Lecture 5 6 .ad hoc network


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Lecture 5 6 .ad hoc network

  1. 1. Chandra Prakash Assistant Professor LPU Ad Hoc Network Lecture (5-6) 1
  2. 2. Introduction Introduction - Ad Hoc Network definition Characteristic/features and application Heterogeneity in Mobile Devices Wireless Sensor Networks Traffic Profiles Types ofAd Hoc Mobile Communications Types of Mobile Host Movements Challenges FacingAd Hoc Mobile Networks Issues and Challenges Facing Ad Hoc Mobile network Ad Hoc wireless Internet 2
  3. 3. A BSS without an AP is called an ad hoc network; a BSS with an AP is called an infrastructure network. 3
  4. 4. Ad hoc networks  Temporary network composed of mobile nodes without preexisting communication infrastructure, such as Access Point (AP) and Base Station (BS).  Each node plays the role of router for multi-hop routing.  Self-organizing network without infrastructure networks  Started from DARPA PRNet in 1970  Cooperative nodes (wireless)  Each node decode-and-forward packets for other nodes  Multi-hop packet forwarding through wireless links  Proactive/reactive/hybrid routing protocols  Most works based on CSMA/CA to solve the interference problem  IEEE 802.11 MAC 4
  5. 5. What Is an Ad Hoc Network?  An ad hoc wireless network  collection of two or more devices equipped with wireless communications and networking capability.  Such devices can communicate with another node that is immediately within their radio range or one that is outside their radio range.  For the latter scenario, an intermediate node is used to relay or forward the packet from the source toward the destination.  Since an ad hoc wireless network does not rely on any fixed network entities, the network itself is essentially infrastructure- less.There is no need for any fixed radio base stations, no wires or fixed routers. 5
  6. 6. (cont…)  An ad hoc wireless network is self-organizing and adaptive.  This means that a formed network can be de-formed on-the- fly without the need for any system administration.  The term "ad hoc" tends to imply "can take different forms" and "can be mobile, standalone, or networked.“  Ad hoc nodes or devices should be able to detect the presence of other such devices and to perform the necessary handshaking to allow communications and the sharing of information and services. 6
  7. 7. Wireless Ad-hoc Network  A wireless ad-hoc network is a decentralized type of wireless network.  The network is ad hoc because it does not rely on a pre- existing infrastructure, such as routers in wired networks or access points in managed (infrastructure) wireless networks.  Each node participates in routing by forwarding data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity.  In addition to the classic routing, ad hoc networks can use flooding for forwarding the data. 7
  8. 8. Mobile Ad Hoc Networks (MANET) Mobile nodes Access points Backbone Wireless Mobile Network MANET 8
  9. 9. Mobile Ad-hoc Network  Self-configuring network of mobile routers (and associated hosts) connected by wireless links  This union forms a random topology  Routers move randomly free  Topology changes rapidly and unpredictably  Standalone fashion or connected to the larger Internet  While MANETs are self contained, they can also be tied to an IP-based global or local network – Hybrid MANETs  Suitable for emergency situations like natural or human-induced disasters, military conflicts, emergency medical situations, etc. 9
  10. 10. Cellular and ad hoc wireless networks 10
  11. 11. Comparison of wireless cellular and wireless ad-hoc network concepts 11
  12. 12. MANET Application Applications Descriptions/Services Tactical Networks •Military communication, operations •Coordination of military object moving at high speeds such as fleets of airplanes or ships •Automated battlefields Sensor networks •Collection of embedded sensor devices used to collect real time data to automate everyday functions. Data highly correlated in time and space, e.g., remote sensors for weather, earth activities; sensors for manufacturing equipments. •Can have between 1000 -100,000 nodes, each node collecting sample data, then forwarding data to centralized host for processing using low homogeneous rates. Emergency services •Search, rescue, crowd control, and commando operations as well as disaster recovery •for e.g. Early retrieval and transmission of patient data ( record, status, diagnosis ) from /to the hospital •Replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc.12
  13. 13. MANET Application Applications Descriptions/Services Commercial environments •E-commerce, e.g., electronic payments from anywhere (i.e., in taxi). •Business: dynamic access to customer files stored in a central location on the fly provide consistent databases for all agents Mobile office •Vehicular services: transmission of news ,road conditions ,weather, music local ad hoc network with nearby vehicles for road/accident guidance Home and enterprise networking •Home/office wireless networking(WLAN), e.g., shared whiteboard application, use PDA to print anywhere, trade shows •Personal area network (PAN) Educational applications •Set up virtual classrooms or conference rooms •Set up ad hoc communication during conferences, meetings, or lectures13
