Lecture 1 Data Communication and Media

Lecture 1 Data Communication and Media • • • Concept and Model of Communications Analogy Signal and Digital Signal Frequency, Spectrum and Bandwidth System Frequency Response and Bandwidth Transmission Media and Types Transmission Modes - Parallel & Serial Transmission - Asynchronous & Synchronous Transmissions - Simplex & Duplex Transmission • Communication Standards: RS/EIA-232 & Others

Lecture 1 Concept and Model of Communications General Communications: face-to-face conversation, write a letter, etc. Electronic Communications: telephone, wireless phone, TV, radar, etc. Our Focus Computer Communication General Communication Model Source S(t) Microphone Telephone Computer Scanner Transmitter Transformer Encoder Compress Modulator T(t) Transmission Tr(t) Sd(t) Receiver Destination System Line/Cable Fiber/Air Satellite Network Transformer Decoder Uncompress Demodulator Speaker Earphone Computer Printer Basic Communication Criteria: Speed, Reliability, Security (SRS)

Lecture 1 Analogy Signal and Digital Signal Information must be converted into electrical energy, called signal, before transmission. s(t) voltage Text, voice Video, etc Digital Text, voice Video, etc Converter Encoder Signal デジタル信号 Digital Signal t s(t) voltage t Analogy Signal Input Signal s(t) 2 Signal Power: s (t) Signal Energy: ʃs 2(t)dt General Communication Component – H() Digital-to-Digital Analogy-to-Digital-to-Analogy-to-Analogy Output Signal o(t) =H[s(t)] 4 classes/types of systems - Input-to-Output

Lecture 1 Signal Frequency, Spectrum and Bandwidth Signal in time domain Wave s(t) Transformation Periodic cos 2πf 1 t Signal in frequency domain Spectrum S(f) T=1/f 1 t T period f: frequency S(f) f 1 A s(t)=Acos 2πf 1 t + Bcos 2πf 2 t T=LCM(1/f 1, 1/f 2) f 1 s(t) Fourier Transform Analogy Signal S(f)=ʃs(t)e -j 2πf df s(t) Digital Signal t B f 2 f S(f) Aperiodic t f B = F 2 – F 1 Bandwidth F 2 S(f) Bandwidth f f

Lecture 1 Time-Frequency Relation and Signal Bandwidth General Relations: Time Domain Change Slow Change Fast Frequency Domain Low Frequency High Frequency Signal Bandwidth small large Frequency Unit: Hertz (Hz), Kilohertz (KHz), Megahertz (MHz), Gigahertz (GHz), Terahertz (THz) • Earthquake wave: 0. 01 ~ 10 Hz • Nuclear explosion signal: 0. 01 ~ 10 Hz • Electrocardiogram (ECG): 0 ~ 100 Hz • Wind noise: 100 ~ 1000 Hz • Speech: 100 ~ 4000 Hz (4 KHz) • Audio: 20 ~ 20000 Hz (20 KHz) • NTSC TV: 6 MHz • HDTV: > 10 MHz

Lecture 1 System Frequency Response & Bandwidth Input Signal x(t) Output Signal System: H() Input Spectrum: X(f) y(t) =H[x(t)] Output Spectrum: Y(f) System Frequency Response: H(f) = Y(f)/X(f) H(f) Transmission Bandwidth System Bandwidth B = F 2 – F 1 Signal can pass Signal can’t pass F 2 f

Lecture 1 Transmission Media A transmission medium: - a connection between a sender and a receiver - a signal can pass but with attenuation/distortion - a special system with a transmission bandwidth Guided (Wired) Media (lines) - Twisted pair (0~10 MHz) - Coaxial cable (100 K~500 MHz) - Optical fiber (180~370 THz) Unguided (Wireless) Media - (air, vacuum, water, etc. ) LF (30~300 KHz, Navigation) MF/HF (300~3000 KHz, AM/SW radio) VHF (30~300 MHz, TV & FM radio) UHF (0. 3~3 GHz, TV, mobile phone) SHF (3~30 GHz, satellite, microwave) EHF (30~300 GHz, experimental com) Infrared (no frequency allocation) Transmission Media

Lecture 1 Frequency and Spectrum ISM band 30 k. Hz 10 km 1 km VHF HF 3 MHz 30 MHz 100 m 10 m 2. 4 – 2. 4835 Ghz TV Ce llu l ar di TV FM ra ra W S/ MF 300 k. Hz o o di ra AM LF 902 – 928 Mhz 5. 725 – 5. 785 Ghz UHF 300 MHz 1 m SHF 3 GHz EHF 30 GHz 300 GHz 1 cm 100 mm 10 cm X rays infrared visible UV 1 k. Hz 1 MHz 1 GHz 1 THz 1 PHz Gamma rays 1 EHz Propagation characteristics are different in each frequency band

