URLs, DNS and bit streaming
| English | Chinese | Pinyin |
|---|---|---|
| URL | 统一资源定位符 | tǒng yī zī yuán dìng wèi fú |
| DNS | 域名系统 | yù míng xì tǒng |
| protocol | 协议 | xié yì |
| domain name | 域名 | yù míng |
| resolver | 解析器 | jiě xī qì |
| streaming | 流式传输 | liú shì chuán shū |
| buffer | 缓冲 | huǎn chōng |
From web address to web page
- You type a web address and a page appears almost instantly.
- Behind that are two ideas: the URL 统一资源定位符 that names the resource, and DNS 域名系统 that finds it.
- Then we look at how media streams to you.
The URL
- A URL locates a resource on the web. Its parts:
https://www.example.com/about/contact.html
└─protocol─┘└──domain name──┘└────path────┘
- protocol 协议 —
http,https, … - domain name 域名 — a readable server address
- path — which resource on that server
In https://www.example.com/about/contact.html, what is https?
https is the protocol; www.example.com is the domain name; /about/contact.html is the path.
Match each part of https://www.example.com/about/contact.html to its name.
A URL is protocol + domain name + path — the protocol says how, the domain says which server, the path says which resource.
The Domain Name System (DNS)
- DNS is a distributed set of servers that turns domain names into IP addresses.
- When you type a URL, the browser asks a resolver 解析器 for the IP; it queries DNS servers (root → top-level → authoritative) until it finds it.
- The browser then connects to that IP and requests the path.
- DNS saves us memorising IP addresses, and lets a site change server without changing its name.
DNS resolves a domain name to an IP address before the browser connects.
How DNS finds a website
Step through a DNS lookup. The network routes by IP, not by name — so before anything loads, DNS must turn the domain name into an IP address.
The Domain Name System (DNS) mainly:
DNS resolves human-readable domain names to the numeric IP addresses the network actually uses.
Put a DNS lookup in order, from typing the address to loading the page.
The resolver walks the hierarchy (root → TLD → authoritative) until it gets the IP, then the browser connects.
Bit streaming 流式传输
- Streaming sends media as a continuous stream the receiver plays as it arrives, instead of downloading the whole file first.
- Real-time (live) — captured and sent as it happens (live sport, calls); you can't rewind, and low latency is vital.
- On-demand — pre-recorded on a server (video sites); you can pause and rewind, and the server can buffer 缓冲 ahead.
- A buffer stores a little data before playback so brief network dips don't interrupt it; lossy compression keeps the stream within the bandwidth.
Streamed media fills a buffer first, so brief network dips don't interrupt playback.
Streaming media plays as it arrives, without first downloading the whole file.
That is the defining feature of streaming — the receiver plays the stream as it comes in (with a small buffer), rather than waiting for a full download.
Compared with real-time (live) streaming, on-demand streaming:
On-demand content is pre-recorded, so you can pause/rewind and the server can buffer well ahead. Live streaming can't be rewound and needs low latency.
Why does a streaming player use a buffer?
The buffer holds a few seconds ahead of what is playing, so short slow-downs in the network don't cause the playback to stall.
You've got it
- a URL = protocol + domain name + path
- DNS turns a domain name into an IP address (resolver → root → TLD → authoritative)
- streaming plays media as it arrives; real-time (no rewind) vs on-demand (pause/rewind)
- a buffer smooths playback; streaming uses lossy compression to fit the bandwidth