Today’s article is about EXPERIMENTAL ANALYSIS OF PROACTIVE AND REACTIVE AD HOC ROUTING PROTOCOLS USING NETWORK SIMULATOR.
EXPERIMENTAL ANALYSIS OF PROACTIVE AND REACTIVE AD HOC ROUTING PROTOCOLS USING NETWORK SIMULATOR
A Mobile Ad hoc Network (MANET) is a collection of wireless mobile nodes forming a temporary network without using any existing infrastructure or any admin- istrative support. Since not many mobile ad hoc net- works are currently deployed, research in this area is mostly simulation based. The main objective of this pa- per is to compare the performance of proactive Desti- nation Sequence Distance Vector (DSDV) and reactive Ad hoc on Demand Distance Vector (AODV) routing bandwidth, and CPU time. protocols using ns-2 Network Simulator.
There are four important performance metrics like delivery ratio, av- erage end-to-end delay, overhead and average hop count are evaluated with varying mobility for perform- ance analysis of Ad hoc routing protocols. Our results show that the performance of MANETs protocols varies with the mobility model used.
I. INTRODUCTION
The 1990s have seen a rapid growth of research inter- ests in mobile Ad hoc networking. The lack of infra- structure and the dynamic nature of these networks de- mands new set of networking strategies to be imple- mented in order to provide efficient end-to-end commu- nication.
The wireless Ad hoc networks are self- creating, self-organizing and self-administrating. The nodes in an Ad hoc network can be a laptop, PDA or any other device capable of communicating with those nodes located within its transmission range. The nodes can function as routers, which discover and maintain routes to other nodes. The Ad hoc network may be used in emergency search-and-rescue operations, battlefield operations and data acquisition in inhospitable terrain.
In Ad hoc networks, dynamic routing protocol must be needed to keep the record of high degree of node mobility, which often changes the network topol- ogy dynamically and unpredictably. Three are several constraints related to design effective routing protocols of Ad hoc networks, they are as follows:
- In MANET (Mobile Ad hoc Network) the rate of topological change is very high compared to the wired networks.
- The lack of fixed base station in Ad hoc network means there is no dedicate agency for managing the resources for the network nodes.
- Links may be unidirectional: a node i can receive signal from nodej, but contrary may not true. As a consequence, a transmission that requires a hand- shake between i and j fails. Several technological limitations on the use of re- sources exist, namely battery power, transmission bandwidth, and CPU time
- Security is challenging in the MANET environ- ment. In the absence of any authentication mecha- nism, due to the nature of radio transmissions, a malicious node can easily corrupt route tables, caches and other similar information, for example advertising false route information.
This paper provides a realistic and quantitative performance analysis of proactive DSDV and reactive AODV routing protocols of Ad hoc network consists of 20 and 50 nodes. The performance metrics of these pro- tocols are evaluated by varying pause time using ns-2 simulator.
The paper is organized as follows: Section 1 de- scribes about the overview of Ad hoc networks, Section 2 elaborately highlights the proactive and reactive rout- ing protocols of Ad hoc networks. We introduce simu- lation model and simulation parameters in Section 3. Section 4 presents the experimental results based on the performance metrics and gives the interpretation of the results obtained. Finally, Section 5 concludes the paper and Section 6 suggests about the future work
A. Related Works
To find an optimal routing algorithm of Ad hoc networks many researches have been performed on different routing protocols. Many of the researcher studies the most common protocols like DSDV, DSR, AODV and TORA.
There are a number of papers that compares the protocols in varying the parameters and metrics that affect the behavior and various issues of routing. These are performed by varying network load parameters, network size metrics, mobility and pause time. We have conducted our simulation study in similar fashion: particularly by varying the number of nodes (20 and 50) and pause time (within range 0 to 500).
II. ROUTING PROTOCOLS OF ADHOC NETWORKS
The protocols of Ad hoc network may generally be categorized into two types:
Table-driven/Proactive:
DSDV(Destination Sequence Distance Vector),WRP(Wireless Routing Protocol), CSGR(Cluster Switch Gate- way Routing)
Source-initiated (demand-driven)/Reactive:
AODV (Ad hoc on Demand Distance Vector), DSR (Dynamic Source Routing), TORA (Tem- porally Ordered Routing Algorithm).
As our paper emphasized on DSDV and AODV proto- cols, the whole paper solely concentrate about these two popular Adhoc routing protocols.
A. Destination Sequence Distance Vector
The Destination-Sequenced Distance-Vector (DSDV) routing algorithm is based on the idea of the classi- cal Bellman-Ford routing algorithm with certain im- provements. Every mobile station maintains a routing table that lists all available destinations, the number of hops to reach the destination and the sequence number as- signed by the destination node. The sequence number is used to distinguish stale routes from new ones and thus avoid the formation of loops.
The stations periodically transmit their routing tables to their immediate neighbors. A station also transmits its routing table if a significant change has occurred in its table from the last update sent. So, the update is both time-driven and event-driven.
