Ad hoc network concepts, features and Comparison

Ad hoc network concepts, features and Comparison

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Author: Zheng Lina and Wu Tongqiang Source: Post and Telecommunications Design Technology

Preface
I. Ad hoc network concept
Ii. ad
Features of the Hoc Network
Iii. Ad hoc network application requirements
Iv. Comparison with other Mobile Communication Systems
V. Combination of Mobile IP addresses and Ad Hoc Networks
VI,
Problems in managing Ad Hoc Networks
VII. Conclusion

Preface

With
Getting rid of the limitations of wired networksThe desire to communicate freely anytime and anywhere has witnessed rapid development in Wireless Network Communication in recent years. Person
You can use a portable computer with a wireless interface or a personal digital assistant to implement mobile communication. Currently, most mobile communications require the support of wired infrastructure (such as base stations. To enable
A new network technology-Ad Hoc network technology emerged as the times require local communication of base stations. Ad
The Hoc network does not require the support of basic wired devices, so communication can be achieved through the free networking of mobile hosts. Ad
The emergence of the Hoc network has promoted the process of free communication in any environment. It also provides effective solutions for military communication, disaster recovery and temporary communication.

I. Concept of ADHOC Network

Ad
A hoc network is a mobile network without the support of wired infrastructure. nodes in the network are composed of mobile hosts. Ad hoc networks were initially used in the military field, and their research originated from grouping in the battlefield environment.
The Wireless Network Data Communication Project, funded by DARPA, was subsequently launched in 1983 and 1994 to defend against the destruction of the adaptive network suran (Adaptive vable)
Adaptive
Network) and Global Mobile Information System glomo (Global Information System) project. Due to the continuous development of wireless communication and Terminal Technologies
In the Civil Environment, ad hoc networks have also developed. If you need to implement temporary communication in areas without wired infrastructure, you can easily build an ad hoc network.

In
In a Hoc network, when two mobile hosts (host a and host B in 1) are in the communication coverage of each other, they can communicate directly. However, because the communication coverage of mobile hosts is limited
To communicate with a distant host (host a and host C in 1), you need to move host B between them for forwarding. Therefore
In a Hoc network, the host is still a router and is responsible for finding routes and forwarding packets. In
In a Hoc network, the communication range of each host is limited. Therefore, a route generally consists of multiple hops. data can be forwarded by multiple hosts to reach the destination. Ad
A hoc network is also called a multi-hop wireless network. Its structure 2 is shown in.

 

Ad hoc networks can be seen as the crossover between mobile communication and computer networks. In
In a Hoc network, the group switching mechanism of computer networks is used instead of the circuit switching mechanism. Communication hosts are generally mobile terminal devices such as portable computers and personal digital assistants (PDAs. Ad
The Hoc network is different from the Mobile IP network in the current Internet environment. In mobile IP networks, mobile hosts can access networks through fixed wired networks, wireless links, and dial-up lines.
There is only one wireless link connection method in the Hoc network. In a Mobile IP network, a mobile host can communicate with each other through the support of neighboring base stations and other wired facilities.
The network still uses the traditional routing protocol of the Internet. Ad
The Hoc network does not support these facilities. In addition, the mobile host in the Mobile IP network does not have the routing function, but is a common communication terminal. The network does not change when the mobile host moves from one zone to another.
Topology, and the movement of hosts in the Ad hoc network will change the topology.

II,
Features of Ad Hoc Networks

As a new networking method, ad hoc networks have the following features.

2.1
Network independence

Ad
Compared with conventional communication networks, a Hoc network can quickly build a mobile communication network at any time and anywhere without the support of hardware infrastructure. Its establishment does not depend on
The existing network communication facilities are independent. Ad hoc networks are suitable for disaster recovery, remote communications, and other applications.

2.2
Dynamically changing network topology

In
In a Hoc network, mobile hosts can be moved freely in the network. The movement of the host will cause the links between hosts to increase or disappear, and the relationships between hosts will change constantly. In the self-group network, the host may still be a route
Therefore, moving will make the network topology change constantly, and the changing mode and speed are unpredictable. For conventional networks, the network topology is relatively stable.

2.3
Limited wireless communication bandwidth

In
No wired infrastructure is supported in the Hoc network. Therefore, communication between hosts is completed through wireless transmission. Due to the physical characteristics of the wireless channel, the network bandwidth provided by the wireless channel is much lower than that provided by the wired channel.
In addition, considering the collision, signal attenuation, noise interference, and other factors produced by competing to share wireless channels, the actual bandwidth available for mobile terminals is much smaller than the maximum bandwidth value in theory.

