chapter 1 introduction to data communications. introduction the second industrial revolution...

Chapter 1Chapter 1

Introduction to Data CommunicationsIntroduction to Data Communications

IntroductionIntroduction

The second industrial revolution radically The second industrial revolution radically changes the way we communicate virtually changes the way we communicate virtually eliminating information lag.eliminating information lag.

What problems does this create?What problems does this create?

Recent Communications HistoryRecent Communications History

1834 Samuel Morse invents the telegraph1834 Samuel Morse invents the telegraph 1876 Alexander Graham Bell makes the 1876 Alexander Graham Bell makes the

first long-distance phone call (10 miles)first long-distance phone call (10 miles) 1915 First transatlantic and transcontinental 1915 First transatlantic and transcontinental

telephone service.telephone service. 1948 Microwave links for telephone calls1948 Microwave links for telephone calls 1951 direct long distance dialing1951 direct long distance dialing

Communications History Cont.Communications History Cont.

1962 Fax service is introduced1962 Fax service is introduced 1965 widespread use of satellite long 1965 widespread use of satellite long

distance.distance. 1968 Non Bell equipment allowed on 1968 Non Bell equipment allowed on

phones systemphones system 1969 Picturephones1969 Picturephones 1969 DARPAnet1969 DARPAnet


1970 Limited long-distance competition 1970 Limited long-distance competition allowedallowed

1984 AT&T is broken up creating a 1984 AT&T is broken up creating a regulatory boundary between local phone regulatory boundary between local phone service and long distanceservice and long distance

1984 Cellular phone service starts1984 Cellular phone service starts 1990’s Cellular phone service explodes1990’s Cellular phone service explodes


1996 Telecommunications Competition and 1996 Telecommunications Competition and Deregulation Act replaced Deregulation Act replaced allall federal and federal and state telecommunications lawstate telecommunications law

1997 68 countries sign agreement to allow 1997 68 countries sign agreement to allow foreign telecommunications competitionforeign telecommunications competition

Information Systems HistoryInformation Systems History

1950’s Batch processing and punch cards1950’s Batch processing and punch cards 1970’s Real-time transaction-oriented 1970’s Real-time transaction-oriented

database-driven systems emergedatabase-driven systems emerge 1990’s Macys is bankrupt in part due to 1990’s Macys is bankrupt in part due to

their “old” 1970’s era IS infrastructuretheir “old” 1970’s era IS infrastructure Read comparison between Macys and Read comparison between Macys and

WalMartWalMart

Components of a NetworkComponents of a Network

Server – a device that stores data and often Server – a device that stores data and often performs functions in addition to storageperforms functions in addition to storage

Client – A terminal or microcomputer from Client – A terminal or microcomputer from which a user or other application performs a which a user or other application performs a work functionwork function

Circuit – a wire, or set of wires and devices Circuit – a wire, or set of wires and devices (modem, router, switch etc…) that carry (modem, router, switch etc…) that carry information from the client to the serverinformation from the client to the server

Types of NetworksTypes of Networks

LAN – Local Area NetworkLAN – Local Area Network BN – Backbone NetworkBN – Backbone Network MAN – Metropolitan NetworkMAN – Metropolitan Network WAN – Wide Area NetworkWAN – Wide Area Network Intranet – A network used within an Intranet – A network used within an

organizationorganization Extranet – Access for people from outsideExtranet – Access for people from outside

Network ModelsNetwork Models

Used to break networks into component Used to break networks into component functions (layers) which then allows each functions (layers) which then allows each layer to be addressed independently.layer to be addressed independently.

The use of layers and different standards The use of layers and different standards (and standards bodies) at these layers (and standards bodies) at these layers allows great flexibility in design, and allows great flexibility in design, and competition between manufacturers.competition between manufacturers.

OSI ModelOSI Model

Produced in 1984Produced in 1984 Consists of seven layersConsists of seven layers

Internet ModelInternet Model

Similar to the OSI modelSimilar to the OSI model Compresses layers 5-7 into a single layer 5Compresses layers 5-7 into a single layer 5 The textbook author claims the internet The textbook author claims the internet

model has won the “war”. Is this true?model has won the “war”. Is this true?

Functions at Layer 4 (TCP)Functions at Layer 4 (TCP)

Error detection/correctionError detection/correction Linking higher layer software to the Linking higher layer software to the

network layernetwork layer Name resolutionName resolution Breaking messages into pieces small Breaking messages into pieces small

enough to send over the network (MTUenough to send over the network (MTU

Functions at Layer 3 (IP)Functions at Layer 3 (IP)

Responsible for end-to-end routing of Responsible for end-to-end routing of messages from sender to receivermessages from sender to receiver

Responsible for attaining the next address Responsible for attaining the next address for messages as they hop from router to for messages as they hop from router to router across the internetrouter across the internet

Functions at Layer 2Functions at Layer 2

Responsible for moving messages from the Responsible for moving messages from the sender to the receiver within a LAN.sender to the receiver within a LAN.

Controls the physical layerControls the physical layer Formats the messagesFormats the messages Provides error detection and correctionProvides error detection and correction

Functions at Layer 1Functions at Layer 1

Get the signal (electrical signal, light pulse, Get the signal (electrical signal, light pulse, smoke signal) from one LAN device to the smoke signal) from one LAN device to the next. next.

This layer includes hardware devices such This layer includes hardware devices such as modems and hubs.as modems and hubs.

