Introduction to Mobile adhoc-network


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Introduction to Mobile adhoc-network

  1. 1. MOBILE AD HOC NETWORKS Seminar Report Submitted in partial fulfilment of the requirements for the award of the degree of Bachelor of Technology in Computer Science Engineering of Cochin University Of Science And Technology by PRAVEEN KUMAR P (12080059) DIVISION OF COMPUTER SCIENCE SCHOOL OF ENGINEERING COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY KOCHI-682022 OCTOBER 2010
  2. 2. DIVISION OF COMPUTER SCIENCE SCHOOL OF ENGINEERING COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY KOCHI-682022 Certificate Certified that this is a bonafide record of the seminar entitled “MOBILE AD HOC NETWORKS” Presented by the following student “PRAVEEN KUMAR P” th of the VII semester, Computer Science and Engineering in the year 2010 in partial fulfillment of the requirements in the award of Degree of Bachelor of Technology in Computer Science and Engineering of Cochin University of Science and Technology. Mr. SUDHEEP ELAYIDOM Seminar guide Dr. DAVID PETER Head Of Division
  3. 3. ACKNOWLEDGEMENT I thank GOD almighty for guiding me throughout the seminar. I would like to thank all those who have contributed to the completion of the seminar and helped me with valuable suggestions for improvement. I am extremely grateful to Dr. David Peter, Head Of Division, Division of Computer Science, for providing me with best facilities and atmosphere for the creative work guidance and encouragement. I am profoundly indebted to my seminar guide, Mr. Sudheep Elayidom, sr.Lecturer, Division of Computer Science, for innumerable acts of timely advice, encouragement and I sincerely express my gratitude to him. I thank all Staff members of my college and friends for extending their cooperation during my seminar. Above all I would like to thank my parents without whose blessings; I would not have been able to accomplish my goal. PRAVEEN KUMAR P
  7. 7. 1 Mobile ad hoc networks Chapter 1 INTRODUCTION Communication is the primary factor which influenced the development of mankind. One of the primary goal of communication is exchanging information between two persons. Today we have advanced technologies for communication. Communication can be between human beings or between machines. For the purpose of communication between machines we provided networks, generally connected by physical channels. Then to avoid the difficulties with wired networks there come wireless networks. Then need for more advanced technology arise and we thought about mobility. Mobile networks established due to this demand and the communication become more flexible. MANET is a type of wireless mobile network. A mobile ad hoc network (MANET), sometimes called a mobile mesh network, is a self-configuring network of mobile devices connected by wireless links. Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently. Each must forward traffic unrelated to its own use, and therefore be a router. The primary challenge in building a MANET is equipping each device to continuously maintain the information required to properly route traffic. Such networks may operate by themselves or may be connected to the larger Internet. MANETs are a kind of wireless ad hoc networks that usually has a routable networking environment on top of a Link Layer ad hoc network. They are also a type of mesh network, but many mesh networks are not mobile or not wireless. The growth of laptops and 802.11/Wi-Fi wireless networking have made MANETs a popular research topic since the mid- to late 1990s. Different protocols are used for the communication between the mobile nodes. There is no particular access points in this networks, instead the nodes itself transfer data between the communication nodes. Like any other networks there is also some algorithms used for the routing of information between nodes. Division Of Computer Science Engineering, SOE, CUSAT
  8. 8. 2 Mobile ad hoc networks Chapter 2 BASICS OF MANET MANET (Mobile Ad hoc Network) is a wireless ad hoc network, which uses mobile devices like laptops, PDAs, mobile phones etc. as nodes which communicate each other for the purpose of information transfer between nodes. MANET does not have any particular infrastructure due to the absence of access points and due to the presence of mobile nodes. To know about MANET first we need to know about a wireless ad hoc network. 2.1WIRELESS AD HOC NETWORKS A wireless ad hoc network is a decentralized network. The network is ad hoc because it does not rely on a pre existing infrastructure, such as routers in wired network or access points in wireless networks. Instead each node participate in routing by forwarding data for other nodes, and so the determination of which nodes forward the data is done dynamically, based on the network connectivity. Fig 2.1 Wireless ad hoc network Above figure shows a typical wireless ad hoc network in which the communication is happening in between mobile nodes. There is also a single base station which is not connected to each and every node in the network, instead there are two nodes which directly communicate with the base station. These nodes will have the complete responsibility of information exchange between the base Division Of Computer Science Engineering, SOE, CUSAT
  9. 9. Mobile ad hoc networks 3 station and any node in the network. Such a node must know protocols for communicating with the nodes in the network as well as protocols required for the communication with base station An ad hoc network is made up of multiple ―nodes‖ connected by ―links‖. Links are influenced by the node's resources (e.g. available energy supply, transmitter power, computing power and memory) and by behavioural properties (reliability, and trustworthiness), as well as by link properties (e.g. line-of-sight interference, length-of-link and signal loss, interference and noise). Since new and old links can be connected or disconnected at any time, a functioning network must be able to cope with this dynamic restructuring, preferably in a way that is timely, efficient, reliable, robust and scalable. The network must allow any two nodes to communicate, often via other nodes that relay the information. A ―path‖ is a series of links that connects two nodes. Often there are multiple paths between any two nodes. Nodes are often limited by transmitter power (transmission range) and available