2.4
Limited host energy

In
In a Hoc network, hosts are all mobile devices, such as PDAs, portable computers, or handheld computers. Because the host may be constantly moving, the energy of the host is mainly provided by the battery
The Hoc network has the characteristics of limited energy.

2.5 distributed features of networks

In
There are no central control nodes in the Hoc network, and hosts are interconnected through the distributed protocol. If one or more nodes in the network fail, the other nodes can still work normally.

2.6
Short Life Cycle

Ad hoc networks are mainly used for temporary communication requirements. Compared with wired networks, ad hoc networks generally have a short life cycle.

2.7
Limited physical security

Mobile Networks are generally more vulnerable to physical security attacks than fixed networks, and are prone to eavesdropping, spoofing, and DoS attacks. Some existing link security technologies have been applied
Reduce security attacks in wireless networks. However, the distributed feature of Ad Hoc networks has a certain degree of anti-destruction compared with the centralized network.

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III,
Ad hoc network application requirements

Ad hoc networks have a wide range of applications. Generally, they can be used in the following scenarios:

A)
Areas without wired communication facilities, such as the absence of hardware communication facilities or the destruction of wired communication facilities.

B) network communication environments requiring distributed features.

C)
The existing wired communication facilities are insufficient, so a temporary and rapid establishment of a communication network environment is required.

D) As a strong standby network.

Ad
The Research of Hoc network technology was initially designed to meet the needs of military applications. Military communication systems need to be self-organized and mobile. In war, communication systems are vulnerable to attacks from the enemy. Therefore
The communication system can defend against certain attacks. If a centralized communication system is used, once the communication center is damaged, the entire system will be paralyzed. A distributed system can ensure that some communication nodes or links are disconnected.
The remaining parts can continue to work. In the war, it is difficult for the battlefield to ensure reliable wired communication facilities. Therefore, it is necessary to combine the communication nodes to form a communication system. In addition, the mobility is
An important part of the combat capability of the troops, which requires the communication system to be quickly established and demolished according to the needs of the war.

Ad hoc networks meet these needs of military communication systems. Ad
The Hoc network adopts the distributed technology and has no central control node management. When some nodes or links in the network fail, other nodes can continue to communicate through related technologies. Ad
The Hoc network is freely composed by mobile nodes and independent from wired devices. Therefore, it is highly self-organized and suitable for harsh communication environments on the battlefield. Ad
The establishment of a hoc network is simple and highly mobile. At present, some developed countries are equipped with sophisticated personal communication systems for combat personnel. In harsh battlefield environments, it is difficult to use wired communication mechanisms or mobile IP machines.
Communication tasks can be completed through the Ad Hoc network. Therefore, studying ad hoc networks has important application value and long-term significance for the development of military communication systems.

Near
In the past few years, the research of Ad Hoc networks has also been paid attention to in both civil and commercial fields. In the civil field, AD
Hoc networks can be used for disaster recovery. After a flood or earthquake, wired communication facilities may be damaged and cannot communicate normally.
The Hoc network can quickly establish an emergency communication network, ensure the smooth operation of rescue work, and complete the tasks of emergency communication requirements. Ad
The Hoc network can be used for communication in remote or underdeveloped areas. In these regions, there are usually no wired communication facilities due to cost, geographical environment, and other reasons.
The Hoc network can solve communication problems in these environments. Ad
The Hoc network can also be used for temporary communication. For example, when participants need to communicate with each other in business meetings, if the existing wired communication system cannot meet the communication requirements
To complete communication tasks.

Ad hoc networks are also very concerned in the field of research. In recent years, most international network conferences have seen ad
With the continuous development of mobile technology and the increasing demand for free communication, ad hoc networks will receive more attention and get more rapid development and popularization.

IV,
Comparison with other Mobile Communication Systems

4.1 Cellular System

The cellular system is the most widely used land-based public mobile system.
Information System. In the cellular system, the coverage area is generally divided into multiple residential areas similar to the honeycomb. A fixed base station is set up in each cell to provide users with access and information forwarding services. Between mobile users and between mobile users and
Non-mobile users must communicate with each other through base stations. Base Stations are generally connected to the backbone exchange network consisting of switches through wired lines. A cellular system is a type of connected network. Once a channel is assigned
A user. This channel can always be used by this user. Cellular systems are generally used for voice communication.

4.2 Cluster System

The cluster system is similar to the cellular system.
It is a type of connected network, which generally belongs to a dedicated network with a small scale and mainly provides voice communication for mobile users.

