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High-Performance Web: Protocols & Edge Systems

Challenge your understanding of HTTP/2, HTTP/3, QUIC, TLS 1.3, TCP tuning, and Content Delivery Network architectures.

This is a free, 16-question multiple-choice quiz. Answer each question to see whether you got it right, with an explanation for every answer. There is no sign-up and no time limit — take it as many times as you like, and scroll down for the full answer key once you are done.

Question 1 of 16

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What underlying transport layer protocol does HTTP/3 utilize instead of TCP?

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Answer key & explanations

Every question in this quiz, with the correct answer marked and an explanation of why it is right. Use it to revise before or after taking the quiz above.

  1. 1.What underlying transport layer protocol does HTTP/3 utilize instead of TCP?

    • ASCTP
    • BQUIC (built on top of UDP)✓ Correct
    • CRaw IP Sockets
    • DWebSockets over TLS

    Correct answer: QUIC (built on top of UDP)

    HTTP/3 replaces TCP with QUIC, an encrypted multiplexed transport protocol running over UDP that eliminates TCP head-of-line blocking.

  2. 2.What is the Head-of-Line (HoL) blocking problem in HTTP/2, and how does HTTP/3 resolve it?

    • AHTTP/2 locks the browser UI thread; HTTP/3 moves rendering to web workers
    • BIn HTTP/2, a dropped TCP packet stalls all multiplexed streams; HTTP/3 uses QUIC over UDP to isolate packet loss to individual streams✓ Correct
    • CHTTP/2 cannot compress headers; HTTP/3 introduces Brotli compression
    • DHTTP/2 limits domain names to 64 characters; HTTP/3 expands this to 256

    Correct answer: In HTTP/2, a dropped TCP packet stalls all multiplexed streams; HTTP/3 uses QUIC over UDP to isolate packet loss to individual streams

    Because HTTP/2 runs over a single TCP stream, a dropped packet stalls the entire connection; QUIC handles streams independently over UDP, isolating loss to the affected stream.

  3. 3.How does TLS 1.3 reduce handshake latency compared to TLS 1.2?

    • AIt removes public key cryptography entirely
    • BIt reduces the standard full handshake to a single round-trip (1-RTT) and supports zero round-trip (0-RTT) resumptions✓ Correct
    • CIt forces clients to download the entire certificate chain through separate UDP channels
    • DIt delegates handshake validation to local DNS resolvers

    Correct answer: It reduces the standard full handshake to a single round-trip (1-RTT) and supports zero round-trip (0-RTT) resumptions

    TLS 1.3 streamlined the cryptographic handshake from two round-trips (2-RTT) to one (1-RTT), and introduced 0-RTT session resumption for returning clients.

  4. 4.What security risk is associated with the 0-RTT (Early Data) feature in TLS 1.3?

    • AThe connection is vulnerable to Replay Attacks unless applications explicitly protect state-modifying requests✓ Correct
    • BThe data is transmitted in unencrypted plaintext
    • CThe client's physical IP address is exposed to external BGP routers
    • DThe server's private certificate is leaked to the browser

    Correct answer: The connection is vulnerable to Replay Attacks unless applications explicitly protect state-modifying requests

    Because 0-RTT data is sent before the full handshake completes, an attacker who intercepts the initial packets can replay them, making it unsafe for non-idempotent operations.

  5. 5.What is HPACK in HTTP/2?

    • AA JavaScript framework for caching dynamic HTML templates
    • BA specialized header compression format that eliminates redundant metadata across requests using static and dynamic tables✓ Correct
    • CA binary serializer for database transactions
    • DA tool for bundling frontend CSS files into single chunks

    Correct answer: A specialized header compression format that eliminates redundant metadata across requests using static and dynamic tables

    HPACK compresses HTTP/2 headers using static and dynamic lookup tables, avoiding the transmission of repetitive headers (e.g., User-Agent, Cookies) and resisting CRIME attacks.

  6. 6.What is the role of the BBR (Bottleneck Bandwidth and RTT) congestion control algorithm?

    • AIt drops all TCP packets that exceed 1500 bytes
    • BIt models the network pipe's actual bottleneck bandwidth and round-trip time to maximize throughput while minimizing packet queues and bufferbloat✓ Correct
    • CIt forces web servers to close idle socket connections after ten seconds
    • DIt limits the maximum number of concurrent HTTP connections to 100

    Correct answer: It models the network pipe's actual bottleneck bandwidth and round-trip time to maximize throughput while minimizing packet queues and bufferbloat

    Developed by Google, BBR measures actual path bandwidth and round-trip time, adjusting pacing rates to achieve high throughput without causing bufferbloat or relying on packet loss as a trigger.

  7. 7.In modern CDN architecture, what is an Edge Worker (e.g., Cloudflare Workers, Fastly Compute)?

    • AA physical data center employee who manually manages server cabling
    • BServerless code (often compiled to WebAssembly or running in V8 isolates) executed at edge locations close to end-users✓ Correct
    • CAn automated web crawler that indexes websites for search engines
    • DA background cron job that purges outdated database rows nightly

    Correct answer: Serverless code (often compiled to WebAssembly or running in V8 isolates) executed at edge locations close to end-users

    Edge workers run lightweight serverless code (e.g., in V8 isolates or Wasm runtimes) on CDN edge nodes globally, executing logic and transformations close to the user.

  8. 8.What does the 'Cache-Control: stale-while-revalidate' directive tell a browser or CDN?

