Notes
In-class Notes
Lecture 3
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What is the web?
Web != Internet
So, what is the Internet?!
Network of networks
What is a network?
Networks allow computers to talk to each other
WiFi, Ethernet, LTE - different standards for computer networks
Layers of networking (OSI)
* Physical layer
* Data link layer
* Network layer <----
* Application layer (and such)
Internet Protocol (IP)
- packet-based protocol (NOT a stream or continuous protocol)
Old POTS
- wire from your house to a switching station
- wires between switching stations A and B
...
...
- wires between switching station Y to Z
- wire from switching station to house
Packet switching networks multiplex physical wires over time. (Multiple communication connections over one wire by them taking turns.)
The "turn" is the packet
IP protocol is a "best effort" protocol. NO error correction or retransmission.
TCP means Transmission Control Protocol
turns packets into a reliable data data stream
Network Firewalls block "unwanted traffic"
- really, block all those protocols that aren't safe on the open Internet
TCP adds a "port" to the IP address
- the port identifies which program to talk to
- some are ephemeral (temporary)
- others are "well known", meaning protocol on that port is standardized
Port 25 is for SMTP (email)
80: HTTP
443: HTTPS
22: ssh
Web is transmitted over HTTP
Major HTTP commands
* GET: get documents from server
- can be CACHED
* POST: send form contents to server
- are not cached
You can GET almost anything
- MS Word .doc
- tiff
- PDF
But the real web is
- JPEG, GIF, PNG for images
- CSS for style sheets
- HTML for content
- JavaScript for code
.swf is flash. Flash is not a web standard. AVOID