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Chapter 4

Chapter 4. Data Communications Applications. Categories of Applications. Human-machine interaction Type of information Timeliness. Human-Machine Interaction. Person-to-person Machine can be in the middle Ex.: phone call Person-to-machine, machine-to-person

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Chapter 4

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  1. Chapter 4 Data Communications Applications

  2. Categories of Applications • Human-machine interaction • Type of information • Timeliness

  3. Human-Machine Interaction • Person-to-person • Machine can be in the middle • Ex.: phone call • Person-to-machine, machine-to-person • User interfaces to computer through terminals • Computer responds to user • ATM transaction • Machine-to-machine • File transfer between computers • Automated instrumentation communicating to computers

  4. Information Types • Voice • Structured data • Has records and fields • Used in data processing apps • Unstructured data • Word processing • Images • Video, photographs, FAX

  5. Timeliness • Online, realtime (fast) • Timesharing computers • Airline reservations • Store and forward (delayed) • Voice mail • e-mail • Batch (offline) • Collect data during day, transmit at end of day

  6. Data Application Evolution • Teletype machines (TTY) - electronic typewriters • Connected in networks to transmit information

  7. Administrative Message Switching • Connecting teletypes using telecom lines • Point-to-point • Teletypes in branch offices connect directly to a teletype in main office, one-to-one • Messages received by one teletype had to be typed into another to relay it • Improvement: • Store messages on paper tape • Relay using paper tape- don’t have to retype

  8. Administrative Message Switching

  9. Administrative Message Switching • Multi-point line • More than one TTY on a line • Messages seen by all TTYs on the line • Polling • Master TTY polls (asks) remote (slave) TTY if it has a message • Avoids message collisions • Requires address information in message (overhead) • Slaves must wait their turn

  10. Administrative Message Switching

  11. Computers and AMS (~1960) • First • Computer could read messages on one line and transmit on another like router • Second • Computers grew more powerful • Added storage and calculation capabilities • Third • Users interacted on-line with computer • Fourth • Multiple users timeshare with computer

  12. Computers and AMS (~1960)

  13. Distributed Processing • Began in late 1970s • Applications executed in parts on different computers • Didn’t work well

  14. Client-Server Computing • Server computers have data bases or run applications that Client computers access or use. • High-speed connections needed between clients and servers to handle multimedia • Most LANs use client-server model

  15. Small LAN

  16. Structured Data Applications • Delta Airlines reservation system (1985) • 4000 voice lines, 18 reservation centers • 66 data lines handling 350 transactions/second peak • 23,000 terminals in data network, including terminals in 2800 travel agencies • Automatic teller network • Retail checkout system • Point of sale terminals • Data collection at night • Accounting and inventory info updated in HQ computer

  17. Airline Reservation System

  18. Automatic Teller Machine Network

  19. Retail Checkout System

  20. Unstructured Data Applications • E-mail • Host computer holds user electronic mailboxes • Disk space is big issue • Security - company can read e-mails • TCP/IP uses Simple Mail Transfer Protocol (SMTP) • Disadvantages • Cannot send executable file with e-mail • Limited e-mail size • No foreign character sets • Multipurpose Internet Mail Extension (MIME) is an extension of SMTP

  21. Unified Messaging System • Some e-mail software allows • E-mail • Voice mail • Fax • Sends to single phone number or mailbox • Computer or phone can access • System can “read” e-mail message if you access via phone

  22. Image Application • Video conferencing • Meetings conducted between locations using cameras and TVs in conference rooms • One-way or two-way • Full motion or freeze frame • Freeze frame uses occasional updating • Reduces data rate • Corporate environment • Conference room with camera for people and camera (or computer) for slides • Compression technology helps data rate

  23. Data Communication Considerations • Response time • Security • Especially for business • Planning for failures • Have backup for computer/system • Disaster recovery - long term failure • Needs planning • Test the plan!

  24. Disaster Recovery Plan

  25. WTC Disaster

  26. Case Study: Dow’s Applications That Use Telecommunications • Dow Corning minimizes the number of mainframes used for business apps • Use a few computer centers accessed throughout company by telecom network • Unit cost of computing is cheaper even though telecom cost is higher percentage of total • Manufacturing centers use smaller computers linked to mainframes

  27. Case Study: Dow’s Applications That Use Telecommunications • Business apps • Customer order processing • Inventory management and control • Manufacturing planning and scheduling • Finance and accounting • Personnel and human resource management • Planning and budgeting • Mainframes handled e-mail starting in 1983 • Intranets growing • Voice mail and video conferencing

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