Data Communication
Understanding How Computers Exchange Information
Before computers can form networks and before the Internet can exist, the most important question is: how does data travel from one device to another. That process is called data communication.
Data communication is the exchange of digital information between two devices using a transmission medium such as wire, fiber, or wireless radio signals. It is the bridge between basic communication and networking.
If communication explains how information moves in general, data communication explains how bits and bytes move in the digital world.
What is Data Communication
Data communication is the process where two devices send and receive data using signals. In data communication, both devices agree on the rules of communication called protocols.
Example:
Your laptop sends data to your Wi Fi router.
The router receives the data and forwards it to the internet.
For communication to work successfully, there are five essential components.
Components of Data Communication
Every data communication system consists of:
Sender: The device that initiates the message. Example: your laptop.
Receiver: The device that receives the message. Example: your router or a server.
Message: The data being transferred. Example: a web request or image.
Medium: The physical path the data uses. Example: Ethernet cable, fiber, Wi Fi radio waves.
Protocol: The agreed rules that define how the communication happens. Without protocols, both ends would talk different languages. Example: TCP, HTTP.
Data Representation: Bits and Bytes
All digital information, no matter how large or complex, eventually becomes bits.
A bit is the smallest unit of data. It can be 0 or 1.
A byte is 8 bits.
Examples:
Text is stored as numbers using ASCII or Unicode.
Images are stored as pixels.
Videos are thousands of images per second.
Data communication is simply moving bits over a medium.
How Data Flows: Direction of Data Transfer
There are three basic modes:
| Mode | Direction | Example |
|---|---|---|
| Simplex | One way only. | Display monitor. |
| Half Duplex | Both ways, but not at the same time. | Walkie talkies. |
| Full Duplex | Both ways simultaneously. | Internet communication, phone calls. |
The internet works on full duplex. Data can be sent and received at the same time.
Data Transmission Methods: Serial vs Parallel
How are bits physically moved in a medium.
Parallel transmission: Multiple bits sent at the same time. Used inside computer motherboards.
Serial transmission: Bits travel one after another, in sequence. Used in Ethernet, USB, Wi Fi, fiber.
Even though parallel seems faster, serial is more reliable and has less noise. That is why modern networking is serial.
Digital Encoding: Turning Bits into Signals
Computers store bits, but wires and airwaves carry signals.
Encoding converts bits into electrical, optical, or radio signals so they can travel. Example encoding styles:
NRZ: High voltage means 1, low voltage means 0.
Manchester Encoding: The bit is represented using transitions, used in Ethernet.
Encoding ensures the receiver understands what 0 and 1 look like on that medium.
Quality of Data Transmission
Data quality is measured by four important concepts.
| Concept | Meaning | Example |
|---|---|---|
| Bandwidth | Maximum amount of data per second. | 100 Mbps internet plan. |
| Latency | Time delay for data to reach destination. | Lag in video calls. |
| Throughput | Actual speed you get. | You may get 70 Mbps on a 100 Mbps plan. |
| Jitter | Variation in delay. | Voice breaking on calls. |
Bandwidth is size of the pipe. Latency is how fast water flows.
Errors and error detection
Noise, interference, and weak signals can corrupt bits. So techniques exist to detect errors.
Techniques:
Parity bit: Adds a bit that indicates if the number of 1s is odd or even.
Checksum: Adds up the data and sends that value along with the packet.
CRC: More advanced math used in Ethernet frames.
If the receiver detects a mismatch, it requests the sender to retransmit.
Flow Control: Preventing data overload
What if a fast device sends data to a slower device. The slower one may get overwhelmed.
Flow control solves that.
Stop and Wait: Sender sends one chunk of data and waits for acknowledgment.
Sliding Window: Sender can send multiple chunks before receiving acknowledgment. Used in TCP. Sliding window increases performance and reduces waiting time.
Putting It All Together.
When you open a website:
Your laptop converts bits into Wi Fi radio waves.
Router receives signal and converts it back into bits.
Router sends bits to your ISP through fiber or cable.
Bits. encode into signals. travel through medium. decode back to bits.
That is data communication.
Conclusion
Data communication is the foundation of networking. It explains how digital bits turn into signals, how they travel, how errors are detected, and how communication stays reliable.