Computer Networks · TEE · papers
Q2(a) · Webmail and POP3 protocol journey
2024-12-06 · AI-only Sem V variant
Exact historical variant. Current-syllabus questions solved; excluded topics and source limitations stated.
Q2(a). Alice sends email from a web-based account; Bob accesses mail through POP3. Explain all application protocols in the journey. For each, state push or pull, TCP or UDP, and port numbers. [10 marks]
Answer
| Alice browser | → | HTTP(S) webmail service | → | SMTP between mail servers | → | Bob mailbox | → | POP3 client |
| Stage | Protocol and role | Transport / conventional ports |
|---|---|---|
| Browser submits message | HTTP POST over HTTPS; application uploads/pushes the message | HTTPS:TCP443; historical HTTP:TCP80 |
| Sender mail server→recipient mail server | SMTP pushes the mail to recipient domain | TCP25 for server relay; client submission commonly587 |
| Bob retrieves/synchronizes | POP3 pulls messages for download | TCP110 (POP3) /995 with implicit TLS |
DNS may first locate the recipient domain’s MX record and mail-host IP (typicallyUDP53, withTCP53 when needed). HTTP is a request/response protocol rather than a pure push-only protocol; classify this particular POST as submission. The named IMAP/POP3 stage is historical email context; SMTP is the explicitly listed current application topic.