1 / 30

Data Communication

Data Communication. Data Communications System. Transmitter – transmit data to another medium. Receiver – receive data from a transmitter. Medium of transfer – the medium for transfer of data. Source System. Destination System. Source. Transmitter. Transmission system. Receiver.

garciammary
Download Presentation

Data Communication

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Data Communication

  2. Data Communications System • Transmitter – transmit data to another medium. • Receiver – receive data from a transmitter. • Medium of transfer – the medium for transfer of data.

  3. Source System Destination System Source Transmitter Transmission system Receiver Destination Workstation Modem Public Telephone Network Modem Server Communications Model

  4. Simplex Transmission • Simplex communication means that communication can only flow in one direction and never flow back the other way. Data

  5. Half-duplex Transmission • Half-duplex data transmission means that data can be transmitted in both directions on a signal carrier, but not at the same time. Data

  6. Full-duplex Transmission • Full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time. Data

  7. Real life examples • Simplex transmission • Pager • Half-duplex transmission • Telephone, facsimile • Full-duplex transmission • Dual Carriageway

  8. Data Transmission Rate • Data transmission rate: bps, Kbps, Mbps • bps – bits per second • Kbps – kilo-bits per second • Mbps – mega-bits per second • Bps – bytes per second • 1 Byte = 8 bits

  9. Serial Transmission • The transfer of discrete signals one after another. • Bits travel sequentially along the same wire. • Send information over a single line one bit at a time, as in modem-to-modem connections.

  10. Parallel Transmission • The simultaneous transmission of a group of bits over separate wires. • The transmission of 1 byte (8-bits) with computers.

  11. Parallel Transmission • Relatively fast • Limited distance before data is lost • As short as possible (no longer than 15 feet) • As the length of cable increases so does the danger of cross-talk.

  12. Serial Transmission • Not as fast as parallel transmission • Can transmit data for longer distances

  13. Data bits Parity bit Start bit Stop bit The coding of a typical character sent in asynchronous transmission Asynchronous Transmission • In modem communication, a form of data transmission in which data is sent one character at a time. In addition, a parity bit is usually used for error checking. • Avoid timing problem by not sending long, uninterrupted streams of bits.

  14. Idle state of line Odd, even, or unused Start bit 5 to 8 data bits 1 – 2 bit times 0 Stop 1 Remain idle or next start bit P bit Asynchronous Transmission Character format

  15. Unpredictable time interval Between characters Start bit Stop bit Start bit Stop bit 1 1 1 1 0 0 0 1 0 0 1 0 1 1 0 0 Asynchronous Transmission 8-bit asynchronous character stream

  16. Transmitter timing Start 0 100 200 300 400 500 600 700 800 1 2 3 4 5 6 7 8 Stop Receiver timing 0 93 186 279 372 465 558 651 744 Asynchronous Transmission Effect of timing error Assumptions: data rate of 10 kbps  0.1 ms each bit. The receiver is off by 7% or 0.007 ms per bit-time The receiver samples the incoming character every 0.093 ms (based on the transmitter’s clock).

  17. Asynchronous Transmission • Advantages: • simple • cheap • Disadvantages: • requires an overhead of 2 – 3 bits per character (start and stop bits) (>=20%) • cannot send large blocks or bits between start and stop bits with great cumulative timing error

  18. Synchronous Transmission • Data transfer in which information transmitted in block (frames) of bits separated by equal time intervals • A block of bits is transmitted in a steady stream without star and stop codes

  19. Synchronous Transmission • Method 1: • Provide a separate clock line between transmitter and receiver • The other side uses these regular pulses as a clock • This technique works well over short distances • Method 2: • Embed the clocking information in the data signal

  20. Synchronous frame format preamble 8-bit flag Control fields Control fields postamble 8-bit flag Data fields Synchronous Transmission

  21. Synchronous Transmission • Advantage: • For sizable/large blocks of data, synchronous transmission is far more efficient that asynchronous. • The control information, preamble, and postamble are typically less than 100 bits. • E.g. 48 bits of control, preamble, and postamble with 1000-character block of data, each frame consists of 48 bits of overhead and 8000 bits of data, so % overhead = 48/8048 x 100% = 0.6%

  22. Data Transfer Directed from PC to PC • Direct Cable Connection • A null modem cable allows you to connect your PC to another nearby PC or serial device using its modem protocol. • A null modem cable is limited to 30 feet in length. • A null modem cable is sometimes called crossover cable.

  23. Crossover Cable • A crossover cable is a cable that is used to interconnect two computers by "crossing over" (reversing) their respective pin contacts. • Either an RS-232C or an registered jack (e.g. RJ-45) connection is possible.

  24. Diagrams on RJ-11 and RJ-45 Interfaces

  25. Data Modem Modem – Modulator and Demodulator Modulator – convert digital signal (data in PC) to analogue signal (data via telephone line) Demodulator – convert analogue signal to digital signal

  26. Data Modem Modulation Digital signal Analogue signal PC Modem Public Telephone Network PC Modem Digital signal Analogue signal Demodulation

  27. Data Modem • Baud Rate • This refers to the number of signals per one second transmitted • Bit Rate • The bit rate is multiplied by the bits per signal

  28. Sources of errors during data transmission • Attenuation • Signal grows weak over distance • White noise • Caused by molecular movement • Impulse noise • Caused by electrical interference • Cross-talk • Caused by interference from adjacent lines

  29. DCE and DTE • DTE • Data Terminal Equipment which is the ultimate source or final destination of data messages • DCE • Data Circuit-Terminating Equipment which connects the DTE to the communication circuits

  30. Bandwidth • The capacity at which you can transfer data is called bandwidth • Typical telephone line: 33,600 kilobits per second (33.6 Kbps) • Cable TV: 10 megabits per second (10 Mbps) – almost 300 times the capacity of the normal phone connection

More Related