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Data Communication & Networking CSCI 3342 Computer Science Department
Digital Transmission Dr. Thomas Hicks Computer Science Department Trinity University 4 1
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Digital To Digital Encoding
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Major 4 Encoding Methods
Digital-To- Digital Analog-To- Digital Digital-To- Analog Analog-To- Analog Binary Data Must Be Encoded/Converted To A Form That Will Propagate Over A Wire
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Digital To Digital Encoding
Digital To Digital Encoding – Converting Binary 0’s and 1’s Into A Sequence Of Voltage Pulses That Can Propagate Over A Wire. Transmit Data From Computer To Printer
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Signal Encoding Signal Level Data Level
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Signal Level vs. Data Level
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Pulse Rate & Bit Rate
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Pulse Rate = No Pulses Per Second Bit Rate = No Bits Per Second
If the pulse carries only one bit, the Bit Rate = Pulse Rate [Not Always The Case]
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BitRate = PulseRate x log2 L L = # Data Levels
General Case: BitRate = PulseRate x log2 L L = # Data Levels BitRate = PulseRate x log2 DataLevels
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Pulse Rate = 1/ 10-3 = 1000 pulses/s
Example 1 A signal has two data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = 1/ = 1000 pulses/s Bit Rate = Pulse Rate x log2 L = 1000 x log = 1000 bps
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Example 2 Pulse Rate = 1/ 10-3 = 1000 pulses/s
A signal has four data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = 1/ = 1000 pulses/s Bit Rate = PulseRate x log2 L = 1000 x log = 2000 bps
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DC Components
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We Shall Examine Numerous Coding Schemes
Most Coding Schemes Will Have Values Above & Below The Line - Positive & Negative Values.
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DC Component Coding Schemes
Some coding schemes have a residual DC [Direct-Current] that has a zero frequency. The positive and negative voltages do not cancel each other. This extra energy on the line is useless and will not pass properly through Transformers! Bad!
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Synchronization
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We Must Have Some Way Of Synchronizing The Signal!
The Receiver's Bit Intervals Must Match The Sender's Bit Intervals If The Signal Is To Be Interpreted Correctly! We Must Have Some Way Of Synchronizing The Signal!
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Lack Of Synchronization
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Solution Example 3 At 1 Kbps:
In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps? Solution At 1 Kbps: 1000 bits sent 1001 bits received1 extra bps At 1 Mbps: 1,000,000 bits sent 1,001,000 bits received1000 extra bps
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Many Line Coding Schemes
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Only Some Of Major Encoding Methods!
Unipolar Polar Bipolar AMI B8ZS HDB3 ETC RZ NRZ NRZ-L NRZ-I Manchester Differential Manchester
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You May Make A 5"x8" Card To Use On Exam
(May Include Titles & Images) NRZ-L
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Unipolar
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Unipolar Encoding uses only One Voltage Level.
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Unipolar Encoding
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Not Essential Assignment,
Unipolar Encoding -1 Unipolar uses either a Positive Or Negative Unipolar – Very Simple & Very Primitive Encoding Scheme (almost obsolete) Unipolar – Only one polarity. Sending Voltage Pulses along a medium link (usually a wire or cable) Voltage Level = 1’s Zero Voltage Level = 0’s Not Essential Assignment, But Logical!
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Unipolar Encoding -2 Unipolar Requires DC Component
Average Amplitude Is Non-Zero Not All Mediums Can Handle A DC Component Unipolar Requires Synchronization No Way Receiver Can Determine Beginning Or End Problem With A Long, Uninterrupted Series Of 1’s Problem With A Long, Uninterrupted Series Of 0’s Solution To Synchronization Problem – Use A Separate Parallel Line To Carry Clock Pulse Doubling # Lines Expensive
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Polar
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uses two voltage levels (positive and negative?)
Polar Encoding uses two voltage levels (positive and negative?)
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Types Of Polar Encoding
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Polar Encoding Polar Encoding – Uses Two Voltage Levels –> 0 Positive & 1 Negative – or Visa Versa Average Amplitude is 0 DC Component Not Needed 4+ Types Of Polar Encoding NRZ RZ Manchester Differential Manchester
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NRZ-L Encoding (Polar)
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Polar NRZ-L Encoding In Polar NRZ-L the Level of the Signal is Dependent upon the State of the Bit.