4.3 Satellite Communication System

Satellite Communication System
It provides the most extensive communication service for users in every corner of the world. In this system, satellites provide similar functions as base stations. Satellite communication systems can be divided into static orbit, medium orbit and low satellite location
Three types of tracks. Satellite communication systems have high costs, high transmission latency, and limited transmission bandwidth.

All the above mobile communication systems require the support of wired network communication infrastructure, such as base stations and communication
Replacement, satellite, etc. The establishment and operation of these facilities requires a large amount of manpower and material resources. Therefore, the cost is high and the construction period is long. Ad
The Hoc network does not require the support of the base station. The host can establish the network by itself. Therefore, the network creation cost is low and the time is short. Generally, it only takes several seconds or minutes to establish the network. In the above communication system, mobile terminals are not directly connected
In addition, the mobile terminal only supports sending and receiving and does not support forwarding. Ad
The Hoc network consists of mobile hosts, which can communicate directly with each other. Mobile hosts not only send and receive data, but also forward data. In addition, the current mobile communication system mainly provides users with voice communication functions.
Circuit Switching is often used, and the topology structure is relatively stable. Ad hoc networks use the group forwarding technology to provide users with data communication services, and the topology structure is easy to change.

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V,
Combination of Mobile IP and Ad Hoc Networks

Achieving mobile and full IP addresses is the two major trends in today's network development. With the increasing use of mobile phones
In general, people have higher and higher requirements on the information that mobile can provide, and people prefer to access the Internet anytime and anywhere.

For ad
In a Hoc network, the network is generated at any time and is easy to construct. It does not need to be supported by existing networks. Therefore, it is widely used and very simple. However, this network is highly independent and can exist independently.
Both the features and the active and on-demand routing protocols it uses make it difficult to communicate with the Internet to achieve interactive information. In order to achieve mobile hosts in the Ad hoc network
The Mobile IP protocol can be used to roam across different networks and integrate with the Mobile IP address and ad hoc network, that is, mipmanet, to provide
The Ad Hoc network uses an on-demand routing mechanism. The Mobile IP address provides a proxy address and a reverse tunnel Ad Hoc network to access the Internet. Figure 3 shows ad
A model for the access of a Hoc network to the Internet.

Vi. Problems in managing Ad Hoc Networks

Ad
The features of a Hoc network make management much more complex than wired networks. Because of the dynamic changes in the network topology, network management is required to be dynamically and automatically configured. In addition, considering the limitations of mobile nodes, such as energy
Limited, link status changes, and limited storage capabilities. Therefore, we need to consider the load brought by management protocols to the entire network. Finally, we need to consider the applicability of network management to different environments.

With
The problems to be solved in the management of the active Ad Hoc network are as follows:

A)
An important task of the Network Management Protocol is to make the network administrator know the network topology. In a wired network, this is easy to achieve because the network does not change frequently. However, in a mobile network, node movement leads to topology structure.
Network administrators need to regularly collect node connection information, which will undoubtedly increase the network load.

B)
Most nodes use battery power, so ensure that the load of network management is limited to the minimum value to save energy. Minimize the number of nodes for sending and receiving and processing, but this is in conflict with regular updates to the topology.

C)
Due to limited energy and node mobility, nodes may be separated from the network at any time. This requires that the Network Management Protocol be able to detect and join nodes in time and update the topology.

D)
The signal quality changes greatly in wireless environments. The signal recession and congestion will make the network administrator mistakenly think that the node has left. Therefore, the network administrator must be able to identify whether the connection is interrupted due to node movement or link quality. Network
Management must ask the physical layer, but this will violate the OSI hierarchical management structure.

F) AD
A hoc network is usually used in military scenarios. Therefore, it is necessary to prevent eavesdropping, destruction, and intrusion. Therefore, the network management must combine the encryption and authentication processes.

Ad
The Network Management of a hoc network is different from that of a traditional network. The problems to be solved include how to effectively collect network topology information and how to handle dynamic network configuration and security and confidentiality issues.

VII. Conclusion

Ad
A hoc network is a new type of mobile computer network. It can be used as an independent network or a complementary form with a fixed network. Its own uniqueness gives
Its huge development prospects. There are still many problems to be solved in the research of Ad Hoc networks: Design routing protocols with extended features such as energy-saving policies, security assurance, multicast functions and QoS support, and
Network Management of ad hoc networks. In the future, we will focus on research on network monitoring, node mobility management, anti-Destruction Management, and security management in ad hoc networks.