Wireless Data Networks

Introduction
Wireless data networks exist in such number and variety as to be difficult to categorize and compare.

Some wireless data networks run over wireless voice networks, such as mobile telephone networks. CPDP, HSCSD, PDC-P, and GPRS are examples. Other wireless networks run on their own physical layer networks, utilizing anything from antennas built into hand held devices to large antennas mounted on towers. 802.11, LMDS, and MMDS are examples. A few wireless networks are intended only to connect small devices over short distances. Bluetooth is an example.

Wireless networks which run over other wireless networks often utilize the lower layer networks to provide security and encryption. Stand-alone wireless networks either provide their own security and encryptions features or rely upon VPN's (Virtual Private Networks) to provide those features. In many cases, multiple layers of security and encryption may be desirable.

Some wireless networks are fixed, meaning that antennas do not move frequently. Other wireless networks are mobile, meaning that the antenna can move constantly. This is sometimes a feature of the specific implementation and antenna design, instead of an inherent limitation of the wireless network specification.
Wireless networks may operate on licensed or unlicensed portions of the frequency spectrum.

Common Wireless Network Types
Major types of wireless networks include:
CDPD Cellular Digital Packet Data
HSCSD High Speed Circuit Switched Data
PDC-P Packet Data Cellular
GPRS General Packet Radio Service
1xRTT 1x Radio Transmission Technology
Bluetooth
IrDA Infrared
MMDS Multichannel Multipoint Distribution Service
LMDS Local Multipoint Distribution Service
WiMAX Worldwide Interoperability for Microwave Access
802.11 Wi-Fi

ROUTING IN AD-HOC WIRELESS NETWORKS
A mobile ad hoc network (MANET), sometimes called a mobile mesh network, is a self-configuring network of mobile devices connected by wireless links. MANETs are a kind of wireless ad hoc networks that usually has a routable networking environment on top of a Link Layer ad hoc network.

Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently. Each must forward traffic unrelated to its own use, and therefore be a router. The primary challenge in building a MANET is equipping each device to continuously maintain the information required to properly route traffic.

An ad hoc routing protocol is a convention, or standard, that controls how nodes decide which way to route packets between computing devices in a mobile ad-hoc network.
In ad hoc networks, nodes do not start out familiar with the topology of their networks; instead, they have to discover it. The basic idea is that a new node may announce its presence and should listen for announcements broadcast by its neighbors. Each node learns about nodes nearby and how to reach them, and may announce that it, too, can reach them.

The following is a list of some ad-hoc network routing protocols:

1. Pro-active (table-driven) routing
This type of protocols maintains fresh lists of destinations and their routes by periodically distributing routing tables throughout the network. The main disadvantages of such algorithms are:
' Respective amount of data for maintenance.
' Slow reaction on restructuring and failures.

2. Reactive (on-demand) routing
This type of protocols finds a route on demand by flooding the network with Route Request packets. The main disadvantages of such algorithms are -
' High latency time in route finding.
' Excessive flooding can lead to network clogging.

3. Flow-oriented routing
This type of protocols finds a route on demand by following present flows. One option is to unicast consecutively when forwarding data while promoting a new link. The main disadvantages of such algorithms are
' Takes long time when exploring new routes without a priori knowledge.
' May refer to entitative existing traffic to compensate for missing knowledge on routes.

4. Adaptive (situation-aware) routing
This type of protocols combines the advantages of proactive and of reactive routing. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding. Some metrics must support the choice of reaction. The main disadvantages of such algorithms are -
' Advantage depends on amount of nodes activated.
' Reaction to traffic demand depends on gradient of traffic volume.

5. Hybrid (both pro-active and reactive) routing
This type of protocols combines the advantages of proactive and of reactive routing. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding. The choice for one or the other method requires predetermination for typical cases. The main disadvantages of such algorithms are -
1. Advantage depends on amount of nodes activated.
2. Reaction to traffic demand depends on gradient of traffic volume.

6. Hierarchical routing protocols
With this type of protocols the choice of proactive and of reactive routing depends on the hierarchic level where a node resides. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding on the lower levels. The choice for one or the other method requires proper attribution for respective levels. The main disadvantages of such algorithms are
1. Advantage depends on depth of nesting and addressing scheme.
2. Reaction to traffic demand depends on meshing parameters.

7. Geographical routing protocols
This type of protocols acknowledges the influence of physical distances and distribution of nodes to areas as significant to network performance. The main disadvantages of such algorithms are
' Efficiency depends on balancing the geographic distribution versus occurrence of traffic.
' Any dependence of performance with traffic load thwarting the negligence of distance may occur in overload.

8. Power-aware routing protocols
Energy required to transmit a signal is approximately proportional to d??, where d is the distance and ?? is the attenuation factor or path loss exponent, which depends on the transmission medium. When ?? = 2 (which is the optimal case), transmitting a signal half the distance requires one fourth of the energy and if there is a node in the middle willing spend another fourth of its energy for the second half, data would be transmitted for half of the energy than through a direct transmission - a fact that follows directly from the inverse square law of physics.

