30-03-2011, 10:33 AM
Presented By
Harisha Reddiboina
[attachment=11302]
Wireless Networks
Introduction:
A network could be defined as an interconnected collection of autonomous computers. Two computers are said to be interconnected if they are able to exchange information.
The type of this connection could be referred to as the communication media. It could be via a copper wire, using fiber optics or even communication satellites could also come into the scene.
Definition:
If the communication medium between the computers of the network is without wires (i.e., infrared rays or some other similar mode of communication), such a network could be referred to as wireless network.
History of Wireless Networks:
The first indication of wireless networking dates back to 1800 and before when Indians used smoke signals as a means of transferring the information. Later evolution of communication means from messengers on horse back to telephones and public and private radio communications marked the progress of communication technology.
Computer networks and radio communications (which, of course used the wireless media) were first brought together in 1971 at the University of Hawaii as a research project called ALOHANET. This project enabled computer sites at seven campuses spread over four islands to communicate with a central computer situated at Oahu. U.S. military used this technology via DARPA to support tactical communication at warfields.
Though the advent of wired Ethernet technology, with it’s hopping 10Mbps speed marked a big blow to the development of wireless networks, ham radio users kept this technology alive.
In 1985, the Federal Communications Commission (FCC) made the com
mercial development of radio-based LAN components possible by authorizing the public use of the Industrial, Scientific and Medical (ISM) bands. This has had a dramatic effect on the wireless industry, prompting the development of wireless LAN components.
During the late eighties, the decreasing size of computers from desktop machines to laptops allowed employees to take their computers with them around the office and on business trips. In 1990, NCR began shipping WaveLAN, one of the first wireless LAN adapters for PCs. Further development was concentrated on meeting the mobility needs of the market. However due to their high cost, initial implementations and lack of standards limited widespread use of wireless networks.
• The 802 Working Group of Institute for Electrical and Electronic Engineers (IEEE), which is responsible for developing LAN standards such as Ethernet and token ring, has developed a standard for wireless LANS under 802.11. End users and network managers have had a difficult time showing a positive business case for purchasing wireless LAN components in the office unless there is a requirement for mobility. Sensing a bleak market for wireless LAN products, wireless LAN vendors began equipping their wireless LAN components in 1995 with directional antennas to facilitate point-to-point connections between buildings located within the same metropolitan area (wireless MANs).
• The most widely accepted wireless network connection has been wireless WAN services, which began surfacing in the early 90s. Companies such as ARDIS and RAM Mobile Data were first in selling the wireless connections between portable computers, corporate networks and the Internet. This service enables employees to access e-mail and other information services from their personal appliance without using the telephone system when meeting with the customers, traveling in the car, or staying in a hotel room.
• Narrowband Personal Communications Services (PCS), a spectrum allocated at 1.9 GHz, is a new wireless communications technology offering wireless access to WWW, e-mail, voice mail, and cellular phone service. These developments paved way for various other related developments such as Bluetooth Technology and Wireless Application Protocol Services.
Architecture of Wireless Nerworks
Networks perform many functions to transfer information from source to destination such as a bit pipe for data transmission, sharing of a common medium by medium access techniques, synchronization and error control mechanisms as well as routing mechanisms. Network architecture describes the protocols, major hardware and software elements that constitute the nwetwork.
There are two views of a computer architecture:
a) Logical View:
A logical architecture defines the network’s protocols – rules by which the two entities communicate. One popular logical architecture is the 7-layer Open System Interconnection (OSI) Reference Model, developed by International Standards Organization (ISO). The OSI layers provide the following network functionality:
Layer 7 – Application Layer: Establishes communication with other users and provides services such as file transfer and e-mail to the end users of the network.
Layer 6 – Presentation Layer: Negotiates data transfer syntax for the application layer and performs translations between different datatypes, if necessary.
Layer 5 – Session Layer: Establishes, manages, and terminates sessions between applications.
