ICSA 411 Data Communication

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ICSA 411Data Communication Networking

• Elizabeth Lane Lawley, Instructor

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Bits and Base 2

• Bit binary digit
• One bit has two possible outcomes
• Number of bits can be expressed as a power of two
• 1 bit 21 2 outcomes
• 4 bit 24 16 outcomes
• 8 bit 28 256 outcomes
• 16 bit 216 65,536 outcomes

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Bits and Outcomes
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Bits and Bytes

• Bits are single digits
• 8 bits 1 byte
• Bits are used when calculating communications
  capacity
• mbps 1,000,000 bits per second
• Bytes are used when calculating storage capacity
• MB 1,048,576 bits of data stored

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Data Storage Implications

• Images of pixels X bit-depth of pixel
• Typical screen 640 X 480 X 8
• 2,457,600 bits / 307,200 bytes
• Voice of samples X bit-depth of sample
• CD Audio 44,100 X 16 X 2 (2 channels)
• 1.41 mbps / 176KB per second
• 84.6megabits/10.5MB per minute
• 600MB CD can hold 1 hour of audio

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Communication Channel Implications

• Digital channels are rated in bits per second
• DS-0 56kbps
• DS-1 1.544mbps
• DS-3 44.736mbps
• Ethernet networks 10mbps, 100mbps
• Number of bits in raw data is not the same as the
  number of bits that need to be communicated
  (compression)

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Data Rate Requirements
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Organizational Data Processing

• Voice, Image, Video Processing
• Data Processing
• Technological Convergence All paths lead to data
  processing

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Centralized Data Processing

• Centralized computers, processing, data, control,
  support
• What are the advantages?
• Economies of scale (equipment and personnel)
• Lack of duplication
• Ease in enforcing standards, security
• Local example RITVAX ISC

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Distributed Data Processing

• Computers are dispersed throughout organization
• Allows greater flexibility in meeting individual
  needs
• More redundancy
• More autonomy

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Why is DDP Increasing?

• Dramatically reduced workstation costs
• Improved user interfaces and desktop power
• Ability to share data across multiple servers

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DDP Pros Cons

• There are no one-size-fits-all solutions
• Key issues
• How does it affect end-users?
• How does it affect management?
• How does it affect productivity?
• How does it affect bottom-line?

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Benefits of DDP

• Responsiveness
• Availability
• Correspondence to Org. Patterns
• Resource Sharing
• Incremental Growth
• Increased User Involvement Control

• End-user Productivity
• Distance location independence
• Privacy and security
• Vendor independence
• Flexibility

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Drawbacks of DDP

• More difficulty test failure diagnosis
• More components and dependence on communication
  means more points of failure
• Incompatibility of components
• Incompatibility of data
• More complex management control
• Difficulty controlling information resources
• Suboptimal procurement
• Duplication of effort

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Reasons for DDP

• Need for new applications
• On large centralized systems, development can
  take years
• On small distributed systems, development can be
  component-based and very fast
• Need for short response time
• Centralized systems result in contention among
  users and processes
• Distributed systems provide dedicated resources

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The DP Pendulum

• Centralized systems (mainframes, etc)
• Distributed systems (PCs)
• Networked systems
• Client-Server computing

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Distributed applications

• Horizontal partitioning
• Different applications on different systems
• One application replicated on systems
• Example Office automation
• Vertical partitioning
• One application dispersed among systems
• Example Retail chain POS, inventory, analysis

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Distributed data

• Centralized database
• Pro No duplication of data
• Con Contention for access
• Replicated database
• Pro No contention
• Con High storage and data reorg/update costs
• Partitioned database
• Pro No duplication, limited contention
• Con Ad hoc reports more difficult to assemble

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Networking Implications

• Connectivity requirements
• What links between components are necessary?
• Availability requirements
• Percentage of time application or data is
  available to users
• Performance requirements
• Response time requirements