A Comparative Performance Analysis of AODV and DSR Routing protocol for Mobile Ad-hoc Network

A Comparative Performance Analysis of AODV and DSR Routing protocol for Mobile Ad-hoc Network

Muamer N. Mohammed, Ayoob Aziz Ayoob, Ghaidaa M. Abdulsahib,

Osamah I. Khalaf, Hussam Alddin S. Ahmed Faculty of Computer Systems & Software Engineering,

Univeristy Malaysia Pahang 26300, Kuantan, Pahang, Malaysia, [email protected], [email protected], [email protected],

[email protected], [email protected]

Abstract Communication between mobile users is becoming more popular than ever due to the recent

technological advances in wireless communication devices. Many routing protocol methods have been proposed in Mobile Ad-Hoc Network but still the challenges are to improve the routing performance. This paper focuses on investigating the performance analysis of two important reactive routing protocols in mobile Ad-hoc networks such as Dynamic Source Routing (DSR) and Ad-Hoc on Demand Distance Vector Routing (AODV). The comparison was done in terms of the number of hop per route, router discoverytime, throughput and end-to-end delay scenario. The simulation results show that the DSR seems to be much better suited to smaller high load network with a table request in table driven protocol such as AODV. DSR outperforms AODV whereas DSR maintains its low overhead even in the presence of high mobility rate.

Keywords: Ad-hoc network, broadcasting algorithm, routing protocols, DS, AODV.

1. Introduction

Wireless ad-hoc networks are used to provide a communication infrastructure in different areas as a fast, deployable, temporary replacement for destroying fixed network or in the areas where wired LANs are impossible or only cost-intensive to deploy such as protected historical buildings, or the venue of a conference. In the ad-hoc network, mobile nodes communicate with each other via multichip wireless links. There is no stationary infrastructure such as the base stations. Each node on the network also serves as a router, forwarding packets to the other node; hence a dynamic routing protocol is essential as to help these networks work properly. There is numerous routing protocol that may do development for accomplishing this task. A network can be referred as a unit of people or a set of systems that seeks to disseminate their information across the unit or the organization to cater for certain intended purposes. In computer jargons, the definition of networks revolves around a group of computers that are reasonably connected for the sharing of information or services or computer networks as a communication platform between the machines. These networks may be permanent or otherwise [1].

A network is easily divided into wired or wireless. They are distinguishable in terms of the existence of the physical linkage between nodes is required. Routing is described as an activity of linking a call from a source to a particular destination. It also assumes a significant position in the world of architecture. Several kinds of radio frequencies rather than physical cables are used by wireless networks for data receiving and transmitting. These networks can boast of one striking plus point: it removes costly cables and maintenance work from the picture. A mobile ad-hoc network (MANET) is one type of wireless network and its network of mobile routers (and related hosts) that configures by itself, connected by wireless links i.e. a combination that constitutes an arbitrary topology. The routers have the freedom to move at random and organize themselves.

In the 1990s, Ad-hoc networks are also wireless by nature as there is communication among the nodes through the multi-hop links[2]. There is an absence of static infrastructure or base station to meet communication purposes. The individual node works as a router; it forwards and receives packets to, or from, other nodes. Ad-hoc network routing has been a complex task to undertake ever since the birth of these wireless networks, mainly caused by the constant change persistent in the inter-network topology owing to the high mobility of the node. To respond to this, several protocols have been constructed for

A Comparative Performance Analysis of AODV and DSR Routing protocol for Mobile Ad-hoc Network Muamer N. Mohammed, Ayoob Aziz Ayoob, Ghaidaa M. Abdulsahib,Osamah I. Khalaf, Hussam Alddin S. Ahmed

International Journal of Digital Content Technology and its Applications(JDCTA) Volume 9, Number 1, February 2015

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this task to be done successfully, and these include the Destination-Sequenced Distance-Vector (DSDV), AODV and DSR routing protocols [3].

