1 / 89

Chapter 13

Chapter 13. Ad Hoc Networks. Outline. Introduction Characteristics of MANETs Applications Routing Table-driven Routing Protocols Source-initiated On-demand Routing Hybrid Protocols Vehicular Area Network (VANET) Security Issues in Mobile Ad hoc Networks (MANETs) Network Simulators

fidelio-langan
Download Presentation

Chapter 13

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 13 Ad Hoc Networks

  2. Outline • Introduction • Characteristics of MANETs • Applications • Routing • Table-driven Routing Protocols • Source-initiated On-demand Routing • Hybrid Protocols • Vehicular Area Network (VANET) • Security Issues in Mobile Ad hoc Networks (MANETs) • Network Simulators • Summary

  3. Introduction • A Mobile Ad hoc Network (MANET) is an autonomous system of nodes (MSs) (also serving as routers) connected by wireless links • No infrastructure exists in a MANET • The network’s wireless topology may change dynamically in an unpredictable manner since nodes are free to move and each node has limited transmitting power • Information is transmitted in a store-and forward manner (peer-to-peer) using multi-hop routing

  4. Introduction (Cont’d) • Each node is equipped with a wireless transmitter and a receiver with an appropriate antenna • We assume that it is not possible to have all nodes within each other’s radio range • When the nodes are close-by i.e., within radio range, there are no routing issues to be addressed • At a given point in time, wireless connectivity in the form of a random multi-hop graph exists between the nodes

  5. MS2 MS4 Asymmetric link MS3 MS5 MS7 Symmetric link MS1 MS6 A Mobile Ad Hoc Network (MANET) MS2

  6. A B Direct Transmission versus Multi-hop A C D E B • Energy Consumption • Time delay

  7. Characteristics of MANETs • Dynamic topologies: Network topology may change dynamically as the nodes are free to move • Bandwidth-constrained, variable capacity links: Realized throughput of wireless communication is less than the radio’s maximum transmission rate Collision occurs frequently • Energy-constrained operation: Some nodes in the ad hoc network may rely on batteries or other exhaustible means for their energy • Limited physical security: More prone to physical security threats than fixed cable networks

  8. Applications • Defense applications: On-the-fly communication set up for soldiers on the ground, fighter planes in the air, etc. • Crisis-management applications: Natural disasters, where the entire communication infrastructure is in disarray • Tele-medicine: Paramedic assisting a victim at a remote location can access medical records, can get video conference assistance from a surgeon for an emergency intervention • Tele-Geoprocessing applications: Combines geographical information system, GPS and high capacity MS, Queries dependent of location information of the users, and environmental monitoring using sensors

  9. Applications Vehicular Area Network: in providing emergency services and other information in both urban and rural setup Virtual navigation: A remote database contains geographical representation of streets, buildings, and characteristics of large metropolis and blocks of this data is transmitted in rapid sequence to a vehicle to visualize needed environment ahead of time Education via the internet: Educational opportunities on Internet to K-12 students and other interested individuals. Possible to have last-mile wireless Internet access

  10. Routing in MANETS - Goals • Provide the maximum possible reliability - use alternative routes if an intermediate node fails • Route network traffic through the path with least cost metric between the source and destination • Give the nodes the best possible response time and throughput

  11. Need for Routing Route computation must be distributed. Centralized routing in a dynamic network is usually very expensive Routing computation should not involve the maintenance of a global state Fewer nodes must be involved in route computation Each node must care about the routes to its destination and must not be involved in frequent topology updates Stale routes must be either avoided or detected Broadcasts should be avoided (highly unreliable) If topology stabilizes, routes must converge to optimal routes It is desirable to have a backup route when the primary route has become stale

  12. Routing Classification The existing routing protocols can be classified as: • Proactive: when a packet needs to be forwarded, the route is already known • Reactive: Determine a route only when there is data to send Routing protocols may also be categorized as: • Table Driven protocols • Source Initiated (on demand) protocols • Hybrid protocols

  13. Table Driven Routing Protocols • Each node maintains routing information to all other nodes in the network • When the topology changes, updates are propagated throughout the network • Examples are: • Destination Sequenced Distance Vector routing (DSDV) • Cluster-head Gateway Switch routing (CGSR) • Wireless Routing Protocol (WRP)

