Data Communications Applications

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- dont have to retype

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Administrative Message Switching
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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

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Administrative Message Switching
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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

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Computers and AMS (1960)
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Distributed Processing

• Began in late 1970s
• Applications executed in parts on different
  computers
• Didnt work well

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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
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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

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Airline Reservation System
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Automatic Teller Machine Network
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Retail Checkout System
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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

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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

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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!

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Disaster Recovery Plan
25
WTC Disaster
26
Case Study Dows 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

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Case Study Dows 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