Networks!

Computers all talk to each other
	They're more useful that way
	Example:  mine all talk
	Example:  What apps did you use this morning?
		- Assuming that you have a phone and use apps
		- Never assume everyone is some particular way
		- Driver's license name length...

The lowest level:  Some kind of physical signal
	"physical" here as in "follows the laws of physics"
	Common Options:
		Electricity
		Radiation traveling through the air
		Light, usually contained in a fiber
		
Communication Protocols
	A system of rules for communication
		Longer definitions are available
	Each side must follow the protocol
	Any means of meeting the rules is ok

To talk, they need to have addresses
	Intial address:  MAC (Media Access Control)
		- More than one per computer?  Sure!
	Later:  IP address (Internet Protocol)
		- IP is sort of variable
		- Campus has a street address, but I can receive mail here
		- NAT
		- There aren't enough addresses with IPv4
		- IPv6 would fix it if we decided to use it
		- Some countries did change which side of the street they drive on
		- If you have two, you can build a bridge

"Server" and "Client"
	These are roles
	"Server" is also used to refer to hardware expected to fulfill a role
	Starting a server on isoptera
		- And connecting to it! 
		- How about a server NOT on isoptera, just on a "regular" computer?

It helps to put a server in a convenient place
	Not always possible
	In this room:  Not a convenient place unless you're also here and not on wifi
	As long as you can find it, it's ok
		- Dynamic DNS
		- SSH tunnels

Networking layers:
	Physical
		Hardware, wires, etc.
	Link
		A bunch of computers linked together
		Protocol examples:  802.11 (WiFi), 802.3 (Ethernet)
		Information is packaged into frames
	Internet
		Routing, going between groups linked by the previous layer
		Example:  IP
		Information is in packets, which fit into a frame usually
		Layer 3 switch uses this layer, hides actual layout of the link layer
	Transport
		Establish a connection across the network
		Lots of error correction
		Example:  TCP
		Most of the functions here are sometimes optional
		Example:  UDP
	Application
		This is the software that uses the network
		Example:  Web browser or server, SSH client or server, WoW client or server
		This is what we write in CS435
	
Security becomes important
	Cryptography is a leading candidate for Topics of Interest week

Couple features to mention:
	DNS
	DHCP

Programming with Networks:
	Brief Python example
	Browser