Layer 4 – Transport Layer: Provides mechanisms for the establishment, maintenance, and orderly termination of virtual circuits, while shielding the higher layers from the network implementation details.
Layer 3 – Network Layer: Provides the routing of packets from source to destination.
Layer 2 – Data Link Layer: Ensures Synchronization and error control between two entities.
Layer 1 – Physical Layer: Provides the transmission of bits through a communication channel by defining electrical, mechanical and procedural specifications.
Wireless LANs and MANs function only within the Physical and Data Link Layers, which provide the medium, page link synchronization and error control mechanisms. Wireless WANs provide these first two layers as well as Network layer routing.
b) Physical architecture of a wireless network:
The physical components of a wireless network implement the physical, data page link and network layer functions. The Network Operating System (NOS) located on client and server machines, communicates with the wireless Network Interface Card (NIC) via driver software, enabling the applications to utilize the wireless network for data transport.
Slide 2
Features of physical architecture:
End User Appliances: It is a visual interface between the user and the network. Various end user appliances are Desktop workstations, laptops, palmtops, pen based computers, PDAs and pagers.
Network Software: A wireless network supports the NOS and it’s applications, such as word processing, databases, and e-mail, enabling the flow of data between all components.
Wireless Network Interface: It’s function is to couple the digital signal from the end-user appliance to the wireless medium, which is air, to enable an efficient data transfer between sender and receiver. This process includes modulation and amplification.
It also manages the use of air for communications and synchronization through a carrier sense protocol. This protocol enables a group of wireless computers to share the same frequency and space. According to the protocol, to avoid two people speaking at the same time, you should wait until the other person has finished talking. Also, no one should speak unless the room is silent.
Wireless networks handle error control by having each station check incoming data for altered bits. The interface also includes the software driver that couples the client’s applications or NOS software to the card.
Antenna: Antennas come in many shapes and sizes. They have the following characteristics:
Propagation pattern, radiation power, gain, bandwidth.
They are of two types unidirectional and omni directional.
The communications channel: All information systems employ a communications channel along which information flows from source to destination.
Harisha Reddiboina
[attachment=11302]
Wireless Networks
Introduction:
A network could be defined as an interconnected collection of autonomous computers. Two computers are said to be interconnected if they are able to exchange information.
The type of this connection could be referred to as the communication media. It could be via a copper wire, using fiber optics or even communication satellites could also come into the scene.
Definition:
If the communication medium between the computers of the network is without wires (i.e., infrared rays or some other similar mode of communication), such a network could be referred to as wireless network.
History of Wireless Networks:
The first indication of wireless networking dates back to 1800 and before when Indians used smoke signals as a means of transferring the information. Later evolution of communication means from messengers on horse back to telephones and public and private radio communications marked the progress of communication technology.
Computer networks and radio communications (which, of course used the wireless media) were first brought together in 1971 at the University of Hawaii as a research project called ALOHANET. This project enabled computer sites at seven campuses spread over four islands to communicate with a central computer situated at Oahu. U.S. military used this technology via DARPA to support tactical communication at warfields.
Though the advent of wired Ethernet technology, with it’s hopping 10Mbps speed marked a big blow to the development of wireless networks, ham radio users kept this technology alive.
In 1985, the Federal Communications Commission (FCC) made the com
mercial development of radio-based LAN components possible by authorizing the public use of the Industrial, Scientific and Medical (ISM) bands. This has had a dramatic effect on the wireless industry, prompting the development of wireless LAN components.
During the late eighties, the decreasing size of computers from desktop machines to laptops allowed employees to take their computers with them around the office and on business trips. In 1990, NCR began shipping WaveLAN, one of the first wireless LAN adapters for PCs. Further development was concentrated on meeting the mobility needs of the market. However due to their high cost, initial implementations and lack of standards limited widespread use of wireless networks.