Two Types of StandardsTwo Types of Standards

FormalFormal– Developed by an official industry or Developed by an official industry or

government agencygovernment agency– These are often slow in developing and follow These are often slow in developing and follow

an already existing de facto standardan already existing de facto standard De factoDe facto

– Emerge in the marketplace and are supported Emerge in the marketplace and are supported by multiple vendors but have to official by multiple vendors but have to official standingstanding

Standards Making BodiesStandards Making Bodies

IEEEIEEE– The Institute of Electrical and Electronic The Institute of Electrical and Electronic

EngineersEngineers– Professional organization based in the United Professional organization based in the United

StatesStates– Primarily responsible for existing LAN Primarily responsible for existing LAN

standardsstandards


ITU-TITU-T– Responsible for creating technical standards for Responsible for creating technical standards for

the united nations international the united nations international telecommunications union (ITU)telecommunications union (ITU)

– Open to public or private operators of Open to public or private operators of communications networks from more then 200 communications networks from more then 200 countriescountries

– Based in Geneva SwitzerlandBased in Geneva Switzerland


IETFIETF– Internet Engineering Task ForceInternet Engineering Task Force– Open to everyoneOpen to everyone– Manages consensus-building process through Manages consensus-building process through

the use of RFC’sthe use of RFC’s– Oversees creation of Internet protocols and Oversees creation of Internet protocols and

standardsstandards

Future TrendsFuture Trends

Pervasive networkingPervasive networking Integration of voice, video and dataIntegration of voice, video and data New information servicesNew information services

Chapter 2Chapter 2

Application LayerApplication Layer

Application ArchitecturesApplication Architectures

Host-Based ArchitecturesHost-Based Architectures– Commonly a mainframe with terminalsCommonly a mainframe with terminals

Client-Based ArchitecturesClient-Based Architectures– Distribute PC based architecture with the Distribute PC based architecture with the

computing power at the desktopcomputing power at the desktop Client-Server ArchitectureClient-Server Architecture

– Applications software divided between desktop Applications software divided between desktop PC’s and central servers (fat vs. thin clients)PC’s and central servers (fat vs. thin clients)

N-tier ArchitecturesN-tier Architectures

Two-tierTwo-tier– A client talks to a server (connecting to a web A client talks to a server (connecting to a web

server)server) Three-tierThree-tier

– A client talks to a web server which in turns A client talks to a web server which in turns queries a database server to obtain the queries a database server to obtain the requested datarequested data

N-tierN-tier– Same concept applied N timesSame concept applied N times

Advantages of Client-ServerAdvantages of Client-Server

ScalabilityScalability– N-tiered architecture gives a high degree of N-tiered architecture gives a high degree of

scalabilityscalability Cost of infrastructureCost of infrastructure

– A set of smaller micro or mini computers and A set of smaller micro or mini computers and the associated software is often far less the associated software is often far less expensive then a mainframe approachexpensive then a mainframe approach

World Wide WebWorld Wide Web

Create in 1989 at the CERN lab in Geneva Create in 1989 at the CERN lab in Geneva Switzerland by Tim Berners-LeeSwitzerland by Tim Berners-Lee

A graphical interface was developed in A graphical interface was developed in 1993 by a team of students led by Marc 1993 by a team of students led by Marc Andreessen at the NCSA lab at the Andreessen at the NCSA lab at the University of IllinoisUniversity of Illinois

Adoption of the technology was immediate Adoption of the technology was immediate and rapidand rapid

Electronic MailElectronic Mail

One of the earliest applications on the One of the earliest applications on the Internet (Early “killer” app)Internet (Early “killer” app)

Cost and speed are among it’s strengths Cost and speed are among it’s strengths when compared with “snail mail”when compared with “snail mail”

Important protocols and extensions to Important protocols and extensions to understandunderstand– SMTP (Simple Mail Transfer Protocol)SMTP (Simple Mail Transfer Protocol)– IMAP (Internet Message Access Protocol)IMAP (Internet Message Access Protocol)– MIME (Multipurpose Internet Mail Extension)MIME (Multipurpose Internet Mail Extension)

Other Important ApplicationsOther Important Applications

ListservListserv– A mailing list of users who have joined to A mailing list of users who have joined to

discuss a topic or receive specific information discuss a topic or receive specific information updatesupdates

UsenetUsenet– A repository of articles on many different A repository of articles on many different

subjectssubjects

Other Important ApplicationsOther Important Applications

FTP – File Transfer ProtocolFTP – File Transfer Protocol– Provides the ability to transfer data to and from Provides the ability to transfer data to and from

systems (primarily used in conjunction with systems (primarily used in conjunction with UNIX servers)UNIX servers)

TelnetTelnet– Provides the ability to login to a server from Provides the ability to login to a server from

anywhere within a connected networkanywhere within a connected network– The name is derived from making a TELephone The name is derived from making a TELephone

connection via the NETwork.connection via the NETwork.

Chapter 3Chapter 3

Physical LayerPhysical Layer

Components in Physical LayerComponents in Physical Layer

MediaMedia– Wires, fiber-optic strandsWires, fiber-optic strands– WirelessWireless

Special-purpose devicesSpecial-purpose devices– ModemsModems– Repeaters/hubsRepeaters/hubs

CircuitsCircuits

Physical CircuitPhysical Circuit– Twisted pair cable, fiber, wireless linkTwisted pair cable, fiber, wireless link– Exclusively committed to your dataExclusively committed to your data

Logical CircuitLogical Circuit– One of several, perhaps many circuits on a One of several, perhaps many circuits on a

single physical circuitsingle physical circuit– Channel 12 on TV is a logical circuit, it rides Channel 12 on TV is a logical circuit, it rides

on a coaxial cable or wireless (a physical on a coaxial cable or wireless (a physical circuit) along with many other logical circuits circuit) along with many other logical circuits

Types of DataTypes of Data

DigitalDigital– Two possible values for any data bit (1 or 0)Two possible values for any data bit (1 or 0)– In a fiber circuit a light being on could In a fiber circuit a light being on could

represent a “1” while off represents a “0”represent a “1” while off represents a “0”– In a copper circuit 5 volts could represent “1” In a copper circuit 5 volts could represent “1”

while 0 volts represents “0”while 0 volts represents “0” AnalogAnalog

– Signals are shaped like sound waves and are Signals are shaped like sound waves and are constantly changingconstantly changing

Modem/CodecModem/Codec

MOdulate/DEModulateMOdulate/DEModulate– Translates digital data into a form that can be Translates digital data into a form that can be

transmitted across an analog circuit such as a transmitted across an analog circuit such as a standard telephone linestandard telephone line

COder/DECoderCOder/DECoder– Translates analog information into a form that Translates analog information into a form that

can be transmitted across a digital circuitcan be transmitted across a digital circuit

