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An improvement in performance of mobile ad hoc networks using modified route maintenance
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An improvement in performance of mobile ad hoc networks using modified route maintenanceR Dhirendra Kumar Sharma a,∗, Amar Nath Patra a, Chiranjeev Kumar b a b
Department of Information Technology, National Institute of Technology Raipur, 492010, Chhattisgarh, India Department of Computer Science and Engineering, Indian School of Mines, Dhanbad 826004, Jharkhand , India
a r t i c l e
i n f o
Article history: Received 11 August 2015 Revised 23 December 2015 Accepted 23 December 2015 Available online xxx Keywords: Neighbour table Routing table Route maintenance AODV routing protocol Overhearing factor Height
a b s t r a c t A mobile ad hoc network (MANET) is a temporary network where nodes are free to move in a given area. Due to this dynamic nature, links in the routes break. Often backup routing is used as a solution in which alternate route tables are used to continue the data transfer. In this paper, we discuss the shortcomings of the existing backup routing, which is due to their inadequate ways of updating alternate route table information by route maintenance. In several routing protocols, hello messages are periodically broadcasted to update the neighbour table entries which help in detecting link failure. We propose an efficient route maintenance mechanism in AODV routing protocol employing the benefits offered by hello messages. Simulation results show that our proposed modified route maintenance (MRM) scheme significantly improves the performance of MANET. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction A mobile ad hoc network (MANET) is a non-permanent infrastructure less network in which mobile nodes communicate with each other without any access point. This makes it useful in disaster areas, battlefield and conference communication. Nowadays, MANETs are integrated with infrastructure based networks to provide internet based services by multi-hop routing [1]. In existing literature survey [2–9], various routing protocols have been proposed to find the optimal route. Routing protocols are categorised as proactive, reactive and hybrid. Proactive routing protocols are known as table driven routing protocol, in which routing table information for all destinations are periodically updated that cause overhead problem. These routing protocols are suitable for small scale static networks. In a dynamic environment, reactive routing protocols provide effective results. In fact, performance of routing protocols varies with traffic, node density, route length, and mobility. Improvement in performance of proactive and reactive routing protocols is an important issue which is discussed in [4,6,18]. In MANETs, route stability is a major concern which affects the performance metrics such as routing overhead, throughput, and latency. In fact, frequent topological changes have a great impact on the route stability. A reactive routing protocol finds a route by route discovery process. In AODV routing protocol route discovery and route maintenance processes are utilised for route establishment and route repair. A link break in an active route often initiates the reroute discovery which causes the broadcast storm problem. In [10,11], improvements over discovery phase have been proposed to control the
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Reviews processed and recommended for publication to the Editor-in-Chief by Associate Editor Dr. A. Isazadeh. Corresponding author. Tel.: +91 8370033126. E-mail addresses: [email protected] (D.K. Sharma), [email protected] (A.N. Patra), [email protected] (C. Kumar).
http://dx.doi.org/10.1016/j.compeleceng.2015.12.020 0045-7906/© 2016 Elsevier Ltd. All rights reserved.
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overhead and excess bandwidth utilisation. The broadcast storm problem is handled by controlled broadcast algorithms which are used to regulate the unnecessary traversal of control packets during reroute discovery [12]. In [21], the author proposes a scheme to increase the lifetime of route by traffic flow. Route timeout is a major problem which occurs due to unregulated flow of data packets. Such type of problem is overcome by increasing the data rate [22]. An active route is updated by a regulated flow of data in static network. In dynamic topology, the lifetime of route is not maintained by data rate. In the paper [13], authors describe the problem of periodic exchange of hello message at fix rate cause unnecessary overhead. This overhead problem is controlled by link change rate estimation which is based on constant measurement of the link connectivity. A link failure is detected by link layer protocol or hello process (network layer) which confirms the link failure in an active route. Another link layer feedback mechanism [14], detects the link failure by maximum retransmission attempts. In [15], hello process is used to improve the lifetime of route. Through hello process, each node maintains its link connectivity with its neighbour nodes by updating neighbour table and routing table entries. In AODV routing protocol [16], on receiving a hello packet, a node checks whether it has an entry for the node from which it received the packet. If no such entry is there then it adds an entry for such a node, otherwise updates the expiry time for the entry. In both cases, the expiry time is set (or updated) to CURRENT_TIME + (1.5 ∗ ALLOWED_HELLO_LOSS ∗ HELLO_INTERVAL). The relationship between neighbour table and routing table is maintained by hello process. Loss of neighbourhood relationship with a neighbour is detected in two ways. In the first method, Layer 2 identifies a link break and notifies layer 3 by calling the function aodv_rt_failed_callback() (in ns2). In the second method, a node identifies the neighbours from whom it has not received hello packets in ’HELLO_INTERVAL ∗ 1.5 s, that is the expired entries in the neighbour table. In both methods, such neighbours are deleted from the neighbour table. This is followed by making the entry ’down’ [16,23] of corresponding neighbour which exist in routing table. In active data session the lifetime of active route is maintained by updating expiry time in routing table. The expiry time of the entries in the routing table may get updated while receiving a route request or route reply packet, or forwarding a packet. After the link failure detection, upstream node starts the route maintenance process in which either backup routing or route repair schemes is followed. In backup routing buffered data packets are sent through alternate paths of neighbour nodes. Here, we observe that due to dynamic topology neighbour nodes move and hence backup routing can fail, causing huge amount of undelivered data packets. The main reason of unsuccessful delivery is ineffective backup routing which is due to incomplete neighbour table (NT) and alternate route table (ART) information. In [18], local repair scheme is introduced which reduce the bandwidth consumption in link failure. In the proposed scheme author uses the link layer mechanism instead of hello process to find the link failure. In [19], authors propose a local repair scheme which does not use hello process. In this paper we discuss the route maintenance problem which arises due to inefficient backup routing and the main reason is inadequate information in neighbour table (NT) and alternate route table (ART). Following which, we propose the modified route maintenance (MRM) scheme. Further, we discuss different scenario for the proposed algorithms which show their utility in the network. 1.1. Contribution The main contribution of our paper is in improving the performance of mobile ad hoc networks by using Modified Route Maintenance algorithms as following: • We use hello process identify the fresh neighbour nodes and update the neighbour table with overhearing factor (OF) which is used for neighbour node selection. • We define the overhearing factor (OF) which shows the capability of a neighbour node with fresh alternate paths in ART. • We introduce the height value for proper selection when two or more eligible neighbours have the same OF. • The modified route maintenance (MRM) algorithms implement over AODV routing protocol using network simulator (ns2.34). The remainder of this paper is organised as follows. The next Section 2 deals with the related work. Network model and route maintenance process are discussed in Section 3. Modified route maintenance and proposed algorithms are described in Section 4. Section 5 presents simulation and implementation of the proposed algorithms in ns2. Finally, conclusions of the paper are drawn in Section 6. 2. Related work In [3], the authors have proposed a route optimisation mechanism Shrink to increase network capacity, and provide faster link failure recovery and reduced end-to-end delay. Route optimisation is performed after route discovery process by reducing unessential hop count in the active route. In [20], every host node has a set of neighbour nodes and packet header is exchanged during the route request forwarding. In this method a spanning tree is used to regulate the traversal of unnecessary control packets in the network. In dynamic topology invalidation of two-hop neighbour nodes information is a major problem that affects the performance of Please cite this article as: D.K. 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network. In [22], route invalidation problem is discussed which is rectified by using two parameters: active route timeout (ART) and delete period constant (n). A route is a set of links and its lifetime is based on the battery power of the mobile nodes. An improvement over link lifetime has been done by energy conservation approach in which authors have considered the battery power of mobile nodes to determine link lifetime [21]. A link is periodically updated by exchange of hello messages. An improvement over discovery phase has been proposed to improve the route establishment and route repair phase in networks [10,11]. In such improvement in route discovery phase, a request packet header field contains the hop count, node power, and average traffic density as metrics. AODV-ABR routing protocol [17], handles link breaks by sending the buffered data packets to most updated shortest alternate paths of neighbour node. Here, it is clear that topological imbalance resulting from such frequent link changes, which requires retransmission and rerouting of packets. Finally, this process affects the network performance in terms of high bandwidth consumption and increased latency. The main reason of retransmission of packets by upstream node is inaccurate neighbour node information in neighbour table. Here effective route maintenance is required to update the neighbour table with sufficient information. 