GATE CS - COMPUTER NETWORKS:Application Layer Protocols
Mastering application layer protocols concepts and implementation.
Application Layer for GATE CS
GATE Application Layer is mostly which protocol / port / layer owns this, plus short DNS or HTTP behaviour. Not full RFCs.
Protocols that recur
| Protocol | Role | Notes |
|---|---|---|
| DNS | Name → IP | UDP 53 usually; recursive vs iterative |
| HTTP / HTTPS | Web | Request/response; 80 / 443 |
| SMTP / IMAP / POP | SMTP send; IMAP/POP retrieve | |
| FTP | File transfer | Separate control/data connections |
| DHCP | Host config | Offer IP, gateway, DNS |
DNS resolution sketch
Stub → resolver → root/TLD/authoritative (iterative) or recursive resolver does the walking. Caching TTLs matter for “why did I get an old address?” style options.
HTTP exam facts
Methods GET/POST; cookies are application-level state; HTTPS = HTTP over TLS (still application data from the network stack’s view, encryption below). Persistent connections reduce handshake overhead.
Pairing with transport
Know “DNS usually UDP, zone transfer TCP,” “HTTP uses TCP,” “SMTP uses TCP.” Wrong transport is a common distractor.
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