data communications
DESCRIPTION
ECE LectureTRANSCRIPT
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The process of electrically communicating binaryinformation between two or more points.
Often referred to as computer communicationsdue to the ever increasing use of computer andtheir support equipment.
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Organizations Standards of Data CommunicationsInternational Standards Organization
(ISO)
Sets the rules and standards for graphics, and document exchange
Consultative Committee for International Telephony and Telegraphy (CCITT)
Consists of government authorities and representatives of UN to develop rules and standards for telephony and
telegraphy
American National Standards Institute (ANSI)
US representative to ISO
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Organizations Standards of Data Communications
Institute of Electrical and Electronics Engineers (IEEE)
Electronics Industries Association (EIA)
Standards Council of Canada (SCC)
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Advantages of Digital Signals over Analog Signals
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Disadvantages of Digital Signals
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DTE DCE DCE DTE
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Essential Data Communication System Components
1. DATA TERMINAL EQUIPMENT
device acting as a source and data sink or both
i. Source or Transmitter
ii. Receiver or Sink
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Essential Data Communication System Components
2. TRANSMISSION PATH / CHANNEL / MEDIUM
a. Bounded Medium
the signals are confined to the medium anddo not leave it except for small leakageamount
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Bounded Medium
i. Pair of Wire
-Made up of wire pairs stretchedbetween telephone sets
ii. Coaxial cable
-Used to transmit higherfrequency than pair of wire
iii. Submarine Cable
-Used to overcome long spacingbetween amplifiers and upperfrequency at which the cablescan be operated lower thanland cable SUBMARINE
CABLE
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Bounded Medium
iv. Waveguides
- Metal tubes that allow high frequency radio waves to travel
v. Fiber optic cables
- Waveguide for light frequencies
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Unbounded Medium
i. Ground or Surface Waves
ii. Space or TroposphericWaves
iii. Sky or IonosphericWaves
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Essential Data Communication System Components
3. DATA COMMUNICATIONS EQUIPMENT (DCE)
> devices that provide functions required to establish, maintain and terminate a data transmission connection.
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Information Capacity
Represents the number of independentsymbols that can be carried through thesystem in the given unit of time
It is expressed in bits per second, bps
A. Shannons Theorem on Information
B. Nyquist Theorem
C. Hartleys Law for Noiseless Channel
D. Shannon-Hartley Law for a Noisy Channel
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A. Shannons Theorem on Information
The Shannon theorem states that given a noisy channel with channel capacity Cand information transmitted at a rate R, then if there exist codes that allow the probability of error at the receiver to be made arbitrarily small, this means that, theoretically, it is possible to transmit information nearly without error at any rate below a limiting rate, C.
CLAUDE SHANNON
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A. Shannons Theorem on Information
Source coding is a mapping from (a sequence of) symbols from an information source to a sequence of alphabet symbols (usually bits) such that the source symbols can be exactly recovered from the binary bits (lossless source coding) or recovered within some distortion (lossy source coding). This is the concept behind data compression.
CLAUDE SHANNON
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B. Nyquist Theorem
The highest sampling frequency required topropagate a signal is twice its input frequency
fs = 2fin
HARRY NYQUIST
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C. Hartleys law for Noiseless Channel
Information capacity is a linear function of bandwidth andtransmission time and is directly proportional to both
Information capacity is proportional to the product of thebandwidth and transmission time
C = 2log2X
C = kfT
Where: C = channel capacity
X = number of coding levels
f = channel bandwidth
T = transmission time
RALPH HARTLEY
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Shannon-Hartley Law for a Noisy Channel
C = f log2(1 + S/N)
Where: S/N = signal-to-noise ratio
S/N = (2(C/ f) 1)
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Net Data Throughput (NDT)
Usually expressed in either characters persecond or bps.
Number of usable data characters or bits thatare received per second and does not countcharacters that have to be retransmitted due toerrors, characters used for control purposes andso on.
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Baud
Named after the French Data Communicationpioneer, Emile Baudot.
The number of signal events or signal elementspassing a point on the line per second.
> If each signal event or element, such aschange from 0 to 10 volts, represents one bit,the baud rate is equal to the bit rate.
> If each signal element can represent a dibit,the bit rate is equal to twice the baud rate.
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Example:
If 1600 signals events occur each second, but
through coding techniques, each signal
element represents 3 bits, what is the baud
rate? Bit rate?
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Data Network Topology
Concerns with the physical configuration of thedevices and the cable that it connects. It is thearchitecture or physical layout of the network.
DATANETWORKTOPOLOGY
BUSTOPOLOGY
STARTOPOLOGY
MESHTOPOLOGY
TREETOPOLOGY
RINGTOPOLOGY
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Data Network Topology
BUS TOPOLOGY
> Consists of nodes strung together in series with eachnode connected to a long cable or bus; many nodescan tap into the bus and begin communication withall other nodes on that cable segment.
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Data Network Topology
TREE TOPOLOGY (Bus variation)
> Uses some form of wideband cable with drop-offpoints as needed each drop is provided with the fullbandwidth or data rate of the cable.
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Data Network Topology
STAR TOPOLGY
> Features a centralcontroller to which allnodes are connected. Alltransmissions from onestation to another passthe central controllerwhich is responsible formanaging and controllingall communication. Thecentral controller acts asa switch.
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Data Network Topology
RING TOPOLOGY
Bucket or token passing.
Signals are transmitted in a rotating fashion.
Tokens give stations the right to transmit messages.
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Data Network Topology
MESH TOPOLOGY
> Signals pass through more than one path.
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Network Configuration
Categorized and identify the point or numberof location.