• The 802 Working Group of Institute for Electrical and Electronic Engineers (IEEE), which is responsible for developing LAN standards such as Ethernet and token ring, has developed a standard for wireless LANS under 802.11. End users and network managers have had a difficult time showing a positive business case for purchasing wireless LAN components in the office unless there is a requirement for mobility. Sensing a bleak market for wireless LAN products, wireless LAN vendors began equipping their wireless LAN components in 1995 with directional antennas to facilitate point-to-point connections between buildings located within the same metropolitan area (wireless MANs).
• The most widely accepted wireless network connection has been wireless WAN services, which began surfacing in the early 90s. Companies such as ARDIS and RAM Mobile Data were first in selling the wireless connections between portable computers, corporate networks and the Internet. This service enables employees to access e-mail and other information services from their personal appliance without using the telephone system when meeting with the customers, traveling in the car, or staying in a hotel room.
• Narrowband Personal Communications Services (PCS), a spectrum allocated at 1.9 GHz, is a new wireless communications technology offering wireless access to WWW, e-mail, voice mail, and cellular phone service. These developments paved way for various other related developments such as Bluetooth Technology and Wireless Application Protocol Services.
Architecture of Wireless Nerworks
Networks perform many functions to transfer information from source to destination such as a bit pipe for data transmission, sharing of a common medium by medium access techniques, synchronization and error control mechanisms as well as routing mechanisms. Network architecture describes the protocols, major hardware and software elements that constitute the nwetwork.
There are two views of a computer architecture:
a) Logical View:
A logical architecture defines the network’s protocols – rules by which the two entities communicate. One popular logical architecture is the 7-layer Open System Interconnection (OSI) Reference Model, developed by International Standards Organization (ISO). The OSI layers provide the following network functionality:
Layer 7 – Application Layer: Establishes communication with other users and provides services such as file transfer and e-mail to the end users of the network.
Layer 6 – Presentation Layer: Negotiates data transfer syntax for the application layer and performs translations between different datatypes, if necessary.
Layer 5 – Session Layer: Establishes, manages, and terminates sessions between applications.
Layer 4 – Transport Layer: Provides mechanisms for the establishment, maintenance, and orderly termination of virtual circuits, while shielding the higher layers from the network implementation details.
Layer 3 – Network Layer: Provides the routing of packets from source to destination.
Layer 2 – Data Link Layer: Ensures Synchronization and error control between two entities.
Layer 1 – Physical Layer: Provides the transmission of bits through a communication channel by defining electrical, mechanical and procedural specifications.
Wireless LANs and MANs function only within the Physical and Data Link Layers, which provide the medium, page link synchronization and error control mechanisms. Wireless WANs provide these first two layers as well as Network layer routing.
b) Physical architecture of a wireless network:
The physical components of a wireless network implement the physical, data page link and network layer functions. The Network Operating System (NOS) located on client and server machines, communicates with the wireless Network Interface Card (NIC) via driver software, enabling the applications to utilize the wireless network for data transport.
Slide 2
Features of physical architecture:
End User Appliances: It is a visual interface between the user and the network. Various end user appliances are Desktop workstations, laptops, palmtops, pen based computers, PDAs and pagers.
Network Software: A wireless network supports the NOS and it’s applications, such as word processing, databases, and e-mail, enabling the flow of data between all components.
Wireless Network Interface: It’s function is to couple the digital signal from the end-user appliance to the wireless medium, which is air, to enable an efficient data transfer between sender and receiver. This process includes modulation and amplification.
It also manages the use of air for communications and synchronization through a carrier sense protocol. This protocol enables a group of wireless computers to share the same frequency and space. According to the protocol, to avoid two people speaking at the same time, you should wait until the other person has finished talking. Also, no one should speak unless the room is silent.
Wireless networks handle error control by having each station check incoming data for altered bits. The interface also includes the software driver that couples the client’s applications or NOS software to the card.
Antenna: Antennas come in many shapes and sizes. They have the following characteristics:
Propagation pattern, radiation power, gain, bandwidth.
They are of two types unidirectional and omni directional.
The communications channel: All information systems employ a communications channel along which information flows from source to destination.
