Review Notes in Digital and Data Communications System for ECE Board Exam

Compiled review notes in Digital and Data Communications System as one topic in ECE Board Exam taken from different sources including but not limited to Communications books, past Board Exams Questions, Journals and the Internet.

Review Notes in Digital and Data Communications System

This is the Review Notes in Digital and Data Communications System as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

Summary of Important Digital and Data Communication Review Notes

Redundancy means the symbol are to be repeated

Optical fiber transmission media is not suitable to CSMA operation

Transducer is a device used to convert a time varying electrical quantity to an appropriate form

The bandwidth of U600 mastergroup is 2520 kHz

Hybrid data – refers to the combined digitally encoded signals transmitted with FDM signals as one composite baseband signal

L carrier systems – transmit frequency-division-multiplexed voice band signals over a coaxial cable for distances up to 4000 miles

Level 5 of Japanese PCM multiplex hierarchy has a channel capacity of 5760 VB channels

The line data rate (in Mbps) for level 4 of CEPT 30 + 2 PCM multiplex hierarchy is 139.264

The guardband between supergroup 18 and supergroup D25 is 56 kHz

Supergroup 17 has a carrier frequency (in kHz) of 2108

A radio channel is composed of 1800 VB channels

The guardband between supergroup 1 and supergroup 2 is 12 kHz

CCITT’s supermastergroup has 900 voice band channels

The transparency mechanism used with SDLC is called zero-bit insertion

2B + D – defines the composition of an ISDN basic access line

Synchronous digital hierarchy (SDH) – a digital network where voice, video, text and data are multiplexed into a single network for processing and are transmitted prior to use

T-1 carrier service has 1.544 Mbps digital bit rate

Non-ISDN equivalent can be connected to ISDN line by the use of terminal adapters

The baseband frequency of standard FDM basic supergroup is 312 to 552 kHz

The transmission signal coding for T1 carrier is Bipolar

The primary purpose of the data modem is to interface digital terminal equipment to analog communications channel

Data terminal equipment (DTE) – the line control unit (LCU) operates on the data in digital form

32 H – SYN character of EBCDIC code

Bit or clock synchronization ensures that the transmitter and receiver agree on prescribed time slot for the occurrence of a bit

2^n >= m + n + 1 – used to determine the number of Hamming bits in the Hamming code

Data means digital information

Network layer determines which network configuration is most appropriate

Ethernet is a baseband system using CSMA/CD operating at 10 Mbps

Channel accessing – mechanism used by a station to gain access to local area network

TDM multiplexing scheme is used by baseband transmission

Use of coaxial cables in interconnecting networks is limited to an overall length of 1500 m

Topology or architecture identifies how the stations are interconnected in a network

Local Area Network is a data communications network designed to provide two-way communications between a large variety of data communications terminal equipment within a relatively small geographic area

Start/stop mode is the mode of transmission in public data network in which data are transferred from source to the network then to the destination in an asynchronous data format

A seven-bit character can represent one of 128 possibilities

Channel capacity is defined to be the maximum rate at which information can be transmitted through a channel

Source coding – circuit that performs the inverse mapping and delivers to the user destination, a reproduction of the original digital source output

PSK digital modulation technique used in modems

Emile Baudot developed the fixed-length binary code for telegraphy

Alex Reeves – inventor of pulse-code modulation for the digital encoding of the speech signals

In 1950’s, computers and terminals start communicating with each other over long distance

PRNET – store-and-forward multiple-access network

Huffman code – a source code whose average world length approaches the fundamental limit set by the entropy of a discrete memoryless source

DCA promulgate communications-related military standards (MIL-STD)

P2 is the class of probability in error detection techniques that is known as residual error rate

RS 232 is normally an interface between DTE and DCE. The signal rate 20 kbps

TMS – digital switching concepts that can handle more channels

The most significant advantage of modular switch than time-and-space switch is flexible size

The biggest disadvantage of PCM systems is the larger bandwidth required

The reason why companding is employed in PCM systems is to protect small signals in PCM from quantizing distortion