1. Point-to-point> each node in the network is connected to othernodes by individual communication lines
2. Multipoint> several nodes in the network will share acommunication link
> Sharing Device a device that enables sharinga single source (modem, MUX, or computer port)among several devices
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Network Configuration
POINT-TO-POINT MULTIPOINT
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Data Communication Equipment /Processing Hardware
Device that provide the function required toestablish, maintain, and terminate a datatransmission connection
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Data Communication Equipment / Processing Hardware
MODEM
A device used to convertserial digital data from atransmitting terminal to asignal suitable fortransmission over atelephone channel, or toreconvert the transmittedsignal to a serial digitaldata for acceptance atthe receiving terminal.
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Data Communication Equipment / Processing Hardware
Speed or bit rate (bps)
Transmission type sync or async
Mode of transmission simplex / half duplex /full duplex
Type of line circuit switched or leased line
Modem standard supported
MODEM PARAMETERS
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MULTIPLEXING TECHNIQUES
Refers to a technique of putting two or lowerspeed transmission onto a single communicationline of higher capacity.
MULTIPLEXINGTECHNIQUES
TIME DIVISIONMULTIPLEXING
FREQUENCY DIVISIONMULTIPLEXING
SYNCHRONOUS / STATICAL TDM
ASYNCHRONOUS /STATISTICAL TDM
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Multiplexing Techniques
FREQUENCY
DIVISION
MULTIPLEXING
Splits the availablebandwidth for a givencommunication link intoa number of channelsequal to the number ofdifferent devices beingmultiplexed.
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Multiplexing Techniques
TIME
DIVISION
MULTIPLEXING
Splits up the capacity ofthe line by assigningeach user a particulartime slot, during whichits data is transmittedover the communicationlink.
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Multiplexing Techniques
2 Types of TDMs1. SYNCHRONOUS / STATICAL TDM
> high speed data is divided into frames whereeach channel has a fixed number of timeslots. Thenumber of timeslots depends on the data speed ofthe terminal.
2. ASYNCHRONOUS / STATISTICAL TDM> instead of assigning a fixed number of timeslots
to each channel, the number of timeslots isdetermined by how much of the total amount ofdata to be transmitted each has. Instead oftransmitting empty timeslots, ATDM transmitschannel-number and data only from activeterminals.
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Open System Interconnect (OSI) Layer
The OSI model was created by the InternationalOrganization for Standardization (ISO). It waspatterned after and is similar to the IBM layerednetworking scheme, Systems NetworkArchitecture (SNA).
OSI Reference Model
Provides a common basis for the coordination ofstandards development for systemsinterconnection, while allowing existingstandards to be placed into perspective withinthe overall OSI Reference Model
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SEVEN OSI LAYERS
APPLICATION LAYER
PRESENTATION LAYER
SESSION LAYER
TRANSPORT LAYER
NETWORK LAYER
DATA LINK LAYER
PHYSICAL LAYER
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Seven OSI Layers
1. PHYSICAL LAYER
Responsible for the transmission of bit stream over a communication channel.
Transmits the unstructured raw bit stream over a physical medium and describes the electrical, mechanical and functional interface to the carrier.
Performs transmission and reception on the network medium.
Functional, electrical, physical specifications.
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Seven OSI Layers
2. DATA LINK LAYER
Provide error free transmission of information between two end stations attached to the same physical cable.
Manages the flow of the data bit stream in and out of each network node.
Transfers units of information to other end of physical link. Framing and synchronization.
Error control and recovery.
Message sequence control.
Message acknowledgement. Link initialization and disconnection.
Addressing
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Seven OSI Layers
3. NETWORK LAYER
Controls the operation of the network or sub-network.
Decides which physical pathway the data should take based on the network conditions, priorities of service and other factors.
Switches and routes information to any node .
Provides the means to establish, maintain and terminate connections between systems
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Seven OSI Layers
4. TRANSPORT LAYER
Forms the interface between the higher application-oriented layers and the underlying network-dependent protocol layers.
Provides end-to-end data integrity and quality of service.
Allows end users to communicate oblivious to network constraints imposed by the lower levels
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Seven OSI Layers
5. SESSION LAYER
Provides the means for two application layer entities to synchronize and manage their data exchange.
Coordinates interaction between end-to-end application processes.
Sets up communication channels, manages the communication and terminates the connections.
Is the users true interface to the network.
Handles the log-on / log-off functions and describes the authentication procedures
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Seven OSI Layers
6. PRESENTATION LAYER
Formats the data to be presented to the Application Layer.
Can be viewed as a translator for the network and provides a common representation for data that can be used between the application processes.
Provides code conversion and data reformatting.
Handles display functions, file formatting, code conversion, and data compression and encryption.
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Seven OSI Layers
7. APPLICATION LAYER
Serves as a window for the application process to access the networking environment.
Represents the services that directly support users and application tasks.
Selects appropriate service for applications (user interface).
Contains recommendations for the specific user programs.
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Network Protocols
Are standards that allow computers to communicate
Define how computers should identify one another on a network
Sets of rules that specify precisely how different parts of the network interact to allow devices to communicate with one
another
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A typical protocol defines the following:
How computers should identify one another on a network
The form that the data should take in transit
How the information should be processed once it reaches its final
destination
Procedures for handling lost or damaged transmission or packets
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HANDSHAKING Exchange of predetermined signals between two devices
establishing a connection; usually a part of communicationprotocols.
