Data Communication and Media

• Concept and Model of Communications• Analogy Signal and Digital Signal• 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

General Communications: face-to-face conversation, write a letter, etc.

Electronic Communications: telephone, wireless phone, TV, radar, etc.

Lecture 1

Concept and Model of Communications

Our Focus Computer Communication

General Communication Model

Source TransmitterTransmission

SystemReceiver Destination

S(t) T(t) Tr(t) Sd(t)

MicrophoneTelephoneComputerScanner

TransformerEncoderCompressModulator

Line/CableFiber/AirSatelliteNetwork

TransformerDecoderUncompressDemodulator

SpeakerEarphoneComputerPrinter

Basic Communication Criteria: Speed, Reliability, Security (SRS)

Information must be converted into electrical energy, called signal, before transmission.

Text, voiceVideo, etc

Lecture 1

Analogy Signal and Digital Signal

Text, voiceVideo, etc

Digital

Analog

ConverterEncoder

t

t

s(t) voltage

s(t) voltage

Digital Signal

GeneralCommunication

Component – H()

Input Signal s(t) Output Signal o(t) =H[s(t)]

Digital-to-DigitalAnalogy-to-DigitalDigital-to-AnalogyAnalogy-to-Analogy

Analogy Signal

Signal Power: s (t)Signal Energy:

ʃ

2

s (t)dt2

4 classes/typesof systems- Input-to-Output

Signal

デジタル信号

Lecture 1

Signal Frequency, Spectrum and Bandwidth

Signal in time domainWave

Signal in frequency domainSpectrum

cos2πf1t

t

s(t)

Tperiod

Transformation

T=1/f1

f

S(f)

f1

s(t)=Acos2πf1t + Bcos2πf2t T=LCM(1/f1, 1/f2) f

S(f)

f1

A

f2

B

f: frequency

t

s(t)

Analogy Signal

t

s(t)

Digital Signal

S(f)=ʃs(t)e df-j2πf

Fourier Transformf

S(f)

f

S(f)

B = F2 – F1

Bandwidth

Bandwidth

Periodic

Aperiodic

F2F1

• 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

Time-Frequency Relation and Signal Bandwidth

General Relations: Time Domain Frequency Domain Signal Bandwidth

Change Slow Low Frequency small

Change Fast High Frequency large

Frequency Unit: Hertz (Hz), Kilohertz (KHz), Megahertz (MHz), Gigahertz (GHz), Terahertz (THz)

Lecture 1

System Frequency Response & Bandwidth

System: H()Input Signal x(t) Output Signal y(t) =H[x(t)]

Input Spectrum: X(f) Output Spectrum: Y(f)

System Frequency Response: H(f) = Y(f)/X(f)

f

H(f)

System BandwidthB = F2 – F1

Signal can pass

Signal can’t pass

F1 F2

TransmissionBandwidth

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 (0~10MHz)- Coaxial cable (100K~500MHz)- Optical fiber (180~370THz)

Unguided (Wireless) Media(air, vacuum, water, etc.)

- LF (30~300KHz, Navigation)- MF/HF (300~3000KHz, AM/SW radio)- VHF (30~300MHz, TV & FM radio)- UHF (0.3~3GHz, TV, mobile phone)- SHF (3~30GHz, satellite, microwave)- EHF (30~300GHz, experimental com)- Infrared (no frequency allocation)

Transmission Media

Frequency and Spectrum

Propagation characteristics are different in each frequency band

LF HF VHF UHF SHF EHFMF

UV

1 MHz1 kHz 1 GHz 1 THz 1 PHz 1 EHz

infrared visible

X raysGamma rays

902 – 928 Mhz

2.4 – 2.4835 Ghz

5.725 – 5.785 Ghz

ISM band

30kHz 300kHz 3MHz 30MHz 300MHz 30GHz 300GHz

10km 1km 100m 10m 1m 10cm 1cm 100mm

3GHz

Lecture 1

Lecture 1

Parallel Transmission and Serial Transmission

Sender Receiver

…011000110111010111…?

Sender Receiver

0110001

7 (N) bits are sent together7 (N) lines are needed

Parallel Transmission

Sender Receiver

0 1 1 0 0 0 1

7 (N) bits are sent one after anotherOnly 1 line is needed

Serial Transmission

0110001

0110001

P/S converter S/P converter

… 01…00 01…10 11…10 10…11 …

N N N N

Segment the 0/1 stream into N bits groups

Timing or synchronization between a sender and a receiver is very important for data transmission

Lecture 1

Asynchronous and Synchronous Transmission

Asynchronous transmission:

1) A bit stream is segmented into small groups characters (5~8 bits)

2) Add a start bit (0) and a stop bit (1) at the beginning and end of each character

3) Frame = start_bit + character + stop_bit (7~10 bits), but 2/9~2/10 no real data

4) Arbitrary long gap/interval/idle between two characters or frames

Sender Receiver0110001 01 1001100 01 0011101 01

Synchronous transmission:

1) A bit stream is segmented into relative large groups/blocks many characters or bytes

2) Add control bits at the beginning and end of each block

3) Frame = H_control_bits + characters (data_bits) + T_control_bits

4) No gap/interval/idle between two characters in a data block/frame

Sender Receiver0110001Con_bits 1001100 0011101 Con_bits

1011100 01

1011100. . .

0110001

Independent clocks

Synchronized clocks

Frame4 Frame3 Frame1Frame2

Frame

idle

HeaderTrailer

Lecture 1

Simplex Transmission and Duplex Transmission

Device A Device BSimplexTransmission

Direction of data

Device A Device BHalf DuplexTransmission

Direction of data at time 1

Device A Device BFull DuplexTransmission

Direction of data all the time

Direction of data at time 2

One can send and the other can receive

Both can send and receive but in different time

Both can send and receive simultaneously

複信 - Wikipedia

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- W3C (World Wide Web Consortium): HTTP, HTML, XML, …- WAP Forum (Wireless Application Protocol): WAP-num

Lecture 1

Serial & Asynchronous Transmission Standards

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

Device ASender

Device BReceiver

• Transmit characters (7 or 8 bits)• Sender: 0 +15v and 1 -15v • Start bit (0) and stop bit (1) for every character 9/10 bits in total

• A sender never leaves wire at 0v; when idle, puts –15v, i.e., 1• Receiver: 0 (+3v, +15v) and 1 (-3v, -15v), otherwise error

Wave form of ‘+’, 2B or 0101101bit 0

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- 300bps, 2.4Kbps, 4.8Kbps, …, 19.2Kbps, 33.6Kbps, 56Kbps

• 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<64Kbps; connection length< 15 meters; 25 pin connector- pin 2: receive (RxD); pin 3: transmit (TxD); pin 7: groud- other pins for transmission control

• EIA-449: rate<10Mbps; 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

t

s(t)

Exercise 1

1. Two signals are given in the following figures. Whose bandwidth is large? Why?

t

s(t)

(a) (b)

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 7bit characters across an EIA-232 or RS-232 connection that operated at 9600 bps (9.6Kbps). How long will the minimum transmission time be required? (Hint: remember to add a start bit and a stop bit on each character.)