Routing Protocols for Ad-hoc Wireless Network - Dissertation Example

?IEEE 802.11b standard is operational on a 2.4 GHz unlicensed frequency spectrum that offers a maximum data rate of 11 Mbps. Likewise, this standard divides the band further to 11 separate channels, as 11 channels are available in north America and 13 channels are in Europe. IEEE 802.11g standard is also operational on a 2.4 GHz unlicensed frequency spectrum that offers a maximum Mbps rate of data by using Orthogonal Division Multiplexing in the frequency band. Chapter 3: Routing Protocols for Ad-hoc Wireless Network 3.1. Routing Protocols As stated previously in this paper, an ad-hoc mobile network refers to a number of wireless mobile hosts linked together to form a network of temporary nature without using any centralized control or stand-alone infrastructure [18]. MANETs are not multi-hop wireless networks that are only self-configuring but also self-organizing, in which the network structure changes dynamically, primarily, because of the portability of the nodes [22]. Such networks have their nodes use the uniform random access wireless channel in order to get involved in multi-hop broadcasting by cooperating with each other in a friendly manner. These nodes serve as both hosts as well as routers routing data to and from other nodes within MANET [21]. Since the MANETs have no support of the infrastructure as opposed to the other wireless networks and there is a possibility of a destination node not being found within the range of the source-node-network of the forwarding packets, hence a mechanism for routing is compulsorily required for determining a path in order to transmit the packets properly from the node of the source to the node of the destination. Commonly, a base station in mobile network within a cell can access all the wireless nodes without the mechanism of routing through the broadcasting method whereas in the MANETs, each node should be transmitting the data on behalf of the other nodes. This gives rise to other issues besides the issue of unpredictable connectivity changes related to dynamic topology (Schiller, 2000). 3.2. Issues with Routing in MANETs Asymmetric links: Many wired networks are based on the fixed symmetric links as opposed to the MANETs where the nodes are wireless and also, dynamic as they keep changing their network position. As for instance, consider a MANET having a node B transmitting a signal towards node A. This information tells nothing in relation to the quality or level of the connection in the reverse order that is sending signal back to node B from node A (Schiller, 2000). Overhead in the Routing Mechanism: The nodes, in a MANET, are dynamic with respect to their network location as mentioned above. Hence, a number of invalid paths are produced in the routing table accounting for excessive overhead. Interference: Interference is a big issue in MANETs since the links are made and broken on the basis of the transmission properties, subsequent to which one transmission might intervene or intrude in another line of transmission causing the corresponding node to tap the communication of the nodes in other transmission lines and thereby, falsify the overall system of transmission. Dynamic Network Topology: This is another issue of great concern in MANET routing as the topology keeps on changing. The nodes of the MANET are dynamic since the change their network location and also, the medium has the changing/dynamic properties. The routing tables, in the MANETS, must be able to indicate such changes taking place in the network topology by adapting the appropriate routing algorithms. As for instance, the routing table is updated in every 30 seconds in a fixed network (Schiller, 2000). On the other hand, the updating frequency for the ad-hoc networks might be very low. 3.3. Various Network Protocols in MANET’s and their Comparisons Although the network protocols in MANETS can be classified in numerous ways however many of these are performed on the basis of both the routing mechanism and the network structure [20]. In accordance to the routing mechanism, the network protocols can be classified in to two types; first type is the Table-driven Routing Protocols and the second type is the Source Initiated Routing Protocols whereas on the basis of the network framework, they can be further divided in to the following types: Flat Routing Protocols, Hierarchical Routing Protocols and Geographic Position Assisted Routing Protocols [20]. Both the two routing protocols that are based on the routing strategy, the Table-driven and the Source Initiated Routing Protocols also fall under the class of Flat Routing Protocols as shown below in figure 3.1. Figure 3.1: Classification of Routing Protocols in MANETs [20]. Table-Driven Protocols The Table Driven protocols are also referred as the proactive routing protocols as they keep track of the data related to the routing mechanism prior enough to its requirement or use. Refer to Table 3.1 above for different types of the routing protocols – which are: FSR, FSLS, OLSR, and TBRPF. All the nodes in the MANET keep track of the routing related data to all the other