Increasing the efficiency of VoIP quality assurance parameters through the improvement of MANET routing protocols

Dissertation

To get Master degree

Computer networks

Chapter 1

1 Introduction

1-1 What is a mobile ad hoc network?

A mobile ad hoc network [1] is a network formed by wireless hosts [2] that can also be mobile. In these networks, no prefabricated infrastructure is necessarily used. This means that there is no infrastructure such as a central station, router[3], switch[4] or anything else that is used in other networks to help structure the network. Rather, there are only a number of wireless nodes [5] that connect to non-neighboring nodes through communication with neighboring nodes.

Figure 1-1 shows the structure of a mobile ad hoc network as an example. Small circles represent wireless nodes and each large circle represents the useful range of a node. This means that any other node located in this distance can receive the data sent by this node and distinguish them from environmental noise. For convenience, this network is represented by a corresponding graph, and the edges of the graph mean that its two vertices are at a distance from each other that can receive each other's messages. In fact, the nodes that are within the useful range of each other are connected to it with an edge in the graph representation.

In case networks, the mobility of the nodes may change the path between two nodes This is what distinguishes these networks from other wireless networks. Despite all these problems, ad hoc networks are used in many cases. The reason for this is the speed and ease of implementing this network, as well as its lack of dependence on pre-built structures. Among the uses of ad hoc networks, we can mention personal applications such as connecting laptops to each other, public applications such as connecting vehicles and taxis, military applications such as the army and battle fleet communication, and emergency applications such as rescue operations. 1-1-1 Features of mobile ad hoc networks This network, like other types of networks, has characteristics such as the following [1]:

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Autonomous terminal[6]: In this network, each terminal is an independent node that may act as a host or router. In other words, it acts as a host during processing and also acts as a router when routing operations are needed.

Distributed operations [7]: Since there is no structure to control operations centrally in the network, the control and management of the network between terminals is done in a distributed manner. The nodes in this network must cooperate with each other and each node acts as an amplifier.

Dynamic network topology[8]: Since the nodes are mobile, the network topology may change rapidly and unpredictably, and the connections between terminals may change at the same time.

Change of connection capacity[9]: The bit error rate in this network is high. An end-to-end path can be shared by multiple sessions. The channel that connects the terminals is subject to noise, fading and interference and has less bandwidth than a wired network. In a number of designs, the path between each pair of users can travel multiple wireless connections.

Lightweight terminals: In some cases, the nodes of this network are mobile devices with low processing capacity, small memory size, and low energy storage capability. These devices need optimized algorithms and methods that optimize computing and communication operations.

Multi-step: Due to the lack of routers and central gateways, hosts perform routing tasks themselves. Therefore, packets follow "multi-hop" routes and pass through different mobile nodes before reaching their destination. Due to the lack of trust in such nodes, this feature presents a serious vulnerability. Amorphism [10]: The mobility and wireless connectivity of nodes allows nodes to enter or leave the network at will, thus allowing a node to intentionally form or break connections. Therefore, the network topology will not have any fixed form neither in terms of size nor in terms of configuration.Any security solution should also consider this feature.

1-1-2 advantages

The advantages of mobile ad hoc network are [1]:

Its development speed is high.

It can be implemented simply and with low cost.

It does not require any infrastructure.

It has automatic configuration.

Each of the stations as a The router also plays a role.

It is flexible. For example, it is possible to access the Internet from different points in the area covered by the network.

Two stations in the network can communicate with each other and transfer information independently of other stations.

1-1-3 Disadvantages

Regardless of the attractive applications, the characteristics of this network have caused limitations in the use of these networks, which should be investigated. One of the most important challenges in this type of network is the lack of a fixed infrastructure. Among the main problems in this type of network, the following can be mentioned: Routing: Since the topology of the network is constantly changing, the operation of routing packets between each pair of nodes is very difficult. Most protocols should be based on reactive rather than proactive routing. Paths between nodes may involve multiple steps, which are more complicated than single-step communication.

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Security and Reliability: In addition to the common functionality of wireless communication, this type of network has specific security issues. The nature of distributed operations requires different plans for management. In addition, wireless connections produce many reliability problems due to the limited range of wireless transmissions, the public nature (broadcast) of wireless media (hidden terminal problem), packet loss and data transmission errors.

Quality of service [11]: Providing different levels of service quality in a network that is constantly changing is a big challenge. The characteristic of change actually makes the quality of communication in this type of network difficult.

Energy consumption: For mobile terminals, communication operations must be optimized in terms of energy consumption.

Other problems and limitations in this type of network can be mentioned as follows:

Errors caused by transmission and as a result of high number of packet deletion

Continuous disconnections and connections

Limited bandwidth

The universal nature of communication

Variable and dynamic routes and topologies

Battery charging

Limited capacity and capabilities of nodes

Need for new applications

Congestion control

Bandwidth limitation

Security provision

Delay in sending information in larger networks

1-1-4 Applications of mobile ad hoc network

The applications of this type of network are:

Military applications

Rescue

Performing distributed computing operations

Vehicle network

Environmental protection

1-2 Voice on the Internet[12]

Voice on the Internet, a program It is a real-time application [13] that has perhaps made the most progress in today's networks. An audio input device, such as a microphone, is required on the transmitter side. The audio signal is converted into digital form by an analog-to-digital converter [14]. Due to the packet-switched nature of computer networks, audio data must be coded and packaged [15] before transmission. Encoding[16] and decoding[17] are performed by codecs[18] that convert and return audio data samples to a specific network layer that can be presented. Most codecs are defined by ITU-T [19] standards. Each of them presents different characteristics regarding the amount of bandwidth required.

After the information is coded and packaged at the sender side, the encapsulated audio data packets [20] can be transmitted in the network. Voice packets on the network interact with packets from other applications that are routed to their destination according to shared connections. The packets are decoded and decapsulated on the receiver side. The digital data stream is then converted back to analog form and presented to an output device, usually a speaker.