What are the Characteristics of wireless media

Many users opt for wireless transmission media because it is more convenient than installing cables. In addition, businesses use wireless transmission media in locations where it is impossible to install cables. Types of wireless transmission media used in communications include infrared, broadcast radio, cellular radio, microwaves, and communications satellites.

Infrared

As discussed earlier in the chapter, infrared (IR) is a wireless transmission medium that sends signals using infrared light waves. Mobile computers and devices, such as a mouse, printer, and smart phone, often have an IrDA port that enables the transfer of data from one device to another using infrared light waves.

Broadcast Radio

Broadcast radio is a wireless transmission medium that distributes radio signals through the air over long distances such as between cities, regions, and countries and short distances such as within an office or home. Bluetooth, UWB, Wi-Fi, and WiMAX communications technologies discussed earlier in this chapter use broadcast radio signals.

Cellular Radio

Cellular radio is a form of broadcast radio that is used widely for mobile communications, specifically wireless modems and cell phones. A cell phone is a telephone device that uses high-frequency radio waves to transmit voice and digital data messages.

Some mobile users connect their notebook computer or other mobile computer to a cell phone to access the Web, send and receive e-mail, enter a chat room, or connect to an office or school network while away from a standard telephone line. Read Looking Ahead 8-2 for a look at the next generation of cellular communications.

Personal Communications Services (PCS) is the term used by the United States Federal Communications Commission (FCC) to identify all wireless digital communications. Devices that use PCS include cell phones, PDAs, pagers, and fax machines. 

Microwaves

Microwaves are radio waves that provide a high-speed signal transmission. Microwave transmission, often called fixed wireless, involves sending signals from one microwave station to another (shown in Figure 8-1 on page 296). Microwaves can transmit data at rates up to 4,500 times faster than a dial-up modem.

A microwave station is an earth-based reflective dish that contains the antenna, transceivers, and other equipment necessary for microwave communications. Microwaves use line-of-sight transmission. To avoid possible obstructions, such as buildings or mountains, microwave stations often sit on the tops of buildings, towers, or mountains.

Microwave transmission is used in environments where installing physical transmission media is difficult or impossible and where line-of-sight transmission is available. For example, microwave transmission is used in wide-open areas such as deserts or lakes; between buildings in a close geo- graphic area; or to communicate with a satellite. Current users of microwave transmission include universities, hospitals, city governments, cable television providers, and telephone companies. Home and small business users who do not have other high-speed Internet connections available in their area also opt for lower-cost fixed wireless plans. 

Communications Satellite

A communications satellite is a space station that receives microwave signals from an earth-based station, amplifies (strengthens) the signals, and broadcasts the signals back over a wide area to any number of earth-based stations.

These earth-based stations often are microwave stations. Other devices, such as smart phones and GPS receivers, also can function as earth-based stations. Transmission from an earth-based station to a satellite is an uplink. Transmission from a satellite to an earth-based station is a downlink.

Applications such as air navigation, television and radio broadcasts, weather forecasting, video conferencing, paging, global positioning systems, and Internet connections use communications satellites. With the proper satellite dish and a sat- ellite modem card, consumers access the Internet using satellite technology. With satellite Internet connections, however, uplink transmissions usually are slower than downlink transmissions. This difference in speeds usually is acceptable to most Internet satellite users because they download much more data than they upload. Although a satellite Internet connection is more expensive than cable Internet or DSL connections, sometimes it is the only high-speed Internet option in remote areas. 

We will discuss several aspects of networks in this lecture. First the communications channels, the transmission medium that the data is transferred over. The transmission medium consists of materials or techniques capable of carrying a signal. Then we will discuss transmission characteristics, which includes things like the transmission mode, transmission direction, and transmission rates. Then we will discuss transmission software, and finally transmission devices any type of  hardware capable of transmitting data, instructions, and information between a sending device and a receiving device. The last thing we will cover is types of networks, such as LAN, and WAN.

TRANSMISSION MEDIUMS

We have two groups of mediums to cover, physical and wireless.

