defined. The allocation of these channels is flexible: One to eight time slots can be allocated to a user, or several active users can share a single time: slot, where the uplink and the downlink are allocated separately. Radio resources can be shared dynamically between speech and data services as a function of traffic load and operator preference. Various radio channel coding schemes are specified to allow bit rates from 9 Kbps to more than 150 Kbps. per user. GPRS fast reservation is designed to start packet transmission within 0.5 to 1 second. GPRS security functionality is equivalent to the existing GSM security, where a ciphering algorithm is optimized for packet data transmission. By allowing information to be delivered more quickly and efficiently, GPRS is a relatively inexpensive mobile data service compared to Short Message Service (SMS) and Circuit-Switched Data. This section provides a GPRS overview. We briefly describe the air interface, and discuss it for enhanced GPRS. We emphasize the individual protocols in the Signaling plane, the industrial solutions of the GPRS network components, GPRS charging, and the development efforts from GSM to GPRS. We first describe the GPRS functional groups and architecture, and then elaborate on GPRS nodes and the interfaces among these nodes. We also describe the GPRS solutions and work in progress by several GPRS vendors. GPRS Components Fig. gives an overview of the components and interfaces of a GPRS overlay to a GSM voice networks.

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The GPRS components perform similar functions as the components of the CDMA2000 system, as discussed in the previous sections, but do not use standard IP protocols such as CDMA. There are many new components and interfaces to learn with GPRS, but it is worthwhile getting familiar with them because GSM networks are so popular. In addition, the third generation network system, the Universal Mobile Telephone System (UMTS) uses the same components. The GPRS components are as discussed below: � The Packet Control

Unit or PCU is similar to the PCF used in CDMA, but is typically placed at the Base Station. Its role is to separate the data packets from the voice packets. Voice traffic gets routed to the Base Station Controller as discussed in Chapter 4, while data packets get routed to the Serving GPRS Support Node (SGSN). Similar to the role of the PCF in CDMA2000 networks, it is involved in the micro-level mobility as the user roams between base stations. The "protocol between the PCU and SGSN is called the Gb protocol, which runs over a Frame Relay connection between the PCU and the SGSN.

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Mobile Computing : December-2009� The SGSN is responsible for setting up the data connection to Gateway GPRS Support Node (GGSN) to provide IP access to the Internet or a private data network. SGSN authenticates the user's ability to use the GPRS data service by querying the users profile on the Home Location Record via an SS7 connection over the Gn interface. � Depending on the network design of the operator, the SGSN handles macro-level mobility by handing off the data connection to neighboring SGSNs in the network over the Gn. This is similar to the Mobile IP Foreign Agent function, but GPRS uses a specialized protocol called the GPRS Tunneling Protocol or GTP. � The SGSN finds the Gateway GPRS Support Node that provides access to the private network of the users or the Internet from an Access Point Name (APN) that is returned from the HLR or requested by the users. The APN is in the form of an IP Domain Name like IBM. The SGSN uses a standard IP Domain Name Server or DNS lookup to find the IP address of the GGSN. � If the destination GGSN is in another operator's network it sets up the user's session over the Gp interface. In GPRS terminology, an operators GPRS network is called a Public Land Mobile Network (PLMN). � After the Internet connection of users is established, the SGSN writes accounting records to the operators accounting server called a Charging Gateway Function over the Ga interface. The Ga interface uses extensions of the GPRS Tunneling Protocol called GTP Prime, usually written GTR � The GPRS Gateway Support Node (GGSN) serves a role very similar to the Home Agent in CDMA2000 networks. It authenticates the user on the Internet or private data network, using the RADIUS protocol, and provides an IP address for the user using the Dynamic Host Control Protocol (DHCP). Note that authenticating the User on the IP network

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Mobile Computing : December-2009is different from authenticating the user to use the radio network, which is done by the SGSN and HLR.

