notes-shivam

02 Transmission media and characteristics

5 min read

  • 1. Transmission Media and Their Characteristics
    • [[#1. Transmission Media and Their Characteristics#1.1 Characteristics of Transmission Media|1.1 Characteristics of Transmission Media]]
  • 2. Guided and Unguided Transmission Media
    • [[#2. Guided and Unguided Transmission Media#2.1 Guided Media (Wired)|2.1 Guided Media (Wired)]]
      • [[#2.1 Guided Media (Wired)#a. Twisted Pair Cable|a. Twisted Pair Cable]]
      • [[#2.1 Guided Media (Wired)#b. Coaxial Cable|b. Coaxial Cable]]
      • [[#2.1 Guided Media (Wired)#c. Optical Fiber Cable|c. Optical Fiber Cable]]
    • [[#2. Guided and Unguided Transmission Media#2.2 Unguided Media (Wireless)|2.2 Unguided Media (Wireless)]]
      • [[#2.2 Unguided Media (Wireless)#a. Radio Waves|a. Radio Waves]]
      • [[#2.2 Unguided Media (Wireless)#b. Microwaves|b. Microwaves]]
      • [[#2.2 Unguided Media (Wireless)#c. Infrared|c. Infrared]]
      • [[#2.2 Unguided Media (Wireless)#d. Satellite Communication|d. Satellite Communication]]
  • 3. Synchronous and Asynchronous Transmission
    • [[#3. Synchronous and Asynchronous Transmission#3.1 Asynchronous Transmission|3.1 Asynchronous Transmission]]
      • [[#3.1 Asynchronous Transmission#Advantages:|Advantages:]]
      • [[#3.1 Asynchronous Transmission#Disadvantages:|Disadvantages:]]
    • [[#3. Synchronous and Asynchronous Transmission#3.2 Synchronous Transmission|3.2 Synchronous Transmission]]
      • [[#3.2 Synchronous Transmission#Advantages:|Advantages:]]
      • [[#3.2 Synchronous Transmission#Disadvantages:|Disadvantages:]]

1. Transmission Media and Their Characteristics

definition

  1. Transmission media refer to the physical pathway or channel through which data is transmitted from one point to another in a communication system.
  2. It can be wired (guided) or wireless (unguided).

1.1 Characteristics of Transmission Media

  1. Bandwidth: Refers to the capacity of the medium to carry data, measured in Hz or bps.

  2. Delay: Time taken for data to travel from source to destination (propagation delay).

  3. Noise: Unwanted signals that interfere with the transmission, causing data corruption.

  4. Attenuation: Signal loss over distance; requires amplification or repeaters.

  5. Cost and Installation: Depends on the type of media; fiber optics are expensive, while twisted pair is cheaper.

  6. Transmission Impairments: Includes distortion, attenuation, and interference.

  7. Security: Wired media are more secure than wireless as they are harder to tap.

2. Guided and Unguided Transmission Media

2.1 Guided Media (Wired)

Data signals are transmitted through a physical medium like cables.

a. Twisted Pair Cable

  • Consists of pairs of insulated copper wires twisted together.
  • Types: UTP (Unshielded), STP (Shielded).
  • Use: Telephony, LANs.
  • Pros: Cheap, easy to install.
  • Cons: Prone to interference, limited bandwidth.
  • Bandwidth: Up to 100 Mbps or more (Cat6/Cat7).
  • This is the least expensive and most widely used guided transmission medium.
  • In twisted pair technology, two copper wires are strung between two points.
  • The two wires are typically twisted together in a helix to reduce interference between the two conductors.
  • Twisting decreases the cross-talk interference between adjacent pairs in a cable.
  • Typically, a number of pairs are bundled together into a helix

b. Coaxial Cable

  • Copper core with insulation, metallic shielding, and outer cover.
  • Use: Cable TV, early Ethernet.
  • Pros: Better shielding than twisted pair.
  • Cons: Bulky, more expensive.
  • Bandwidth: Up to 1 Gbps.
  • Coaxial cable consists of a stiff copper wire as the core, surrounded by an insulating material.
  • A cylindrical conductor encases the insulator, often as a closely woven braided mesh.
  • This is enclosed in a protective plastic sheath.
  • The Signal is transmitted by the inner copper wire and is electrically shielded by the outer metal sleeve.
  • Two kinds of coax are widely used: – (Base band coaxial cable) used for digital transmission. – (Broad band coaxial cable) used for analog transmission.

c. Optical Fiber Cable

  • Uses light to transmit data through glass or plastic fibers.
  • Types: Single-mode (long distance), Multi-mode (short distance).
  • Use: Backbone networks, high-speed ISPs.
  • Pros: High speed, low attenuation, immune to EMI.
  • Cons: Expensive, fragile, needs skilled installation.
  • Bandwidth: Tens of Gbps over long distances.
  • The source is a laser which emits light when an electrical current is applied. • The detector converts light energy to electrical signal. • The core and cladding are designed such that the light signal is trapped inside the core and does not escape outside.
  • In fiber optic technology, the medium consists of a hair-width strand of silicon or glass, and the signal consists of pulses of light.
  • For instance, a pulse of light means 1'', lack of pulse means 0”.
  • It has a cylindrical shape and consists of three concentric sections: the core, the cladding, and the jacket as shown in following figure.
  • Optical fibers may be single mode or multimode.
  • Single mode fibers allow the light to travel in a straight line and require Laser as source.

2.2 Unguided Media (Wireless)

Data is transmitted through air or vacuum using electromagnetic waves.

a. Radio Waves

  • Frequency: 3 kHz – 1 GHz.

  • Use: AM/FM radio, mobile phones, wireless LANs.

  • Pros: Covers long distance, omnidirectional.

  • Cons: Subject to interference.

b. Microwaves

  • Frequency: 1 GHz – 300 GHz.

  • Use: Satellite, cellular networks, microwave links.

  • Pros: High frequency, used in point-to-point links.

  • Cons: Requires line-of-sight, affected by weather.

c. Infrared

  • Frequency: 300 GHz – 400 THz.

  • Use: Remote controls, short-range communication.

  • Pros: Secure, line-of-sight, no interference.

  • Cons: Short range, cannot pass through walls.

d. Satellite Communication

  • Uses geostationary or low-earth orbit satellites.

  • Use: Global communication, TV broadcast, GPS.

  • Pros: Wide coverage.

  • Cons: High cost, propagation delay.

3. Synchronous and Asynchronous Transmission

These are two methods of transmitting data between devices.

3.1 Asynchronous Transmission

  1. Data sent one byte at a time, each with a start and stop bit.

  2. No clock signal is shared; receiver uses the start/stop bits for timing.

  3. Slower and less efficient due to extra bits.

  4. Suitable for low-speed, infrequent data transfer.

  5. Example: Keyboard to computer communication, RS-232 protocol.

Advantages:

  • Simple and cost-effective.

  • Ideal for small amounts of data.

Disadvantages:

  • Lower efficiency.

  • Higher overhead due to start/stop bits.

3.2 Synchronous Transmission

  1. Data sent in blocks or frames without start/stop bits.

  2. Requires synchronized clocks between sender and receiver.

  3. Efficient for large data volumes and high-speed transmission.

  4. Used in networks and high-speed communication systems.

  5. Example: Ethernet, HDLC protocol.

Advantages:

  • High efficiency and speed.

  • Suitable for real-time applications.

Disadvantages:

  • Complex setup with synchronization.

  • More expensive hardware.

Let me know if you’d like diagrams or comparisons in tabular form for quick revision.

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