Lecture 1 Parallel Transmission and Serial Transmission … 01100011010111… Segment the 0/1 stream into N bits groups N N Sender N ? Receiver N … 01… 00 01… 10 10… 11 … Parallel Transmission Sender 0 1 1 0 0 0 1 Receiver Serial Transmission Sender 0 1 1 0 0 0 1 0110001 P/S converter 7 (N) bits are sent together 7 (N) lines are needed 0 1 1 0 Receiver 0 0 1 S/P converter 7 (N) bits are sent one after another Only 1 line is needed

Lecture 1 Asynchronous and Synchronous Transmission Timing or synchronization between a sender and a receiver is very important for data transmission Asynchronous transmission: 1) 2) 3) 4) A bit stream is segmented into small groups characters (5~8 bits) Add a start bit (0) and a stop bit (1) at the beginning and end of each character Frame = start_bit + character + stop_bit (7~10 bits), but 2/9~2/10 no real data Arbitrary long gap/interval/idle between two characters or frames Sender Frame 4 1 0110001 0 Frame 2 Frame 3 Frame 1 idle 1 1001100 0 1 0011101 0 1 1011100 0 Receiver Independent clocks Synchronous transmission: 1) 2) 3) 4) A bit stream is segmented into relative large groups/blocks many characters or bytes Add control bits at the beginning and end of each block Frame = H_control_bits + characters (data_bits) + T_control_bits No gap/interval/idle between two characters in a data block/frame Trailer Sender Con_bits 0110001 . . . Frame Header 0110001 1001100 0011101 1011100 Con_bits Synchronized clocks Receiver

Lecture 1 Simplex Transmission and Duplex Transmission Simplex Transmission Half Duplex Transmission Direction of data Device A Device B One can send and the other can receive Direction of data at time 1 Device A Device B Direction of data at time 2 Both can send and receive but in different time Direction of data all the time Full Duplex Transmission 複信 - Wikipedia Device A Device B Both can send and receive simultaneously

Lecture 1 Communication Standards and Related Organizations Communications need standards for inter-operations of different devices Standard Organizations: - ISO (International Standards Organization): ISO number ITU (International Telecommunication Union): V. num & X. num EIA (Electronic Industries Association): EIA-num IEEE (Institute of Electronics Engineers): IEEE. num ANSI (American National Standards Institute): ASCII, etc. ATM Forum and ATM Consortium IETF (Internet Society and Internet Engineering Task Force): RFC num W 3 C (World Wide Web Consortium): HTTP, HTML, XML, … WAP Forum (Wireless Application Protocol): WAP-num

Lecture 1 Serial & Asynchronous Transmission Standards of transmission in short distance: - EIA-232 or RS-232 - V. 24 - ISO 2110 - EIA-449/RS-422/RS-423 - EIA-530 - X. 21 Their common features - Serial & asynchronous transmission Transmissions of ASCII code, byte, char Use twisted copper lines Low speed: several Kbits ~ Mbits per second Short distance: < several tens of meters

Lecture 1 EIA/RS-232 Standard bit 0 Wave form of ‘+’, 2 B or 0101101 Device B Receiver Device A Sender • • • Transmit characters (7 or 8 bits) Sender: 0 +15 v and 1 -15 v Start bit (0) and stop bit (1) for every character 9/10 bits in total A sender never leaves wire at 0 v; when idle, puts – 15 v, i. e. , 1 Receiver: 0 (+3 v, +15 v) and 1 (-3 v, -15 v), otherwise error RS-232, Wikipedia

Lecture 1 EIA/RS-232 Standard (cont. ) • Agreement of transmission timing or rate/speed bps bits per second, bit rate or transmission speed - 300 bps, 2. 4 Kbps, 4. 8 Kbps, …, 19. 2 Kbps, 33. 6 Kbps, 56 Kbps • Setting bit rate (transmission speed) of devices/hardware - switch (manually), software, auto-detection • Either simplex or duplex T: Transmitter R: Receiver G: Ground

Lecture 1 EIA/RS-232 and Other Standards • EIA-232: rate<64 Kbps; connection length< 15 meters; 25 pin connector - pin 2: receive (Rx. D); pin 3: transmit (Tx. D); pin 7: groud - other pins for transmission control • EIA-449: rate<10 Mbps; connection length< 12 meters; 37/9 pin connector • EIA-530: same as the above; 25 pin connector • X. 21: 64/192 Kbps (N-ISDN rate); 15/8 pin connector RS-232 - ウィキペディア

Exercise 1 1. Two signals are given in the following figures. Whose bandwidth is large? Why? s(t) (a) t (b) t 2. Draw the RS-232 waveform diagrams of ASCII letters of R (1010010) and S (1110011). 3. Give at least one example for each of the following transmission/communication modes: parallel transmission, serial transmission, simplex transmission and duplex transmission. 4. Suppose one sent 10000 7 bit characters across an EIA-232 or RS-232 connection that operated at 9600 bps (9. 6 Kbps). How long will the minimum transmission time be required? (Hint: remember to add a start bit and a stop bit on each character. )