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UNIT IVDATA COMMUNICATION             Prepared by             P SAJID AKRAM             Lecturer/ ECE             CAHCET
IntroductionTerminologies of Data communicationData- Information that has been processed, organized  and stored.Data com...
What is Data Communications?Exchange of digital information between two digital devicesis data communication
History of Data Communication• 1838: Samuel Morse & Alfred Veil Invent Morse CodeTelegraph System• 1876: Alexander Graham ...
Standard Organization for DataCommunicationInternational Standards Organization(ISO)International Telecommunications Uni...
Data Communication Circuit• Simplified block diagram of data communication network
Data Transmission• Data Transmission means movement of the bits over atransmission medium connecting two devices• Two type...
Parallel TransmissionIn this all the bits of a byte are transmitted simultaneously onseparate wires.Practically, if two de...
Serial Transmission• Bits are transmitted one after the other• Usually the Least Significant Bit (LSB) is transmitted firs...
Data Communication circuit arrangementsCircuit Configuration:  Two point configuration  Multipoint configuration
Transmission Modes• Simplex  • signals transmitted in one direction     • eg. Television• Half duplex  • both stations tra...
Network topologies• It describes the layout or appearance of a network• A multi point topology connects 3 or more stations...
Simple and low-costBus topology-   A single cable called a trunk (backbone,                segment)                 Coaxia...
Each computer has a cable connected to a single pointStar topology-   More cabling, hence higher cost                 All ...
Ring topology  Every computer serves as a repeater to boost signals  Disadvantages     • If one computer fails, whole netw...
Mesh topology• Each and every node of the network is interconnected
Hybrid topology• Combination of two or more topologies
Data Communication CodesThese are prescribed bit sequence used for encoding characters and symbolsOften called as charac...
CHARACTER CODES• Various character codes have been used in data communication including:  • Morse, Baudot  • EBCDIC, ASCII...
MORSE CODE
BAUDOT CODE• One of first codes developed for machine to machine  communication• Uses 1’s and 0’s instead of dots and dash...
BAUDOT CODE (cont.)• Problems:  • required shift code to switch between character sets  • no lower case, few special chara...
BAUDOT CODE
EBCDIC• Extended Binary Coded Decimal Interchange Code• 8-bit character code developed by IBM  • used for data communicati...
EBCDIC CODE
ASCII CODE• American Standard Code for Information Interchange• 7-bit code developed by the American National Standards In...
7-BIT ASCII CODE
SUMMARY OF CHARACTER CODES    Morse           =    .-    Baudot          =    5 bit (no parity)    Int. Baudot     =    6 ...
Error control• What is error?• Types of error:   • Single bit error   • Burst error  Methods : 1) error detection         ...
Error Correction1. Retransmission      resending of message when it is received incorrectly      often called as ARQ- Au...
Hamming codeNumber of redundancy bits needed• Let data bits = m• Redundancy bits = n  Total message sent = m+rThe value of...
??????
Data Communication Hardware• A multipoint data communication circuit block diagram       Host                             ...
Line control unit(LCU)@ primary:       Directs traffic to and from many circuits(which havedifferent characteristics)@ s...
• LCU operates only on digital data• Most of the functions of LCU are performed by single IC called as UART/USRT• UART- Un...
UART- Universal asynchronousreceiver/transmitterAsynchronous- no clocking information is transferred between DTE and DCE...
UART TRANSMITTER
Control wordTo indicate no of bits, nature of parity, and the no of stop bits
Timing diagram of UART• TBMT-Transmit Buffer Empty• TD-Transmit Data• TDS-Transmit Data Strobe• TEOC-Transmit End of Char•...
Receiver of UART
Timing diagram of UART Receiver• RSI-receive serial input• RDA-receive data available• RPE- receive parity error• SWE- sta...
USRT- Universal synchronousreceiver/transmitterSynchronous- clocking information is transferred between DTE and DCEPrima...
Transceiver of USRT
Interfaces
Serial InterfaceSerial communication is the mostsimplistic form of communication between two devices.RS-232 is a standar...
RS 232 Pin functions- data pins
Control pins
Timing pins
Miscellaneous
Parallel interface• Transfers data between two devices eight or more bits at    a time.•   Also referred to as serial by w...
Interface btw computer & printer An interface that accepted data in same format used internally by  most computers (8 bit...
Status line: unidirectional, and transmission from printer to computer   ACK: acknowledge, active low, response to STB l...
Data ModemsNeed for modem To interface computers, computer networks, and other digital terminal equipment with analog comm...
Types of modemsBroad classification can be made as:Synchronous modems:   Clocking information is recovered at the receiv...
