Reducing Link Failures in MANETs using Link Breakage Pridiction Algorithm

Reducing Link Failures in MANETs using Link Breakage Pridiction Algorithm

Reducing Link Failures in MANETs using Link Breakage Pridiction Algorithm

K SHANWAZ M.Tech student D SHARATH BABU RAO Faculty Department of Electronics & Communication Engineering (DSCE) Jawaharlal Nehru Technological University

Anantapur, Andhrapradesh, India

Abstract- Dynamic Source Routing (DSR) algorithm is simple and best suited for high mobility nodes in wireless ad hoc networks. Due to high mobility in ad-hoc network, route may not exit for long time. Hence, DSR algorithm finds an alternative route when the existing communicating route goes down. It becomes a time consuming process if the communicating route fails frequently. In order to avoid this, we propose a modification to the existing DSR protocol. In this paper, we add a link breakage prediction algorithm to the Dynamic Source Routing (DSR) protocol. The mobile node uses signal power strength from the received packets to predict the link breakage time, and sends a warning to the source node of the packet if the link is soon-to-be-broken. The source node can perform a pro-active route rebuild to avoid disconnection. Intermediate nodes in the route continuously monitor the signal strength at the time of communication, based on a predefined threshold signal value. Intermediate node sends a message to the source node that the route is likely to be disconnected, if signal strength falls below the threshold value. If source receive this message it starts using backup route and if back route also fails then it finds alternative route. The backup route will minimize the time consuming process of finding an alternative route to some extent. Experiments demonstrate that adding link breakage prediction to DSR can significantly reduce the total number of dropped data packets (by at least 25%). Simulation results shows the probability of the communication breakage decreases when parallel routes are used and comparisons between DSR and Modified DSR(Preemptive Version) with respective to no of broken paths and routing overhead.

KeyWords-Ad-Hoc Networks, Preemptive, Dynamic Source Routing, Proactive, age of path.

1. INTRODUCTION

   T

   here are currently two variations of mobile wireless networks. The first is known as infrastructure network. The bridges for these networks are known as base stations.

   1 Research Scholar at Sathyabama University, Chennai & Assoc.Prof, CMR CET, Hyderabad, AP, India.

   2 Principal, Veerabrahmendra Institute of Technology, Badvel, Kadapa, AP, India.

   3Asst.Professor,BVRIT,Narsapur,AP, India.

   A mobile unit within these networks connects to and communicates with, the nearest base station that is within its communication radius. As the mobile unit travels out of range of one base station into the range of another, a "handoff" occurs from the old base station to the new, allowing the mobile to be able to continue communication seamlessly throughout the network. Typical applications of this type of network include office wireless local area networks (WLANs). The second type of mobile wireless network is the mobile ad-hoc network or MANET. Unlike infrastructure network, this type of network needs no base station. Mobile nodes communicate to each other by either directly or through intermediate nodes. Ad-hoc network becomes popular since it can be applied in many situations, such as emergency search-and-rescue operations, classroom, meetings or conference and many more. To facilitate communication within the network, routing protocols used to discover routes between nodes. Building a MANET routing protocol is not an easy job, since efficiency and correctness becomes the main concern. Some approach had been proposed to make routing protocol becomes efficient and correct. Routing protocols in MANET, generally, can be categorized as table-driven and on- demand. In table-driven (also called proactive protocol), like in most routing protocol for wired network, each node is required to maintain routing table keep updated whether there is or not a request for routes. In on-demand (also called as reactive protocol), each node seeks for routes only when there is need to do so. [1]

2. DYNAMIC SOURCE ROUTING

   The Dynamic Source Routing (DSR) protocol is a simple and efficient routing protocol designed specifically for use in multi-hop wireless ad hoc networks of mobile nodes. It is based on the concept of source routing, a routing technique in which the sender of the packet determines the complete sequence of the nodes through which to forward the packet. The sender explicitly lists this route in the packets header, identifying each forwarding hop by the address of the next node to which to transmit the packet on its way to the destination host.

