Mobile Communication - Assignment Example

Mobile Communication Answer: 01 a) The IP allocates the second address when the host is in motion (away from the home network) and wants to connect with the foreign network. This temporary address sends the datagram to the host’s current location. b) Home address: It is the permanent IP address assigned to a mobile device in order to connect with the home network. The data grams intended for the mobile node are always sent through this address and it remains unchanged regardless of the location of the mobile node. Home network: It is a network which allows a person’s digital devices to communicate with each other within the user’s home. It may include multiple computers and their peripheral devices, stereos, television, game systems, telephones, home security systems, internet access, file sharing etc. It reduces the need of redundant equipments in a single house and makes thing easier. Foreign network: When a mobile node moves from its assigned network (home IP address) and seeks a new network to operate in motion then this new network is known as a foreign network. Care-of-address: It is a temporary IP address assigned to a mobile device in order to connect with a foreign network. Normally, it is a 32-bit IP address mostly used by mobile IP for forwarding IP data grams and other administrative functions. c) In order to travel a packet from a static host, P, to a mobile host, M, which travels away from the home network, a care-of-address is registered with the home agent or through the foreign agent depending upon the mode of attachment. The datagram with this care-of-address is forwarded to the home network. The home agent designates the incoming datagram into a new datagram and this process is known as tunneling. The foreign agent opens the datagram which delivers the packet using conventional IP routing. The foreign agent removes the original datagram from the tunnel and delivers to the mobile node’s IP address. d) Triangle routing refers to a situation in which the mobile node can directly send packets to any correspondent node but that node or any other internet node is unable to communicate directly with the mobile node. The IP data gram has to pass through the home network in order to reach the destination residing in the foreign network. This is due to the malicious routers which guide the packets in the wrong direction and creates problems such as network partition, network congestion, service denial etc. In order to overcome this problem, an operation known as Route Optimization has been introduced which enables the packets to take a shorter route by creating a binding between the mobile node’s permanent IP address and the current temporary care-of-address. This binding allows the home agent to send an authenticated Binding Update to the correspondent node which updates the binding cache with the mobile node’s care-of-address in order to send the packets. Answer: 02 a) In an ad hoc network, nodes are free to move and can change their position randomly and rapidly at unpredictable times. It can consist of both bidirectional and unidirectional links. The capacity bandwidth in an ad hoc network is relatively lower than that of wired networks. It has limited physical security as mobile wireless networks are more prone to security issues. b) AODV discovers the route to a node with which it has no contact before by sending a route request (RREQ) message to its neighbor. Each node that receives the message sets up a reverse route towards the node that originally sent the message. When the destination node receives the message, it replies by sending a route reply (RREP). c) When the communication between two adjacent nodes is lost, a Route Error (RERR) message is sent to the other nodes. This message is only sent to the unreachable destination to notify about the link breakage. Answer: 03 a) Piconet: Piconet is an ad-hoc computer network which connects a group of Bluetooth devices using protocols that are part of Bluetooth technology. The device that initiates the piconet acts as the master device which can interconnect with up to seven active slave devices (using a three-bit MAC address) and 255 inactive slave devices which can be made active at any time by the master device. It has typically a range of 30 feet (10 meters) which may vary according to the class of the bluetooth device. The data transfer rate vary between 400kbps and 700kbps (kilo bits per second) depending upon the connection used i.e. synchronous or asynchronous. Scatternet: Scatternet is a group of interconnected and non-synchronized piconets in which at least one device is a member of more than one piconet. It enables many devices to share the same area by making the efficient use of bandwidth. In order to establish a scatternet communication, bluetooth devices must have point to multipoint capability. In a scatternet, there may be a maximum of 10 fully loaded piconets. b) There are three ways to avoid interference between two or more piconets sharing the same physical area: By assigning unique addresses for a particular set of devices. In this way, the Bluetooth network will ignore any transmissions from the devices outside of its assigned address range. By using a technique called frequency hopping spread spectrum which rapidly switches to a new frequency after receiving or transmitting a packet. Thus, it helps in minimizing the risk of any collision as the rate of frequency change is 1600 times per second. By measuring and controlling the level of noise carefully generated by different devices. This can be done by building a variety of filters which limits the impact of random noise and prevents the blockage of devices. c) The transmission rate of the channel reduces in a piconet because as the devices connect with each other noise is produced which lowers the basic rate of the network. The trafficking of the wave lengths due to the crowding of the devices results in the reduction of the effective bandwidth. d) Since piconet is based on Bluetooth technology and its ad-hoc network, it uses Bluetooth standard protocols and reason it takes too long as that the slave connection has to wait for the master connection reply to connect. Answer: 04 a) b) I don’t agree with this statement because as advancements are taking place in every field the personal requirements of the people will keep rising. In order to meet those requirements, the need for specialized environments in programming will also increase to experience a whole range of individual preferences and making it more user-friendly. c) This can be explained by an example: The user types a message in the string form. This message (string) is sent to the JAVA servlet on a Web server using the HTTP post method. After the string is received by the JAVA servlet, it reverses the string and sends it back to the MIDlet application in order to display. Answer: 05 a) The TCP/IP protocol is not suitable for low bandwidth, high latency mobile devices as it is based on packets and to transfer new packets the used medium of mobile transmission latency for small TCP/IP data packets suffers this problem. Hence because of the lag/latency, the packets get dropped or corrupted. b) Responsibility of home agent: To track the mobile node’s COA by interacting with the foreign agent. To update the mobile node’s current location. To figure out