Who decides if you scored?
You play a football game online with nine other people. You press the shoot button.
Your phone shows the ball moving at once. But who decides if it is a goal? Your phone? Or a computer far away that sees all ten players?
Splitting work between your device and a far computer is a key design choice.
Key words
| Word | What it means | Example |
|---|---|---|
| Local | Done on the user's own device. | reading a button press |
| Remote | Done on another computer, such as a server. | sharing all player positions |
| Network | Computers joined together so they can send data to each other. | |
| Remote call | A request that one computer sends to another to do a job and answer. | |
| Latency | The delay between sending a request and getting the answer. | 50 milliseconds |
| System boundary | The line that shows what is inside your system and what is outside. | |
| External system | A system run by someone else that yours connects to. | a sports data feed |
| API | A set of rules that lets one program ask another for data or a job. |
The cells students fill in are left blank in this preview.
Local or remote?
Some jobs must be local. They must be fast, and only your device needs them. Reading a button press is local.
Some jobs must be remote. They need data from many people, or the result must be trusted. The score of a multi-player game is remote, so nobody can cheat.
Every remote job adds latency. That is a delay.
Quick check: local or remote?
Have a go
Quick check: local or remote?
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Reading the boundary
| Part | Where it is | Why |
|---|---|---|
| Read buttons | Local | Must feel instant |
| Draw the screen | Local | Your device has the screen |
| Check the rules | Remote | The result must be trusted |
| Share positions | Remote | Needs data from all players |
| Sports data feed | External | Run by another company; we only connect to it |
The cells students fill in are left blank in this preview.
How are they connected?
Data moves between local and remote parts over a network. The type of network matters. Home Wi-Fi is fast. Mobile data can be slow or stop working. A college network may block some data.
Often your design combines networks. A phone uses Wi-Fi at home, mobile data on a bus, and then the internet to reach the server.
Quick check: the network
Have a go
Quick check: the network
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.