energy resources. Transmitter power often consumes the most energy in the node. According to the inverse square law, it is more energy efficient to relay information across a network via multiple nodes The decentralized nature of wireless ad hoc networks makes them suitable for a variety of applications where central nodes can't be relied on, and may improve the scalability of wireless ad hoc networks compared to wireless managed networks, though theoretical and practical limits to the overall capacity of such networks have been identified. Minimal configuration and quick deployment make ad hoc networks suitable for emergency situations like natural disasters or military conflicts. The presence of a dynamic and adaptive routing protocol will enable ad hoc networks to be formed quickly. Wireless ad hoc networks can be further classified according to their applications - Mobile ad hoc networks (MANET): It is a wireless ad hoc network in which mobile nodes are mobile devices like laptops, PDAs, mobile phones etc. In this type of networks each node will act as routers hence no need of access points. One or more nodes can be connected to an external router, which is connected to the internet, so that each node in the network, if need can connect to internet and can transfer information bi directionally. Division Of Computer Science Engineering, SOE, CUSAT
  10. 10. Mobile ad hoc networks - 4 Wireless mesh networks (WMN): It is a communication network made up of radio nodes organised in a mesh topology. Wireless mesh networks often consist of mesh clients, mesh routers and gateways. The mesh clients are often laptops, cell phones and other wireless devices while the mesh routers forward traffic to and from the gateways which may but need not connect to the Internet. - Wireless sensor networks (WSN): This type of networks consist of spatially distributed autonomous sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants. The development of wireless sensor networks was motivated by military applications such as battlefield surveillance and are now used in many industrial and civilian application areas, including industrial process monitoring and control, machine health monitoring, environment and habitat monitoring, healthcare applications, home automation, and traffic control 2.2 Characteristics of MANET - - - - Dynamic Topologies: Since nodes are free to move arbitrarily, the network topology may change randomly and rapidly at unpredictable times. The links may be unidirectional bidirectional. Bandwidth constrained, variable capacity links: Wireless links have significantly lower capacity than their hardwired counterparts. Also, due to multiple access, fading, noise, and interference conditions etc. the wireless links have low throughput. Energy constrained operation: Some or all of the nodes in a MANET may rely on batteries. In this scenario, the most important system design criteria for optimization may be energy conservation. Limited physical security: Mobile wireless networks are generally more prone to physical security threats than are fixed- cable nets. The increased possibility of eavesdropping, spoofing, and denial-of-service attacks should be carefully considered. Existing link security techniques are often applied within wireless networks to reduce security threats. As a benefit, the decentralized nature of network control in MANET provides additional robustness against the single points of failure of more centralized approaches. Division Of Computer Science Engineering, SOE, CUSAT
  11. 11. 5 Mobile ad hoc networks Chapter 3 AD HOC ROUTING PROTOCOLS 3.1 Why Routing Protocols Routing support for mobile hosts is presently being formulated as mobile IP technology. When the mobile agent moves from its home network to a foreign (visited) network, the mobile agent tells a home agent on the home network to which foreign agent their packets should be forwarded. In addition, the mobile agent registers itself with that foreign agent on the foreign network. Thus, the home agent forwards all packets intended for the mobile agent to the foreign agent, which sends them to the mobile agent on the foreign network. When the mobile agent returns to its original network, it informs both agents (home and foreign) that the original configuration has been restored. No one on the outside networks need to know that the mobile agent moved. But in Ad Hoc networks there is no concept of home agent as it itself may be moving. Supporting Mobile IP form of host mobility requires address management, protocol inter operability enhancements and the like, but core network functions such as hop by hop routing still presently rely upon pre existing routing protocols operating within the fixed network. In contrast, the goal of mobile ad hoc networking is to extend mobility into the realm of autonomous, mobile, wireless domains, where a set of nodes, which may be combined routers and hosts, themselves to form the network routing infrastructure in an ad hoc fashion. Hence, there is need to study special routing algorithms to support this dynamic topology environment. Routing protocols for mobile ad-hoc networks have to face the challenge of frequently changing topology, low transmission power and asymmetric links. 3.2 Ad Hoc Routing Protocols: A number of routing protocols have been suggested for ad-hoc networks. These protocols can be classified into two main categories: Table driven routing protocols Division Of Computer Science Engineering, SOE, CUSAT
  12. 12. Mobile ad hoc networks 6 Source initiated on demand routing protocols Table Driven Routing Protocols: Table-driven routing protocols attempt to maintain consistent, up-to-date routing information from each node to every other node in the network. These protocols require each node to maintain one or more tables to store routing information, and they respond to changes in network topology by propagating updates throughout the network in order to maintain a consistent network view. The areas in which they differ are the number of necessary routingrelated tables and the methods by which changes in network structure are broadcast. Source Initiated On Demand Routing: A different approach from table-driven routing is source-initiated on demand routing. This type of routing creates routes only when desired by the source node. When a node requires a route to a destination, it initiates a route discovery process within the network. This process is completed once a route is found or all possible route permutations have been examined. Once a route has been established, it is maintained by a route maintenance procedure until either the destination becomes inaccessible along every path from the source or until the route is no longer desired. Fig 3.1: Categorization of ad hoc routing protocols . Division Of Computer Science Engineering, SOE, CUSAT
