Chapter 7: Transmission Media & Devices

For computers to communicate, they must be physically or wirelessly connected.

7.1 Transmission Media (Channels)

Transmission media are the pathways that carry data signals from one computer to another. They are broadly divided into two categories.

7.1.1 Wired Communication Media (Guided Media)

Data travels through solid physical conductors.

1. Twisted Pair Cable:
   • Consists of pairs of insulated copper wires twisted together. Twisting reduces electromagnetic interference (noise).
   • Common in older telephone systems and standard local networks (Ethernet).
   • Pros: Inexpensive, easy to install.
   • Cons: Susceptible to noise, lower bandwidth, short range.
2. Coaxial Cable:
   • Has an inner copper core surrounded by an insulating layer, covered by a braided metal shield, and an outer plastic jacket.
   • Often used for cable television lines.
   • Pros: Better shielding than twisted pair, higher bandwidth, longer range.
   • Cons: Thicker, less flexible, slightly more expensive.
3. Fiber-Optic Cable:
   • Made of thin strands of glass or plastic.
   • Uses pulses of light to transmit data instead of electrical signals.
   • Pros: Extremely high bandwidth, very fast, immune to electromagnetic interference, very secure, transmits over very long distances.
   • Cons: Very expensive, fragile, difficult to install and splice.

7.1.2 Wireless Media (Unguided Media)

Data travels through the air or space using electromagnetic waves.

1. Radio Waves:
   • Used for AM/FM radio, television, and mobile phones.
   • Omnidirectional (travel in all directions). Can penetrate solid objects (walls).
2. Microwaves:
   • Used for point-to-point communication (like between tall antennas) and satellite communication.
   • They require line-of-sight (antennas must see each other without obstacles). Cannot easily penetrate solid objects.
3. Infrared Waves:
   • Used for short-range communication.
   • Cannot penetrate solid objects (e.g., a TV remote control sending signals to a TV).

7.2 Network Devices

Network devices are physical hardware components used to connect computers together and regulate traffic.

1. Modem (Modulator-Demodulator): Converts digital signals from a computer into analog signals to travel over telephone lines, and vice versa. It literally connects your home to your Internet Service Provider (ISP).
2. Ethernet Card (Network Interface Card - NIC): A hardware component installed in a computer that allows it to connect to a network. It provides the physical connection port.
3. RJ45 (Registered Jack 45): This is the physical plastic connector (the plug) at the end of an Ethernet twisted-pair cable.
4. Repeater: An electronic device that receives a weak signal, cleans it, amplifies it, and retransmits it so the data can travel longer distances without degradation.
5. Hub: A simple device that connects multiple computers. It operates via broadcasting: when it receives an incoming data packet, it blindly sends it out to all other connected ports. It is considered “dumb” and creates a lot of unnecessary network traffic.
6. Switch: A much “smarter” alternative to a hub. A switch connects devices, but it learns the MAC addresses of connected devices. When it receives a packet, it sends it only to the specific intended destination port, reducing network congestion significantly.
7. Router: Operates at a higher level than switches. Routers connect completely different networks together (like connecting your home network to the global Internet). They read IP addresses and determine the best path (route) for packets to travel to reach their final destination.
8. Gateway: A device (or software) that acts as a bridge between two networks that use completely different protocols. It translates the data so the two incompatible networks can communicate.
9. Wi-Fi Card: Similar to an Ethernet card, but it contains a radio antenna to allow a computer to connect to a network wirelessly.