POLLING Permanent Master-Slave relationship The master controls the data flow by polling and selecting the
slaves All data are transmitted between the master and slaves selected
one at a time
CONTENTION Neither end of the data link has permanent control over the link To transmit data, a station must contend for the master status Station at the other end of the data link will then become a slave Data are transmitted from Master to Slave The master controls flow of data along the link
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PROTOCOL FUNCTIONS
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PROTOCOL FUNCTIONS
i. Link Control
Specifies the rules for data transfer between two stations
a. Link Initialization data link and stations at both ends are in idle state when there is no data exchange
b. Link Termination
c. Link Recovery
d. Relationship of stations
e. Mode of operation
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PROTOCOL FUNCTIONS
ii. Synchronization
Data are sent in blocks or frames. The beginning and end of each block must be clearly identifiable
For character oriented protocol
- character synchronization
- message synchronization
For bit oriented protocol
- frame synchronization
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PROTOCOL FUNCTIONS
iii. Flow Control To ensure that the transmitter does not
overwhelm the receiver
a. Stop and Wait Scheme Half duplex operation
b. Sliding Window Scheme Full duplex operation
iv. Error Controlv. Addressing
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NETWORK BREADTH
A. Local Area Network (LAN)
Collection of independent computers whichcan communicate with one another over ashared medium, usually confined to a smallgeographical area, such as a single building ora college campus.
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NETWORK BREADTH
B. Metropolitan Area Network (MAN)
Are developed primarily by data carriers inresponse to the demand to interconnect LANsacross metropolitan area.
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NETWORK BREADTH
C. Wide Area Network (WAN)
Essentially interconnected LANs and MANs,they can be homogenous (like networks) butare often heterogonous (different topologies).It can span campuses, cities, or continents.
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Local Area Network (LAN)
Are a special, high speed, dedicated networkthat provides data communications capabilitywithin an office or group of offices in a campusenvironment.
Provide a simple and cost effective means ofinterconnecting data equipment on a single site,permitting each user to communicate with anyother end to share central resources such asprinters and data stores.
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Local Area Network (LAN)
Applications:
1. Sharing resources
2. Quick communication
3. Sharing work documents
4. Sharing applications
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IEEE LAN Standard 802.3 Defines rules for configuring an Ethernet as well
as specifying how elements in a network interactwith one another.
IEEE Standard 8 0 2.3Februaryyear 1980
> Ethernet was chosen in honor of the undefinedsubstance called ether through which it was oncethought electromagnetic radiation propagated.
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Types of Ethernet Media
1. Thick Wire or 10Base5
Generally used to create large backbones
A thick, hefty, coaxial cable which can support asmany as 100 nodes in a bus topology and a segmentcan be up to 500 meters long
0.4 inch, RG11
Ethernet segment < 500 m. each
Transceivers attach workstations to the cable
Distance between transceivers > 2.5 m.
1,024 stations per network
Often called Thick Net
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10BASE5
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Types of Ethernet Media
2. Thin Coax or 10Base2 Is considerably thinner and more flexible than Thick
Wire, but it can support 30 nodes, each at least 0.5m apart. Each segment must not be longer than 185meters
A thin coax segment is actually composed of manylengths of cables, each with a BNC type connectoron both ends
0.2 inch RG58 ohm cable
Thin Ethernet segment < 185 m. each
Distance between T-connectors > 0.5 m
30 stations maximum per segment
10 Mbps data transmission
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10BASE2
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Types of Ethernet Media
3. Unshielded Twisted Pair or 10BaseT
Uses a star topology
A computer is located at one end of the segment and the other end is terminated in a central location with a repeater or hub
UTP segments are limited to 100 meters
Each node is connected to a central point called Hub
Problem node can be easily isolated
Easy to add user or segment
Maximum distance to network hub < 100m
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10BASE-T
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Types of Ethernet Media
4. Fiber Optic or 10BaseFL
Invaluable for situations where electronic emissionsand environmental hazards are concern
Effectively insulate networking equipment since theydo not conduct electricity
Allows segments up to 2 km long
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10BASE-FL
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bridge
repeater
hub
router
LAN Terms
node
transceiver
gateway
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LAN Terms
1. NODE An active device connected to the network, such as
a computer or a piece of networking equipment likea repeater, a bridge or a router
2. REPEATER Is relatively simple LAN devices which allow longer
transmission distances along a given LAN mediumand operate at the physical layer only
Takes an incoming signal and regenerate it, boostingits amplitude back to its original strength andeliminating distortions
Used not to interconnect dissimilar networks but toconnect individual network segments to form alarger extended network
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LAN Terms
3. BRIDGES
Connect separate Ethernets together
Are used to interconnect physically distinct networks
4. TRANSCEIVER
Is used to connect nodes to the various Ethernetmedia
Also known as Media Attachment Units (MAUs),attach to the Ethernet cable and provide anApplication User Interface (AUI), connector for thecomputer
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LAN Terms
5. HUB
Is a central connection point for cables radiating outto multiple stations
Also called Multiport repeaters or concentrator
6. ROUTER
Its primary purpose is to find the best path from onenetwork to another and forward packets betweenthem
7. GATEWAY
A LAN device which is used to interconnect networksthat may have entirely different architectures
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LAN Protocols
1. TCP / IP
Used by UNIX systems
Used by the Internet
TCP (Transmission Control Protocol)
Guaranteed delivery, handles retransmission, connection oriented
IP (Internet Protocol)
Takes care of routing, non-guaranteed delivery, connectionless UNIX a multitasking, multi-user computer operating system
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LAN Protocols
2. DECNetTM Digital Equipment Corporation proprietary network
architecture
Runs on point-to-point, X.25, and Ethernet networks
3. Apple Talk A communication protocol developed by Apple
Computer to allow networking between Macintoshes
4. LAT (Local Area Transport) A DEC proprietary network communication protocol
based on the idea of a relatively small, knownnumber of hosts on a local area network sendingsmall network packets at regular intervals
Will not work on a WAN scale, as TCP / IP does
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LAN Architectures
1. PEER-TO-PEER LAN
No single station is intended to control all LAN operations or resources.