  13. 13. Mobile ad hoc networks 7 3.3 TABLE DRIVEN ROUTING PROTOCOLS 3.3.1 Destination Sequenced Distance Vector Routing Algorithm: The Destination Sequenced Distance Vector (DSDV) Routing Algorithm is based on the idea of the Distributed Bellman Ford (DBF) Routing Algorithm with certain improvements. The primary concern with using a Distributed Bellman Ford algorithm in Ad Hoc environment is its susceptibility towards forming routing loops and counting to infinity problem. DSDV guarantees loop free paths at all instants. Each node maintains a routing table, which contains entries for all the nodes in the network. Each entry consists of:  the destination's address  the number of hops required reaching the destination (hop count)  the sequence number as stamped by the destination. Whenever a node B comes up, it broadcasts a beacon message ("I am alive message") stamping it with a locally maintained sequence number. The nodes in its neighbourhood listen to this message and update the information for this node. If the nodes do not have any previous entry for this node B, they simply enter B's address in their routing table, together with hop count and the sequence number as broadcasted by B. If the nodes had previous entry for B, then sequence number of broadcasted information is compared to the sequence number stored in the node for destination B. If the message received has a higher sequence number, then this means that the node B has propagated a new information about its location so the entry must be updated in accordance with the new information received. The information with a newer sequence number is definitely new as the node B itself stamps sequence number. The new information that a node receives is scheduled for broadcasting to its neighbours so that they can know about the changes in topology. The neighbouring nodes also follow the same rule i.e. updating the information when information about a node with a newer sequence number is received. The metrics for routes chosen from the newly received broadcast information are each incremented by one hop. So, the new information is updated gradually at all nodes and they now know the next hop node in order to correctly route the packet to destination B. B also generates the new information with a newer sequence number when it sees that it is moving. By moving, it is meant that B observes that there is a change in topology because it's neighbours are changing, may be due to it's motion or other nodes Division Of Computer Science Engineering, SOE, CUSAT
  14. 14. Mobile ad hoc networks 8 (neighbours) motion. And it comes to know that the neighbours are changing since it receives new beacon messages or does not receive beacon messages from its current neighbours. The information is broadcasted periodically to neighbours. It could be advertised when specifically asked for or when there is a significant change in topology. Thus, it is both 'event driven' and 'time driven'. The routing table updates can be sent in two ways. The first is known as a full dump. This type of packet carries all available routing information and can require multiple network protocol data units (NPDUs). During periods of occasional movement, these packets are transmitted infrequently. Smaller incremental packets are used to relay only that information which has changed since the last full dump. Each of these broadcasts should fit into a standard-size NPDU, thereby decreasing the amount of traffic generated. The mobile nodes maintain an additional table where they store the data sent in the incremental routing information packets. Routes that show an improved metric are scheduled for an advertisement at a time which depends on the average settling time for routes to the particular destination under consideration. To avoid a burst of new advertisements in case of rapidly changing routes, the Mobile host delays the advertisement of such routes, when it can determine that a route with a better metric is likely to show up soon. For this, the Mobile Host has to keep a history of weighted average time that routes to a particular destination fluctuate until the route with the best metric is received. Though it delays advertising the new route, it uses it for routing. Thus, it maintains two tables one for forwarding packets and another to be advertised. In order to bias the damping mechanism in favour of recent events, the most recent measurement of the settling time of a particular route must be counted with a higher weighting factor than are less recent measurements. A parameter must be selected which indicates how long a route has to remain stable before it is counted as truly stable. When no broadcasts are received from a neighbour within a particular time interval, the link is supposed to be broken. Now, any route through that next hop is immediately assigned Division Of Computer Science Engineering, SOE, CUSAT
  15. 15. 9 Mobile ad hoc networks an infinite metric (i.e. any number greater than the maximum allowed metric) and assigned an updated sequence number. Note that this sequence number is assigned by the Mobile host other that the destination Mobile Host. Sequence numbers defined by the originating Mobile host are defined to be even numbers and sequence numbers generated to indicate infinite metrics are odd numbers. This information is broadcasted to the neighbouring nodes. If the neighbouring nodes have chosen this node as a next hop neighbour for any destination then they also set the route to destination as infinity. If the neighbouring nodes, do have a path to destination through some other neighbour and they ignore this information though it has a higher sequence number, which is odd. Thus, it is just like any distance vector algorithm with the added novelty of sequence numbers, which is used to distinguish stale routes from new routes. The concept of sequence numbers also ensures loop free routes. Destination A B C D E F Next Hop A B C D D D Distance 0 1 1 1 2 2 Sequence Number S205_A S334_B S198_C S567_D S767_E S45_F A‘s routing table before change Division Of Computer Science Engineering, SOE, CUSAT
