Application-layer protocols
| English | Chinese | Pinyin |
|---|---|---|
| application layer | 应用层 | yìng yòng céng |
| HTTP | 超文本传输协议 | chāo wén běn chuán shū xié yì |
| HTTPS | 安全超文本传输协议 | ān quán chāo wén běn chuán shū xié yì |
| TLS | 传输层安全 | chuán shū céng ān quán |
| FTP | 文件传输协议 | wén jiàn chuán shū xié yì |
| SMTP | 简单邮件传输协议 | jiǎn dān yóu jiàn chuán shū xié yì |
| POP3 | 邮局协议3 | yóu jú xié yì 3 |
| IMAP | 互联网邮件访问协议 | hù lián wǎng yóu jiàn fǎng wèn xié yì |
| BitTorrent | 比特流 | bǐ tè liú |
The protocols apps speak
- The application layer 应用层 defines the protocols that user programs use.
- Each common task — web, files, email — has its own protocol.
- This is where a programmer most often works.
Network route lab
Follow data from a device through network hardware and protocols.
Web and file transfer
- HTTP 超文本传输协议 — browsers fetch web pages from servers (over TCP, port 80).
- HTTPS 安全超文本传输协议 — HTTP over TLS 传输层安全: encrypted, port 443. Use it whenever data is sensitive.
- FTP 文件传输协议 — transfers files between a client and a server.
The parts of a typical Ethernet frame
TCP connects and delivers in order; UDP sends and forgets
HTTPS is:
HTTPS runs HTTP over TLS encryption (port 443), protecting the data in transit.
- SMTP 简单邮件传输协议 — sends email (client → server, and server → server).
- POP3 邮局协议3 — downloads email and usually deletes it from the server.
- IMAP 互联网邮件访问协议 — leaves email on the server and syncs across devices, so the same inbox appears everywhere.
A fibre-optic cable: data travels as light through thin glass strands
Which protocol is used to SEND email?
SMTP sends mail; POP3 and IMAP are used to receive/read it.
IMAP leaves mail on the server and syncs it across all your devices, while POP3 typically downloads the mail and deletes it from the server.
That is why IMAP shows the same inbox on your phone and laptop, whereas POP3 ties mail to one device.
Match each protocol to its use.
HTTP = web, FTP = files, SMTP = sending email (POP3/IMAP receive it).
BitTorrent 比特流
- BitTorrent is a peer-to-peer protocol.
- A file is split into pieces, downloaded from many peers in parallel.
- No single server carries all the load, so popular files distribute efficiently.
BitTorrent: peers share file pieces through a tracker
BitTorrent reduces load on any single server because it:
As a peer-to-peer protocol, each peer shares pieces, so no single server carries the whole load.
You've got it
- HTTP (web, port 80); HTTPS = HTTP over TLS (encrypted, port 443); FTP (files)
- SMTP sends email; POP3 downloads (and deletes); IMAP leaves it on the server and syncs
- BitTorrent is peer-to-peer — file pieces shared among many peers