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Data Communications

Data Communications. The Basic Communication Model . Sender Coder Channel Decoder Receiver. Coder. Send. Sender. Coder. Channel. Decoder. Receiver. The Basic Communication Model. Computer-based Data Communications. Data communications definition:

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Data Communications

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  1. Data Communications

  2. The Basic Communication Model • Sender • Coder • Channel • Decoder • Receiver

  3. Coder Send Sender Coder Channel Decoder Receiver The Basic Communication Model

  4. Computer-based Data Communications Data communications definition: The movement of coded data and information from one point to another by means of electrical or electromagnetic devices, fiber-optical cables, or microwave signals. Also called teleprocessing, telecommunications, telecom, and datacom.

  5. The Basic Data Communications Schematic Channel Computer Modem Modem Terminal

  6. Basic Data Communications Schematic Terminal to Modem to Channel to Modem to Computer A modem is always required between a telephone and a digital computer.

  7. Types of Networks (interconnected datacom devices) • WAN (wide area network) • Covers a large geographic area • Includes a wide variety of circuits • Usually includes host computers • LAN (local area network) • Limited area but could include 100 or so micros • Facilitates office automation • MAN (metropolitan area networks) • spans one city/metropolitan area

  8. An Expanded Data Communications Network Visual display terminals Multiplexer Cluster control unit Modem Hard copy terminals Other types of terminals Channel Multiplexer Host computer Front-end processor Modem

  9. Terminal Types • Keyboard CRT - Cathode Ray Tube VDT - Video Display Terminal Hardcopy terminal Teleprinter terminal

  10. Terminal Types (continued) • Keyboard terminals • Push-button telephone • Point-of-Sale (POS) • Data collection • Special purpose

  11. Other DataCommunications Hardware • Cluster control unit -- controls multiple terminals in an area • Modem -- rated speed of bits per second determines transmission speed. Like a pipe determines water flow. • Multiplexer -- allows multiple terminals to share a single channel.

  12. Channel • WAN channel components • Local loop • Typical circuitry • Twisted pair (4 wires) • Coax (buried) • IXC circuit (interexchange) • Typical circuitry • Microwave • Fiber-optical cable

  13. User’s modem User’s modem The Channel of a Wide Area Network Satellite IXC circuit Local loop Earth station (interexchange channel) Earth station Telephone company central office Microwave tower IXC circuit (interexchange channel) Microwave tower Local loop Telephone company central office Telephone company central office Telephone company central office

  14. Front-end Processor • Ports • Serial versus parallel transmission • Message switching, store and forward Host

  15. The Front-end Processor Software Host Computer Interface Channel Interface Units Parallel transmission Serial To host transmission Secondary storage

  16. Data Communications Software • Host (telecommunications monitor or TCM) • Front-end processor (network control program)

  17. Security log Telecommunications Monitor (TCM) Host Prioritize message 3 4 1 2 Maintain security log Interface with DBMS DBMS Primary storage status Backup and restart

  18. Network Control Program (NCP) • Poll terminals such as roll call polling • Maintain a record of activity; date and time stamps • Convert codes • Editing such as error checking and reformatting • Add and delete routing codes • Maintain a history file of messages • Maintain statistics on network use

  19. Data Communications Links the General Systems Model Elements T = terminal Standards Information processor T Environment T Management T Input T Transformation T Output T

  20. Basic Network Approaches • Timesharing • Distributed processing • Client/server computing • Clients are users, typically using workstations networked to form LANs • Server is a mainframe, mini, or even a micro

  21. Basic Network Approaches (continued) • Complex software permits resource sharing • Combines central computing (MIS, DP) with end-user computing

  22. A Timesharing Network Legend: Computer Terminal

  23. A Distributed Processing Network Legend: Distributed Central Computer Computer

  24. Common Carriers • Services • Public-measured • Private (a.k.a. leased or dedicated line) • Integrated services digital network (ISDN)

  25. ISDN- Integrated Services Digital Network • Simultaneous multimedia transmissions • Two types of channels • B channel carries data • D channel carries signals Data Signals

  26. Two Standard Structures • Basic access (typically residential) • 2 B channels @ 64 kbps ea. • 1 D channel @ 16 kbps • Primary access (typically business) • 23 B channels @ 64 kbps ea. • 1 D channel @ 64 kbps

  27. Local Area Networks • File server, network server • Peripherals • Circuitry • Owned by using firm • Twisted pair is least expensive • Coax handles videoconferencing • Fiber-optics is most secure

  28. LAN Software • Novell (NetWare) and Microsoft (Windows NT) are leading vendors of LAN software • Software allows servers and peer-to-peer connections

  29. Workstation 1 Manager 1 Letter Quality Printer Workstation 2 Network Server Secretary 1 Users Workstation 3 Plotter Secretary 2 Hard Disk Workstation 4 Manager 2 A Local Area Network

  30. LAN Control Methodologies • Contention-based (Ethernet) • First-come, first-served • Collisions occur when load is heavy • Token-passing (IBMs Token Ring Network) • Token -- set of data bits required to send a message

  31. Highlights in MIS • Mobile computing • Wireless networks • cellular • wireless Lans • wide-area wireless • paging networks

  32. A Network with Mobility Capability MU MU MU MU MU MU Fixed host MSS MSS Fixed network Fixed host Fixed host MSS MSS Fixed host MU MU MU MU MU MU MSS = mobile support station MU = mobile units

  33. Network Management • 1. Network planning • Capacity planning • Staff planning • Performance monitoring 2. Network control 3. Network manager • Staff • Network analysts (a type of systems analyst) • Software analysts (specialize in datacom software) • Datacom technicians (specialize in hardware) • LAN managers

  34. The Intranet • Intranet applications • policy and procedure manuals • Product and pricing information • Employee information • Job openings • Documents needing signatures • Schedules and calendars • Access to databases • Access to groupware

  35. The Intranet (continued) • Steps to a successful Intranet 1. Determine information needs 2. Establish Intranet policy 3. Build an Intranet staff 4. Provide for end user document preparation 5. Determine whether to outsource the Intranet service 6. Select the Intranet outsourcer 7. Provide datacom services 8. Build in Intranet security 9. Monitor system performance

  36. Intranet Implementation Steps Yes No 1. Determine information needs 5. Outsource? 2. Establish Intranet policy 6. Select the Intra- net outsourcer 7. Provide datacom resources 3. Build an Intranet staff 8. Build in Intra- net security 4. Provide for end user document preparation 9. Monitor system performance

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