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Que. 3 A]

Attempt following (Any four):

Explain Mobile OS A mobile operating system, also known as a mobile OS, a mobile

platform, or a handheld operating system, is the operating system that controls a mobile device or information appliance—similar in principle to an operating system such as Windows, Mac OS, or Linux that controls a desktop computer or laptop. However, they are currently somewhat simpler, and deal more with the wireless versions of broadband and local connectivity, mobile multimedia formats, and different input methods. Typical examples of devices running a mobile operating system are smart phones, personal digital assistants (PDAs), and information appliances, or what are sometimes referred to as smart devices, which may also include embedded systems, or other mobile devices and wireless devices. B] How does roaming works Visiting Location Register (VLR)

� � � � C]

Active Subscriber is registered in VLR. It is a temporary data base of all the active subscribers. HLR validates subscriber before registration. MSC ask VLR before routing incoming call. Why Cell is Hexagonal

In a cellular System a land area is divided into regular shaped cells, which can be hexagonal, square, circular or some other irregular shapes,

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Mobile Computing : December-2009although hexagonal cells are conventional. This is because there are some criteria for the cell shape, which are 1. Geometric shape 2. Area without overlap 3. Area of the cell And the eligible shapes for these criteria are Square, circle, equilateral triangle & hexagon. The Geometric shape & Area without overlap is satisfied by a hexagon, square, equilateral triangle as they can be fitted in a manner where there is no area of overlap. The circle on the other hand would overlap (which implies interference of signals) or leave gaps (which means loss of coverage in those areas) when not overlapping. When the area factor is considered a circle has the highest area however it does not satisfy the second criteria of overlap. Therefore we have to consider a shape which fits correctly and also has maximum area. For this purpose we shall compare the area of the remaining shapes to the area of circle to see which has the maximum area. � The area of an equilateral triangle to a circle approx = 17.77% � The area of a square to a circle approx = 63.7% � The area of a hexagon to a circle approx = 83% This means hexagon has the highest coverage area after a circle from the lot. Thus of the lot hexagon satisfies all the conditions which is why the shape of a cell is hexagonal in cellular network. D] Write benefits of VOIP

Integration of Voice and Data - The integration of voice and data traffic will be demanded by multi application software. The inevitable evolution will be web servers capable of interacting with voice, data and images.

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Mobile Computing : December-2009Simplification - An integrated infra structure that supports all forms of communication allows more standardization and lesser equipment management. The result is a fault tolerant design. Network Efficiency - The integration of voice and data effectively fills up the data communication channels efficiently, thus providing bandwidth consolidation. The idea is to move away from the TDM scheme wherein the user is given bandwidth when he is not talking. Data networks do not do this. It is a big saving when one considers the statistics that 50% of a conversation is silence. The network efficiency can be further boosted, by removing the redundancy in certain speech patterns. Cost redaction - The Public Switched Telephone Networks toll services can be bypassed using the Internet backbone, which means slash in prices of the long distance calls. However these reductions may slightly decrease when the Federal communications Commission (FCC) removes the Enhanced Service Provider (ESP) status granted to Internet service providers (ISPs) by which they do not have to pay the local access fees to use the telephone company (TELCO) local access facilities. Access fees form a significant part of all long distance calls. But in spite of this, the circuit switched telephony would be expensive because of lack of bandwidth consolidation and speech compression techniques. Directory Services over Telephones - Ordinary telephones can be enhanced to act as an Internet access device. Directory services could be implemented by submitting a name and receiving a reply. Inter Office trucking over the corporate intranet - The tie trunks between companies owned PBXs could be replaced by an Intranet link and would provide large savings at a good quality of service. Remote access to the office from your home - One's home could be converted to a home office and gain access to the company's voice, data and fax services using the company's Intranet.

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Mobile Computing : December-2009IP-based call centers - With the advent of the Internet, companies have experienced large increase in their web site inquiries. These may not result in immediate financial transaction but at least people get to know about their products. This is the beginning of E-commerce. With VOIP there can be interaction with the customers. Fax over IP - Real time facsimile transmission is an immediate application of Voice over IP. Facsimile services which use dial-up PSTN services are affected by high cost for long distance, analog signal quality and machine compatibility. Instead a fax interface unit can convert the data to packet form, handle the conversion of signaling and controlling protocols and ensure complete delivery of the data in correct order. E] Compare AOC and SOC Client Mobile technology can be implemented with Sometimes On

Connectivity (SOC) to mobile devices or Always On Connectivity (AOC). BSI Consulting coined SOC and AOC terminology in order to effectively describe to our clients the communications frequency and performance: capabilities of alternatives for mobile computing solutions. SOC clients can work effectively in a disconnected mode and take advantage of wireless or wired connections when they are available while AOC clients must be connected all or most of the time to be effective. SOC clients have the ability to store large amounts of data on the mobile device and provide the user with a complete application solution even when the user does not have a wireless or wired data connection. Data updates can occur when wireless, Internet dialup, network or desktop synchronization connections are available. Regardless of connectivity, productive work can proceed. Data updates, when they do occur, can be fast bursts of small amounts of data rather than entire screen images that AOC clients employ. SOC client technology typically requires a Pocket PC or WinCE device in order to have sufficient processing power and data storage capability.