wireless nodes. In general, the routing information is kept in the routing tables and is updated on constant intervals with the change of the network topology. Most of these protocols belong to the link-state mechanism of routing [20]. The protocols that fall under this category have some differences between them due to the updates taking place in each routing table in relation to the routing information. Moreover, the routing protocols as such keep numerous routing tables. The table-driven routing protocols are not appropriate for the larger networks since they require keeping track of the routing entries for all the nodes stored within the routing table of every network-node. This increases the overhead in the routing table that further increases the bandwidth consumption. On Demand Routing Protocols On-demand protocols are also referred as the reactive routing protocols as they do not keep track of the routing activity or the routing information at the nodes of the network when there is no communication. For the list of the Reactive routing protocols refer to the Table3.1 given above, which are: AODV and DSR. When a network node desires to transmit the signal or the data to the other network node then this protocol finds the route on request and sets up the link for sending and receiving the data packet. Usually, the route discovery takes place through transmitting the route request packets across the entire network. ADOV Routing Protocol ADOV protocol is very simple. It stands for Ad-hoc On Demand. It is both effective and efficient for routing in MANETs that have dynamic topology. It was instigated by the limited available bandwidth in the media deployed in wireless communications. The ADOV adopts many beneficial features from the DSR and DSDV algorithms. For example, it borrows the mechanisms of not only on-demand discovery of the route but also on-demand maintenance of the route from the DSR algorithm and the hop-by-hop routing. Whereas the employment of sequence numbers of the node has been taken from the DSDV algorithm so that it is able to cope with the information related to the topology and routing mechanism. The AODV algorithm becomes a very effective and desired algorithm for the MANETS by getting the routes purely on-demand. Route Table Management All the mobile nodes within the MANET keep track of the route table entries in its route table for the corresponding node destination of interest. Every route entry in the route table includes the following elements: Network-Node of the Destination Next Node/Hop Hop Count Sequence number of the Destination-Node Valid neighboring nodes for the destination route Duration or Time of expiry of the route table entry The route table entries also contain the soft-state data related to the destination route. The information related to the valid neighboring nodes is maintained for the destination route in order to notify all the active source nodes that whether a link in the destination path is broken or not. Furthermore, the objective of the expiration of the route request is to remove the entries of the stale routes for the reverse path from all the nodes that are either not located anymore or unavailable on the active route. Significant Features of the AODV The important features of the AODV protocol making it suitable for the Mobile Ad-hoc Networks with limited bandwidth have been described below: – Minimal Space Complexity: The ADOV algorithm ascertains that the nodes unavailable on the active path do not keep track of the data related to the destination route. Once a node gets the RREQ and it establishes a reverse path for this route in its route-table and then transmits the RREQ to its neighboring nodes, for which it does not get any RREP response then it removes the route-information that has been saved by it previously. – Optimum Use of the Bandwidth: The most significant benefit of the ADOV algorithm is the optimum use of the bandwidth. The demand on the available bandwidth is less in this protocol since it does not need to advertise globally on periodic basis. Each node of the MANET also maintains a sequence number that is increased monotonically for taking place of any expired cached routes. In an active path, all the intermediary nodes that update their routing tables also ensure the optimum use of the bandwidth. These routing tables will be repeatedly used when the intermediary nodes get the RREQ for the same destination node from some other source node. Moreover, any RREPs being accepted by the nodes are then analyzed in contrast to the RREP being broadcasted last that employ the sequence numbers of the destination-node and are removed when they are not lesser as compared to the previously broadcasted RREPs. – Simple: The ADOV protocol is simple since it makes each node to serve as a router that keeps record of the simple route-table, and the node that introduces the path discovery request, which in turn makes the network self-starting. – Most Useful Routing Information: If a node, after broadcasting an RREP request, gets an RREP having lesser number of hops then it replaces its route-information with this efficient route/path and