1. Introduction
A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. The network allows computers to communicate with each other and share resources and information.
Categories of network and their comparative study
1) Wired network
Wired networks are the best way to connect the desktop computer to the Internet and to other computers at home. While wireless networks offer flexibility for portable computers, wired networks offer unbeatable performance, reliability, and security. If we have a single computer, connecting to the Internet is as simple as plugging a network cable into computer and modem. If we have more than one computer, we need to connect a router between modem and computers. If one (or more) computers is in a different room from router, can use a network extender to connect the computer [1].
Figure 1 Wired Network
(2)Wireless network
Wireless network refers to any type of computer network that is wireless, and is commonly associated with a telecommunications network whose interconnections between nodes is implemented without the use of wires. Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or "layer" of the network.
Wireless networks have had a significant impact on the world as far back as World War II. Through the use of wireless networks, information could be sent overseas or behind enemy lines easily, efficiently and more reliably. Since then, wireless networks have continued to develop and their uses have grown significantly. Cellular phones are part of huge wireless network systems. People use these phones daily to communicate with one another. Sending information overseas is possible through wireless network systems using satellites and other signals to communicate across the world. Emergency services such as the police department utilize wireless networks to communicate important information quickly. People and businesses use wireless networks to send and share data quickly whether it be in a small office building or across the world [2].
Compatibility issues also arise when dealing with wireless networks. Different components not made by the same company may not work together, or might require extra work to fix these issues. Wireless networks are typically slower than those that are directly connected through an Ethernet cable.
Table 1 Comparison between wire and wireless networks
|
|
Wired |
Wireless |
|
Installation |
moderate difficulty |
easier, but beware interference |
|
Cost |
Less |
more |
|
Reliability |
High |
reasonably high |
|
Performance |
very good |
good |
|
Security |
reasonably good |
reasonably good |
|
Mobility |
Limited |
outstanding |
2. Introduction of MAC
Medium Access Control (MAC) protocol is a form of communications protocol used to regulate the way nodes in communication networks communicate with each other through a shared medium. It corresponds with data link layer (layer 2) of the ISO Open System Interconnect (OSI) reference model. Many MAC protocols have been developed for communication networks, for example Ethernet IEEE 802.3 for wired LANs.
MAC is responsible for controlling access to the channel amongst various entities. Its role is important in networks where multiple users can transmit at the same time over the same channel (Ethernet segment, same radio channel etc.), such as IEEE 802.11, Bluetooth, etc. Various MAC protocols have been defined in literature that employs different techniques to regulate access. They can be grouped into two categories: distributed and centralized. In the former, each node decides on its own when is the best time for it to transmit such that it is the only one which transmits to avoid collision. These are also referred to as random access protocols. If multiple nodes transmit, then these protocols provide mechanisms to resolve the collision. In the centralized version, a node is responsible for deciding who can access the channel, and the duration for which that node has control over the channel. The centralized node is generally referred to as a base station (BS). There are two ways to provide access to other nodes. One is in a round-robin fashion. Here the BS would poll every node periodically to find if it has data to transmit or not. The other can be a Request-Grant mechanism wherein the nodes contend to send channel access requests to the base station. The BS then allocates a time slot for every node from which it would have received the request.
Today, Wireless sensor networking is used in environment monitoring, defense, smart spaces, scientific application, medical systems and robotic exploration, target tracking, intrusion detection, wildlife habitat monitoring, climate control and disaster management etc. Wireless sensor network (WSN) consist of one or more battery-operated sensor devices with embedded processor, small memory and low power radio. Coverage and communication range for sensor nodes compared to other mobile devices is limited due to low power capacities of sensor nodes. Sensor networks are composed of large number of nodes to cover the target area. Nodes in wireless sensor network communicate with each other to give a common task [3].
2.1 The Position of Mac in OSI reference model
The Open Systems Interconnection (OSI) reference model was developed by the International Organization for Standardization (ISO) aiming to standardize the protocols used in various network layers.
Figure 2: IEEE 802.11 standards mapped to the OSI reference model and a standard Linux Router implementation.
IEEE 802.11[12] is a family of specifications for Wireless Local Area Networks (WLANs). Like all IEEE 802.11 standards, the 802.11 works on the two lower levels of the OSI model. Although wireless networks are not restricted to any special hardware, nodes in such networks are likely to operate according to the IEEE 802.11.
Figure 2 shows the IEEE 802.11 standards mapped to the OSI reference model. The figure Also shows how the implementation of a typical Linux router corresponds to these models. In wireless networks, nodes typically use radio frequency channels as their physical medium. This corresponds to the lowest layer in the OSI model. Since the nodes need not be physically connected, the network offers data connectivity along with user mobility.