2. Theoretical Background 2.1. Routing protocol

Routing is the act of carrying a piece of information from a source to a destination in an inter-network. There is an encounter of a minimum of one intermediate node inside the Internet works in this process. Since routing was already employed in the networks in the 70s, this concept is no longer a novelty in the field of computer science. However, this concept has slowly been gaining popularity from the middle of the 1980s as the earlier networks, despite being less complicated and functioning in homogeneous environments; high-end and large-scale internetworking strives in the most updated development [4]. Fundamentally, the routing concept deals with two activities: firstly, making sure that the routing paths are optimal and secondly, moving the information groups or more specifically termed as packets along and across an internetwork. The latter concept is termed as packet switching which is very easy to understand, and the path determination can possibly become rather complicated. Routing protocols adopt several metrics for calculating the best path before the packets are sent to their intended destination. This metrics is a standard measurement using a number of hops, normally used by the routing algorithm to decide on the optimal path that should be used by the packet towards its destination. The path determination process suggests that the routing algorithms kick-start and retain the routing tables, which have the entire route information for the packet that varies across the routing algorithms. Routing tables contain a wide range of information generated by the routing algorithms[5].

Most common entries emerging in the routing table appears in a form of IP address prefix and the next hop. Routing tables destination or next hop associations suggests to the router that a destination can be reached in an optimal manner by having the packet sent to a router, at the same time representing the “next hop” on its way to the final destination, and the IP address prefix searches for a set of destinations for which the routing entry is valid.

Switching is relatively simpler than the path determination, where a host is determined to send some packets to another server. The host is needed by the router address, and it will send the packet addressed specifically to the writers of the MAC address, with the protocol address from the host to the destination given. The protocol address is then analyzed by the router and verified in terms of whether it knows how the data reach the destination. If the answer is positive, then the packet is forwarded to its destination, and if it is negative, the packet would be dropped.

Routing is sub-categorized into static routing and dynamic routing. The former indicates the routing strategy being stated through a static, manual manner, in the router. This kind of routing keeps intact a routing table typically written by a network administrator, and it is not relying on the network status, whether the destination is found active or otherwise.

Dynamic routing or the latter is the routing strategy that is being learnt by either the interior or exterior routing protocol. It largely depends on the state of the network, meaning that the routing table is impacted by the destination in an active manner. One great flaw evident in static routing is that if a new router is brought into, or extracted from the network, then it is the administrator job to revise the changes taking place in the routing tables. However, this is not the case with the dynamic routing, as each router is confirmed to be presented through the flooding of the information packet into the network, and subsequently propelling every router within the network to learn about the ’new visitor’ and its entries. This works the same way with the network segments in the dynamic routing.

According to the routing strategy, the routing protocols are table-driven and source-initiated and they rely on the network structure[6]. There are classified as flat routing, hierarchical routing and geographic position assisted routing both the table-driven and source initiated protocols are placed under the flat routing as shown in Figure 1[7].


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Figure 1. Classification of Ad-hoc Routing.

2.2. Dynamic Source Routing (DSR)

DSR is a protocol that was introduced for routing in mobile Ad-hoc networks and brought forth for MANET by Brooch, Johnson, and Maltz [8,9,23]. In brief, the nodes deliver a ROUTE REQUEST message, where all nodes which get this message will be set in the source route and forwarded to their neighbors, unless they have received the same request previously. If a receiving node has a route to the destination, the request is not forwarded, but a REPLY message informing about the full source route is sent. The answer may be committed along the source route reversibly or a ROUTE REQUEST is issued including the route to return to the source, if the former is not regarded to be possible due to asymmetrical connections. ROUTE REPLY messages can be provoked by ROUTE REQUEST messages. After receiving several routes at most, the source picks out the best, by default the shortest, having it stored and messages sent through the path. The better the route metrics, i.e. number of hops, delay, bandwidth, or other criteria, the faster the REPLY reaches the source. The higher the preference granted to the route and the longer it will stay in the cache. When a ROUTE REPLY arrives soon after a ROUTE REQUEST is sent, this may highlight the existence of a short path, since the nodes are usually required to wait until a time to correspond with the length of the route, they can advertise before having it posted. This is done to overcome abundant replies[10]. If a connection fails, the node that is not able to forward the packet to the next node will present an error message to the author. Routes that have broken links can be rescued by taking an optional partial path that has no bad link. The former advantage Dynamic Source Routing protocol that is use source routing, also it is on-demand protocol which nodes are allowed to find out a route over network dynamically[9,11,23]. The good idea behind the use of source routing back to the backed headers of DSR is to have a complete list of nodes duration that they will sink to reach its distance. There is no mechanism of route discovery packed of broadcasting in DSR. This will bring down the overhead bandwidth network. If there is a better route, then the node will update their route cache. The DSR has two modes of processing; route discover and route maintained[8,12]. Figure 2 shows the initiate of Route Discovery in which a node S transmits a Route Request message attempting to discover a route to node D. Then, all nodes will receive within wireless transmission range of D. Each Route Request message identifies the source and destination of the Route Discovery. This route record is initialized to an empty list by the source of the Route Discovery.