broadcasts this information for other nodes as well. – Most Current Routing Information: In ADOV protocol, the route information is acquired on demand. Moreover if a node, after broadcasting an RREP, finds a receiving RREP with bigger sequence number of the destination then it replaces its route-information with this new route and also broadcasts it for the other nodes. – Loop-Free Routes: The ADODV algorithm keeps record of the loop free routes with the help of the simple logic that eliminates the non efficient packets for the same broadcast-id. – Dealing with Dynamic Topology and Invalid Routes: If the nodes in the MANET change their location and the topology is changed as well or the nodes becomes invalid in the active path, then the intermediary node finding this invalid node broadcasts an RERR. Then the source-node re-sets the route-information, provided that it still requires that route. This ascertains rapid response to the invalid nodes or routes. – High Scalability: The ADOV has high scalability since it avoids the minimum space complexity and in contrast transmits to the DSDV algorithm. Advanced Functions of ADOV The advanced functions of the ADOV algorithm are listed below: –The ADOV can deal with the extreme dynamic behavior of the VANETS because of its reactive nature. – The ADOV algorithm is used for both unicasts and multicasts through the ’J’ flag (that stands for joining the multicast group) in the request-packets. Drawbacks of the ADOV Algorithm The disadvantages of the ADOV algorithm are listed below: – Demand on the Medium of the Transmission: The ADOV demands that the nodes in the transmission-medium are able to identify the broadcasts of the other nodes. – Bandwidth Overhead: In ADOV, the bandwidth-overhead will take place in comparison to the DSR, if an RREQ moves across the nodes for determining the route information on request, it establishes the backward path in itself from the node-locations coming in its path and it maintains or updates all this information throughout its path. – No Re-use of the Routing Information: The AODV algorithm does not include an efficient technique for the purpose of maintain the route. The route-information is acquired on request every time that even includes for general case-traffic. – Misuse: The data-packets, in the ADOV algorithm, can be exploited by the insider attacks such as route invasion, route disruption, resource consumption and node isolation. – No High Throughput Routing Metrics: The AODV algorithm has been developed for supporting the shortest hop count metric, which in turn supports long links with low bandwidth in contrast to short links that have high-bandwidth. – High Path Discovery Latency: The AODV is unable to determine a path until a flow is introduced since it is based on the principle of reactive routing. In the case of large-scale mesh networks, the outcome of this path discovery latency can be high. Comparison of ADOV with DSDV The two routing protocols: ADOV and DSDV are compared with other as under: – DSDV routing protocol is proactive keeping track of the routes to all the nodes within the MANET whereas the AODV protocol is reactive determining the path to the destination on demand or whenever required. – DSDV broadcasts periodically for keeping routing updates while the AODV routing protocol only broadcasts the hello messages to its neighboring nodes for maintaining local connectivity. – The DSDV routing protocol keeps track of a sequence number concept in order to update the latest information related to a path, which is also followed by the AODV routing protocol. – The bandwidth is wasted in DSDV, due to the broadcasts of the periodic updates, when the nodes are stationary, in contrary to the AODV algorithm that broadcasts only the hello messages to its neighboring nodes. –It is not required to find a route to transmit data to a certain node since the DSDV keeps record of all the paths for each node in the route-tables whereas the AODV determines a route prior to transmitting the data. – In large networks, the overhead in DSDV is more and it becomes difficult to keep track of the routing tables at each node. On the other hand, the overhead n ADOV is less since it keeps small tables for maintaining local connectivity. – At high speeds, the DSDV protocol is unable to handle mobility because it does not support alternative routes due to which the routes in the routing table becomes invalid. On the contrary, the AODV offers alternative routes since it determines the routes on demand. – In DSDV, the throughput is comparatively reduced since it requires advertising the periodic updates as well as the event-driven updates. The probability of event driven updates is high when the node mobility is high. However, the AODV does not need to broadcast any route-updates due to which the throughput is stable. Random Waypoint Based Performance Comparisons Researches are mostly focused on the utilization of the Random Waypoint by considering the mobility model as a core element and Constant Bit Rate (CBR) traffic thus paring as the traffic pattern consisting randomly chosen source and destination. Following are the metrics on which the