Asynchronous modems• Example of asynchronous modems areBell Systems 202 T/S modems, uses FSK  • 202 T- full duplex, four w...
Synchronous modems• Used for medium and high speed modems• For medium speed:  • QPSK for 2.4Kbps(eg: Bell Systems 201C)  •...
Additional requirements for synchronousmodemsSince the medium and high speed modems aresynchronous, these modems contain t...
Modem control• Initial modems- dumb modems   • Basic function include only modulation and demodulation• Intelligent modems...
AT command mode• When a modem is not communicating with any other  modem, then it is command mode• All commands begin with...
Any doubts????????????
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Data communication and networking

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  1. 1. UNIT IVDATA COMMUNICATION Prepared by P SAJID AKRAM Lecturer/ ECE CAHCET
  2. 2. IntroductionTerminologies of Data communicationData- Information that has been processed, organized and stored.Data communication-transmission, reception & processing of digital information.Network/ nodes/ stations- set of devices interconnected by media links Simple- two computers or a computer with a printer Complex- one or more main frame computers with athousand remote terminals.
  3. 3. What is Data Communications?Exchange of digital information between two digital devicesis data communication
  4. 4. History of Data Communication• 1838: Samuel Morse & Alfred Veil Invent Morse CodeTelegraph System• 1876: Alexander Graham Bell invented Telephone• 1910:Howard Krum developed Start/Stop Synchronisation• 1930: Development of ASCII Transmission Code• 1945: Allied Governments develop the First LargeComputer• 1950: IBM releases its first computer IBM 710• 1960: IBM releases the First Commercial Computer IBM360
  5. 5. Standard Organization for DataCommunicationInternational Standards Organization(ISO)International Telecommunications Union- Telecommunication Sector(ITU-T)American National Standard Institute(ANSI)Institute of Electrical and Electronics Engineers(IEEE)Electronics Industry Association(EIA)
  6. 6. Data Communication Circuit• Simplified block diagram of data communication network
  7. 7. Data Transmission• Data Transmission means movement of the bits over atransmission medium connecting two devices• Two types of Data Transmission are:Parallel TransmissionSerial Transmission
  8. 8. Parallel TransmissionIn this all the bits of a byte are transmitted simultaneously onseparate wires.Practically, if two devices are close to each other e.g. Computer toPrinter, Communication within the ComputerHigh speed but complex circuit
  9. 9. Serial Transmission• Bits are transmitted one after the other• Usually the Least Significant Bit (LSB) is transmitted first• Suitable for Transmission over Long distance• Less speed but simple circuit
  10. 10. Data Communication circuit arrangementsCircuit Configuration: Two point configuration Multipoint configuration
  11. 11. Transmission Modes• Simplex • signals transmitted in one direction • eg. Television• Half duplex • both stations transmit, but only one at a time • eg. police radio• Full duplex • simultaneous transmissions • eg. telephone
  12. 12. Network topologies• It describes the layout or appearance of a network• A multi point topology connects 3 or more stations through a single transmission mediumEg:star, bus, ring, mesh & hybrid
  13. 13. Simple and low-costBus topology- A single cable called a trunk (backbone, segment) Coaxial cable BNC T-Connector
  14. 14. Each computer has a cable connected to a single pointStar topology- More cabling, hence higher cost All signals transmission through the hub; if down, entire network down
  15. 15. Ring topology Every computer serves as a repeater to boost signals Disadvantages • If one computer fails, whole network fails
  16. 16. Mesh topology• Each and every node of the network is interconnected
  17. 17. Hybrid topology• Combination of two or more topologies
  18. 18. Data Communication CodesThese are prescribed bit sequence used for encoding characters and symbolsOften called as character sets, character codes, symbol codes, character languagesTypes of characters used in data communication: 1) Data link control: For orderly flow of data from source to destination 2) Graphic control: Presentation of data at the receivers 3) Alpha/numeric characters: Various alphabets, numbers, etc.