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Figure 2. An Example of Route Request: Node S is the source and Node D is the destination

When another node receives a Route Request as a destination of the Route Discovery, it returns a Route Reply message to the source, giving a copy of the accumulated route record from the Route Request; then the source will caches this Route Reply and use it to send subsequent packets to this destination[23]. Otherwise, if this node receiving the Route Request that has recently seen from another Route Request message, this source bearing this same request ID, or if it finds that its own address is already listed in the route record then, it discards the request. Otherwise, this node will add its own address to the route record and propagates it by transmitting it as a local broadcast packet, as shown in Figure 3. Finally, it avoids routing loops easily because the complete route is determined by a single node instead of making the decision hop-by-hop.

Figure 3. An Example of Route Reply: Node S is the source, and Node D is the destination.

2.3. Ad-hoc On-Demand Distance Vector (AODV)

The AODV is easy and effecient routing protocol for Mobile Ad-hoc Networks, which does not contain any fixed topology. This algorithm was fueled by limited bandwidth effective for wireless communications[17]. The majority of the concepts are borrowed from DSR and DSDV algorithms. The route discovery and route maintenance on-demand from both the DSR and hop-by-hop routing operation of node sequence numbers from the DSDV enable the algorithm to deal with both the topology and routing information, being able to get the route points to the fact that this algorithm very useful and desirable for MANETs.

AODV is a combination of DSR, and DSDV protocols. Its basic route-discovery and route-maintenance are derived from the DSR and the hop-by-hop routing, sequence numbers and beacons from the DSDV[15,18].

Each mobile host on the network has the role to play as a specialized router and routes are obtained as intended, highlighting the fact that the network is self-starting. Each node on the network has a routing table with the routing information entries attached to its neighboring nodes and two different counters: a node sequence number and a broadcast-id. When A node (e.g., Source node ‘S’) is to communicate with another (e.g., Destination node ‘D’), it increases its broadcast-id and sets off on a path discovery by establishing a route request packet route request packet (RREQ) to its neighbors. The RREQ contains the following fields [7].


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source-addr. source-sequence # -to maintain new info about the route to the source. dest-addr. dest-sequence# - makes specific about the ‘freshness’ of a route to the destination before it is received

by the source.

The source-addr and broadcast-id pair is used to recognize the RREQ in a distinctive manner. Then the dynamic route table entry starts to be established at all the nodes in the network, on the path from S to D as shown in Figure 4. As the RREQ travels from node to node, the reverse path is automatically built from these nodes back to the beginning. In a process called the Reverse Path Setup, each node, which makes this package will keep tabs of the node address that sends the packet. The nodes keep this info for some time enough for the RREQ to travel across the network and generate a reply to the sender, in which time is dependent upon the network size[19]. If an intermediate node contains a route entry for a desired particular destination in its routing table, the destination sequence number is compared with that in the RREQ. In the circumstance where the destination sequence number is less than that in the RREQ, the RREQ broadcast back to its neighbors. Otherwise, a route reply packet is unicast to its neighbor from which it has taken in the RREQ if the same request is not processed properly in the previous function. This is identifiable using the broadcast-id and source-addr.

Once the route reply (RREP) is produced, it goes back to the beginning using the reverse path in which it is set, until it travels to this node. As the RREP returns to the source, each node sets a forward pointer along this route to the node from where it gets the RREP and records the newest destination sequence number to the request address.

This is called the Forward Path Setup. If an intermediate node gets another RREP after propagating the first RREP towards its source, then the destination sequence number of new RREP is checked. The routing information is updated by an intermediate node and only new RREP is propagated.

