Introduction
Fifteen GATE-style questions on Phase 2: error detection, medium access and Ethernet.
Practice questions
- MCQ · 2 marks
CRC of data 101101 with G = 1011?
- 011
- 110
- 101
- 111
- NAT · 2 marks
Internet checksum of the 16-bit words 0x7000 and 0x9000, written in decimal?
Write your answer before opening the key.
- NAT · 1 mark
A code has d_min = 7. Maximum number of errors it can correct?
Write your answer before opening the key.
- MSQ · 1 mark
Which does a single even-parity bit detect?
- 1 error
- 2 errors
- 5 errors
- 6 errors
- NAT · 1 mark
Hamming check bits for 57 data bits (single-error correction)?
Write your answer before opening the key.
- NAT · 2 marks
Pure ALOHA, frame time 0.5 ms, attempts 1000 frames/s. Throughput in frames/s (nearest whole)?
Write your answer before opening the key.
- MCQ · 1 mark
Vulnerable time of slotted ALOHA with frame time T:
- T/2
- T
- 2T
- 3T
- NAT · 2 marks
CSMA/CD at 100 Mbps, longest path 1 km, v = 2 × 10⁸ m/s. Minimum frame in bits?
Write your answer before opening the key.
- NAT · 2 marks
Two stations at their 3rd collision. P(they collide again) (4 decimals)?
Write your answer before opening the key.
- NAT · 1 mark
Token ring, N = 10, a = 1, early release. Efficiency (3 decimals)?
Write your answer before opening the key.
- MCQ · 1 mark
Which MAC scheme wastes capacity when only one station is active?
- Slotted ALOHA
- TDMA
- CSMA/CD
- Pure ALOHA
- NAT · 1 mark
Ethernet frame size for 30 data bytes?
Write your answer before opening the key.
- MCQ · 1 mark
MAC address 0F:00:00:00:00:00 is:
- unicast
- multicast
- broadcast
- invalid
- NAT · 1 mark
Shared Ethernet: T_t = 0.1 ms, T_p = 4 µs. Efficiency with 1/(1 + 5a) (3 decimals)?
Write your answer before opening the key.
- MSQ · 2 marks
A router has 3 interfaces; one connects to a switch with 6 hosts. Which are true?
- The switch side forms one broadcast domain.
- The 6 host links are 6 collision domains.
- The router splits broadcast domains per interface.
- The 6 hosts share one collision domain.
Answer key
Try the questions first. Open when you are ready to check.
- A — Append 000, divide by 1011 modulo 2 → remainder 011.
- B: Arithmetic slip.
- C: Arithmetic slip.
- D: Arithmetic slip.
- 65534 — 0x7000 + 0x9000 = 0x10000 → 0x0000 + 1 = 0x0001; complement 0xFFFE = 65534.
- 3 — ⌊6/2⌋ = 3.
- AC — Odd numbers of errors.
- B: Even.
- D: Even.
- 6 — 2⁶ = 64 ≥ 57 + 6 + 1 = 64.
- 368 — G = 1000 × 0.0005 = 0.5 → S = 0.184 per frame time → 0.184 / 0.0005 s ≈ 368 frames/s (= 1000 × e⁻¹).
- B — Same slot only.
- A: Too small.
- C: Pure ALOHA.
- D: Too large.
- 1000 — 2 × 5 µs × 10⁸ = 1000 bits.
- 0.125 — 8 ties out of 64 = 0.125.
- 0.909..0.91 — 1/(1 + 0.1) = 0.909.
- B — Fixed slots of idle stations go unused.
- A: A lone station succeeds in its slots.
- C: A lone station gets the full rate.
- D: A lone station gets the full rate.
- 64 — Padded to 46: 64 bytes.
- B — 0x0F is odd → group (multicast).
- A: First byte odd.
- C: Not all 1s.
- D: Valid format.
- 0.833..0.834 — a = 0.04 → 1/1.2 = 0.833.
- ABC — Switch interfaces = collision domains; router interfaces = broadcast domains.
- D: That would need a hub.