The Internet:

Internet is like a really bad mail system. The abstraction we are given is that we can package some
information into a packet, and then send it off, with not guarantee that the data will be received, and
even if it is received, that the data won't be corrupted. 
ie: we given an abstraction for communicating from machine to machine.

Socket is a virtual networking abstraction that will move us to the abstraction of process to process communication.

TLS is a protocol, implemented in the OS, for providing socket abstractions.

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Sockets:

    NIC   
   /   \
  /     \
  v      ^
----    ----
|  |    |  |
|  |    |  |
|  |    |  |
|  |    |  |
|  |    |  |
----    ----
 \       ^
  v     /
  Process

Socket is attached to a bounded buffer. The OS is responsible for managing how data enters, leaves
that buffer.


Creating a socket really amounts to creating the mailbox in the os, and returning a file descriptor corresponding
to the socket buffer. The OS needs to implement how that data actually gets to the network.
OS needs to handle fairness, efficiency, etc.

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Internet Protocols:

UDP: Wrap IP with a [source, destination] ip [address, port] and checksum
-- inherits all the problems of IP.

TCP: provides reliable ordered byte streams within a connection. Have all UDP header info, plus a sequence #

Defn. a connection is a sequence of three events: (1) initializing a connection, (2) sending packets, (3) closing the connection.

// client pseudo-code

	s = socket();
	connect(s, IPAddress, Port #)

// server pseudo-code

	s = socket();

	//
	// Note, we get a new, second socket for actually conducting the particular connection.
	//
	connection = accept(s);
	// ...

How to doest TCP deal with the receiving packets in the incorrect order:

0 1 2 3 4 ...

is received as

0 1 3 2 4 ...

Solution 1: wait until you receive the next packet.

Solution 2: leave a gap in the buffer for the skipped elements, and don't let the user read until
the gap is filled.

But what if 2 is never received.

Solution 3: Only accept packets that increase monotonically (throw out the rest).
Pro: Don't need to buffer for packets.
Con: lose data.

This is okay for a real-time chat, where a late message is a useless message.

Next time: adding reliability and byte streams.