  16. 16. 10 Mobile ad hoc networks Destination A B C D E F Next Hop A D C D D D Distance Sequence Number 0 3 1 1 2 2 S304_A S424_B S297_C S687_D S868_E S164_F A‘s routing table after change Fig 3.2 ad hoc network having routing tables 3.3.2 Clusterhead Gateway Switch Routing (CGSR): The Clusterhead Gateway Switch Routing (CGSR) protocol differs from the previous protocol in the type of addressing and network organization scheme employed. Instead of a flat network, CGSR is a clustered multi hop mobile wireless network with several heuristic routing schemes. In that by having a cluster head controlling a group of ad hoc nodes, a framework for code separation (among clusters), channel access, routing, and bandwidth allocation can be achieved. A cluster head selection algorithm is utilized to elect a node as the cluster head using a distributed algorithm within the cluster. The disadvantage of having a cluster head scheme is that frequent cluster head changes can adversely affect routing protocol performance since nodes are busy in cluster head selection rather than packet relaying. Hence, instead of invoking cluster head reselection every time the cluster membership changes, a Least Cluster Change (LCC) clustering algorithm is introduced. Using LCC, cluster heads only change when two cluster heads come into contact, or when a node moves out of contact of all other cluster heads. CGSR uses DSDV as the underlying routing scheme, and hence has much of the same overhead as DSDV. However, it modifies DSDV by using a hierarchical cluster-head-togateway routing approach to route traffic from source to destination. Gateway nodes are nodes that are within communication range of two or more cluster heads. A packet sent by a node is first routed to its cluster head, and then the packet is routed from the cluster head to a gateway to another cluster head, and so on until the cluster head of the destination node is reached. The packet is then transmitted to the destination. Figure illustrates an example of Division Of Computer Science Engineering, SOE, CUSAT
  17. 17. Mobile ad hoc networks 11 this routing scheme. Using this method, each node must keep a cluster member table where it stores the destination cluster head for each mobile node in the network. Each node periodically using the DSDV algorithm broadcasts these cluster member tables. Nodes update their cluster member tables on reception of such a table from a neighbor. In addition to the cluster member table, each node must also maintain a routing table, which is used to determine the next hop in order to reach the destination. On receiving a packet, a node will consult its cluster member table and routing table to determine the nearest cluster head along the route to the destination. Next, the node will check its routing table to determine the next hop used to reach the selected cluster head. It then transmits the packet to this node. Fig 3.3 CGSR routing from node 1 to node 8 3.4 SOURCE INITIATED ON DEMAND ROUTING 3.4.1 Ad Hoc On-Demand Distance Vector Routing (AODV): The Ad Hoc On Demand Distance Vector (AODV) routing protocol builds on the DSDV algorithm previously described. AODV is an improvement on DSDV because it typically minimizes the number of required broadcasts by creating routes on a demand basis, as opposed to maintaining a complete list of routes as in the DSDV algorithm. AODV classify as a pure on-demand route acquisition system, since nodes that are not on a selected path do not maintain routing information or participate in routing table exchanges . When a source node desires to send a message to some destination node and does not already have a valid route to that destination, it initiates a path discovery process to locate the Division Of Computer Science Engineering, SOE, CUSAT
  18. 18. Mobile ad hoc networks 12 other node. It broadcasts a route request (RREQ) packet to its neighbors, which then forward the request to their neighbors, and so on, until either the destination or an intermediate node with a fresh enough routes to the destination is located. Figure 3.4(a) illustrates the propagation of the broadcast RREQs across the network. AODV utilizes destination sequence numbers to ensure all routes are loop free and contain the most recent route information. Each node maintains its own sequence number, as well as a broadcast ID. The broadcast ID is incremented for every RREQ the node initiates, and together with the node‘s IP address, uniquely identifies an RREQ. Along with its own sequence number and the broadcast ID, the source node includes in the RREQ the most recent sequence number it has for the destination. Intermediate nodes can reply to the RREQ only if they have a route to the destination whose corresponding destination sequence number is greater than or equal to that contained in the RREQ. During the process of forwarding the RREQ, intermediate nodes record in their route tables the address of the neighbor from which the first copy of the broadcast packet is received, thereby establishing a reverse path. If additional copies of the same RREQ are later received, these packets are discarded. Once the RREQ reaches the destination or an intermediate node with a fresh enough route, the destination intermediate node responds by unicasting a route reply (RREP) packet back to the neighbor from which it first received the RREQ(Fig3.4(b)). As the RREP is routed back along the reverse path, nodes along this path set up forward route entries in their route tables which point to the node from which the RREP came. These forward route entries indicate the active forward route. Associated with each route entry is a route timer that will cause the deletion of the entry if it is not used within the specified lifetime. Because the RREP is forwarded along the path established by the RREQ, AODV only supports the use of symmetric links. Routes are maintained as follows. If a source node moves, it is able to reinitiate the route discovery protocol to find a new route to the destination. If a node along the route moves, its upstream neighbor notices the move and propagates a link failure notification message (an RREP with infinite metric) to each of its active upstream neighbors to inform them of the erasure of that part of the route. These nodes in turn propagate the link failure notification to their upstream neighbors, and so on until the source node is reached. The source node may then choose to reinitiate route discovery for that destination if a route is still desired. Division Of Computer Science Engineering, SOE, CUSAT