Folding frequency – the highest frequency that can be processed at a sampling rate (fs) without aliasing

The overlapping of the original spectrum and the first translated component is known as aliasing

Full duplex – transmission sent in both directions simultaneously

Multiplexing in a time division multiplexer occurs based upon the position of data within a frame

Multiplexing – a technique that enables more than one data source to share the use of a common line

One of the reasons whey FDM is being replaced by TDM is because noise is amplified with voice when an FDM system is used

In pulse modulation the carrier is a periodic train of pulses

The process that uses the orthogonality of sines and cosines that makes possible to transmit and receive to different signals simultaneously on the same carrier frequency is Quadrature multiplexing

Pulse code modulation technique is a digital transmission system

Bandwidth utilization is not an advantage of digital transmission

Dynamic range is the ratio of the largest possible magnitude to the smallest possible magnitude that can be decoded by the DAC

Companding – a process where the higher amplitude analog signals are compressed prior to transmission then expanded at the receiver

Delta Modulation (DM) uses a single bit PCM code to achieve a digital transmission of analog signal

The line speed of Bell System T1 carrier system is 1.544 Mbps

T2 lines carry 96 channels

A super group has 60 channels

The output frequency at the channel combiner of channel 7 is 80 – 84 kHz

The carrier frequency of the supergroup D25 is 2652 kHz

Data in video is not a hybrid data

Baudot Code was the first fixed-length 5-bit character code

CCITT V.26 modem has a modulation rate of 1200 bauds

A smart modem accepts commands from the terminal via RS232 interface

An advantage of PTM over PAM is much better noise immunity

ISO adapted the seven-layer OSI model in 1983

Amplitude shift keying is also known as ON/OFF keying

FSK modulation system is used in telephony

FSK – modulation used by asynchronous data

PCM systems require large bandwidth

Shanon-Hartley theorem sets the limit on the maximum capacity of a channel with a given noise level

Quantizing noise is present in PCM system

Quantizing noise is the difference between the original and reconstructed signal

The reason why companding is employed in PCM system is to protect small signals in PCM from quantizing distortion

FDM – band of frequencies in a transmission medium allotted to each communication channel on a continuous time basis

ARQ – error control used in high frequency radio data transmission

Sampling, quantizing and coding are the steps to follow to produce a PCM signal

Network topology identifies how the difference stations in a multipoint system are interconnected

Baseband – a transmission where data are inputted directly on the cable

Broadband – a transmission where data are inputted inside the carrier wave

Polling – a transmission system for a multidrop network

CSMA/CD – before attempting to transmit data, each station has to listen to the channel

Synchronous modems cost more than asynchronous modems because they must contain clock recovery circuits

When one station is designated as master and the rest of the stations are considered slaves, massage handling is polling

Master – the computer that initiates information transfer

Message switching – a store and forward switching

LAN is used to connect computers in the same building or in same area

WAN – two or more LAN linked together over a wide geographical area

OSI system allows different types of network to be linked together

OSI consist of 7 layers of interconnection

Session layer determines if the user can send or receive based on whether they can send and receive simultaneously or alternately

A bridge that interconnects LAN having identical protocols at the physical and data link layers

A router interconnects LAN having identical protocols at the physical data link and network layers

A gateway interconnects LAN that have totally different protocols and format

Parallel data – all bits in a character can be sent/received simultaneously

Serial data – the bits in a character which are sent/received one at a time

DTE – a system that performs parallel-to-serial and serial-to-parallel conversion of a data link

EIA stands for Electronic Industry Association

An acoustic modem converts a computer digital signal into audio tones

Echoplex mode of transmission achieves less than full-duplex but more than half-duplex

Line protocol – rules governing the transmission of digital information

Codes must be agreed upon in advance between sender and receiver

The standard ASCII has 132 characters including 32 control characters

The Baudot code requires shift characters to provide sufficient combinations

The corrections and accuracy of the transmitted message content is determined by the sender and the receiver

