Introduction:
	Syllabus
	Calendar
	Course Website

No textbook this semester!
	Weird, huh?
	I never found one I really liked
	Instead, I'm going to produce documentation for the class examples
		What else can I do?

Notes:
	The client/server project, done well, is a lot of work
	Project is a client/server system
		- It is a text-based multi-user RPG
	This is a project-focused course
	Dual-purpose, but less so this semester
		- Learn to develop network software (main)
		- Learn how networks work (secondary, but important for #1)
		- This odd dual nature is sometimes considered disconcerting
		- Common comment:  "It feels like two separate classes"
	But this semester, most of you had Cyb251
		I can get the others of you through just fine
		Might assign a couple youtube videos or something
	This class will be focused on network programming
	Nobody can show you the matrix
	
The rain forest and ssh	
Comparison with Distributed System
	Cluster is a distributed system
Access to information and tyranny of geography
client/server systems
Metcalfe's Law
peer to peer networks
mobile vs. wireless
	- not the same, but related
mobile phone users expect to pay for stuff
network neutrality

More technical, review from 251 if you had it, overview if not

packets, frames, connections, datagrams, and packaging
broadcast, multicast, vs. point to point
LAN vs. WAN
units:  bits per second, not bytes.  Why?
switch vs. hub (and wireless)
Other little boxes you probably have (all of these can be stuffed into one box):
	gateway
	router
	firewall
	access point
	modem

WAN:
	Diverse locations, link may (usually is) through the Internet
	Can be unified to look like LAN

The Internet:
	subnets managed by different ISPs, all linked together
	Addressing scheme
	IPv4 and IPv6

Network layers and protocols
	layers can be replaced
	lowest layer is physical layer
	headers

Making the network work
	Error correction
	routing
	scalability
	connections
	acknowledgement
	lower levels are unreliable
	services provided by layers

OSI Network Layers

Physical Layer:
	Transmits 0's and 1's
	This must happen reliably
	More than one method is used here
	Not in TCP/IP, although this function must be performed

Data link layer:
	Form 0's and 1's into frames
	Send acks
	Hide errors from network layer
	For broadcast:  Manage shared channel
	Link layer in TCP/IP

Network layer:
	routing
	For broadcast:  Do nothing
	Internet layer in TCP/IP
	Packet format in TCP/IP is called IP (Internet Protocol)
	IP routing is not always effective

Transport layer:
	Separate messages into packets and put them back together
	TCP and UDP handle this in TCP/IP
	TCP is reliable, UDP is not
	
Session layer:
	maintain sessions
	Sessions involve keep track of which computer should send data, checkpointing long transmissions, etc.
	Not in TCP/IP, TCP handles some of these functions

Presentation layer:
	Convert internal information to a representation that can be transmitted
	Allows high-level structures to be defined and transmitted (objects, etc)
	Not in TCP/IP

Application layer:
	Contains protocols like HTTP, SMTP, SSH, etc.
	Servers, etc. are here

We will use the TCP/IP model, because it exists
	And we're programming this semester, not philosophizing

Why TCP/IP?
	It put existing protocols into a model
	OSI is complex and includes layers nobody needs
	Initial implementations were slow compared to BSD UNIX
	Politics:  Friendly old UNIX had TCP/IP, OSI standard was from the government

Was that bad?
	TCP/IP isn't that generic
	No physical layer definition

Simple client and server in C