The IEEE 802.11 MAC layer corresponds to the data link layer in the OSI model. The main
Objective of the OSI data link layer is to provide error free transmission of data across a physical link. IEEE 802.11 protocols’ version of this scheme consists of two sub-layers: Logical Link Control (LLC) and Medium Access Control (MAC). The (possibly) most important services that the LLC offers is error- and flow control. The MAC directly interfaces with the physical layer, and provides services such as addressing, framing, and medium access control.
2.2 Architecture of MAC
The MAC Layer Architecture (MLA) provides a component-based architecture for MAC protocols in wireless sensor networks. MLA extends the Unified Power Management Architecture to provide the hardware-independent interfaces required by timing sensitive MAC protocols, and defines platform-independent reusable components that implement MAC layer logic on top of them. The MLA architecture can be used to develop a large number of platform-independent MAC implementations, with little or no further effort required to adapt these implementations to new hardware platforms.
Figure.3 Architecture Of IEEE802.11
3. Routing Protocols for Mobile Ad Hoc Networks
A directional routing approach [4] for multihop ad-hoc networks, is presented which has been applied to two on-demand routing protocols: namely dynamic source routing (DSR) and ad-hoc on-demand distance vector routing (AODV). Both DSR-based and AODV-based directional routing protocols are designed to balance the tradeoff between co-channel interferences from nodes hops away and the total power consumed by all the nodes. In order to select the best route, three metrics are considered in the route discovery process. They consist of hop count, power budget and overlaps between adjacent beams. By exploiting the direction of directional antennas, both routing protocols are capable of reducing overlaps between beams of the nodes along the route, thus eliminating interference. Arbitrary networks and random networks are considered in the simulations. The results show considerable performance gains for transmission of real-time traffic over ad hoc networks [5].
3.1 Classification of MANETs Routing Protocol
The routing protocols proposed for MANETs are generally categorized as table driven and on-demand driven based on the timing of when the routes are updated. With table-driven routing protocols, each node attempts to maintain consistent, up-to date routing information to every other node in the network. Many routing protocols including Destination-Sequenced Distance Vector (DSDV) and Fisheye State Routing (FSR) protocol belong to this category, and they differ in the number of routing tables manipulated and the methods used to exchange and maintain routing tables. With on demand driven routing, routes are discovered only when a source node desires them. Route discovery and route maintenance are two main procedures: The route discovery process involves sending route-request packets from a source to its neighbor nodes, which then forward the request to their neighbors, and so on. In contrast to table-driven routing protocols, not all up-to-date routes are maintained at every node. Dynamic Source Routing (DSR) and Ad-Hoc On- Demand Distance Vector (AODV) are examples of on-demand driven protocols.
1) Table-Driven routing protocols (Proactive)
In this protocols work similar as wired network. It can maintain the routing table. It is also use periodic message and extra network overhead. It has some basic characteristics
1. Keep routing information current at all times.
2. Good for static network.
3. Examples: DSDV (Destination Sequence Distance vector Routing protocols) LS (Link State) Algorithm etc.
In distance-vector routing, each router maintains a table containing the distance from itself to all possible destinations. Each router periodically transmits this table information to all its neighbor routers, and updates its own table by using the values received from its neighbors. Based on the comparison of the distances obtained from its neighbors for each destination, a router can decide the next hop as the shortest path from itself to the specified destination. When each router has a packet to send to some destination, it simply forwards the packet to the decided next hop router. When the routing table is frequently updated, the algorithm speeds up the convergence to the correct path [6].
2) On Demand routing protocols (Reactive routing)
These protocols are also called reactive protocols since they do not maintain routing information or routing activity at the network nodes if there is no communication. If a node wants to send a packet to another node then this protocol searches for the route in on demand manner and establishes the connection in order to transmit and receive the packet. The route discovery usually occurs by flooding the route request packets throughout the network. It has some basic characteristics:
1. Find route to destination only after request comes in.
2. Good for dynamic network.
Example: AODV, DSR (Dynamic Source Routing protocol)
3.1.1 Ad hoc On-demand Distance Vector (AODV)
The ad hoc on demand Distance vector routing protocol (AODV) is reactive uni cast routing protocols for mobile ad hoc .As a reactive routing protocol, AODV only needs to maintain the routing table in nodes. Every node keeps a nest hop routing table, which contains the destination to which it currently has a route. A routing table entry expires if it has not been used or reactive for a pre-specified expiration time. AODV adopts destination sequence number technique used by DSDV in an on-demand way [7].
The Ad hoc On-Demand Distance Vector (AODV) algorithm enables dynamic, self-starting, multihop routing between participating mobile nodes wishing to establish and maintain an ad hoc network. AODV allows mobile nodes to obtain routes quickly for new destinations, and does not require nodes to maintain routes to destinations that are not in active communication. AODV allows mobile nodes to respond to link breakages and changes in network topology in a timely manner. The operation of AODV is loop-free, and by avoiding the Bellman-Ford "counting to infinity" problem offers quick convergence when the ad hoc network topology changes (typically, when a node moves in the network). When links break, AODV causes the affected set of nodes to be notified so that they are able to invalidate the routes using the lost link.