Circuit ConfigurationCircuit Configuration

Point-to-PointPoint-to-Point– A circuit with a device at each endA circuit with a device at each end– Home modemHome modem

MultipointMultipoint– A single device at one end with many devices A single device at one end with many devices

at the other end with either time-slicing or at the other end with either time-slicing or circuit switchingcircuit switching

Data FlowData Flow

SimplexSimplex– One way transmission (i.e. cable TV)One way transmission (i.e. cable TV)

Half-duplexHalf-duplex– Communication in both directions, only one Communication in both directions, only one

way at a time (i.e. walkie-talkie)way at a time (i.e. walkie-talkie) Full-duplexFull-duplex

– Communication in both ways, at the same time Communication in both ways, at the same time (i.e. telephone)(i.e. telephone)

Communication MediaCommunication Media

Guided mediaGuided media– Twisted-pair, coaxial, fiber-opticTwisted-pair, coaxial, fiber-optic

Wireless mediaWireless media– Radio, infrared, satelliteRadio, infrared, satellite

Fiber OpticFiber Optic

Multi modeMulti mode– Attenuation (weakening of the signal)Attenuation (weakening of the signal)– Dispersion (spreading of the signal)Dispersion (spreading of the signal)

Single modeSingle mode– Must use the precision of lasers as opposed to Must use the precision of lasers as opposed to

LED’sLED’s

CodingCoding

CharacterCharacter– A symbol with a constant understood meaningA symbol with a constant understood meaning

ByteByte– A group of (typically) eight bits that is treated A group of (typically) eight bits that is treated

as a characteras a character ASCII (American Standard Code for ASCII (American Standard Code for

Information Interchange)Information Interchange)– 7 or 8 bit code (typically 8)7 or 8 bit code (typically 8)

Transmission ModesTransmission Modes

ParallelParallel– All bits are sent simultaneously, in a 32-bit All bits are sent simultaneously, in a 32-bit

system then there must be paths to send all 32 system then there must be paths to send all 32 bits at the same timebits at the same time

SerialSerial– Each bit is sent one at a time, Each bit is sent one at a time,

Digital TransmissionDigital Transmission

Transmission of 1’s and 0’sTransmission of 1’s and 0’s– With electricity this can be voltages with With electricity this can be voltages with

perhaps 0 volts representing a zero and 5 volts perhaps 0 volts representing a zero and 5 volts representing a 1 (unipolar)representing a 1 (unipolar)

– With light this can be using the state of the light With light this can be using the state of the light with perhaps off representing a 0 and on with perhaps off representing a 0 and on representing a 1representing a 1

Manchester EncodingManchester Encoding

Used in EthernetUsed in Ethernet Unipolar coding scheme with a twistUnipolar coding scheme with a twist

– Voltage moving from a lower level to a higher Voltage moving from a lower level to a higher level represents a “1”level represents a “1”

– Voltage moving from high to low is a “0”Voltage moving from high to low is a “0”

Analog TransmissionAnalog Transmission

Telephone systems were originally Telephone systems were originally designed to carry analog transmissions, designed to carry analog transmissions, electrical representations of the human electrical representations of the human voicevoice

Three key characteristicsThree key characteristics– AmplitudeAmplitude– FrequencyFrequency– PhasePhase

ModulationModulation

A carrier wave (ugly noise heard when A carrier wave (ugly noise heard when modems are negotiating) is sent between modems are negotiating) is sent between modems, the shape of the wave is altered to modems, the shape of the wave is altered to represent 1’s and 0’srepresent 1’s and 0’s

These “shape changes” are referred to as These “shape changes” are referred to as modulationmodulation

Modulation TechniquesModulation Techniques

AmplitudeAmplitude– Modifying the height of the waveModifying the height of the wave

FrequencyFrequency– Modifying the frequency (the number of waves Modifying the frequency (the number of waves

per second) of the waveper second) of the wave PhasePhase

– Modifying the point in phase at which the wave Modifying the point in phase at which the wave startsstarts

Amplitude ModulationAmplitude Modulation

Frequency ModulationFrequency Modulation

Phase ModulationPhase Modulation

Two-bit Amplitude ModulationTwo-bit Amplitude Modulation

Modulation TechniquesModulation Techniques

The various modulation techniques The various modulation techniques discussed can be combined as welldiscussed can be combined as well

QAM (Quadrature Amplitude Modulation)QAM (Quadrature Amplitude Modulation)– Combines eight phases (three bits) and two Combines eight phases (three bits) and two

amplitudes (one bit) for a total of four bitsamplitudes (one bit) for a total of four bits TCM (Trellis Code Modulation)TCM (Trellis Code Modulation)

– Similar to QAM but can transmit up to ten bits Similar to QAM but can transmit up to ten bits per symbolper symbol

Bits Baud and SymbolBits Baud and Symbol

Bits (specifically bits per second) are Bits (specifically bits per second) are generally the important measurement in generally the important measurement in data communications as symbols are data communications as symbols are composed of bitscomposed of bits

There is a common misconception that There is a common misconception that these terms are interchangeable, baud refers these terms are interchangeable, baud refers to the number of symbols per second as to the number of symbols per second as opposed to the number of bits per secondopposed to the number of bits per second

Voice Circuit CapacityVoice Circuit Capacity

Home analog phone lines have a bandwidth Home analog phone lines have a bandwidth range from 0 to 4000 Hzrange from 0 to 4000 Hz

The human ear can detect sounds up to The human ear can detect sounds up to ~14,000 Hz so very high pitch sounds can’t ~14,000 Hz so very high pitch sounds can’t be transmitted over an analog phone linebe transmitted over an analog phone line

Digital circuits used to tie analog phone Digital circuits used to tie analog phone lines together have a bandwidth of 64,000 lines together have a bandwidth of 64,000 bits per second (bps)bits per second (bps)

Modem TechnologiesModem Technologies

V.34+V.34+– Transmits up to 33,600 bpsTransmits up to 33,600 bps

V.44 (Compression)V.44 (Compression)– Builds a dictionary of character combinations Builds a dictionary of character combinations

being sent over the circuitbeing sent over the circuit– When a combination is repeated the dictionary When a combination is repeated the dictionary

reference is sent as opposed to the charactersreference is sent as opposed to the characters– Average throughput is ~ 6:1Average throughput is ~ 6:1

