KOMUNIKASI DATA DAN TRANSMISI DATA PERTEMUAN KESEPULUH

Pengertian Komunikasi Data  Komunikasi Data: Penggabungan antara dunia komunikasi dan komputer,  Komunikasi umum  antar manusia (baik dengan bantuan alat maupun langsung)  Komunikasi data  antar komputer atau perangkat digital lainnya (PDA, Printer, HP)

Tipe data dalam komunikasi data?  Semua tipe data yang dapat disimpan dan diolah pada sebuah komputer dapat ditransfer melalui jaringan komputer 3 TeksSuaraGambarVideo Informasi Digital

Aplikasi Komunikasi Data  Akses online sumber informasi:  Sistem informasi akademik  Website kampus  Katalog toko buku  Pengunduhan perangkat lunak   Online chatting  Video conference  Belanja online 4

Perangkat jaringan komputer 5 Jutaan perangkat komputer yang terhubung: – hosts = end systems  Jalur komunikasi  kabel jaringan (fiber, tembaga, coax), nirkabel  Kecepatan transmisi: bandwidth  Meneruskan paket data  router dan switch wired links wireless links router Jaringan bergerak global ISP regional ISP Jaringan rumah Jaringan institusi smartphone PC server wireless laptop switch * ISP = Internet Service Provider

Server  Komputer yang didedikasikan untuk menyediakan sejumlah layanan yang diperlukan komputer lain (klien)  Kebutuhan perangkat keras server bervariasi, tergantung dari layanan yang disediakan  Contoh layanan : server database, server mail, server file sharing 6

Router Berfungsi:  Sebagai penghubung beberapa subjaringan yg berbeda  Untuk meneruskan data pada subjaringan yang berbeda 7

Switch Berfungsi:  Sebagai penghubung beberapa perangkat pada subjaringan yang sama  Untuk meneruskan data pada subjaringan yang sama 8

Modem  Modulator-DEModulator (MODEM)  Modulator  mengubah sinyal digital ke dalam sinyal analog  Demodulator  mengubah sinyal analog menjadi sinyal digital, sehingga informasi dapat dibaca dengan baik 9

Access Point (AP)  Digunakan pada jaringan nirkabel  Perangkat jaringan yang berisi transceiver (transmitter- receiver) dan antena untuk transmisi dan menerima sinyal ke dan dari klien  Seringkali berfungsi juga sebagai router 10

Data and Signals

To be transmitted, data must be transformed to electromagnetic signals. Note:

Signals can be analog or digital. Analog signals can have an infinite number of values in a range; digital signals can have only a limited number of values. Note:

Comparison of analog and digital signals

Frekuensi, Spektrum dan Bandwidth Konsep domain Waktu  Sinyal Kontinu Bentuk bervariasi yang mulus dengan berjalannya waktu  Sinyal Diskret Berada pada tingkat konstan tertentu kemudian berubah pada tingkat konstan yang lain  Sinyal Periodik Mempunyai bentuk yang berulang dengan berjalannya waktu  Sinyal Aperiodik Bentuk tidak berulang dengan berjalannya waktu

Sinyal Kontinu & Diskret

Sinyal Periodik

Berbagai Gelombang Sinus

Period and frequency

Units of periods and frequencies UnitEquivalentUnitEquivalent Seconds (s)1 shertz (Hz)1 Hz Milliseconds (ms)10 –3 skilohertz (KHz)10 3 Hz Microseconds (ms)10 –6 smegahertz (MHz)10 6 Hz Nanoseconds (ns)10 –9 sgigahertz (GHz)10 9 Hz Picoseconds (ps)10 –12 sterahertz (THz)10 12 Hz

Frequency is the rate of change with respect to time. Change in a short span of time means high frequency. Change over a long span of time means low frequency. Note:

22 Phase describes the position of the waveform relative to time zero. Note:

Relationships between different phases

Example 1 A sine wave is offset one-sixth of a cycle with respect to time zero. What is its phase in degrees and radians? Solution We know that one complete cycle is 360 degrees. Therefore, 1/6 cycle is (1/6) 360 = 60 degrees = 60 x 2  /360 rad = rad Radian adalah satuan sudut dalam bidang yang dilambangkan dengan "rad"

Wavelength  Wavelength is the distance a simple signal (sine wave) can travel in one period. Wavelength=Propagation speed x Period = Propagation speed/Frequency  The wavelength is normally measured in micrometers (microns,10 -6 )  For example, the wavelength of red light (frequency=4x10 14 ) in air is: λ=c/f=(3x10 8 )/(4x10 14 ) =0.75x10 -6 m=0.75μm dimana: λ= wavelength, c=speed of light, f=frequency

Wavelength

Time and frequency domains

Time and frequency domains (continued)

Frequency Spectrum and Bandwidth  The description of a signal using the frequency domain and containing all its components is called the frequency spectrum.  A medium (cable or air) may pass some frequencies and may weaken others. To maintain the integrity of the signal, the medium needs to pass every frequency (and also preserve the amplitude and phase). However, no transmission medium is perfect.  The range of frequencies that a medium can pass (Maximum frequency-Minimum frequency) is called the bandwidth of the medium

Frequency Spectrum and Bandwidth  If the bandwidth of a medium does not match the bandwidth of a signal (Maximum frequency of the signal-Minimum frequency of the signal), some of the frequencies are lost.  Passing a square wave through a medium will always deform the signal.  Voice normally has a spectrum of 300 to 3300 Hz (a bandwidth of 3000 Hz). If we use a transmission line with a bandwidth of 1000 (between 1500 and 2500), the voice may not be recognizable

