WIRELESS NETWORKS

TYPES OF WIRELESS NETWORK There are three types of Wireless Network and the uses of each are described below.  Wireless networks can be divided into three categories based on their technology:  a. Wireless LAN (Local Area Networks) b. Extended Local Area Networks c. Mobile Computing The primary difference between these categories is the transmission facilities.  Wireless LANs and Extended LANs use transmitters and receivers owned by the company in which the network operates.  Mobile computing uses public carriers and the local telephone companies and their public service, to transmit and receive the signals.  A.Wireless LAN (Local Area Networks) In this wireless LAN system, a wireless network adapter card with a transceiver is installed into each computer, and users communicate with the network just as if they were at cabled comouters. The transceiver, sometimes called an access point, broadcasts and receives signals to and from the surrounding computers and passes data back and forth between the wireless computers and the cabled network. These wireless LANs use small wall-mounted transceiver to connect to the wired network. The transceivers establish radiocontact with portable networked devices.

Network Introduction Network Cabling Wireless Network Network Interface Card OSI Model Protocols Ethernet - Network architecture Token Ring - Network architecture AppleTalk and ArcNet - Network architectures Repeaters, Bridges, Routers, and Gateways E-mail Standards Modem & Async Comm. T1, T3, and Switched 56 Digital Connectivities Packet-Switching Network,Frame Relay and ATM ISDN & FDDI

Wireless LANs use four techniques for transmitting data: Infrared, Laser, Narrow-band (single-frequency) radio, andSpread-spectrum radio.

The infrared method can transmit signals at high rates because of infrared light?s high bandwidth. An infrared network can normally broadcast at 10 Mbps. While the speed of infrared and its convenience are generating interest, infrared hasas difficulty transmitting distances greater than 100 feet. It is also subject to interference from the strong ambient light found in most business environments.

Laser technology is similar to infrared in that it requires a direct line of sight, and any person or thing that breaks the laser beam will block the transmission.

The narrow-band (single-frequency) radio approach is similar to broadcasting from a radio station. The user tunes both the transmitter and the receiver to a certain frequency. This does not require line of sight focusingg because the broadcast range is 5,000 meters square. However, because the signal is high frequency, it cannot go through steel or load-bearingg walls. This method is relatively slow where the transmission is in the 4.8 Mbps range.

Spread-spectrum radio broadcasts signals over a range of frequencies. This helps it avoid narrow-band communication problems. The available frequencies are divided into channels or hops. The spread-spectrum adapters tune in to a specific hop for a predeter-mined length of time and then switch to a different hop.

Other types of wireless components are able to do jobs in the extended LAN environment similar to their cabled counterparts. A wireless LAN bridge, for example, can connect networks up to three miles apart.

A wireless bridge offers an easy way to link buildings without using cable. As a foot bridge provides a path between two points for people, a wireless bridge provides a data path between two buildings. If the wireless bridge will not reach far enough, an organization might consider a long-range wireless bridge. These also use spread-spectrum radio technology to provide both ethernet and token ring bridging for up to 25 miles.

C. Mobile Computing

Wireless, mobile networks involve telephone carriers and public services to transmit and receive signals using:

1. Packet-radio communication

2. Cellular network

3. Satellite stations

In a packet-radio communication, the system breaks a transmission into packets, similar to other network packets, that include the source address, the desti-nation address, and error-correction information. The packets are uplinked to a satellite which broadcast them. Only devices with the correct address can receive the broadcast packets.

The Cellular Network or Cellular Digital Packet Data (CDPD) uses the same technology and some of the same systems as cellular telephones. In a satellite systems, a microwave system is commonly used. Microwave systems are good for interconnecting buildings in small, short-distance systems such as those on a campus or in an industrial park.

A microwave is excellent for communicating between two line of sight points such as satellite to ground links and between two buildings. A microwave system consists of :

• Two radio transceivers: one to generate (transmitting station) and one to receive (receiving station) the broadcast.
• Two directional antennas pointed at each othe to implement communication of the signals broadcast by the transceivers. These antennas are often installed on towers to give them more range and raise them above anything which might block their signals.

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