📝 IntServ limitations and problems (10 MCQs)

📖 From Data Communication and Networks • 30. Quality of Service • 10 questions available

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What is IntServ limitations and problems?

IntServ suffers from scalability issues because maintaining per-flow state and processing RSVP signaling at every router creates excessive overhead in core networks, making it impractical for large-scale Internet deployment despite its precise QoS guarantees.

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📝 All IntServ limitations and problems MCQs

Q1. In the Chord protocol, when a node N fails, what immediate change occurs to the successor pointer of its predecessor node?

A.The predecessor's successor pointer is updated to point to N's former successor. ✅

B.The predecessor loses its successor pointer and must discover a new one.

C.Only the predecessor's finger table entries become invalid.

D.There is no immediate effect on the predecessor.

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: When a node crashes, its immediate predecessor learns of the failure during the next stabilization round. It then replaces the lost successor with the failed node's own successor, preserving the ring continuity. This update is localized to the predecessor and does not require global knowledge, ensuring quick recovery of the pointer.

Q2. With identifier space size $m = 5$ (i.e., $2^{5}=32$ identifiers), node $N = 7$ builds its finger table. What is the target key for the 3rd entry ( $i = 3$ )?

A.9

B.10

C.11 ✅

D.12

💡 Difficulty: medium | ✅ Correct: C

📖 Explanation: The target key for entry $i$ is calculated as $N + 2^{i-1}$ modulo $2^{m}$ . Substituting $N = 7$ and $i = 3$ gives $7 + 2^{2} = 7 + 4 = 11$ . Since 11 is less than 32, the modulo operation does not change the value, so the correct target key is 11.

Q3. How does the size of Chord's finger table compare to Kademlia's routing table for the same identifier length $m$ ?

A.Chord's table grows logarithmically, Kademlia's grows linearly.

B.Both grow logarithmically, but Kademlia stores more contacts per bucket.

C.Chord's table is fixed at

m

entries, while Kademlia's has

m

buckets each potentially holding multiple nodes. ✅

D.Kademlia uses a finger table identical to Chord's.

💡 Difficulty: easy | ✅ Correct: C

📖 Explanation: Chord maintains exactly $m$ finger entries, each pointing to the first node that succeeds $N + 2^{i-1}$ . Kademlia, on the other hand, defines $m$ buckets based on XOR distance; each bucket may contain several nodes, providing redundancy and faster lookups. Therefore, while both structures have $m$ logical positions, Kademlia's routing table can hold many more contacts.

Q4. If the identifier length $m$ is increased, what is the expected effect on the average number of hops required for a lookup in Chord?

A.Hops increase linearly with

m

B.Hops stay constant because routing uses successor lists.

C.Hops decrease because more nodes are available.

D.Hops increase logarithmically with the number of nodes, which grows with

2^{m}

. ✅

💡 Difficulty: medium | ✅ Correct: D

📖 Explanation: Chord’s lookup algorithm follows a logarithmic progression: each hop roughly halves the distance to the target identifier. Raising $m$ expands the identifier space exponentially, which typically adds more nodes. The average hop count therefore grows as $\log_2 N$ , where $N$ is the number of nodes, leading to a logarithmic increase relative to the larger space.

Q5. In Chord, a node stores a key-value pair \ $(k, v)\$ where \ $k \$ is the hash of a data item and \ $v \$ is the address of the peer that actually holds the data. What does this separation imply?

A.The node responsible for \

k \

may be different from the node that stores the actual file. ✅

B.All data must be stored on the same node that holds the key.

C.The value \

v \

is redundant and never used.

D.Keys and values are always stored on the same physical machine.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: Chord decouples responsibility for a key from the location of the data itself. The node whose identifier succeeds \ $k \$ (the successor) holds the \ $(k, v)\$ pair, but \ $v \$ can point to any other peer that hosts the actual file. This design enables load balancing and flexible data placement while preserving deterministic lookup via the successor.

Q6. A series of node departures partitions the Chord ring into two disjoint segments. Which strategy best restores a consistent view of the identifier space?

A.Ignore the partition and let lookups fail.

B.Run a stabilization protocol that updates successor and predecessor pointers across the partition boundary. ✅

C.Rehash all keys to a new identifier space.

D.Increase the finger table size temporarily.

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: When a partition occurs, the ring’s continuity is broken, causing incorrect routing. The standard stabilization process periodically checks and corrects successor and predecessor links. By forcing nodes at the partition edges to exchange updated pointers, the ring can be re‑joined without global rehashing, restoring a single coherent identifier circle.

Q7. Given node 14 with key \ $(110.34.56.20, 5200)\$ and its successor listed as 80.201.52.40, which sequence of hops will a lookup for key 5200 from node 14 most likely follow?

A.Directly to 80.201.52.40 because it is the successor. ✅

B.Through node 14’s finger table entry for \

N+2^{0} \

C.It will first query its predecessor before reaching the successor.

D.The lookup fails because the key is stored locally.

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: In Chord, a node forwards a query to its immediate successor when that successor is responsible for the target key. Since node 14’s successor is 80.201.52.40 and the key 5200 falls within the range that the successor owns, the lookup is resolved in a single hop directly to that successor.

Q8. Treating a node failure as a 'departure' versus a 'crash' influences Chord's stabilization. Which of the following best describes the impact of treating failures as departures?

A.Stabilization messages are suppressed, leading to slower recovery.

B.Successor lists are not updated, causing stale pointers.

C.The protocol assumes the node will rejoin, so it does not remove references promptly.

D.The departure model triggers immediate finger table repairs, improving resilience. ✅

💡 Difficulty: hard | ✅ Correct: D

📖 Explanation: When a failure is interpreted as a departure, the protocol follows the normal leave procedure: successors and predecessors are updated, and finger tables are repaired during the next stabilization round. This proactive handling removes stale references quickly, ensuring that routing information remains accurate and that the system can tolerate further churn.

Q9. Why does Chord use modulo \ $2^{m} \$ arithmetic for its identifier space?

A.To avoid collisions between keys.

B.To ensure identifiers are prime numbers.

C.To wrap around the circular identifier space, allowing continuous successor lookup. ✅

D.To simplify hash function computation.

💡 Difficulty: easy | ✅ Correct: C

📖 Explanation: Modulo \ $2^{m} \$ arithmetic creates a closed ring where the highest identifier wraps back to zero. This circular arrangement enables each node to define a successor as the next identifier clockwise, guaranteeing that any key has a well‑defined owner and that lookups can traverse the ring without encountering gaps.

Q10. In Chord terminology, what is the 'successor' of a key \ $k \$ ?

A.The first node whose identifier is greater than or equal to \

k \

when moving clockwise on the identifier circle. ✅

B.The node with the smallest identifier in the entire ring.

C.The node that originally inserted the key into the DHT.

D.The node that stores the value \

v \

associated with \

k \

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The successor of a key is defined as the node encountered first when moving clockwise from \ $k \$ around the identifier circle whose identifier meets or exceeds \ $k \$ . This node is responsible for storing the \ $(k, v)\$ pair, ensuring that every possible key maps to a unique location in the distributed hash table.

🔗 Related Topics (MCQs)

📝 Data flow characteristics in QoS MCQs 📝 QoS definitions in computer networks MCQs 📝 Application sensitivity to QoS parameters MCQs 📝 Flow classes in quality of service MCQs 📝 Flow control techniques for QoS MCQs

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