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Polar Encoding NRZ-L NRZ - NonReturn to Zero – Two Most Popular Methods Are NRZ-L and NRZ-I NRZ-L Usually 0 Positive & 1 Negative {For Us!} Biggest Problem With Long Stream Of 1’s or 0’s [Clocks Might Not Be Synchronized]
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NRZ-L Practice Sketch The NRZ-L Encoding For The Signal Below.
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NRZ-I Encoding (Polar)
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In NRZ-I the signal is Inverted If a 1 is Encountered.
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Polar Encoding NRZ-I Synchronization Occurs With Every 1 Bit NRZ-I
An Inversion Of The Voltage Represents 1 If Pos Neg If Neg Pos No Change Represents 0 Synchronization Occurs With Every 1 Bit 0’s Can Still Cause Problem – More 1’s Than 0’s 0 First Pos 1 First Neg Next Bit Is 1
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NRZ-I Practice Sketch The NRZ-I Encoding For The Signal Below.
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RZ Encoding (Polar)
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Polar RZ RZ - Return to Zero – A Signal Change With Every Bit To Assure Synchronization Several Solutions RZ Positive Voltage Means 1 Negative Voltage Means 0 Signal Returns To 0 Voltage Half-Through
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Polar RZ RZ – 3 Levels Of Amplitude – 3 Voltage Levels
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Polar RZ Practice Best So Far!
Sketch The RZ Encoding For The Signal Below. Best So Far!
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A Good Encoded Digital Signal Must Contain a Provision for Synchronization.
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Manchester Encoding (Polar)
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In Manchester Encoding, the Transition at the Middle of the Bit is used for both Synchronization and Bit Representation.
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Polar Manchester Manchester Positive To Negative Transition For 0
Negative To Positive Transition For 1 Two Levels Of Amplitude Inversion At Middle Middle Of Bit Time
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Polar Manchester (cont)
Inversion At Middle Middle Of Bit Time Synch Signal Change Middle Of Each Bit Green Blue
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Polar Manchester Practice
Sketch The Manchester Encoding For The Signal Below. Two Levels Of Amplitude Same Synchronization As RZ
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I Would Provide KEY Manchester
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Differential Manchester Encoding
(Polar)
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In Differential Manchester Encoding, the Transition at the Middle of the Bit is used only for synchronization. The Bit Representation is defined by the Inversion or Non-Inversion at the beginning of the bit.
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Polar Differential Manchester
Synch Signal Change Middle Of Each Bit Inversion At Beginning Of Bit Time Transition At Start Of Bit Time = 0 No Transition At Start Of Bit Time = 1 2 Signal Changes For 0, 1 Signal Change for 1
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Polar Differential Manchester Practice
Sketch The Differential Manchester Encoding For The Signal Below.
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Bipolar
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In Bipolar Encoding, we use Three Levels: positive, zero, and negative.
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Bipolar Bipolar – Three Most Most Common Solutions – AMI, B8ZS, & HDB3
Uses 3 Voltage Levels Positive, Negative, Zero Zero Level Is 0 Alternating Positive & Negative Are 1
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AMI Encoding (Bipolar)
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Bipolar - AMI AMI – Alternate Mark Inversion
Mark In Telegraphy Means 1 Zero Voltage Represent 0 Alternating Positive & Negative Represent 1 Synchronize Long Sequence 1’s No Synchronize Long Sequence 0’s DC Component = 0
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Bipolar AMI Practice Sketch The AMI Encoding For The Signal Below.
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Bipolar - Pseudoternary
“A Variation Of Bipolar AMI is called Pseudoternary, In Which Binary 0’s Alternate Between Positive & Negative Voltages.” NEW!
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BZPS Encoding (Bipolar)
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Bipolar – BZPS B8ZS – Bipolar 8 Zero Substitution
Same As AMI Until 8 Consecutive 0’s Use Chart Below [Will Be Provided On Exam/ Quiz]
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Used A Lot In North America
Bipolar – B8ZS Practice Sketch The B8ZS Encoding For The Signal Below. Used A Lot In North America
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Bipolar – HDB3 HDB3 – High Density Bipolar 3
Similar To B8ZS – Except Done In Sets Of 4 Use Chart Below [Will Be Provided On Exam/ Quiz]
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2B1Q Encoding (Bipolar)
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2B1Q Encoding 2 Binary 1 Quaternary Encoding
2B1Q Encoding 2 Binary 1 Quaternary Encoding 4 Voltages
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MLT-3 Encoding (Bipolar)
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MLT-3 Encoding MLT-3 Encoding Similar to NRZ-I
Uses 3 Levels Of Signal +1, 0, -1 The Signal Transitions From One Level To The Next At The Beginning Of A 1 Bit There Is No Transition At The Beginning Of A 0 Bit
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Block Encoding
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Figure Block coding Need Some Kind Of Redundancy To Assure Synchronization! High Performance! Need Some Of The Chapter 10 Error Detection To Assure Delivery!