   The DSR protocol consists of two mechanisms: Route Discovery and Route Maintenance. When a mobile node wants to send a packet to some destination, it first checks its route cache to determine whether it already has a route to the destination. If it has one, it will use this route to send the packet. Otherwise, it will initiate route discovery by

   broadcasting a route request packet. When receiving a request packet, a node appends its own address to the route record in the route request packet if it did not receive this request message before, and re-broadcasts the query to its neighbors. Alternatively, it will send a reply packet to the source without propagating the query packet further if it can complete the query from its route cache. Furthermore, any node participating in route discovery can learn routes from passing packets and gather this routing information into its route cache.

   When sending or forwarding a packet to a destination, Route Maintenance is used to detect if the network topology has changed such that the link used by this packet is broken. Each node along the route, when transmitting the packet to the next hop, is responsible for detecting if its link to the next hop has broken. When the retransmission and acknowledgement mechanism detects that the link is broken, the detecting node returns a Route Error packet to the source of the packet. The node will then search its route cache to find if there is an alternative route to the destination of this packet. If there is one, the node will change the source route in the packet header and send it using this new route. This mechanism is called salvaging a packet. When a Route Error packet is received or overheard, the link in error is removed from the local route cache, and all routes which contain this hop must be truncated at that point. The source can then attempt to use any other route to the destination that is already in its route cache, or can invoke Route Discovery again to find a new route.[4][9]

   Fig: 1 DSR Route Request

3. PROACTIVE ROUTE MAINTENANCE

   We assume that all nodes wishing to communicate with other nodes within the ad hoc network are willing to participate fully in the protocols of the network. Each node participating in the network should also be willing to forward packets for other nodes in the network. We refer to the minimum number of hops necessary for a packet to reach from source to destination. We assume that he diameter of an ad-hoc network will be small(5 to 10 hops), but greater than 1. Packets may be lost or corrupted in transmission on the ad-hoc wireless network. A node receiving a corrupted packet can detect the error and discard the packet.

   The GPS and signal strength methods both use physically measured parameters to predict the link status. The node with GPS can know the position o itself directly. But GPS currently is not a standard component of mobile devices, and in the metropolitan area and indoor, the signal can be too weak to be received. The signal strength method only consumes receiving nodes computing power, and does not depend on any additional device. It is used in this paper. At first we assume that the sender power level is constant. Received signal power samples are measured from packets received from the sender. From this information it is possible to compute the rate of change for a particular neighbors signal power level. Because the signal power threshold for the wireless network interface is fixed, the time when the power level drops below the acceptable value can be computed.[7] Characteristics of PRM include: Freshness. All nodes near an active route have the up-to- date routing information. Broken paths are eliminated, new paths recognized, and non-optimal paths replaced by optimal ones.

   Robustness. An active node that is forwarding data packets usually maintains several fresh alternative paths. After one path fails, the data packet is usually forwarded via another path without causing packet loss or extra delay. PRM will resort to a route discovery operation only after all alternative paths have failed.

   Lightweight maintenance. Unlike in existing proactive routing protocols, the route maintenance is confined to those small areas surrounding active routes, where control packets make only a small portion of data transmission. As the lifetime of a route is lengthened, the overhead of the proactive route maintenance can be compensated by the less frequent route discovery operations.[10]

   The proposed Concept is illustrated using the following example.

   Fig:2 DSR Route Reply

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   Fig. 3

   2

   When a source node S want to send message to the destination node D, it initiates route discovery by broadcasting the RREQ packet to its neighbors (A, E, F) as shown in Fig 3. The intermediate nodes (A, E, F) on receive the RREQ packet rebroadcast the packet to its neighbors by appending its id in the route record of the RREQ packet. Similarly, other intermediate nodes also forward the RREQ packet to the destination. When the destination node D receives two or more RREQ packets from the same source through different routes, it finds the two best routes based on the no of hopes. The route, which has least number of hopes. The route which has least number of hops it becomes primary<S, F, G>, and second least number of hops route becomes backup route<S, A, B, C>. The destination node D sends Route Reply (RREP) packet using the Primary (<S, F, G>) and Backup(<S, A, B, C>) route as shown in the following Fig. Each RREP packet contains the Primary as well as the Backup route information. When source node S receives first RREP packet form destination, it treats this is the primary route and wireless communication is more error prone compared to wired network. To improve the reliability we are sending route reply (primary + backup routes information) through the primary and the secondary route. If any one packet gets corrupted at the time of transmission, source must be able to use the other packet.[6]

