Notes
The internet
- The internet is a global network of networks. The web is a service that runs on it. A LAN covers a small area. Bandwidth is data per second; latency is delay.
Addresses and DNS
- Devices use IP addresses: IPv4 has four numbers from 0 to 255 (32 bits); IPv6 has 128 bits. DNS translates domain names to IP addresses.
Packets and routing
- Data is split into packets with headers (source, destination, order). Routers forward packets. Packets may take different paths and be reassembled in order. Many paths make the internet fault tolerant.
Protocols
- A protocol is a set of communication rules. TCP/IP handles addressing and reliable delivery. HTTP sends web pages; HTTPS adds encryption. Status code 200 means OK, 404 means not found. UDP is fast but not guaranteed.
- A web request: DNS lookup, connect, request, packets travel by routers, response, page displayed.
Topics in this unit
Each topic has its own short notes and practice.
Practice
The web (websites) is just one of many services that use the internet.
Packets may arrive out of order, so numbers allow reassembly.
DNS translates domain names to IP addresses.
Four numbers, each between 0 and 255.
HTTPS encrypts the data in transit.
The data amount per second (bandwidth) limits large downloads, while latency affects response delay.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A student opens https://school.org/news and the page appears.
(a) Identify the protocol and the domain name in the URL.
Show the answer and scoring guide
The protocol is https and the domain name is school.org.
Check off the points you earned:
(b) Describe what DNS does in this process and why it is needed.
Show the answer and scoring guide
DNS translates the domain name school.org into an IP address. Browsers and routers need an IP address to send packets to the correct server.
Check off the points you earned:
(c) The page's data travels as packets. Explain what routers do and why one broken cable does not stop the page from loading.
Show the answer and scoring guide
Routers read each packet's destination address and forward it toward the destination. Because the internet has many paths, packets can be sent another way around the broken cable, so it is fault tolerant.
Check off the points you earned: