By: Sebastian Andrews
Std.# 00051843
WARNING THIS WEB PAGE WAS CREATED BY A STUDENT OF THE UNIVERSITY OF TECHNOLOGY SYDNEY AS AN ASSIGNMENT FOR THE SUBJECT COMMUNICATION NETWORKS (48740)
Declaration of Originality:
The work contained in this assignment, other than that specifically attributed to another source, is that of the author(s). It is recognised that, should this declaration be found to be false, disciplinary action could be taken and the assignments of all students involved will be given zero marks. In the statement below, I have indicated the extent to which I have collaborated with other students, whom I have named.
Acknowledgements
I would like to thank all the good people at UTS library for helping me with my research, and of course for William Stallings because if it wasn't for him, I would not be here right now.
1.1 Digital Signals
1.2 Advantages of Signal Processing
1.2.1 High Interference Immunity
1.2.2 Short-Term and Permanent Storage
1.2.3 Flexible Processing
1.2.4 Various Transmission Options
1.3 Transmission of Digital Signals
2. Encoding Evaluation Factors
3. Types of Digital Wave Formatting
3.3 NRZ I - Nonreturn to Zero Invertive
3.4 Bipolar AMI - Alternate Mark Inversion
3.5 Pseudoternary
3.6 PE - Phase Encoder (Manchester)
3.9 HDB3 - High Density Bipolar 3
3.10 Bipolar with 8-zeros Substitution (B8ZS) Signal Encoding
3.11 MLT-3
3.12 FSR - Feedback Shift Register
3.13 4B/5B
4. Conclusion
7. Answers to Review Questions
8. References
10. Acronyms
In electronic signal and information processing and transmission, digital technology is increasingly being used because, in various applications, digital signal transmission has many advantages over analog signal transmission.
Unlike analog technology which uses continuous signals, digital technology encodes the information into discrete signal states. When only two states are assigned per digital signal, three signals are termed binary signals. One single binary digit is termed a bit.
A binary signal representing only two states contains very little information compared to an analog signal. If a quantity to be represented digitally requires a wider range of values, it must be divided into several bits, the range of values increases rapidly with the number of bits used.
1 bit = 21 states = 2 values
2 bits = 22 states = 4 values
3 bits = 23 states = 8 values
4 bits = 24 states = 16 values
8 bits = 28 states = 256 values
12 bits = 212 states = 4096 values
16 bits = 216 states = 65536 values
20 bits = 220 states = 1048576 values
Range of values of digital quantities
An increasing number of bits also increases the complexity of data processing and transmission. Digital technology rarely operates with the smallest possible digital quantity, but often groups 8 bits together to form a byte. So 8, 16 or 32 bit units are termed accordingly 1, 2 or 4 byte units.
The binary system can become unclear when it comes to large range values, more clarity can be achieved when using the hexadecimal system. In this numbering system, each character can assume 16 different values: 0 – 9 and A – F.
Each hexadecimal value is assigned a value of a 4-bit unit.
|
Binary Hex |
Binary Hex |
Binary Hex |
Binary Hex |
|
0000 0 |
0100 4 |
1000 8 |
1100 C |
|
0001 1 |
0101 5 |
1001 9 |
1101 D |
|
0010 2 |
0110 6 |
1010 A |
1110 E |
|
0011 3 |
0111 7 |
1011 B |
1111 F |
Binary and hexadecimal representation of a 4-bit unit
To be able to process data and messages digitally, they have to be encoded into binary digits. Whether letters, texts, numbers or states are involved, each piece of information must be converted into a binary unit using an ambiguous code scheme. This process is also called data encoding. Effective data processing is only possible if cooperating computers and programs all use the same code.
1.2 Advantages of digital signal processing
Digital signal transmission may seem like it is a very complex process compared to analog representation, but the advantages outweigh the disadvantages of digital technology, some of these advantages are
1.2.1 High interference immunity
Analog information is highly liable to interference, i.e. errors are caused by –even the smallest- disturbance signals, whereas digitally encoded information will be distorted only when the disturbance signal is larger than the signal-to-noise ratio of the digital level used. The signal-to-noise ratio results from the difference between the transmitting and the receiving level. It determines how strong capacitive or inductive interference noise or voltage fluctuations can be without distorting the digital signal. By selecting the binary information representation the signal-to-noise ratio can be adjusted within broad limits to the environmental condition
1.2.2 Short-term and permanent storage
Digital data can be stored very easily on a variety of often very cost-effective data carriers. There is the option of storing in volatile semiconductor memories (RAM), or permanently on magnetic and optical data carriers
Microprocessor-based and software-controlled data enables even complex algorithms to be computed in almost no time with a high degree of flexibility.
1.2.4 Various transmission options
The two states of a binary signal can be encoded in many different ways thus offering a broad spectrum of application. For data transmission over long distances, for example, optical fiber cables are used because of their low energy consumption and high interference immunity. Binary signals can be assigned directly to the ON/OFF states of a light signal, while analog signals can only be transmitted optically after expensive and time-consuming linearization and intensity analysis which is liable to errors .
1.3 Transmission of digital signals
There are two ways to transmit digital data between one or several devices or communication participants, either parallel or serial transmission.
Bit-parallel transmission
With parallel transmission, all bits of a piece of information are transmitted at the same time via an appropriate number of signal lines. The installation costs are high and only acceptable for short distance. The transmission of one byte alone requires a minimum of nine lines, 8 bits and a reference potential. Therefore, this technique is only used for device busses. This application requires high transmission rates while doing without conversion methods that need a large number of components.
Bit-serial transmission
For long distances, serial transmission is a good solution. Here, only one signal line transmits the bit after the other. As a result, the transmission will take longer than bit-parallel transmission, but the costs and efforts of installation are greatly reduced. Since all the information is generated and processed in bit-parallel mode, the transmitter must convert the signal to bit-serial.
(Most of the information for ‘digital signals’ was obtained from Source 1)
2. Encoding Evaluation Factors
Signal Spectrum - A lack of high-frequency components means that less bandwidth is required for transmission. With a dc component to the signal there must be direct physical attachment of transmission components. With no dc components, ac coupling via transformer is possible; this provides excellent electrical isolation, reducing interference, so no dc component is desirable. The magnitude of the effects of signal distortion and interference depend on the spectral properties of the transmitted signal. This usually happens that the transfer function of a channel is worse near the band edges. Therefore a good signal design should concentrate the transmitted power in the middle of the transmission bandwidth. A smaller distortion should be present in the received signal.
Clocking - Suitable encoding provide some synchronization mechanism to determine the beginning and end of each bit position.
Error Detection - Some error detection can be built into the encoding scheme. This permits errors to be detected more quickly
Signal Interference and Noise Immunity - Some encoding schemes have superior performance in the presence of noise.
Cost and Complexity - Higher signaling rate to achieve a greater data rate results expensive devices.
3. Types of Digital Wave Formatting
The digital data is represented as follows :
Every 0 bit has a voltage of zero
Every 1 bit has a voltage of +V volts.
This is the basic and most simple method but it has several drawbacks :
The digital data is represented as follows :
Every 0 bit has a voltage of zero
Every 1 bit has a voltage of +V volts during the first half of the bit and zero volts during the second half.
This method has the following advantages over NRZ
However, there are also worse features as the maximum bandwidth which is the data rate itself (for a sequence containing only 1's).
3.3 NRZ I - Nonreturn To Zero Invertive
The digital data is represented as follows :
Every 0 bit has a voltage of zero.
Every 1 bit has a voltage of +V or a voltage of zero according to the previous voltage. If the previous voltage was 0 volts the current one will be +V volts, on the other hand if the previous voltage was +V volts then the current one will be 0 volts.
This method combines the smaller bandwidth of NZR and the frequent changes in voltage of RZ while adding a major advantage of a non polarized signal.
3.4 Bipolar AMI - Alternate Mark Inversion
The digital data is represented as follows :
Every 0 bit has a voltage of zero.
Every 1 bit has a voltage of +V or -V which alternate every time.
Some of the advantages of this coding scheme are
No loss of synchronization with a long string of 1 bits
Each 1 bit introduces a transition and the receiver can resynchronize on transition
Because 1 signals alternate in voltage from positive to negative, there is no net dc component
Bandwidth of resulting signal considerably less than bandwidth for NRZ
Pulse alternation provides a simple means of error detection; any isolated error (addition or deletion of pulse) causes a violation
The disadvantage is that a long string of 0 bits still cause problems
The digital data is represented as follows
Every 1 bit has a voltage of zero
Every 0 bit has a voltage of +V or -V which alternate every time
This is almost the opposite of Bipolar AMI
Long strings of 0's in Bipolar AMI and long strings of 1's in Pseudoternary still present a problem
May insert additional bits to force transitions
Used in ISDN for relatively low data rate transmission
Expensive in high data rates because it results in an increase in already high signal transmission rate
possible to apply at high data rate using data scrambling
Line signal may take one of three levels
Each signal element may represent log23=1.58 bits of information but actually represents only one bit
Loss of efficiency compared to NRZ
Receiver has to discriminate between 3 levels (+V, 0, -V)
3.6 PE - Phase Encode (Manchester)
The digital data is represented as follows :
'0' bits by a voltage of +V volts in the first half of the bit and -V volts in the second one.