CodecCodec

Converts Analog data into a digital form for Converts Analog data into a digital form for transmission over a digital system and backtransmission over a digital system and back

The analog signal is translated into a binary The analog signal is translated into a binary numbernumber

This digital signal is an approximation of This digital signal is an approximation of the original with the quality depending on the original with the quality depending on the resolution by either increasing the the resolution by either increasing the amplitude levels or increasing the sampling amplitude levels or increasing the sampling raterate

Telephone TransmissionTelephone Transmission

The “local loop” is the circuit from the The “local loop” is the circuit from the phone company CO (the building between phone company CO (the building between 33rdrd and 4 and 4thth streets and Chestnut and Hazel streets and Chestnut and Hazel streets) uses analog transmissionstreets) uses analog transmission

Once the signal reaches the phone company Once the signal reaches the phone company office it is converted to digital form and is office it is converted to digital form and is then sent to it’s destination COthen sent to it’s destination CO

Even local calls are converted to digitalEven local calls are converted to digital

Pulse Code ModulationPulse Code Modulation

PCM is used in phone company CODEC’s PCM is used in phone company CODEC’s in North Americain North America

PCM samples the data 8,000 times (twice PCM samples the data 8,000 times (twice the highest frequency within the phone the highest frequency within the phone systemsystem

Eight bits are generated for each sample, Eight bits are generated for each sample, thus the phone system uses the 8 bits * thus the phone system uses the 8 bits * 8,000 samples for a data rate of 64,000 bps8,000 samples for a data rate of 64,000 bps

ADPCMADPCM

Adaptive Differential Pulse Code ModulationAdaptive Differential Pulse Code Modulation Similar to PCM except it only sends the difference Similar to PCM except it only sends the difference

between the former and the new signalbetween the former and the new signal Data rates as low as 8Kbps can be obtained, Data rates as low as 8Kbps can be obtained,

32Kbps is the lowest providing sufficient quality 32Kbps is the lowest providing sufficient quality so that the user doesn’t noticeso that the user doesn’t notice

The use of ADPCM is the reason that some users The use of ADPCM is the reason that some users can’t get a modem connection above 26,200 bpscan’t get a modem connection above 26,200 bps

Analog/Digital ModemsAnalog/Digital Modems

Uses PCM backwardUses PCM backward Sends 8,000 samples per secondSends 8,000 samples per second Uses 7 bits (one is lost for control purposesUses 7 bits (one is lost for control purposes 7 bits * 8,000 samples = 56,000 bits7 bits * 8,000 samples = 56,000 bits V.92 modems do this in each direction and V.92 modems do this in each direction and

due to technical constraints are limited to due to technical constraints are limited to ~52,000 bps downstream and ~42,000 bps ~52,000 bps downstream and ~42,000 bps upstreamupstream

MultiplexingMultiplexing

Using one high-speed circuit to carry the Using one high-speed circuit to carry the traffic of multiple lower-speed circuitstraffic of multiple lower-speed circuits

FDMFDM TDMTDM WDM (form of FDM)WDM (form of FDM) DWM (combination of FDM and TDM)DWM (combination of FDM and TDM)

– Has reached 1.25 terabits already and is Has reached 1.25 terabits already and is expected to reach 1 petabit within a few yearsexpected to reach 1 petabit within a few years

Frequency Division MultiplexingFrequency Division Multiplexing

Time Division MultiplexingTime Division Multiplexing

Inverse MultiplexingInverse Multiplexing

Using a series of lower-speed circuits to Using a series of lower-speed circuits to connect two high-speed circuits togetherconnect two high-speed circuits together

Technology has been proprietary until just Technology has been proprietary until just recentlyrecently

The BONDING (Bandwidth ON Demand The BONDING (Bandwidth ON Demand Interoperability Networking Group) Interoperability Networking Group) standard is allowing vendors to interoperate standard is allowing vendors to interoperate today but this is still in its infancytoday but this is still in its infancy

Inverse MultiplexingInverse Multiplexing

Digital Subscriber LineDigital Subscriber Line

Much of the available bandwidth in the Much of the available bandwidth in the local loop has gone unused for many yearslocal loop has gone unused for many years

DSL uses this bandwidth by applying FDM DSL uses this bandwidth by applying FDM to create three circuits comprised of the to create three circuits comprised of the original phone line, a upstream data circuit original phone line, a upstream data circuit and a downstream data circuitand a downstream data circuit

TDM and PM are also used to obtain TDM and PM are also used to obtain various data rates and featuresvarious data rates and features

Chapter 4Chapter 4

Data Link LayerData Link Layer

Media Access ControlMedia Access Control

A mechanism used to control when A mechanism used to control when computers transmitcomputers transmit

Important when using half-duplex circuits Important when using half-duplex circuits or multipoint configurationsor multipoint configurations

Two fundamental approachesTwo fundamental approaches– Controlled AccessControlled Access– ContentionContention

Controlled AccessControlled Access

X-ON/X-OFFX-ON/X-OFF PollingPolling

– Roll Call Polling: one device in the circuit is a Roll Call Polling: one device in the circuit is a “master” and checks with each other device on “master” and checks with each other device on its wire to see if they have something to sayits wire to see if they have something to say

– Hub Polling (token passing): one computer Hub Polling (token passing): one computer starts the poll and passes it to the next, when a starts the poll and passes it to the next, when a computer with something to say receives the computer with something to say receives the “token” then it can send its data“token” then it can send its data

ContentionContention

The opposite of controlled access, each The opposite of controlled access, each device listens to see if someone else is device listens to see if someone else is talking, if not then it sends carrier and starts talking, if not then it sends carrier and starts to talkto talk

CSMA/CD (Carrier Sense Multiple Access CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is used in with Collision Detection) is used in Ethernet networksEthernet networks

Network ErrorsNetwork Errors

Two types of network errorsTwo types of network errors– Data lossData loss– Data corruptionData corruption

Three approaches to dealing with errorsThree approaches to dealing with errors– PreventionPrevention– DetectionDetection– CorrectionCorrection