Signal corruption

32 The bandwidth is a property of a medium: It is the difference between the highest and the lowest frequencies that the medium can satisfactorily pass. Note:

We use the term bandwidth to refer to the property of a medium (bandwidth of a medium) or the width of the frequency spectrum of a signal (bandwidth of a signal) Note:

Bandwidth

Example 2 If a periodic signal is decomposed into five sine waves with frequencies of 100, 300, 500, 700, and 900 Hz, what is the bandwidth? Draw the spectrum, assuming all components have a maximum amplitude of 10 V. Solution B = f h  f l = 900  100 = 800 Hz The spectrum has only five spikes, at 100, 300, 500, 700, and 900

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Digital Signals  Most digital signals are aperiodic, and thus period or frequency is not appropriate.  Two new terms-bit interval (instead of period) and bit rate (instead of frequency)- are used to describe digital signals.  Bit interval is the time required to send one single bit.  The bit rate is the number of bit intervals per second, i.e., the number of bits sent in one second. This is expressed as bps.  A digital signal with all its sudden changes, is actually a composite signal having an infinite number of frequencies.

A digital signal

Bit rate and bit interval

Example 3 A digital signal has a bit rate of 2000 bps. What is the duration of each bit (bit interval) Solution The bit interval is the inverse of the bit rate. Bit interval = 1/ 2000 s = s = x 10 6  s = 500  s

41 A digital signal is a composite signal with an infinite bandwidth. Note: The bit rate and the bandwidth are proportional to each other.

Data Rate Limits Data rate depends on 3 factors:  The bandwidth available  The levels of signals (i.e number of signal levels) we can use  The quality of the channel (the level of the noise). For Noiseless Channel: Nyquist Bit Rate BitRate = 2*Bandwidth*log 2 L where L is the number of signal levels used to represent data

Data Rate Limits For Noisy Channels: Shanon Capacity  In reality we cannot have a noiseless channel; the channel is always noisy Capacity (Max.Bitrate)=Bandwidth*log 2 (1+SNR) Where SNR is the signal-to-noise ratio. We cannot achieve a data rate higher than, the capacity of the channel, no matter how many levels of signals we use. Thus Capacity characterizes the channel not the method of transmission.

44 Example 4 Consider a noiseless channel with a bandwidth of 3000 Hz transmitting a signal with two signal levels. The maximum bit rate can be calculated as Bit Rate = 2  3000  log 2 2 = 6000 bps

45 Example 5 Consider the same noiseless channel, transmitting a signal with four signal levels (for each level, we send two bits). The maximum bit rate can be calculated as: Bit Rate = 2 x 3000 x log 2 4 = 12,000 bps Bit Rate = 2 x 3000 x log 2 4 = 12,000 bps

46 Example 6 Consider an extremely noisy channel in which the value of the signal-to-noise ratio is almost zero. In other words, the noise is so strong that the signal is faint. For this channel the capacity is calculated as C = B log 2 (1 + SNR) = B log 2 (1 + 0) = B log 2 (1) = B  0 = 0

47 Transmission Impairment (Gangguan)  Types of impairment

Transmission Impairments  Sinyal yang diterima bisa jadi berbeda dari sinyal yang dikirimkan  Analog - degradasi kualitas sinyal  Digital - kesalahan bit  Disebabkan oleh  Atenuasi dan distorsi atenuasi  Delay distortion  Noise

Atenuasi  Kuat Sinyal menurun dengan bertambahnya jarak  Tergantung pada Media transmisinya  Kuat sinyal yang diterima: harus cukup untuk dideteksi harus cukup lebih tinggi dibanding “noise” yang akan diterima tanpa kesalahan  Atenuasi merupakan suatu fungsi kenaikan dari frekuensi

50 Figure 3.21 Attenuation

Delay Distortion  Hanya ada di guided media  Kecepatan penjalaran (Propagasi) bervariasi terhadap frekuensinya

Noise (1)  Sinyal tambahan yang masuk diantara transmitter dan receiver  Thermal (suhu)  Akibat dari “thermal agitation” dari elektron  Tersebar secara uniform  White noise  Intermodulation  Sinyal yang merupakan penjumlahan dan pengurangan dari frekuensi aslinya yang menggunakan media bersama

Noise (2)  Crosstalk  Suatu sinyal dari satu jalur yang diambil oleh jalur lain  Impulse  Pulsa yang tidak beraturan atau spike (lonjakan)  Contoh; Interferensi elektromagnetik eksternal  Short duration  Amplitudo yang tinggi

Kapasitas Channel  Kecepatan Data (Data rate)  Dalam bit per detik (bit per second : bps)  Rata-rata dimana data dapat dikomunikasikan  Bandwidth  Dalam putaran per detik (cycle per second : cps) dari Hertz  Dibatasi oleh transmitter dan media

More about signals  Throughput is the measurement of how fast data can pass through an entity (such as a point or a network).  Propagation speed measures the distance a signal can travel through a medium in one second. This depends on the medium and the frequency. Light is propagated in a vacuum with a speed of 3*10 8 m/s. It is lower in air and much lower in a cable.  Propagation time measures the time required for a signal (or a bit) to travel from one point in the medium to another.  Wavelength is the distance a simple signal (sine wave) can travel in one period. Wavelength=Propagation speed x Period= Propagation speed/Frequency( λ=c/f )

Throughput

Propagation time