3. Network model In MANETs, all active nodes use neighbour table and routing table for delivery of data packets. Neighbour tables are associated with routing table of all active nodes which is utilised for data transmission. A neighbour table has two entries: node id and expiry time. With the help of hello process neighbour table entries are periodically updated by exchange of hello messages. On a link break, the upstream node performs route maintenance either by utilising the alternate paths [17] of neighbour nodes or repairing the broken route locally (local repair or global repair) [18]. In adaptive backup routing (AODV-ABR) alternate routing table entries are updated by overhearing of RREP and data packets. In this paper, we are enhancing the route maintenance process with the help of four algorithms which use the overhearing process to update the Alternate Route Table (ART) and Neighbour Table (NT) with new parameters: overhearing factor (OF) and height. With the help of network simulator ns2.341 , we notice that only the existence of entries of neighbours in Neighbour Table (NT) does not provide efficient delivery of packets. We observe that neighbour tables add entries of new neighbours in the top. When a route break happens then an upstream node selects the upper most entry from the Neighbour Table (NT). Such a selection of neighbour node as the next node for transmission is not always effective. This may cause serious problem during route maintenance. In this paper proposed algorithms are used to select a neighbour node from the neighbour table on the basis of OF and height for efficient delivery of data packets. We are using hello messages to update the Alternate Route Table (ART) and Neighbour Table (NT). 3.1. Route maintenance Route maintenance is the process to maintain active route(s) without affecting the performance of routing protocol [23]. By route maintenance we can increase the re-usability of a route; actually it is associated by link update or maintenance of link connectivity. Maintenance of route is important to increase the productivity of any type of networks; it helps to achieve better result in terms of Quality of Service (QoS) performance metrics. Different types of link update mechanisms have been developed to short out the connectivity issues. Loss of link connectivity results route failure. In reactive routing protocols, route discovery and route maintenance have separate functionality. A route is discovered by route discovery process but its longevity and stability is maintained by proper maintenance. Backup routing, local repair, global repair, error notification and link connectivity techniques are the parts of route maintenance process. In Fig. 1(a), three-hop route has been established by source node 1 to destination node 4. In dynamic environment the position of mobile nodes 5–8 changes with respect to time which is shown in Fig. 1. After some time mobile node 2 invokes the hello process and all neighbouring nodes replying to node 2 which is shown in Fig. 1(b). Fig. 1(c) shows that when active node 3 has mobility then there is a link break between 2 and 3 and node 8 has been selected for backup routing (as shown in Fig. 1(d)). It is clearly shown in Fig. 1(e), there is unavailability of neighbour nodes around upstream node 2 so backup routing become useless. Thus, it is clear that neighbour node density indicates the availability of neighbour nodes which is essential for backup routing. By above example, it is clear that neighbour table (NT) and alternate route table (ART) play an important role during route maintenance. If NT entries are unavailable then it is difficult to invoke the backup routing, so hello process is used to periodically update the NT. However, improper update of neighbour table information degrades the performance of networks. In route maintenance process, neighbour table information should be properly updated before including it in the active session for data transmission. In [24], the alternate routes are formed by the overhearing of route reply (RREP) packets and updated by overhearing of data packets, but its utility is only effective when less topological changes. Due to topological changes the positions of neighbour nodes changed and thus, wrong node selection for alternate route gives ineffective results. Following Fig. 2 shows the function of existing AODV routing protocol route maintenance process.
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www.isi.edu/nsnam/ns/.
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Fig. 1. Illustration of AODV routing protocol route maintenance.
4. Modified route maintenance (MRM) In this section we describe the proposed scheme (MRM) which is an improvement of existing route maintenance scheme for mobile ad hoc networks. In a network, routing protocols are used to establish a route between two end points. Every link in the route has a fixed life time which is updated by hello process. In case of link break in the active route, the upstream node initialises the route maintenance process (as shown in Fig. 2). In route maintenance process, upstream node makes the decision of continuing the data transfer through backup routes or alternate paths otherwise it starts different types of local repair processes [18], which helps to improve performance of network. In fact alternate paths are stored in alternate route table (ART) of neighbour nodes. These alternate paths are created by overhearing of data packets [17]. For upstream node it is difficult to know the availability of alternate paths at neighbour node. This type of problem arises due to lack of query process that confirms the availability of alternate paths at neighbour nodes. In AODV routing protocol every node has neighbour table which is used during the route discovery. In this paper, we are using exchange of hello messages Please cite this article as: D.K. Sharma et al., An improvement in performance of mobile ad hoc networks using modified route maintenance, Computers and Electrical Engineering (2016), http://dx.doi.org/10.1016/j.compeleceng.2015.12.020
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Fig. 2. Flow chart of existing AODV routing protocol route maintenance process [16].
to update neighbour table entries, for counteracting the demerits of topological changes. After overhearing of route reply packets, alternate paths are created in alternate route table (ART).
4.1. Description of modified route maintenance Usually, on the occurrence of a link break, instead of establishing a new route or repairing the existing route, a neighbour can be selected on the basis of its neighbour relationships (neighbour discovery) with the active members of the concerned active route [16]. This is determined by the overhearing factor (OF) of the neighbour node. If a neighbour is sharing relationships with only one member then it has OF (overhearing factor) value 1. Similarly, if such relationships are shared with two members by a neighbour then it’s OF is 2. In Fig. 4, neighbour Y is having overhearing factor 1 whereas neighbour X is having overhearing factor 2. A member establishes relationship with its neighbour (s) by periodically exchange of hello packets. In the proposed method, a new field, OF, has been added in the header of the Hello packet.
4.1.1. Overhearing The process of receiving packets without any response is called overhearing. Promiscuous mode is used to enable overhearing in ns2. On overhearing RREP packets, the neighbour node records the next hop to destination into its alternate route table (ART) [24]. Existence of alternate paths for a long time is needed which is made possible by overhearing of data packets. We have assumed overhearing factor (OF) which indicates the availability of alternate route for destination. Please cite this article as: D.K. Sharma et al., An improvement in performance of mobile ad hoc networks using modified route maintenance, Computers and Electrical Engineering (2016), http://dx.doi.org/10.1016/j.compeleceng.2015.12.020
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Fig. 3. Modified alternate route table, neighbour table and hello packet of AODV routing protocol.
4.1.2. Height In [25], height table is managed by all mobile nodes. A height value is used to select the forward and backward node in route repair process. This height value segregates the forward and backward node from the neighbour table. We are adding this advantage in OF based neighbour node selection to select the forward and backward node along active route. The calculation of height value is explained in the example described below. 4.1.3. Calculation of overhearing factor (OF) and height On overhearing a packet, a neighbour node constructs an Alternate Route Table (ART). Fig. 3(a) shows the format of existing ART of a node. On receiving a hello packet, if there is no entry for the node from which the hello packet is received, then the receiving node adds an entry for it in its neighbour table (shown in Fig. 3(b)). After adding the entry, the node checks its ART and finds out the number of entries having the same destination field value. This gives the OF value for the node which it inserts in the hello packet header and then broadcasts the packet. The default value of OF is 1. The modified hello packet header format is shown in Fig. 3(c). The calculation of height value is mentioned in Algorithm 4. 4.1.3.1. Proposed algorithms. Example: Let us take an example, in Fig. 4(a), S and D are the source and destination nodes respectively, whereas I1 , I2 , I3 , I4 , I5 and I6 are the intermediate nodes. U, V, W, X, Y and Z are the remaining nodes in the network. The dotted blue circles around the nodes I4 and I5 show their corresponding ranges. Initially none of the remaining nodes are in the range of any of the intermediate nodes. Now suppose the nodes X and Y move towards the intermediate nodes such that Y becomes the neighbour of I4 by coming in its range and similarly X becomes the neighbour of both,
Fig. 4. Routing of data packets. (For interpretation of the references to colour in this figure, the reader is referred to the web version of this article).