  14. Destination Sequenced Distance Vector Routing (DSDV) • Based on the Bellman-Ford algorithm • Each mobile node maintains a routing table in terms of number of hops to each destination • Routing table updates are periodically transmitted • Each entry in the table is marked by a sequence number which helps to distinguish stale routes from new ones, and thereby avoiding loops

  15. DSDV • A new route broadcast contains: • Destination address • Number of hops required to reach destination • Sequence number of information received about the destination • To minimize the routing updates: • Either full dump carrying all available routing information • Smaller incremental packets containing the change in information since last full dump

  16. DSDV (Cont.) • Advantages: • Route setup process is very fast • Make the existing wired network protocol apply to ad hoc network with fewer modifications • Disadvantages: • Excessive control overhead during high mobility • Node must wait for a table update message initiated by the destination node • Cause stale routing information at nodes

  17. Cluster-head Gateway Switch Routing (CGSR) • CGSR is a clustered multi-hop mobile wireless network with several heuristic routing schemes • A distributed cluster-head (CH) selection algorithm is used to elect a node as the cluster head • It modifies DSDV by using a hierarchical CH to route traffic • Gateway nodes serve as bridge nodes between two or more clusters • A packet sent by a node is first routed to its CH and then the packet is routed from the CH to a gateway of another cluster and then to the CH and so on, until the destination cluster head is reached • Frequent changes in the CH may affect the performance of the routing protocol

  18. CGSR (Cont’d) 6 12 5 11 10 4 7 2 1 9 8 Gateway Node 3 Cluster Head Internal Node Routing in CGSR from node 1 to node 12

  19. CGSR (Cont’d) • Advantages: • Better bandwidth utilization • Easy to implement priority scheduling scheme • Disadvantages: • Increase in path length • Instability when cluster-head are high mobility • Battery-draining rate at cluster-head is more than a normal node • Frequent changes in the cluster-head = multiple path break

  20. Source-Initiated On-Demand Routing • Reactive Protocol: • Dynamic Source Routing (DSR) • Ad hoc On-Demand Distance Vector (AODV) • Temporary Ordered Routing Algorithm (TORA) • Associativity Based Routing (ABR) • Signal Stability Routing (SSR)

  21. Dynamic Source Routing Protocol (DSR) • Beacon-less: no hello packet • Routing cache • DSR contains two phases • Route Discovery (find a path) • Flooding RouteRequest with TTL from source • Response RouteReply by destination • If an forwarding node has a route to the destination in its route cache, it sends a RouteREply to the source • Route Maintenance (maintain a path) • RouteError packets are generated when a node encounters a fatal transmission

  22. Routing Discovery

  23. Routing Maintain

  24. DSR (Cont’d) • Advantage • No need to updating the routing tables • Intermediate nodes are able to utilize the Route Cache information efficiently to reduce the control overhead • There are no “hello” messages needed (beacon-less) • Disadvantage • The Route Maintenance protocol does not locally repair a broken link • There is always a small time delay at the begin of a new connection

  25. Ad hoc On-Demand Distance Vector Routing (AODV) • AODV is an improvement over DSDV, which minimizes the number of required broadcasts by creating routes on demand • Nodes that are not in a selected path do not maintain routing information or participate in routing table exchanges • A source node initiates a path discovery process to locate the other intermediate nodes (and the destination), by broadcasting a Route Request (RREQ) packet to its neighbors

  26. AODV (Cont’d) • Every node has a routing table. When a node knows a route to the destination, it sends a route reply to the source node • The major difference between DSR and AODV • DSR uses source routing in which a data packet carries thecomplete pathto traversed. • AODV stores the next-hop information corresponding to each flow for data packet transmission. • Message types • Route Requests (RREQs) • Route Replies (RREPs) • Route Errors (RERRs)

  27. AODV (Cont’d) • RouteRequest packet carries: • SreID, DestID, DestSeqNum, BcastID, and TTL • DestSeqNum indicates the freshness of the route is accepted • An intermediate node receives a RouteRequest packet. It either forwards it or prepares a RouteReply if it has a valid route to the destination • RouteReply packet: • A node receives RouteReply packet will record the information as the next hop toward the destination • AODV does not repair a broken path locally