  19. 19. Mobile ad hoc networks 13 An additional aspect of the protocol is the use of hello messages, periodic local broadcasts by a node to inform each mobile node of other nodes in its neighborhood. Hello messages can be used to maintain the local connectivity of a node. However, the use of hello messages is not required. Nodes listen for retransmission of data packets to ensure that the next hop is still within reach. If such a retransmission is not heard, the node may use any one of a number of techniques, including the reception of hello messages, to determine whether the next hop is within communication range. The hello messages may list the other nodes from which a mobile has heard, thereby yielding greater knowledge of network connectivity. Fig 3.4 AODV routing protocol Division Of Computer Science Engineering, SOE, CUSAT
  20. 20. Mobile ad hoc networks 14 3.4.2 Dynamic Source Routing Protocol (DSR): The Dynamic Source Routing (DSR) protocol presented in is an on-demand routing protocol that is based on the concept of source routing. Mobile nodes are required to maintain route caches that contain the source routes of which the mobile is aware. Entries in the route cache are continually updated as new routes are learned. The protocol consists of two major phases: route discovery and route maintenance. When a mobile node has a packet to send to some destination, it first consults its route cache to determine whether it already has a route to the destination. If it has an unexpired route to the destination, it will use this route to send the packet. On the other hand, if the node does not have such a route, it initiates route discovery by broadcasting a route request packet. This route request contains the address of the destination, along with the source node‘s address and a unique identification number. Each node receiving the packet checks whether it knows of a route to the destination. If it does not, it adds its own address to the route record of the packet and then forwards the packet along its outgoing links. To limit the number of route requests propagated on the outgoing links of a node, a mobile only forwards the route request if the mobile has not yet seen the request and if the mobile‘s address does not already appear in the route record. A route reply is generated when the route request reaches either the destination itself, or an intermediate node, which contains in its route cache an unexpired route to the destination. By the time the packet reaches either the destination or such an intermediate node, it contains a route record yielding the sequence of hops taken. Figure 3.5 (a) illustrates the formation of the route record as the route request propagates through the network. If the node generating the route reply is the destination, it places the route record contained in the route request into the route reply. If the responding node is an intermediate node, it will append its cached route to the route record and then generate the route reply. To return the route reply, the responding node must have a route to the initiator. If it has a route to the initiator in its route cache, it may use that route. Otherwise, if symmetric links are supported, the node may reverse the route in the route record. If symmetric links are not supported, the node may initiate its own route discovery and piggyback the route reply on the new route request. Figure 3.5 (b) shows the transmission of the route reply with its associated route record back to the source node. Division Of Computer Science Engineering, SOE, CUSAT
  21. 21. 15 Mobile ad hoc networks Route maintenance is accomplished through the use of route error packets and acknowledgments. Route error packets are generated at a node when the data link layer encounters a fatal transmission problem. When a route error packet is received, the hop in error is removed from the node‘s route cache and all routes containing the hop are truncated at that point. In addition to route error messages, acknowledgments are used to verify the correct operation of the route links. Such acknowledgments include passive acknowledgments, where a mobile is able to hear the next hop forwarding the packet along the route. Fig 3.5 DSR routing protocol One trade off between source routing and distance vector routing is the handling of partitioned networks. Under dynamic source routing, if a host wishes to communicate with an unreachable host, then though the rate at which route request are made will be reduced by a back off mechanism but Division Of Computer Science Engineering, SOE, CUSAT
  22. 22. 16 Mobile ad hoc networks the protocol continues to make periodic efforts to find a route to the unreachable host, consuming some network resources. Under distance vector routing, with the assumption that routes have had time to converge once the host become unreachable, no network resources are used trying to send packets to unreachable host, as none of the host in the sender's partition of the network has a routing table entry for the destination. 3.5 HYBRID SCHEME 3.5.1 Zone Routing Protocol (ZRP) Proactive routing uses excess bandwidth to maintain routing information, while reactive routing involves long route request delays. Reactive routing also inefficiently floods the entire network for route determination. The Zone Routing Protocol (ZRP) aims to address the problems by combining the best properties of both approaches. ZRP can be classed as a hybrid reactive/proactive routing protocol. In an ad-hoc network, it can be assumed that the largest part of the traffic is directed to nearby nodes. Therefore, ZRP reduces the proactive scope to a zone centered on each node. In a limited zone, the maintenance of routing information is easier. Further, the amount of routing information that is never used is minimized. Still, nodes farther away can be reached with reactive routing. Since all nodes proactively store local routing information, route requests can be more efficiently performed without querying all the network nodes. Despite the use of zones, ZRP has a flat view over the network. Nodes belonging to different subnets must send their communication to a subnet that is common to both nodes. This may congest parts of the network. ZRP can be categorized as a flat protocol because the zones overlap. Hence, optimal routes can be detected and network congestion can be reduced. Further, the behavior of ZRP is adaptive. The behavior depends on the current configuration of the network and the behavior of the users. Architecture: The Zone Routing Protocol, as its name implies, is based on the concept of zones. A routing zone is defined for each node separately, and the zones of neighbouring nodes overlap. The routing zone has a r-radius expressed in hops. The zone thus includes the nodes, whose distance from the node in question is at most r-hops. Division Of Computer Science Engineering, SOE, CUSAT