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Algorithm 1 Calculating Overhearing factor (OF). (A node executes this algorithm when it receives a hello packet from a new neighbour) 1. find the no_of_entries in ART having the same destination field 2. if no_of_entries > 1, 2.1. then OF = no_of_entries 3. otherwise 3.1. OF = 1 4. end
I4 and I5 , which is shown in Fig. 4(b). Node Y receives Hello packet from I4 whereas X receives it from I4 and I5 . Upon receiving a Hello packet from a new node, a neighbour adds it in its ART. Following addition of a new entry in the table, the neighbour node runs Algorithm1 and computes it’s updated OF. In Fig. 5(a), we observe that the number of entries in the ART of Y and X (with the same destination field, D) are 1 and 2, respectively. Y computes it’s OF to be 1. X, however runs the algorithm twice, the first run is when the entry for I4 is made and the second is when the entry for I5 is added. In the first run, X computes it’s OF as 1, but during the second run it calculates it’s OF as 2 because both the entries have the same ‘Destination ID’ field, D (Algorithm 1). All nodes are free to move. Let us see what happens when an intermediate node moves away from its peer(s). In Fig. 6(a), we notice that I5 moves away from its peer I4 . This results in the link break between them. I4 is the upstream node now; hence, it runs Algorithm 3, which in turn calls Algorithm 2. Fig. 5(a) indicates that neighbour table of I4 has two entries. The entry with the highest OF is chosen; hence, node X (OF = 2) is chosen over Y (OF = 1) and is returned by Algorithm 2 (skipping the condition for height in step 1). In Algorithm 3, I4 searches the routing entry for the broken peer (I5 ) in its routing table and replaces the next hop field with the node returned (X) by Algorithm 2 (as shown in Fig. 5(b)). Upon receiving the first data packet, X picks up the entry matching with the destination field of the received packet (I5 ) from its ART and adds it to its own routing table to forward the packet. I4 is not picked as X has received the packet from it. Finally, in Fig. 6 we have repaired the route by our proposed algorithms. Each active and neighbour node maintains its height, nheight to ensure proper node selection during link breaks. The upstream node chooses a node among all its neighbour s with the highest OF as well as a height value greater than its own. In route discovery process, the source node, S assigns itself a height value of 1. We have added a new field, height in the common header for the correct height assignment throughout the route and neighbourhood. Source node S puts 1
Fig. 5. (a) Entries in existing alternate route table and neighbour table. (b) Routing table entry for broken node.
Fig. 6. Modified Route Maintenance (MRM) process.
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D.K. Sharma et al. / Computers and Electrical Engineering 000 (2016) 1–13 Algorithm 2 Finding suitable neighbour from the neighbour list. (This algorithm returns the most suitable neighbour and is called by Algorithm 3) 1. find the neighbour, neighbr_sel, with the highest OF with height > nheight 2. if no such neighbour available 2.1 then neighbr_sel = NULL 3. return neighbr_sel 4. end
Algorithm 3 Handling link break. (The upstream node executes this algorithm during link break) 1. run Algorithm 2 2. if it does not return NULL 2.1 then find the entry in the routing table of the broken peer 2.2 replace it with the return value of Algorithm 2 3. otherwise 3.1 continue with the existing mechanism of route repair of AODV 4. end
Algorithm 4 Calculating height. (On receiving/overhearing a data packet, the node executes this algorithm) 1. the source assigns itself a height value of 1 and puts this value in the data packet while sending 2. the receiving node sets its height 1 more than that of the received data packet and forwards it with its own height value 3. the overhearing node sets its height with the average value of the heights of the overheard nodes 4. end
in the height field of the data packet header which it sends to I1 . Upon receiving the packet, I1 assigns itself a height of 1 greater than the height value in the header. Thus, I1 ’s nheight is 1(value of the height field in the header of the received data packet) + 1(increment value) = 2. While forwarding the packet (to I2 ), I1 puts its own height value in the height field of the data packet header. This process goes on and finally destination node D sets its nheight = 8. The neighbours overhear the (data) packets. They take the average value of the ‘height fields’ of the packets overheard from multiple active nodes (Algorithm 4). So, Y sets its nheight = 5 as it overhears data packet only from I4 , whereas X sets its nheight = 5.5 because it overhears data packets from I4 (nheight = 5) and I5 (nheight = 6). To show the necessity of the concept of height, let us make a small change in the previous example by moving Y in the ranges of both I3 and I4 , which is shown in Fig. 7 (assuming the link break happened after Y attained its new position). This results in an additional entry in Y’s ART (for I3 ), consequently changing it’s OF to 2 (Fig. 8). As I4 (upstream node) has both
Fig. 7. Link failure and backup routing.
Fig. 8. Description of ART and NT in same OF.
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Fig. 9. Loop formation due to same OF value.
its neighbours (X and Y) with the same OF values, it chooses the first one, i.e. Y as its next peer. On receiving the first data packet, Y uses its ART to select its next peer. It chooses I3 over I4 because it should not send packets back to the node from which it received. Now, I3 has already a path through I4 towards destination D, so it sends the received packet to I4 ; hence, a loop is formed between I3 , I4 and Y which is shown in Fig. 9. On the other hand, if we consider heights as well, in this example, I4 (nheight = 5) will choose X (nheight = 5.5) over Y (nheight = 4.5) because X is having a height greater than that of I4 (whereas, the height of Y is less than that of I4 ).
5. Simulation We are using network simulator (ns-2.34, see footnote 1) for implementation and validation of proposed algorithms. AODV routing protocol is used as the base for the implementation. After the simulations we have obtained improved results compared to the latest local repair techniques of AODV routing protocol. In the paper [18], hello is disabled for overhead control, as a result no neighbour connectivity is updated, and hence its performance is degraded in dynamic topology. We also compared our results with that of AODV-ABR [17] routing protocol and modified route repair, an improvement over the AODV routing protocol.
5.1. Simulation environment In total, four different scenarios are simulated with number of link breaks from 1 to 4, and the results are averaged. Channel bandwidth is 2 Mbps. The path loss model is Two-Ray Ground Model. The CBR data packet size is 512 bytes and the packet rate is 5 packets per second. After a link break, the upstream node selects a neighbour with the highest OF value and suitable height value as its successor in the chain. Table 1 shows the various simulation parameters [17,18].
Table 1. Simulation parameters. Parameter Simulation time Topology size Number of mobile nodes MAC type Radio propagation model Range Size of packet Transmitter power Receiver threshold Traffic type CBR rate Promiscuous mode Hello interval Data size Speed
Value 600 s 2000∗1000 m2 50 MAC 802.11 Two ray ground 250 m 512 Bytes 0.281 W 7.69113∗10−8 W CBR 1 Mbps Enable 1000 ms 5MB 10–40 m/s
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Fig. 10. Comparing Routing Overhead of existing and proposed method.