  14. 14. MANET Application Applications Descriptions/Services Entertainment Multiuser games Robotic pets outdoor internet access Location- aware Services Follow- on services, e.g., automatic call forwarding, transmission of the actual workspace to the current location Information services push, e.g., advertise location-specific services, like gas stations pull, e.g., location-dependent travel guide; services( printer, fax, phone, server, gas stations) availability information; caches, intermediate results, state information, etc. 14
  15. 15. Issues in Ad-Hoc  Ad hoc wireless devices can take different forms (for example, palmtop, laptop, Internet mobile phone, etc.), the computation, storage, and communications capabilities and interoperability of such devices will vary tremendously.  Ad hoc devices should not only detect the presence of connectivity with neighbouring devices/nodes, but also identify what type the devices are and their corresponding attributes.  Due to the presence of mobility, routing information will have to change to reflect changes in link connectivity.  The diversity of ad hoc mobile devices also implies that the battery capacity of such devices will also vary. Since ad hoc networks rely on forwarding data packets sent by other nodes, power consumption becomes a critical issue.15
  16. 16. Heterogeneity in Mobile Devices (a) Heterogeneous mobile device ad hoc networks, and (b) homogeneous ad hoc network comprising powerful laptop computers.16
  17. 17. Heterogeneity in Mobile Devices  The presence of heterogeneity implies that some devices are more powerful than others, and some can be servers while others can only be clients.  It is evident that there are differences in size, computational power, memory, disk, and battery capacity.  Mobile devices can exist in many forms.There are great differences among these devices,  heterogeneity can affect communication performance and the design of communication protocols. 17
  18. 18. Characteristics of some existing mobile devices 18
  19. 19. Heterogeneity in Mobile Devices  Come in different favours:  Sensor Network  PersonalArea Network  Traditional MobileAd Hoc Network 19
  21. 21. INTRODUCTION TO WSN  A wireless sensor network is one form of an ad hoc wireless network.  A sensor network is a collection of a large number of sensor nodes that are deployed in a particular region.  Sensors are wirelessly connected and they, at appropriate times, relay information back to some selected nodes.  These selected nodes then perform some computation based on the collected data to derive an ultimate statistic to allow critical decisions to be made.  There are a variety of sensors, including acoustic(sound related) , seismic (Subject to an earthquake or earth vibration), image, heat, direction, smoke, and temperature sensors. 21
  22. 22. Basic features of sensor networks  A large number of low-cost, low-power, multifunctional, and small sensor nodes  Sensor node consists of sensing, data processing, and communicating components  A sensor network is composed of a large number of sensor nodes,  which are densely deployed either inside the phenomenon or very close to it.  The position of sensor nodes need not be engineered or pre-determined.  sensor network protocols and algorithms must possess self-organizing capabilities. 22
  23. 23. Basic features of sensor networks  Self-organizing capabilities  Short-range broadcast communication and multihop routing  Dense deployment and cooperative effort of sensor nodes  Frequently changing topology due to fading and node failures  Limitations in energy, transmit power, memory, and computing power 23
  24. 24. Wireless Sensor Networks  A sort of ad-hoc networks  A network of low cost, densely deployed, untethered sensor nodes  Application areas: heath, military, and home  Placed in inaccessible terrains or disaster areas  It may be impossible to recharge batteries  Different Node Characteristics fromTraditional nodes  No of nodes in a sensor network can be several orders of magnitude higher than the nodes in an Ad Hoc network (100s to 1000s nodes)  Densely deployed (20 nodes/m3)  Mobility of nodes is not mendatory  Prone to failures  Topology changes very frequently  Mainly use a broadcast communication, whereas most Ad Hoc networks are based on point-to-point  Limited in power, computing capacities, and memory  May not have global ID because of the large amount of overhead and large number of sensors Ad Hoc Net Wireless Sensor Network 24
