Performance of Routing Protocols in Mobile Ad hoc

Networks (MANETs)

Minh Hoang Nguyen

College of Technology, Vietnam National University

Department of Telecommunications & Engineering

Mentor: Dr. Hoang Nam Nguyen

MANET MANET is the short form of Mobile Ad hoc Network.

Ad hoc is a Latin phrase meaning "for this".

It is completely similar to Ad hoc Network except for its nodes are mobile devices connected by wireless.

MANETs are a kind of Wireless Ad hoc Network that usually has a routable networking environment on top of a Link Layer Ad hoc Network.

I. Routing Protocols in MANETs Like other kind of networks, MANETs also use protocols for routing. Routing

Protocols in MANET are classified into 3 types: Proactive, Reactive, and Hybrid between Proactive and Reactive.

Reactive establishes paths base on each connectivity’s demands. It could save bandwidth and optimize the routes, but this method might cause a big delay because it has to spend time processing and figuring out the shortest path to send packets. This type is suitable for massive network. Examples of Reactive are TORA (Temporally-Ordered Routing Algorithm), AODV (Ad hoc On-Demand Distance Vector Routing), and DSR (Dynamic Source Routing).

Proactive uses Floating to send info to all nodes, this method’s con is saving time of sending packets and increasing throughput in small and medium network due to all routes and parameters are ready for connectivity. However, bandwidth could be occupied and lead to the deduction of performance as network size grows bigger. DSDV (Dynamic Destination-Sequenced Distance-Vector Routing) and OLSR (Optimized Link State Routing) are typical examples of Proactive.

1. Ad hoc On-Demand Distance Vector Routing (AODV)

AODV is a Reactive Protocol.

AODV is jointly developed in NOKIA Research Center, University of California, Santa Barbara and University of Cincinnati by C. Perkins, E. Belding-Royer and S. Das.

AODV uses Route Requests (RREQs), Route Errors (RERRs), and Route Replies (RREPs) messages to discover and maintain routes across the network from source to destination. AODV could figure out the optimized routes.

AODV is table-driven, routing information in the network is stored in Routing Tables.

How AODV works:

Assume Node 1 needs to send a data packet to Node 7 and Node 6 knows a route to Node 7.

Node 1 broadcasts RREQs to its neighbors.

Node 2 and 4 verify new RREQs and realize that they are not the destination and they also do not know the route to Node 7, so Node 2 and 4 forward the RREQs. Forwarded RREQ from Node 4 to Node 3 is eliminated because Node 3 has received a similar RREQ from Node 2 before.

When RREQ from Node 4 reaches Node 6, which has known a route to Node 7, Node 6 will send a RREP message to Node 1 through Node 4 to confirm the route has been established. Node 3 and Node 5 also forward RREQs, but the receivers detect the packets as duplicates and take them down.

2. Optimized Link State Routing (OLSR) OLSR is a Proactive Protocol.

OLSR makes use of HELLO messages to find its one hop neighbors and its two hop neighbors through their responses. The sender can then select its Multipoint Relays (MPR) based on the one hop node that offers the best routes to the two hop nodes.

Node 4 broadcasts HELLO messages to its neighbors, then listens to their

feedbacks to determine its own MPR.

Each node has also an MPR Selector set (MS), which enumerates nodes that have selected it as an MPR node. OLSR uses Topology Control (TC) messages and MSs to generate link-state information to route to any node in the network.

Like AODV, OLSR is table-driven as well.

How OLSR works:

Node 3 sends a TC message to nodes in MS(3) = {2, 4, 5}.

Since Node 3 is in MS(4) = {1, 3, 5,6}, Node 4 will forward Node 3’s TC(3) message

to the rest of MS(4).

Node 6 also forwards TC(3) message from Node 4 since Node 4 is in MS(6) = {4, 5, 7}.

Node 4 sends a TC message to nodes in MS(4) = {1, 3, 5, 6}.Node 3 and Node 6 forward TC(4) message since Node 4 is in both MS(3) and MS(6).

Node 6 sends a TC message to nodes in MS(6) = {4, 5, 7}.

Node 4 forwards TC(6) from Node 6 and Node 3 forwards TC(6) from Node 4.

After Nodes 3, 4, and 6 have generated TC messages, all nodes have link-state

information to route to any node.

