FPSC- Programmer (BS-17) - Pakistan Meteorological Department (PMD) Model Papers - 2026 — Part 5 (100 Q)

Correct Answer: C. OSI has 7; TCP/IP has 4
Explanation: Some textbooks use a 5-layer hybrid model, but the original TCP/IP model has 4 layers: Link, Internet, Transport, and Application. ALSO KNOW (related points): • What is the range of TCP and UDP port numbers? → 0 to 65535

Correct Answer: D. Layer 3 (Network)
Explanation: Routers use logical (IP) addresses at Layer 3.

Correct Answer: D. Destination MAC addresses
Explanation: Layer 3 switches can also route on IP addresses, but a basic switch learns and uses MAC addresses.

Correct Answer: A. Presentation (Layer 6)
Explanation: A common mistake is to assign encryption to the Application or Transport layer. ALSO KNOW (related points): • At which OSI layer does routing between different networks happen? → Layer 3 (Network) • Which OSI layer establishes, manages, and synchronizes dialogs, for example with checkpoints? → Session (Layer 5) • Which OSI layers does the TCP/IP Application layer correspond to? → Layers 5, 6, and 7 (Session, Presentation, Application)

Correct Answer: A. Session (Layer 5)
Explanation: Dialog control and synchronization points are Session layer functions.

Correct Answer: B. Transport: segment; Network: packet; Data Link: frame; Physical: bits
Explanation: UDP's PDU is often called a datagram. ALSO KNOW (related points): • In what order does data pass down the stack when an application sends it? → Data → Segment → Packet → Frame → Bits

Correct Answer: D. Layers 5, 6, and 7 (Session, Presentation, Application)
Explanation: TCP/IP merges the top three OSI layers into a single Application layer.

Correct Answer: D. It resolves a known IPv4 address to a MAC address on the local network
Explanation: DNS resolves names, DHCP assigns addresses, and RARP (now obsolete) mapped MAC addresses to IP addresses. IPv6 uses NDP instead of ARP. ALSO KNOW (related points): • What does a standard (Layer 2) switch use to forward frames? → Destination MAC addresses

Correct Answer: C. 48, 32, and 128
Explanation: IPv6 addresses are 128 bits, not 64. A common confusion arises because the IPv6 interface identifier is 64 bits.

Correct Answer: C. 0 to 65535
Explanation: Port numbers are 16 bits. Ports 0–1023 are the 'well-known' ports, not the whole range.