Framing is concerned with the boundaries between characters

Asynchronous transmission is less efficient but simpler

Digital transmission provides a higher level of signal quality than analog transmission because repeaters regenerate digital pulses and remove distortion

Digital to analog converter in synchronous modems send signals to the equalizer

Binary codes are transformed in modem into Gray code

Synchronous modems cost more than asynchronous modem because they must contain clock recovery circuits

The best type of data communications test equipment is a protocol analyzer

The data rate of the ISDN Basic access B channel is 64 kbps

The data rate of the ISDN Basic access D channel is 16 kbps

Baudot code uses 5 bits per symbol

3 bits are there to present 8 combinations

Intelligent terminal can be programmed to perform new functions

EBCDIC character code is used without parity bit

Modem is used when the host computer and the terminal are in separate locations

Front end processor is a data communications hardware that assists the host computer in handling input and output tasks

ASCII means terminals using asynchronous transmission in ASCII

Bit – a unit of information used in data communications

Transmission of binary signals requires more bandwidth than analog

The modulation rate of the CCITT V.26 modem is 1200 bauds

The digital-to-analog converter in a synchronous modem sends signal to the equalizer

Unknown – the number of bits that are zeros in each symbol when one is transmitting odd parity coded symbols

FSK – a digital modulation technique that results in two different frequencies representing binary 1 and 0

The input to the Digital-to-Analog Converter of a PCM decoder circuit is a series of bits

The output of the DAC at a PCM decoder circuit is a parallel output of binary-coded digits

Serial printer prints one character at a time

Delta modulation is a 1-bit differential PCM system

Delta modulation – alternative way of digitizing analog signals

One dit is equal to 3.32 bits

Information theory was developed by Shannon

A quadratic signaling has 4 possible states

Bit is the smallest unit of information in binary transmission system

Physical layer is the lowest layer in the ISO protocol hierarchy

64 kbps is the basic speed rate of digital system

Protocol – a formal set of conventions governing the formatting and relative timing of message exchange between two communications system

Null modem – a device that connects 2 data terminal equipment (DTE) directly by emulating the physical connections of a data communications equipment (DCE)

Impact printer strikes a ribbon against the paper to produce character image

Modem is referred to as data communications equipment

Common channel signaling – a signaling method relating to a multiplicity of circuits is conveyed over a single channel by labeled messages

Ring – a data highway in LAN, this type of topology allows workstations to be connected to a common line where all messages pass stations on the way to their destination

A packet format has an error detecting code at the end of packet framing

X.75 – it is a protocol used to connect the other packet switching network

Novel Netware is a network operating system within several buildings in compound

FSK – used by Bell 103/113 series for full duplex, 2 transmission speed of 0 to 300 bps

Channel capacity is directly proportional to bandwidth

Quantizing level does not affect noise in a channel

Bisync is a character oriented protocol

STX character signifies the start of the test for Bisync

In synchronous data the clock pulse is used to time the sending and receiving of the characters

All bits in a character are sent and received in one at a time in serial port

Bridge can only interconnect LANs having identical protocols at the physical and data link layers

OSI stands for Open System Interconnection

ISO stands for International Standardization Organization

Message switching is store and forward network

Packet switching is hold and forward network

Polling is an invitation by the primary to a secondary equipment to transmit a message

Bit rate is the rate of change at the input of the modulator

Morse code – a code that uses three unequal length symbols, dot, dash and space to encode a character

BAUDOT - A 5-bit character code

EBCDIC – an 8-bit character code

Modem – an equipment that interfaces the data terminal equipment to the analog transmission line

Protocol – set of rules governing the orderly exchange of data information

Public data network (PDN) – a communication network designed for transferring data from one point to another

Half-duplex – radio communications between points using a single share frequency

RS232C interface had 25 numbers of pins

A modem is sometimes referred to as Data Communication Equipment

Adaptive equalizers – provide post equalization to the received analog signal

The receive equalizer in a synchronous modem is called an adaptive equalizer

Compromise equalizer settings typically affect amplitude delay

Training sequence (a bit pattern used to synchronize the receive modem) accomplishes activate RLSD