Sources of ErrorsSources of Errors

Line noise, distortionLine noise, distortion Line outagesLine outages Impulse noiseImpulse noise Cross-talkCross-talk AttenuationAttenuation Intermodulation noiseIntermodulation noise JitterJitter

Error PreventionError Prevention

Shielded cablingShielded cabling Cable locationCable location Cable selection (fiber vs. twisted pair)Cable selection (fiber vs. twisted pair) Cable installation and maintenanceCable installation and maintenance

Error DetectionError Detection

ParityParity Longitudinal redundancy checkingLongitudinal redundancy checking Polynomial checkingPolynomial checking

– ChecksumChecksum– Cyclic Redundancy CheckCyclic Redundancy Check

» 16-bit CRC used in TCP16-bit CRC used in TCP

» 32-bit CRC used in Ethernet32-bit CRC used in Ethernet

Error Correction via Retrans.Error Correction via Retrans.

Stop-and-wait ARQStop-and-wait ARQ Continuous ARQContinuous ARQ

Forward Error CorrectionForward Error Correction

Sufficient redundant data is included within Sufficient redundant data is included within the transmission to correct errors without the transmission to correct errors without retransmissionretransmission

Used heavily in satellite transmissionUsed heavily in satellite transmission

Ethernet ProtocolsEthernet Protocols

Ethernet (IEEE 802.3)Ethernet (IEEE 802.3)– Byte-count protocolByte-count protocol– Destination, length, LLC, SNAP, CRC-32Destination, length, LLC, SNAP, CRC-32

Point-to-Point Protocol (PPP)Point-to-Point Protocol (PPP)– AddressAddress– ProtocolProtocol– Message length = 1,500 bytesMessage length = 1,500 bytes

Bridging/SwitchingBridging/Switching

MAC-layer address table for each interfaceMAC-layer address table for each interface Addresses behind a port are stored in Addresses behind a port are stored in

memorymemory Ethernet frames are checked at each Ethernet frames are checked at each

interface to determine if they should be interface to determine if they should be forwardedforwarded

Transmission EfficiencyTransmission Efficiency

Transmission efficiency = total information Transmission efficiency = total information bits/total bitsbits/total bits

Throughput = transmission efficiency Throughput = transmission efficiency adjusted for errors and retransmissionsadjusted for errors and retransmissions

TRIBTRIB

Chapter 5Chapter 5

Network and Transport LayersNetwork and Transport Layers

TCP/IPTCP/IP

TCPTCP– Layer 4Layer 4– Provides error detection (CRC-16)Provides error detection (CRC-16)– Breaks data into appropriate size blocks (MTU)Breaks data into appropriate size blocks (MTU)

IPIP– Provides routing and addressingProvides routing and addressing– IPv4 (32-bit address)IPv4 (32-bit address)– IPv6 (128-bit address)IPv6 (128-bit address)

TCP PortsTCP Ports

A computer can have multiple applications A computer can have multiple applications running, i.e. a machine can be running both running, i.e. a machine can be running both a web server and an email servera web server and an email server

Commonly used portsCommonly used ports– SMTP – port 26SMTP – port 26– WWW – port 80WWW – port 80– FTP – port 21FTP – port 21– Telnet – port 23Telnet – port 23

PacketizingPacketizing

Taking an outgoing message with a length Taking an outgoing message with a length too great to fit within the data-link too great to fit within the data-link maximum frame length (MTU) and maximum frame length (MTU) and breaking the message into appropriate breaking the message into appropriate lengthslengths

Function is performed by the transport layerFunction is performed by the transport layer With IPv4 the packet size is set for the local With IPv4 the packet size is set for the local

LAN and is adjusted if the message is sent LAN and is adjusted if the message is sent across a link that requires a smaller MTUacross a link that requires a smaller MTU

Connection-oriented RoutingConnection-oriented Routing

A specific route “virtual route” is A specific route “virtual route” is determined when the session is createddetermined when the session is created

A SYN packet is sent to create the virtual A SYN packet is sent to create the virtual circuitcircuit

A FIN packet is sent to tear the circuit downA FIN packet is sent to tear the circuit down

Connectionless RoutingConnectionless Routing

Uses UDP instead of TCPUses UDP instead of TCP Packets can travel different routesPackets can travel different routes Commonly used with applications such as Commonly used with applications such as

DNS and DHCP which are not likely to DNS and DHCP which are not likely to send a packet that will have to be broken send a packet that will have to be broken into piecesinto pieces

Quality of ServiceQuality of Service

A special type of connection-oriented A special type of connection-oriented routingrouting

Classes of service are established and each Classes of service are established and each application is assigned one of the classesapplication is assigned one of the classes

Applications such as VoIP and video-Applications such as VoIP and video-conferencing may be in a higher priority conferencing may be in a higher priority class then SMTP or WWWclass then SMTP or WWW

Internet AddressesInternet Addresses

Assigned by ICANN (Internet Corporation Assigned by ICANN (Internet Corporation for Assigned Numbers and Names)for Assigned Numbers and Names)

Blocks of network addresses are assigned to Blocks of network addresses are assigned to organizationsorganizations

Often a large block of addresses are Often a large block of addresses are assigned to an organizationassigned to an organization

These large blocks of addresses are broken These large blocks of addresses are broken into smaller blocks referred to as “subnets”into smaller blocks referred to as “subnets”

SubnetsSubnets

There are many possible combinations There are many possible combinations when dividing a network address block into when dividing a network address block into subnetssubnets

It is also possible to merge two adjacent It is also possible to merge two adjacent networks together into a single “supernet”networks together into a single “supernet”

Whether dividing a network into subnets or Whether dividing a network into subnets or combining two or more networks into a combining two or more networks into a supernet the subnet mask is the keysupernet the subnet mask is the key

Subnet MaskSubnet Mask

A subnet mask is a string of 1’s and 0’sA subnet mask is a string of 1’s and 0’s A subnet mask of 255.255.255.0 indicates A subnet mask of 255.255.255.0 indicates

the first three bytes of the IP address are the first three bytes of the IP address are part of the networkpart of the network