  25. 25. Existing Wireless Net vs. Sensor Net Cellular system Bluetooth, MANET Sensor Network Single Hop Multi-hop Multi-hop High QOS Bandwidth efficiency High QOS Power conservation Limited bandwidth Large number of node Narrow radio range Frequent topology change Station to Base station Peer to peer Peer to multi node Peer to multi node 25
  26. 26. Factors influencing sensor network design  Fault tolerance;  Scalability;  Production costs;  Operating environment;  Sensor network topology;  Hardware constraints;  Transmission media;  Power consumption. 26
  27. 27. Sensor Network Model SourceStimulus Sink Sink 27
  28. 28. Sensor Networks Architecture  Sensor node  Made up of four basic components  Sensing unit, Processing unit,Transceiver unit, and Power unit  Additional application-dependent components  Location finding system, power generator, and mobilizer  Scattered in a sensor field  Collect data and route data back to the sink  Sink  Communicate with the task manager node (user) via Internet or satellite 28
  29. 29. Components of Sensor Node A sensor node is made up of four basic components  sensing unit  usually composed of two subunits: sensors and analog to digital converters (ADCs).  processing unit,  Manages the procedures that make the sensor node collaborate with the other nodes to carry out the assigned sensing tasks.  Transceiver unit  Connects the node to the network.  Power units (the most important unit) 29
  30. 30. Sensor network topology  Pre-deployment and deployment phase  Sensor nodes can be either thrown in mass or placed one by one in the sensor field.  Post-deployment phase  Sensor network topologies are prone to frequent changes after deployment.  Re-deployment of additional nodes phase  Addition of new nodes poses a need to re-organize the network. 30
  31. 31. DEPLOYMENT OF NODES IN WSN Deploy Sensors 31
  32. 32. Environment  Sensor nodes may be working  in busy intersections,  in the interior of a large machinery,  at the bottom of an ocean,  inside a twister,  in a battlefield beyond the enemy lines,  in a home or a large building Transmission media  Industrial, scientific and medical (ISM) bands  offer license-free communication in most countries.  Infrared  License-free and robust to interference  requirement of a line of sight between sender and receiver 32
  33. 33. Micro-sensors  Uses  In military: surveillance and target tracing  health-care industry: allow continuous monitoring of life- critical information.  food industry: biosensor technology applied to quality control can help prevent rejected products from being shipped out,  Agriculture: help to determine the quality of soil and moisture level; they can also detect other bio-related compounds.  Sensors are also widely used for environmental and weather information gathering.They enable us to make preparations in times of bad weather and natural disaster. 33
  35. 35. Wireless Mesh Networks  Mesh networking is the holy grail of wireless networking. “Mesh” refers to many types of technology that enable wireless systems to automatically find each other and self- configure themselves to route information amongst themselves. 35
  36. 36. 36 Wireless Mesh Networks  Mesh network implemented over WLAN  “Mesh” refers to many types of technology that enable wireless systems to automatically find each other and self-configure themselves to route information amongst themselves.  Industrial standardsActivities  IEEE 802.11, IEEE 802.15, IEEE 801.16 have established sub-working groups to focus on new standards for WMNs
  37. 37.  In a wireless mesh network, the network connection is spread out among dozens or even hundreds of wireless mesh nodes that "talk" to each other to share the network connection across a large area.  Mesh nodes are small radio transmitters that function in the same way as a wireless router.  In a wireless mesh network, only one node needs to be physically wired to a network connection like a DSL Internet modem.That one wired node then shares its Internet connection wirelessly with all other nodes in its vicinity.Those nodes then share the connection wirelessly with the nodes closest to them.The more nodes, the further the connection spreads, creating a wireless "cloud of connectivity" that can serve a small office or a city of millions. 37
  38. 38. Wireless Mesh Networks  Possible deployment scenarios:  Residential zone : where broadband connectivity is required  Highway: where a communication facility for moving automobiles is required  Business zones: where an alternative communication system to cellular network is required  Important civilian regions: where a high degree of service availability is required  University campus: where inexpensive campus wide network coverage can be provided. Operates at license-free ISM band -2.4 GHz and 5 GHz. Speed - 2Mbps to 60 Mbps38
  39. 39. 39