network protocols like the DSR, DSDV, AODV and TORA are determined: Data Transmission Ratio (ratio of the data-packets received to the data-packets delivered), Bandwidth Overhead (routing control packets delivered). The research concludes that the performance of on-request protocols for example, DSR and AODV is superior to the proactive protocols like the DSDV that have high mobility rates. On the other hand the performance of DSDV protocol on low mobility rates is better. The recent study reveals the comparison among the two on-demands protocols for instance, DSR and AODV and utilizing the data transmission ratio, its performance metrics and end to end delay. The result shows that the out performance of the DSR is less in demanding situation as compared to the AODV. On the contrary, AODV performs better than the DSR when traffic load is heavy and mobility is high. Therefore, the bandwidth overhead of the DSR is less as compare to the AODV. We have discussed the performance calculation of the protocols, above. In fact, the parameters are used to evaluate the mobility model and its changes in the optimum velocity and pause-time. In this case, different scenarios are chosen that spare large set of mobility functions. However, different mobility models like the Random Waypoint, Reference Point Group Mobility (RPGM), Freeway and Manhattan are used in order to evaluate the efficiency of the protocols. 4.1 Proposal for Implementation of Wireless Ad-Hoc Network for the First Responders in Kazakhstan The basic study of currently used communication technologies by first responders in Kazakhstan have shown that unfortunately communication technology used by first responders today does not scale well. Further, we will discuss the possible technology implementation proposal of wireless ad-hoc network for first responders. The basic benefit of a wireless network lies in the capability of its node to communicate to any location while being mobile. The wireless network paradigm has developed two basic system models for itself. The first is the fixed backbone wireless system model comprising of a vast number of mobile nodes and comparatively lesser in number, but more robust, fixed nodes that are hard wire with the help of the landlines. A fixed node communicates with a mobile node that is within its range through the wireless medium. Nevertheless, a fixed permanent infrastructure is required for the occurrence of this communication. The other proposed model is the mobile ad hoc network (MANET) that establishes a network when required. Nevertheless, each low-power node has the transmission range confined to each other’s proximity, and the nodes that are not within the range are being routed by means of the intermediate nodes. Since a MANET is regarded as a group of wireless mobile nodes that do not require any centralized administration or some sort of a network infrastructure in order to communicate with each other, therefore, the MANET model is best suited for the first responders operating in Almaty, Kazakhstan as their communication network for emergency services is not centralized despite being well equipped with all the other required facilities. The mobile hosts are not confined to any centralized control system such as the mobile switching centers or the base stations. While this provides unbounded connectivity and mobility to the users, however, the entire burden of network management is now only on the nodes of the network. As a result of the small range of transmission for mobile-interfaces, the wireless network requires multiple hops so that one node is able to exchange data with another node. In this type of a network, every wireless node functions as both a host and a router and transfers data to other wireless nodes across the network that does not compulsorily lie under each other’s direct wireless transmission range. Every node takes part in an ADOV protocol due to which it is able to determine multi-hop routes to the other nodes across the network. The concept of MANET is commonly referred as networking without an infrastructure, as the wireless nodes in the MANET set-up the paths dynamically among themselves in order to develop the network of their own, on the fly. This network gets developed immediately and it employs multi-hop routing for transferring information. MANET technology offers an extremely flexible procedure for communications under the circumstances as such in which a completely distributed communication network system is required without having any fixed base station due to the geographical or terrestrial constraints, as for instance: the emergency and disaster situations battlefields, and the military applications. Apparently, security is a major concern in these areas. Definitely, in a MANET, some or all of the nodes may obtain energy from exhaustible sources like batteries. Subsequent to the limited battery power and network capacity of wireless nodes, it is quite common in wireless MANETs that a connection gets disconnected. Generally, the wireless MANET is especially prone because of its distinguishing features of open medium, no central control, dynamic topology, constrained