  23. 23. Mobile ad hoc networks 17 An example routing zone is shown in Fig 3.6, where the routing zone of S includes the nodes A–I, but not K. In the illustrations, the radius is marked as a circle around the node in question. It should however be noted that the zone is defined in hops, not as a physical distance. The nodes of a zone are divided into peripheral nodes and interior nodes. Peripheral nodes are nodes whose minimum distance to the central node is exactly equal to the zone radius r. The nodes whose minimum distance is less than rare interior nodes, in figure, the nodes A–F are interior nodes, the nodes G–J are peripheral nodes and the node K is outside the routing zone. Note that node H can be reached by two paths, one with length 2 and one with length 3 hops. The node is however within the zone, since the shortest path is less than or equal to the zone radius. Fig 3.6 Zone routing protocol with radius = 2. ZRP refers to the locally proactive routing component as the Intra-zone Routing Protocol (IARP). The globally reactive routing component is named Inter-zone Routing Protocol (IERP). IARP maintains routing information for nodes that are within the routing zone of the node. IERP offer enhanced route discovery and route maintenance services based on local connectivity monitored by IARP. The fact that the topology of the local zone of each node is known can be used to reduce traffic when global route discovery is needed. Instead of broadcasting packets, ZRP uses a concept called border casting. Border casting utilizes the topology information provided by IARP to direct query request to the border of the zone. The Border cast Resolution Protocol (BRP) provides the border cast packet delivery service. In order to detect new neighbor nodes and link failures, the ZRP relies on a Neighbor Discovery Division Of Computer Science Engineering, SOE, CUSAT
  24. 24. Mobile ad hoc networks 18 Protocol (NDP) provided by the Media Access Control (MAC) layer. NDP transmits ―HELLO‖ beacons at regular intervals. Upon receiving a beacon, the neighbor table is updated. Neighbors, for which no beacon has been received within a specified time, are removed from the table Route updates are triggered by NDP, which notifies IARP when the neighbor table is updated. IERP uses the routing table of IARP to respond to route queries. IERP forwards queries with BRP. BRP uses the routing table of IARP to guide route queries away from the query source. A node that has a packet to send first checks whether the destination is within its local zone using information provided by IARP. In that case, the packet can be routed proactively. Reactive routing is used if the destination is outside the zone. The reactive routing process is divided into two phases: the route request phase and the route reply phase. In the route request, the source sends a route request packet to its peripheral nodes using BRP. If the receiver of a route request packet knows the destination, it responds by sending a route reply back to the source. Otherwise, it continues the process by border casting the packet. In this way, the route request spreads throughout the network. If a node receives several copies of the same route request, these are considered as redundant and are discarded. The reply is sent by any node that can provide a route to the destination. To be able to send the reply back to the source node, routing information must be accumulated when the request is sent through the network. The information is recorded either in the route request packet, or as next-hop addresses in the nodes along the path. In the first case, the nodes forwarding a route request packet append their address and relevant node/link metrics to the packet. When the packet reaches the destination, the sequence of addresses is reversed and copied to the route reply packet. The sequence is used to forward the reply back to the source. In the second case, the forwarding nodes records routing information as next-hop addresses, which are used when the reply is sent to the source. This approach can save transmission resources, as the request and reply packets are smaller. The source can receive the complete source route to the destination. Alternatively, the nodes along the path to the destination record the next-hop address in their routing table. In the border casting process, the border casting node sends a route request packet to each of its peripheral nodes. This type of one-to-many transmission can be implemented as multicast to reduce resource usage. One approach is to let the source compute the multicast tree and attach Division Of Computer Science Engineering, SOE, CUSAT
  25. 25. 19 Mobile ad hoc networks routing instructions to the packet. This is called Root-Directed Border casting (RDB). The zone radius is an important property for the performance of ZRP. If a zone radius of one hop is used, routing is purely reactive and border casting degenerates into flood searching. If the radius approaches infinity, routing is reactive. The selection of radius is a tradeoff between the routing efficiency of proactive routing and the increasing traffic for maintaining the view of the zone. Route maintenance In ZRP, the knowledge of the local topology can be used for route maintenance. Link failures and sub-optimal route segments within one zone can be bypassed. Incoming packets can be directed around the broken link through an active multi-hop path. Similarly, the topology can be used to shorten routes, for example, when two nodes have moved within each other‘s radio coverage. For source-routed packets, a relaying node can determine the closest route to the destination that is also a neighbor. Sometimes, a multi-hop segment can be replaced by a single hop. If next-hop forwarding is used, the nodes can make locally optimal decisions by selecting a shorter path. 3.6 COMPARISON Parameters TABLE DRIVEN ON DEMAND Availability of routing information Available when needed Always available regardless of the need Routing philosophy Flat Mostly flat except CGSR Periodic route updates Not required Required Coping with mobility Use localized route recovery Grows with increasing Inform other nodes to achieve a consistent routing Greater than that of on Signaling traffic generated Tab 3.1 Comparison between table driven and on demand routing protocols Division Of Computer Science Engineering, SOE, CUSAT