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LAN Architectures
2. CLIENT SERVER LAN
One computer will have control of the network,running the network operating system software.
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LAN Hardware
1. NETWORK ADAPTER BOARD
Provides the physical and electronic connection between the computer and the network
Provides the interface to the I/O bus and to the LAN cable
2. CABLING
3. SERVERS
4. REPEATERS
5. HUBS AND CONCENTRATORS
NETWORK ADAPTER BOARD
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Servers
FILE SERVER A network computer with a
large hard disk drive wherefiles or applications are savedfrom the entire LAN
DATA BASE SERVER Could be physically
implemented in the sameway as a file server, but witha specific responsibility ofserving a data baseapplication and data basefiles to the LAN
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Servers
COMMUNICATION SERVER A networked PC or other
computer connected to one ormore communication devicessuch as modem, multiplexer orother transmission equipment
PRINT SERVER A networked PC connected to
a printer
Should be centrally locatedwhere it can be easily sharedby a workgroup
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BASEBAND TRANSMISSION A transmitting station uses the entire capacity or
bandwidth of transmission medium Each device gets its own turn to transmit Its advantage are lower components cost and
simplicity of installation and maintenance
BROADBAND TRANSMISSION Provides relatively higher capacity transmission
technique in which one cable can simultaneouslycarry signals from several devices
Have the benefit of being able to support manystations over a long distance and to carry voice,video, and data simultaneously but they areexpensive in very difficult to set up and test
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Baseband Transmission
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Broadband Transmission
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Available Networks
1. ETHERNET
Strikes a good balance between speed, price and ease of installation
Wide acceptance into the computer marketplace
Ability to support virtually all popular network protocols
2. TOKEN RING
3. FDDI (FIBER DATA DISTRIBUTED INTERFACE)
4. CDDI (COPPER DATA DISTRIBUTED INTERFACE)
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FDDI
ETHERNET
TOKEN RING
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LAN Components
1. COMPUTERS
2. FILE SERVER
A computer that centrally stores the data to beshared
It is where shared equipment (hard disk, printers,modems) are connected
3. NETWORK OPERATING SYSTEM
The software that runs on the file server andprovides the functions for data and equipmentsharing
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LAN Components
4. NETWORK INTERFACE CARDS
Devices installed in a computer that provide the physical connection to the LAN through the cabling
5. CABLES / TRANSMISSION MEDIA
6. EXTENSION DEVICES
Devices like repeaters and bridges that extend the range of the LAN
7. APPLICATION SOFTWARE
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INTERNET A global computer network
that connects thousands ofnetworks together allowingthem to exchange files, sentmessages, download graphicsand text, and share otherresources.
ARPANET Advanced Research Projects
Agency Network Computer network which broke
information into small chunksknown as packets
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Internet Terms
WORLD WIDE WEB A menu based search tool that
enables users to access the Internetresources world wide while usinglinks embedded documents
This linked documents allow usersto move easily from place to placewithin the Internet in a nonlinearfashion
CYBERSPACE A term coined by William Gibson in
his fantasy novel, Neuromancer todescribe the world of computersand the society that gathers aroundthem
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Internet TermsGOPHER
A menu based program used toexplore and access the Internetresources
NETSCAPE NAVIGATOR Essentially a tool or program
that makes Internet surfing alot easier
Capable of showing graphicsand movies, producing audio ormusic and best of all, you candownload it all for free, if theauthor of the webpage permitsyou to do so
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Internet Terms
TELNET
A program that allowsInternet nodes to log-inand access program andother data on anotherInternet node
Enables you to connectoutside your server, forexample, outside thecountry
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MINIMUM SYSTEM REQUIREMENTS
386 or better CPUs
At least 40 MB free hard disk space
At least 8 MB RAM
Video Graphics Adapter monitor
Modem
Windows 3.1 or higher
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Electronic Mail (E-Mail)
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Electronic Mail (E-Mail) Send messages back and forth between
computers that are electronically connectedProcedure1. User types a message onto the computer while
signed on the Internet or an online service.Message may include:a. Textb. Graphicsc. Filesd. Multimedia
2. User then tells the system where to send themessage.
3. The message is sent over the Internet until itreaches its final destination.
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Functions of E-mail1. Creation
2. Sending
3. Reception
4. Storage
E-mail Address Basic Structure
1. Username
2. Organizations name
3. Domain
4. Suffix
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E-mail Address Basic Structure
Format: Username@organization.[domain].suffix
Domain could be:
com commercial
edu educational
net network
org organization
mil military
gov government
ngo non-governmental organization
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Public Data Network
A switched data communication network similarto the PSTN except that a PDN is designed fortransferring data only.
Combines VANs and packet switching network.
VAN Value Added Network
Adds value to the services or facilities providedby a common carrier to provide new types ofcommunications services
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PACKET SWITCHING
Involves dividing data messages into small bundles ofinformation and transmitting them thru communicationsnetwork to their intended destination.
Is a switching technique wherein the message is dividedinto blocks called packets preceded and followed bycontrol characters which allow the network to decide onthe final destination. Switching is done on a packet-by-packet basis.
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CIRCUIT SWITCHING (TRANSPARENT SWITCH)
Used for making a standard telephone call on the PSTN.
A switching technique wherein a direct connection has to be set up through the network as in a telephone exchange but in a higher speed to avoid long delays. Switching is done on a call-by-call basis.