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Mobile Computing : December-2009AOC clients have small amounts of data or no data on board the device. AOC clients require a wireless connection that is always on to be able to access data and the user interface, or screen image. AOC clients typically use a browser for application interactions. Internet-like HTML or WAP is employed by the browser to view web pages that are especially designed for the smaller screens of mobile devices. AOC clients require transmission of the data and screen image for each user action. Consequently, mobile workers need a wireless connection constantly available in order to effectively use AOC client mobile devices. F] Write Wireless n/w Application

Retail Retail organizations need to order, price, sell, and keep inventories of merchandise. A wireless network in a retail environment enables clerks and store room personnel to perform their functions directly from the sales floor. Salespeople are equipped with a pen-based computer or small computing device with bar code reading capability and a wireless link to the store's database. They are then able complete transactions—such as price checks, special orders, and inventory - from anywhere within the store. Warehousing Warehouse staff must manage the receiving, shipping, and inventory of stored goods. These responsibilities keep the staff mobile. Warehouse operations have traditionally bean a paper-intensive and time-consuming environment. An organization, however, can eliminate paper, reduce errors, and decrease the time necessary to move items in and out by giving each warehouse employee a handheld computing device with a bar code scanner interfaced via wireless network to a warehouse inventory system. Upon receiving an item for storage within the warehouse, a clerk can enter the item's nomenclature and part number by keying the information into the database via the handheld device. A forklift operator can then move the item to a storage place and enter the location via a similar handheld device.

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Mobile Computing : December-2009Thus, the inventory system identifies which items the warehouse contains and where the items are located. As shipping orders enter thd warehouse, the inventory system produces a list of the items and their locations. A clerk can view this list from the database via the handheld device and locat the items needed to assemble a shipment. As the clerk removes the^ items from the storage bins, the database can be updated via the handheld device. Real Estate Real estate salespeople perform a great deal of their work away from the office, usually talking with customers at the property being sold or rented: Before leaving the office, salespeople normally identify a few sites to show a customer, print the MLS (Multiple Listing Service) information that describes the property, and then drive to each location with the potential buyer. If the customer is unhappy with that round of sites, the real estate agent must drive back to the office and run more listings. Even if the customer is decides to purchase the property, they must both go back to the real estate office to finish paperwork that completes the sale. Wireless networking makes the sale of real estate much more efficient. The real estate agent can use a computer away from the office to access a wireless MLS record. IBM's Mobile Networking Group and Software Cooperation of America, for example, have wireless MLS information available that enables real estate agents to access information about properties, such as descriptions, showing instructions, outstanding loans, and pricing. An agent can also use a portable computer and printer to produce contracts and loan applications for signing at the point of sale. Hospitality Hospitality establishments check customers in and out and keep track of needs, such as room service orders and laundry requests. Restaurants need to keep track of the names and numbers of people waiting for entry, table status, and drink and food orders. Restaurant staff must perform these activities quickly and accurately to avoid making patrons unhappy. Wireless networking satisfies these needs very well. Someone can greet patrons at the

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Mobile Computing : December-2009door and enter their name, size of the party, and smoking preference- into a common database via a wireless device. The greeter can then query the database and determine the availability of an appropriate table. Those who oversee the tables also would have a wireless device used to update the database to show whether the table is occupied, being cleaned, or available. After obtaining a table, the waiter will transmit the order to the kitchen via the wireless device, eliminating the need for paper order tickets.

