Learning Objectives
By the end of this chapter, you will be able to:
- Identify the components of a data communication system.
- Differentiate between guided (wired) and unguided (wireless) transmission media.
- Identify common types of wired media, such as twisted-pair and fiber optic cable.
- Define bandwidth and its importance in data transmission.
- Explain transmission modes (simplex, half-duplex, full-duplex), and serial vs parallel transmission.
Components of Data Communication
Every data communication system has five components:
- Sender — the device that sends the message (e.g., a computer).
- Receiver — the device that receives it (e.g., a server or phone).
- Message — the data being sent (text, image, audio, video).
- Transmission medium — the path the message travels (cable or air).
- Protocol — the rules both sides follow so they understand each other.
Data Communication Media
Transmission media is the physical path between the sender and receiver in a data communication network. It is the channel through which data is sent from one place to another. Transmission media can be broadly classified into two categories.
flowchart TB
TM[Transmission Media]
TM --> GUIDED[Guided - Wired]
TM --> UNGUIDED[Unguided - Wireless]
GUIDED --> TP[Twisted-Pair]
GUIDED --> COAX[Coaxial Cable]
GUIDED --> FIBER[Fiber Optic]
UNGUIDED --> RADIO[Radio Waves]
UNGUIDED --> MICRO[Microwaves]
Figure 1: Guided vs Unguided Transmission Media
1. Guided (Wired) Media
In guided media, the signal is directed along a physical path.
- Twisted-Pair Cable: Consists of pairs of insulated copper wires twisted together. It is the most common type of media, used in traditional telephone lines and Ethernet networks (LAN cables).
- UTP (unshielded twisted pair) is cheap and common in offices (Cat 5e, Cat 6); STP (shielded) adds protection against interference.
- Coaxial Cable: Has a single copper conductor at its center, surrounded by a layer of insulation and a metallic shield. It is used for cable television and early computer networks.
- Fiber Optic Cable: Transmits data as pulses of light through thin strands of glass or plastic. It is much faster than copper cables, has a much higher bandwidth, and is less susceptible to interference. It is the backbone of the modern internet.
| Aspect | Twisted pair | Coaxial cable | Fiber optic |
|---|---|---|---|
| Signal | Electrical | Electrical | Light |
| Bandwidth / speed | Low to moderate (up to ~10 Gbps over short runs) | Moderate | Very high (many Gbps and beyond) |
| Distance | Short (about 100 m per run) | Medium | Very long (many kilometers) |
| Interference | Affected by electrical noise | Better shielded | Immune to electrical interference |
| Cost | Cheapest | Moderate | Highest to install and repair |
| Typical use | Office LANs, telephone lines | Cable TV, older networks | Internet backbone, FTTH, between buildings |
2. Unguided (Wireless) Media
In unguided media, the signal is broadcast through the air or space.
- Radio Waves: Used for a wide range of communication, including Wi-Fi, Bluetooth, and cellular networks. They travel in all directions and can pass through walls.
- Microwaves: Used for point-to-point communication and satellite communication. Terrestrial microwave needs line of sight between dish antennas on towers, which is why towers are placed on hilltops.
- Infrared: Short-range, line-of-sight communication, as in TV remote controls; cannot pass through walls.
- Satellite: A microwave relay station in space that covers very large areas, useful for remote regions, TV broadcasting, and ships.
Data Transmission Concepts
- Signal: Data is transmitted as an electromagnetic signal, which can be either analog (a continuous wave) or digital (a series of discrete pulses).
- Bandwidth: This refers to the transmission capacity of a network, stated in bits per second (bps). It is the maximum amount of data that can be transmitted over a network connection in a given amount of time.
- Throughput: The actual amount of data transferred per second, often lower than the bandwidth because of congestion, distance, or interference.
- Latency: The delay before data begins to arrive, measured in milliseconds.
flowchart LR
SIMP[Simplex<br/>One direction only] --- HALF[Half-Duplex<br/>Both ways, not at once] --- FULL[Full-Duplex<br/>Both ways simultaneously]
Figure 2: Data Transmission Modes
Worked example: a 50 MB file over a 20 Mbps connection takes about 50 × 8 ÷ 20 = 20 seconds in ideal conditions. If the actual throughput is only 10 Mbps, it takes about 40 seconds.
Transmission modes (direction of flow)
| Mode | Direction | Example |
|---|---|---|
| Simplex | One direction only | Keyboard to computer, TV broadcast |
| Half-duplex | Both directions, but one at a time | Walkie-talkie |
| Full-duplex | Both directions at the same time | Telephone call, modern Ethernet |
Serial vs parallel transmission
- Serial: bits are sent one after another over a single channel; used for long distances (USB, network cables).
- Parallel: several bits are sent at the same time over multiple wires; fast over very short distances (inside the computer), but signals get out of step over longer cables.
Nepal Context
Nepal’s internet backbone relies on optical fiber laid along highways and connected to India for international links, while microwave towers on hilltops and satellite links serve areas where laying fiber is difficult. Inside homes and offices, FTTH fiber brings the connection to the door, UTP cables connect desktops, and Wi-Fi radio waves connect phones and laptops — a single connection often uses several media.
Summary
Data communication needs a sender, receiver, message, medium, and protocol. Transmission media carry signals from a sender to a receiver. This media can be guided (wired), such as twisted-pair, coaxial, and high-speed fiber optic cables, or unguided (wireless), such as radio waves, microwaves, infrared, and satellite. The capacity of these media to transmit data is measured by their bandwidth, while throughput and latency describe real performance. Data can flow in simplex, half-duplex, or full-duplex modes, and be sent serially or in parallel. Understanding these physical layer components is the first step in understanding computer networking.
Key Takeaways
- A data communication system has five components: sender, receiver, message, medium, and protocol.
- Transmission media can be guided (wired) or unguided (wireless).
- Fiber optic cable is the fastest type of guided media.
- Radio waves are the basis for most modern wireless communication.
- Bandwidth measures the data transmission capacity of a network.
- Simplex, half-duplex, and full-duplex describe the direction of data flow.
Discussion Questions
- What are the main advantages of fiber optic cable over twisted-pair copper cable?
- Why is wireless communication more susceptible to interference than wired communication?
- What is the difference between bandwidth and the speed of your internet connection?
Exam-Style Questions
Short answer
- List the five components of data communication.
- Differentiate between guided and unguided media.
- Differentiate between simplex, half-duplex, and full-duplex with examples.
Long answer
- Compare twisted-pair, coaxial, and fiber optic cables.
- Explain unguided transmission media and their uses, with examples from Nepal.