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MESSAGE SWITCHING (TRANSACTIONAL SWITCH)
A form with store and forward network
Data are transmitted into the network and stored in a switch
The network transfer the data from switch to switch when it is convenient to do so
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X.25
Defines the structures contents and sequencingprocedures for the transmission of data amongDTE, DCE and a public data network.
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X.25 Packet Format
1. Call request packet
2. Data transfer packet
3. Call clearing
Note: An X.25 packet contains 5 bytes of header and 128 bytes of user data.
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X.25 Operation1. Data is taken from the source device and is stored for processing and to make
retransmission possible.
2. Packet envelope is then placed around the data. This envelope contains the addressof the destination and information for error detection.
3. Based on the packet envelope information, the network makes a determination asto where the data should now be sent.
4. A frame envelope is placed around the packet envelope which is responsible forensuring data integrity across a single physical line.
5. The data is then sent, via the physical layer, over the appropriate copper or fiber orsatellite facility to the next node in the network
6. In the next node, the data is once again stored.
7. It is examined for errors. If error is found, the faulty data can be retransmittedfrom the previous node, where it was stored before transmission.
8. If no error is found, the network strip off the frame envelope and look at the packetwithin the frame to determine the destination of this data.
9. If necessary, it will then route it to yet another node. This process will continueuntil the ultimate destination node is reached.
10. When the final node is reached, all envelopes are examined, and then removed,and the data is delivered to the endpoint device.
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X.25 Layers
1. Link layer (frame level)
2. Network layer (packet level)
3. Physical layer
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PAD Packet Assembler / DisassemblerAssembles and disassembles data packets for X.25 network communications
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VIRTUAL CIRCUIT
Permit communications between distinct networkelements through any number of intermediate nodewithout the dedication of portion of the physical circuits.
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Permanent Virtual Circuit (PVC)
Logically equivalent to a 2-point dedicated private line circuit except that it is slower
Switched Virtual Circuit
Logically equivalent to making a telephone call thru the DDD network except that no end-to-end connector is made
A one to many arrangement
A virtual circuit set up on a call-by-call basis
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FRAME RELAY
A wide area networktechnology that usesfast packet switchingtechnique to meet thedemands of high speedbursty traffic.
A technique used indata transport networkwhere error checking isperformed end-to-endinstead of on eachindividual link.
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Frame Relay Network
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Frame Relay Operation1. In frame relay technology, an intelligent endpoint, such as LAN, will
send its data to the link layer.2. No more storing of data before sending to another node. When each
node receives the beginning of a frame, it may immediately transmitthat frame to the next node without waiting for the whole frame to bereceived and stored, therefore, a much faster transmission andswitching.
3. An envelope (specifically, LAPD frame) is added. Alternatively, theintelligent endpoint may send the data to the network alreadyencapsulated in the LAPD frame.
4. The LAPD frame contains routing information, eliminating the need forthe network to examine level three. Instead, the frame itself isexamined for a destination and the routing takes place at thenetworks frame layer.
5. No error correction in the frame relay nodes because frame relay relieson low bit error rate lines to minimize errors, and on intelligentendpoints running an end-to-end protocol across the network torecover from the few errors that do occur.
6. After reaching its destination node, the envelope is removed and thedata is delivered to the endpoint.
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TWO TYPES OF CONGESTION IN FRAME RELAY
1. Receiver Congestion
2. Line Congestion
FECN - Forward Explicit Congestion Notification
BECN - Backward Explicit Congestion Notification
Error Control in Frame Relay
Cyclic Redundancy Check (CRC) error detection
Automatic Repeat Request (ARQ) error correction
DE Discard Eligibility
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Definition of Terms
1. CIR Committed Information Rate
The average rate (in bps) at which the network guarantees to transfer information units over a measurement interval.
2. Bc Committed Burst Size
The maximum number of information units that can be transmitted during the time interval.
3. Be
The maximum number of uncommitted information units that the network will attempt to carry during the time interval
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Frame Relay Equipment
1. Bridge
2. Router
3. Host
4. Frame Relay Access Device
Frame Sizes(variable lengths)
Maximum number of bytes
Per frame
Ethernet 1500 bytes
Token frame 4.096 Mbps
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ASYNCHRONOUS TRANSFER MODE (ATM)
A cell-based, connection oriented, switching andmultiplexing technology that allows voice, videoand data to be sent along the same network.
A high speed, connection oriented switching andmultiplexing technology that uses 53 byte cells(5-byte header, 48-byte payload) to transmitdifferent types of traffic simultaneously, includingvoice, video and data. It is asynchronous in thatinformation streams can be sent independentlywithout a common clock.
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ASYNCHRONOUS TRANSFER MODE (ATM)
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ATM Components
1. Routers and switches to connect carrier on aglobal basis
2. Backbone devices to connect all the LANswithin a large organization
3. Switches and adapters which link desktopcomputers to high speed ATM connection forrunning multimedia applications
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ATM Media
1. Coaxial cables
2. Twisted pair cables
3. Fiber optic cables
Constant bit rate: voice and video
Variable bit rate: data
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ATM LAYERS
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ATM LAYERS
1. Physical Layer
Responsible for the electrical or optical transmission and reception along the physical media between two devices.
2. ATM Layer (Network Layer)
Deals with moving cells from source to destination
Involves routing algorithms and protocols within the ATM switches
3. ATM Adaptation Layer
Adapts user traffic to a cell format
4. ATM Services and Application Layer
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ATM INTERFACES
1. User to Network Interface (UNI)
Boundary between a host and an ATM network
2. Network to Network Interface (NNI)
A line between two ATM switches
3. Data Exchange Interface (DXI)
4. Intercarrier Interface (ICI)
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ATM INTERFACES
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ATM APPLICATIONS
1. Home working2. Home shopping3. Video on demand4. Interactive multimedia games5. Distance learning
ATM Speeds: 2.4 GbpsFR Speeds: 1.024 Gbps
Bit Error Rate:ATM: 10-12
X.25: 10-6
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ISDN (INTEGRATED SERVICES DIGITAL NETWORK)
A digital telecommunications technology thatcan simultaneously transmit voice and data overthe same pair of telephone wires.