5.1.1. Results and discussion The inherent dynamic nature of MANETs results in link breaks in the active routes. Moreover nodes moving with high speed cause frequent link breaks. To evaluate the proposed scheme we have obtained the results focussing on two parameters: speed of nodes and number of link breaks. Both of them depict the ever changing topology of MANETs. (a) Impact of link breaks: Overhead: routing overhead occurs due to the transmission of additional control packets for successful delivery of data packets. It is the ratio of the total number of routing control packets sent by all nodes to the number of data packets received at destination node. Route Request (RREQ), Route Reply (RREP), Route Error (RERR) and Hello packets comprise the control packets in AODV protocol. In the existing route repair process of AODV, after a link break, the source node starts reroute discovery, but in case of local repair, the upstream node broadcasts RREQ packets and waits for RREP packets. In other case, extra control packets, viz., RERR, RREQ and RREP packets are generated. Reroute discoveries result in considerable increase in the routing overhead in a dynamic network where nodes move and cause numerous link breaks. Increase in routing overhead is directly proportional to the number of the link breaks occurrence. In the above Fig. 10, it is observed that the routing overhead is more in the case of existing method than that of the proposed method, when there is a single link break. With increase in the number of the link breaks, the routing overhead increases more in existing method than when proposed method is used. Packet delivery ratio: packet delivery ratio is defined as the total amount of data received divided by the total amount of data transmitted during the simulation. AODV performs a local repair when the distance to the destination is not farther than MAX_REPAIR_TTL [7], or initiates a new route discovery. During local repair or reroute discovery, the data packets are queued. But, delay in the repair process causes packet drop which is due high data rate. In the Fig. 11, it is observed that the packet delivery ratio is more in the case of proposed method than that of the existing method, when there is a single link break. The difference in the packet delivery ratios remains same in both the cases with the increase in number of link breaks. Throughput: throughput is the average rate of successful message delivery over a communication channel. It is usually measured in bits per second (bit/s or bps). The process of reroute discovery or local repair causes packet drop. The number of packet drops increases with the length of the route and the number of link breaks. Hence, there is a considerable decrease in throughput in such cases of increased packet drops. The proposed method does not rely on such route discovery or maintenance processes and grabs the best possible neighbour for forwarding the data packets. In the Fig. 12, it is observed that the throughput is more in the case of proposed method than that of the existing method, when there is a single link break. The difference in the throughputs remains same in both the cases with the increase in number of link breaks. (b) Impact of mobility: In this section, we have described the impact of mobility on the performance of the proposed scheme (AODV+MRM) and compare it with that of the AODV routing protocol. We are employing 7 different speed values (m/sec) for the nodes which are 10, 15, 20, 25, 30, 35 and 40. There are 50 nodes spread in a terrain of area 2000 × 1000 m2 with each node having a range of 250 m. Several CBR applications are run for 600 s. The routing overhead values for all these node speeds show a great difference, both in the proposed and the existing methods. So, for a wide range of speed, we observe that the proposed method incurs routing overhead, which is comparatively very low as shown in Fig. 13. For the same set of speed values, the packet delivery ratio for the existing method is a downward sloping line with small variations. The graph for the proposed method however is having a lot of variations, but the values fall inside a small Please cite this article as: D.K. Sharma et al., An improvement in performance of mobile ad hoc networks using modified route maintenance, Computers and Electrical Engineering (2016), http://dx.doi.org/10.1016/j.compeleceng.2015.12.020
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Fig. 11. Comparing Packet Delivery Ratio of existing and proposed method.
Fig. 12. Comparing Throughput of existing and proposed method.
Fig. 13. Comparing Routing Overhead of existing and proposed method.
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Fig. 14. Comparing Packet Delivery Ratio of existing and proposed method.
Fig. 15. Comparing Throughput of existing and proposed method.
range as shown in Fig. 14. These values are not decreasing and always better than the corresponding values of the existing method. The graphs for the throughput are somewhat similar to that of the packet delivery ratio. Although, the existing method graph does not resemble a line but the values do decrease with speed. The values of the proposed method are far superior to the corresponding values of the existing method as shown in Fig. 15. 6. Conclusions The problem of inefficient backup routing in MANET has been solved by modified route maintenance. Overhearing factor (OF) based node selection has confirmed the availability of alternate paths. The height based technique has been implemented to provide forward and backward nodes along active route. The proposed modified route maintenance has controlled the use of additional control packets, which results less energy consumption. Overhearing process helps to update the alternate route table which is used in backup routing. The main cause of excess energy consumption is frequent initialisation of re-route discovery and maximum local repair attempts. Proposed algorithms make better route maintenance by fresh neighbour table and alternate routing table information which increases the performance of network by low routing overhead, increased packet delivery ratio and throughput. With the increase in number of link breaks, these metrics in the existing method deteriorate, thereby degrading the routing protocol performance. References [1] Conti Marco, Giordano Silvia. mobile ad hoc networking: milestones, challenges, and new research directions. IEEE Commun Mag 2014;52(1):85–96. [2] Boukerche Azzedine, Turgut Begumhan, Aydin Nevin, Mohammad Z, Ahmad Ladislau, Bölöni Damla Turgut. Routing protocols in ad hoc networks: a survey. Comput Netw 2011;55(13):3032–80. [3] Bilgin Zeki, Khan Bilal. A dynamic route optimization mechanism for AODV in MANETs. In: Proceedings of IEEE international conference on communications (ICC); 2010. p. 1–5.
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[4] Guo Lei, Peng Yuhuai, Wang Xingwei, Jiang Dingde, Yu Yinpeng. Performance evaluation for on-demand routing protocols based on OPNET modules in wireless mesh networks. Comput Electr Eng 2011;37(1):106–14. [5] Zhang Xu, Qian Zhi-Hong, Guo Yu-Qi, Wang Xue. An efficient hop count routing protocol for wireless ad hoc networks. Int J Autom Comput 2014;11(1):93–9. [6] Al-Jarrah Omar, Megdadi Omar. Enhanced AODV routing protocol for bluetooth scatternet. Comput Electr Eng 2009;35:197–208. [7] Wang Zehua, Chen Yuanzhu, Li Cheng. A new loop-free proactive source routing scheme for opportunistic data forwarding in wireless networks. IEEE Commun Lett 2011;15(11):1184–6. [8] Kim Jung-Hun, Lee SuKyoung. Reliable routing protocol for vehicular ad hoc networks. Int J Electron Commun 2011;65(3):268–71. [9] Hawa Mohammed, Taifour Sinan, Qasem Mohammad, Tuffaha Waleed. A dynamic cross-layer routing protocol for mobile ad hoc networks. Int J Electr Commun 2012;66(12):996–1005. [10] Reina DG, Toral SL, Johnson P, Barrero F. Improving discovery phase of reactive ad hoc routing protocols using Jaccard distance. J Supercomput 2014;67(1):131–52. [11] Chuang Po-Jen, Yen Po-Hsun, Chu Ting-Yi. Efficient route discovery and repair in mobile ad-hoc networks. In: Proceedings of 26th IEEE international conference on advanced information networking and applications; 2012. p. 391–8. [12] Leu S, Chang R-S. Simple algorithm for solving broadcast storm in mobile ad hoc network. IET Commun 2011;5(16):2356–63. [13] Hernandez-Cons Nelson, Kasahara Shoji, Takahashi Yutaka. Dynamic hello/timeout timer adjustment in routing protocols for reducing overhead in MANETs. Comput Commun 2010;33:1864–78. [14] Ashraf Usman, Abdellatif Slim, Juanole Guy. Route maintenance in IEEE 802.11 wireless mesh networks. Comput Commun 2011;34(13):1604–21. [15] Valera Alvin, Tan Hwee-Pink, Winston KG, Seah. Improving link failure detection and response in IEEE 802.11 wireless ad hoc networks. In: Proceedings of 21st annual IEEE international symposium on personal, indoor and mobile radio communications; 2010. p. 1814–19. [16] M. Ad, C. E. Perkins, and S. R. Das, “Ad hoc on-demand distance vector (AODV) routing,” Nov. 30 2000. Available: http://tools.ietf.org/pdf/ draft-ietf-manet-aodv-08.pdf [17] Lai WeiKuang, Hsiao Sheng-Yu, Lin Yuh-Chung. Adaptive backup routing for ad-hoc networks. Comput Commun 2007;30(2):453–64. [18] Jain Jyoti, Gupta Roopam, Tushar K, Bandhopadhyaya. Performance analysis of proposed local link repair schemes for ad hoc on demand distance vector. IET Netw 2014;3(1):129–36. [19] Gupta SachinKumar, Sharma Rohit, Saket RK. Effect of variation in active route timeout and delete period constant on the performance of AODV protocol. Int J Mob Commun 2014;12(2):177–91. [20] Yen Y-S, Chang H-C, Chang R-S, Chao H-C. Routing with adaptive path and limited flooding for mobile ad hoc networks. Comput Electr Eng 2010;36(2):280–90. [21] Varaprasad G. Lifetime enhancement routing algorithm for mobile ad hoc networks. IET Commun 2011;5(1):119–25. [22] Claude Richard, Charles Perkins, and Cedric Westphal, “Defining an optimal active route time-out for the aodv routing protocol”, In IEEE SECON 2005 (poster submission), 2005. [23] Srinivasan P, Kamalakkannan P. Enhancing route maintenance in RSEA-AODV for mobile ad hoc networks. In: Proceedings of IEEE international conference on intelligent systems and control (ISCO); 2013. p. 464–9. [24] Lee SJ, Gerla M. AODV-BR: backup routing in ad hoc networks. In: Proceedings of IEEE WCNC 2000, Chicago, IL; 2000. [25] Yu Chang Wu, Wu Tung-Kuang, Cheng ReiHeng. A low overhead dynamic route repairing mechanism for mobile ad hoc networks. Comput Commun 2007;30(5):1152–63. Dhirendra Kumar Sharma has completed Ph.D. in Computer Science and Engineering from Indian School of Mines Dhanbad, India. Currently, he is working as a teaching assistant at National Institute of Technology Raipur. His main research interest in development of Routing and MAC protocols for wireless networks. He is a reviewer of IEEE System journal.