capability and distributed cooperation. The security solutions in practice for the wired networks are not directly feasible for the wireless MANETs. MANETs and WMN are self-configuring and self-organizing mobile networks that are conventionally deployed through IEEE 802.11 hardware. Conventionally, the clients connect with the access points through a single-hop mobile connection and the access points are connected with each other through a wired backbone infrastructure. Such a wired backhaul is not required in WMNs and MANETs and they get connected through a multi-hop wireless network. They become an attractive platform for many applications due to their strength, cost-effectiveness of broad area deployment, and self-configuring and self-organizing nature, as for instance: intelligent transportation systems, emergency response and public safety communications, or community networks. In MANETs and WMNs, routing protocols are an essential element that enable them to self-configure and self-heal themselves. These routing protocols attempt to determine the routes by travelling through several hops in an extremely dynamic environment. Such protocols are mainly classified into two types, which are: Reactive and Proactive as stated in the previous section. They establish the paths only if it is required; they usually use flooding for determining the routes in the network. On the other hand, the proactive routing protocols establish the routes prior to their need; they use periodical exchanges related to connectivity. The Reactive and Proactive protocols have their own benefits. Reactive protocols concentrate over the reduction of the bandwidth overhead whereas the proactive protocols endeavor to reduce the path establishment delays. The multi-hop mobile networks have the basic issue of small scalability and decline in efficiency with the rising number-of-hops or path-lengths. The prime reason behind this limitation is the co-channel interference and that the interfaces of IEEE 802.11 do not facilitate simultaneous reception and transmission of data i.e., the full-duplex operation. One way to solve this issue is to employ multi-radio or multi-homed nodes that have wireless transceivers modulated to orthogonal channels. Subsequent to the lowered interference and the capability to execute full-duplex communication, the capacity of the multi-homed nodes have been raised considerably capacity that is not facilitated through the single-radio nodes. Numerous reactive protocols have been put forward having the ability to determine the routes effectively in multi-radio mobile networks. Some of these protocols are also able to determine multiple paths between node pairs. AODV is the most famous example of reactive protocols. Reactive protocols broadcast a data-packet of Route Request in the network in order to find a path between a source and a destination. The final destination node among the other nodes, having a fresh and valid path to the destination, sent back a data-packet of Route Reply to the source through uni-cast. In AODV protocol, intermediary nodes keep track of these routes through making entries to the routing table when such packets are delivered. The reverse routes are formed, when Route Request packets are delivered, by making an entry to the transient route-table, which link the source-node of the Route Request to its receiving-node. When the relative data-packet of the Route Reply are sent back to the source-node then the nodes in-between form the relative forward paths that comprises of an entry in to the route-table linking the source-node of the Route Reply to its receiving-node. This study proposes a variation of the AODV protocol to be implemented for the first responders’ communication in Almaty Kazakhstan, which can successfully determine the available bi-directional connections, in a multi-hop mobile network, between the adjacent nodes. This process of determining routes is associated with the protocol’s process of establishing route and, hence, it attains a high level of performance through minimizing the bandwidth overhead. The route discovery procedure is feasible for a vast number of multi-hop mobile networks such as the networks that are highly heterogeneous have an arbitrary combination of static/mobile and single-radio/multi-radio nodes. Moreover, the discovery procedure functions at the network level and it does not depend on the physical and the connection layer and hence it can facilitate any kind of a network interface. The Rhino-wireless mesh network by Rinicom would be implemented in Almaty, Kazakhstan in its various modes for assisting the first responders working in the city in emergency situations so that the various crisis management services and agencies and health facilities can exchange important information with each other through their different and distributed communications networks. The advanced ad-hoc networking system of the Rhino is completely based on the Internet Protocol. It is suitable for general public being a revolutionary non line-of-sight wireless system. Every Rhino module comprises of a single transceiver. It can have up to fifteen nodes that can be