Edge Computing Week 6 NPTEL Assignment Answers 2025

NPTEL Edge Computing Week 6 Assignment Answers 2024

1. Which event is concurrent with the vector clock (3, 8, 4)?

• (6, 8, 4)
• (5, 10, 5)
• (2, 8, 5) ✅
• (2, 6, 2)

Answer: (2, 8, 5)

Explanation:
Two events are concurrent if neither happened before the other. For vector clocks A and B, they are concurrent if:

• A is neither ≤ B nor ≥ B element-wise.

(2, 8, 5) and (3, 8, 4) are not comparable as:

• 2 < 3, 8 = 8, but 5 > 4
  Hence, they are concurrent.

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2. A client’s clock reads 3:20:00. The server’s clock reads 3:10:00 when they synchronize using the Berkeley algorithm. Assume message delays are negligible. What is the time at the client after synchronization?

• 3:15:00 ✅
• 3:20:00
• 6:20:00
• 6:30:00

Answer: 3:15:00

Explanation:
Berkeley algorithm takes the average of clocks.
Average time = (3:20 + 3:10) / 2 = 3:15

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3. The Chandy-Lamport algorithm uses a control message, called a marker whose role in a FIFO system is to separate messages in the channels. This statement is,

• True ✅
• False

Answer: True

Explanation:
Chandy-Lamport snapshot algorithm uses marker messages to record consistent global states. In FIFO channels, markers help separate pre-snapshot and post-snapshot messages.

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4. For the given event diagram, identify the correct events with vector clocks.

• Option 1: a: (2, 2, 4)…
• Option 2: a: (2, 2, 0)…
• Option 3: a: (1, 0, 0)… ✅
• Option 4: a: (2, 1, 0)…

Answer: Option 3

Explanation:
The vector clock must increment correctly along causal lines. Option 3 has the correct causal flow among events as per vector clock rules.

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5. Select the need for multiple data centers.

• Better data availability ✅
• Load Balancing ✅
• Latency Reduction ✅
• Local Data Laws ✅

Answer: All of the above

Explanation:
Multiple data centers ensure:

• Higher availability
• Load distribution
• Proximity to reduce latency
• Compliance with geographic regulations

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6. In MPLS, what does “multi-protocol” indicate?

• MPLS can run over several different protocols as long as routers support the protocol ✅
• MPLS can install a router with multiple protocols
• MPLS can support prioritized protocols
• MPLS allows communication between routers

Answer: MPLS can run over several different protocols…

Explanation:
MPLS supports multiple Layer 2 and Layer 3 protocols, allowing it to operate over various network infrastructures.

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7. MPLS suffers from which of the following?

• Inefficiency in terms of bandwidth usage ✅
• Does not support multiple protocols
• Network wide fairness is hard to achieve ✅
• Cannot handle multiple datacenters connected over fiber links

Answer: Inefficiency in bandwidth usage, Network-wide fairness

Explanation:
While MPLS is efficient in routing, fair bandwidth distribution and optimal bandwidth utilization can be challenging.

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8. In Google’s B4, at the top level we have _____________ that is responsible to talk to an SDN gateway.

• Super controller
• Link controller
• Global controller ✅
• SDN controller

Answer: Global controller

Explanation:
In Google’s B4 WAN, the global controller communicates with the SDN gateway to manage traffic and bandwidth across datacenters.

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9. DTP (Datacenter Time Protocol) uses the physical layer of network devices to implement a decentralized clock synchronization protocol. The statement is,

• True ✅
• False

Answer: True

Explanation:
DTP leverages the physical layer to timestamp and synchronize clocks directly in network hardware with very high accuracy.

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10. Which of the following are examples of External Synchronization?

• Christian’s Algorithm ✅
• NTP ✅
• DTP
• Berkley Algorithm

Answer: Christian’s Algorithm, NTP

Explanation:
External synchronization aligns clocks with an external time source, such as a server (Christian’s) or NTP.
Berkeley is internal (peer-to-peer), and DTP is hardware-based.