Amar Nath Patra has done M.Tech. in Computer Application from Indian School of Mines Dhanbad and currently working as a faculty in Information Technology department, National Institute of Technology Raipur. His research interest includes routing protocol for wireless ad hoc networks.
Chiranjeev Kumar is working as an Associate Professor in the Department of Computer Science and Engineering Indian School of Mines Dhanbad, India. He obtained the Ph.D. from Allahabad University. He has 10 years of teaching and research carrier; he has contributed many research papers in several refereed journals. His main research interests include Mobility Management in Wireless Networks, Ad Hoc Networks, and Software Engineering.
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Computers and Electrical Engineering journal homepage: www.elsevier.com/locate/compeleceng
An improvement in performance of mobile ad hoc networks using modified route maintenanceR Dhirendra Kumar Sharma a,∗, Amar Nath Patra a, Chiranjeev Kumar b a b
Department of Information Technology, National Institute of Technology Raipur, 492010, Chhattisgarh, India Department of Computer Science and Engineering, Indian School of Mines, Dhanbad 826004, Jharkhand , India
a r t i c l e
i n f o
Article history: Received 11 August 2015 Revised 23 December 2015 Accepted 23 December 2015 Available online xxx Keywords: Neighbour table Routing table Route maintenance AODV routing protocol Overhearing factor Height
a b s t r a c t A mobile ad hoc network (MANET) is a temporary network where nodes are free to move in a given area. Due to this dynamic nature, links in the routes break. Often backup routing is used as a solution in which alternate route tables are used to continue the data transfer. In this paper, we discuss the shortcomings of the existing backup routing, which is due to their inadequate ways of updating alternate route table information by route maintenance. In several routing protocols, hello messages are periodically broadcasted to update the neighbour table entries which help in detecting link failure. We propose an efficient route maintenance mechanism in AODV routing protocol employing the benefits offered by hello messages. Simulation results show that our proposed modified route maintenance (MRM) scheme significantly improves the performance of MANET. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction A mobile ad hoc network (MANET) is a non-permanent infrastructure less network in which mobile nodes communicate with each other without any access point. This makes it useful in disaster areas, battlefield and conference communication. Nowadays, MANETs are integrated with infrastructure based networks to provide internet based services by multi-hop routing [1]. In existing literature survey [2–9], various routing protocols have been proposed to find the optimal route. Routing protocols are categorised as proactive, reactive and hybrid. Proactive routing protocols are known as table driven routing protocol, in which routing table information for all destinations are periodically updated that cause overhead problem. These routing protocols are suitable for small scale static networks. In a dynamic environment, reactive routing protocols provide effective results. In fact, performance of routing protocols varies with traffic, node density, route length, and mobility. Improvement in performance of proactive and reactive routing protocols is an important issue which is discussed in [4,6,18]. In MANETs, route stability is a major concern which affects the performance metrics such as routing overhead, throughput, and latency. In fact, frequent topological changes have a great impact on the route stability. A reactive routing protocol finds a route by route discovery process. In AODV routing protocol route discovery and route maintenance processes are utilised for route establishment and route repair. A link break in an active route often initiates the reroute discovery which causes the broadcast storm problem. In [10,11], improvements over discovery phase have been proposed to control the
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Reviews processed and recommended for publication to the Editor-in-Chief by Associate Editor Dr. A. Isazadeh. Corresponding author. Tel.: +91 8370033126. E-mail addresses: [email protected] (D.K. Sharma), [email protected] (A.N. Patra), [email protected] (C. Kumar).
http://dx.doi.org/10.1016/j.compeleceng.2015.12.020 0045-7906/© 2016 Elsevier Ltd. All rights reserved.
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overhead and excess bandwidth utilisation. The broadcast storm problem is handled by controlled broadcast algorithms which are used to regulate the unnecessary traversal of control packets during reroute discovery [12]. In [21], the author proposes a scheme to increase the lifetime of route by traffic flow. Route timeout is a major problem which occurs due to unregulated flow of data packets. Such type of problem is overcome by increasing the data rate [22]. An active route is updated by a regulated flow of data in static network. In dynamic topology, the lifetime of route is not maintained by data rate. In the paper [13], authors describe the problem of periodic exchange of hello message at fix rate cause unnecessary overhead. This overhead problem is controlled by link change rate estimation which is based on constant measurement of the link connectivity. A link failure is detected by link layer protocol or hello process (network layer) which confirms the link failure in an active route. Another link layer feedback mechanism [14], detects the link failure by maximum retransmission attempts. In [15], hello process is used to improve the lifetime of route. Through hello process, each node maintains its link connectivity with its neighbour nodes by updating neighbour table and routing table entries. In AODV routing protocol [16], on receiving a hello packet, a node checks whether it has an entry for the node from which it received the packet. If no such entry is there then it adds an entry for such a node, otherwise updates the expiry time for the entry. In both cases, the expiry time is set (or updated) to CURRENT_TIME + (1.5 ∗ ALLOWED_HELLO_LOSS ∗ HELLO_INTERVAL). The relationship between neighbour table and routing table is maintained by hello process. Loss of neighbourhood relationship with a neighbour is detected in two ways. In the first method, Layer 2 identifies a link break and notifies layer 3 by calling the function aodv_rt_failed_callback() (in ns2). In the second method, a node identifies the neighbours from whom it has not received hello packets in ’HELLO_INTERVAL ∗ 1.5 s, that is the expired entries in the neighbour table. In both methods, such neighbours are deleted from the neighbour table. This is followed by making the entry ’down’ [16,23] of corresponding neighbour which exist in routing table. In active data session the lifetime of active route is maintained by updating expiry time in routing table. The expiry time of the entries in the routing table may get updated while receiving a route request or route reply packet, or forwarding a packet. After the link failure detection, upstream node starts the route maintenance process in which either backup routing or route repair schemes is followed. In backup routing buffered data packets are sent through alternate paths of neighbour nodes. Here, we observe that due to dynamic topology neighbour nodes move and hence backup routing can fail, causing huge amount of undelivered data packets. The main reason of unsuccessful delivery is ineffective backup routing which is due to incomplete neighbour table (NT) and alternate route table (ART) information. In [18], local repair scheme is introduced which reduce the bandwidth consumption in link failure. In the proposed scheme author uses the link layer mechanism instead of hello process to find the link failure. In [19], authors propose a local repair scheme which does not use hello process. In this paper we discuss the route maintenance problem which arises due to inefficient backup routing and the main reason is inadequate information in neighbour table (NT) and alternate route table (ART). Following which, we propose the modified route maintenance (MRM) scheme. Further, we discuss different scenario for the proposed algorithms which show their utility in the network. 1.1. Contribution The main contribution of our paper is in improving the performance of mobile ad hoc networks by using Modified Route Maintenance algorithms as following: • We use hello process identify the fresh neighbour nodes and update the neighbour table with overhearing factor (OF) which is used for neighbour node selection. • We define the overhearing factor (OF) which shows the capability of a neighbour node with fresh alternate paths in ART. • We introduce the height value for proper selection when two or more eligible neighbours have the same OF. • The modified route maintenance (MRM) algorithms implement over AODV routing protocol using network simulator (ns2.34). The remainder of this paper is organised as follows. The next Section 2 deals with the related work. Network model and route maintenance process are discussed in Section 3. Modified route maintenance and proposed algorithms are described in Section 4. Section 5 presents simulation and implementation of the proposed algorithms in ns2. Finally, conclusions of the paper are drawn in Section 6. 