Data Transmission

What is Data Transmission?

• Data transmission is the process of sending digital or analogue data over a network or communication medium from one computer to another.
• It can happen over different types of media, including wired networks like Ethernet cables, or wireless methods like WiFi or Bluetooth.
• Two common methods of data transmission are serial transmission and parallel transmission.

Serial vs. Parallel Transmission

• In serial transmission, data bits are sent one after another in a sequence over a communication channel. Examples include USB and Ethernet connections.
• Parallel transmission involves sending multiple bits at once, each along its own separate channel. This method is generally faster but requires more complex wiring and is often used within devices rather than between them.

Simplex, Duplex and Half-Duplex Transmission

• Simplex transmission mode is a one-way communication where data can only be sent, not received. An example of this is a keyboard communicating with a computer.
• Duplex transmission mode provides two-way communication in which data can be sent and received simultaneously. Telephone calls are an example of duplex transmission.
• Half-duplex transmission mode also provides two-way communication, but data can either be sent or received at one time, not simultaneously. Walkie-talkies operate on half-duplex mode.

Synchronous and Asynchronous Transmission

• In synchronous transmission, data is sent as a steady stream in the form of blocks or frames. The sender and receiver must have a stable clock rate to prevent data loss. It’s used for high-speed communication channels, such as Optical Fibre or Co-axial cables.
• In asynchronous transmission, data is sent as separate units with start and stop bits to indicate the beginning and ending of data. It’s used in less speed-demanding transmission, such as emails.

Error Checking Methods

• Parity check is a simple error-checking mechanism where an extra bit, called a parity bit, is added to the data to ensure the number of 1-bits is even (even parity) or odd (odd parity).
• Check-sum involves summing up the values in a block of data and sending this along with the data. The receiver can then perform the same summation and compare the results to check for errors.
• A more complex method is Cyclic Redundancy Check (CRC), in which a divisor is chosen and used to divide the data. The remainder is then sent along with the data, and the receiver then performs the same division to check for errors.
• Automatic Repeat Request (ARQ) is where the receiver sends an acknowledgement to the sender if the data is received correctly. If acknowledgement is not received within a certain timeframe, the sender will retransmit the data.

Functions of a Modem

• A modem (Modulator-Demodulator) is a device facilitating data transmission. It modulates digital signals into analogue signals for transmission over telephone lines and demodulates analogue signals back into digital form for the computer to understand.
• The use of a modem makes it possible to use existing telephone infrastructure for internet connectivity.