The main disadvantages of such algorithms are:
1. This method induces a delay for each transmission.
2. No relevance for energy network powered transmission operated via sufficient repeater infrastructure.

 

Intelligent Agent
Intelligent agent technology provides a mechanism for information systems to act on behalf of their users. They can be programmed to search, acquire, and store information on behalf of the wants and needs of users.

Attributes
' Intelligent agents are task-oriented. Examples of intelligent agent tasks include data mining, profile management, privacy management, rules management, and application management.
' Data mining agents seek data and information based on the profile of the user and instructions carried out by the rules manager agent.
' The profile management agent's role is to maintain the user profile, constantly adding, deleting and modifying profile information based on new information.
' The privacy management agent's role is to safeguard privacy of the user, including identity, location, or other personal information.
' An application agent manages application(s) and interactions between the network, other networks, content, and other applications.

Agent Locations and Technologies
Intelligent agent software may consist of embedded technology within the mobile device, servers on the Internet, and/or programs within applications on/off the mobile network.

Agency vs. Intelligence
Agency is the degree of authority given to a program - how much it is allowed to perform on its own accord, based on the instructions given by user.
Intelligence is the degree of reasoning and independent "learning" enabled within the program. A truly intelligent agent has the ability to adapt itself to its environment, sensing events and objects, evaluating circumstances and objects, and act over time in pursuit of a specific agenda.

Intelligent Agent Applications
The numbers of applications benefiting from intelligent agent technology are virtually limited only by the imagination. One of the key goals is to enable the autonomous delivery of information for the benefit of various applications. For example, a location detection intelligent agent in a mobile device would inform application middle-ware once a user is in a certain location, perhaps engaging additional positioning and or applications.

MARKET PLACE GROWTH AND DOMINANT TECHNOLOGIES.
The Information Technology (IT) Revolution is driven by four interlinked core industries: computers, semiconductors, software and telecommunications. These industries are built around the technologies of:
' Microelectronics (the design and fabrication of integrated circuits);
' Software (the instruction sets that tell the circuits what to do); and
' Wireless and Photonics (the generation, control and detection of EM radiation, for example, to transmit and receive signals).

This interconnected cluster generates widespread innovation. It creates new products like Blackberries and GPS location. The trigger for these major eras of technology-driven change is a breakthrough innovation that opens up a whole new frontier of design and product possibilities, sparking the imagination of engineers, entrepreneurs and investors.

VALUE-ADDED-SERVICES

Existing Mobile Communication Technologies
The cellular radio network system facilitates mobility in communication. Systems achieve mobility by transmitting data via radio waves. The following are some examples of mobile communication systems currently in use.

1. Paging (SMS)
A simple and inexpensive form of mobile communication . An antenna or satellite broadcasts short messages to subscribers. Receivers are usually devices such as beepers, which display messages on a small screen. Transmission of data is one-way. Paging systems are designed to provide reliable communication to subscribers wherever they are. This necessitates high-powered transmitters and low data rates for maximum coverage of each transmitter's designated area.

2. Communication Satellites
Satellites consist of large transponders that listen to a particular radio frequency, amplify the signal, and then rebroadcast it at another frequency. They are inherently broadcast devices. A drawback of satellites is that they have quite a large propagation delay due to the distances traveled by radio waves.

3. Cellular Radio Networks
Cellular networks are divided up into cells, each cell being serviced by one or more radio transceivers (transmitter/receiver). Communication in a cellular network is full duplex, where communication is attained by sending and receiving messages on two different frequencies - frequency division duplexing (FDD). The reason for the cellular topology of the network is to enable frequency reuse. Cells, a certain distance apart, can reuse the same frequencies, which ensure the efficient usage of limited radio resources.

4. Personal Handyphone
The Personal Handyphone System (PHS) is used in Japan. It is similar to cellular networks, however phones can also communicate directly with one another when in range. This is an advantage over cellular phones, which can only communicate with one another via base station transceivers. This system is very popular within heavily populated metropolitan areas.

5. Mobile Radio
Mobile radio is in many ways the predecessor to the cellular radio network. It is mostly analogue, and makes use of single frequencies for sending and receiving signals. Communication is half-duplex, and a button must be pressed to switch modes. They are most commonly used for emergency services, the transport sector, and the security industry.

Exercise
1. Explain what is meant by value added services (VAS)
2. Identify and describe some of the provider VAS especially the most recent
3. Differentiate between GSM and CDMA
4. Give the various existing mobile communication technologies.

Assignment
Carry out a brief case study of Safaricom cellular infrastructure. Identify and describe some of the provider VAS especially the most recent.

Source: Essay UK - http://www.essay.uk.com/free-essays/information-technology/wireless-data-networks.php



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