2. Related work In [3], the authors have proposed a route optimisation mechanism Shrink to increase network capacity, and provide faster link failure recovery and reduced end-to-end delay. Route optimisation is performed after route discovery process by reducing unessential hop count in the active route. In [20], every host node has a set of neighbour nodes and packet header is exchanged during the route request forwarding. In this method a spanning tree is used to regulate the traversal of unnecessary control packets in the network. In dynamic topology invalidation of two-hop neighbour nodes information is a major problem that affects the performance of Please cite this article as: D.K. 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network. In [22], route invalidation problem is discussed which is rectified by using two parameters: active route timeout (ART) and delete period constant (n). A route is a set of links and its lifetime is based on the battery power of the mobile nodes. An improvement over link lifetime has been done by energy conservation approach in which authors have considered the battery power of mobile nodes to determine link lifetime [21]. A link is periodically updated by exchange of hello messages. An improvement over discovery phase has been proposed to improve the route establishment and route repair phase in networks [10,11]. In such improvement in route discovery phase, a request packet header field contains the hop count, node power, and average traffic density as metrics. AODV-ABR routing protocol [17], handles link breaks by sending the buffered data packets to most updated shortest alternate paths of neighbour node. Here, it is clear that topological imbalance resulting from such frequent link changes, which requires retransmission and rerouting of packets. Finally, this process affects the network performance in terms of high bandwidth consumption and increased latency. The main reason of retransmission of packets by upstream node is inaccurate neighbour node information in neighbour table. Here effective route maintenance is required to update the neighbour table with sufficient information. 3. Network model In MANETs, all active nodes use neighbour table and routing table for delivery of data packets. Neighbour tables are associated with routing table of all active nodes which is utilised for data transmission. A neighbour table has two entries: node id and expiry time. With the help of hello process neighbour table entries are periodically updated by exchange of hello messages. On a link break, the upstream node performs route maintenance either by utilising the alternate paths [17] of neighbour nodes or repairing the broken route locally (local repair or global repair) [18]. In adaptive backup routing (AODV-ABR) alternate routing table entries are updated by overhearing of RREP and data packets. In this paper, we are enhancing the route maintenance process with the help of four algorithms which use the overhearing process to update the Alternate Route Table (ART) and Neighbour Table (NT) with new parameters: overhearing factor (OF) and height. With the help of network simulator ns2.341 , we notice that only the existence of entries of neighbours in Neighbour Table (NT) does not provide efficient delivery of packets. We observe that neighbour tables add entries of new neighbours in the top. When a route break happens then an upstream node selects the upper most entry from the Neighbour Table (NT). Such a selection of neighbour node as the next node for transmission is not always effective. This may cause serious problem during route maintenance. In this paper proposed algorithms are used to select a neighbour node from the neighbour table on the basis of OF and height for efficient delivery of data packets. We are using hello messages to update the Alternate Route Table (ART) and Neighbour Table (NT). 3.1. Route maintenance Route maintenance is the process to maintain active route(s) without affecting the performance of routing protocol [23]. By route maintenance we can increase the re-usability of a route; actually it is associated by link update or maintenance of link connectivity. Maintenance of route is important to increase the productivity of any type of networks; it helps to achieve better result in terms of Quality of Service (QoS) performance metrics. Different types of link update mechanisms have been developed to short out the connectivity issues. Loss of link connectivity results route failure. In reactive routing protocols, route discovery and route maintenance have separate functionality. A route is discovered by route discovery process but its longevity and stability is maintained by proper maintenance. Backup routing, local repair, global repair, error notification and link connectivity techniques are the parts of route maintenance process. In Fig. 1(a), three-hop route has been established by source node 1 to destination node 4. In dynamic environment the position of mobile nodes 5–8 changes with respect to time which is shown in Fig. 1. After some time mobile node 2 invokes the hello process and all neighbouring nodes replying to node 2 which is shown in Fig. 1(b). Fig. 1(c) shows that when active node 3 has mobility then there is a link break between 2 and 3 and node 8 has been selected for backup routing (as shown in Fig. 1(d)). It is clearly shown in Fig. 1(e), there is unavailability of neighbour nodes around upstream node 2 so backup routing become useless. Thus, it is clear that neighbour node density indicates the availability of neighbour nodes which is essential for backup routing. By above example, it is clear that neighbour table (NT) and alternate route table (ART) play an important role during route maintenance. If NT entries are unavailable then it is difficult to invoke the backup routing, so hello process is used to periodically update the NT. However, improper update of neighbour table information degrades the performance of networks. In route maintenance process, neighbour table information should be properly updated before including it in the active session for data transmission. In [24], the alternate routes are formed by the overhearing of route reply (RREP) packets and updated by overhearing of data packets, but its utility is only effective when less topological changes. Due to topological changes the positions of neighbour nodes changed and thus, wrong node selection for alternate route gives ineffective results. Following Fig. 2 shows the function of existing AODV routing protocol route maintenance process.
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www.isi.edu/nsnam/ns/.
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Fig. 1. Illustration of AODV routing protocol route maintenance.
4. Modified route maintenance (MRM) In this section we describe the proposed scheme (MRM) which is an improvement of existing route maintenance scheme for mobile ad hoc networks. In a network, routing protocols are used to establish a route between two end points. Every link in the route has a fixed life time which is updated by hello process. In case of link break in the active route, the upstream node initialises the route maintenance process (as shown in Fig. 2). In route maintenance process, upstream node makes the decision of continuing the data transfer through backup routes or alternate paths otherwise it starts different types of local repair processes [18], which helps to improve performance of network. In fact alternate paths are stored in alternate route table (ART) of neighbour nodes. These alternate paths are created by overhearing of data packets [17]. For upstream node it is difficult to know the availability of alternate paths at neighbour node. This type of problem arises due to lack of query process that confirms the availability of alternate paths at neighbour nodes. In AODV routing protocol every node has neighbour table which is used during the route discovery. In this paper, we are using exchange of hello messages Please cite this article as: D.K. Sharma et al., An improvement in performance of mobile ad hoc networks using modified route maintenance, Computers and Electrical Engineering (2016), http://dx.doi.org/10.1016/j.compeleceng.2015.12.020
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Fig. 2. Flow chart of existing AODV routing protocol route maintenance process [16].
to update neighbour table entries, for counteracting the demerits of topological changes. After overhearing of route reply packets, alternate paths are created in alternate route table (ART).
