Ch. 3: Networking
  1. Communication types.
    1. Synchronous (interactive) v. asynchronous (message).
    2. Broadcast, multicast, point-to-point.
  2. Protocol.
    1. Rules both ends must follow to communicate correctly.
    2. Different classes of protocols govern different aspects of communication.
    3. Several can be in operation at once.
  3. Client and Server
    1. Client makes request.
    2. Server responds.
    3. Communication is over; server goes on to the next bit of work.
    4. No lengthy connection; just a series of exchanges.
    5. The web works this way.
  4. Simulating a long-term connection.
    1. Session information is recorded on the server, in a file or database.
    2. The browser records an identifier, which is sends with each request.
    3. Cookies or extended URLs.
    4. Division of labor.
      1. Work can be assigned to the client or server.
      2. Many tasks can be solved with various divisions.
  5. The Internet.
    1. Each machine has a numeric Internet Protocol Address (IP address), e. g.,
      Think: phone number
    2. All messages are directed to destination by number.
    3. Interconnected computers.
      1. The net consists of links connected through routers.
      2. Each router forwards the message toward its destination. store-and-forward.
      3. Parts of a communication may take different paths.
    4. TCP/IP
      1. Two primary Internet protocols.
      2. Information broken into small parts: packets.
      3. Packets have sequence numbers.
      4. Each packet is sent separately; may take different routes.
      5. Packets reassembled at receiver.
  6. LAN and WAN.
    1. Local Area Network (LAN).
      1. Connect within a building or small campus.
      2. All computers connected together.
      3. Each packet delivered to all.
      4. Share the channel.
      5. Ethernet is most common.
        1. Wait for quiet.
        2. Check for talking at once.
        3. If so, wait and try again.
      6. Wireless LANs
        1. Computers transmit packets by radio.
        2. Sharing protocol similar to Ethernet.
        3. A wireless hub.
          1. Transfers between wired and wireless.
          2. Forwards packets between clients.
    2. Wide Area Network (WAN).
      1. Covers a larger area.
      2. Generally store-and-forward, described above.
  7. Connecting to the Internet.
    1. Large organizations: High-speed line to own LAN.
    2. Home: ISP.
      1. Dial-up modem.
      2. ADSL.
      3. Cable modem.
      4. Home networks are now common, most often mainly wireless.
    3. Cell phone connections, usually when traveling.
  8. Addresses and naming.
    1. Instead of sending messages by IP address, names are more convenient.
    2. Instead of everyone having a private “phone book” for IP addresses, there is a public one.
    3. Domain Name Service (DNS).
    4. Names are hierarchical.
      1. For example,
      2. Each section is a subdivision.
      3. Names are looked up by a series of servers for the levels.
      4. Historic top-level: .com, .edu, .org, .net, .mil, .gov.
      5. National domains: .ca, .de, .us, etc.
      6. Many more.
      7. Rules for creating new TLDs are looser now, but I don't see a lot of unfamiliar ones in practice.
      8. Here is the official list, but the Wikipedia has a more readable one.
      9. Rules for creating new TLDs are looser now, but I don't see a lot of unfamiliar ones in practice.
  9. The World-Wide Web.
    1. World-Wide Web is part of the Internet.
    2. Clients request files from servers; servers send them.
    3. Universal Resource Locator (URL):
      1. Protocol, hostname, pathname. HTTP = Hypertext Transfer Protocol.
      2. Path is through folders to a file; must like a file path.
      3. The www is a convention.
    4. Redirection.
      1. Server answers, “Go look here instead”
      2. www.whatever often forwards to another server.
      3. Tiny-URL is a URL forwarding service.
    5. Hypertext Markup Language (HTML).
      1. Text and tags.
      2. Images are in separate files; own URLs.

CSPAN interview with Vint Cerf, one of the founders of the Internet.