UNIT 2: Transmission Media and Network Components

2.1. Transmission Media

Transmission Media refers to the physical pathways used to transmit data between network devices. It can be divided into two broad categories: wired (guided) media and wireless (unguided) media.

2.1.1. Principles of Transmission Media

Transmission media are the channels through which data signals travel from the sender to the receiver. The principles of transmission media are based on the following concepts:

Signal Transmission: Data is transferred in the form of signals (either electrical, optical, or electromagnetic waves) through these media.
Signal Integrity: The ability of the medium to maintain signal quality over a distance is crucial.
Bandwidth: The capacity of the medium to carry data. Higher bandwidth means more data can be transmitted at once.
Attenuation: Signal strength reduces over long distances, and this is known as attenuation. Some media have higher attenuation rates than others.
Interference: External sources like electromagnetic radiation may interfere with the signal, reducing its quality.

2.1.2. Issues and Examples of Transmission Media

Issues in Transmission Media:

Attenuation: The signal weakens as it travels through the medium. It is most pronounced over long distances, requiring amplifiers or repeaters.
Noise and Interference: External environmental factors (like electrical machines, other cables) cause unwanted signals, degrading the data integrity.
Bandwidth Limitation: Different transmission media have varying bandwidth capacities. Higher bandwidth allows more data transmission, but some media are more limited in bandwidth.
Cost: Some transmission media, like fiber optics, are expensive to install, while others, like copper cables, are relatively inexpensive.
Distance Limitation: Certain transmission media (like copper wires) have a maximum distance over which they can effectively transmit data.

Examples of Transmission Media:

Wired media: Coaxial cables, twisted pair cables, and fiber optics.
Wireless media: Radio waves, microwaves, and infrared.

2.2. Wired Media

Wired media refers to physical cables that carry data signals. Common types of wired media include:

Coaxial Cable (Coax Cable):
- A copper cable surrounded by insulation, a shield, and an outer cover.
- Advantages: Reliable, relatively low cost, and resistant to electromagnetic interference (EMI).
- Use: Cable TV, broadband internet.
- Diagram:
```
[Copper Core] -> [Insulation] -> [Metal Shield] -> [Outer Cover]
```
Unshielded Twisted Pair (UTP) Cable:
- Consists of pairs of copper wires twisted together. The twisting reduces electromagnetic interference.
- Advantages: Low cost, easy to install, and flexible.
- Disadvantages: Susceptible to EMI in long-distance transmission.
- Use: Telephone lines, Ethernet cables.
- Diagram:
```
[Twisted Pairs of Wires] -> [Insulation]
```
Shielded Twisted Pair (STP) Cable:
- Similar to UTP but has an additional shielding layer to reduce interference.
- Advantages: Higher protection from external interference.
- Use: Ethernet networks, industrial environments.
- Diagram:
```
[Twisted Pairs of Wires] -> [Shielding] -> [Insulation]
```
Fiber Optic Cable:
- Transmits data as light signals through glass or plastic fibers.
- Advantages: Very high bandwidth, low attenuation, resistant to interference.
- Disadvantages: Expensive installation, fragile.
- Use: Long-distance internet, undersea cables, high-speed connections.
- Diagram:
```
[Glass/Plastic Core] -> [Cladding] -> [Outer Jacket]
```

2.3. Wireless Media

Wireless transmission uses electromagnetic waves to carry data. There are several types of wireless media, such as:

HF (High Frequency)
- Frequency range: 3-30 MHz.
- Used in long-range communication, especially for amateur radio and military communications.
- Disadvantages: Prone to atmospheric interference.
VHF (Very High Frequency)
- Frequency range: 30-300 MHz.
- Used for FM radio, television broadcasts, and two-way radios.
- Disadvantages: Limited to line-of-sight communication.
UHF (Ultra High Frequency)
- Frequency range: 300 MHz to 3 GHz.
- Used for mobile phones, Wi-Fi, Bluetooth.
- Advantages: Higher bandwidth, less prone to interference.
Microwave
- Frequency range: 1 GHz to 300 GHz.
- Used for long-distance communication between two fixed locations (like satellite communication).
- Disadvantages: Requires line-of-sight; affected by weather conditions.
Ku Band
- Frequency range: 12–18 GHz.
- Used in satellite communication and broadcasting.
- Advantages: Supports high bandwidth for communication.

2.4. Network Topologies

A network topology defines the physical and logical arrangement of network devices and how they communicate. Common topologies include:

Bus Topology:
- All devices are connected to a single central cable (bus).
- Advantages: Easy to implement.
- Disadvantages: Single point of failure (if the bus fails, the entire network is affected).
- Diagram:
```
[Device]---[Device]---[Device]---[Device] (Single Cable)
```
Star Topology:
- All devices are connected to a central device (usually a switch or hub).
- Advantages: Easy to add devices, easy to manage.
- Disadvantages: Single point of failure at the central hub.
- Diagram:
```
   [Device]
      |
[Hub/Switch]---[Device]
      |
   [Device]
```
Ring Topology:
- Devices are connected in a circular fashion where each device connects to two other devices.
- Advantages: Consistent and predictable data flow.
- Disadvantages: A failure in any one device or connection can disrupt the entire network.
- Diagram:
```
[Device]---[Device]---[Device]
    |                   |
[Device]---[Device]---[Device]
```
Mesh Topology:
- Every device is connected to every other device in the network.
- Advantages: Redundant paths ensure network reliability.
- Disadvantages: Expensive and complex to maintain.
- Diagram:
```
[Device]---[Device]---[Device]
   |         |         |
[Device]---[Device]---[Device]
```
Hybrid Topology:
- A combination of two or more topologies.
- Advantages: Flexible and scalable.
- Disadvantages: Complexity in design and maintenance.
- Diagram:
```
[Star]---[Bus]---[Ring]
```

2.5. Data Link Layer

The Data Link Layer (Layer 2) in the OSI model is responsible for node-to-node data transfer, error detection and correction, and addressing.

2.5.1. Design Issues of Data Link Layer

The design of the data link layer involves various issues:

Error Detection and Correction: Detecting and correcting errors that occur during transmission.
Flow Control: Managing the rate of data transmission to prevent congestion.
Framing: Dividing data into manageable units called frames.
Addressing: Unique identifiers (such as MAC addresses) are used for data transmission between devices.

2.5.2. Example Protocols

Ethernet:
- The most commonly used LAN protocol. It defines how data is formatted and transmitted over the network.
- Standard: IEEE 802.3.
WLAN (Wireless Local Area Network):
- A wireless version of Ethernet, commonly used for Wi-Fi networks.
- Standard: IEEE 802.11.
Bluetooth:
- A short-range wireless communication protocol used for personal area networks (PANs).
- Standard: IEEE 802.15.

2.5.3. Switching Techniques

Switching techniques are used to direct data from the source to the destination in a network:

Circuit Switching:
- A dedicated path is established for communication between two devices for the duration of the session.
- Example: Traditional telephone networks.
Packet Switching:
- Data is divided into packets and sent through the network independently, possibly via different paths.
- Example: Internet data transfer.
Message Switching:
- Entire messages are sent to intermediate nodes, where they are stored and forwarded.
- Example: Email message routing.

Summary

Transmission Media are physical paths for data transmission, either wired (coaxial, UTP, fiber optics) or wireless (HF, VHF, microwaves, Ku-band).
Network Topologies define the arrangement of devices in a network, such as bus, star, ring, mesh, and hybrid topologies.
The Data Link Layer is responsible for data framing, error detection, and node-to-node communication. Example protocols include Ethernet, WLAN, and Bluetooth.

UNIT 2: Transmission Media and Network Components