Transmission Media Quiz

Study Notes

The physical path between the transmitter and the receiver is called the transmission medium or channel.
The physical layer controls and is located below the transmission medium.

Guided media uses a physical cable to transmit signals.
Guided media is divided into 3 types: Twisted-pair cable, Coaxial cable, and Fiber-optic cable
Twisted-pair cable consists of two insulated copper wires twisted in a regular spiral pattern.
Each wire pair acts as a single communication link.
The twists are used to reduce electrical interference from similar pairs close by, more twists means better quality.
Twisted-pair cables are used in telephone networks and local area networks (LANs).

Coaxial cable consists of three concentric sections:
- A center copper wire
- An insulating layer
- A braided copper shield.

Fiber-optic cable consists of a core, cladding, and jacket.
The core is made of glass or plastic fiber and carries the light signal.
The cladding surrounds the core and has a different optical property than the core.
The jacket protects the cable from environmental dangers.

Advantages of fiber-optic cable include:
- Higher bandwidth, supporting data rates of hundreds of Gbps.
- Smaller size and weight.
- Lower attenuation (signal loss), allowing for longer repeater spacing (up to 50 Km without repeaters).
- No crosstalk (no light leaking).
- Not affected by noise.
- Highly secure (no light leaking).
Disadvantages of fiber optic cables include:
- Requires special skills to install.
- More expensive interfaces than electrical interfaces used with other types of cable.

Unguided media transmits signals through air and are available to everyone with a receiving device.
Wireless transmission uses various frequencies on the electromagnetic spectrum.

Radio waves have frequencies less than 300 GHz.
Radio waves propagate in all directions (omnidirectional).
Radio waves support long distances.
Radio waves can be easily interfered with by other signals at the same frequency range.
Used in broadcast radio (AM, FM), TV, and cellular phones.
Radio waves are used for multicast communications (broadcast to many receivers) such as radio and television.

Microwaves have frequencies from 300 MHz to 300 GHz.
Microwaves travel in one direction (unidirectional) using line-of-sight propagation.
Used for point-to-point communication, such as between buildings to connect their LANs.
High-frequency microwaves cannot penetrate walls.
Used in wireless networks and satellite communication.
Microwaves are used for unicast communications (communication with a single receiver) such as cellular telephones, satellite networks, and wireless LANs.

Infrared waves have frequencies from 300 GHz to 400 THz.
Infrared waves have a large bandwidth.
Infrared waves can be used only for local, short-distance communication as they cannot penetrate walls.
Infrared waves use line-of-sight propagation.
Used in local point-to-point transmission.
Applications include: wireless keyboards, mice, remote controls using Infrared Data Association (IrDA) protocol.
Infrared cannot be used under direct sunlight because of interference with the sun’s infrared rays.
IrDA operates at 75 kbps over 8 m, and 1.15 Mbps – 4 Mbps over 1 m.
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.