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Lecture 1: Preliminaries

Lecture 1: Preliminaries. Lecture 1.1 : Introduction to mobile ad hoc networks Lecture 1.2 : Introduction to networking and wireless communication & A brief overview of the course. Course Administration.

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Lecture 1: Preliminaries

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  1. Lecture 1: Preliminaries • Lecture 1.1 : Introduction to mobile ad hoc networks • Lecture 1.2 : Introduction to networking and wireless communication & A brief overview of the course Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  2. Course Administration • Lectures : Tuesday, Wednesday and Friday 14-16h, Room 106-00-007 • Exercises : Thursday, 14-16h • Lab : Monday, 16-18h, Room 051-03-026 • Exam : March 15, 10h , Room 101-00-036 Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  3. Course Organization • To be able to write the exam : • You must attend the lab every week, starting from next Monday, January 17 • You must attend the exercise group every week, starting from January 20. You should submit every exercise sheet and show your solution in exercise group. • Deadline for exercise sheets is Thursday 14h. Submit via email : pomplun@informatik.uni-freiburg.de or in letterbox in building 051. First exercise sheet will be released this Thursday. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  4. The Importance of Mobile and Wireless Computing • There is tremendous technological advance in producing small and smart devices. • It is a natural consequence that such devices work in a collaborative way. • However, users carry around many such smart devices and they are not fixed in the sense of a desktop computer. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  5. Networking without an Infrastructure • Hence, there is a need for networking such mobile devices without any infrastructural support. • Cellular phones work with infrastructural support like mobile phone towersand satellitecommunication. • However, such support comes at a cost like pre-registration with a mobile service provider. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  6. Networking Anywhere and Anytime • On the other hand, there is a growing demand of using networks of mobile devices anywhere and anytime. • In many situations, the Internet may not be an efficient solution. • For example, a collection of people trying to communicate in a hotel or conference hall. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  7. Smart Devices • Another important application of wireless communication is the use of small smart devices. • The number of embedded devices in appliances and vehicles is increasing at a rapid rate. • There is a growing need of networking such embedded devices without infrastructural support. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  8. Sensor Dust • Sensor dust is a collection of small and inexpensive devices which work through collaboration. • Thousands of such devices can be used for applications like : environmental data collection, weather forecasting, measuring toxicity levels at hazardous sites etc. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  9. Sensor Dust • Small sensor devices can be used in a large scale for monitoring climate. • The purpose of a sensor dust is to collect data through inexpensive sensor devices and gather this data in a base station through wireless transmission for analysis. • Sensor dust is typically deployed in places where there is no infrastructural support. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  10. Wireless Sensor Devices • Several companies are manufacturing small devices equipped with a radio transmitter and a plug-in sensor device. • Berkeley Mica mote is one such device. It is possible to plug-in temperture, pressure or motion sensors on a mote. • The operating system TinyOS is specifically designed for programming motes. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  11. Ad hoc Networks • This course is about ways of information exchange in a network of mobile and wireless nodes without any infrastructural support. • Such networks are often called ad hocnetworks to emphasize that they do not depend on infrastructural support. • The purpose of an ad hoc network is to set up (possibly) a short-lived network for a collection of nodes. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  12. Ad hoc Networks • Most network operations involve exchange of information among the computers participating in a network. • There are numerous protocols for networks with infrastructural support , starting from LANs, Ethernets and global networks like the Internet. • However, most of these protocols do not work well for ad hoc networks. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  13. Routing in an Ad hoc Network • If all the wireless nodes are within the transmission range of each other, routing is easy. Every node can listen to all transmissions. • However, this is not true in most situations, due to short transmission range. Hence, most ad hoc neworks are multi-hop. • A message from a source node must go through intermediate nodes to reach its destination. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  14. Routing in multi-hop networks • All nodes cooperate in delivering messages across the network. • The nodes must collect local neighbourhood information in order to make global routing decisions. • This situation is quite different from wired networks where the routing decisions are made based on the infrastructure. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  15. An Example Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  16. Personal Area Network (PAN) • The aim of a PAN is to create a very localized network for devices associated with a single person. • Such devices include PDAs, virtual reality devices and laptop computers. • Such devices usually need not have connection to the wider internet, but they should be able to network among themselves. