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TDC 461 Basic Communications Systems

This review covers the basics of data communications systems, including the OSI 7-Layer Model, standards, architectures, protocols, error detection/correction, simplex/half duplex/full duplex, multiplexing, and the difference between baseband and broadband.

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TDC 461 Basic Communications Systems

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  1. TDC 461Basic Communications Systems 8 May, 2001

  2. Midterm Exam Review Six Steps to Data Communications OSI 7-Layer Model Big Concepts: Standards Architectures Protocols Error Detection / Correction Simplex / Half Duplex / Full Duplex Multiplexing Baseband v Broadband Agenda

  3. Data Communications

  4. 6 Steps to Data Com 1. Select and Deal with transmission media 2. Use communicating devices that will present the proper signal to the line 3. Set up or abide by already-accepted rules (protocols)

  5. 6 Steps, cont. 4. Use an alphabet (character set) that the devices can understand 5. Ensure the integrity of information before, during, and after transmission (through error detection and correction) 6. Deliver information to the receiving device

  6. Big Concept #1: Standards • Standards: a definition or description of a technology • 2 Types:

  7. Big Concept #2: Architectures • Architectures=>

  8. Big Concept #3: Protocols • Protocols=>

  9. Asynchronous Transmission Protocols • Data is clocked or synchronized one byte at a time

  10. Asynchronous - Cont. • Speed calculation => • Clocking • Serial (RS232) Interface

  11. Asynchronous - Cont.

  12. Synchronous Transmission Protocols • Data clocked on blocks of bytes rather than a single byte

  13. Synchronous Transmission Protocols • Flag - Fixed bit pattern to start and end frame - set to 01111110 • Address - Address of destination device • Control - Contains frame sequence number and acknowledgement bits • CRC - Allows error detection

  14. Synchronous Transmission Protocols, cont. • Clocking

  15. Synchronicity • Modems communicating at 2400+bps are synchronous “over the wire”

  16. Big Concept #4: Error Detection • Relates to step 5 of the Data Comm Basics • 3 modes of error control • Recognition and Flagging • Recognition and Retransmission • Recognition and Forward Error Correction

  17. Recognition and Flagging

  18. Recognition and Retransmission

  19. Recognition and Retransmission

  20. Recognition and Forward Error Correction

  21. Parity Checking • Odd Parity => • Even Parity =>

  22. Parity Checking • Example

  23. Parity Checking • Example:

  24. Longitudinal Redundancy Checking (LRC) • Adds a parity bit to each row and each column of a block of data • Detects a greater range of errors than simple parity. • Can also be used to correct errors (Forward Error Correction)

  25. Longitudinal Redundancy Checking (LRC)

  26. LRC Error Correction1-bit error

  27. Cyclic Redundancy Checking

  28. Big Concept #5: Plexing • Simplex • Half Duplex • Full Duplex

  29. Simplex Data flows one way only

  30. Half Duplex Data flows only one way at any particular time, but can flow either direction.

  31. Full Duplex Data can flow both ways simultaneously

  32. Big Concept #6: Multiplexing (Review) • Space Division Multiplexing • Frequency Division Multiplexing • Time-division Multiplexing

  33. Big Concept #7: Baseband vs. Broadband • Baseband: • Broadband:

  34. Baseband vs. Broadband • History—3 Factions • Voice people • Data people • Radio people

  35. Motivations for Baseband LANs • Wiring schema. • Date rates. • Internconnection. • Compatibility. • Cost.

  36. Baseband Cable Systems • Signaling: • Plug-n-Play:

  37. Baseband Claims • Baseband is cheaper. • Baseband is scalable. • Baseband is efficient.

  38. Broadband Cable Systems • D=>any of a specific set of services offerings from common carriers (e.g., T1, T3, ATM, Frame Relay, SONET). The specific technique of using coaxial cable to carry multiple channels over LAN distances • Signaling. • Components • Plug-n-play? • Target market:

  39. Broadband Network Configurations • Head end • Tuners • Modulation techniques

  40. Trends

  41. OSI • Open Systems Interconnect model (1977)

  42. OSI-7 Layers • Layer 7-Application Layer • Examples: File Transfer Protocol (FTP), Telnet, Simple Mail Transport Protocol (SMTP) • Layer 6-Presentation Layer

  43. OSI-7 Layers cont. • Layer 5 - Session Control Layer • Example: NetBIOS Extended User Interface (NETBEUI) (Microsoft) • Layer 4 -Transport Protocol • Example: Transmission Control Protocol (TCP)

  44. OSI-7 Layers, cont. • Layer 3-Network Layer • Examples: IP (Internet Protocol), Appletalk, Novell IPX

  45. OSI-7 Layers, cont. • Layer 2 - Data Link Control • Examples: HDLC, Ethernet, Token Ring

  46. OSI-7 Layers, cont. • Layer 1 - Physical Layer • Examples: Ethernet, Token Ring, T-1, SONET

  47. OSI-7 Layers, cont. • Example: A Windows 95 PC might use: • Layer 7: Microsoft Network Protocol (SMB) • Layer 6: ASCII • Layer 5: NetBEUI • Layer 4: TCP • Layer 3: IP • Layer 2: Ethernet Framing • Layer 1: Ethernet Physical Network

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