Question 47

Question

Question 47

BlackTom AI · Accepted Answer

CDNs cache and serve static assets from geographically distributed edge servers to reduce latency and improve load times, so answer c is correct.

1) Relevant knowledge points and concepts
- CDN (Content Delivery Network): a distributed system of servers (edge nodes) that cache static content (images, CSS, JS, videos) close to end users.  
- Cache hit vs miss: if an edge node has the asset (hit) it serves it directly; otherwise it fetches from the origin server (miss) and caches it.  
- Benefits: lower latency, reduced bandwidth and load on the origin, improved scalability and often improved availability.

2) Step-by-step reasoning process
- User requests a static asset.  
- DNS directs the user to a nearby CDN edge node.  
- If the edge node has the asset cached (hit), it returns it immediately; if not, the edge fetches from origin, returns it to the user, and caches it for subsequent users.  
- Because the physical distance and network hops are reduced, round-trip time is lower and perceived page load improves.

3) Simple illustrative calculation (intermediate steps)
- Suppose origin server RTT = 150 ms; edge node RTT = 30 ms.  
- Latency improvement = 150 ms − 30 ms = 120 ms.  
- Percent improvement = (120 / 150) × 100% = 80% faster for that request. This quantifies why CDNs improve load time.

4) Why the correct answer is correct
- Option c explicitly states delivering static content from servers closer to users to improve load time and reduce latency, which matches the CDN’s main purpose.

5) Why other options are incorrect
- a: CDNs do not replace databases or store application state in the browser; they cache static files at edge servers.  
- b: Encryption of traffic is provided by TLS/HTTPS; CDNs may terminate TLS but their primary role isn’t to “encrypt all traffic.”  
- d: CDNs improve availability but cannot guarantee websites never experience server failures.

6) Conclusion
The best choice is c, which matches the provided correct answer: "To deliver static content from servers closer to users, often improving load time and reducing latency."

Question 47单项选择题

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