Chapter 1

• Like every chapter 1, this is an overview of the book.
• Three broad categories of study
  • Data Communications - The transmission of signals in a reliable and efficient manner.
  • Networking - The technology and architecture of the communications networks used to interconnect communicating devices. (LANS and WANS)
  • Protocols - Is a set of standards defining how two entities communicate The rules for communication.
• Stallings makes three observations:
  • There is no fundamental difference between data processing (computers) and data communications (transmission and switching equipment)
  • There are no fundamental differences among data, voice, and video communications.
  • The distinction among single-processor computer, multiprocessor computer, local network, metropolitan network and long haul network has blurred.
• Another aspect of this is one of Sun's marketing slogans "The Network is the Computer"
• What do these statements mean and how do these statements motivate this course?
• A simple communications model
  • A source generates a set of data to be transmitted.
    • Voice (ie telephone conversation)
    • Digital data (ie Web page request)
  • A transmitter encodes the data into a signal and delivers it to the transmission system.
  • The transmission system delivers the signal from the source to the destination.
  • The receiver accepts the signal from the transmission system and converts it to a form that can be handled by the destination device.
  • The destination receives the data from the receiver.
  
• Note, the source and transmitter may be inside of the same device, as could the receiver and destination.
• There are a number of issues associated with such a system.
  • Efficient utilization of the transmission system.
  • Transmission system/device interfaces
  • Signal Generation
  • Synchronization of sender and receiver
  • Exchange Management
  • Error Detection and Correction
  • Flow Control
  • Addressing and routing
  • Error Recovery
  • Message Formatting
  • Security
  • Network management.
• Stallings states that there could be more or less categories here.

• Data Communications

  • A message m is to be sent from one user to another.
  • This is turned into digital data in memory g , literally bits in memory.
  • This is turned into a series of voltage shifts g(t) on the bus as it is sent to a network interface device (modem, lan card, ...)
  • It is turned into a signal s(t) depending on the transmission media.
  • The signal is transmitted, possibly changed, and distorted to the receiver, where it is received as r(t)
  • These are converted back to a digital signal g'(t)
  • And finally into a message m'
  • Consider the differences between a phone message and a email.

• Data Communication Networking

  • Here we consider Wide Area Networks (WANs) and Local Area Networks (LANs)
  • Usually a WAN is considered to cross multiple public right-of-ways.
  • It probably includes routing
  • Four basic types
    • Circuit Switching Networks
    • Packet Switching Networks
    • Frame Relay
    • ATM
  • LANS are usually within the scope of a campus.
  • Usually controlled by a single organization.
  • Much higher speed than WANs.
• Go read chapter 1, and two as well.