GATE CS 2016 Set 1 Q.35 (CS Q.25): Application Layer: DNS, HTTP, SMTP, FTP

Which of the following is/are example(s) of stateful application layer protocols?
(i) HTTP
(ii) FTP
(iii) TCP
(iv) POP3

(i) and (ii) only

(ii) and (iii) only

(ii) and (iv) only

(iv) only

Official answer and solution

Solution

Filter protocols by layer (Application layer) and by statefulness (maintaining session state).

First, evaluate the layer of each protocol:

Next, evaluate statefulness for the application layer protocols:

(i) HTTP: Designed as a stateless protocol (each request-response transaction is independent; state must be managed artificially via cookies/sessions).
(ii) FTP (File Transfer Protocol): Stateful. The control connection maintains session state including user authentication, transfer mode, and current directory path across commands.
(iv) POP3 (Post Office Protocol v3): Stateful. A client session progresses through distinct sequential states: AUTHORIZATION, TRANSACTION, and UPDATE.

Since TCP is a transport layer protocol, only (ii) FTP and (iv) POP3 are stateful application layer protocols.

Final answer

Common trap

Including TCP because it is stateful, forgetting that TCP operates at the transport layer, not the application layer.

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