Physical Transmission media

These are cables usually used in buildings, or underground. The three main types of physical transmission mediums I will cover are twisted pair lines, coaxial cable, and fiber-optic cable

• Channel's capacity is rated by the number of bits it can transmit per second
  • Modems often have a bps rating - 28bps, 33bps, 54bps
  • To the average user the baud rate is basically the same thing as bps rating
• Twisted pair wire
  • One of the most commonly used transmissions medias
  • Link your telephone with the telephone system
  • Two insulated copper wires twisted together
• Coaxial cable
  • Copper wire that permits high-speed transmissions with a minimal signal distortion
  • Hooked up any stereos, VCRs, or TVs lately?
  • Not used much today because other transmission media such as fiber-optic cable transmit signals at faster rates.
• Fiber optic cable
  • Glass fibers thinner than a strand of hair
  • Carry data faster, are lighter, less expensive (sorta)
  • Twisted pair and coaxial cable carry data as electrical signals
  • Fiber optic carries data as laser-generated pulses of light
  • Harder to intercept pulses of light than electrical signals

Wireless Transmission Media

Wireless transmission is becoming more and more popular these days. One of the leading protocols that is being used is called 802.11b. The sub and a few other buildings on campus are talking about putting in a wireless network using 802.11, this means that if you turn on your laptop in the sub and you have a 802.11 modem you will have Internet access without plugging in a cable.

Here are some other wireless protocols:

• Broadcast Radio
  • Wireless transmission medium that distributes radio signals through the air over long distances such as between cities, regions, and countries.
  • AM/FM radio is broadcast radio.
  • Slower and more susceptble to noise than physical transmission media.
  • Provides flexibility and portability
• BlueTooth
  • Proposed radio frequency
  • Short range wireless communications
  • Range is from 10 to 100 meters
  • Wireless mice and keyboards are beginning to use this technology. 
• Cellular Radio
  • Broadcast Radio
  • Cell phones are the same
• Microwaves
  • Radio waves that provide a high-speed signal transmission.
  • Limited to line-of-site
• Communications Satellite
  • Space station that recieves microwave signals from an Earth-based station
  • 22,300 miles above the Earth's equator
  • These satelites orbit at the same rate as the Earth, they are considered geosynchronous satelites
• Infared
  • Wireless transmission media that sends signals using infrared light waves.
  • Requires line of site.

TRANSMISSION CHARACTERISTICS

Characteristics include signal type, transmission mode, transmission direction, and transmission rate.

Signal Type

• Analog - continuous electrical wave
• Digital - individual electrical pulses that represent the bits grouped together into bytes.

Transmission Modes

How the bits are moved between devices

• Asynchronous - send at anytime, no synchronization needed.
• Synchronous - sending large blocks of bytes at regular intervals, everything is synchronized.

Transmission direction

• simplex - sends only in one direction (mouse only needs to send the signal one direction).
• half-duplex -  Data can flow in both directions, just not at the same time.(walkie-talkie).
• full-duplex - Data can flow both directions at the same time. (phone line).
  

Transmission rate

• The speed in which a transmission medium can carry data
• expressed in bits per second
• Bandwidth - The quantity of information which can be transferred through a connection. This is generally measured in bits-per-second.
• Broadband vs. Baseband
  • Baseband - Some types of media can transmit only one signal at a time.
  • Broadband -  Some types of media can transmit multiple signals simultaneously
    • CableTV - all the channels you receive come across the line at the same time.

Common carriers that you can get from the phone companies

• Private line - dedicated channel between two points
  • Pay for it whether you use it or not
  • More reliable
  • More secure
• Switched line
  • Pay for only the time you use it
  • Greater flexibility
• ISDN - Integrated Services Digital Network
  • Source-to-destination digital channel
  • No need for modems
• DSL -Digital Subscriber Line
• Uses sophisticated techniques to transmit a greater number of bytes over your normal phone lines.
• Changes a baseband phone line to Broadband.
• Bridgeband and Multiband are two companies that provide DSL in Bozeman.
• T - lines
  • T1 lines are much more expensive, they are equivalent to 24 phone lines.
  • MSU has five T1 lines connecting to Spokane
  • T3 lines are even more expensive, usually just for very large Internet companies, these lines are equivalent to 28 T-1 lines

TRANSMISSION SOFTWARE

• Telnet
• FTP - a protocol for transferring files from one computer to another computer.
• Terminal emulation mode - allows a personal computer to act as a specific type of terminal, allows the PC to access data and resources on a server or mainframe computer.

COMMUNICATION DEVICES

The hardware that allows or helps allow the transmitting of data, instructions, and information between a sending device and a receiving device.

What are the four types of wireless media?

What are the 3 types of wireless media?

What is the function of wireless media?

Which media is wireless media?