  28. Route Maintenance

  29. AODV (Cont’d) • Advantage • Establish on demand • Destination sequences are used to find the latest path to destination • The connection setup delay is less • Disadvantage • Intermediate node can lead to inconsistent route • Beacon-base • Heavy control overhead

  30. Temporarily Ordered Routing Algorithm (TORA) • TORA is a highly adaptive loop-free distributed routing algorithm based on the concept of link reversal • TORA minimizes reaction due to topological changes • Algorithm tries to localize messages in the neighborhood of changes • TORA exhibits multipath routing capability • Can be compared with water flowing downhill towards a sink node • The height metric is used to model the routing state of the network • Nodes maintain routing information to one-hop neighbors

  31. Updatestream DownStream Link reversal routing algorithms

  32. TORA (Cont’d) • The protocol performs three basic functions: --- Route creation --- Route maintenance --- Route erasure • A separate directed acyclic graph (DAG) is maintained by each node to every destination • Route query propagates through the network till it reaches the destination or an intermediate node containing route to destination

  33. TORA (Cont’d) • This node responds with update and sets its height to a value greater than its neighbors • When a route to a destination is no longer valid, it adjusts its height • When a node senses a network partition, it sends CLEAR packet to remove invalid routes • Nodes periodically send BEACON signals to sense the link status and maintain neighbor list

  34. Route Establishing (logical time, NodeID’, Height’, Height, NodeID)

  35. Route Maintenance (logical time,NodeID’,Height’,Height,NodeID)

  36. TORA (Cont’d) • The height metric in TORA depends on logical time of a link failure • The algorithm assumes all nodes to be synchronized. • TORA has 5-tuple metric: • Logical time of link failure • Unique ID of the node that defined the new reference level • A reflection indicator bit • A propagation ordering parameter • Unique ID of the node

  37. TORA (Cont’d) The first three elements together describe the reference level Oscillation can occur using TORA, similar to count-to-infinity problem TORA is partially reactive and partially proactive

  38. Hybrid Protocols • Zone Routing Protocol (ZRP) • Fisheye State Routing (FSR) • Landmark Routing (LANMAR) • Location-Aided Routing (LAR)

  39. Zone Routing Protocol (ZRP) • Intra-zone routing protocol (Proactive routing) • It is only used in the routing zone. • It brakes all nodes in the routing zone into interior nodes and peripheral nodes. • Each node maintain routing path to all nodes in the routing zone by exchanging periodic route update packets. • Inter-zone routing protocol (Reactive routing)

  40. When a node s has packets to be sent to a node d It checks whether node d is with in its zone. If d isn’t in the zone, s broadcasts (uses unicast routing) the RouteRequest to its peripheral nodes. If any peripheral node finds d in its zone, it sends a RouteReply back to s indicating the path. Otherwise, the peripheral node rebroadcasts the RouteRequest again. The query control must ensure that redundant or duplicate RouteRequests are not forwarded. The zone radius has significant impact on the performance. ZRP (Cont’d)

  41. ZRP (Cont’d) • Advantage • ZRP reduces the control overhead employed in on-demand approach and the periodic flooding of routing information in table-driven. • Disadvantage • In the absence of a query control, ZRP tends to produce higher control overhead (redundant or duplicate packets). • The decision on the zone radius has a significant impact on the performance of the protocol

  42. Location-Aided Routing • Main Idea • Using location information to reduce the number of nodes to whom route request is propagated. • Location-aided route discovery based on “limited” flooding • With the availability of GPS, the mobile hosts knows their physical locations • Assumption: • Each host in the ad hoc network knows its current location precisely (location error considered in one of their simulations) • Source node S knows that destination node D was at location L at time t0, and that the current time is t1

  43. Location-Aided Routing (LAR) Expected Zone: the destination node is expected to be presented in the area Request Zone: the path-finding control packets are permitted to be propagated in the area LAR1: the source node specifies the request-zone in the RouteRequest packet LAR2: source node includes the distance between itself and the destination node

  44. Expected Zone Expected zone of D: the region that node S expects to contain node D at time t1, only an estimate made by node S

More Related