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  17. Bluetooth • Mobility becomes much more important when there is a need to network between several PANs. • Bluetooth is a short-range radio technology for wireless connectivity of PDAs and other similar devices. • If each device is equipped with a Bluetooth radio, it is possible to connect upto 8 such devices into a piconet. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  18. Scatternets • When there are more than eight devices, Bluetooth can be used to form multiple piconets. • These piconets can be connected together into a scatternet. • Mobility is again an issue if individual piconets are not static. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  19. Factors Affecting Ad hoc Networking • There are several factors specifically important for ad hoc networking : • Address assignment • Scalability • Power budget versus latency • Incompatible standards Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  20. Addressing Problems • Nodes in an ad hoc network are assumed to have addresses that are preassigned. • These addresses are not directly related to the current positions of the nodes relative to the overall network. • This is significantly different from the way addresses are assigned within the Internet. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  21. Addressing within the Internet • Routing within the Internet depends on the ability to collect reachability information to IP nodes. • All the nodes within the same network share the same routing prefix. • Nearby networks have similar routing prefixes. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  22. Hierarchy of Addresses • Smaller prefixes sit at the higher levels of the hierarchy. • Reachability to all nodes within the hierarchy can be described by advertising a single, smallest routing prefix. • The key to the scalability of the internet is the collection of routing information in hierarchies. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  23. Addressing in Ad hoc Networks • Such a hierarchy is typically not available for ad hoc networks. • It is possible to introduce this hierarchy by controlling the IP addresses of the mobile nodes. • However, this requires that the IP addresses change depending on the movement of the nodes. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  24. Addressing in Ad hoc Networks • However, changing IP addresses introduces extensive changes in the routing tables. • It is not clear whether maintaining a hierarchy is useful since it causes major revisions of the routing tables. • There may be major limitations for ad hoc network protocols for large collections of nodes. With increased mobility, route maintenance will consume a major part of the bandwidth. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  25. Scalability • Ad hoc networks are not as easily scalable as the Internet. Loss of hierarchy introduces larger routing tables. • Hence, we have to look for other means of introducing hierarchy by not using IP addresses. • Hence, IP based protocols must maintain additional routing information. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  26. Other Scalability Issues • Since routing tables change as the nodes move, control messages have to be sent around the network to maintain the current connectivity information. • The control messages have to be sent more often if mobility is high. • If the network has a large number of highly mobile nodes, the control messages take up a lot of bandwidth. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  27. Role of Control Messages • Efficient routing protocols should try to send less number of control messages for maintaining connectivity information. • Otherwise, there will be no bandwidth left for sending useful messages. • Also, processing a large number of control messages put a heavy load on individual nodes. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  28. Evaluating Protocols for Ad hoc Networks • If the nodes are slow in processing control messages, they may generate more control messages and hence flood the network. • Routing protocols must be evaluated carefully with increased number of nodes and increased mobility to see their effect on control mesages. • The network should settle down fast (or converge) when a node moves. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  29. Power Budget versus Latency • One of the key issues in ad hoc networks is power management. • Most nodes in an ad hoc network are powered by batteries. Batteries cannot be recharged easily in many cases. • Each node participates in two kinds of activities, sending and receiving messages useful for itself and forwarding messages for other nodes. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  30. Power Management • The second activity is essential for maintaining an ad hoc network, since nodes should forward messages in a multi-hop network. • However, the battery-power of a node will deplete fast if there are too many control messages to forward. • A node may refuse to forward messages if its power level is too low. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  31. Energy-efficient Protocols • Hence, routing protocols should be designed to be energy-efficient. • However, good routing decisions can only be taken if the nodes have good knowledge of the network topology. • On the other hand, the nodes need to send more control messages for maintaining topology information. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

  32. Incompatible Standards • There are many different proocols and engineering solutions existing for ad hoc networks. • IETF(Internet Engineering Task Force) is currently evaluating several protocols and standards within its MANET(Mobile Ad hoc Network) working group. Institute for Computer Science, University of Freiburg Western Australian Interactive Virtual Environments Centre (IVEC)

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