Solution

The correct answer is A-I, B-IV, C-II, D-III.

Key Points

• A. SMTP → Application Layer (I)
  • SMTP is used to send emails and works at the Application layer.
• B. BGP → Network Layer (IV)
  • BGP is a routing protocol used for path selection between networks.
• C. TCP → Transport Layer (II)
  • TCP provides reliable data transfer between hosts.
• D. PPP → Data Link Layer (III)
  • PPP establishes direct communication between two nodes.

Additional Information

• OSI Layer Summary:
  • Application: SMTP, HTTP, FTP.
  • Transport: TCP, UDP.
  • Network: IP, BGP, routing protocols.
  • Data Link: PPP, Ethernet.