Abstract. Broadcasting is a fundamental operation in Mobile Ad Hoc Network MANETs whereby a source node sends the identical or same packet to all the nodes in the network. Simple flooding technique used for route discovery where a mobile node blindly rebroadcast received route request packet until a route established for particular destination. While broadcasting has many advantages, it also have some disadvantage such as the broadcast storm problem, it cause redundant retransmission, collision, and contention. Neighbor coverage based probabilistic rebroadcast routing protocol reduce overhead in MANET. This approach combines the neighbor coverage knowledge method and probabilistic method which can solve the broadcast storm problem and also reduce the routing overhead to improve performance. In this approach first calculate rebroadcast delay is to determine forwarding order and also calculate rebroadcast probability by multiplying the additional coverage ratio and connectivity factor.
Keywords: MANET, Rebroadcast Probability, Neighbor Coverage Knowledge, Broadcasting, AODV.
1. Introduction
MANET (Mobile Ad-hoc Network) is a collection of movable nodes which can move anywhere in Network. As nodes are mobile it can dynamically change their topology at any time. In MANET nodes can communicate with each other without any access point. Due to considerations such as radio power limitation, channel utilization, and power-saving concerns, a mobile host may not be able to communicate directly with other hosts in a single-hop fashion. So instead of using single ‘hop communication multi hop communication used, where the source node send the packets to the destination node through the several intermediate nodes.
Figure 1 show the typical example of a MANET.
Suppose node A want to send the data packet to node D. Node D and node A are outside the transmission range of each other. bvTherefore node A and D are cannot directly communicate with each others. For these nodes B and C act as router and forward the packet through an intermediate node that are within the transmission range of node A and node D. Routing Protocol is divided into 2 types, Proactive Routing Protocol and Reactive Routing Protocol. Proactive Routing Protocol maintains the information of all the node and update the routing information of each and every node in the network. Example is DSDV [8] and OLSR [10]. In Reactive Routing Protocol whenever there is the need of route then only it establishes the route. Example is AODV [1] and DSR [2]. Broadcasting is the fundamental and effective mechanism to discover the route, some broadcasting techniques helps to solve the problem of redundant retransmission, contention and collision in network. Broadcasting Techniques classified into 5 groups.
Simple Flooding is used to blindly rebroadcast the received route request packet until the particular destination is established. In Probability Based method when node received the RREQ packet first time it will assign certain probability in RREQ packet and send it to another node. If P=1 then it act as the simple Flooding. If network is sparse Probability set to high else set to low. In Counter Based method firstly by counting how many identical packets that have received during random delay and according to that node decides whether to rebroadcast the packet or not. In Area Based Method used additional Coverage Area concept to decide whether to rebroadcast the packet or not. Additional Coverage area is directly proportional to the distances between the two nodes. Neighbor Coverage Based Method is based on the information of neighbor node which decides whether to rebroadcast the packet or not. In conventional AODV (Ad-Hoc On demand Distance Vector Routing Protocol) used Simple Flooding method to discover the route. But it cause broadcast storm problem i.e. redundant retransmission, contention and collision in the network. To overcome this neighbor Coverage Based Probabilities routing protocol is used to reduce overhead in MANET. First calculate the rebroadcast Delay to determine the order to rebroadcast the packet i.e. forwarding Order. Second set the rebroadcast Probability by multiplying the additional coverage ratio and connectivity factor.
The rest of this paper is organized as follows: Section 2 introduces the literature Survey. Section 3 Mathematical Model of Proposed System. Section 4 Design Details of Proposed System. In Section 5 we have concluded with our observations.
2. Literature Survey
Williams et al [3] classified the broadcasting mechanism into the following four categories: simple flooding, probability-based, area-based, and neighbour knowledge scheme. Simple flooding blindly rebroadcast the received route request packet until the particular destination is established. Probability Based Method is used in which certain probability is assigned as P=1 it act as simple flooding. In Probability Based method, counter scheme used to decide whether to rebroadcast the packet or not by counting how many identical packets it has been received during random delay. Area Based Method is used to decide whether to broadcast the packet or not with the help of Additional Coverage Concept and in Neighbour Coverage based method decide with the help of neighbour information.
Kim et al. [4] proposed a probabilistic broadcasting method based on coverage area and neighbour confirmation. Protocol set the rebroadcast probability with the help of coverage area as the distance between the sender and node is small the coverage area is small else coverage area is larger. It combines the advantages of probabilistic and area based approach to reduce the overhead in MANET. In the shadowing effect it chooses the different probability according to the distance from the sender. As distance is far it set high retransmission probability else set low retransmission probability.
Peng and Lu [5] proposed a neighbour knowledge scheme named Scalable Broadcast Algorithm. In this approach local neighbourhood discovery and data Broadcast are utilized to avoid unnecessary rebroadcasting and reduce the overhead in network. Sender transmit a packet and when receiver receive the packet first time receiver knows all its neighbour common to sender and start Random Access Delay, until RAD expired it accepts the packet. After expired check all nod e covered or not if not send the packet to that node.