   Primary Route {<S.F.G> + {<S.A.B.C>}} Backup Route {<S.A.B.C>+{<S.F.G>}}

   The communication between the source node S and

   destination node D commence using the primary path<S, F, G>. During communication, the node F starts moving away from S. When the signal strength of node F falls below threshold T, it sends a warning message Path likely to be disconnect to source node S. As soon as S receives the warning message, it starts using the Backup route along with primary route. Whenever destination node receives the data packets from the source node through two different paths (Primary + Backup), it sends acknowledgement through both the paths. If source node S receives an acknowledgement from the destination node through the Backup route, it makes preemptive switch over to the Backup route; otherwise S initiates the route discovery process.

   1. Generating the Warning Message based on the

   Signal Strength

   Let us consider the following scenario while using the Backup route.

   Case 1:

   Node C is moving toward node G, as shown in Fig 4

   As node C is moving towards node G, the signal strength increases and Backup route become more stable.

   Case 2:

   Node C is moving away from node G, as shown in Fig 5.

   As node C is moving away from node G, the signal strength of C falls below the threshold T and as a result the Backup route fails. Let p(0 p 1) is the probability of the route failure in case of DSR. In the best-case p=0 and in the worst case p=1. Hence on an average case the probability of route failure p=0.5 (50%). Similarly in the proposed Proactive routing in Dynamic Source Routing Protocol for Wireless Ad-hoc Networks with Backup Route.

   The probability of Primary route failure is p=0.5 (50%) —–

   ——– (1)

   The probability of backup route failure is p=0.5 (50%) ——

   —– (2)

   Form (1) and (2) we conclude that the probability of both the route failure p=0.25 (25%). Therefore, Modified Dynamic Source Routing Protocol for Wireless Ad-Hoc Networks with Backup Route has a significant effect on the performance as it improves the reliability form 50% to 75% with minimal control overhead.

   The threshold value plays an important role for control packet overhead.

   Case 1:

   If threshold T is large:

   It may send false warning to source node to use backup route.

   Case 2:

   If threshold T is small:

   Source node may not get sufficient time to discover new route, if backup route fails.

   Therefore threshold T value is set moderate, to overcome above-mentioned drawbacks.

   A Preemptive region is defined around every node as shown in the figure 6 for node A. As soon as node C enters the preemptive region, a warning message is sent to the sender node A. Then the node A initiates a route discovery process. With the establishment of a new route, data transmission is continued along this new route. The time required to discover a new path can be termed as recovery time Trec. Hence the time between the warning and the path break Twarn should be atleast or slightly greater than Trec.

   Fig: 6 Preemptive Region

   In order to determine the optimal range, it is necessary to exchange the location and velocity information of the nodes amongst all the nodes depending on the receiver signal power. The receiver signal power,

   Pr = P0 / rn

   at a distance r from the transmitter, where P0 is the transmitted power and path loss exponent n is typically between 2 and 4. The minimum power receivable by the device is the power at the maximum transmission range,

   Pd = P0 / d4

   Similarly, the preemptive signal power threshold is the signal power at the edge of the preemptive region. In addition, for a preemptive region of width of w, the signal power threshold is

   Psafe = P0 / d4 safe

   Where dsafe is equal to (d- w) and w=relative speed*Twarn The preemptive ratio is defined as =Psafe / Pd = range/ (range- w)

   In reality, the received signal power may experience sudden fluctuations due to channel fading and multipath effects, which will trigger a false warning, causing unnecessary route request floods. This may result in lower quality routes being initiated and also increasing the routing overheads. In cellular networks, an exponential average of the signal power is used to verify that the signal power drop was not due to fading. However, if the traffic is bursty or infrequent, the preemptive region may be fully crossed by the time enough packets are received to drop the average below the threshold. Therefore quicker power estimates can be achieved by sending a warning whenever the instantaneous

   power drops below the threshold and checking the warning packet received power when it is received by the source. If the waning packet power is also below the threshold, there is a good probability that the warning is real.

