Unit 4.2 - Data Transfer

• Packets

  Data broken into smaller parts containing a header, message and footer. Protocols add data to the header and footer.
• Simplex Transmission


  Data travels in one direction with no return packets; used in satellite connections for TVs
• Half-Duplex Transmission


  Data may travel in both directions but not at the same time; used in walkie-talkies
• Full Duplex Transmission


  Data can travel in both directions simultaneously by using separate cables for each direction so data cannot interfere with each other
• Define Routing


  Method of selecting paths to send packets along in a network
• Routing Methods

  Devices search for the fastest node and shortest route; network hardware construct routing tables that store the potential paths; forwarding tables store costs for a destination and the first node it must travel to.
• Bandwidth


  A measure of the amount of data that can fit on a cable at any time; data flows at the same speed regardless of bandwidth
• Bit rates


  A way of expressing bandwidth when describing software requirements
• Text Based Emails


  Only a few kilobytes in size; low transmission rates
• Streaming

  Videos send large amounts of data in short time periods; high transmission rates
• File Server

  Handles many requests simultaneously and aims to respond as fast as possible; high transmission rates
• Web Browsing

  Typically small in size and data is transferred over a long period of time; low transmission rates
• Instant Messaging

  Text based, real time communication between two or more people; can be encrypted; multimedia may be sent
• Blogs

  A regularly updated website containing commentaries on topics; Reverse chronological order
• Webcasts

  Broadcasts that are distributed across the internet; A single content source is distributed to many viewers/listeners; can be live or on-demand
• Podcasts

  Video/Audio files released as part of a series; can be syndicated to allow other podcast directories to display your content; uses an RSS feed to update content
• The internet


  Large infrastructure of interconnected packet switched networks; Provides infrastructure for both WWW and non-WWW applications; consists of network hardware communicating through TCP/IP