4.1. Description of modified route maintenance Usually, on the occurrence of a link break, instead of establishing a new route or repairing the existing route, a neighbour can be selected on the basis of its neighbour relationships (neighbour discovery) with the active members of the concerned active route [16]. This is determined by the overhearing factor (OF) of the neighbour node. If a neighbour is sharing relationships with only one member then it has OF (overhearing factor) value 1. Similarly, if such relationships are shared with two members by a neighbour then it’s OF is 2. In Fig. 4, neighbour Y is having overhearing factor 1 whereas neighbour X is having overhearing factor 2. A member establishes relationship with its neighbour (s) by periodically exchange of hello packets. In the proposed method, a new field, OF, has been added in the header of the Hello packet.
4.1.1. Overhearing The process of receiving packets without any response is called overhearing. Promiscuous mode is used to enable overhearing in ns2. On overhearing RREP packets, the neighbour node records the next hop to destination into its alternate route table (ART) [24]. Existence of alternate paths for a long time is needed which is made possible by overhearing of data packets. We have assumed overhearing factor (OF) which indicates the availability of alternate route for destination. Please cite this article as: D.K. Sharma et al., An improvement in performance of mobile ad hoc networks using modified route maintenance, Computers and Electrical Engineering (2016), http://dx.doi.org/10.1016/j.compeleceng.2015.12.020
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Fig. 3. Modified alternate route table, neighbour table and hello packet of AODV routing protocol.
4.1.2. Height In [25], height table is managed by all mobile nodes. A height value is used to select the forward and backward node in route repair process. This height value segregates the forward and backward node from the neighbour table. We are adding this advantage in OF based neighbour node selection to select the forward and backward node along active route. The calculation of height value is explained in the example described below. 4.1.3. Calculation of overhearing factor (OF) and height On overhearing a packet, a neighbour node constructs an Alternate Route Table (ART). Fig. 3(a) shows the format of existing ART of a node. On receiving a hello packet, if there is no entry for the node from which the hello packet is received, then the receiving node adds an entry for it in its neighbour table (shown in Fig. 3(b)). After adding the entry, the node checks its ART and finds out the number of entries having the same destination field value. This gives the OF value for the node which it inserts in the hello packet header and then broadcasts the packet. The default value of OF is 1. The modified hello packet header format is shown in Fig. 3(c). The calculation of height value is mentioned in Algorithm 4. 4.1.3.1. Proposed algorithms. Example: Let us take an example, in Fig. 4(a), S and D are the source and destination nodes respectively, whereas I1 , I2 , I3 , I4 , I5 and I6 are the intermediate nodes. U, V, W, X, Y and Z are the remaining nodes in the network. The dotted blue circles around the nodes I4 and I5 show their corresponding ranges. Initially none of the remaining nodes are in the range of any of the intermediate nodes. Now suppose the nodes X and Y move towards the intermediate nodes such that Y becomes the neighbour of I4 by coming in its range and similarly X becomes the neighbour of both,
Fig. 4. Routing of data packets. (For interpretation of the references to colour in this figure, the reader is referred to the web version of this article).
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Algorithm 1 Calculating Overhearing factor (OF). (A node executes this algorithm when it receives a hello packet from a new neighbour) 1. find the no_of_entries in ART having the same destination field 2. if no_of_entries > 1, 2.1. then OF = no_of_entries 3. otherwise 3.1. OF = 1 4. end
I4 and I5 , which is shown in Fig. 4(b). Node Y receives Hello packet from I4 whereas X receives it from I4 and I5 . Upon receiving a Hello packet from a new node, a neighbour adds it in its ART. Following addition of a new entry in the table, the neighbour node runs Algorithm1 and computes it’s updated OF. In Fig. 5(a), we observe that the number of entries in the ART of Y and X (with the same destination field, D) are 1 and 2, respectively. Y computes it’s OF to be 1. X, however runs the algorithm twice, the first run is when the entry for I4 is made and the second is when the entry for I5 is added. In the first run, X computes it’s OF as 1, but during the second run it calculates it’s OF as 2 because both the entries have the same ‘Destination ID’ field, D (Algorithm 1). All nodes are free to move. Let us see what happens when an intermediate node moves away from its peer(s). In Fig. 6(a), we notice that I5 moves away from its peer I4 . This results in the link break between them. I4 is the upstream node now; hence, it runs Algorithm 3, which in turn calls Algorithm 2. Fig. 5(a) indicates that neighbour table of I4 has two entries. The entry with the highest OF is chosen; hence, node X (OF = 2) is chosen over Y (OF = 1) and is returned by Algorithm 2 (skipping the condition for height in step 1). In Algorithm 3, I4 searches the routing entry for the broken peer (I5 ) in its routing table and replaces the next hop field with the node returned (X) by Algorithm 2 (as shown in Fig. 5(b)). Upon receiving the first data packet, X picks up the entry matching with the destination field of the received packet (I5 ) from its ART and adds it to its own routing table to forward the packet. I4 is not picked as X has received the packet from it. Finally, in Fig. 6 we have repaired the route by our proposed algorithms. Each active and neighbour node maintains its height, nheight to ensure proper node selection during link breaks. The upstream node chooses a node among all its neighbour s with the highest OF as well as a height value greater than its own. In route discovery process, the source node, S assigns itself a height value of 1. We have added a new field, height in the common header for the correct height assignment throughout the route and neighbourhood. Source node S puts 1
Fig. 5. (a) Entries in existing alternate route table and neighbour table. (b) Routing table entry for broken node.
Fig. 6. Modified Route Maintenance (MRM) process.
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D.K. Sharma et al. / Computers and Electrical Engineering 000 (2016) 1–13 Algorithm 2 Finding suitable neighbour from the neighbour list. (This algorithm returns the most suitable neighbour and is called by Algorithm 3) 1. find the neighbour, neighbr_sel, with the highest OF with height > nheight 2. if no such neighbour available 2.1 then neighbr_sel = NULL 3. return neighbr_sel 4. end
Algorithm 3 Handling link break. (The upstream node executes this algorithm during link break) 1. run Algorithm 2 2. if it does not return NULL 2.1 then find the entry in the routing table of the broken peer 2.2 replace it with the return value of Algorithm 2 3. otherwise 3.1 continue with the existing mechanism of route repair of AODV 4. end
Algorithm 4 Calculating height. (On receiving/overhearing a data packet, the node executes this algorithm) 1. the source assigns itself a height value of 1 and puts this value in the data packet while sending 2. the receiving node sets its height 1 more than that of the received data packet and forwards it with its own height value 3. the overhearing node sets its height with the average value of the heights of the overheard nodes 4. end
in the height field of the data packet header which it sends to I1 . Upon receiving the packet, I1 assigns itself a height of 1 greater than the height value in the header. Thus, I1 ’s nheight is 1(value of the height field in the header of the received data packet) + 1(increment value) = 2. While forwarding the packet (to I2 ), I1 puts its own height value in the height field of the data packet header. This process goes on and finally destination node D sets its nheight = 8. The neighbours overhear the (data) packets. They take the average value of the ‘height fields’ of the packets overheard from multiple active nodes (Algorithm 4). So, Y sets its nheight = 5 as it overhears data packet only from I4 , whereas X sets its nheight = 5.5 because it overhears data packets from I4 (nheight = 5) and I5 (nheight = 6). To show the necessity of the concept of height, let us make a small change in the previous example by moving Y in the ranges of both I3 and I4 , which is shown in Fig. 7 (assuming the link break happened after Y attained its new position). This results in an additional entry in Y’s ART (for I3 ), consequently changing it’s OF to 2 (Fig. 8). As I4 (upstream node) has both
Fig. 7. Link failure and backup routing.
Fig. 8. Description of ART and NT in same OF.
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Fig. 9. Loop formation due to same OF value.
its neighbours (X and Y) with the same OF values, it chooses the first one, i.e. Y as its next peer. On receiving the first data packet, Y uses its ART to select its next peer. It chooses I3 over I4 because it should not send packets back to the node from which it received. Now, I3 has already a path through I4 towards destination D, so it sends the received packet to I4 ; hence, a loop is formed between I3 , I4 and Y which is shown in Fig. 9. On the other hand, if we consider heights as well, in this example, I4 (nheight = 5) will choose X (nheight = 5.5) over Y (nheight = 4.5) because X is having a height greater than that of I4 (whereas, the height of Y is less than that of I4 ).