    • AThe asset must never be cached under any circumstances
    • BThe client can serve a stale cached response immediately while asynchronously fetching the fresh asset in the background✓ Correct
    • CThe cache must re-download the file every sixty seconds regardless of changes
    • DThe asset is permanently cached and cannot be invalidated until the browser restarts

    Correct answer: The client can serve a stale cached response immediately while asynchronously fetching the fresh asset in the background

    'stale-while-revalidate' permits clients to serve cached stale content immediately for fast responses, while an asynchronous request updates the cache in the background for future visits.

  9. 9.How does Anycast routing operate in global Content Delivery Networks?

    • AIt broadcasts every client request to all data centers simultaneously worldwide
    • BMultiple physical servers advertise the same IP address via BGP, routing clients automatically to the topologically nearest point of presence✓ Correct
    • CIt switches connections between IPv4 and IPv6 based on network latency
    • DIt routes all international traffic through a single primary server in Switzerland

    Correct answer: Multiple physical servers advertise the same IP address via BGP, routing clients automatically to the topologically nearest point of presence

    Anycast assigns the same IP address to multiple edge locations worldwide; BGP routing directs user packets to the topologically closest data center, minimizing network distance.

  10. 10.What does TCP Fast Open (TFO) accomplish during connection establishment?

    • AIt increases the size of the initial window from 10 to 100 packets
    • BIt allows data to be included and exchanged directly within the initial TCP SYN packet using a secure cryptographic cookie✓ Correct
    • CIt disables the TCP three-way handshake entirely
    • DIt routes packets over raw UDP infrastructure

    Correct answer: It allows data to be included and exchanged directly within the initial TCP SYN packet using a secure cryptographic cookie

    TCP Fast Open uses a pre-shared TFO cookie to allow data payloads inside the initial SYN packet, cutting out a full round-trip delay during connection setup.

  11. 11.What is the purpose of Server Timing headers (Server-Timing) in HTTP responses?

    • ATo set the system clock of client devices automatically
    • BTo communicate backend server performance metrics (e.g., database lookup, cache hits) directly to the browser's DevTools and Performance API✓ Correct
    • CTo limit the maximum execution time of client-side JavaScript
    • DTo synchronize video frames during WebRTC streaming calls

    Correct answer: To communicate backend server performance metrics (e.g., database lookup, cache hits) directly to the browser's DevTools and Performance API

    The Server-Timing header passes server-side timing metrics (e.g., db=52ms, cache_miss) to the client, visible in browser developer tools and accessible via the Navigation Timing API.

  12. 12.What optimization does Early Hints (HTTP status code 103) enable?

    • AIt tells the browser to display a loading spinner animation
    • BIt allows the server to send link headers to the browser to preload critical CSS and JS assets while the main response is still being computed✓ Correct
    • CIt redirects the user to a mobile-optimized subfolder
    • DIt compresses the subsequent HTML body using Gzip

    Correct answer: It allows the server to send link headers to the browser to preload critical CSS and JS assets while the main response is still being computed

    HTTP 103 Early Hints returns critical link relations (preload, preconnect) while the server is still assembling the final response, allowing the browser to download assets early.

  13. 13.Why is Brotli compression generally preferred over Gzip for compressing static web assets (HTML, CSS, JS)?

    • ABrotli can only compress binary files
    • BBrotli utilizes a built-in pre-populated static dictionary, achieving 15-25% better compression ratios than Gzip at similar speeds✓ Correct
    • CGzip is no longer supported by modern web browsers
    • DBrotli runs directly on graphics cards

    Correct answer: Brotli utilizes a built-in pre-populated static dictionary, achieving 15-25% better compression ratios than Gzip at similar speeds

    Brotli includes a static dictionary of common web words and patterns, delivering substantially smaller file sizes than Gzip, which directly improves page load times.

  14. 14.What problem occurs during a 'cache stampede' (or thundering herd) on high-traffic web servers?

    • AThe server's solid-state drive runs out of physical write sectors
    • BA cached key expires, causing thousands of concurrent requests to hit the origin database simultaneously to regenerate the same asset✓ Correct
    • CThe browser's local storage runs out of memory
    • DThe CDN purges all assets simultaneously due to an invalid regex pattern

    Correct answer: A cached key expires, causing thousands of concurrent requests to hit the origin database simultaneously to regenerate the same asset

    A cache stampede happens when a hot cache entry expires under heavy load; hundreds of incoming requests miss the cache simultaneously, overwhelming the origin database.

  15. 15.What is the impact of excessive Bufferbloat on real-time web applications?

    • AIt crashes the web server's memory allocation pool
    • BExcessive packet buffering in unmanaged network queues causes high latency and jitter, degrading real-time performance✓ Correct
    • CIt forces browsers to downgrade from HTTPS to HTTP
    • DIt permanently corrupts SSL certificate handshakes

    Correct answer: Excessive packet buffering in unmanaged network queues causes high latency and jitter, degrading real-time performance

    Bufferbloat occurs when oversized router buffers hold packets instead of dropping them, introducing massive latency and jitter that severely degrades interactive connections.

  16. 16.What is Connection Coalescing in HTTP/2 and HTTP/3?

    • AMerging multiple database records into a single JSON object
    • BReusing an existing open connection to fetch resources from different hostnames if they resolve to the same IP and share an SSL certificate✓ Correct
    • CCombining audio and video packets into a single WebRTC channel
    • DSplitting a single TCP connection across multiple physical network cables

    Correct answer: Reusing an existing open connection to fetch resources from different hostnames if they resolve to the same IP and share an SSL certificate

    Connection coalescing lets a client reuse an existing HTTP/2 or HTTP/3 connection for requests to different domains if the domains resolve to the same IP and match the TLS certificate.

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