Lectures
Telegraph
  First(?) electrical broadcast network.
    Broadcast multiple stations.
    Operators provided computational logic.
      Used Morse code - ternary encoding dots, dashes, and silence.
      Converted messages to Morse.
      Provided timing.
      Monitored congestion.
      Provided addressing and recognition of receiving address.
      Provided repeater function.
    Late 1700s, early 1800s

Telephone
  Networked to optimize resources.
  Sometimes lines were shared by multiple houses on block/neighborhood.
    Used ring counts to address specific home.
  Use operator and plug boards to route calls.
  Allowed a limited number of lines to provide connections for many
    Just not at same time.
  Once connection established, dedicated use of line until connection broken.
    Reason for charging by minute even if no talking.
  Mid 1800s

Electronic age.
  Digital sampling of voice. 
  Compressing and packetizing data.
  Requires more overhead and addressing.
  Computerized switching.
  Digitization and packetization 
    allows limited number of lines to carry multiple calls.
  Voice over IP.
 


Point to point physical connection vs. network connected packet communication.

Point to point physical connection.
  Pluses
    Very secure.
    High speeds.
    Low overhead/meta-data.

  Minuses
    Circuits dedicated to one task
      even when idle.
    Each device individually wired to
      dedicated port.
    Port protocols often limited in nature.
      - task specific.

  Examples :
    Keyboard
    Monitor 
    Parallel printer.
    Teletype terminal as interface into computer system
       over serial port.
  
Network - packet driven.
  Pluses
    Most of the inter-connection (lines) shared.
    Jobs packetized - uses lines only when needed.
    Task protocols embedded in packets, not concern of network. 
    Single interface for multiple tasks.    

  Minuses
    Packets can be 'spied' on. Requiring additional security.
    Large amount of meta-data or overhead needed to deliver packets.
      Addressing.
      Sequencing.
    Different tasks competing for same line.
    Time sensitive task require additional protocols and priority.

  Network/packet driven technologies.
    Ethernet, Wireless, Bluetooth.

As technology became better, 
  networking/packet driven communication won out even for short distances.


Hybrid
  Network encoded packets over serial.
    Advantages of point to point hardware with serialized data stream.

  Internet
  PCIe
  SATA
  USB
  
Early phone systems used networked but not packetized connections.
  Allowed reuse of a few common lines between towns.

As computer technology came into its own,
  Phone companies realized packetize/digitizing technology could
  optimize their hardware use even more.




ISO - OSI  see : en.wikipedia.org/wiki/Iso_osi

  International Standards Organization
  Open System Interconnection 
    Standard driven by phone companies (AT&T and European).
    Basic concept 1978, published 1984 (Ma Bell broken up in 1984).

  Broad description of a non-proprietary packet switched network.

  Application Layer - User interface to network.

  Presentation Layer - converts data to common syntax. 

  Session Layer - establish type of connection between two machines FTP,etc.

  Transport Layer - converting files to frames and back.

  Network Layer - successful delivery individual blocks (frames) of data.
    Logical address of node.

  Data Link Layer - bits and and formatting blocks of bits. Physical address
    of device.

  Physical Layer - electrical, physical technology

layer details