Digital Transmission Modes

Mode of Digital Transmission

• Parallel transmission uses "n" wires to send "n" bits simultaneously.
• It's faster than serial transmission but more expensive and limited to short distances.
• Serial transmission sends one bit at a time over a single channel.
• Serial transmission is less expensive and suitable for longer distances.
• Asynchronous transmission sends data in bytes, each with a start and stop bit.
• Not suitable for large amounts of data due to these start and stop bits.
• Synchronous transmission uses a synchronization byte to synchronize internal clocks.
• Suitable for large amounts of data because no start/stop bits are needed.

Transmission Modes

• Transmission modes define the direction of data flow.
• Simplex transmission allows data flow in one direction only (like TV).
• Half-duplex transmission allows data flow in both directions, but only one way at a time (like walkie-talkies).
• Full-duplex transmission allows data flow in both directions simultaneously (like two-way radio or multiple computer network).

Physical Topologies

• Mesh Topology: Every device has a dedicated link to every other device.

• Each link only carries traffic between the two devices it connects.

• Requires numerous connections and I/O ports.

• Advantages: less traffic, robust, secure, easy maintenance.

• Disadvantages: needs more resources (cables and ports), expensive.

• Star Topology: Each device has a dedicated link to a central controller (hub).

• No direct traffic or links between devices.

• Advantages: less expensive, easy to install, robust.

• Disadvantages: single point of failure.

• Bus Topology: All devices are connected to a single cable (backbone).

• Devices use taps to connect to the main cable.

• Advantages: ease of installation.

• Disadvantages: difficult reconnection and fault isolation, broken cable stops transmission.

• Ring Topology: Each device connects to two other devices in a closed ring.

• Signal travels around the ring.

• Advantages: relatively easy installation, fault isolation simplified.

• Disadvantages: unidirectional traffic, single point of failure.

• Tree Topology: Integrates multiple topologies.

• Example: multiple star topologies linked onto a bus.

• Advantages: point-to-point wiring for individual segments, supported by several vendors.

• Disadvantages: overall length, segment limited by the cabling, backbone breaks, stops the entire segment

Networks

• Networks link multiple computers to share resources.
• Different network types have different ranges.

Network Categories

• Local Area Networks (LANs): networks within a home, building, or campus.
• Wide Area Networks (WANs): connect LANs over long distances.
• Internet: a global network of interconnected networks.

Transmission Media

• Transmission media are the channels for carrying data.
• Guided media: twisted pair cable, coaxial cable, fiber optic cable.
• Unguided media: free space (wireless).