'1' bits by a voltage of -V volts in the first half of the bit and +V volts in the second one.
This method has all the needed advantage but the ones which are the large bandwidth and the polarity of the signal.
Manchester used for baseband coaxial cable and twisted pair bus LANs
Encoding in which data and clock signals are combined to form a single self-synchronizing data stream , one of the two bits, i.e., "0" or "1", is represented by no transition at the beginning of a pulse period and a transition in either direction at the midpoint of a pulse period, and the other is represented by a transition at the beginning of a pulse period and a transition at the midpoint of the pulse period.
Midbit transition is used only to provide clocking
0 is represented by presence of transition at the beginning of bit period
1 is represented by the absence of transition at the beginning of bit period
Advantage of employing differential encoding (no dc)
Maximum modulation rate is twice that for NZR due to one transition per bit time
Bandwidth required is correspondingly greater
Advantages
Synchronization
Predictable transition during each bit time
Can be used for synchronization
Self-clocking codes
No dc component
Error detection
Can be detected by absence of expected transition
Impervious to noise as noise will have to invert the signal both before and after the expected transition
Bandwidth reasonably narrow with no dc component
Bandwidth wider than that for multilevel binary codes
Popular for data transmission
Differential Manchester used for token ring LAN using shielded twisted pair
Manchester and Differential Manchester are grouped under the term BIPHASE codes, that overcome the limitations of the NRZ codes.
The BIPHASE schemes have the following advantages
Synchronization: Because there is a predictable transition during each bit time the receiver can synchronize on that transition. Because of this, these schemes are known as self-clocking codes.
No dc component: Biphase codes have no dc components.
Error Detection: The absence of an expected transition can be used to detect errors. Noise on the line would have to invert both the signal before and after the expected transition to cause an undetected error
This method combines the NRZI and the PE methods as follows :
'0' bit is represented by a voltage change in the same direction as the previous bit (from +V to -V or from -V to +V).
'1' bit is represented by a voltage change in the opposite direction of the previous bit (from +V to -V or from -V to +V).
This method is not sensitive to the polarization of the signal.
3.9 HDB3 - High Density Bipolar 3
The bipolar-AMI encoding supplemented with the following substitution scheme for `0000' runs.
| Number of bipolar pulses (ones) since last substitution | ||
|---|---|---|
| Polarity of preceding pulse | Odd | even |
| - | 000- | +00+ |
| + | 000+ | -00- |
3.10 Bipolar with 8-zeros Substitution (B8ZS) Signal Encoding
The bipolar-AMI encoding supplemented with a scrambling scheme, which uses two code violations to ensure synchronization in runs of 0's.
This scheme was specified by ANSI X3T9.5 committee. It is used by FDDI to obtain 100MB/s out of a 31.25MHz signal.
UTP is low pass in nature, meaning that it hinders high frequency signal (like a low-pass filter). So it is not feasible to merely increase the clock frequency by 10 to 100MHz and use Manchester encoding to give us 100Mbps. In addition, the FCC (Federal Communications Commission) have severely curtailed the power that is allowed to be emitted above 30MHz. We have to use another encoding technique in order to transmit high data rates across UTP.
If you take an averaging spectrum analyzer and look at the output signal of the 10Mbps Ethernet phase-encoded signal, you will see a power peak at 10MHz where there is a stream of '1's or '0's, you will see a smaller harmonic at 30MHz and if there is a stream of '1's and '0's, you will see a peak at 5MHz. Now 100BaseT uses a master clock running at 125MHz instead of 10MHz. The equivalent peaks would then be at 125MHz, 375MHz and 62.5MHz. Transmission electronics designed to work within the FCC rules will block the frequencies higher than 30MHz.
To get around this issue we need to concentrate the signal power below 30MHz if possible. To do this the encoding method Multi-Level Transition 3 (MLT-3) is used. This involves using the pattern 1, 0, -1, 0. If the next data signal is a '1' then the output 'transitions' to the next bit in the pattern e.g. if the last output bit was a '-1', and the input bit is a '1', then the next output bit is a '0'. If the next data signal is a '0' then there is no transition which means that the next output bit is the same as last time, in our case a '0'.