Abdulai et al. [6] proposed a Dynamic Probabilistic Route Discovery (DPR) method based on neighbour coverage. In this method Probabilistic based scheme is used in which source node broadcast the packet by using flooding mechanism and every mobile node rebroadcast the packet based on a predetermined fixed probability P determine by the neighbourhood coverage and local density of the node. In local density using the Hello packet it collect the neighbourhood information by sending hello packet to its neighbour and Covered node decide whether to forward the packet or not if all node are covered by broadcast no need to broadcast the packet and if some node are not received the packet send it to that node.
PROBLEM STATEMENT:
Broadcast-storm problem is caused due to unnecessary broadcasting which degrades routing performance and increases routing overhead. By integrating additional coverage ratio and connectivity factor, a rebroadcast probability is computed which reduces number of retransmission, thus it helps to reduce routing overhead and improves routing performance.
OBJECTIVE:
1) To reduce routing overhead and increase the packet delivery ratio.
2) To reduce the End to End Delay.
3) To provide technique to minimize congestion.
3. Mathematical Model
Let s is source node and Ai is the neighbour nodes. Calculate initial Uncovered Neighbour Set is as follows
(1)
Where N(s) and N(Ai) are the neighbour set of node s and Ai and s is node which node Ai receives RREQ packet from s. The Rebroadcast Delay Td(Ai) of node Ai is as follows
(2)
Where Tp(Ai) is the delay ratio of node Ai. Adjust Uncovered Neighbour Set as follows
(3)
The Additional Coverage ratio as follows
(4)
Where U(Ai) is the final UCN set of node Ai. The Connectivity Factor as follows
(5)
The Rebroadcast Probability as follows
(6)
4. Proposed System and Implementation Details
4.1 Algorithm of NCPR (Neighbour Coverage Based on Probabilities Rebroadcast Protocol):
Assumptions: Ai is intermediate node, s is Source node, E(s) is the neighbour set of node s, RREQs is the route request packet received from node s, Rs.id is unique identifier of route request, U(s , i) is Uncovered Neighbour Set of node s for RREQ whose id is i and Timer(s , i) is timer of node s whose id is i.
In NCPR Protocol, when source node sends different RREQ need uncovered neighbour set and Timer.
Step 1: If Ai received new RREQs from s then
Step 2: Calculate initial uncovered neighbour set U(Ai, Rs.ID) for RREQs
Step 3: Compute the Rebroadcast Delay i.e. Td(Ai)
Step 4: Set a Timer (Ai, Rs.ID) according to T(Ai)
Step 5: end if
Step 6: if Ni received new RREQs from S then repeat from step 2 to step 4
Step 7: While Ai receives a duplicate RREQm from node Am before Timer (Ai, Rs.ID) expires do’
Step 8: Adjust U (Ai, Rs.ID)
Step 9: Discard (RREQm)
Step 10: Repeat step 7 to 9 until Timer expired
Step 11: end while other node received a duplicate RREQ message repeat step 7 to 9
Step 12: If Timer (Ai, Rs.ID) expires then
Step 13: calculate Rebroadcast Probability P(Ai)
Step 14: Check random probability <=P(Ai)
Step 15: If Yes Broadcast (RREQs)
Step 16: Else Discard (RREQs)
Step 17: Repeat until it reach to Destination.
4.2 Working of Modules
Proposed system is divided into modules and these modules are integrated together for the execution of the system. Each module has its basic operation.
4.2.1 Route Discovery Process
This module is divided into 2 part RREQ (Route Request) Packet, RREP (Route Reply) Packet. When the source node wants to communicate with destination node, it checks its route table to confirm whether it has the valid route to destination. . If so, it sends the packet to the appropriate next hop towards the destination. However, if the node does not have a valid route to the destination, it must initiate a route discovery process. To begin such a process, the source creates a RREQ (Route Request) packet. This packet contains message type, source address, current sequence number of source, destination address, the broadcast ID and route path. The broadcast ID is incremented every time when the source node initiates a RREQ. When intermediate node accept packet first time it calculate its uncovered neighbor set, Rebroadcast Delay and set its timer in RREQ packet and send to neighbor node. If node received duplicate RREQ packet it Adjust its UCN set till timer expired. As time expired calculate Rebroadcast Probability and decide whether to Rebroadcast the packet or not. When destination node or intermediate node with valid route to destination received the RREQ packet, it create RREP packet contain destination IP address, destination sequence number, source IP address, lifetime, hop count and send it to intermediate node. Repeat until RRP packet reach to source node.
4.2.2 Data Transmission Process
When source node receives a data packet it reads Destination IP address from RREP packet which it has already received. If destination IP addresses matches with its node IP address, then data packet has arrived at destination. If destination IP address doesn’t matches with node’s IP address, given node forwards the data packet to next node towards destination.
