Data Communications

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.

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

Organizations Standards of Data Communications

Institute of Electrical and Electronics Engineers (IEEE)

Electronics Industries Association (EIA)

Standards Council of Canada (SCC)

Advantages of Digital Signals over Analog Signals

Disadvantages of Digital Signals

DTE DCE DCE DTE

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


2. TRANSMISSION PATH / CHANNEL / MEDIUM

a. Bounded Medium

the signals are confined to the medium anddo not leave it except for small leakageamount

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

Bounded Medium

iv. Waveguides

- Metal tubes that allow high frequency radio waves to travel

v. Fiber optic cables

- Waveguide for light frequencies

Unbounded Medium

i. Ground or Surface Waves

ii. Space or TroposphericWaves

iii. Sky or IonosphericWaves


3. DATA COMMUNICATIONS EQUIPMENT (DCE)

> devices that provide functions required to establish, maintain and terminate a data transmission connection.

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


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


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

B. Nyquist Theorem

The highest sampling frequency required topropagate a signal is twice its input frequency

fs = 2fin

HARRY NYQUIST

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

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)

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.

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.

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?

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


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.


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.


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.


RING TOPOLOGY

Bucket or token passing.

Signals are transmitted in a rotating fashion.

Tokens give stations the right to transmit messages.


MESH TOPOLOGY

> Signals pass through more than one path.

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

Network Configuration

POINT-TO-POINT MULTIPOINT

Data Communication Equipment /Processing Hardware

Device that provide the function required toestablish, maintain, and terminate a datatransmission connection

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.

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

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

Multiplexing Techniques

FREQUENCY

DIVISION

MULTIPLEXING

Splits the availablebandwidth for a givencommunication link intoa number of channelsequal to the number ofdifferent devices beingmultiplexed.


TIME

DIVISION

MULTIPLEXING

Splits up the capacity ofthe line by assigningeach user a particulartime slot, during whichits data is transmittedover the communicationlink.


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.

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

SEVEN OSI LAYERS

APPLICATION LAYER

PRESENTATION LAYER

SESSION LAYER

TRANSPORT LAYER

NETWORK LAYER

DATA LINK LAYER

PHYSICAL LAYER

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.

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

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

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

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

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.

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.

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

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

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

PROTOCOL FUNCTIONS

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

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

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

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.

NETWORK BREADTH

B. Metropolitan Area Network (MAN)

Are developed primarily by data carriers inresponse to the demand to interconnect LANsacross metropolitan area.

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.

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.

Local Area Network (LAN)

Applications:

1. Sharing resources

2. Quick communication

3. Sharing work documents

4. Sharing applications

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.

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

10BASE5


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

10BASE2


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

10BASE-T


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

10BASE-FL

bridge

repeater

hub

router

LAN Terms

node

transceiver

gateway

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

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

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

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

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

LAN Architectures

1. PEER-TO-PEER LAN

No single station is intended to control all LAN operations or resources.

LAN Architectures

2. CLIENT SERVER LAN

One computer will have control of the network,running the network operating system software.

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

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

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

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

Baseband Transmission

Broadband Transmission

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)

FDDI

ETHERNET

TOKEN RING

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

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

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

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

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

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

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

Electronic Mail (E-Mail)

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.

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

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

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

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.

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.

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

X.25

Defines the structures contents and sequencingprocedures for the transmission of data amongDTE, DCE and a public data network.

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.

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.

X.25 Layers

1. Link layer (frame level)

2. Network layer (packet level)

3. Physical layer

PAD Packet Assembler / DisassemblerAssembles and disassembles data packets for X.25 network communications

VIRTUAL CIRCUIT

Permit communications between distinct networkelements through any number of intermediate nodewithout the dedication of portion of the physical circuits.

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

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.

Frame Relay Network

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.

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

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

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

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.

ASYNCHRONOUS TRANSFER MODE (ATM)

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

ATM Media

1. Coaxial cables

2. Twisted pair cables

3. Fiber optic cables

Constant bit rate: voice and video

Variable bit rate: data

ATM LAYERS

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

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)

ATM INTERFACES

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

ISDN (INTEGRATED SERVICES DIGITAL NETWORK)

A digital telecommunications technology thatcan simultaneously transmit voice and data overthe same pair of telephone wires.

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

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

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

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

Data Communications

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