Internet Services and Protocols
What is really going on when I open a website?
- Match common Internet services to their protocols
- Explain the role of TCP/IP
- Trace a request from browser to server
Overview
Behind every 'just open this app' there is a stack of protocols doing the actual work. TCP/IP is the family of protocols that makes the Internet possible; each service on top uses its own protocol.
The TCP/IP stack
Four conceptual layers: Application (HTTP, SMTP, FTP), Transport (TCP for reliability, UDP for speed), Internet (IP, routes packets across networks), Network access (Ethernet, Wi-Fi). Each layer only worries about its own job and hands the packet to the layer below.
Common services and protocols
The Web uses HTTP/HTTPS. Email uses SMTP (send), IMAP or POP3 (receive). File transfer uses FTP or SFTP. Remote login uses SSH. Video calls often use WebRTC over UDP. DNS translates names to IPs; DHCP hands out addresses.
Match Service to Protocol
- Match each service to its protocol: web page, email send, email fetch, file transfer, remote login, name lookup, address assignment.
- Check answers with another pair.
- Which protocol is used for encrypted web traffic?
Reveal answer
HTTPS.
- Which is more reliable, TCP or UDP?
Reveal answer
TCP.
- What does DNS translate?
Reveal answer
Domain names to IP addresses.
Open your browser's dev-tools Network tab and load a page. Count how many HTTP requests it makes. Which is the biggest?