1. TDC 461 Basic Communications Systems 8 May, 2001

2. Agenda 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

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. –

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 Correction 1-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