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ISDN Channels1. B-channel (Bearer Channel)
Used to carry the digital information Building block of the ISDN 64 kbps
2. D-channel Used to carry signaling and supervisory information to the
network Kbps (BRI) or 64 kbps (PRI)
3. H channel Provided for user information at higher bit rates Combination of several B channels
a. H0 - 384 kbps (6 B channels)b. H11 - 1.536 Mbps (24 B channels)c. H12 - 1.92 Mbps (30 B channels)d. H21 - 32 Mbps (512 B channels)e. H22 - 44 Mbps (690 B channels)f. H4 - 135 Mbps (2112 B channels)
-
TYPES OF ISDN ACCESS INTERFACES
1. Basic Rate Interface (BRI) 2B + D
For individual users
2. Primary rate Interface (PRI) For business with large data needs
American 23B + D (T1 = 1.544 Mbps)
European 30B + D (E1 = 2.048 Mbps)
3. Broadband ISDN 150 Mbps
For future HDTV projects
H channels
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CUSTOMER PREMISES EQUIPMENT
NTE (Network Termination Equipment)
Draws the demarcation line between theISDN network and your equipment
Device responsible for converting the 2-wireline from your local exchange into a 4-wireline configuration to couple with the ISDNequipment
-
CUSTOMER PREMISES EQUIPMENT
TA (Terminal Adapter)
Allows a non-ISDN equipment to beconnected to the ISDN line
Analog signal are digitized and put into ISDNformat before entering the network
-
ISDN APPLICATIONS
1. Digital telephony
2. Video communications
3. Leased line overflow or Back-up
4. LAN and WAN
5. Internet access
-
36. Redundancy means the ________
a. Transmission rate of the system
b. Symbols are to be repeated
c. Time between failures
d. Time between successes
-
37. The digital information is contained in
both the amplitude and phase of the
modulated carrier.
a. PSK
b. FSK
c. QAM
d. ASK
-
38.The input signal is a binary data signaland a limited number of output phasesare possible.
a. PSK
b. FSK
c. QAM
d. ASK
-
39.A radio channel is composed of _____ VBchannels.
a. 1800
b. 900
c. 10800
d. 8064
-
40.What equation defines the compositionof an ISDN basic access line?
a. 2B + D
b. B + D
c. B + 2D
d. 2B + 2D
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41.A digital network where voice,, video,text and data are multiplied into as inglenetwork for processing and aretransmitted prior to use.
a. Frame delay
b. Asynchronous transfer mode (ATM)
c. ISDN
d. Synchronous digital hierarchy (SDH)
-
42.Non-ISDN equivalent can be connectedto ISDN line by the use of _________.
a. Terminal equipment
b. Terminal adapter
c. Modem
d. Network adaptor
-
43.A special voice encoder / decoder used indigitizing speech signal only is
a. PCM
b. PWM
c. Vocoder
d. PFM
-
44.Equation used to determine the numberof Hamming bits in the Hamming code.
a. 2n
= m + n + 1
b. 2n m + n + 1
c. 2n m + n + 1
d. 2n
< m + n + 1
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45.What determine which networkconfiguration is most appropriate?
a. Application layer
b. Presentation layer
c. Network layer
d. Data link layer
-
46.Ethernet is a baseband system usingCSMA/CD operating at _________.
a. 10 Mbps
b. 20 Mbps
c. 30 Mbps
d. 40 Mbps
-
47.Used of coaxial cables in interconnectingnetworks is limited to an overall length of_______.
a. 1500 ft
b. 1500 m
c. 1500 km
d. 1500 kft
-
48.What identifies how the stations areinterconnected in a network?
a. Topology
b. Architecture
c. Topology or architecture
d. Topology and architecture
-
49.________ is a data communicationsnetwork designed to provide two-waycommunications between a large varieties ofdata communication terminal equipmentwithin a relatively small geographic area.
a. Private area network
b. Local area network
c. Wide area network
d. Ethernet
-
50._______ is the mode of transmission inpublic data network in which data aretransferred from source to the networkthen to the destination in an asynchronousdata format.a. Synchronous mode
b. Start / stop mode
c. Packet mode
d. Circuit mode
-
51.A seven digit character can represent oneof ________ possibilities.
a. 7
b. 14
c. 64
d. 128
-
52._______ is defined to be the maximumrate at which information can betransmitted through a channel.
a. Bit rate
b. Baud rate
c. Coding
d. Channel capacity
-
53.Who developed the fixed-length binarycode for telegraphy?
a. Samuel Morse
b. Emile Baudot
c. Alexander Graham Bell
d. Guglielmo Marconi
-
54.Inventor of pulse code modulation forthe digital encoding of speech signals.
a. R. V. L. Hartley
b. J. R. Carson
c. H. Nyquist
d. Alex Reeves
-
55.Serial binary data interchange betweenDTE and DCE at rates up to 20 kbps. RS232 is its EIA equivalent.
a. V.26
b. V.24
c. V.42
d. V.32
-
56.RS 232 is normally an interface betweenDTE and DCE. What is its signal rate?
a. 20 kbps
b. 30 kbps
c. 40 kbps
d. 50 kbps
-
57.What is multiplexing?a. The process of increasing bandwidth on a channel
b. A technique that enables more than one data source to share the use of a common line
c. Mailing letter at the post office
d. The ability to share frequency by time
-
58.In ______ modulation the carrier is aperiodic rain pulses.