connected under the umbrella of a secure network. Every unit of RHINO has fifteen RF channels with five non-overlapping that allows five wireless networks to operate in the same band for functioning concurrently within the same vicinity. Every node of RHINO deals with the data, its transmission and reception and authentication of the connection without having any inputs from an operator. Due to these capabilities, the system becomes perfect for vehicle mounted and body worn operations that constitute the basic requirement of the ad-hoc wireless network, for the first responder emergency operations, to be implemented in Almaty, Kazakhstan since the different emergency services providing agencies in the Almaty city have been unable to share the critical information with each other at the time of a crisis situation. Rhino network by Rinicom allows multiple independent networks to be connected with each other with the help of using simple routers for the purpose of developing the master networks. RHINO is also able to function between the vehicles in motion, vehicles to the troops on the ground, troops having worn body systems that have been enabled for remote functionality and optimized for local operation. It provides various options such as the PTT voice radio over IP (VoIP) and the direct video input. It can also be customized on the basis of the application, power consumption, size constraints, performance, etc. The various modes of Rhino suitable for the first responder emergency operation in Almaty, Kazakhstan have been illustrated below in figure 4.4, figure 4.5, figure 4.6, figure 4.7, figure 4.8, figure 4.9, figure 4.10, and figure 4.11. CHAPTER 5: SIMULATION STUDY 5.1 Programming and simulation of AODV Protocol in Java 5.1.1 AODV Protocol Description In this chapter, we will describe the implementation of AODV routing protocol in java. Before moving to implementation, further AODV protocol will be briefly studied and all general concepts and properties of mentioned protocol will be discussed: ADOV routing protocol allows multi-hop routing between the involved nodes of the mobile network that want to develop and maintain the network. This protocol has been developed on the basis of the distance vector algorithm. The AODV is comparatively reactive in relation to proactive protocols, such as DV, suggesting that AODV requests a route only if required and does not need nodes for maintaining routes to destinations, which are not actively involved in communication. The ADOV does not come in to play as long as, in a communication connection, the end-points have valid routes towards each other. Loop freedom is an important element of this protocol that connects the broken links to send instant alerts only to the set of nodes that has been affected. Moreover, ADOV offers multicast routing and prevents the issue of Bellman Ford “counting to infinity”. By using the sequence numbers of the destination for ensuring a ‘fresh’ route. In order to determine and maintain links, the algorithm uses various messages. If a node desires to find and try a path to the other node then it transmits a Route Request (RREQ) to all its neighboring nodes. This request travels across the network until it reaches a node that has a fresh route to the destination. In response, a RREP is sent back to the source to make the route is available. The algorithms employ special RREP, hello messages, which are periodically transmitted to all the direct neighbors across the network. Such messages serve as local advertisements that confirm the availability of the node and the neighboring nodes that use the paths through the transmitting node, will keep labeling the paths as available. When the hello messages, transmitting from a certain node, stop then the neighboring node can think that this node is unavailable and label this connection to the node as unavailable and intimate the involved set of nodes by broadcasting a notification of link failure to (in the form of a special RREP) them. 5.1.2 Route Table Management ADOV requires maintaining the record of the following information for every entry to the route table: IP for the node of the destination address. Sequence Number for this destination. Number of hops to the node of destination. The neighboring node (referred as the Next Hop) that has been assigned to broadcast data to the node of the destination for this entry of the route. The duration (Lifetime) for which the path is available. Set of the neighboring nodes (the list of active neighbors) that have been currently using this entry to the route. Assure that a request is processed only once by using the Request Buffer. 