Data communication is the exchange of data between two or more devices through a transmission medium. For it to work reliably, three things matter: delivery (to the correct destination), accuracy (data arrives unaltered) and timeliness (data arrives soon enough to be useful, which is vital for voice and video).
What "data" means here
In networking, data is any information that has been turned into a form a computer can store and send: text, numbers, pictures, sound and video. Inside a computer all of it is held as bits (binary digits, 0 or 1). Data communication is the job of moving those bits from one device to another, correctly and quickly enough to be useful.
The three goals explained
- Delivery: the data must reach the right device, and only that device. A message meant for the accounts PC must not end up on a student's laptop. Networks use addresses (MAC and IP addresses, see Unit 4) to make this possible.
- Accuracy: the data must arrive exactly as it was sent. One wrong bit in a bank transfer could change Rs. 1,000 into Rs. 9,000. Networks detect damaged data and either throw it away or ask for it again (see 1.8).
- Timeliness: data must arrive soon enough to be useful. An email that takes ten seconds is fine, but in a voice call, sound that arrives half a second late makes conversation difficult. Data that must be delivered as it is produced, such as live voice or video, is called real-time data.
A fourth goal is often added: jitter (uneven delay) must be low. If video packets arrive at irregular intervals, the picture stutters even when the average delay is small (see 1.7).
Everyday example: sending a WhatsApp message to a friend uses data communication. Your phone (sender) turns the text into bits, sends them through Wi-Fi and the Internet (medium), following agreed rules (protocols), to your friend's phone (receiver). The two ticks are a form of acknowledgement: proof of delivery.
Local and remote communication
Communication can be local, between devices in the same room or building (a PC printing to an office printer), or remote, between devices that are far apart (a laptop in Kandy loading a website hosted in Singapore). The same basic ideas apply to both; remote communication simply passes through more devices and links on the way.
Remember
- Data communication is the exchange of data (bits) between devices through a transmission medium.
- It must deliver to the correct destination, accurately and on time.
- Real-time traffic such as voice and video is the most sensitive to delay and jitter.