  19. 19. CHARACTER CODES• Various character codes have been used in data communication including: • Morse, Baudot • EBCDIC, ASCII • Unicode • Bar code• Regardless of the character code, both the terminal/ host or sender/receiver must recognize the same coding scheme
  20. 20. MORSE CODE
  21. 21. BAUDOT CODE• One of first codes developed for machine to machine communication• Uses 1’s and 0’s instead of dots and dashes• For transmitting telex messages (punch tape)• Fixed character length (5-bits) • 32 different codes • increased capacity by using two codes for shifting • 11111 (32) Shift to Lower (letters) • 11011 (27) Shift to Upper (digits, punctuation) • 4 special codes for SP, CR, LF & blank • Total = 26 + 26 + 4 = 56 different characters
  22. 22. BAUDOT CODE (cont.)• Problems: • required shift code to switch between character sets • no lower case, few special characters • no error detection mechanism • characters not ordered by binary value • designed for transmitting data, not for data processing• International Baudot • Added a 6th bit for parity • Used to detect errors within a single character
  23. 23. BAUDOT CODE
  24. 24. EBCDIC• Extended Binary Coded Decimal Interchange Code• 8-bit character code developed by IBM • used for data communication, processing and storage • extended earlier proprietary 6-bit BCD code • designed for backward compatibility or marketing? • still in use today on some mainframes and legacy systems.• Allows for 256 different character representations (28) • includes upper and lower case • lots of special characters (non-printable) • lots of blank (non-used codes) • assigned to international characters in various versions • used with/without parity (block transmissions)
  25. 25. EBCDIC CODE
  26. 26. ASCII CODE• American Standard Code for Information Interchange• 7-bit code developed by the American National Standards Institute (ANSI) • most popular data communication character code today• Allows for 128 different character representations (27) • includes upper and lower case • lots of special characters (non-printable) • generally used with an added parity bit • better binary ordering of characters than EBCDIC• Extended ASCII uses 8 data bits and no parity • Used for processing and storage of data • Allows for international characters • 8th bit stripped of for transmission of standard character set
  27. 27. 7-BIT ASCII CODE
  28. 28. SUMMARY OF CHARACTER CODES Morse = .- Baudot = 5 bit (no parity) Int. Baudot = 6 bsit (5 data + 1 parity) ASCII = 8 bit (7 data + 1 parity) EBCDIC = 9 bit (8 data + 1 parity) UNICODE = 16 bits (no parity)• Normally terminals and hosts must use the same code• However, code conversion hardware/software can be used to allow different machines to communicate
  29. 29. Error control• What is error?• Types of error: • Single bit error • Burst error Methods : 1) error detection 2) error correction Error detection: i. redundancy ii. parity iii. checksum iv. longitudinal and horizontal redundancy check v. Cyclic redundancy check(CRC)
  30. 30. Error Correction1. Retransmission resending of message when it is received incorrectly often called as ARQ- Automatic Repeat reQuest for retransmission positive and negative acknowledgment2. Forward error correction(FEC) only technique which detects and corrects errors atthe receiver without the need for retransmissionEg : Hamming code
  31. 31. Hamming codeNumber of redundancy bits needed• Let data bits = m• Redundancy bits = n Total message sent = m+rThe value of n must satisfy the following relation: 2n ≥ m+n+1
  32. 32. ??????
  33. 33. Data Communication Hardware• A multipoint data communication circuit block diagram Host Secondary or remote
  34. 34. Line control unit(LCU)@ primary: Directs traffic to and from many circuits(which havedifferent characteristics)@ secondary: Directs traffic between one data link and other fewdevices(all of similar char)LCU with a software is called as front end processor(FEP)Usually LCU of primary is an FEP
  35. 35. • LCU operates only on digital data• Most of the functions of LCU are performed by single IC called as UART/USRT• UART- Universal asynchronous receiver/transmitter• USRT- Universal synchronous receiver/transmitter• INTEL’s USART 8251• Motorola’s UART – asynchronous communication interface adapter(ACIA)
  36. 36. UART- Universal asynchronousreceiver/transmitterAsynchronous- no clocking information is transferred between DTE and DCEPrimary functions of UART:  To perform serial to parallel and vice-versa  To perform error detection(parity bits)  To insert and detect start/stop bitsHardware consists of 2 sections:  Transmitter  receiver
  37. 37. UART TRANSMITTER
  38. 38. Control wordTo indicate no of bits, nature of parity, and the no of stop bits
  39. 39. Timing diagram of UART• TBMT-Transmit Buffer Empty• TD-Transmit Data• TDS-Transmit Data Strobe• TEOC-Transmit End of Char• TSO-Transmit serial out
  40. 40. Receiver of UART
  41. 41. Timing diagram of UART Receiver• RSI-receive serial input• RDA-receive data available• RPE- receive parity error• SWE- status word enable• RDE-receive data enable• RDAR-receive data available reset