– If the Destination sequence number is larger, OR – If the new sequence number is similar and hop count is small, OR Otherwise, it just misses the new RREP.

This ensures that the algorithm is loop-free, and only the most successful route is used. Figure 4 is an example which shows how the route to the destination is found by the AODV routing protocol[20,21]. The process steps are as shown below: Source ’S’ has to send data to the destination. S sends a RREQ to its neighbors A, B, C. B seeks for the path in its routing table (with destseq-number s1 and hop count c1) and sends RREP

to S. C establishes the reverse path. C forwards RREQ to its neighbors D and E. E establishes the reverse path. E forwards RREQ to its neighbors F and G. E eases the reverse path after a time-out period as it does not get any RREPs From F and G. D searches for the path (with dest seq-number s2 which is greater than s1 and hop count c1) in its

routing table and sends RREP to C. C receives the RREP from D and establishes the forward path and forwards RREP to S. A sets the reverse path; forwards RREQ to its neighbors; ir receives the RREP (with the path of hop

count c2 which is greater than c1); sets the forward path; and forwards this RREP to S. S receives path info from C (with dest seq-number s2 and hop count c1), another path info from B

(with dest seq-number s1 and hop count c1), and another path info from A (with dest seq-number x which is not more than s1 and s2 and hop count c2 which is not more than c1).

S chooses the track info from C (which originated from D), giving the first priority to the path with the greatest destination sequence number and then the second priority is given to the path with the


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lowest hop count. Though a path given by A is of the smallest hop count, it is dismissed because the destination sequence number is larger than the path from C. The active neighbors for this route expiration time for the route table entry the other useful information

contained in the entries along with the source and destination sequence numbers is called the soft-state information that is related to the route entry. The info about the active neighbors for this route is maintained so that all active source nodes are informed when a link along with a path to the destination experiences a break. The objective of the route request time expiration timer is to purge the reverse path routing entries from all the nodes that do not rest on the active route.

Figure 4. Route discovery process in AODV Routing Protocol

2.4. Comparison between AODV and DSR

All the routing information about the path that is to be taken from the source to the destination in DSR is included in the header of the request, whereas in AODV, each node maintains a routing table that contains routing information to all the nodes in the network. If any link failure occurs on the network, DSR sends a unicast packet to the source giving the information about the broken link whereas AODV broadcast the route error message to all its neighbors as it is possible that the reverse path from the problematic node as the source has timed out. Stale caches, i.e. caches with information that are outdated or broken, can cause problems in routing. In DSR, this problem is solved by stopping the response from the intermediate host if the reply packet causes a loop formation [24].

3. Network Simulation

There is different performance metrics for DSR and AODV protocol. We represented three scenarios with 30, 50 and 80 nodes.

Number of hops per route: these statistics show the numbers of hop in each route from source to destination and in the router cache for all the nodes in the ad-hoc network[17].


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Router discovery time: the time of discovering a route to a specific destination at the time when a route demand has sent out to discover a route to that destination until the route response is received with a route to this destination. In this statistic, the time to discover the path to a specific destination on all the nodes in the network will be represented. Average End-to-end delay of data packets: it refers to all the time, which is taken by packet to transmit across the network from source to the destination node which includes all delay caused through route discovery latency, retransmission of delays at MAC, transfer time and propagation. If the protocol shows higher end-to-end delay that means the performance of this protocol is unsuitable due to the network congestion[8]. Throughput: it shows the number of bits (bits/sec) forward and receives between nodes in an ad-hoc network. The throughput has referred as the ratio of the total amount data which are received from a sender to a time takes for the receiver to make a final packet[22].The routing overhead represents the total number of routing packet transmission during the simulation whereas each transmission of the packet means each hop is counted as one transmission. To implement simulation, wireless area network (WLAN) which consists of simple network entities as nodes (mobile) and base station was set up. The simulation consists of three scenarios. The first scenario involves 30 node workstation. The following scenario involves 50 node workstation, and the third scenario contains 80 node workstation. The parameter for all the scenario, including number of hops per route, route discovery, average delay and throughput for both routing protocol are used. The behavior of these protocols in all the scenarios were analysed in terms of network performance, and comparison with another protocol was made. This protocol was evaluated in order to determine which works best under circumstances required. All the network nodes are modeled on area 1000*1000 under high network load. The Entity of the base station of this network communicates with nodes on the network.