  26. 26. 20 Mobile ad hoc networks Chapter 4 VEHICULAR AD HOC NETWORK (VANET) A Vehicular Ad-Hoc Network, or VANET, is a technology that uses moving cars as nodes in a network to create a mobile network. VANET turns every participating car into a wireless router or node, allowing cars approximately 100 to 300 metres of each other to connect and, in turn, create a network with a wide range. As cars fall out of the signal range and drop out of the network, other cars can join in, connecting vehicles to one another so that a mobile Internet is created. It is estimated that the first systems that will integrate this technology are police and fire vehicles to communicate with each other for safety purposes. Fig 4.1 Typical vehicular ad hoc network (VANET) Division Of Computer Science Engineering, SOE, CUSAT
  27. 27. Mobile ad hoc networks 21 4.1 ARCHITECTURE OF VANET In general, protocol architecture achieves for communication among network nodes and provides the framework for implementation. When designing the communication suit for VANETs two approaches can be taken: First, following the traditional approach, the overall functionality could be de-composed and organized in layers such that at the protocols fulfill small, well-defined tasks and form a protocol stack as in TCP/IP and OSI. Second, one could try to build a customized solution that meets the requirements of VANETs. With such non-layered . The first approach—called layered approach and depicted in Fig. 1 attempts to retain the order of functions and protocol layers with well-defined interfaces between them. It adapts system functionalities to the needs of a VANET communication system resulting, e.g., in protocol layers for single-hop and multi-hop communication. The limitations and inflexibility of traditional network stacks when used in ad hoc networks are well known. E.g., each layer is implemented as an independent module with interfaces (SAPs) only to the above and below layers. Consequently, protocols cannot easily access state or metadata of a protocol on a different layer what makes data aggregation difficult. Moreover, some of VANET-specific functions do not fit into the traditional layered OSI model, such as those for network stability and control, and cannot be uniquely assigned to a certain layer. It is also worth noting that every layer accesses external information separately with no common interface which might lead to problems when this information influences protocol flow. The second un-layered approach would be the result of tailoring a whole new system to the needs of VANETs‘ main focus, i.e., safety applications. Having accurate specifications of these applications and willing to use the ‗probabilistic‘ channel in the most efficient manner leads to have a highly coupled set of protocols. Therefore, all application and communication protocols are placed in one single logical block right over the physical interface and connected to the external sensors (Fig. 2). Inside this block, all protocol elements are modularized such that there are no restrictions for interaction, state information is arbitrary accessible. Note though, that this ‗architecture‘ inherits a high design complexity due to arbitrary and complex interactions of their modules. This makes protocol specification a complicated work and so, once designed becomes an extremely inflexible system for other types of application. Also it would be tough to systematically Division Of Computer Science Engineering, SOE, CUSAT
  28. 28. Mobile ad hoc networks 22 avoid control loop, what is rather easy in the layered approach with its clean top-down or bottomup packet traversal. While both approaches would certainly be feasible. Fig 4.2 Layered architecture Fig 4.3 Un-layered architecture 4.2 APPLICATIONS OF VANET There are many applications for vehicular networks. Just name a few important ones: Collision Avoidance – About 21,000 of the 43,000 deaths that occur each year on U.S. highways result from Division Of Computer Science Engineering, SOE, CUSAT
  29. 29. Mobile ad hoc networks 23 vehicles leaving the road or travelling unsafely through intersections. Data transmitted from a roadside base station to a vehicle could warn a driver that it‘s not safe to enter an intersection. Communication between vehicles and between vehicles and the roadsides can save many lives and prevent injuries. Some of the worst traffic accidents involve many vehicles rear-ending each other after a single accident at the front of the line suddenly halts traffic. In this application, if a vehicle reduces its speed significantly, it will broadcast its location to its neighbor vehicles. And other receivers will try to relay the message further. And the vehicles behind the vehicle in question will emit some kind of alarm to its drivers and other drivers behind. In this way, more drivers far behind will get an alarm signal before they see the accident. Cooperative Driving – Like violation warning, turn conflict warning, curve warning, lane merging warning etc. These services may greatly reduce the life-endangering accidents. In fact, many of the accidents come from the lack of cooperation between drivers. Given more information about the possible conflicts, we can prevent many accidents. Traffic Optimization – Traffic delays continue to increase, wasting more than a 40-hour workweek for peak time travelers. A significant reduction in these numbers could be achieved through vehicular networks. Vehicles could serve as data collectors and transmit the traffic condition information for the vehicular network. And transportation agencies could utilize this information to actively relieve traffic congestion. To be more specifically, in this application, vehicles could detect if the number of neighboring vehicles is too many and their speed is too slow, and then relay this information to vehicles approaching the location. To make it work better, the information can be relayed by vehicles travelling in the other direction so that it may be propagated faster to the vehicles toward the congestion location. In this way, the vehicles approaching the congestion location will have enough time to choose alternate routes. Vehicles can also collect the data about weather, road surface, construction zones, highway rail intersection, emergency vehicle signal preemption and relay them to other vehicles. Payment Services – Like toll collection. It‘s very convenient and desirable to pass a toll collection without having to decelerate your car, waiting in line, looking for some coins and something like that. Division Of Computer Science Engineering, SOE, CUSAT
