Digital transmission refers to the process of sending data from one device to another in a digital format.
• This is essential for modern communication networks, where data is represented as discrete signals rather than continuous waves.
Coding
Coding is the process of converting data into a form suitable for transmission.
• It involves two key aspects: line coding and error detection/correction.
1.) Line Coding: This refers to the representation of binary data on a transmission medium.
Common line coding schemes include:
- Non-Return to Zero (NRZ): A simple scheme where 1s and 0s are represented by different voltage levels.
- Manchester Encoding: Combines synchronization and data representation by encoding each bit with a transition; for instance, a transition from high to low voltage represents a 1, and low to high represents a 0.
- Differential Manchester Encoding: Similar to Manchester but uses changes in voltage levels to represent data, improving robustness against noise.
2.) Error Detection/Correction: Ensures data integrity by adding redundant information that allows the detection and correction of errors.
- Parity Bits: Simple error detection by adding a bit that makes the number of 1s either even (even parity) or odd (odd parity).
- Checksums: A value computed from the data that helps in detecting errors.
- Cyclic Redundancy Check (CRC): A more sophisticated error-checking method that can detect burst errors.
Transmission Modes
Transmission modes define how data is transmitted between devices.
The three primary modes are:
- Simplex: Data flows in only one direction. Example: Keyboard to computer.
- Half-Duplex: Data flows in both directions, but not simultaneously. Example: Walkie-talkies.
- Full-Duplex: Data flows in both directions simultaneously. Example: Telephone conversations.
Digital Transmission
Digital transmission involves sending digital signals over a transmission medium.
Key components include:
- Bit Rate: The number of bits transmitted per second (bps). Higher bit rates indicate faster transmission.
- Bandwidth: The range of frequencies available for transmission. Higher bandwidth allows higher bit rates.
- Noise: Unwanted disturbances that affect signal quality. Effective coding and transmission techniques are used to minimize noise impact.
How Ethernet Transmits Data
Ethernet is the most widely used technology for local area networks (LANs). It transmits data using frames over a variety of physical media, including twisted pair cables, coaxial cables, and fiber-optic cables.
• Ethernet Frame Structure: An Ethernet frame includes fields for preamble, destination MAC address, source MAC address, type/length, data, and frame check sequence (FCS).
- Preamble: 7 bytes of alternating 1s and 0s followed by 1 byte of 1s, used for synchronization.
- MAC Addresses: Unique identifiers for source and destination devices.
- Type/Length: Indicates the protocol used (e.g., IPv4) or the length of the data field.
- Data: The actual payload being transmitted.
- Frame Check Sequence (FCS): Used for error checking.
Transmission Process:
- Carrier Sense Multiple Access with Collision Detection (CSMA/CD): Used to control access to the shared medium in Ethernet. Devices listen to the medium and wait for it to be idle before transmitting. If a collision is detected, they stop, wait for a random period, and retry.
- Switching: Modern Ethernet networks use switches to create point-to-point connections between devices, reducing collisions and improving performance.
- Speed and Duplex Modes: Ethernet supports various speeds (10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps) and can operate in half-duplex (rare in modern networks) or full-duplex mode.