Another way of looking at this subnet mask Another way of looking at this subnet mask would be would be 11111111.11111111.11111111.0000000011111111.11111111.11111111.00000000

A 1 indicates the corresponding bit in the IP A 1 indicates the corresponding bit in the IP address is part of the network designationaddress is part of the network designation

Dynamic AddressingDynamic Addressing

DHCP (Dynamic Host Configuration DHCP (Dynamic Host Configuration Protocol)Protocol)

When the computer is started it sends a When the computer is started it sends a message requesting that a DHCP server message requesting that a DHCP server provide an IP address and other provide an IP address and other configuration allowing the computer to configuration allowing the computer to communicate via IPcommunicate via IP

Layer 2 Address ResolutionLayer 2 Address Resolution

ARP (Address Resolution Protocol)ARP (Address Resolution Protocol) Broadcast Message (all 1’s)Broadcast Message (all 1’s) Whoever has IP address xxx.xxx.xxx.xxx Whoever has IP address xxx.xxx.xxx.xxx

send me your Ethernet addresssend me your Ethernet address

Domain Name ServiceDomain Name Service

An Internet phone bookAn Internet phone book When typing in When typing in www.csuchico.eduwww.csuchico.edu DNS DNS

will translate this application-layer address will translate this application-layer address to the network-layer address of to the network-layer address of 132.241.82.24132.241.82.24

RoutingRouting

Packets are routed between networks based Packets are routed between networks based on a set of routing tableson a set of routing tables

The routing tables can be manually The routing tables can be manually programmed (static routing) or created by a programmed (static routing) or created by a routing protocol (dynamic routing)routing protocol (dynamic routing)

Routing ProtocolsRouting Protocols– Distance Vector (RIP)Distance Vector (RIP)– Link State (OSPF)Link State (OSPF)

Routing ProtocolsRouting Protocols

Interior routing protocolsInterior routing protocols– RIP, OSPF, EIGRPRIP, OSPF, EIGRP

Exterior routing protocolsExterior routing protocols– OSPF, BGPOSPF, BGP

Autonomous SystemAutonomous System

MulticastingMulticasting

Three types of messagesThree types of messages– UnicastUnicast– BroadcastBroadcast– MulticastMulticast

IGMP (Internet Group Management IGMP (Internet Group Management Protocol)Protocol)– Each participating computer uses a common Each participating computer uses a common

data-link layer addressdata-link layer address

TCP/IP ExampleTCP/IP Example

Work through the entire TCP/IP example at Work through the entire TCP/IP example at the end of chapter 5the end of chapter 5– Known addresses, same subnetKnown addresses, same subnet– Known addresses, different subnetKnown addresses, different subnet– Unknown addressesUnknown addresses– TCP connectionsTCP connections

Chapter 6Chapter 6

Local Area NetworksLocal Area Networks

Why Use a LAN?Why Use a LAN?

Information SharingInformation Sharing– EmailEmail– File accessFile access– Video conferencingVideo conferencing

Resource SharingResource Sharing– PrintersPrinters– Applications serversApplications servers

Dedicated Server vs. Peer-to-PeerDedicated Server vs. Peer-to-Peer

Dedicated ServerDedicated Server– One or more server computers permanently One or more server computers permanently

assigned to being a network serverassigned to being a network server» File serversFile servers

» Print serversPrint servers

Peer-to-PeerPeer-to-Peer– No dedicated serverNo dedicated server

LAN ComponentsLAN Components

NIC (Network Interface Card)NIC (Network Interface Card) Network cablesNetwork cables

– Twisted pairTwisted pair» UTP/STPUTP/STP

» See Category Ratings in Technology FocusSee Category Ratings in Technology Focus

– Coaxial cablesCoaxial cables» BALUNsBALUNs

– Fiber-optic cablesFiber-optic cables» Single-mode vs. multi-modeSingle-mode vs. multi-mode

LAN Components Cont.LAN Components Cont.

Network hubsNetwork hubs Network bridges/switchesNetwork bridges/switches Network routersNetwork routers Network Operating SystemNetwork Operating System

– Server/client softwareServer/client software Network profileNetwork profile Storage Area Networks (SAN)Storage Area Networks (SAN) Network Attached Storage (NAS)Network Attached Storage (NAS)

Ethernet (IEEE 802.3)Ethernet (IEEE 802.3)

TopologyTopology– Logical vs. physicalLogical vs. physical

The logical topology of a traditional The logical topology of a traditional Ethernet network is a busEthernet network is a bus

The physical topology is often a starThe physical topology is often a star

Media Access ControlMedia Access Control

With a bus topology there must be a With a bus topology there must be a mechanism to either prevent, or detect and mechanism to either prevent, or detect and deal with, collisions on the mediadeal with, collisions on the media

CSMA/CDCSMA/CD Full-duplex EthernetFull-duplex Ethernet

Types of EthernetTypes of Ethernet

10Base-510Base-5 10Base-210Base-2 10Base-T10Base-T 100Base-T100Base-T 10/100 Ethernet10/100 Ethernet 1000Base-T1000Base-T

Switched EthernetSwitched Ethernet

The switch replaces the hub in the networkThe switch replaces the hub in the network The hub repeats every bit of data out every The hub repeats every bit of data out every

portport The switch sends the data out the port The switch sends the data out the port

which is connected to the message recipientwhich is connected to the message recipient The switch uses a forwarding table that The switch uses a forwarding table that

contains the Ethernet addresses of the contains the Ethernet addresses of the computers connected to each portcomputers connected to each port

Wireless EthernetWireless Ethernet

IEEE 802.11IEEE 802.11 The WEP standard has been completely The WEP standard has been completely

crackedcracked Uses CSMA/CA for media controlUses CSMA/CA for media control Subject to the “hidden node” problemSubject to the “hidden node” problem Has VCSM (Virtual Carrier Sense Method) Has VCSM (Virtual Carrier Sense Method)

as an option to work around the hidden as an option to work around the hidden node problemnode problem