  30. 30. 24 Mobile ad hoc networks Location-based Services – Like finding the closest fuel station, restaurant, lodge etc. In fact, these kinds of services are not specific to the vehicular networks. Many GPS systems have such kinds of services already. Intelligent vehicular ad hoc networks (InVANETs) use Wi-Fi IEEE 802.11p(WAVE standard)and Wi-MAX IEEE 802.16 for easy and effective communication between vehicles with dynamic mobility. Effective measures such as media communication between vehicles can be enabled as well methods to track automotive vehicles. InVANET is not foreseen to replace current mobile (cellular phone) communication standards. Automotive vehicular information can be viewed on electronic maps using the Internet or specialized software. The advantage of Wi-Fi based navigation system function is that it can effectively locate a vehicle which is inside big campuses like universities, airports, and tunnels. InVANET can be used as part of automotive electronics, which has to identify an optimally minimal path for navigation with minimal traffic intensity. The system can also be used as a city guide to locate and identify landmarks in a new city. Communication capabilities in vehicles are the basis of an envisioned InVANET or intelligent transportation systems (ITS). Vehicles are enabled to communicate among themselves (vehicle-tovehicle, V2V) and via roadside access points (vehicle-to-roadside, V2R). Vehicular communication is expected to contribute to safer and more efficient roads by providing timely information to drivers, and also to make travel more convenient. The integration of V2V and V2R communication is beneficial because V2R provides better service sparse networks and long distance communication, whereas V2V enables direct communication for small to medium distances/areas and at locations where roadside access points are not available. Providing vehicle-to-vehicle and vehicle-to-roadside communication can considerably improve traffic safety and comfort of driving and travelling. For communication in vehicular ad hoc networks, position-based routing has emerged as a promising candidate. For Internet access, Mobile IPv6 is a widely accepted solution to provide session continuity and reachability to the Internet for mobile nodes. While integrated solutions for usage of Mobile IPv6 in (non-vehicular) mobile ad hoc networks exist, a solution has been proposed that, built upon on a Mobile IPv6 proxy-based architecture, selects the optimal communication mode (direct in-vehicle, vehicle-to-vehicle, and vehicle-to-roadside communication) and provides dynamic switching between vehicle-to-vehicle and vehicle-toroadside communication mode during a communication session in case that more than one communication mode is simultaneously available. Division Of Computer Science Engineering, SOE, CUSAT
  31. 31. 25 Mobile ad hoc networks Chapter 5 APPLICATIONS OF MANET The field of wireless networking emerges from the integration of personal computing, cellular technology, and the Internet. This is due to the increasing interactions between communication and computing, which is changing information access from "anytime anywhere" into "all the time, everywhere." 1. Tactical networks: military communications and operation, automated battle fields 2. Emergency services: search and rescue operations, disaster recovery, replacement of fixed infrastructure in case of environmental disaster, policing and fire fighting, supporting doctors and nurses in hospitals 3. Commercial and civilian environments: E-commerce, dynamic database access, mobile offices, road or accident guidance, transmission of road and weather conditions, taxi cab network, inter-vehicle networks, sports stadiums, trade fairs, shopping malls, networks of visitors at airports 4. Home and enterprise networking: home/office wireless networking, conferences, meeting rooms, personal area networks, networks at construction sites 5. Education: universities and campus settings, virtual class rooms 6. Entertainment: multiuser games, wirelessP2P networking, outdoor internet access, robotic pets, theme parks 7. Sensor networks: smart sensors and actuators embedded in household electronic devices, body area networks, data tracking of environmental conditions, animal movements, chemical or biological detection 8. Context-aware services: call forwarding, mobile workspace, location-specific services, time dependent services, infotainment touristic information 9. Coverage extension: extending cellular network access, linking up with the internets intranets etc. Division Of Computer Science Engineering, SOE, CUSAT
  32. 32. 26 Mobile ad hoc networks Chapter 6 CONCLUSION In conclusion, mobile ad-hoc networks allow the construction of flexible and adaptive networks with no fixed infrastructure. These networks are expected to play an important role in the future wireless generation. Future wireless technology will require highly-adaptive mobile networking technology to effectively manage multi-hop ad-hoc network clusters, which will not only operate autonomously but also will be able to attach at some point to the fixed networks. Division Of Computer Science Engineering, SOE, CUSAT
  33. 33. 27 Mobile ad hoc networks Chapter 7 REFERENCE 1. Ad-hoc networks: Fundamental properties and network topologies by Ramin Hekmat 2. Ad hoc networks technologies and protocols by Prasant Mohapatra and Srikanth V. Krishnamurthy 3. Elizabeth M. Royer, Chai-Keong Toh, A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks , Proc. IEEE,1999. 4. Division Of Computer Science Engineering, SOE, CUSAT