Advanced uses of AODV
Because of its reactive nature, AODV can handle highly dynamic behavior of Vehicle Ad-hoc networks
· This protocol give loop free routing and it has option of multicasting broadcasting.
Limitations/Disadvantages of AODV
· Requirement on broadcast medium: The algorithm expects/requires that the nodes in the broadcast medium can detect each others’ broadcasts.
No reuse of routing info: AODV lacks an efficient route maintenance technique. The routing info is always obtained on demand, including for common case traffic.
It is vulnerable to misuse: The messages can be misused for insider attacks including route disruption, route invasion, node isolation, and resource consumption.
High route discovery latency: AODV is a reactive routing protocol. This means that AODV does not discover a route until a flow is initiated. This route discovery latency result can be high in large-scale mesh networks.
3.1.2 Dynamic Source Routing (DSR)
The Dynamic Source Routing protocol (DSR) is simple and efficient routing protocol designed specifically for use in multi-hop wireless and ad hoc networks of mobile nodes. DSR allows the network to be completely self-organizing and self-configuring, without the need for any existing network infrastructure or administration. The protocols is composed of the two mechanisms of Route Discovery and route Maintenance, which works together to allow nodes to discover and maintain source routes to arbitrary destinations in the ad hoc networks .The use of source routing allows packet routing to be trivially loop free, avoids the need for the up-to-date routing information in them for their own future use. All aspects of the protocol operate entirely on the demand allowing the routing packet overhead of DSR to scale automatically to only that needed to react to changes in the routes currently in use.
Advantages of DSR protocol
Some advantages of DSR protocol. This protocol is reactive protocols so it is better uses in small devices.
1. It reduces the overhead of route maintenance.
2. It No periodic message requires.
3. It has higher latency and lower overhead
4. It uses Source routing
Limitation of DSR protocol
1 Packet header size is high when number of nodes is increase.
2. DSR protocol always takes care must be taken to avoid collision between route request propagated by neighboring nodes. We have to insertion of random delay before forwarding RREQ.
3.1.3 Destination Sequenced distance Vector (DSDV) Protocol
The Destination Sequenced Distance Vector (DSDV) routing protocol is a proactive routing protocol, which is a modification of conventional Bellman –ford routing algorithm. This protocol adds like a new attribute, sequence number, to each rout table entry at each node. Routing table is maintained at each node and with this table; node transmits the packets to other nodes in the network. This protocol was motivated for the use of data exchange along changing and arbitrary paths of interconnection, which may not be close to any base station.
Destination-Sequenced Distance-Vector Routing (DSDV) is a table-driven routing scheme for ad hoc mobile networks based on the Bellman-Ford algorithm. It was developed by C. Perkins and P.Bhagwat in 1994. The main contribution of the algorithm was to solve the Routing Loop problem. Each entry in the routing table contains a sequence number, the sequence numbers are generally even if a link is present; else, an odd number is used. The number is generated by the destination, and the emitter needs to send out the next update with this number. Routing information is distributed between nodes by sending full dumps infrequently and smaller incremental updates more frequently.
Advantages of DSDV
DSDV was one of the early algorithms available. It is quite suitable for creating ad hoc networks with small number of nodes. Since no formal specification of this algorithm is present there is no commercial implementation of this algorithm. Many improved forms of this algorithm have been suggested.
DSDV protocol guarantees loop free paths.
Count to infinity problem is reduced in DSDV
We can avoid extra traffic with incremental updates instead of full dump updates.
Limitations of DSDV
Wastage of bandwidth due to unnecessary advertising of routing information even if there is no change in the network topology.
DSDV doesn’t support Multi path routing table’s advertisement for larger network.
Each and every host in the network should maintain a routing table for advertising. But for larger network this would lead to overhead, which consumes more bandwidth.
DSDV requires a regular update of its routing tables, which uses up battery power and a small amount of bandwidth even when the network is idle.
3.1.4 DumbAgent
Disable Multi-hop Routing (Dumb Agent) is created for the MAC layer and it work for shortest network.
When we used a one hop routing agent or protocol it is called DumbAent. The dumb agent simply forwards both unicast and broadcast packets to the ping agent. Hence it does not support multi-hop scenarios.
The dumb-agent is implemented under ~ns/mobility/dumb-agent{.cc,.h}.