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Utilities Utility companies operate and maintain a highly distributed system that delivers power and natural gas to industries and residences. Utility companies must continually monitor the operation of the electrical distribution system and gas lines, and must check usage meters at least monthly to calculate bills. Traditionally, this means a person must travel from location to location, record information, and then enter the data at a service or computing center. Several utility companies are employing wireless networks to support the automation of meter reading and system monitoring, saving time and reducing overhead costs. Kansas City Power & Light, for example, operates one of the largest wireless metering systems, (serving more than 150,000 customers in eastern Kansas and western Missouri. This system employs a monitoring device at each customer site that takes periodic meter readings and sends the information back to a database that tracks usage levels and calculates bills, avoiding the need for a staff of meter readers. In addition, the Jacksonville Electric Authority (JEA) in Jacksonville, Florida, uses a RAM Mobile Data wireless WAN service to save time and reduce paperwork. This system eliminates radio conversations and paperwork between central-site dispatchers and maintenance seeding UP the service to customers. Field Service Field service personnel spend most of their time on the road installing and maintaining systems or inspecting facilities under construction. In order to complete their jobs, these individuals need access to product documentation and procedures. Traditionally, field service employees have had to carry several binders of documentation with them to sites that often lack a phone and even electricity in some cases, the field person might not be able to take all the documents with him to a job site, causing him to delay the work while obtaining the proper information. On long trips this information may also become outdated. Updates require delivery that may

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Mobile Computing : December-2009take days to reach the person in the field. Wireless access to documentation can definitely enhance field service. A field service employee, for example, can carry a portable computer connected via wireless network to the office LAN containing accurate documentation of all applicable information. Field Sales Sales professionals are always on the move meeting with customers. While on site with a customer, a salesperson needs access to vast information that describes products and services. Salespeople must also place orders, provide status, such as meeting schedules, to the home office, and maintain

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SECTION II Que. 4 A] 1] Attempt Following

Explain: Mobile Node a node which is capable of mobility; i.e., a node which can change its point-of-attachment from one link to another while maintaining all existing communications and using only its (permanent) IP home address.

2]

Home Agent A router with at least one interface on a mobile node's (current) foreign link. When a mobile node uses a foreign agent's care-of address; the foreign agent de-tunnels and delivers packets to the mobile node that were tunneled by the mobile node's home agent. A foreign agent might also serve as a default router for packets sent by a registered mobile node. foreign agent care-of address an address of a foreign agent that has at least one interface on a mobile node's current foreign link Foreign link (foreign network) any link other than a mobile node's home link; i.e. any link whose network-prefix does not equal the network-prefix of a mobile node's home address.

3]

Foreign Agent A router with at least one interface on a mobile node's home link. A home agent intercepts packets destined to a mobile node's home address and tunnels them to the mobile node's care-of address when the mobile

B]

Explain Source Addressing Mobile IP, as described in [RFC 2002], does indeed assume that IP

unicast packets (i.e., those with a single destination, as opposed to multicast packets) are routed based solely on their IP Destination Address

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Mobile Computing : December-2009and without regard to their IP Source Address. However, new attacks being waged on the Internet by Bad Guys might cause Internet Service Providers to implement policies which invalidate this assumption. Specifically, Internet Service Providers are being advised by the Internet Architecture Board (IAB) to filter packets by Source Address and discard those, whose Source Address appears to be coming from the "wrong" place. Packets fitting this description are those, whose Source Addresses have network-prefixes that do not match any of the networkprefixes assigned to the links that are known to exist in the direction from which the packets arrived. This type of filtering, called network ingress filtering, presents a very large problem for Mobile IP. This is because packets sent by mobile nodes connected to a foreign link are exactly the type of packets that fit the above description and that network ingress filtering is designed to block! C] Write short note on Ad-Hoc N/W. Mobility support described in earlier section so far relies on the existence of at least some infrastructure. Mobile IP requires, e.g., a home agent, tunnels, and default routers. DHCP requires servers and broadcast capabilities of the medium reaching all participants or relays to servers. Cellular phone networks require base stations, infrastructure networks etc. However, there are several situations where users of a network cannot rely on an infrastructure, the, infrastructure is too expensive, or there is no infrastructure at all in these situations ad hoc networks are the only choice. Examples, for the use of ad hoc networks are: Instant infrastructure: Unplanned meetings, spontaneous interpersonal

communications etc. cannot rely on any infrastructure!

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Mobile Computing : December-2009Infrastructures need planning and administration. It would take too long to set up this kind of infrastructure; therefore, ad hoc connectivity has to be set up.

