Communications, Connectivity and Networks

A. Introduction

   1. Connectivity - ability to connect >= 2 computers together
   2. Data communications systems - electronic systems to transmit data
   3. Networks - data communications systems connecting computers
   4. Basic protocol - sender initiates, converts signal, sends signal,
        receiver receives, reconverts, accepts
   5. Uses - email, voice mail, fax, telecommuting, videoconferencing, etc.

B. Basic Terms

   1. Communications Channel
      a. wired - twisted pair phone line, coaxial cable, fiber optic cable
      b. wireless - broadcast radio, cellular radio, microwave, satellite,
   2. Transmission characteristics
      a. analog vs. digital
      b. synchronous vs. asynchronous
      c. direction
         i. simple
         ii. half-duplex
         iii. duplex
   3. Network categories
      a. Intranet - within organization
      b. Extranet - available to users outside organization (often in controlled

C. Communications lines

   1. Public Switched Telephone Network (PSTN)
      - Plain Old Telephone Service
      - digital converted to analog
   2. Dedicated lines
      - faster than conventional phone
      - ISDN (Integrated Services Digital Network)
   3. Digital Subscriber Line (DSL)
   4. T-Carrier Lines
      - powerful, digital
      T-1 1.5MBps
      T-3 43MBps

D. Communication devices

   1. Modem (MODulate/DEModulate)
      - 28.8-56KBps
   2. Cable Modem
      - faster than standard modem
   3. Network interface card
      - for PCs attached to networks
   4. Multiplexers
      - to support multiple devices connected to one line

E. Networks

   1. Devices
      a. Hub
      b. Repeater
      c. Bridge
      d. Gateway
      e. Router
   2. Network Types
      a. Local Area Networks (LANs)
         i. networks in discrete, local area (ie. building or office suite)
         ii. may be linked to other LANs through a gateway node
         iii. the most common way of linking nodes together
         iv. Subtypes
            A. peer-to-peer
            B. client/server
      b. Metropolitan Area Networks (MANs)
         i. cell-phone/wireless communications linking buildings
      c. Wide Area Networks (WANs)
         i. networks interlinked by satellite, microwave, etc.
         ii. best example is Internet
   3. Network Configurations
      a. Star network - computers linked to a central host or server
         i. all communications take place through the center
         ii. time-sharing
      b. Bus network - no central host or server
         i. communications handled alone the bus line
         ii. each machine examines messages to see if they belong to them
         iii. efficient only for small group of users (ie. sharing a printer)
         iv. inexpensive and therefore common in small offices
      c. Ring network - no central host or server
         i. each node connected to two others
         ii. tokens passed around the ring
   4. Communications protocols
      a. Ethernet
      b. Token Ring
      c. TCP/IP (Transmission Control Protocol/Internet Protocol)