When asynchronous data are used with synchronous modems this is called isochronous transmission

H factor is defined as a figure of merit used to express the degree of modulation achieved in an FSK modulator

Low-band channel in the 103 modem occupies a passband from 300 to 1650 Hz

Low speed modems generally have bit rates of 2400 bps

Medium speed modems have bit rates of 2400 – 4800 bps

High speed modems have bit rates of 9600 bps

Line conditioning – a means of improving the quality of a private-line circuit by adding amplifiers and equalizers to it

A voice-grade circuit using the PTN has an ideal passband from 0 to 4 kHz

The digital-to-analog converter in a synchronous modem is called an adaptive equalizer

The minimum-quality circuit available using the PTN is called basic voice channel (VC)

Direct distance dialing (DDD) network is commonly called dial-up network

The line control unit (LCU) operates on the data when it is in digital form and is therefore called data terminal equipment (DTE)

With asynchronous data, each character is framed between a start and a stop bit

With synchronous data, rather than frame each character independently with start and stop bits, a unique synchronizing character called a SYN character is transmitted at the beginning of each message

A logic 0 is used for the start bit

All stop bits are logic 1

Bit or clock synchronization ensures that the transmitter and receiver agree on a prescribed time slot for the occurrence of a bit

Characters that must be transmitted other than data are called overhead

In the United States, the most common CRC code is CRC – 16

Parallel transmission is also called parallel-by-bit and serial-by-character

Data means digital information

Go-ahead sequence 01111111

Flag field are used to achieve character synchronization in SDLC

DISC – a command that places a secondary station in the normal disconnect mode

Asynchronous – character oriented protocol

Network layer determines which network configuration is most appropriate

ISO 7809 – a standard that combines previous standards 6159 (E) (unbalanced) and 6256 (E) (balanced) and outlines the class of operation necessary to establish the link-level protocol

Ethernet is a baseband system using CSMA/CD operating at 10 Mbps

Manchester – a type of digital encoding technique used to detect collision in CSMA/CD

With CSMA/CD, a station monitors the line to determine if the line is busy

Channel accessing describes the mechanism used by a station to gain access to local area network

Broadband uses FDM

TDM – a typical multiplexing scheme used by baseband transmission

Baseband transmission uses the connecting medium as a single-channel device

Broadband transmission uses the connecting medium as a multi-channel device

The use of coaxial cables in interconnecting networks is limited to an overall length of approximately 1500 m

Topology or architecture identifies how the stations are interconnected in a network

Local Area Network – a data communications network that is designed to provide two-way communications between a large variety of data communications terminal equipment within a relatively small geographic area

2B1Q encoding – the type of encoding used in the transmission of data on an ISDN line between a customer’s premises and a carrier’s central office

Start/stop mode – a mode of transmission in public data network in which data are transferred from source to the network to the destination in an asynchronous data format

IEEE 802.3 standard is CSMA/CD

IEEE 802.4 standard is Token passing for bus topology

IEEE 802.5 standard is Token passing for ring topology

The data rate of the ISDN Basic access B channel is 64 kbps

The data rate of the ISDN basic access D channel is 16 kbps

2B + D equation defines the composition of an ISDN Basic access line

The number of channels on which different operations can occur simultaneously on one ISDN Basic access line is 3

Digital telephones and integrated voice-data workstations are examples of TE type of ISDN equipment

X.25 standard have 3 OSI layers covered

Physical layer – an Open System Interconnection (OSI) layer which has the responsibility for the physical transportation of the bits of data from one end of a point-to-point link to the other

Handshaking – a technique involving signaling by both ends of a link to ensure correct data transfer

XON/XOFF is a method of flow control

V.14 – a recommendation which allows a synchronous modem to be used to transmit asynchronous characters, without error control