4.3 Detail Diagrams of NCPR
4.3.1 Block Diagram of NCPR
4.3.2 Data Flow Diagram of Proposed System
4.3.3 Class Diagram of the Proposed System
Route Discovery, Route Selection and Operation communication is the main modules. Route Discovery contain Broadcast RREQ message and maintain cache. RREQ id, destination sequence number, hop count, num_neighbour, node_id, source sequence number are the attribute of Broadcast RREQ message. calculate_seq_no, Rebroadcast_delay , UCN_set and timer are the function of these module. Operation Communication module provide communication and monitor communication link. In that request_communication, get_route_info, display_info, send_packet, request_path_info, check_packet are the function.
4.4 Pseudo code
Notation:
Rs ‘ Route Request packet from S node
Ai’ node
Rs.id’ unique id for RREQ
N (Ai) ‘ neighbor set of node Ai
U (Ai, i) ‘ uncovered neighbor set of node Ai for RREQ with id
T (Ai, i) ‘ Timer of node Ai with id
Tp(Ai) ‘ delay ratio
Td(Ai) ‘ Rebroadcast Delay
M’ MaxDelay
1. If Ai = new(Rs) then
2. Compute
3. Set T(Ai , Rs.id)
End if
4. While Ai = Duplicate(Rj) then
do delete(Rj)
End while
5. If T(Ai ,Rs.id) time out then
6. If R(0,1) ‘ P(Ai) then
Send (Rs)
Else
Delete (Rs)
End if
End if
5. Conclusion
Broadcasting is the effective and fundamental techniques to discover the route for particular destination. Neighbour coverage based method is used in route discovery process and once the route is established the data packet are flow through that route. In exiting system simple flooding method is used in that it causes the problem of redundant retransmission, contention and collision in the networks. To overcome the problem neighbour coverage based probabilities rebroadcast routing protocol is used. In these first calculate the rebroadcast Delay to find the order to rebroadcast the data and by multiplying the additional coverage ratio and connectivity factor set the rebroadcast probability. Main aim of the protocol is to reduce the overhead in network, end to end delay, increase the packet delivery ratio and performance in network.
6. ACKNOWLEDGEMENT
I would like to thank the anonymous referees for their helpful guidance that have improved the quality of this paper. Also I would like to thank my Project Guide Prof. S. A. Jain for his valuable guidance.
7. Reference
[1] C. Perkins, E. Belding-Royer, and S. Das, Ad Hoc On- Demand Distance Vector (AODV) Routing, IETF RFC 3561, 2003.
[2] D. Johnson, Y. Hu, and D. Maltz, The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks (DSR) for IPv4, IETF RFC 4728, vol. 15, pp. 153-181, 2007.
[3] B. Williams and T. Camp, ‘Comparison of Broadcasting Techniques for Mobile Ad Hoc Networks,’ Proc. ACM MobiHoc, pp. 194- 205, 2002.
[4] J. Kim, Q. Zhang, and D.P. Agrawal, ‘Probabilistic Broadcasting Based on Coverage Area and Neighbor Confirmation in Mobile Ad Hoc Networks,’ Proc. IEEE GlobeCom, 2004
[5] W. Lou and J. Wu, ‘On reducing broadcast redundancy in ad hoc wireless networks,’ IEEE Transactions on Mobile Computing, vol. 1, no. 2, pp. 111’123, Apr.-June 2002.
[6] J.D. Abdulai, M. Ould-Khaoua, L.M. Mackenzie, and A. Mohammed,’Neighbour Coverage: A Dynamic Probabilistic Route Discovery for Mobile Ad Hoc Networks,’ Proc. Int’l Symp. Performance Evaluation of Computer and Telecomm. Systems (SPECTS ’08), pp. 165-172, 2008.
[7] Y. C. Tseng, S. Y. Ni, Y. S. Chen, and J. P. Sheu, ‘The broadcast storm problem in a mobile ad hoc network,’ Wireless Networks, vol. 8, no. 2/3, pp. 153’167, Mar.-May 2002.
[8] C. E. Perkins and P. Bhagwat, "Highly dynamic destination-sequenced distance vector routing (DSDV) for mobile computers," Proceedings of ACM SIGCOMM’94, pp. 234-244, September 1994.
[9] Q. Zhang and D. P. Agrawal, "Dynamic probabilistic broadcasting in MANETs," Journal of Parallel and Distributed Computing, vol. 65, pp. 220-233, 2005.
[10] T. Clausen and P. Jacquet, "Optimized Link State Routing Protocol (OLSR)," IETF Mobile Ad Hoc Networking Working Group INTERNET DRAFT, 2003.
[11] Xin Ming Zhang, Member, IEEE, En Bo Wang, Jing Jing Xia, and Dan Keun Sung, ‘A Neighbor Coverage-Based Probabilistic Rebroadcast for Reducing Routing Overhead in Mobile Ad Hoc Networks’ Senior Member, IEEE. IEEE Transaction On Mobile Computing Vol. 12, No. 3, March 2012.
[12] Y. Sasson, D. Cavin, A. Schiper, Probabilistic broadcast for flooding in wireless mobile ad hoc networks, EPFL Technical Report IC/2002/54, Swiss Federal Institute of Technology(EPFL), 2002.