📝 Chord identifier space and hashing (10 MCQs)

📖 Explanation: SIP is a signaling protocol whose main role is to set up, modify, and terminate multimedia sessions. It does this by creating and exchanging session descriptions, which effectively establishes the media streams between endpoints. The other options describe functions handled by lower‑layer protocols, not the core purpose of SIP.

📖 Explanation: When the identifier space is large (128 bits), the chance that two users pick the same ID follows the birthday problem. Doubling the number of users increases the collision probability, but because the space is astronomically large, the increase is only slight rather than a dramatic rise. Hence the probability slightly increases.

📖 Explanation: SIP identifiers are expressed as URIs (e.g., sip:user@example.com), giving a flexible, globally unique namespace that can embed domain information. H.323, by contrast, relies on numeric endpoint IDs assigned by a gatekeeper within a local domain. This structural difference means SIP can interoperate across disparate domains more readily, while H.323 requires explicit gatekeeper coordination.

📖 Explanation: The birthday‑paradox approximation gives $p \approx n^2/(2N)$. For $n = 10^9$ and target $p < 10^{-6}$, solving yields $N > 5 \times 10^{23}$. The nearest power of two is $2^{64} \approx 1.8 \times 10^{19}$, which is the smallest feasible size that keeps the collision risk below the threshold, so a 64‑bit space is sufficient.

📖 Explanation: In VoIP, the identifier that a device presents is processed by the signaling layer (e.g., SIP or H.323). If the identifier is unknown, the signaling server cannot route the request, causing the call setup to fail. This failure originates at the application layer, where protocol logic validates identifiers, rather than at lower transport or network layers.

📖 Explanation: A 16‑bit fixed identifier reduces packet overhead and simplifies storage, which benefits low‑power or bandwidth‑constrained devices. However, with billions of devices the probability of collisions becomes significant, leading to address conflicts and additional resolution traffic. A 128‑bit UUID virtually eliminates collisions, at the cost of larger headers and more processing, making it preferable for large‑scale deployments where uniqueness outweighs overhead.

📖 Explanation: An identifier space abstracts the concrete format of IDs into a universal namespace. Different signaling protocols can map their native identifiers onto this shared space, enabling translation and routing between protocols without needing to understand each other's internal naming rules. This abstraction promotes interoperability by allowing heterogeneous systems to reference the same logical entity through a common identifier.

📖 Explanation: When the identifier length doubles from 32 to 64 bits, each entry in a routing table occupies twice as many bits for the identifier field. Assuming the number of routes stays constant, the total memory required for the identifier portion roughly doubles, leading to larger routing tables while the overall table structure remains unchanged.

📖 Explanation: Sequential identifiers are predictable; an attacker can enumerate possible IDs to discover active endpoints, facilitating denial‑of‑service or eavesdropping attacks. Random identifiers are statistically unpredictable, making enumeration far more difficult and reducing the risk of targeted attacks. Therefore, random IDs improve security at the cost of potentially larger identifier representations.

📖 Explanation: Hierarchical naming divides the identifier space into parent and child domains, mirroring organizational or geographic structures. This allows delegation of identifier management to sub‑domains, simplifies routing decisions, and scales more gracefully as the network grows. Consequently, a protocol that adds hierarchy to the SIP‑style space gains better manageability and scalability.)