The routing table updates can be sent in two ways: – a “full dump” or an “incremental update”. A full dump sends the full routing table to the neighbors and could span many packets whereas in an incremental update only those entries from the routing table are sent that has a metric change since the last update and it must fit in a packet. If there is space in the incremental update packet then those entries may be included whose sequence number has changed.
When the network is relatively stable, incremental updates are sent to avoid extra traffic and full dump are relatively infrequent. In a fast-changing network, incremental packets can grow big so full dumps will be more frequent.
B. Ad Hoc On-Demand Distance Vector (AODV) Routing Protocol
The AODV routing protocol supports multi-hop routing among mobile nodes for establishing and main- taining an Ad hoc network. Unlike DSR , which uses source routing, AODV uses hop-by-hop routing. AODV is based on the Destination Sequence Distance Vector (DSDV) routing protocol. The main difference is that AODV is reactive, while DSDV is proactive. AODV requests a route only when it is needed, but it does not require mobile nodes to maintain routes to the destination that are not actively used.
AODV retains the desirable feature of DSR that routes are maintained only between nodes that need to communicate. When node S wants to send a packet to node D shown in figure 1(a), it checks its route table to determine whether it has a route to D. If S has route to D, S forwards the packet to the next-hop node toward D. If S does not have a route to D, S initiates route discovery. Source node S floods a Route Request (RREQ) message, which contains source address, destination address, sequence number, and broadcast ID.
After sending the RREQ message, S sets a timer to wait for a reply. When a node receives a RREQ message, it checks whether it has already seen the RREQ message by noting the source ad- dress/broadcast ID pair. If so, it discards the message. Otherwise, it sets up a reverse path pointing towards the source.
A node can send a Route Reply (RREP) mes- sage provided that it has an unexpired entry for the des- tination in its route table, and it knows a more recent path than the one previously known to sender S. To determine whether the path known to an intermediate node is more recent, a destination sequence number is used.
A new RREQ message by a node is assigned a higher destination sequence number. If the node cannot send a RREP message, it increments the RREQ’s hop count and then broadcasts the RREQ message to its neighbors. When the intended destination receives a RREQ message, it replies by sending a RREP message.
When an intermediate node receives the RREP mes- sage, it sets up a forward path entry to the destination in its route table. The RREP travels along the reverse path set up when the RREQ message was forwarded. Source node S can begin data packet transmissions as soon as the first RREP is received and later update its routing info if it discovers a better route.
Figure 1 shows an example of a route discovery by the AODV routing protocol. As shown in Figure 1(a), a RREQ message from node S is flooded thorough the network until it reaches node D. On its way through the network, the RREQ initiates the creation of temporary route table entries for the reverse path at all the nods it passes, as shown in Figure 1(b).
Next, a RREP message from node D is transmitted back to node S along the temporary reverse path, as shown in Figure 1(c). When the RREP message is routed back along the reverse path, all nodes on this route set up a forward path by pointing to the node that transmitted the RREP message.
A route selected by the route discovery proce- dure is maintained as follows. If a route is broken due to the movement of the source, the source initiates route discovery to find a new route to the destination. If a route is broken due to the movement of either the desti- nation or an intermediate node on the route, the node upstream of the break transmits a Route Error (RERR) message to the source node. When the source node re- ceives the RERR message, it can reinitiate a route dis- covery if a route is still needed.
Neighborhood information is obtained from hello message periodically transmitted by neighboring nodes. Each time a node receives a hello message from a given neighbor, it updates the info associated with the neighbor in its route table. Hello message can be used to maintain the local connectivity of a node. When a mobile node uses its shared link layer pro- tocol such as IEEE 802.11, instead of using hello message, the node.
III. SIMULATION MODEL
In this evaluation, simulation model based on ns-2 is used. Ns-2 is a discrete event simulator developed by the University of California at Berkeley and the VINT project .Ns-2 simulator is based on two languages: an object oriented simulator, written in C++, and a OTcl(an Object Oriented Extension of Tool command language).
It has a rich library of network and protocols object. There are two class hierarchies in ns: the com- plied C++ hierarchy and the interpreted OTcl one, with one to one correspondence between them. The details installation process of ns-2 in describe in this web- site . In this paper, we have simulated to analysis the per- formance of DSDV and AODV protocols. Simulation environment consists of following parameter:
For the simulation we have used the ns-2.28 that can run under the Fedora Core-2 environment. NAM is the basic visualization tool used for ns-2 simulations.
A. PERFORMANCE METRICS FOR SIMULATION
There are four important performance metrics are evaluated for performance analysis of Ad hoc routing protocols:
- Packet delivery ratio: The delivery ratio refers to the ratio between the numbers of application data received at the destination and the applica- tion data sent from the source. The calculation of the packet delivery ratio uses the ratio of the total number of CBR (Constant Bit Rate) packets re- ceived in the network to the total number of CBR packets sent during the simulation.
- Average end-to-end delay: This is measured as the time delay between the application packets sent at the source node to the destination node. This in- cludes all possible delays caused by buffering dur- ing route discovery latency, queuing at the interface queue, retransmission delays at the MAC, and propagation and transfer times.