Dumb Agents routing, run no programs of their own, they simply host agents and provide a place to store a database of routing information. In our system the nodes are “dumb”: they run no programs of their own, they simply host agents and provide a place to store a database of routing information. The mobile agents embody the “intelligence” in the system, moving from node to node and updating routing information as they go. Routing agents have one goal: to explore the network, updating every node they visit with what they have learned in their travels. Routing agents discover edges in the network by traversing them. Each routing agent keeps a history of where it has been. When an agent lands on a node it uses the information in its history to update the routing table on its host as to what possible routes might be, by writing the best routes the agent knows about into the node's table.
4. Concept of Simulation
Simulation is the imitation of some real thing, state of affairs, or process. The act of simulating something generally entails representing certain key characteristics or behaviors of a selected physical or abstract system. The network simulation is a technique where a program models the behavior of a network either by calculating the interaction between the different network entities such as routers, data links, packets, etc using mathematical formulas, or Networks tools. The behavior of the network and the various applications and services it supports can then be observed in a test lab; various attributes of the environment can also be modified in a controlled manner to assess how the network would behave under different conditions. We have various simulation tools for different purpose in our work we need a Network Simulator that create a scenario and used our routing protocols.
4.1 Introduction to Network simulator
A network simulator is a piece of software or hardware that predicts the behavior of a network, without an actual network being present.
Network simulators serve a variety of needs. Compared to the cost and time involved in setting up an entire test bed containing multiple networked computers, routers and data links, network simulators are relatively fast and inexpensive. They allow engineers to test scenarios that might be particularly difficult or expensive to emulate using real hardware- for instance, simulating the effects of a sudden burst in traffic or a DOS attack on a network service. Networking simulators are particularly useful in allowing designers to test new networking protocols or changes to existing protocols in a controlled and reproducible environment.
4.1.1 Performance Metrics
In the evaluation of routing protocols different performance metrics are used. They show different characteristics of the whole network performance. In this performance comparison we evaluate the Network Load, throughput and End-to-End delay of selected protocols in order to study the effects on the whole network.
A) Network Load
It is the total load measured in bits/sec, which all higher layers put forward on the WLAN layers in network. It represents the effectiveness of routing protocols when the packets are being received. When there is rush of traffic on the network and it is not easy to manage this is referred as network load. For the best performance it is the quality of network to handle all the traffic in smooth manners so that the deadlock may not occur.
B) Throughput
Throughput is the ratio of total amounts of data that reaches the receiver from the source to the time taken by the receiver to receive the last packet [8]. It is represented in packets per second or bits per second. In the MANET unreliable communication, limited energy, limited bandwidth and frequent topology change affect throughput [9]. A network requires high throughput and can be represented mathematically by the following equation.
C) End-to End Delay
The average time taken by the packets to pass through the network is called end-to-end delay. This is the time when a sender generates the packet and it is received by the application layer of destination, it is represented in seconds. This is the whole time that includes all delay of network such as transmission time, buffer queues, MAC control exchanges and delay produced by routing activities. Different applications require different packet delay levels. Low average delay is required in the network of delay sensitive applications like voice. MANET has the characteristics of packet transmissions due to weak signal strengths of nodes, connection make and break, and the node mobility. These are several reasons that increase the delay in the network. Therefore the end-to-end delay is the measure of how a routing protocol accepts the various constraints of network and show the reliability. End-to.end delay can be represented mathematically by the following equation.
Where
Hence the end-to-end delay can also be defined as combination of the N times transmission, propagation and processing delay.
D) Normalized Routing Load
The normalized routing load is defined as the fraction of all routing control packets sent by all nodes over the number of received data packets at the destination nodes. This metric discloses how efficient the routing protocol is. Proactive protocols are expected to have a higher normalized routing load than reactive ones. The bigger this fraction is the less efficient the protocol.
5. Simulation Results of MANETs Protocols
We will analyze and discuss the results of simulations we done, in two sections; In first we have the result on varying 10 nodes. And the second we have the result on varying 50 nodes. We begin the analysis of AODV, DSR, DSDV and DumbAgent .We check these protocols by four parameters such as Throughput, average End to End Delay, Normalized routing load, and Packet Delivery Fraction. The results obtained in the form of graphs, all the graphs are displayed as average.
(A) Varying 10 Nodes
In section of the simulation we vary the number of nodes in the network. Our objective is to investigate the impact of node density on the protocol’s performance. We use another parameter as in table 2. A desirable property of a protocol is to have stable behavior regardless of the number of nodes in the network.
Table 2 Parameter of Varying Node Density (A)Throughput
|
Simulation Parameter |
|
|
Routing Protocols |
AODV,DSDV,DSR,DUMBAGENT |
|
Simulation Time |
200 |
|
Number of Nodes |
10,20,30,40,50 |
|
Simulation Area |
x=250m,y=250m |
|
Speed |
3 m/sec |
|
Pause Time |
3 sec |
|
Traffic Type |
CBR |
|
Packet Size |
512 byte |
|
Rate |
4 pkt/sec |
|
No. of connection |
1 |