  40. 40. Benefits  Using fewer wires means it costs less to set up a network, particularly for large areas of coverage.  The more nodes you install, the bigger and faster your wireless network becomes.  They rely on the same WiFi standards (802.11a, b and g) already in place for most wireless networks.  They are convenient where Ethernet wall connections are lacking -- for instance, in outdoor concert venues, warehouses or transportation settings.  They are useful for Non-Line-of-Sight (NLoS) network configurations where wireless signals are intermittently blocked. For example, in an amusement park a Ferris wheel occasionally blocks the signal from a wireless access point.  Wireless mesh configurations allow local networks to run faster, because local packets don't have to travel back to a central server.  Wireless mesh nodes are easy to install and uninstall, making the network extremely adaptable and expandable as more or less coverage is needed. 40
  41. 41.  Electric meters now being deployed on residences transfer their readings from one to another and eventually to the central office for billing without the need for human meter readers or the need to connect the meters with cables.  Mesh networks are "self configuring;" the network automatically incorporates a new node into the existing structure without needing any adjustments by a network administrator.  Mesh networks are "self healing," since the network automatically finds the fastest and most reliable paths to send data, even if nodes are blocked or lose their signal. 41
  42. 42. 42 Taxonomy Wireless Networking Multi-hop Infrastructure-less (ad-hoc) Infrastructure-based (Hybrid) Infrastructure-less (MANET) Single Hop Cellular Networks Wireless Sensor Networks Wireless Mesh Networks Car-to-car Networks (VANETs) Infrastructure-based (hub&spoke) 802.11 802.16 Bluetooth802.11
  43. 43. 43 Mesh vs. Ad-Hoc Networks  Multihop  Nodes are wireless, possibly mobile  May rely on infrastructure  Most traffic is user-to-user Ad-Hoc Networks Wireless Mesh Networks  Multihop  Nodes are wireless, some mobile, some fixed  It relies on infrastructure  Most traffic is user- to-gateway
  44. 44. 44 Mesh vs. Sensor Networks  Bandwidth is limited (tens of kbps)  In most applications, fixed nodes  Energy efficiency is an issue  Resource constrained  Most traffic is user-to-gateway Wireless Sensor Networks Wireless Mesh Networks  Bandwidth is generous (>1Mbps)  Some nodes mobile, some fixed  Normally not energy limited  Resources are not an issue  Most traffic is user-to-gateway
  45. 45. 45 Broadband Internet Access
  46. 46. 46 Extend WLAN Coverage Source: www.belair.com Source: www.meshdynamics.com
  47. 47. 47 WMN Architecture  WMNs (Wireless Mesh Networks) consist of:  mesh routers and mesh clients  Mesh routers  Conventional wireless AP (Access Point) functions  Additional mesh routing functions to support multi-hop communications  Usually multiple wireless interfaces built on either the same or different radio technologies  Mesh clients  Can also work as a router for clientWMN  Usually one wireless interface  Classification ofWMN architecture  Infrastructure/BackboneWMNs  ClientWMNs  HybridWMNs
  48. 48. 48 Infrastructure/backbone WMNs Internet Wi-Fi Networks Cellular Networks WiMAX Networks Sensor NetworksBase Station Sink node Sensor Wireless Mesh Backbone Wired Clients Mesh RouterMesh Router with Gateway Mesh Router with Gateway Mesh Router with Gateway/Bridge Mesh Router with Gateway/Bridge Mesh Router with Gateway/Bridge Access Point Base Station Mesh Router with Gateway/Bridge Wireless Clients
  49. 49. 49 Client WMNs Mesh Client Mesh Client Mesh Client
  50. 50. 50 Hybrid WMNs Wi-Fi, Wi-MAX, Sensor Networks, Cellular Networks, etc. Internet Wireless Mesh Clients Wireless Mesh Backbone Conventional Clients Mesh Router Mesh Router Mesh Router with Gateway Mesh Router with Gateway Mesh Router with Gateway/Bridge Mesh Router Mesh Router Mesh Router with Gateway/Bridge
  51. 51. Types of Ad Hoc Mobile Communications  Mobile hosts in an ad hoc mobile network can communicate with their immediate peers (peer-to-peer) that are a single radio hop away.  If three or more nodes are within range of each other (but not necessarily a single hop away from one another), then remote-to-remote mobile node communications exist.  Remote-to-remote communications are associated with group migrations. 51
  52. 52. Types of traffic patterns in Adhoc Ad hoc wireless communications can occur in several different forms. 1) Peer-to-peer communication  Mobile host communicates in pair  For a pair of ad hoc wireless nodes, communications will occur between them over a period of time until the session is finished or one of the nodes has moved away. 2) Remote-to-remote communication  when two or more devices are communicating among themselves and they are migrating in groups.  The traffic pattern is, therefore, one where communications occur over a longer period of time. 52
