Digital Transmission Modes

Study Notes

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 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).

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