CS 453
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Transcript of CS 453
CS 453CS 453
Computer NetworkingComputer Networking
Data and Computer Data and Computer CommunicationsCommunications
Networking StandardsNetworking Standards
So why can all of these devices from different So why can all of these devices from different vendors in different countries interoperate?vendors in different countries interoperate?StandardsStandardsLack of standards – a big problem – most of the Lack of standards – a big problem – most of the time – consider wireless networkingtime – consider wireless networkingStandards can be –Standards can be – Per companyPer company Per country Per country InternationalInternational
More concrete, specific than reference modelsMore concrete, specific than reference models
Networking StandardsNetworking Standards
Usually, Usually, starts with an identified problem domainstarts with an identified problem domain The a proposed or draft standardThe a proposed or draft standard A review and comment processA review and comment process Adoption of the standardsAdoption of the standards
Standards OrganizationsStandards Organizations
Telecommunications Telecommunications ITU-T (previously known as CCITT)ITU-T (previously known as CCITT) About 200 government membersAbout 200 government members About 500 industry membersAbout 500 industry members
Networking (International StandardsNetworking (International Standards ISO (International Standards Organization)ISO (International Standards Organization) Members are national standards bodyMembers are national standards body
US = ANSI, GB=BSI, France=AFNOR, Germany=DINUS = ANSI, GB=BSI, France=AFNOR, Germany=DIN
89 or so countries89 or so countries
Standards OrganizationsStandards Organizations
NIST (National Institute of Standards and NIST (National Institute of Standards and Technology)Technology) U.S. Dept. of CommerceU.S. Dept. of Commerce Primarily concerned with government Primarily concerned with government
standards, except DoDstandards, except DoD
IEEEIEEE
IEEE StandardsIEEE Standards
From Tanenbaum, 2003
Internet StandardsInternet Standards
The Internet Society (ISOC)The Internet Society (ISOC) The Internet Architecture Board (IAB)The Internet Architecture Board (IAB) The Internet Engineering Task Force (IETF)The Internet Engineering Task Force (IETF) The Internet Research Task Force (IRTF)The Internet Research Task Force (IRTF) ICANN ICANN
Internet Corporation for Assigned Names and Internet Corporation for Assigned Names and NumbersNumbers
Layer 1 – The Physical LayerLayer 1 – The Physical Layer
The physical layer is concern with, literally, The physical layer is concern with, literally, the physical connections between the physical connections between machines that allows them to machines that allows them to communicatecommunicate
This layer is concerned with physical This layer is concerned with physical properties of communications devices --- properties of communications devices --- voltages, timing, etc.voltages, timing, etc.
Coaxial cable, twisted pair, fiber,…Coaxial cable, twisted pair, fiber,…
Layer 1 – the Physical LayerLayer 1 – the Physical Layer
A channel is a physical path between two A channel is a physical path between two machinesmachines
It can use several different forms of mediaIt can use several different forms of media
A brief theoretical analysis of data A brief theoretical analysis of data communicationscommunications
Ever wonder why we talk about data rates Ever wonder why we talk about data rates being limited by distance or the length of a being limited by distance or the length of a cable?cable?
Several factors can limit the bandwidth Several factors can limit the bandwidth and, therefore, the data rate of a and, therefore, the data rate of a communications channelcommunications channel
This is limited by the amplitude of the This is limited by the amplitude of the signalsignal
Layer 1 – The Physical LayerLayer 1 – The Physical LayerBandwidth is a characteristic of the Bandwidth is a characteristic of the communication mediumcommunication mediumUsing wire as an example, these include Using wire as an example, these include the length of the wire – longer wire - more attenuationthe length of the wire – longer wire - more attenuation The gauge of the wire – the thinner the wire the more The gauge of the wire – the thinner the wire the more
attenuationattenuation Heat, bend radii*,etc.Heat, bend radii*,etc. All transmission media attenuate different signal All transmission media attenuate different signal
frequencies at different amounts…frequencies at different amounts… With higher frequencies attenuated more than lower With higher frequencies attenuated more than lower
frequenciesfrequencies
Bandwidth (Hz) is the highest frequency at which Bandwidth (Hz) is the highest frequency at which at least 50% of power gets throughat least 50% of power gets through
Physical Layer - BandwidthPhysical Layer - Bandwidth
A bit of trivia (sort of)A bit of trivia (sort of) Traditionally phone wire has a bandwidth of Traditionally phone wire has a bandwidth of
about 1 Mhz for short runs of wireabout 1 Mhz for short runs of wire Telephone companies used low-pass filters to Telephone companies used low-pass filters to
cap the bandwidth at around 3100 Hzcap the bandwidth at around 3100 Hz OK for human speech, not much elseOK for human speech, not much else Limits communications data rates (more later)Limits communications data rates (more later) Why did they do this?Why did they do this? So how did we ever get 38.4Kbps, 56Kbps?So how did we ever get 38.4Kbps, 56Kbps?