5. Simulation We are using network simulator (ns-2.34, see footnote 1) for implementation and validation of proposed algorithms. AODV routing protocol is used as the base for the implementation. After the simulations we have obtained improved results compared to the latest local repair techniques of AODV routing protocol. In the paper [18], hello is disabled for overhead control, as a result no neighbour connectivity is updated, and hence its performance is degraded in dynamic topology. We also compared our results with that of AODV-ABR [17] routing protocol and modified route repair, an improvement over the AODV routing protocol.
5.1. Simulation environment In total, four different scenarios are simulated with number of link breaks from 1 to 4, and the results are averaged. Channel bandwidth is 2 Mbps. The path loss model is Two-Ray Ground Model. The CBR data packet size is 512 bytes and the packet rate is 5 packets per second. After a link break, the upstream node selects a neighbour with the highest OF value and suitable height value as its successor in the chain. Table 1 shows the various simulation parameters [17,18].
Table 1. Simulation parameters. Parameter Simulation time Topology size Number of mobile nodes MAC type Radio propagation model Range Size of packet Transmitter power Receiver threshold Traffic type CBR rate Promiscuous mode Hello interval Data size Speed
Value 600 s 2000∗1000 m2 50 MAC 802.11 Two ray ground 250 m 512 Bytes 0.281 W 7.69113∗10−8 W CBR 1 Mbps Enable 1000 ms 5MB 10–40 m/s
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Fig. 10. Comparing Routing Overhead of existing and proposed method.
5.1.1. Results and discussion The inherent dynamic nature of MANETs results in link breaks in the active routes. Moreover nodes moving with high speed cause frequent link breaks. To evaluate the proposed scheme we have obtained the results focussing on two parameters: speed of nodes and number of link breaks. Both of them depict the ever changing topology of MANETs. (a) Impact of link breaks: Overhead: routing overhead occurs due to the transmission of additional control packets for successful delivery of data packets. It is the ratio of the total number of routing control packets sent by all nodes to the number of data packets received at destination node. Route Request (RREQ), Route Reply (RREP), Route Error (RERR) and Hello packets comprise the control packets in AODV protocol. In the existing route repair process of AODV, after a link break, the source node starts reroute discovery, but in case of local repair, the upstream node broadcasts RREQ packets and waits for RREP packets. In other case, extra control packets, viz., RERR, RREQ and RREP packets are generated. Reroute discoveries result in considerable increase in the routing overhead in a dynamic network where nodes move and cause numerous link breaks. Increase in routing overhead is directly proportional to the number of the link breaks occurrence. In the above Fig. 10, it is observed that the routing overhead is more in the case of existing method than that of the proposed method, when there is a single link break. With increase in the number of the link breaks, the routing overhead increases more in existing method than when proposed method is used. Packet delivery ratio: packet delivery ratio is defined as the total amount of data received divided by the total amount of data transmitted during the simulation. AODV performs a local repair when the distance to the destination is not farther than MAX_REPAIR_TTL [7], or initiates a new route discovery. During local repair or reroute discovery, the data packets are queued. But, delay in the repair process causes packet drop which is due high data rate. In the Fig. 11, it is observed that the packet delivery ratio is more in the case of proposed method than that of the existing method, when there is a single link break. The difference in the packet delivery ratios remains same in both the cases with the increase in number of link breaks. Throughput: throughput is the average rate of successful message delivery over a communication channel. It is usually measured in bits per second (bit/s or bps). The process of reroute discovery or local repair causes packet drop. The number of packet drops increases with the length of the route and the number of link breaks. Hence, there is a considerable decrease in throughput in such cases of increased packet drops. The proposed method does not rely on such route discovery or maintenance processes and grabs the best possible neighbour for forwarding the data packets. In the Fig. 12, it is observed that the throughput is more in the case of proposed method than that of the existing method, when there is a single link break. The difference in the throughputs remains same in both the cases with the increase in number of link breaks. (b) Impact of mobility: In this section, we have described the impact of mobility on the performance of the proposed scheme (AODV+MRM) and compare it with that of the AODV routing protocol. We are employing 7 different speed values (m/sec) for the nodes which are 10, 15, 20, 25, 30, 35 and 40. There are 50 nodes spread in a terrain of area 2000 × 1000 m2 with each node having a range of 250 m. Several CBR applications are run for 600 s. The routing overhead values for all these node speeds show a great difference, both in the proposed and the existing methods. So, for a wide range of speed, we observe that the proposed method incurs routing overhead, which is comparatively very low as shown in Fig. 13. For the same set of speed values, the packet delivery ratio for the existing method is a downward sloping line with small variations. The graph for the proposed method however is having a lot of variations, but the values fall inside a small Please cite this article as: D.K. Sharma et al., An improvement in performance of mobile ad hoc networks using modified route maintenance, Computers and Electrical Engineering (2016), http://dx.doi.org/10.1016/j.compeleceng.2015.12.020
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Fig. 11. Comparing Packet Delivery Ratio of existing and proposed method.
Fig. 12. Comparing Throughput of existing and proposed method.
Fig. 13. Comparing Routing Overhead of existing and proposed method.
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Fig. 14. Comparing Packet Delivery Ratio of existing and proposed method.
Fig. 15. Comparing Throughput of existing and proposed method.
range as shown in Fig. 14. These values are not decreasing and always better than the corresponding values of the existing method. The graphs for the throughput are somewhat similar to that of the packet delivery ratio. Although, the existing method graph does not resemble a line but the values do decrease with speed. The values of the proposed method are far superior to the corresponding values of the existing method as shown in Fig. 15. 6. Conclusions The problem of inefficient backup routing in MANET has been solved by modified route maintenance. Overhearing factor (OF) based node selection has confirmed the availability of alternate paths. The height based technique has been implemented to provide forward and backward nodes along active route. The proposed modified route maintenance has controlled the use of additional control packets, which results less energy consumption. Overhearing process helps to update the alternate route table which is used in backup routing. The main cause of excess energy consumption is frequent initialisation of re-route discovery and maximum local repair attempts. Proposed algorithms make better route maintenance by fresh neighbour table and alternate routing table information which increases the performance of network by low routing overhead, increased packet delivery ratio and throughput. With the increase in number of link breaks, these metrics in the existing method deteriorate, thereby degrading the routing protocol performance. References [1] Conti Marco, Giordano Silvia. mobile ad hoc networking: milestones, challenges, and new research directions. IEEE Commun Mag 2014;52(1):85–96. [2] Boukerche Azzedine, Turgut Begumhan, Aydin Nevin, Mohammad Z, Ahmad Ladislau, Bölöni Damla Turgut. Routing protocols in ad hoc networks: a survey. Comput Netw 2011;55(13):3032–80. [3] Bilgin Zeki, Khan Bilal. A dynamic route optimization mechanism for AODV in MANETs. In: Proceedings of IEEE international conference on communications (ICC); 2010. p. 1–5.
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Amar Nath Patra has done M.Tech. in Computer Application from Indian School of Mines Dhanbad and currently working as a faculty in Information Technology department, National Institute of Technology Raipur. His research interest includes routing protocol for wireless ad hoc networks.
Chiranjeev Kumar is working as an Associate Professor in the Department of Computer Science and Engineering Indian School of Mines Dhanbad, India. He obtained the Ph.D. from Allahabad University. He has 10 years of teaching and research carrier; he has contributed many research papers in several refereed journals. His main research interests include Mobility Management in Wireless Networks, Ad Hoc Networks, and Software Engineering.
Please cite this article as: D.K. Sharma et al., An improvement in performance of mobile ad hoc networks using modified route maintenance, Computers and Electrical Engineering (2016), http://dx.doi.org/10.1016/j.compeleceng.2015.12.020