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Block Encoding 1. Divide Into Groups Of M Bits
2. Substitute N-Bit Code For M-Bit Group N > M 3. Use A Line Encoding Scheme To Create A Signal Comes At A Cost - Requires Increase Bandwidth!
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Figure 4.16 Substitution in block coding
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4B5B 8B10B Encoding
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Table 4.1 4B/5B encoding -- Not All 5 Bit Codes Used!
Data Code 0000 11110 1000 10010 0001 01001 1001 10011 0010 10100 1010 10110 0011 10101 1011 10111 0100 01010 1100 11010 0101 01011 1101 11011 0110 01110 1110 11100 0111 01111 1111 11101
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8B/10B Encoding Table 4.1 4B/5B encoding (Continued) Q (Quiet) 00000
Data Code Q (Quiet) 00000 I (Idle) 11111 H (Halt) 00100 J (start delimiter) 11000 K (start delimiter) 10001 T (end delimiter) 01101 S (Set) 11001 R (Reset) 00111 8B/10B Encoding Groups of 8 Bits - Substituted Into A 10 Bit Code - More Efficient & Better Error Detection! Long Table!
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8B6T Encoding
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28 8-Bit Sequences <== Translated Into ==> 36 Ternary
8B/6T Block Encoding Take Advantage Of Speed & Error Detection Of Block Encoding Requires Much Less Bandwidth 8 Binary Bits Substituted Into A 6 Bit Ternary Table 8 Bits Translated Into 6 Bit of +1, 0, -1 [Table In Appendix D] 28 8-Bit Sequences <== Translated Into ==> 36 Ternary
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Analog To Digital Encoding
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Encoding Methods Review
Digital-To- Digital Analog Analog-To- Binary Data Must Be Encoded/Converted To A Form That Will Propagate Over A Wire
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Analog To Digital Encoding
Analog To Digital Encoding – Digitizing An Analog Signal Reducing The Potentially Infinite Number Of Values In An Analog Signal So That They Can Be Represented In A Digital Stream With A Minimum Loss Of Information.
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Codec PAM PCM
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Analog To Digital Converter Called A Codec coder –decoder codec
Conversion Requires Two Steps: Pulse Amplitude Modulation (PAM) Pulse Code Modulation (PCM)
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Pulse Amplitude Modulation has some applications, but it is not used by itself in data communication. However, it is the first step in another very popular conversion method called Pulse Code Modulation.
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Step 1: Pulse Amplitude Modulation (PAM)
I. Pulse Amplitude Modulation (PAM) Sample Analog Signal At Regular Intervals Generate Pulses Accuracy Depends Upon # Of Samples Selected
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Step 2: Pulse Code Modulation (PCM)- 1
II. Pulse Code Modulation (PCM) 3 Steps Step 1: Quantitize PAM Signals
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Step 2: Pulse Code Modulation (PCM) - 2
II. Pulse Code Modulation (PCM) 3 Steps Step 2: Translate Each Value Into 7 Bit Binary Equivalent
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Step 2: Pulse Code Modulation (PCM) - 3
II. Pulse Code Modulation (PCM) 3 Steps Step 3: Convert To Digital Using Appropriate Technique. Review Unipolar Bipolar Polar … …
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Complete Analog-To-Digital Conversion Flow Diagram
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Nyquist According to the Nyquist Theorem,
the Sampling Rate must be at least 2 times the Highest Frequency.
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NYQUIST Theorem Sampling Rate
Remember : Analog-To-Digital Accuracy Depends Upon # Of Samples Selected How Many? Nyquist Theorem : The Sampling Rate Must Be At Least Two Times The Highest Frequency!
