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Official PYQ · 2016Set 1 · Q25Application Layer Protocols: DNS, SMTP, HTTP, FTP, EmailMCQ1 mark

GATE CS 2016 Set 1 Q25 — Application Layer Protocols: DNS, SMTP, HTTP, FTP, Email

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Which of the following is/are example(s) of stateful application layer protocol?

  1. HTTP\textsf{HTTP}
  2. FTP\textsf{FTP}
  3. TCP\textsf{TCP}
  4. POP3\textsf{POP3}
Choose one option
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Answer: C

To identify the stateful application layer protocols, let us analyze each of the given protocols based on their layer of operation and whether they are stateful (maintain session state information across multiple requests):

  1. HTTP (Hypertext Transfer Protocol):
    • Layer: Application Layer
    • State: Stateless. Each request is treated as an independent transaction, unrelated to any previous requests.
  2. FTP (File Transfer Protocol):
    • Layer: Application Layer
    • State: Stateful. The FTP server maintains state information for each user session (such as the current working directory and authentication status) over the control connection.
  3. TCP (Transmission Control Protocol):
    • Layer: Transport Layer (not Application Layer). While TCP is stateful (it tracks sequence numbers, acknowledgment numbers, and connection states), it does not satisfy the "application layer" constraint of the question.
  4. POP3 (Post Office Protocol version 3):
    • Layer: Application Layer
    • State: Stateful. A POP3 session progresses through distinct states: AUTHORIZATION (authenticating the user), TRANSACTION (fetching and marking emails for deletion), and UPDATE (actually deleting marked emails and closing the connection).

Thus, the stateful application layer protocols are (ii) FTP and (iv) POP3.

Correct Option: C ( (ii) and (iv) only )

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