  53. 53. Types of traffic patterns in Adhoc 3) Hybrid Communication  have a scenario where devices communicate in a non- coherent fashion and their communication sessions are, therefore, short, abrupt, and undeterministic. MH: Mobile host 53
  54. 54. Types of Mobile Host Movements  Movements by Nodes in a Route  Movements by Subnet-Bridging Nodes  Concurrent Node Movements 54
  55. 55. Movements by Nodes in a Route Source nodes Downstream link Intermediate nodes Destination nodes Upstream link 55
  56. 56. Cont… An ad hoc route comprises the source (SRC), destination (DEST), and/or a number of intermediate nodes (INs).  Movement by any of these nodes will affect the validity of the route.  An SRC node  has a downstream link, and  when moves out of its downstream neighbour's radio coverage range, the existing route will immediately become invalid.  all downstream nodes may have to be informed so they can erase their invalid route entries.  DEST node  moves out of the radio coverage of its upstream neighbour, the route becomes invalid.  The upsteam nodes will have to be informed so they can erase their invalid route entries.  IN node : any movement by an IN supporting an existing route may cause the route to be invalid. 56
  57. 57.  Movements cause many conventional distributed routing protocols to respond in sympathy with the link changes.  Need to update all the remaining nodes within the network so that consistent routing information can be maintained.  Updating process involves broadcasting over the wireless medium, which results in wasteful bandwidth and an increase in overall network control traffic. Hence, new routing protocols are needed. 57
  58. 58. Movements by Subnet-Bridging Nodes  Subnet-bridging node movement between two mobile subnets can fragment the mobile subnet into smaller subnets  Movements by certain nodes can result in subnets merging (yielding bigger subnets) while sometimes subnet is partitioned by some subnet- bridging mobile nodes  Updating all the nodes' routing tables  Choose to update only the affected nodes' association tables. 58
  59. 59.  Concurrent movements by nodes (SRC, DEST, or INs)  Ensure there is consistency when multiple route reconfiguration or repair processes are invoked.  Ultimately converge where the most appropriate route reconfiguration is performed. Concurrent Node Movements 59
  60. 60. Challenges in Ad Hoc Networks  Limited wireless transmission range  Broadcast nature of the wireless medium  Packet losses due to transmission errors  Mobility-induced route changes  Mobility-induced packet losses  Battery constraints  Potentially frequent network partitions  Ease of snooping on wireless transmissions (security hazard) 60
  61. 61. Issues in Ad Hoc Networks 1. SpectrumAllocation and Purchase 2. Medium access scheme 3. Routing 4. Multicasting 5. Transport layer protocol Performance 6. Pricing shceme 7. QoS provisioning 8. Security 9. Energy management 10. Addressing and service discovery 11. Scalability 12. Deployment considerations61
  62. 62. 1. Spectrum Allocation and Purchase  FCC control the regulations regarding the use of radio spectrum.  Who regulates the use of radio spectrum in INDIA??  To prevent interference, ad hoc networks operate over some form of allowed or specified spectrum range.  Most microwave ovens operate in the 2.4GHz band, which can therefore interfere with wireless LAN systems.  Frequency spectrum is not only tightly controlled and allocated, but it also needs to be purchased.  With ad hoc networks capable of forming and deforming on- the-fly, it is not clear who should pay for this spectrum. 62
  63. 63. 63 2.Medium Access Scheme  Distributed operation  Synchronization  Hidden terminal problem  Exposed terminal problem  Throughput  Access delay  Fairness: especially for relaying nodes  Real-time traffic support  Resource reservation  Ability to measure resource availability  Capability for power control  Adaptive rate control  Use of directional antennas
  64. 64. Media Access  TDMA and FDMA schemes are not suitable.  Many MAC (Media Access Control) protocols do not deal with host mobility.  The scheduling of frames for timely transmission to support QoS is difficult.  In ad hoc wireless networks, since the same media are shared by multiple mobile ad hoc nodes, access to the common channel must be made in a distributed fashion, through the presence of a MAC protocol.  There are no static nodes, nodes cannot rely on a centralized coordinator. The MAC protocol must contend for access to the channel while at the same time avoiding possible collisions with neighboring nodes.  The presence of mobility, hidden terminals, and exposed nodes problems must be accounted for when it comes to designing MAC protocols for ad hoc wireless networks. 64
  65. 65. 65 Difference Between Wired and Wireless  If both A and C sense the channel to be idle at the same time, they send at the same time.  Collision can be detected at sender in Ethernet.  Half-duplex radios in wireless cannot detect collision at sender. A B C A B C Ethernet LAN Wireless LAN
