Question 1

What is actually inside a network packet?

Accepted Answer

Layers of **headers** wrapped around your data, each added by a different part of the networking stack and each read by a different piece of equipment along the way.

**Why layers exist.** Each layer solves one problem and does not need to understand the others. A router moving a packet across the internet does not care whether it contains an email or a video frame; a web browser does not care whether the packet travelled over Wi-Fi or fibre. This separation is what allows the internet to run over any physical medium and carry any application.

**Working outward from your data:**

**Application data** — the actual content: the HTTP request, the DNS query, the video frame.

**Transport header (TCP or UDP)** — source and destination **port numbers**, identifying which application on each machine. TCP adds sequence and acknowledgement numbers, flags and a window size.

**Network header (IP)** — source and destination **IP addresses**, plus a **TTL** (time to live) that decrements at each router, a protocol field, and fragmentation information. This is the header routers actually use.

**Link header (Ethernet or Wi-Fi)** — source and destination **MAC addresses**, identifying the immediate next device on the local link only. **This header is rewritten at every hop**, which is the key thing people miss: MAC addresses are local, IP addresses are end to end.

**Frame check sequence** at the end, detecting corruption.

**What changes as it travels.** The IP addresses stay the same end to end (unless NAT rewrites them). The **MAC addresses change at every router**. The TTL decreases by one each hop — and if it reaches zero, the packet is discarded and an error is returned, which is exactly how **traceroute** works.

**What encryption hides.** TLS encrypts the application data. **It does not encrypt the IP and TCP headers** — so anyone observing the path still sees who is talking to whom, how much, and when. That metadata is frequently more revealing than the content.

**MTU** limits packet size, typically 1500 bytes on Ethernet.

Question 2

What is the difference between TCP and UDP?

Accepted Answer

TCP guarantees delivery; UDP does not — and that single trade-off determines which one every internet application uses. TCP (Transmission Control Protocol). A connection-oriented, reliable protocol:

Question 3

How do video calls actually connect?

Accepted Answer

By establishing a direct path between the two devices wherever possible, which is harder than it sounds because almost every device sits behind a router that blocks incoming connections by default.

Question 4

How is internet filtering and censorship actually implemented?

Accepted Answer

Through several techniques operating at different layers, each with different costs, different accuracy and different ease of circumvention — and most real systems combine them. The techniques, in

Question 5

What is QUIC, and what did HTTP/3 change?

Accepted Answer

QUIC is a transport protocol built on UDP rather than TCP, designed to fix problems that could not be fixed in TCP itself. HTTP/3 is HTTP running over QUIC. The problem it solves: head-of-line

Question 6

What is Quality of Service on a router?

Accepted Answer

A set of techniques for deciding which traffic gets priority when there is not enough capacity for everything — because the only time prioritisation matters is when a link is full. The problem. A

Question 7

What are jitter and packet loss, and why do they matter more than speed?

Accepted Answer

Because a video call does not need much bandwidth — it needs packets arriving consistently, and these two measures describe whether they do. Latency is how long a packet takes to travel, measured as

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