The cycle length of the output signal is therefore going to be 1/4 that of the MPE method so that instead of the main signal peak being at 125MHz as measured by the averaging spectrum analyzer, it will be at 31.25MHz which is near enough to be OK as far as FCC are concerned. 5 bits are transmitted for every 4 bits of data so that the data bit rate is actually 125Mb/s for 100Mb/s data throughput.
There is an issue with this in that you can end up with a series of '0's or '1's which force the local circuitry to count the bits using its own free running clock rather than have the check of the clock synchronization from the transmit source.
There is an issue with some encoding schemes of the power of the higher frequency harmonics. To minimize these there is another small step before wave shaping such as MLT-3 encoding. This step uses a Feedback Shift Register (FSR) to produce a 'pseudo-random' bit pattern which is Exclusive-ORed with the data stream. This pseudo random stream is a known quantity and is reversed at the other end by another Excusive-OR operation using the same known pseudo-random bit pattern. The purpose of the randomness is to reduce the regularity of the signal frequency and consequently the harmonics. The FSR used in 100BaseT is an 11-bit register that shifts one bit at a time from bit 0 to bit 10 on each clock cycle.
4B/5B encoding is sometimes called 'Block coding'. To get around this problem, an intermediate encoding takes place before the MLT-3 encoding. Each 4-bit 'nibble' of received data has an extra 5th bit added. If input data is dealt with in 4-bit nibbles there are 24 = 16 different bit patterns. With 5-bit 'packets' there are 25 = 32 different bit patterns. As a result, the 5-bit patterns can always have two '1's in them even if the data is all '0's a translation occurs to another of the bit patterns. This enables clock synchronizations required for reliable data transfer.
Notice that the clock frequency is 125MHz. The reason for this is due to the 4B/5B encoding. A 100MHz signal would not have been enough to give us 100Mbps, we need a 125MHz clock.
As we have seen there are numerous methods to encode digital data. From the simplest NRZ which is used in RS232 based protocols, through PE which is used in Ethernet up to the most complicated HDB3 which is used in telephone services. The choice of the encoding technique is up to the designer who knows the restrictions of bandwidth, cabling systems, data rate etc.
High Interference Immunity - The Signal-to-Noise Ratio can be adjusted within broad limits to suit the surrounding environment
Short term and permanent storage - Digital data can be stored very easily on a variety of often very cost-effective data carriers
Flexible processing - Microprocessor-based and software-controlled data enables even complex algorithms to be computed in almost no time with a high degree of flexibility.
Transmission options - Data can be sent in many different ways due to the fact that digital data only has two states
There are two ways to transmit digital data between one or several devices or communication participants, either parallel or serial transmission.
With parallel transmission, all bits of a piece of information are transmitted at the same time via an appropriate number of signal lines
With serial transmission, all bits of a piece of information are transmitted at the same time via 1 signal line, it is more time consuming, but cheaper to install.
Signal Spectrum - A lack of high-frequency components means that less bandwidth is required for transmission.
Clocking - Suitable encoding provide some synchronization mechanism to determine the beginning and end of each bit position.
Error Detection - Some error detection can be built into the encoding scheme. This permits errors to be detected more quickly
Signal Interference and Noise Immunity - Some encoding schemes have superior performance in the presence of noise.
Cost and Complexity - Higher signaling rate to achieve a greater data rate results expensive devices.
Nonreturn To Zero - This is the basic and most simple method but it has several drawbacks
The signal is polarized
Large bandwidth
High dc level
Return To Zero - This method has the following advantages over NRZ
The average DC level is only 1/4V.
When the data sequence contains only 1's there are still voltage changes
Nonreturn To Zero Invertive This method combines the smaller bandwidth of NZR and the frequent
changes in voltage of RZ while adding a major advantage of a non
polarized signal
Bipolar AMI - Some of the advantages of this coding scheme are
No loss of synchronization with a long string of 1 bits
Bandwidth of resulting signal considerably less than bandwidth for NRZ
Pulse alternation provides a simple means of error detection
Pseudoternary - Expensive in high data rates
Loss of efficiency compared to NRZ
Manchester - Manchester used for baseband coaxial cable and twisted pair bus LANs
This method has all the needed advantage but the ones which are the
large bandwidth and the polarity of the signal.
