DNS & HTTP formulas
Application layer: DNS and HTTP. 6 formulas for GATE CS Computer Networks, each with when to use it. Each is explained in the topic notes.
IAE Academy: Application layer: DNS and HTTP formulas (GATE CS)
All 6 DNS & HTTP formulas
TIME FOR AN ITERATIVE RESOLUTION BY THE RESOLVER
R_host is the RTT from host to local resolver and R_i the RTT from the resolver to each server it queries in turn. Assumes processing time is negligible and each query and its reply is one UDP exchange costing one RTT (no losses or retransmissions). With a cached TLD referral, drop the root term; with a cached final answer, only R_host remains.
AVERAGE ACCESS TIME WITH A WEB CACHE
h is the hit ratio (fraction of requests the cache answers), T_hit the time to get an object from the cache and T_miss the time to get it through the cache from the origin server. Assumes every request takes one of these two times.
NON-PERSISTENT, SERIAL
Each of the n+1 files costs 1 RTT for the handshake and 1 RTT for request and response.
NON-PERSISTENT, M PARALLEL CONNECTIONS
Base file fetched alone first; objects then go in batches of m. Assumes equal object times and negligible transmission time.
PERSISTENT WITHOUT PIPELINING
One handshake, one RTT for the base file, one RTT for each object.
PERSISTENT WITH PIPELINING
One handshake, one RTT for the base file, one RTT for all objects together (requests sent without waiting). Transmission time is ignored.
Where this was asked: 2020 (1), 2022 (1), 2023 (1), 2024 (1), 2026 (1). See the 5 previous-year questions on DNS & HTTP. This shows what was asked, not what will be asked.