  66. 66. IEEE has defined the specifications for a wireless LAN, called IEEE 802.11, which covers the physical and data link layers. In IEEE 802.11, carrier sensing is performed at the air interface (physical carrier sensing), and at the MAC layer (virtual carrier sensing) Physical carrier sensing detects presence of other users by analyzing all detected packets Detects activity in the channel via relative signal strength from other sources Virtual carrier sensing is done by sending MPDU duration information in the header of RTS/CTS and data frames Channel is busy if either mechanisms indicate it to be Duration field indicates the amount of time (in microseconds) required to complete frame transmission Stations in the BSS use the information in the duration field to adjust their network allocation vector (NAV) 802.11 - Carrier Sensing 66
  67. 67.  A and C cannot hear each other.  A sends to B, C cannot receiveA.  C wants to send to B, C senses a “free” medium.  Collision occurs at B.  A cannot receive the collision.  A is “hidden” for C. Hidden Terminal Problem BA C 67
  68. 68. Exposed Terminal Problem  A starts sending to B.  C senses carrier, finds medium in use and has to wait for A->B to end.  D is outside the range of A, therefore waiting is not necessary.  A and C are “exposed” terminals A B C D 68
  69. 69. 69 3. Routing  Challenges  Mobility  results in path breaks, packet collisions, transient loops, stale routing information, and difficulty in resource reservation  BW constraints  Error-prone and shred channel  Bit error rate BER: 10-5 ~ 10-3 wireless vs. 10-12 ~ 10-9 wired  Location-dependent contention  Distribute load uniformly
  70. 70. Routing  The presence of mobility implies that links make and break often and in an indeterministic fashion.  Classical distributed Bellman-Ford routing algorithm is used to maintain and update routing information in a packet radio network.  Yet distance-vector-based routing not designed for wireless networks, still applicable to packet radio networks since the rate of mobility is not high.  Mobile devices are now small, portable, and highly integrated.  Ad hoc mobile networks are different from packet radio networks since nodes can move more freely, resulting in a dynamically changing topology.  Existing distance-vector and link-state-based routing protocols are unable to catch up with such frequent link changes in ad hoc wireless networks, resulting in poor route convergence and very low communication throughput. Hence, new routing protocols are needed70
  71. 71. Routing protocols Routing protocols  Purpose is to dynamically communicate information about all network paths used to reach a destination and to select the from those paths, the best path to reach a destination network. Types of routing protocol  Distance –vector Routing Protocol  Distance vector protocols use a distance calculation (distance metric) plus an outgoing network interface (a vector) to choose the best path to a destination network.  The network protocol (IPX, SPX, IP,Appletalk, DECnet etc.) will forward data using the best paths selected  Well Supported Protocols such as RIP have been around a long time and most, if not all devices that perform routing will understand RIP. 71
  72. 72.  Link state based  Selects the best routing path by calculating the state of each link in a path and finding the path that has the lowest total metric to reach the destination.  Link State protocols track the status and connection type of each link and produces a calculated metric based on these and other factors, including some set by the network administrator.  Link state protocols know whether a link is up or down and how fast it is and calculates a cost to 'get there'.  Link State protocols will take a path which has more hops, but that uses a faster medium over a path using a slower medium with fewer hops. 72
  73. 73. Difference  If all routers were running a DistanceVector protocol, the path or 'route' chosen would be from A B directly over the ISDN serial link, even though that link is about 10 times slower than the indirect route from A C D B.  A Link State protocol would choose the A C D B path because it's using a faster medium (100 Mb ethernet).  In this example, it would be better to run a Link State routing protocol, but if all the links in the network are the same speed, then a Distance Vector protocol is better. 73
  74. 74. 74 Routing (2)  Requirements  Minimum route acquisition delay  Quick route reconfiguration  Loop-free routing  Distributed routing approach  Minimum control overhead  Scalability  QoS provisioning  Support for time-sensitive traffic  Security and privacy