Once the time difference between every CBR packet sent and received was recorded, dividing the total time difference over the total number of CBR packets re- ceived gave the average end-to-end delay for the re- ceived packets.
- Routing Overhead: Routing overhead indicates the total number of routing packets transmitted dur-ing the simulation. As a ratio of the number of rout- ing packets (total number of control packets) re- quired to route a CBR generated data packet.
Where P is the number of control packets generated to route the data packets, P, is the number of data pack- ets received at the destination and t is the simulation time.
- Average Hop Count: It refers total number of hops are needed by a packet to reach the destina- tion.
Where h; the number of hops the i packet takes to reach the destination and t is the simulation time.
B. GENERATING TRAFFIC AND MOBILITY MODELS
Traffic models: Random traffic connections of TCP and CBR can be setup between mobile nodes using a traffic-scenario generator script. This traffic generator script is available under ~ns/indep-utils/cmu-scen-gen that folder will be created after successful installation of ns-2 and is called cbrgen.tel. It can be used to create CBR and TCP traffics connections between wireless mobile nodes. So the command line looks like the fol- lowing:
ns cbrgen.tcl [-type cbr tcp] [-nn nodes]
[-seed seed] [-mc connections][-rate rate]
For the simulations carried out, traffic models were generated for 20 and 50 nodes with cbr traffic sources, with maximum connections of 12 at a rate of 4kbps.
- Mobility models: The node-movement generator is available under ~ns/indep-utils/cmu-scen-gen/setdest directory and consists of setdest(.cc,.h},setdest.exe and Makefile. The command would look like:
/setdest [-n num_of_nodes] [-p pausetime] [-s max- speed] [-t simtime] [-x maxx] [-y maxy]
C. SIMULATION CODE
For the simulation, Tel code is used to set up the wire- less simulation components like network components types, parameters like antenna type, radio-propagation model, type of Ad-hoc routing protocol, traffic models and node movement models used by mobile nodes etc. The complete documented simulation code is available
in the ns-2 simulator official site .
D. PARSING THE SIMULATION TRACE FILES
After each simulation, trace files recording the traffic and node movements. These files need to be parsed in order to extract the information needed to measure the following.
82.213406765_1_ AGT 1983 cbr 512 [a2
1 2 800][0:0 1:0 32 1] [350]
From the format, it is observed that a packet was sent (s) at time (t) 82.213406765 sec, from source node 1 with trace level AGT (Agent Level Trace) and type cbr. Here packet id is 1983 and packet size is 512 bytes and MAC-id of the sending node and receiving nodes is 1 and 2 respectively.
IV. SIMULATION RESULT
In this section, we will present the results of the simula- tion to analysis the performance of the DSDV and AODV Ad hoc routing protocols.
A. Delivery Ratio
From the simulation result shown in figure 2, it is ob- served that in AODV average delivery ratio does not depend on pause time or number of nodes. The value is almost constant and very close to 1.But in DSDV; at low pause (higher mobility) delivery ratio is low and dramatically increases with higher pause time (low mo- bility). Considering the metric of delivery ratio, AODV performs better than DSDV. Because the optimal value of delivery ratio is 1 which means no packet loss for AODV.
B. End-to-End Delay
From the simulation result shown in figure 3, it is ap- parent that since DSDV is a proactive routing protocol, in most of the cases it uses already established routes, so delay is low in comparison with AODV. AODV re- quires complete route at the source itself before trans- ferring the packet and since it is reactive routing proto- col significant delay is introduced before transferring the packet. As, the low end-to-end is desirable, DSDV performs better than AODV in this case.
C. Overhead
From the simulation result shown in figure 4, it is ob- served that in both cases (no. of mobile nodes 20 and 50) the overhead of AODV is higher than DSDV but decreases drastically when pause time increases. In DSDV the overhead increases with the pause time and maintains approximate constant ratio that is higher than AODV for higher pause time.
D. Average Hop Count
From the simulation result in figure 5, it is observed that the average hop count for AODV increases with num- ber of mobile nodes. Optimal value 1 indicates efficient algorithm with no overhead packets. For AODV it is away from optimal value 1. Averages hop count for DSDV is lower than AODV and very close to optimal value.
V. CONCLUSION
Ad hoc network is an open ended research subject for many researches all over the world. Many problems regarding Ad hoc network needs to solve. We have pre- sented a detailed simulation studies to compare AODV and DSDV routing protocol using a varying workload such as mobility, load and size of the Ad hoc network. From our experiments, it is found that delivery ratio forAODV routing protocol exhibits a constant value and very close to optimal value regardless of the mobility change.
But the delivery ratio of DSDV is very low compare to AODV when mobility is high. But it in- creases its delivery ratio as we increase the pause time. Both protocol exhibits a very short end-to-end delay, but if we compare them, AODV shows slightly higher delay than DSDV. Our result also indicates that AODV exhibits very high overhead compare to DSDV with high mobility. But when we increase the pause time (low mobility) AODV shows very low overhead com- pare to DSDV.
So it can be concluded that when low delay is desir- able rather that all other matters then DSDV perform well. In all the other cases AODV is better than DSDV and could be a good candidate for Ad hoc networks.
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