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Mobile Computing : December-2009Disaster Relief: Infrastructures typically break down in disaster areas. Hurricanes cut phone and power lines, floods destroy base stations, fires bum servers. Thus, emergency teams can only rely on an infrastructure they can set up themselves. No forward planning can be done, and the setup must be done extremely fast and reliably. The same applies to many military activities. Remote areas: Even if infrastructures could be planned ahead, it is sometimes too expensive to set up an infrastructure in sparsely populated areas. Depending on the communication pattern, ad hoc networks or satellite infrastructures can be a solution. Effectiveness: Services of existing infrastructures might be too expensive for certain applications. If, for example, only connection-oriented .cellular networks exist, but an application sends only small status information every other minute, a cheaper ad hoc packet-oriented network might be a better solution. Furthermore, registration procedures might take too long, and communication overhead might be too large with existing networks, thus, application-tailored ad hoc networks can offer a better solution. The reason for having a special section about ad hoc networks, within a chapter about the network layer is that routing of data is one of, the most difficult issues in ad hoc networks. While the sections following give some examples for routing algorithms suited to ad hoc networks. It has to be mentioned that routing functions sometime also exist in layer 2, not only in the network layer (layer 3) of the reference model. HlPERLAN for example, offers forwarding/ routing capabilities in layer 2 based on MAC addresses for ad hoc networks. One of the first ad hoc wireless networks was the packet radio networks started by ARPA in 1973. It allowed up to 138 nodes in the ad hoc network used IP packets for data transport. This made an easy, connection possible

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Mobile Computing : December-2009to the ARPAnet, the starting point of today's Internet.

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Mobile Computing : December-2009Que. 5 A] 1) Attempts following.

Explain Following Tags Do

The <do> tag can be used to activate a task when the user clicks on a word/phrase on the screen. A <do> tag can also be nested inside a <template> tag. The <do> tag will then apply to all cards in the deck. Syntax <do type="type"> TASK TO PERFORM </do>

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2]

Table

The <table> tag defines a table. The <table> tag is used together with the <tr> and <td> tag to create a table. The number attribute is required. A value of zero is not allowed. WML tables have no borders. Syntax <table columns="a number"> <tr> <td></td> </tr> </table>

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3]

Select

The <select> tag defines a selectable list. The <option> tag is used to define the options in the selectable list. Syntax <select> <option>text</option> <option>text</option> </select>

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4]

Input

The <input> tag defines an input field (a text field where the user can enter some text). Syntax <input name="some name"/>

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B] 1]

Write following Write WML Program to trigger ontimer event.

<? xml version=”1.0”?> <! DOCTYPE wml PUBLIC “-//WAPFORUM//DTD WML 1.3//EN” http://www.wapforum.org/DTD/wml13.dtd”> <wml> <card id=”card1” title=”Card 1”> <onevent type=”ontimer”> <go href=”#card2”/> </onevent> <timer value=”50”/> <p align=”center”> Timer Example First Card </p> </card> <card id=”card2” title=”Card 2”> <p align=”center”> <big> Welcome to Second Card </big> </p> </card> </wml>

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2]

Write WML program to trigger onpick event.

<? xml version=”1.0”?> <! DOCTYPE wml PUBLIC “-//WAPFORUM//DTD WML 1.3//EN” http://www.wapforum.org/DTD/wml13.dtd”> <wml> <card id=”card1” title=”Card 1”> <p align=”center”> <select name=”s1”> <option onpick=”mouse”>Mouse</option> <option onpick=”keyboard”>Keyboard</option> <option onpick=”monitor”>Monitor</option> </select> </p> </card> <card id=”mouse” title=”Mouse Info”> <p align=”center”> <big>Mouse Specification: < /big><br/> Type=Optical Mouse<br/> Mrp=300Rs </p> </card> <card id=”keyboard” title=”Keyboard Info”> <p align=”center”> <big>Keyboard Specification:</big><br/> Type=PS/2<br/>

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Mobile Computing : December-2009Mrp=500Rs </p> </card> <card id=”monitor” title=”Monitor Info”> <p align=”center”> <big>Monitor Specification :< /big><br/> Type=LCD Wide<br/> Mrp=5000Rs </p> </card> </wml>

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Que. 6 A]

Attempt any Four

Compare HTML and WML

B]

What is WML Script?

