Easy Notes Of Data Communication and Computer Network unit-2 @Computer Diploma

Description

Unit II: Transmission Media and Switching – Key Concepts

2.1 Guided Transmission Media (Bounded Media)

Keywords focus on structure, performance metrics, and standards:

• • Twisted-Pair Cable:

    • Unshielded Twisted Pair (UTP) vs. Shielded Twisted Pair (STP): Key distinction based on electromagnetic interference (EMI) protection.

    • Crosstalk: Signal interference between adjacent twisted pairs.

    • Category Ratings (e.g., Cat 5e, Cat 6, Cat 7): Standards defining performance and data rate (bandwidth) capabilities.

    • Attenuation: Loss of signal strength over distance.

    • Local Area Network (LAN) Connectivity.

  • Coaxial Cable:

    • Broadband Coaxial (Analog) vs. Baseband Coaxial (Digital): Different modes of data transmission.

    • Radio Frequency (RF) Signal Transmission: The type of signal used.

    • Electromagnetic Shielding (Braid/Foil): Mechanism for noise immunity.

    • Cable Television (CATV) Distribution.

  • Fiber-Optic Cable:

    • Total Internal Reflection: The fundamental principle of light transmission.

    • Core, Cladding, and Jacket: The three main structural components.

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* **Single-Mode Fiber (SMF) vs. Multimode Fiber (MMF):** Distinction based on core diameter and light propagation path.
* **Wavelength Division Multiplexing (WDM):** Technique for transmitting multiple light signals simultaneously.
* **High Bandwidth and Long-Distance Backbone Networks.**

2.2 Unguided Transmission Media (Wireless/Unbounded Media)

Keywords focus on the electromagnetic spectrum, propagation, and applications:

• Radio Waves:

  • Omnidirectional Propagation: Signals travel in all directions.

  • Ground Propagation, Sky Propagation, and Line-of-Sight: Different ways radio waves travel.

  • Multicasting (Broadcasting): Ideal for one sender to many receivers (e.g., AM/FM radio).

  • Low-Frequency/Long-Wavelength Transmission.

• Microwaves:

  • Unidirectional/Directional Antennae (Parabolic Dishes): Required for focused transmission.

  • Terrestrial Microwave (Repeater Towers): Used for line-of-sight communication over land.

  • Satellite Communication (Uplink/Downlink Frequencies): Global coverage using geostationary satellites.

  • High-Frequency Transmission.

• Infrared:

  • Short-Range Communication (IrDA): Applications like TV remotes.

  • Line-of-Sight Transmission (Short Distance): Cannot penetrate walls or solid objects.

  • High Attenuation: Signal loss increases significantly over distance.

2.3 Transmission Modes and Path

Keywords describing signal direction and network scope:

• Line-of-Sight Transmission (LOS): A necessary condition for high-frequency transmissions like microwaves and infrared, requiring a clear path between transmitter and receiver.

• Point-to-Point (Unicast): Communication between exactly two parties (e.g., a phone call).

• Broadcast (Multicast/Simplex): Communication from one transmitter to multiple receivers simultaneously (e.g., radio, television).

2.4 Multiplexing

Keywords describing how a channel’s capacity is shared:

• Multiplexing (MUX) and Demultiplexing (DEMUX): The process of combining and separating multiple data streams.

• Frequency-Division Multiplexing (FDM):

  • Analog Technique: Used primarily for analog signals.

  • Guard Bands: Unused frequency ranges inserted between channels to prevent interference (Crosstalk).

  • Channel Bandwidth Allocation: Each signal is allocated a specific, non-overlapping frequency band.

• Time-Division Multiplexing (TDM):

  • Digital Technique: Primarily used for digital data, but can be used for analog signals as well.

  • Time Slots/Frames: Each signal is allocated a specific, recurring time interval on the shared link.

  • Synchronization Pulse: Required to keep the MUX and DEMUX in sync.

  • Synchronous TDM vs. Asynchronous (Statistical) TDM: Distinction based on fixed vs. dynamic time slot allocation.

2.5 Switching

Keywords describing the method of establishing communication links:

• Circuit-Switched Network:

  • Connection-Oriented: A dedicated path (circuit) must be established before communication begins.

  • Fixed Bandwidth Allocation: The capacity is reserved for the entire duration of the connection.

  • Dedicated Physical Path: The path remains exclusively reserved even during idle times.

  • Constant Bit Rate (CBR) Transmission: Ideal for real-time applications like traditional telephone networks.

  • Call Setup Delay: Delay incurred before data transfer begins.

• Packet-Switched Network:

  • Connectionless (Datagram Approach) vs. Connection-Oriented (Virtual Circuit Approach): The two main methods of packet routing.

  • Store-and-Forward Networking: Routers temporarily store packets before forwarding them.

  • Dynamic Bandwidth Sharing (Statistical Multiplexing): Bandwidth is allocated on demand, leading to better link utilization.

  • Variable Latency/Jitter: Delay can vary due to network congestion (queueing delay).

  • Header and Payload (Packet Structure): Data is broken into small, individually addressed units called packets.