Given TC information, each node forms a topology table. A routing table is calculated from the topology table.

II. Simulation In this mini-project, I will design and present the following parameters of the

system, using AODV and OLSR:

Delay is the average time that packets take to traverse the network. This is the time

from the generation of the packet by the sender up to their reception at the

destination’s application layer.

Throughput is the average rate of successful packet delivery over a communication

channel (throughput’s dimension is bits per second or bps).

The software used in this project is OPNET IT Guru (for educational purpose only), designed and distributed by OPNET Technologies, Inc.

Objective: I simulated a MANET in a 1000m x 1000m Campus environment with a certain number of nodes moving with the same fixed speed of 10m/s. I changed the number of nodes (load) to observe and compare the differences of given parameters of AODV and OLSR. From that, I evaluated the performances of these two protocols in three following situations:

Situation 1: Light load, 5 nodes moving at the speed of 10m/s.

Situation 2: Medium load, 20 nodes moving at the speed of 10m/s.

Situation 3: Heavy load, 50 nodes moving at the speed of 10m/s.

1. Delay Blue: AODV

Green: OLSR

5 Nodes 20 Nodes 50 Nodes

Result Analysis:

In light load, AODV’s delay is quite bigger than OLSR. While in medium load and heavy load, AODV’s delay is quite equal.

AODV could find out the most optimized routes for traffic, while OLSR could not. However, in light load, distances between nodes are pretty small, so packets take almost the same time to come to the receiver in both protocols. In OLSR with available routes map, packets could be sent immediately, while in AODV, it takes time to figure out the routes. This causes a big delay in AODV.

As the number of nodes increases, distances between nodes are bigger and bigger and become an important factor. AODV with the ability to optimize the routes could provide the shortest routes to the final destination, while in OLSR, although it does not need to spend time finding routes, packets could have to go long paths to reach the destination. All of these narrow down the gap between the delays of two protocols.

2. ThroughputBlue: AODV

Red: OLSR

5 Nodes 20 Nodes 50 Nodes

Result Analysis:

As can be seen, OLSR’s throughput by far outperformed AODV in light load. But in medium load, AODV’s throughput starts improving and when it reaches the stable state, it is nearly equal to OLSR and sometimes better.

We have known that in OLSR, routes have been established and are available for traffic, as a result, this leads to the low delay in OLSR. Therefore, the rate of received packets is high and stable from start to end.

Vice versa, in light load, AODV’s delay is super high, and the distances is also not too important in traffic, AODV’s performance is quite low. However, in medium load, distances become much more significant, AODV’s throughput starts to increase and approach OLSR since AODV could provide the most optimized routes for traffic. At some times, AODV’s throughput even exceeds OLSR.

As the size of network grows bigger, the routing tables in OLSR may be too large and it could not avoid congestion and other problems in wireless networks. While AODV with the ability of optimizing routes still works efficiently.

3. Summary

In light load, OLSR’s performance is much better than AODV.

When the number of nodes increase to medium load, AODV’s performance improves and quite equals to OLSR.

As the network grows to heavy load, OLSR’s weak points are performed, while AODV’s strong points works. This leads to the outperformance of AODV.

Overall, we could apply OLSR into small and medium network. If we want to build a massive network, we should use AODV instead.

References

Bained Nyirenda & Jason Mwanza, “Performance Evaluation of Routing Protocols in Mobile Ad hoc Networks (MANETs)” Thesis, Blekinge Institute of Technology, 2009.

Jun Takei, "Mobile Networks: IP Routing and MANET Routing Algorithms“ Lecture, WIDE Project School of Internet, 2007.

Tu Van Pham, “Survey: Impact of Moving Nodes to the Performance of Routing Protocols in MANETs” Thesis, College of Technology, Vietnam National University, 2010.

Hoang Nam Nguyen, “Networks Modelling and Simulation” Lecture, College of Technology, Vietnam National University, 2013.

Wikipedia, “Ad hoc On-Demand Distance Vector Routing”, http://en.wikipedia.org/wiki/Ad_hoc_On-Demand_Distance_Vector_Routing.

Wikipedia, “Optimized Link State Routing”, http://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol.

Wikipedia, “Mobile Ad hoc Network”, http://en.wikipedia.org/wiki/Mobile_ad_hoc_network.