Table 1. The Simulation Parameters

Parameters

Examiner Protocol AODV, DSR

Simulation Time 15 mount

Simulation Area Campus 500M ×500M

Node in all scenarios 30,50 and 80

Application configuration Video conference Email for all nodes

Performance metric Number of hop per route, Route discovery, delay average and throughput

Type of node Mobile

Packet size 512 bytes

PPP server Configuration with all nodes in scenario

IP cloud ip32_cloud

MANET Gateway wlan_ethernet_slip4 Operate on IEEE802.11b standard


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4. Analysis and Result

4.1. Scenario 1

Number of hop per route

Figure 5 shows the AODV Routing protocol produces a steady one hop per route. However, DSR fluctuates between 1 and 1.7. This is due to the method of AODV offering one main route to the destination and DSR offering multiple routes.

Figure 5. Number of hops per route for AODV and DSR routing protocol

Router discovery time

Figure 6 show the comparison of AODV with DSR protocol, the route discovery time is minimal and

varies for DSR protocol. However it shows that AODV is a faster protocol at finding the route due to using one route instead of multiple.

Figure 6. Route discovery time AODV and DSR Routing protocol.

Throughput:

From Figure 7, AODV seems to have a peak throughput at the beginning.


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Figure 7. Throughput for AODV and DSR Routing protocol.

4.2. Scenario 2

In scenario 2, the number of nodes are increased to 50 nodes.

Number of hop per route. The AODV has a minimum number of hops, but DSR has a higher number of hops, as shown in

Figure 8.

Figure 8. Number of hops per route for AODV and DSR Routing protocol.

Router discovery time(50 node) :

When the network increases, the AODV has less route discovery time than DSR, as shown in Figure 9.

\ Figure 9. Route discovery time, AODV and DSR Routing protocol


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Average of delay: The delay has increased both in DSR and AODV. However, in AODV, the delay seems to

increase more when the node increases, as shown in Figure 10.

Figure 10. Average of delay for AODV and DSR Routing protocol.

Throughput:

The throughput for AODV is much more than DSR. When the node increases, the throughput

will increase as well, as shown in the Figure11.

Figure 11. throughput for AODV and DSR Routing protocol.

4.3. Scenario 3 In scenario 2, the number of nodes are increased to 80 nodes.

Number hope per route:

The AODV has a minimum number of but DSR has a higher number, as seen in Figure 12.


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Figure 12. Number of hops per route for AODV and DSR Routing protocol.

Router discovery time:

The route discovery time for AODV is less than DSR when the number of node has increased, as shown in Figure13.

Figure 13. Route discovery time AODV and DSRRouting protocol.

Average of delay:

When the number of nodes increases, the delay will increase as well. However, in AODV, the delay is more than the DSR, as shown in Figure 14.

Figure 14. Average of delay for AODV and DSR Routing protocol.

Throughput:

The throughput in AODV is much more than DSR. Figure 15 shows that when the node increase, the throughput will increase too.


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Figure 15. Throughput for AODV and DSR.

5. Conclusions

This paper presented an evolution and comparison of the two protocol DSR and AODV for routing Ad hoc using performance metric evaluation such as the number of hop per route, route discovery time, average delay and throughput. AODV and DSR simulation was carried out for three different scenarios 30, 50 and 80 in the mobile node workstation. In each scenario, all the nodes use source nodes for sending data to the common base station. The results were analysis and evaluated.

In general, DSR seems much better suited for smaller load networks as it does not need to flood the network with table update requests in the table driven protocols such as AODV. When the number of node increases, AODV can handle the increase in nodes arriving and leaving, with its structured table approach as long as the overall bandwidth can cope with the other head of table sharing. DSR has to store the whole route in the header, so when a network increases in nodes, this extra overhead goes up exponentially.

To conclude, for both AODV and DSR protocol have advantages and disadvantages. DSR protocol is expected to perform better in the case of low mobility with a low number of source, and AODV would be suffering from high routing overhead and high normalized routing load. However, if the number of nodes is increased and the speed is high, AODV is expected to give a better performance and more successful in maintaining the table topology comparable to DSR.

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