the incoming datagram addressed to nodes whose home network is that of the home agent but are currently located on the foreign network. Responsibility of foreign agent: To create a care-of-address (COA) for the mobile node matching the network portion of the COA with that of the foreign network. To inform the home agent that the mobile node is resident in its foreign network and has the given COA. In the process of tunneling, the foreign agent is responsible for removing the original data gram from the tunnel and sending it to the mobile node. c) Triangle routing refers to a situation in which the mobile node can directly send packets to any correspondent node but that node or any other internet node is unable to communicate directly with the mobile node. The IP data gram has to pass through the home network in order to reach the destination residing in the foreign network. This is due to the malicious routers which guide the packets in the wrong direction and creates problems such as network partition, network congestion, service denial etc. In order to overcome this problem, an operation known as Route Optimization has been introduced which enables the packets to take a shorter route by creating a binding between the mobile node’s permanent IP address and the current temporary care-of-address. This binding allows the home agent to send an authenticated Binding Update to the correspondent node which updates the binding cache with the mobile node’s care-of-address in order to send the packets. d)In a Bluetooth connection, the interference is avoided by using unique IP address or by frequency hopping technique. However, a Wi-Fi connection may tune the access point to avoid the frequencies of the disturbing signals. It can also provide adequate LAN coverage to avoid interference. The available bandwidth and maximum throughput by Wi-Fi (802.11) is 54 Mbps, 30 Mbps in practice and that of Bluetooth is 1 Mbps. Bluetooth can connect as many as one master and seven slave devices. On the other hand, Wi-Fi technology has the ability to network 255 devices with a single access point but it is not practically recommended as the performance of such network will be very poor. d) Bluetooth devices take time to connect with the network because initially the devices are not synchronized and need to search different channels to connect with the devices in the same area. Answer: 06 a) An ad-hoc network is an autonomous system of mobile nodes with the absence of a fixed infrastructure and centralized point. Due to this a different style of routing algorithm is preferred because the existing algorithms were designed to support the network with a fixed structure. The decrease in the accuracy of the route information is also one reason which leads to an increase in the overhead produced by the periodic route update messages. Another reason is that in ad-hoc networks the real traffic of the node is concentrated in a small number of particular nodes which has not been identified while designing the existing routing algorithms. b) AODV uses route table management to keep the information regarding the destination location. It includes destination IP address, destination sequence number, valid destination sequencing number flag, network interface, list of precursors, hop count, next hop, expiration time of the route and other state and routing flags. c) A route discovery process is initiated to find the destination node by sending a route request (RREQ). Each node first creates or updates the reverse route and then moves the request to the next node. d) In AODV, when a mobile which is not the destination has a route of the destination node with corresponding sequence number greater than or equal to that present in the route reply then in such a situation a route reply is sent to the source node. e) When a link fails between two mobiles, a notification is sent to the unreachable destination by sending the RERR messages. Answer: 07 a) In order to develop a mobile application one important characteristic that differs mobile programming from computer programming is that the client application are developed on one platform i.e. the computer and tested and deployed in an another i.e. the mobile device. Another characteristic is the issue of specificities and constraints attached with mobile devices that must be accounted in the development process. Device fragmentation is a big impact in this regard that poses many restrictions during the process of mobile application. b) State charts are a useful UML construct for designing application because of the following reasons: State charts acts as a tool to test and improve the model of the design. They help in detecting the defects at an early stage of designing the device. The strength of the state charts can be automatically checked. Once a state chart has been checked, it automatically generates the code which reduces coding errors. d) A design for a mobile phone application that searches a database for any names that match one entered depends on how effectively the language encoded for the message can serve as natural metaphor to find the information that is required by the user. To extract the key word in the database the approach of filtering out is used. Once the key similar to the search is identified the name is associated with the corresponding uploaded number in order to send the SMS. Answer: 08 a) The advantage of AWT (Abstract Windows Toolkit) includes stability, availability in every version of JAVA technology and Java implementations in old web browsers. It provides a rich graphic environment such as drawing and charting packages. The main disadvantage is that it does not support many commonly used components like tables; progress bars etc and has limited GUI components, layout managers and events. In order to solve these issues Java Swing also known as Java Foundation Classes was introduced. It is more complex but shares the same parts as that of AWT. Swing is more robust with a larger code base and multiple looks. The performance is slow but improvements are being made to make it less noticeable. b) The internet access from J2ME MIDlets is usually supported by HTTP rather than other network protocols because it is simple and powerful. It enables to write Web browsers, Web servers, automatic page downloader and other useful tools. It is essential for all MIDP implementations and hence it is available in on all MIDP devices. Moreover, there are many other factors like the ease of configuration, performance, authentication, firewall support, power etc. c) An application can have many displayable objects such as forms, alerts, lists, textboxes and canvases. In order to enter the dimensions and description details of a house on a PDA is the canvas class can be used to enhance the graphical appearance and textboxes can be drawn to enter the dimensions such as the area , width etc of the room. d) In order to upload the data from a PDA into the office system a connection between HTTP will be established with a servlet and tested by passing it with a string. This string is then sent to the server where the servlet is used to read the string and create a file in the server. The file is than parsed using a DOM parser and the data is stored in an array. e) The photo uploads via HTTP are SSL coded so that the information is encrypted using during the transmission. Read More