WMLScript serves as a complement to WML and provides „a general scripting capability in the WAP architecture (WAP Forum, 1998). While all WML content is static, WMLScript offers several capabilities not supported by WML: Validity check of user input: Before user input is sent to a server, WMLScript can check the Validity and save bandwidth and latency in case of an error. Otherwise, the server has to perform all checks which always include at least one round-trip time if problems occur. Access to device facilities: WMLScript offers functions to access hardware components and software functions of the device. On a phone a user could, e.g., make a phone call,

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Mobile Computing : December-2009access the address book, or send a message via the message service of the mobile phone. Local user interaction: Without introducing round-trip delays WMLScript can directly and locally interact with a user, show messages or prompt for input. Only, for example, the result of several interactions could be transmitted to a server. Extensions to the device software: With the help of WMLScript a device can be configured and new functionality can be added even after deployment. Users can download new software from vendors and, thus, upgrade their device easily. D] Write a short note on TCP While slow start is one of the most useful mechanisms in fixed networks, it drastically decreases the efficiency of TCP if used together with mobile receivers or senders. The reason for this is the use of slow start under the wrong assumptions. From a missing acknowledgement, slow start concludes a congestion situation. While this may also happen in networks with mobile and wireless end-systems, it is not the main reason for packet loss. Error rates on wireless links are much higher compared to fixed fiber or copper links. Thus, packet loss is much more common and cannot always be compensated for by layer two retransmissions. Trying to retransmit on layer two could, for example, trigger TCP retransmission if it takes too long. Now layer two faces the problem of transmitting the same packet twice over a probably bad link. Detecting these duplicates on layer two is not an option, because more and more connections use end-to-end encryption, making it impossible to look into the packet Furthermore, mobility itself can cause packet loss. There are many situations where a soft handover from one access point to another is not possible for a mobile end-system. Using, for example, mobile IP, there could still be some packets in transit to the old foreign agent while the mobilePage 43

Mobile Computing : December-2009node moves to the new foreign agent. It may now be the case that the old foreign agent cannot forward those packets to the new foreign agent or not even buffer the packets if disconnection of the mobile node takes too long. This packet loss has nothing to do with wireless access but is caused by the problems of rerouting traffic. The TCP mechanism detecting missing acknowledgements via timeouts and concluding packet loss due to congestion cannot distinguish between the different causes. TCP reacts with slow start, which does not help in the case of transmission errors over wireless links and which does not really help during handover. This behavior results in a severe performance degradation of an unchanged TCP if used together with wireless links or mobile nodes. However, one cannot change TCP completely just to support mobile users or wireless links. The same arguments that were given to keep IP unchanged also apply for TCP. The installed base of computers using TCP is too large to be changed and, more important, mechanisms such as slow start keep the Internet operable. Every enhancement to TCP, therefore, has to remain compatible to the standard TCP and must not geo paradise the continuous behavior of TCP in case of congestion. E] Explain Transcoding Transcoding involves transforming data/ application sources (HTML, XML) using extraction media (Hardware or software), to render into other formats, appropriate for any mobile devices. Moreover that extraction media can clip useful content, fragment pages in to multiple pages, image manipulation, manage large tables, manage frames, and other operation from which we can get hand-held friendly content. Therefore Transcoding is the best method for getting hand held friendly content. Transcoding

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Mobile Computing : December-2009Computers, of course, are not inherently intelligent; they need to be told exactly what things are, how they are related and how-to deal with them. Clearly, a simple way for computers to communicate and readily exchange data is needed. And transcoding is a key element in that solution. Transcoding is the process of transforming the format and representation of content. Enterprise and Web content may be filtered, transformed, converted or reformatted to make it universally accessible by a plethora of devices, to exploit specific application requirements for customized content and to personalize general content. What all of this means is that enterprise data and applications or Web based data can be leveraged by multiple users with multiple devices in a manner that's seamless across the network and is tailored to the specific user and device. The challenge is to deliver data to any devices filled with countless variables, including: � The limited storage capacity of pervasive devices may prevent them from being able to store larger pages - content truncation might otherwise result. � The limited display capabilities of pervasive devices would likely prohibit adequate rendering of large and complicated pages. � The bandwidth available to transport page data (such as images and HTML) to pervasive devices is, in. general, several orders of magnitude less than that available to wired clients. Pages that are large and/or graphically intensive may yield excessive load delays when accessed via pervasive devices: � � � � Network latency (milliseconds to seconds) Computational power (CPU speed, available memory) User input capabilities (none, voice, pen, buttons, keyboard)

A wide range of application markup languages (HTML, industry dialects of XML, WML)

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