Question 1

What is a CDN, and why does it make websites faster?

Accepted Answer

A **content delivery network** is a distributed set of servers that store copies of a website's content close to its users — so the data travels a shorter distance and arrives sooner.

**The physical problem it solves.** Data cannot travel faster than light, and in fibre it travels slower still — roughly two thirds of light speed. A request from London to a server in Sydney and back covers something like 34,000 km, which costs well over 150 milliseconds in pure propagation delay before any processing. No amount of bandwidth fixes that; it is **latency**, and it is governed by distance.

**How a CDN works.** The provider operates **points of presence (PoPs)** in many cities. When a user requests a file, DNS or anycast routing directs them to the **nearest** PoP. If that PoP holds a cached copy, it serves it immediately — a **cache hit**. If not, it fetches from the **origin** server, serves it, and keeps a copy for the next request.

**Why the benefit compounds.** Web pages make many requests, and TCP and TLS each require round trips to establish a connection. Halving the round-trip time improves every one of those handshakes, so the total page load improves far more than the raw distance saving suggests.

**What else a CDN does, beyond speed:**

**Absorbs traffic spikes**, so a sudden surge hits hundreds of edge servers rather than one origin.

**Provides DDoS protection**, because the distributed capacity is vastly larger than any single origin's.

**Terminates TLS at the edge**, reducing handshake latency.

**Compresses and optimises** images and other assets.

**Runs code at the edge** in modern platforms, so some logic executes near the user rather than at origin.

**The caching controls that matter:** `Cache-Control` headers set how long content may be held; **cache purging** forces refresh after a change; and **static content caches well** while personalised content generally cannot.

**The concentration concern.** A handful of CDNs now front an enormous share of the web, and their outages have repeatedly taken down large numbers of unrelated sites simultaneously.

Question 2

What is a point of presence?

Accepted Answer

A point of presence (PoP) is a physical location where a network has equipment that other networks or customers can connect to — the places where an abstract "network" actually touches the ground.

Question 3

Why does satellite internet have such different latency?

Accepted Answer

Because latency over satellite is dominated by orbital altitude, and the difference between orbits is a factor of forty. Geostationary orbit (GEO), at roughly 35,786 km. A satellite there orbits at

Question 4

What are peering and transit?

Accepted Answer

The two ways networks connect to each other — and the distinction is essentially who pays whom. The internet is a network of networks. No single organisation runs it. Around a hundred thousand

Question 5

What is the difference between bandwidth and latency?

Accepted Answer

Bandwidth is how much data can move per second. Latency is how long a single piece of data takes to make the trip. They are independent, and confusing them leads people to buy capacity that does not

Question 6

Why is my upload speed so much slower than my download speed?

Accepted Answer

Most residential connections are deliberately asymmetric, meaning far more capacity is allocated to downloading than uploading. This is a design decision rather than a fault. Historically households

Question 7

What is TTL, and why do DNS changes take time?

Accepted Answer

Time to live is how long a DNS record may be cached before it must be looked up again — and it is the reason a change you made an hour ago is still not visible to everyone. Why caching exists.

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