📝 P2P networks in computer networks (18 MCQs)

📖 Explanation: The abbreviation P2P is universally understood as Peer-to-Peer, describing a network model where each participant can act as both client and server, sharing resources directly without a central coordinator. This definition forms the foundation for all subsequent discussions of P2P architectures.

📖 Explanation: Structured P2P systems often maintain a distributed index or central directory that maps file identifiers to responsible nodes. When a peer requests a file, it queries this directory to obtain the location, avoiding the costly broadcast approach used in unstructured overlays.

📖 Explanation: Super‑nodes act as indexing hubs; their removal forces remaining peers to search more hops or fallback to broader queries, which lengthens the time required to locate resources. Consequently, search operations become slower, reflecting the increased latency caused by the missing index point.

📖 Explanation: When peers frequently appear and disappear, duplicating file fragments on several independent nodes creates redundancy. If one holder leaves, other replicas remain accessible, preserving the overall availability of the content despite the volatile membership characteristic of many P2P environments.

📖 Explanation: In a ring, each node’s predecessor and successor must be re‑linked when an intermediate node disappears. The predecessor’s successor reference must point to the original successor, and the successor’s predecessor reference must point to the original predecessor, thereby closing the gap and maintaining the circular structure.

📖 Explanation: A pure P2P system benefits from each joining node contributing bandwidth, storage, and processing power, effectively expanding the system’s capacity. In contrast, a client‑server architecture adds load to a fixed set of servers, limiting scalability as the number of clients grows.

📖 Explanation: Structured overlays employ algorithms such as Chord or Kademlia that assign keys to nodes via a distributed hash table, enabling predictable O(log N) lookup paths. Unstructured networks lack this deterministic placement, relying on random walks or flooding, which leads to less predictable performance.

📖 Explanation: NAT traversal (e.g., STUN, TURN) helps peers behind routers discover public endpoints, thereby expanding the set of reachable nodes. The additional handshake and relay steps, however, can introduce extra round‑trip time, so overall connectivity improves while latency may rise modestly.

📖 Explanation: Reciprocity encourages balanced contribution: a peer receives credits proportional to the amount it uploads, which it then spends to download. This creates a self‑regulating economy where free‑riding is discouraged because peers cannot obtain data without first contributing resources to the network.

📖 Explanation: A tracker maintains a list of peers participating in a torrent and supplies this information to newcomers. By informing peers about who holds which pieces, the tracker shapes the distribution pattern, encouraging efficient exchange and balanced load across the swarm, which accelerates overall download completion.

📖 Explanation: In a hybrid design, the cloud layer stores essential fragments of shared files, ensuring that even if many peers disappear, the data can be reconstructed from the cloud backup. This off‑site redundancy complements the decentralized P2P overlay, offering resilience against massive churn or localized failures.

📖 Explanation: Tit‑for‑tat punishes non‑cooperative participants by refusing to serve them. Peers monitor each other's contribution histories; a node that only downloads and never uploads quickly loses trust, leading others to drop connections or deprioritize its requests, effectively isolating the leech.

📖 Explanation: End‑to‑end encryption encrypts data on the sender’s device and decrypts only on the recipient’s device, preventing intermediate nodes—including super‑nodes or relays—from accessing the plaintext. Application‑level encryption, performed by the app but not the protocol, can still expose data to the host environment, reducing overall confidentiality.

📖 Explanation: When nodes join or leave, the DHT must adjust finger tables, successor lists, and key ownership mappings. Each change triggers messages to neighboring nodes, thereby increasing the volume of control traffic. High churn therefore raises the maintenance cost, consuming bandwidth and processing resources to keep the overlay consistent.

📖 Explanation: Gossip spreads information exponentially: each informed node contacts another uninformed node per round, roughly doubling the informed population each step. This binary growth leads to a logarithmic number of rounds, $\Theta(\log N)$, to reach every participant in the network, assuming random peer selection.

📖 Explanation: The primary goal of a P2P distribution scheme is to deliver content quickly to all participants. Measuring the average time each peer requires to finish its download directly reflects how effectively the system utilizes bandwidth, piece selection, and peer collaboration, making it a comprehensive efficiency indicator.

📖 Explanation: Low‑power radios such as BLE or Zigbee consume far less energy than Wi‑Fi, and opportunistic forwarding lets devices transmit only when nearby peers are present. This strategy reduces active radio time while still allowing data to propagate through the mesh, balancing energy constraints with availability.

📖 Explanation: When a node reduces its upload capacity, the total upload bandwidth contributed by the network diminishes. This directly lowers the aggregate bandwidth available for distributing pieces, which can slow overall dissemination rates and increase the time required for other peers to obtain needed data.