It is a Biphase coding scheme
Diff Manchester - It is a self-clocking code
Has error detection
No dc component
It is a Biphase coding scheme
Conditional Diphase - It combines the NRZI and the PE methods
It is not sensitive to the polarization of the signal
HDB3 - It changes the signals when there are 4 successive pulses
Based on Bipolar AMI
It is used widely in Japan
B8ZS - It changes the signal when there are 8 successive 0 bits
There is no dc component
Based on Bipolar AMI
Causes two violations of AMI code
Unlikely to occur as a result of noise
MLT-3 - 5 bits are transmitted for every 4 bits of data
It check the synchronization on it's own clock
Feedback Shift Register - It produces a pseudo-random bit pattern
The purpose of the randomness is to reduce the regularity of the signal
frequency
4B/5B - It is sometimes called Block coding
It enables clock synchronizations required for reliable data transfer
1. How many states can 12 bits have?
a. 8
b. 16
c. 4096
d. None of the above
2. What is the hexadecimal number '6' in binary?
a. 0000
b. 0100
c. 1111
d. 0110
3. Which is not an advantage of having digital signal transmission?
a. High interference immunity
b. Flexible Processing
c. Faster Data Rate
d. Short-term Storage
4. When evaluating the encoding methods which is not a factor?
a. Clocking
b. Differential encoding
c. Signal Spectrum
d. Cost
5. What is the coding scheme called represented by the diagram?
a. Nonreturn to Zero
b. Pseudoternary
c. Bipolar AMI
d. HDB3
6. What is the coding scheme called represented by the diagram?
a. Nonreturn to Zero
b. Manchester
c. B8ZS
d. Feedback Shift Register
7. What is the coding scheme called represented by the diagram?
a. Pseudoternary
b. Return to Zero
c. HBD3
d. B8ZS
8. What message is sent when there is a string of 8 zeros in B8ZS coding scheme?
a. 00++0-
b. 000+-0+-
c. 000-
d. -00-
9. Which two schemes are part of Biphase
A Pseudoternary
B Manchester
C Bipolar AMI
D Differential Manchester
a. A and B
b. D and A
c. B and D
d. A and D
e. None of the above
f. All of the above
10. What is a characteristic of Pseudoternary coding scheme?
a. Every 1 bit has a voltage of zero
b. Every 1 bit has a voltage of +V
c. Every 1 bit has a voltage of -V
d. None of the Above
11. What is 100Base10?
a. A coding scheme
b. An Ethernet connection type
c. A waveform
d. A type of receiver
12. What coding scheme changes when there is four consecutive pulses?
a. 100BaseT
b. HBD3
c. B8ZS
d. MLT-3
13. What is sometimes called 'Block Coding'?
a. Bipolar AMI
b. Feedback Shift Register
c. MLT-3
d. B4/B5
14. What Methods does Conditional Diphase combine?
a. B8ZS and HBD3
b. NZR I and Manchester
c. NZR and Pseudoternary
d. Manchester and Diff Manchester
15. What is a characteristic of Differential Manchester?
a. Self-Clocking
b. Creates a dc component
c. No error detection
d. Creates a different signal when repeated bits come in
16. What is a characteristic of Bipolar AMI?
a. No error detection
b. 5 bits are transmitted for every 4 bits of data
c. It is sometimes called Block coding
d. No loss of synchronization with a long string of 1 bits
17. What coding scheme is usually used in coaxial cable?
a. NZR
b. 100Base10
c. Manchester
d. Return to Zero
18. What is signal spectrum?
a. A lack of high-frequency components means that less bandwidth is required for transmission.
b. It permits errors to be detected more quickly
c. It can store digital data very easily
d. Data can be sent in many different ways
19. What is a characteristic of the MLT-3 coding scheme?
a. It produces a pseudo-random bit pattern
b. It check the synchronization on it's own clock
c. Causes two violations of AMI code
d. It combines the NRZI and the PE methods
20. What is High Interference Immunity?
a. Higher signaling rate to achieve a greater data rate results expensive devices.
b. All bits of a piece of information are transmitted at the same time.
c. The Signal-to-Noise Ratio can be adjusted within broad limits to suit the surrounding environment
d. All bits of a piece of information are transmitted at the same time via 1 signal line
1. c
2. d
3. c
4. b
5. a
6. b
7. a
8. b
9. c
10. a
11. b
12. b
13. d
14. b
15. a
16. d
17. c
18. a
19. b
20. c
Source 1 Digital signals
Source 2 INTRODUCTION TO COMPUTER NETWORKING - Eitan Gurari
Digital Data, Digital Signals
www.cis.ohio-state.edu/~gurari/course/cis677/cis677.html#cis677No1.html
Source 3 Digital Encoding - Ronen Halevi and Udi Nir
www.rad.com/networks/1994/digi_enc/main.htm
Source 4 Data Encoding
www.cs.umsl.edu/~sanjiv/cs373/lectures/encode.pdf
Source 5 Rhys Haden's Technical Resource - Rhys Haden 1997-2002
Source 6 www.whatis.com search engine
Source 7 www.google.com search engine
Source 8 Computer Network Architectures And Protocols (2nd Ed) Sunshine, Carl A.
