# Unit 6: redraw four message flows

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/revision/tee-revision/u6

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/revision/tee-revision--u6/

TEE · Use after the full lessons and solved papers · current syllabus 702AI0C023

| Protocol | Draw and explain |
| --- | --- |
| HTTP | Browser → DNS → server connection → request(method,target,headers) → response(status,headers,body) → render/extra objects |
| DNS | Root → TLD → domain/subdomain; stub → recursive resolver → referrals → authoritative record; explain full-name uniqueness |
| FTP | Control TCP21 persists; separate data connection; active server initiation versus passive client initiation |
| SMTP | 220/EHLO → MAIL FROM → RCPT TO → DATA/354 → message/dot/250 → QUIT/221; recipient later retrieves via another protocol |

A good 10-mark answer has labelled actors and arrow directions, the ordered mechanism, important fields/commands and one practical example. Keep security and version qualifications precise without replacing the main mechanism.