a. Amplitude
b. Analog
c. Digital
d. Pulse
-
59.Which of the following pulse modulationtechniques is a digital transmissionsystem?
a. Pulse duration modulation
b. Pulse position modulation
c. Pulse width modulation
d. Pulse code modulation
-
60.A process where the higher amplitudeanalog signals are compressed prior totransmission then expanded at thereceiver.
a. Compressing
b. Expanding
c. Encoding
d. Companding
-
61._______ uses a single bit PCM code toachieve a digital transmission of analogsignal.
a. Quadrature amplitude modulation
b. Frequency shift keying
c. Delta modulation
d. Phase modulation
-
62.The line speed of Bell system T1 carrier system is
a. 64 kbps
b. 3.152 Mbps
c. 1.544 Mbps
d. 6.312 Mbps
-
63.How many channels does a super grouphave?
a. 60
b. 600
c. 1800
d. 10800
-
64.The output frequency at the channel combiner of channel 7 is
a. 76 80 kHz
b. 80 84 kHz
c. 84 88 kHz
d. 88 92 kHz
-
65.______ was the first fixed-length 5-bitcharacter code.
a. EBCDIC
b. ASCII
c. Morse code
d. Baudot code
-
66.Amplitude shift keying is also known as________.
a. Up / down keying
b. On / off keying
c. Front / back keying
d. I / O keying
-
67.PCM system require ________.
a. Analog signal
b. Large bandwidth
c. Digital signals
d. Fiber optics cable
-
68.Which theorem sets the limit on themaximum capacity of a channel with agiven noise level?
a. Nyquist theorem
b. Hartley theorem
c. Shannon-Hartley theorem
d. Shannon theorem
-
69._______ is the difference between theoriginal and reconstructed signal.
a. Quantizing noise
b. Fade margin
c. Noise margin
d. Noise figure
-
70.What are the steps to follow to produce a PCM signal?
a. Sampling, coding and quantizing
b. Sampling, quantizing and coding
c. Quantizing, sampling and coding
d. Coding, quantizing and sampling
-
71.______ identifies how the differentstations in a multipoint system areinterconnected.
a. Network topology
b. Star network
c. Ring topology
d. Bus network
-
72.A transmission where data are inputteddirectly on the cable.
a. Broadband
b. Baseband
c. Digital
d. Analog
-
73.Synchronous modems cost more thanasynchronous modems because
a. They are larger
b. They must contain clock recovery circuits
c. The production volume is larger
d. They must operate on a larger bandwidth
-
74.When one station is designated asmaster and the rest of the stations areconsidered slaves, message handling is______.
a. Store and forward
b. Polling
c. CSMA / CD
d. Token passing
-
75.A store and forward switching.
a. Circuit switching
b. Packet switching
c. Message switching
d. PSTN
-
76.A timing signal generated by anoscillating circuit that is used tosynchronize data transmission.
a. Clock
b. Star bit
c. Quantizing
d. BCC
-
77.Which system allows different types ofnetworks to be linked together?
a. OSI
b. CCITT
c. Bell system
d. AT&T
-
78.A ______ that interconnects LAN havingidentical protocols at the physical anddata link layers.
a. Bridge
b. Router
c. Gateway
d. Hub
-
79.A _____ that interconnects LAN that hastotally different protocols and format.
a. Bridge
b. Router
c. Gateway
d. Hub
-
80.All bits in a character can be sent /received simultaneously.
a. Serial data
b. Parallel data
c. Full duplex
d. Half duplex
-
81.A system that perform parallel-to-seriesconversion of a data link.
a. DTE
b. DCE
c. Modem
d. FEP
-
82.Which mode of transmission achieves less than full duplex but more than half duplex?
a. Full/full duplex
b. Echoplex
c. Isochronous
d. Synchronous
-
83.Rules governing the transmission ofdigital information.
a. Data communications standard
b. Line protocol
c. Isochronous
d. Digital communications
-
84.Codes must be
a. Eight bits per character
b. Either seven or eight bits per character
c. Agreed upon in advance between sender and receiver
d. The same in all modem computers
-
85.Clear to send is a signal passed from thelocal modem to the local terminal whendata port is ready to transmit data. Itusually occurs in response to
a. Data set ready
b. Request to send
c. Data terminal ready
d. Data carrier detect
-
86.Digital to analog converter insynchronous modems send signals to the
a. Modulator
b. Transmission lines
c. Terminal
d. Equalizer
-
87.What is the data rate of the ISDN Basicaccess B channel?
a. 32 kbps
b. 64 kbps
c. 144 kbps
d. 192 kbps
-
88.How many bits are there to present 8combinations?
a. 3
b. 4
c. 2
d. 5
-
89.How many number of equiprobableevents are there for 8-bits of information?
a. 256
b. 132
c. 2400
d. 512
-
90.Which character code is used withoutparity bit?
a. CCITT number 2
b. ASCII
c. CCITT number 5
d. EBCDIC
-
91.The percentage of bit errors relative to aspecific number of bits received; usuallyexpressed as a number referenced to apower of ten.
a. Bit error rate
b. Transmission rate
c. Distortion
d. Parity check
-
92.The process of one type of deviceimitating another via a hardware /software package.
a. Conversion
b. Emulation
c. Imitation
d. Simultation
-
93.A digital modulation technique thatresults in two different frequenciesrepresenting binary 1 and 0.
a. FSK
b. QPSK
c. ASK
d. DPSK
-
94.One dit is equal to ____ bits.
a. 3
b. 3.5
c. 3.32
d. 4
-
95.A quadratic signaling has ______possible states.