  42. 42. USRT- Universal synchronousreceiver/transmitterSynchronous- clocking information is transferred between DTE and DCEPrimary functions of UART:  To perform serial to parallel and vice-versa  To perform error detection(parity bits)  To insert and detect SYN characters(difference between USRT& UART)
  43. 43. Transceiver of USRT
  44. 44. Interfaces
  45. 45. Serial InterfaceSerial communication is the mostsimplistic form of communication between two devices.RS-232 is a standard by which two serial devices communicate • The connection must be no longer than 50 feet. • Transmission voltages are –15V and +15V. • It is designed around transmission of characters (of 7 bits of length). • Defines a 25 wire cable with a DB 25S/9S connector. • Data rate of up-to 20kbps for a distance of 50ft • driver, terminator, noise margin
  46. 46. RS 232 Pin functions- data pins
  47. 47. Control pins
  48. 48. Timing pins
  49. 49. Miscellaneous
  50. 50. Parallel interface• Transfers data between two devices eight or more bits at a time.• Also referred to as serial by word transmission• advantage: faster transmission• Disadvantage: higher cost for transmission• Eg: Centronics parallel interface, IEEE 488 bus
  51. 51. Interface btw computer & printer An interface that accepted data in same format used internally by most computers (8 bit parallel using TTL logic) Comes with a 36 pin Amphenol connector (Champ connector) Pins are classified as data, control and status Data lines: Pins 2 to 9 are eight bit parallel data bus. Control lines: 4 control signals are used  STB: active low, edge triggered, o/p from computer & tells printer to accept data from data lines  AF: autofeed, active low,tells printer whether to perform line feed after it receives a carriage return character from computer  PRIME: also called initialize, active low, o/p from computer, clears the printer’s memory, usually used to abort printing action suddenly  SLCTIN: select line, not mostly used, usually it is grounded
  52. 52. Status line: unidirectional, and transmission from printer to computer  ACK: acknowledge, active low, response to STB line  Busy: active high, and goes high anytime printer is busy When printer is busy? 1. when printer is accepting data from computer 2. when printer is printing 3. when printer is switched off or offline 4. when printer’s ERROR line is low  PO: paper out, active high  SLCT: select, active high, indicates whether printer is selected or not.
  53. 53. Data ModemsNeed for modem To interface computers, computer networks, and other digital terminal equipment with analog communication lines and radio channelWhat is modem modulator and demodulator Modem @ transmitter:  Digital signals modulate an analog carrier Modem @ receiver:  Analog signals are demodulated and converted to digital signalsAlso called as DCE, data set, dataphone.
  54. 54. Types of modemsBroad classification can be made as:Synchronous modems:  Clocking information is recovered at the receiver  Use PSK or QAM modulation technique  Used for mostly medium and high speed applications(up to 57.6kbps)Asynchronous modems:  No clocking information is sent  Mostly use ASK/ FSK  Restricted to use for low speed applications(< 2.4 kbps)
  55. 55. Asynchronous modems• Example of asynchronous modems areBell Systems 202 T/S modems, uses FSK • 202 T- full duplex, four wire operation • 202 S- half duplex, two wire operation• 202T modems use 1700Hz carrier• Another modem standard is Bell Systems 103 modems, has full duplex over a two wire line at a rate of 300bps• Has 2 data channels,(low band/ high band) with each mark & space frequency • Low band channel- originate channel • High band channel-answer channel• Circuit which originates the call has to transmit on low band and the receiver has to respond on the high band channel
  56. 56. Synchronous modems• Used for medium and high speed modems• For medium speed: • QPSK for 2.4Kbps(eg: Bell Systems 201C) • 8-PSK for 4.8 Kbps(eg: Bell Systems208A) • Both are full duplex, 4 wire systems• For high speed: • 16-QAM for a 9.6Kbps(eg: Bell Systems 209A) • Full duplex, four wire transmission• Sometimes asynchronous data format is used in a synchronous modem, this is referred to as isochronous transmission
  57. 57. Additional requirements for synchronousmodemsSince the medium and high speed modems aresynchronous, these modems contain the followingadditional hardware:clock recoveryscramblers and descrambler circuitequalizers
  58. 58. Modem control• Initial modems- dumb modems • Basic function include only modulation and demodulation• Intelligent modems- smart modems • Consists of mostly microprocessor which performs routine function• Smart modems are controlled by a set of system commands.• Most widely used are AT command set or Hayes command set• Has two modes of operation: • AT command mode • AT on-line mode
  59. 59. AT command mode• When a modem is not communicating with any other modem, then it is command mode• All commands begin with ASCII character AT(attention)• AT online mode:• Once communication begins, modem is said to be in online mode• In this, modem accepts information and allows them to modulate its carrier before transmission• To switch from online to command mode, DTE transmits consecutive three plus sign(+++). This sequence is called as escape code.
  60. 60. Any doubts????????????
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