The scrambler in a synchronous modem is found in the modular section

V.24 – A CCITT recommendation which gives the definition for the interchange circuits between DTE’s and DCE’s

Binary codes are sometimes transformed in modems into Gray code

A Western Electric 2911 modem operates with a carrier frequency of 1800 Hz

Flag – a special bit pattern used to denote the start and end of a data link layer frame

A bipolar violation occurs when two successive pulses have the same polarity and are separated by a zero level

Flow control – the process of starting and stopping the terminal output to avoid loss of characters by the receiving device

Buffering refers to temporarily storing data to allow for small variations in device speeds

The reason why many cables have RS-232 connectors with some wires crossed is because asynchronous modems reverse the direction of transmitted and received data from the standard

RS-232, RS-530, RS-449, V.21 and V.24 are examples of standards for interfaces between terminals and modems

Request To Send (RTS) / Clear To Send (CTS) is the way the DTE indicates that is ready to transmit data, or the way the DCE indicates that it is ready to accept data

Extended command sets supported by modern modems use different commands to control many advance modem features

A smart modem accepts commands from the terminal via the RS-232 interface

Communications protocols always have a set of symbols

The Baudot code uses 5 bits per symbol

ZMODEM protocol adjusts its block size based on the line error rate

DEREP-RB is not a common DNA repeater

Unknown is the number of bits that are zeros when transmitting odd-parity coded symbols

X.200 – standard for the 7-layer model for Open System Interconnection

Application-independent interfaces option is a characteristic of a LAN

Twin lead is not a common LAN medium

Cable TV system is not a local area network (LAN)

V-series – CCITT standard concentrating on data communications over the telephone network

Fiber optic transmission cannot be provided in a broadband LAN

PBX – a small telephone switching system that can be used as a LAN

Digital PBX – a LAN architecture that can be expanded to the greatest total system bandwidth

Bus is considered as the fastest LAN topology

Data communications refers to the transmission of computer data

Protocol is a procedure or rule that defines how data is to be transmitted

XMODEM is a popular PC protocol

ASCII is the most widely used data communications code

The ASCII code has 7 bits

Both analog and digital method are used in data communications

Telephone is not a primarily a type of data communications

Mark and space refer respectively to binary 1 and binary 0

A modem converts both analog signals to digital and digital signals to analog

I.120 – an I-series recommendation which describe what an ISDN is

Slow speed modems use FSK digital modulation method

When the data signal is transmitted directly over the medium, this is called baseband transmission

Broadband is the technique of using modulation and FDM to transmit multiple data channels of a common medium

Noise cause bit errors in data transmission

The other name for parity is VRC

QAM is the combination of ASK and QPSK

I-series – a CCITT standard that refers to various aspects of Integrated Service Digital Network (ISDN)

XNOR is not a part of a QAM modulator

Redundancy is not a commonly used method of error detection

Block check character (BCC) is produced by a longitudinal redundancy check (LRC)

Balanced modulators is the basic modulator / demodulator circuit in PSK

The main reason why serial transmission is preferred over parallel transmission is because it requires only a single channel

30 stations per segment – limitation of 10base-2 network

Optical fiber transmission media is not readily suitable to CSMA operation

Entropy refers to the measurement of an uncertainty

Logical is not an important characteristic of the physical layer

The bit rate of B-channel is 64 kbps

V.26bis – defines a 2400-bps, PSK, half-duplex modem operating at 1200 baud

V.100 – describe the interconnection techniques between PDNs and PSTNs

Complete List of Communications Engineering Review Notes

Important List of Communications Engineering Materials

Share your Notes in Digital and Data Communications System

If you have some important review notes on this topic kindly write the notes on the comment section below. This will absolutely beneficial to those aspiring to become professional engineers by taking the Board Exam and eventually to become successful in their chosen field. Thank you.

Labels:

Post a Comment

Contact Form

Name

Email *

Message *

Powered by Blogger.
Javascript DisablePlease Enable Javascript To See All Widget