Intro to Sockets

• This is chapter 58
• An internetwork or internet connects different computer networks allowing hosts to communicate with one another.
• A goal is to hide the details of different physical networks
• And present an unified architecture to all machines connected to the network.
• This includes a single address space
• TCP/IP is the dominate network protocol.
• A network protocol is a set of rules defining how information is transmitted across the network.
• These are frequently designed in a series of layers.
  • Messages are sent down through the layers
  • Across the network
  • And back up the layers.
  • Hillman is happy to explain all of this in 475.
  • 
• Each layer needs to know how to supply/receive messages from the lower layer
• And each layer wraps the information with what it needs to keep track of messages. (See page 1183)
• Data Link Layer
  • Lowest level.
  • Our programs don't need to worry about this layer.
  • You will potentially travel across many different types of networks,
  • But the hardware takes care of this for you.
  • Error detection, transmission control, rebroadcast, ....
• Network Layer (IP)
  • Concerned about packets
  • Breaks the data in packets small enough for transmission
  • Routes the data across the internet
  • Communicates with transport layer
  • IPV4 vs IPV6
  • Datagrams
    • Small packets of data
    • A message may be composed of multiple datagrams
    • Header information used to route and reassemble packets
  • Connectionless and Unreliable
    • Packets might not arrive in order.
    • Packets might not arrive.
  • IP Addresses
    • In IPV4 it is a 32 bit number
    • Generally written as nnn.nnn.nnn.nnn
    • A network mask tells what part of the ip address is network and what part is machine.
    • nnn.nnn.nnn.mmm/24 means the top 24 bits are network.
    • Some addresses have a default meaning
      • 127.0.0.1 is the local machine (loopbakc)
  • Transport layer (TCP)
    • Two main protocols
      • UDP : User Datagram Protocol
      • TCP : Transmission Control Protocol
    • Port Numbers:
      • Like mail boxes
      • Some are pre-assigned (sort of) /etc/services
      UDP
      • Connectionless
      • Does error checking
      • unreliable
      • Good for small (~500 byte) messages
      • Faster, but at a cost of the above.
      • TCP
        • Does everything you want
        • But at a price: speed.
      • A connection is:
        • A transport protocol
        • A source ip address
        • A source port number
        • A destination ip address
        • A destination port number
  • RFC: Request for Comment
    • This is how the internet is defined.
    • RFC 791 IP
    • RFC 768 UDP
    • RFC 1149