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Nyquist In The Real World Sampling Rate Practice
Telephone Voice Maximum Frequency = 4000 Hz 8,000 Sampling Rate = __________ Samples/Second A Bandwidth of 11,000 Is Needed To Transfer A Signal Whose Frequency Range Is 1,000 Hz to 12,000 Hz. Sampling Rate = __________ Samples/Second 24,000
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Bit Rate Bit Rate = Sampling Rate x Number Bits Per Sample
Bit Rate : Also Called The Data Rate
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Sampling Rate = __________ Samples/Second Bit Rate = __________ Kbps
Bit Rate Practice Want To Digitize Human Voice Using Eight Bit Samples. Human Voice Has Frequency Range of 0 to 4 KHz. Sampling Rate = 2 * Highest Frequency (4000 Hz) 8,000 Sampling Rate = __________ Samples/Second Bit Rate = Sampling Rate (8,000) * NoBitsPerSample (8) Bit Rate = 64,000 bps 64 Bit Rate = __________ Kbps
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Example 4 What sampling rate is needed for a signal with a bandwidth of 10,000 Hz (1000 to 11,000 Hz)? Solution The sampling rate must be twice the highest frequency in the signal: Sampling rate = 2 x (11,000) = 22,000 samples/s
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Example 5 A signal is sampled. Each sample requires at least 12 levels of precision (+0 to +5 and -0 to -5). How many bits should be sent for each sample? Solution We need 4 bits; 1 bit for the sign and 3 bits for the value. A 3-bit value can represent 23 = 8 levels (000 to 111), which is more than what we need. A 2-bit value is not enough since 22 = 4. A 4-bit value is too much because 24 = 16.
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Example 6 We want to digitize the human voice. What is the bit rate, assuming 8 bits per sample? Solution The human voice normally contains frequencies from 0 to 4000 Hz. Sampling rate = 4000 x 2 = 8000 samples/s Bit rate = sampling rate x number of bits per sample = 8000 x 8 = 64,000 bps = 64 Kbps
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Transmission Modes
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Data Transmission Parallel Serial Synchronous Asynchronous
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Parallel Transmission
Parallel Transmission – Eight or More Lines Are Bundled Together To Send One Byte At A Time
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Serial Transmission Serial Transmission – Requires Only One Communication Channel
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Serial or Parallel Transmission Which Is Faster?
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Serial or Parallel Transmission Which Is Least Expensive?
Usually Limited To Short Distances
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There may be a gap between each byte.
In Asynchronous Transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte. There may be a gap between each byte.
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Serial Transmission Asynchronous - 1
Asynchronous – Information Sent & Received In Agreed Upon Patterns; Timing Is Unimportant!
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Serial Transmission Asynchronous - 2
Asynchronous Serial Transmission Start Bit [0] Is Sent To Alert Receiver 8 Bits – 1 Byte – Of Data Transmitted 1-2 Stop Bits [1’s] Is/Are Sent To Let User Know Finished A Brief Time Gap Often Follows Some Type Of Synchronization Must Be Embedded Within Data Cheap/Effective Choice For Low Speed Communication [Great For Terminal – Computer!]
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Asynchronous here means “asynchronous at the byte level,” but the bits are still synchronized; their durations are the same.
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Serial Transmission Synchronous - 1
Synchronous – Information Combined Into Frames [Multiple Bytes]; Timing Is Essential!
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Serial Transmission Synchronous - 2
Synchronous Serial Transmission No Gaps – Unbroken String 1’s & 0’s Gaps Generally Filled In With Agreed Upon Sequences Of 1’s & 0’s – Idle Timing Essential Much Faster Than Asynchronous
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In Synchronous Transmission, we send bits one after another without start/stop bits or gaps It is the responsibility of the receiver to group the bits.
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Good Practice Problem Sketch The Encoding Of Signal With Each Of The Following On A New Page. Write NothingElse On This/These Pages Except Encoding Type & Your Name(s). Each Person On Team Must Do Their Own Copy Of This Problem! A. Unipolar B. NRZ-L C. NRZ-I D. RZ E. Manchester F. Differential Manchester G. AMI H. Pseudoternary I. B8ZS J. Quaternary 2B1Q K. MLT-3 L. 4B5B M. 8B6T
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Data Communications & Networking CSCI 3342
Dr. Thomas E. Hicks Computer Science Department Trinity University Textbook: Computer Networks By Andrew Tanenbaum Textbook: Data Communications & Networking By Behrouz Forouzan Special Thanks To WCB/McGraw-Hill For Providing Graphics For Many Text Book Figures For Use In This Presentation.
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