1982 Plenum Press, New York
Source 9 Computer Networks (3rd Ed) Tanenbaum, Andrew S.
1996 Prentice Hall, New Jersey
Source 10 Data & Computer Communication (sixth edition) Stalling, William
2000 Prentice Hall, New Jersey
100Base10 - Another term for fast Ethernet, an upgraded standard for connecting computers into a local area network (LAN). 100BaseT Ethernet works just like regular Ethernet except that it can transfer data at a peak rate of 100 mbps. It's also more expensive and less common than its slower 10BaseT sibling.
Analog - An analog signal can be represented as a series of sine waves. The term originated because the modulation of the carrier wave is analogous to the fluctuations of the human voice or other sound that is being transmitted.
Bandwidth - The difference between the limiting frequencies of a continuous frequency spectrum.
Baseband - Transmission of signals without modulation. In a baseband local network, digital signals (1's and 0's) are inserted directly onto the cable as voltage pulses. The entire spectrum of the cable is consumed by the signal. This scheme does not allow frequency-division multiplexing.
Binary - Pertaining to a number system have 2 as its base; "a binary digit" 2: consisting of two (units or components or elements or terms) or based on two.
Bits - A fundamental unit of information having just two possible values, as either of the binary digits 0 or 1.
Bus - One or more conductors that serve as a common connection for a related group of devices.
Byte - A sequence of adjacent bits, usually eight, operated on as a unit by a computer.
Coaxial Cable - A cable consisting of one conductor, usually a small copper tube or wire, within and insulated from another conductor of larger diameter, usually copper tubing or copper braid.
Codec (Coder-Decoder) - Transforms analog data into a digital bit stream (coder), and digital signals into analog data (decoder).
Data - Representation of facts, concepts, or instructions in a formalized manner suitable for communication, interpretation, or processing by humans or by automatic means. Any representations such as characters or analog quantities to which meaning is or might be assigned.
Data Element – A single Binary One or Zero.
Data Encoding - Information that is converted into a binary unit using an ambiguous code scheme.
Data Rate – The Rate at which the data is being transmitted.
Data signaling rate – is the rate, in bits per second, that the data are transmitted.
Digital - Relating to a device that can read, write, or store information that is represented in numerical form.
Ethernet - Ethernet is the most widely-installed local area network technology. Ethernet was originally developed by Xerox and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. The most commonly installed Ethernet systems are called 10Base-T and provide transmission speeds up to 10 Mbps.
Error Rate - The ratio of the number of data units in error to the total number of data units.
Hexadecimal - A number representation using the digits 0-9, with their usual meaning, plus the letters A-F (or a-f) to represent hexadecimal digits with values of (decimal) 10 to 15.
Interference - Errors that are caused by disturbance signals.
Local Area Network - A communication network that provides interconnection of a variety of data communicating devices within a small area.
Noise - Unwanted signals that combine with and hence distort the signal intended for transmission and reception.
Polar Signaling – One logic state is represented by a positive voltage level, the other by a negative voltage level.
Signal-to-Noise Ratio - Measures the amount of unwanted electromagnetic noise relative to a signal's strength.
Signal Element – That part of a signal that occupies the shortest interval of a signaling code.
Transmission System - This can be a single transmission line or a complex network connecting source and destination.
Unipolar signal - If the signal elements all have the same algebraic sign (that is all positive or negative).
AC Alternating Current
AMI Alternate Mark Inversion
ANSI American National Standards Institute
B8ZS Bipolar with 8-Zeros Substitution
CDP Conditional Diphase
DC Direct Current
FCC Federal Communications Commission
FDDI Fiber Distributed Data Interface
FSR Feedback Shift Register
HDB3 High Density Bipolar 3
ISDN Integrated Services Digital Network
LAN Local Area Network
NRZ Nonreturn to Zero
NZR I Nonreturn to Zero Invertive
PE Phase Encoder
RZ Return to Zero
UTP Unshielded Twisted Pair