   B.Generating the Warning Message based on Age of the Path

   With transmissions being done along the same path, relay nodes will experience a continuous drain of their battery power for the same source destination pair, which may result in path failure. Therefore alternate route discoveries are required before the onset of failure.

   Nodes keep a record of their most recent encounter times with all other nodes. With a path discovery being made, the source node sets a timer. The preemptive warning is generated based on two parameters- Age of the path defined as the time difference Tage between the transmissions of two consecutive route discovery packets from the source to the same destination and threshold value is defined for the age of the path. As long as Tage is lesser than , data transmission can be continued on the same path. When the timer value exceeds the threshold , a warning message is generated leading to a new path discovery. However, this new path may or may not be the shortest path to the destination. The choice of the threshold depends on node density of the network. If the node density is small with lesser number of paths available, must be large.

4. MULTIPLE ROUTES

   Use of multiple routes simultaneously, instead of a single route at a time, would help to improve the ongoing communication between the two ends. The source node will use each of these routes alternatively to send packets to the destination node. Use of multiple routes reduces the dependency on a single route, which results in more stable communication. This is because, if a single route fails, we need to again initiate the Route Discovery process. However, if multiple routes are used, when one route fails, another route can be used. Only when all the routes fail, the Route Discovery is to be done to search a new route. We note that the use of multiple routes is different from the backup route theory of DSR. In the backup route approach, the source node uses the primary route for communication and keeps a backup (secondary) route in its route cache. Whenever the primary route fails, the backup route is used.[6] The problem with this approach is that, while the source is still using the primary route, the backup route might fail and the source would remain unaware of that. If after some time the primary route fails and the source node switches to the backup route, it discovers that the backup route has been already broken. But if multiple routes are used in parallel, the source node will be informed of the route failure immediately whenever it occurs. Thus, the source node will never attempt to use a stale route.

5. SIMULATION STUDY

   The discrete event network simulator NS-2 has been used for analysis and comparison of the adhoc routing protocols. The mobile node movement is restricted to a square cell of 600 X 600m containing 70 nodes. Random waypoint model was used here. Figure 9 shows the plot of Pk (k =no. of parallel routes) with respect to time. The different parameters of the plot are listed in Table.

   No. of parallel routes (k)	1-5
   No. of intermediate nodes (n)	5
   Motion time	10s
   Pause time	2s after every 10s
   Total time	200s

   Figure 9 shows that when multiple parallel routes are used, the communication between the source node and the destination node reduces exponentially. That is, greater the number of parallel routes, the more stable the communication becomes. This is because when multiple routes are used, dependency on a single route is reduced. Therefore, even if a single route fails, we have other routes in hand to use for transmitting packets. If a very long time is considered, the fluctuation in the probability values stops and reaches a saturation level.

   Fig: 7 Comparison based on broken paths

   Fig: 8 Comparison based on Packets sent

   Fig: 9 Probability of communication breakage decreases when parallel routes are used

6. CONCLUSION

   Reactive ad hoc routing algorithms initiate route discovery only after a path breaks, it has significant control overhead for detecting the disconnection and re-construction of a new route. DSR with PRM mechanism detects early about the link that is likely to break soon, and hence it uses a backup path before the existing link fails.

   The paper explains the preemption of Primary to Backup route by the source node S, whenever the signal strength of the primary route falls below the threshold value T. The modified DSR will improve the communication reliability between the source and destination node even if the mobility is high. In addition, Proactive routing improves the overhead of rediscovering route whenever the primary route fails.

7. REFERENCES

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3. Elizabeth M. Royer, University of California, Santa Barbara Chai-Keong Toh, Georgia Institute of Technology A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks, IEEE personal communications, April 2007.

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