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Digital Signals and Digital Encoding

Digital Signals and Digital Encoding. Digital Encoding. unipolar digital signal high = +v low = 0 bipolar digital signal high = +v low = -v time period duration of signal NRZ non return to zero. Manchester. Manchester encoding the transitions & direction of matter up(1)

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Digital Signals and Digital Encoding

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  1. Digital Signals and Digital Encoding

  2. Digital Encoding • unipolar digital signal • high = +v • low = 0 • bipolar digital signal • high = +v • low = -v • time period • duration of signal • NRZ • non return to zero

  3. Manchester • Manchester encoding • the transitions & direction of matter • up(1) • down (0) • Differential Manchester encoding • the presence (1) • or absence (0) of transition matters

  4. Synchronizing • synchronous transmission • reference signal used for timing • asynchronous transmission • no reference signal is used • special pattern of bits used • indicate beginning/end of frames • bit stuffing • what if the special pattern is part of data? • Insert a bit to avoid pattern, ignore bit

  5. Data Packaging and Transmission • Segments / packets hold chunks of the intended message. • Info is added to aid re-assembly • Why segment?

  6. Parity Checking • extra bit is added to ensure significant bits are (odd/even) • Odd Parity   • Even Parity

  7. Cyclic Redundancy Checks (CRC) • CRC codes offer better parity check analysis

  8. Segmentation and Encapsulation • Segment, frame, data-gram, protocol data-unit (PDU) packet • blocks of data

  9. Connection-Oriented and Connectionless Communications • Connection oriented communications • connection established then data sent • connection may "reserve" channel • Connectionless communications • data is sent without establishing a connection

  10. Circuit Switching / Packet Switching • Circuit Switching • permanent connection established between two points for communication • Packet Switching • no permanent connection established between two points for communication • each packet switched independently • virtual circuit

  11. Routing • Packet Routing - each packet routed independently • Message Routing - all packets of a communique routed the same 

  12. Data Codes • ASCII • originally a 7bit code • BCD/EBCDIC • IBM Mainframe - COBOL • Unicode • 16bit extended ASCII includes Cherokee, Mongolian, Hebrew, Latin, Klingon, etc... • HTML • Color Codes - Hexadecimal

  13. Protocol Frame Structures • UDP • Ethernet

  14. UDP Frame Structure • User Datagram Protocol 4 bit header and data  • Simple header – • source port • destination port • Length • Checksum • 16 bit 1's Complement

  15. Ethernet Frame Structure • evolving • Xerox 1970 developed first iteration • IEEE 1985 802.3 CSMA/CD • Ethernet SNAP and Ethernet II

  16. Common Structure • Preamble 64 bits  • Destination Address 48 bits  • Source Address 48 bits • Type/Length 16 bits • Data 368 - 12000 bits (1500B) • Frame Check Sequence 32 bits

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