Types of Wireless EthernetTypes of Wireless Ethernet

IEEE 802.11bIEEE 802.11b– DSSS – Allows speeds from 1 – 11 Mbps DSSS – Allows speeds from 1 – 11 Mbps

depending on distance and interferencedepending on distance and interference– FHSS – Allows speeds from 1 – 2 MbpsFHSS – Allows speeds from 1 – 2 Mbps

IEEE 802.11aIEEE 802.11a– The standard is still incompleteThe standard is still incomplete– Data rate is likely to be 54 Mbps on first Data rate is likely to be 54 Mbps on first

iterationiteration– Actual throughput will likely be ~20MbpsActual throughput will likely be ~20Mbps

Other Wireless TechnologiesOther Wireless Technologies

Infrared wirelessInfrared wireless– Requires line of site or white ceilings and walls Requires line of site or white ceilings and walls

with diffused infraredwith diffused infrared BluetoothBluetooth

– Slated to become standardized as IEEE 803.15Slated to become standardized as IEEE 803.15– Short range networks referred to as piconets Short range networks referred to as piconets

with no more then 8 deviceswith no more then 8 devices– Uses controlled access media access controlUses controlled access media access control– Less then 1Mbps throughputLess then 1Mbps throughput

Reducing Network DemandReducing Network Demand

Placing heavily-used applications or data Placing heavily-used applications or data modules on each client computermodules on each client computer

Network segmentation – note this is really Network segmentation – note this is really increasing supply rather then reducing increasing supply rather then reducing demanddemand

Chapter 7Chapter 7

Backbone NetworksBackbone Networks

Backbone Network ComponentsBackbone Network Components

BridgesBridges– Operating at the data-link layer (MAC address)Operating at the data-link layer (MAC address)

RoutersRouters– Operating at the network layer (IP address)Operating at the network layer (IP address)

GatewaysGateways– Operating at the transport layer (note that this Operating at the transport layer (note that this

disagrees with the authors table 7-1)disagrees with the authors table 7-1)

Backbone Network ComponentsBackbone Network Components

Collapsed backboneCollapsed backbone– Chassis-basedChassis-based– Rack-basedRack-based

VLAN’sVLAN’s– Port-basedPort-based– MAC-basedMAC-based– IP-basedIP-based– Application-basedApplication-based

ATMATM

Four key differences between Ethernet and Four key differences between Ethernet and ATM in the backboneATM in the backbone– 53-byte fixed-length cells53-byte fixed-length cells– No error correctionNo error correction– Virtual Channel addressing as opposed to fixed Virtual Channel addressing as opposed to fixed

addresses with the path and circuit numbersaddresses with the path and circuit numbers– Built in Class-of-Service (CoS) and Quality-of-Built in Class-of-Service (CoS) and Quality-of-

Service (QoS)Service (QoS)

ATMATM

Classes of ServiceClasses of Service– CBRCBR– VBR-RTVBR-RT– VBR-NRTVBR-NRT– ABRABR– UBRUBR

LANE vs. MPOALANE vs. MPOA SVC vs. PVCSVC vs. PVC

Chapter 8Chapter 8

MAN’s and WAN’sMAN’s and WAN’s

MAN’sMAN’s

Generally constrained to a city or small Generally constrained to a city or small region between 3 and 30 milesregion between 3 and 30 miles

Generally deployed via either wireless Generally deployed via either wireless technology or services leased from a carriertechnology or services leased from a carrier

Moderate levels of regulationModerate levels of regulation

WAN’sWAN’s

Connecting over potentially great distancesConnecting over potentially great distances Generally deployed via circuits leased from Generally deployed via circuits leased from

Common CarriersCommon Carriers Very heavily regulated within North Very heavily regulated within North

America and usually even worse overseesAmerica and usually even worse oversees

Circuit Switched NetworksCircuit Switched Networks

Usually depicted by a cloud with your Usually depicted by a cloud with your organizations data traveling with many organizations data traveling with many others across the same physical circuitsothers across the same physical circuits

POTSPOTS ISDNISDN

– BRIBRI– PRIPRI– BroadbandBroadband

Dedicated Circuit NetworksDedicated Circuit Networks

Dedicated circuits or dedicated bandwidth Dedicated circuits or dedicated bandwidth within carrier circuitswithin carrier circuits

Ring ArchitectureRing Architecture Star ArchitectureStar Architecture Mesh ArchitectureMesh Architecture

T Carrier ServicesT Carrier Services

Based on the 64Kbps channel required for a Based on the 64Kbps channel required for a digitized voice connectiondigitized voice connection

T1 – 24 channels * 64Kbps = 1.536 MbpsT1 – 24 channels * 64Kbps = 1.536 Mbps– Control information is included bringing the Control information is included bringing the

total circuit bandwidth for a stand-alone T1 to total circuit bandwidth for a stand-alone T1 to 1.544 Mbps1.544 Mbps

T3 – 28 T1’s – 28 * 1.544Mbps = T3 – 28 T1’s – 28 * 1.544Mbps = 43.008Mbps43.008Mbps– With control information = 44,736MbpsWith control information = 44,736Mbps

SONETSONET

SONET is a North American standard but SONET is a North American standard but the ITU recently adopted the SDH standard the ITU recently adopted the SDH standard set which is nearly identicalset which is nearly identical

OC-1 = 51.84MbpsOC-1 = 51.84Mbps OC-3 = 3*OC-1 = 155.52 MbpsOC-3 = 3*OC-1 = 155.52 Mbps OC-12 = 12*OC-1 = 622.08 MbpsOC-12 = 12*OC-1 = 622.08 Mbps

Packet Switched NetworksPacket Switched Networks

X.25 – older standard now seldom used in X.25 – older standard now seldom used in North AmericaNorth America

ATMATM Frame RelayFrame Relay Ethernet/IP NetworksEthernet/IP Networks

Virtual Private NetworksVirtual Private Networks

IntranetIntranet– Used to connect your organizations office via Used to connect your organizations office via

the Internetthe Internet ExtranetExtranet

– In addition to your organizations office you In addition to your organizations office you may also include other organizations with may also include other organizations with which you do businesswhich you do business