a. 16
b. 4
c. 8
d. 32
-
96.What is the smallest unit of informationin binary transmission system?
a. Byte
b. Digit
c. Bit
d. Nibble
-
97.The lowest layer in the ISO protocolhierarchy.
a. Network layer
b. Physical layer
c. Transport layer
d. Data link layer
-
98.Modem is referred to as
a. Universal asynchronous receiver transmitter
b. Universal synchronous receiver transmitter
c. Data terminal equipment
d. Data communication equipment
-
99.A signaling method relating to amultiplicity of circuits is conveyed over asingle channel by labeled messages.
a. Code signaling
b. Synchronous
c. Common channel signaling
d. Asynchronous
-
100._______ is a network operating systemwithin several buildings in compound.
a. Internet
b. Novell netware
c. 10Base-T
d. Intranet
-
101.What is the Nyquist sample rate for avoice input of 10 kHz?
a. 10 kHz
b. 20 kHz
c. 30 kHz
d. 40 kHz
-
102.What is the minimum number of bitsrequired in PCM code for a range of10,000?
a. 12
b. 9
c. 14
d. 8
-
103. How many levels can be represented inPCM transmission system if the binarynumbers 00000000 to 11111111 are usedto represent signal levels?
a. 256
b. 64
c. 128
d. 512
-
104.A symbol to represent a datacommunications facility within the widearea network.
a. Hub
b. Cloud
c. Server
d. Gateway
-
105.All bits in a character are sent andreceived _______ in serial port.
a. One at a time
b. Simultaneously
c. In group of 2 bits
d. In group of 3 bits
-
106.Message switching is ______ network.
a. Hold and forward
b. Forward
c. Hold
d. Store and forward
-
107.Packet switching is ______ network.
a. Hold and forward
b. Forward
c. Hold
d. Store and forward
-
108.Polling is an invitation by the primary tosecondary equipment to _______ amessage.
a. Store
b. Receive
c. Transmit
d. Read
-
109.An 8-bit character code.
a. EBDCDIC
b. BAUDOT
c. ASCII
d. HOLLERITH
-
110. Equipment that interfaces the dataterminal equipment to the analogtransmission line.
a. Modem
b. Muldem
c. Multiplexer
d. Codec
-
111.A communication network design fortransferring data from one point toanother.
a. Public Telephone Network
b. Public Data Network
c. Value Added Network
d. Packet Switching Network
-
112.A conceptual network in which alltransmission lines handle digital ordigitized data.
a. LAN
b. WAN
c. ISDN
d. PSTN
-
113.A data communications component thatprovides control or supporting servicesfor other computers , terminals ordevices in a network.
a. Host
b. Communication controller
c. Cluster controller
d. Interface equipment
-
114.Which data network configuration letcomputers share their resources?
a. Peer to peer
b. Hierarchical
c. PVC
d. LAN
-
115.A means of improving the quality of aprivate-line circuit by adding amplifiersand equalizer to it.
a. Line equalizer
b. Line amplifying
c. Line conditioning
d. Line encoding
-
116.Direct distance dialing (DDD) network iscommonly called
a. Private-line network
b. PT network
c. Dial-up network
d. Trunk network
-
117.A type of server that allows multipleusers to take advantage of a singleprinting device.
a. Print
b. Client
c. Network
d. File
-
118.______ ensures that the transmitterand the receiver agree on a prescribedtime slot for the occurrence of a bit.
a. Bit or clock synchronization
b. Modem or carrier synchronization
c. Character synchronization
d. Message synchronization
-
119.Characters that must be transmittedother than the data are called
a. Parity
b. Error
c. Overhead
d. Hamming bits
-
120.The generating power polynomial x7
+x
5+ x
4+ x
2+ x
1+ x is equivalent
a. 101101110
b. 101101111
c. 010010001
d. 10110111
-
121.A central device into which each nodeof a star network is directly connected
a. Hub
b. Central pointer
c. Router
d. Repeater
-
122.To _____ is to send a file to a remotecomputer.
a. Upload
b. Download
c. Call
d. Transmit
-
123.A microcomputer attached to a networkrequires a
a. NIC
b. RS 232
c. Software
d. Protocol
-
124.Digital telephones and integrated voice-data workstations are examples of whattype of ISDN equipment?
a. TE
b. TA
c. NT2
d. TP
-
125.How many OSI layers are coveredunder the X.25 standard?
a. 3
b. 4
c. 7
d. 2
-
126.With ______, a station monitors the lineto determine if the line is busy.
a. CSMA/CD
b. CSMA/CA
c. Token passing
d. PDDI
-
127.CCITT standard concentrating on datacommunications over the telephonenetwork.
a. V series
b. X series
c. I series
d. T series
-
128.Broadband uses
a. TDM
b. Space multiplexing
c. FDM
d. Statistical multiplexing
-
129.______ uses the connecting medium asa single-channel device.
a. Broadband transmission
b. Digital transmission
c. Base band transmission
d. Analog transmission
-
130.Which is considered as the fastest LANtopology?
a. Ring
b. Bus
c. Star
d. Tree
-
131.What is the most widely used datacommunications code?
a. Gray
b. EBCDIC
c. Baudot
d. ASCII
-
132.Mark and space refer respectively to
a. 1 and 0
b. Dot and dash
c. Message and interval
d. On and off
-
133.What is the other name for parity?
a. BCC
b. LRC
c. VRC
d. CRC
-
134.A device that performs routing functionsand protocol translation from onenetwork to another.
a. Gateway
b. Bridge
c. Router
d. Repeater
-
135.Not important characteristic of thephysical layer.
a. Electrical
b. Mechanical
c. Logical
d. All of them