  75. 75. 4. Multicasting  Multiparty communcations are enabled through the presence of multicast routing protocols.  The multicast backbone (MBone) comprises an interconnection of multicast routers that are capable of tunnelling multicast packets through non-multicast routers.  Some multicast protocols use a broadcast-and-prune approach to build a multicast tree rooted at the source.Others use core nodes where the multicast tree originates.  All such methods rely on the fact that routers are static, and once the multicast tree is formed, tree nodes will not move. However, this is not the case in ad hoc wireless networks. 75
  76. 76. 76 Multicasting  Robusteness  recover and reconfigure quickly from potential mobility- induced link breaks  Efficiency  Min control overhead  QoS support  Efficient group management  Scalability  security
  77. 77. 5. Energy Efficiency  Mobile devices today are mostly operated by batteries. Battery technology is still lagging behind microprocessor technology.  The lifetime of an Li-ion battery today is only 2-3 hours. Such a limitation in the operating hours of a device implies the need for power conservation.  For ad hoc mobile networks, mobile devices must perform both the role of an end system (where the user interacts and where user applications are executed) and that of an intermediate system (packet forwarding).  Hence, forwarding packets on the behalf of others will consume power, and this can be quite significant for nodes in an ad hoc wireless network. 77
  78. 78. 78 Energy Management  Tx power mgmt  MAC: sleep mode  Routing: consider battery life time: load balancing  Transport: reduce ReTx  App  Battery energy mgmt  Extend battery life by taking adv of chemical properties, discharge patterns, and by the selection of a battery from a set of batteries  Processor power mgmt  Device power mgmt
  79. 79. 6. TCP Performance  TCP is an end-to-end protocol designed to provide flow and congestion control in a network. TCP is a connection- oriented protocol; hence, there is a connection establishment phase prior to data transmission.The connection is removed when data transmission is completed.  TCP (Transmission Control Protocol) assumes that nodes in the route are static, and only performs flow and congestion activities at the SRC and DEST nodes. 79
  80. 80.  TCP relies on measuring the round-trip time (RTT) and packet loss to conclude if congestion has occurred in the network.  In telecommunications, the round-trip delay time (RTD) or round-trip time (RTT) is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received.This time delay therefore consists of the transmission times between the two points of a signal.  TCP is unable to distinguish the presence of mobility and network congestion.  Mobility by nodes in a connection can result in packet loss and long RTT.  Enhancements needed to ensure that the transport protocol performs properly without affecting the end-to-end communication throughput.80
  81. 81. 7. Service Location, Provision, and Access  Ad hoc networks comprise heterogeneous devices and machines and not every one is capable of being a server.  The concept of a client initiating task requests to a server for execution and awaiting results to be returned may not be attractive due to limitations in bandwidth and power.  Concept of remote programming as used in mobile agents is more applicable since this can reduce the interactions exchanged between the client and server over the wireless media.  Also, how can a mobile device access a remote service in an ad hoc network? How can a device that is well-equipped advertise its desire to provide services to the rest of the members in the network?All these issues demand research. 81
  82. 82. 8. Security & Privacy  Ad hoc networks are intranets and remain as intranets unless connected to Internet.  Such confined communications have already isolated attackers who are not local in the area.  Through neighbor identity authenication, a user can know if neighboring users are friendly or hostile.  Information sent in an ad hoc route can be protected in some way but since multiple nodes are involved, the relaying of packets has to be authenicated by recognizing the originator of the paket and the flow ID or label. 82
  83. 83. 83 Security  DoS attack  Resource consumption  Energy depletion  Buffer overflow  Host impersonation  Information disclosure  Interference
  84. 84. 84 9. Deployment Consideration (1)  Adv. in ad hoc net  Low cont of deployment  Incremental deplyment  Short deplyment time  Reconfigurablity  Scenario of deployment  Military deployment: data-centric or user-centric  Emergency operation deployment: hend-held, voice/data, < 100 nodes  Commercial wide-area deployment: e.g.WMN  Home network deplyment
  85. 85. 85 Deployment Consideration (2)  Required longevity of network  Area of coverage  Service availability: redundancy  Operational integration with other infrastructure  Satellite network, UAV(unmanned aerial vehicles), GPS  Cellular network  Choice of protocols  TDMA or CSMA-based MAC?  Geographical routing (using GPS)  Power-saving routing ?  TCP extension ?