5.1.3 Route Discovery A node forwards a RREQ if it requires a path to a destination, which is unavailable. This occurs when the previously valid path expires or when the route is unknown. The node waits for a RREP after transmitting a RREQ. If it does not receive a reply within a given time then the node can retransmit the RREQ or consider that the path to the destination does not exist. RREQs are forwarded when the receiving node does not have a path to the destination-node. Then it transmits the RREQ again. The node also forms a transient backward path to the IP address of the source node in its routing table having the IP address field of the neighbor as the next hop sending the broadcast RREQ. In this way, a backward path to the source-node is maintained, which might be utilized for an eventual RREP for reaching back to the source node. The route is temporary in the way that it is only valid for a time much shorter than a real entry to the route. A RREP is produced and delivered back to the source node when the RREQ gets to a node that is either the final destination or the node having an available path to the destination. A route is established to the destination while this RREP is transmitted and there exists a route from the source to the destination when the RREP is received at the source node. 5.1.4 Route Maintenance If a node identifies that a path to a neighboring node is no more available then it deletes the entry of this path and transmits a link failure notification, which refers to a triggered route reply message to the neighboring node that are using the route actively, which tells them that this route does not exist anymore. This is the reason why AODV employs an active neighbor list for maintaining the record of the neighbors that are using a certain route. This process is repeated by the nodes that receive this message. Eventually, the message will get to the affected source nodes that can opt to either stop transmitting data or broadcast a new RREQ for requesting a new route. 5.1.5 Properties The benefit of AODV as opposed to traditional routing protocols such as the link state and the distance vector is that the AODV has managed to significantly reduce the amount of routing messages in the network, with the help of employing a reactive approach. This is probably essential in an MANET to achieve considerable efficiency when the topology is so changing often. Also, the AODV is performed in a more conventional way as opposed to, for example, source routing based protocols such as DSR. In an ad-hoc network, the benefit of a more traditional protocol is that the connections to a wired network such as the Internet from the ad-hoc network are probably easier. The sequence numbers used by the AODV denotes the freshness of a route that increases when something occurs in the neighborhood. Although the sequence inhibits loops from being created, however, can also bring new issues. For example, what if the sequence numbers in the network are no more synchronized? This occurs when the sequence numbers wrap around or when the network gets partitioned. The AODV offers only one route for every destination. However, it should be rather easy to change AODV in order to enable multiple routes for each destination. So, when an old route expires then the next stored route between the source and the destination could be used rather than requesting a new route for this purpose. It is most likely that that route still be valid. Despite reducing the number of the Triggered Route Replies by simply forwarding the Triggered Route Replies for affecting the senders, they should travel through the whole way to senders from the node of failure. The number of hops of this distance can be quite high. AODV transmits one Triggered RREP for each active node in the surroundings in the list of the active neighbors for all the route-entries that have been affected by a link failure. This infers that every active neighbor can get multiple Triggered RREPs telling in relation to the same link failure. However, if a large portion of the network traffic, for different destinations, is routed by using the same node and if this node expires then an accumulative solution would be a better option here. The Ad-hoc on Demand Vector Protocol used hello messages at the IP level, which signify that this protocol does not require any assistance from the link layer for working properly. But the question is that if this type of protocol can work with good efficiency without requiring any assistance from the link layer then a significant overhead is added to the protocol by the hello messages. The AODV protocol does not offer unidirectional connections. If a node gets a RREQ then it will establish a backward path to the source by using the source-node of the RRES as the next hop. This signifies that, most of the times, the route reply is sent back in the same way as the route request was sent. But the question is that if the unidirectional connections are required in a real environment then the acknowledgments, for example, in the MAC protocol, the IEEE 802.11 would not function with unidirectional connections. References Perkins, E.C. (2001). Ad Hoc Networking. Addision Wesley. Johnson, B.D. and Maltz, A.D. (1996). Dynamic source routing in ad hoc wireless networks. Technical report, Carnegie Mellon University. Schiller, J. (2000). Mobile Communications. Addison-Wesley. Abolhasan, M. et al. (2003). A review of routing protocols for mobile ad hoc networks. Technical report, Telecommunication and Information Research Institute, University of Wollongong, Australia. Hong, X. et al. (2002). Scalable routing protocols for mobile ad hoc networks. Read More