Fundamentals of Information Technology

Transmission Media

What is a Channel?The communications path between two communications devices.

Bandwidth: Width of the communications channel

The higher the bandwidth, the more data

and information the channel can transmit

Transmission Media

• Materials or techniques capable of carrying one or more signals

• When you send data from your computer to another device, the signal carrying the data most likely travels over a variety of transmission media

Can you identify two examples of transmission media in the picture?

Characteristics of Transmission Media

1. Voiceband: transmit data at a rate of 300bps(bits per second). Eg. Via telephone lines (twisted pair wires)

2. Broadband: transmits data at a rate of thousands of characters per second (cps). Eg. Via coaxial cable (used in Cable TV)and fibreoptic cables (used in video conferencing).

3. Narrowband: transmits data at rates less than 300bps. Eg. Used in telegraph lines

4. Physical Media: transmits data through physical cables/wires that can be touched.

5. Wireless Media: transmits data through the air.

Baseband vs Broadband

• Baseband media can transmit only one signal at a time

• Broadband media can transmit multiple signals simultaneously

Physical vs Wireless Media

Physical Media

• Twisted Pair Cable

• Coaxial Cable

• Fibre Optic Cable

Wireless Media

• Broadcast radio

• Cellular radio

• Microwave

• Satellite

• Infrared

• Bluetooth

• 802.11

• Wi-fi

Physical Transmission Media: Transfer Rate

• Transfer Rate refers to the speed with which a line carries data and information.

• The faster the transfer rate, the faster you can send and receive data and information

• This is measured in bps(bits per second).

• Larger units include: Kilobits Per

Second(kbps) Megabits Per Second

(mbps) Gigabits Per Second

(gbps)

Twisted Pair Cable

• Consists of one or more twisted pair wires bundled together

• Each twisted pairwire consists of two separate insulated copper wires

• Twisted together to reduce noise

• Two types are:– Shielded Twisted Pair

(STP)– Unshielded Twisted Pair

(UTP)

twisted pair

cable

twisted pair

wire

Advantages and Disadvantages of Twisted Pair Cable

Advantages

• Inexpensive and readily available

• Flexible and light weight

• Easy to set up and install

Disadvantages

• Susceptible to interference and noise– Noise is an electrical

disturbance that can degrade communications

• Low bandwidth

Coaxial Cable

• Consists of a single copper wire surrounded by at least three layers

• Often called coax

• Often used for cable television wiring

Advantages and Disadvantages of Coaxial Cables

Advantages

• Less susceptible to interference than twisted pair

• Higher bandwidth than twisted pair

• Better shielding allow for higher transfer rates

Disadvantages

• Bulky

• Expensive over long distances

Fibre Optic Cable

• Contains a core of dozens or hundreds of thin strands of glass or plastic

• Uses light to transmit signals• Each strand is called an optical fibre

Thin as a human hair

Advantages and Disadvantages of fibre-Optic Cables

Advantages

• Able to carry significantly more signals than wire

• Faster data transmission

• Less susceptible to noise from other devices

• Better security for signals during transmission

• Smaller physical size

Disadvantages

• Costs more than twisted pair and coaxial cable

• Can be difficult to install and modify

• More expensive over shorter distances

Wireless Transmission Media

Broadcast Radio

• …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.

• Transfer rate = up to 54 Mbps

Cellular Radio

• a form of broadcast radio that is used widely for mobile communications, specifically wireless modems and cellular telephones.

• Transfer rate = 9,600 bps to 384 Kbps

Infrared Transmission

• Uses infrared light signals to transmit signals to transmit data

• used for very short range communication purposes such as television and it’s remote.

• Infrared travels in a straight.

• Infrared cannot cross wall-like obstacles. i.e it requires line-of-sight transmission.

• Many computers and devices have an IrDA port that enables transfer of data using infrared light rays.

• Transfer rate= 1 Mbps- 4 Mbps

Bluetooth

• Uses short-range radio waves to transmit data at a rate of 1 Mbps among Bluetooth-enabled devices.

• To communicate between each other a small chip is embedded in the devices.

• Bluetooth-enabled devices include desktop PC, notebook PC, hand-held computers, Internet appliances, cellular telephones, fax machines and printers.

Microwaves

• …radio waves that provide a high- speed signal transmission.

• Earth-based reflective dish that contains antenna, transceivers, and other equipment necessary for microwave communications.

Communications Satellites

• 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.

• Transfer rate = Up to 1Gbps

Wi-Fi (short for Wireless Fidelity)

• Provides high-speed wireless access to a network using radio waves

• Wireless LAN (or WLAN) provides easy access to information between wireless devices from different manufacturers

• Devices with Wi-Fi can connect to the Internet if a wireless network is in a certain range

• Hotspot is a public area as small as a room or as large as many square miles that offers Internet access over a wireless LAN. These might include cafes, airports, and hotels.