AccessAccess– Remote access for employeesRemote access for employees

Chapter 9Chapter 9

The InternetThe Internet

Internet StructureInternet Structure

Internet architectureInternet architecture NAP’s, MAE’s, and ISP’sNAP’s, MAE’s, and ISP’s

– POP’sPOP’s PeeringPeering Autonomous systemsAutonomous systems

Internet Access TechnologiesInternet Access Technologies

DSLDSL– Digital Subscriber LineDigital Subscriber Line– Uses the local-loopUses the local-loop– A modem is placed in the home converting the A modem is placed in the home converting the

data from the DSL format to Ethernetdata from the DSL format to Ethernet ADSLADSL

– G.LiteG.Lite VDSLVDSL

Internet Access TechnologiesInternet Access Technologies

Cable ModemsCable Modems– DOCSISDOCSIS

Shared media means users compete with Shared media means users compete with each other for bandwidth and unscrupulous each other for bandwidth and unscrupulous neighbors could intercept your dataneighbors could intercept your data

Throughput suffers due to hardware Throughput suffers due to hardware compatibility issues that stem from cable compatibility issues that stem from cable TV infrastructure differencesTV infrastructure differences

WirelessWireless

Fixed wirelessFixed wireless– Wireless DSLWireless DSL– SatelliteSatellite

Mobile WirelessMobile Wireless– WAPWAP– WAEWAE

Internet GovernanceInternet Governance

ISOC (Internet SOCiety)ISOC (Internet SOCiety)– www.isoc.orgwww.isoc.org

IETF (Internet Engineering Task Force)IETF (Internet Engineering Task Force) IESG (Internet Engineering Steering Group)IESG (Internet Engineering Steering Group)

– Each IETF working group is chaired by a Each IETF working group is chaired by a member of the IESGmember of the IESG

IABIAB IRTFIRTF

Internet Domain Name Reg.Internet Domain Name Reg.

Internet name and address registration was Internet name and address registration was handled by John Postel until his death in handled by John Postel until his death in 19981998

In 1998 ICANN (Internet Corporation for In 1998 ICANN (Internet Corporation for Assigned Names and Numbers) was formedAssigned Names and Numbers) was formed

In 1999 ICANN established the SRS and In 1999 ICANN established the SRS and has now authorized more then 80 has now authorized more then 80 companies to issue Internet names and companies to issue Internet names and numbersnumbers

Internet 2Internet 2

Next Generation InternetNext Generation Internet– vBNSvBNS

AbileneAbilene CA*net 3CA*net 3

Chapter 10Chapter 10

Network SecurityNetwork Security

Why Networks Need SecurityWhy Networks Need Security

The average cost to companies for a single The average cost to companies for a single security breach is slightly less then $1Msecurity breach is slightly less then $1M

This is a minor cost when compared to the This is a minor cost when compared to the loss of customer confidenceloss of customer confidence

The text indicates that 24 hours of The text indicates that 24 hours of downtime would cost Bank of America downtime would cost Bank of America $50M$50M

Types of Security ThreatsTypes of Security Threats

DisruptionsDisruptions– Minor cable breaks to earthquakesMinor cable breaks to earthquakes

Unauthorized AccessUnauthorized Access– More often the work of an employee then an More often the work of an employee then an

outside hackeroutside hacker

Network ControlsNetwork Controls

Controls are processes or steps to reduce or Controls are processes or steps to reduce or eliminate threatseliminate threats

Three types of controlsThree types of controls– Controls that prevent threatsControls that prevent threats– Controls that detect threatsControls that detect threats– Controls that correct threatsControls that correct threats

LAN SecurityLAN Security

Although sometimes overlooked a good Although sometimes overlooked a good first step is to ensure that the LAN hardware first step is to ensure that the LAN hardware is physically secureis physically secure

FirewallsFirewalls– Packet-levelPacket-level– Application-levelApplication-level

NAT (Network Address Translation)NAT (Network Address Translation)

LAN SecurityLAN Security

EncryptionEncryption– SymmetricSymmetric

» DESDES

» Triple DESTriple DES

» AESAES

– Asymmetric (PKI)Asymmetric (PKI)» PGP (Pretty Good Privacy)PGP (Pretty Good Privacy)

» SSL (Secure Sockets Layer)SSL (Secure Sockets Layer)

» IPSec (IP Security)IPSec (IP Security)

Detecting Unauthorized AccessDetecting Unauthorized Access

IDS (Intrusion Detection Systems)IDS (Intrusion Detection Systems)– Network-basedNetwork-based– Host-basedHost-based– Application-basedApplication-based

Two IDS TechniquesTwo IDS Techniques– Misuse detectionMisuse detection– Anomaly detectionAnomaly detection


Network DesignNetwork Design

Network Design ProcessNetwork Design Process

Traditional design processTraditional design process Building Block Design ProcessBuilding Block Design Process

– Needs analysisNeeds analysis– Technology designTechnology design– Cost assessmentCost assessment

Why network projects failWhy network projects fail– Management focus 11-2Management focus 11-2

Request For ProposalRequest For Proposal

Background informationBackground information Network requirementsNetwork requirements Service requirementsService requirements Bidding processBidding process Information required from vendorInformation required from vendor


Network ManagementNetwork Management

Network ManagementNetwork Management

Tasks performed by the network managerTasks performed by the network manager Five key management tasksFive key management tasks Key network management skillsKey network management skills Configuration managementConfiguration management

Performance & Failure StatisticsPerformance & Failure Statistics

AvailabilityAvailability MTBFMTBF MTTRepairMTTRepair Policy-Based ManagementPolicy-Based Management Service-Level AgreementsService-Level Agreements

Cost ManagementCost Management

Sources of costSources of cost TCO (Total Cost of Ownership)TCO (Total Cost of Ownership)

– $8,000 - $12,000 per device per year?$8,000 - $12,000 per device per year?– $1,500 - $3,500 per device per year? (NCO)$1,500 - $3,500 per device per year? (NCO)

Five steps to reduce network costsFive steps to reduce network costs

Network Management ToolsNetwork Management Tools

Three types of network management Three types of network management softwaresoftware– Device managementDevice management– System managementSystem management– Application managementApplication management

SNMPSNMP– MIBMIB– RMONRMON

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