Describe the functions performed within a communication system and the role of protocols and handshaking in transmitting and receiving data

What this dot point is asking

NESA wants you to describe what a communication system does and how protocols let different devices exchange data reliably. You need the basic model (source, transmitter, medium, receiver, destination), the functions performed during communication, and an understanding of protocols and handshaking, including the idea of layered standards such as TCP/IP.

The answer

The communication system model

At its simplest a communication system has a source that creates a message, a transmitter that encodes and sends it, a transmission medium that carries it, a receiver that decodes it, and a destination that uses it. Noise can interfere along the medium, which is why error detection matters. This model frames the transmitting and receiving information process: moving data from one place to another and arriving with it intact.

Functions performed in communication

Several distinct jobs happen whenever data is communicated:

• Message generation: the source produces the data to be sent.
• Control and flow management: the system manages the rate of sending so the receiver is not overwhelmed.
• Addressing: the data is labelled with the address of its destination so the network can route it.
• Formatting and encoding: the data is structured and converted into signals suitable for the medium.
• Transmission: the encoded data travels across the medium.
• Error detection and correction: the receiver checks for and, where possible, fixes corruption introduced by noise.
• Decoding and reassembly: the receiver converts the signal back into usable data and reassembles it into the original message.

Protocols

A protocol is a set of agreed rules that governs how two devices communicate. Because a sender and receiver may be built by different makers, they must agree on the format of the data, how it is addressed, the timing of signals, and how errors are handled. Without a shared protocol, devices cannot interpret each other's signals. Examples include HTTP for web pages, SMTP for email, and FTP for file transfer, each running over the underlying internet protocols.

Handshaking

Handshaking is the exchange of control signals that establishes and agrees the parameters of a connection before data is sent. The devices confirm they are ready, agree on speed and format, and acknowledge receipt. A familiar example is the exchange that sets up a connection between two devices before payload data flows. Handshaking ensures both ends are synchronised so data is not lost or misread.

Layered protocols

Because communication involves many jobs, protocols are organised into layers, each handling one part and passing data to the layer below for sending or above for receiving. The OSI model describes seven such layers as a teaching framework; the TCP/IP model used on the internet groups them into four. IP handles addressing and routing of packets across networks; TCP handles reliable delivery, breaking data into packets, numbering them, and requesting retransmission of any that are lost. Layering means a change in one layer, for example a new physical medium, does not force a rewrite of the others.

Error detection and correction

Noise can flip bits during transmission. Error detection methods add redundant information so corruption can be spotted: a parity bit adds a single check bit, a checksum sums the data, and a cyclic redundancy check applies a more robust calculation. When an error is detected, the receiver either requests retransmission or, with more advanced codes, corrects the error itself. This function is what keeps received data faithful to what was sent.