Physical Layer -BandwidthPhysical Layer -Bandwidth
Nyquist at AT&T in 1920s theorized that Nyquist at AT&T in 1920s theorized that any communications channel has a any communications channel has a maximum possible data rate…maximum possible data rate…
That is a function of the bandwidth (Hz) of That is a function of the bandwidth (Hz) of the channel media…the channel media…
… … in the case of a perfect signal (no in the case of a perfect signal (no noise)noise)
Physical Layer Physical Layer
Nyquist’s theorem –Nyquist’s theorem –
Max data rate (in bps) = 2(Hz)LogMax data rate (in bps) = 2(Hz)Log2222
Where Hz is the signal bandwidth of the Where Hz is the signal bandwidth of the communication mediumcommunication medium
With a pure signal – no noiseWith a pure signal – no noise
Physical LayerPhysical Layer
……but what about noise…but what about noise…
……there’s always noisethere’s always noise
Noise is measured as the Signal to Noise Noise is measured as the Signal to Noise ratio S/Nratio S/N
Usually reported in decibels (dB)Usually reported in decibels (dB) dB = 10*LogdB = 10*Log1010(S/N)(S/N) So S/N = 10 … dB = 10So S/N = 10 … dB = 10 .. S/N = 1000 …dB = 30.. S/N = 1000 …dB = 30
Physical LayerPhysical Layer
Shannon (1948) introduced noise to Shannon (1948) introduced noise to Nyquist’s equation…Nyquist’s equation…
Max Data Rate (in bps) = Hz*LogMax Data Rate (in bps) = Hz*Log22(1+S/N)(1+S/N)
Where Hz is the bandwidth of the mediumWhere Hz is the bandwidth of the medium S = signal powerS = signal power N = noise powerN = noise power
Physical LayerPhysical Layer
So what does this mean?So what does this mean? That with an analog phone line…That with an analog phone line… ……with very little noise (say 30 dB S/N)with very little noise (say 30 dB S/N) You should never be able to transmit more You should never be able to transmit more
than about …than about … 30,000 bps30,000 bps Have you ever seen a 56Kbps modem?Have you ever seen a 56Kbps modem?
Classes of Transmission MediaClasses of Transmission Media
Guided Transmission MediaGuided Transmission Media Twisted pair Twisted pair Coaxial CableCoaxial Cable Fiber OpticsFiber Optics
Wireless Transmission MediaWireless Transmission Media RadioRadio MicrowaveMicrowave Iaser/infrared/millimeter waveIaser/infrared/millimeter wave SatelliteSatellite
Thought ExperimentThought Experiment
Imagine that you have a massive amount Imagine that you have a massive amount of data that you need to regularly transfer of data that you need to regularly transfer to and store at an off-site storage locationto and store at an off-site storage locationYou have to establish a system for You have to establish a system for transmitting the data to the storage transmitting the data to the storage location and you have to options-location and you have to options- Build a fiber optic network from your location Build a fiber optic network from your location
to the off-site location… orto the off-site location… or Have the data routinely transported by truckHave the data routinely transported by truck
Thought ExperimentThought Experiment
So, your question is –So, your question is –
What is the bandwidth (data rate) of the What is the bandwidth (data rate) of the highway?highway?
Thought ExperimentThought ExperimentSome parameters for your problemSome parameters for your problem You have about 200 Terabytes (~10You have about 200 Terabytes (~101212) of data ) of data
to transmit every dayto transmit every day A magnetic tape will hold about 200 Gbytes of A magnetic tape will hold about 200 Gbytes of
datadata Your 200 Tbytes will fit on about 1000 Your 200 Tbytes will fit on about 1000
magtapesmagtapes 1000 magtapes will fit in a large box, which 1000 magtapes will fit in a large box, which
will fit in the back of a carwill fit in the back of a car The storage location is one hour by car from The storage location is one hour by car from
your system locationyour system location
Thought ExperimentThought Experiment
So, what is the bandwidth of the highway?So, what is the bandwidth of the highway?
Suppose you choose to build the networkSuppose you choose to build the network How long will it take you to transmit your 200 How long will it take you to transmit your 200
Tbytes of data…Tbytes of data… On a 100 Mbs network?On a 100 Mbs network? On a 1 Gbps network?On a 1 Gbps network?
Guided Transmission MediaGuided Transmission Media
Twisted PairTwisted Pair Cable contains mutual pairs of wireCable contains mutual pairs of wire Each pair is twisted togetherEach pair is twisted together Wire acts as an antennae – radiating its signalWire acts as an antennae – radiating its signal Wires twisted together tend to cancel out the Wires twisted together tend to cancel out the
radiated signals.radiated signals.So less cross-talk from other signals…So less cross-talk from other signals…… … less noise…less noise…Greater effective bandwidth in the mediumGreater effective bandwidth in the medium
Don’t untwist the conductor pairs!Don’t untwist the conductor pairs!
Twisted Pair CableTwisted Pair Cable
Two typesTwo types UTP – Unshielded Twisted PairUTP – Unshielded Twisted Pair
Multiple twisted pairs of conductors in an insulation Multiple twisted pairs of conductors in an insulation jacketjacket
STP – Shielded Twisted PairSTP – Shielded Twisted PairJust like UTP except the bundle of conductors are Just like UTP except the bundle of conductors are wrapped in a metal braided jacket, then an out wrapped in a metal braided jacket, then an out insulation jacketinsulation jacketUsed by IBM, primarily for Token Ring (802.5), and Used by IBM, primarily for Token Ring (802.5), and few other thingsfew other thingsNot popular outside of IBM systemsNot popular outside of IBM systems
Twisted Pair CableTwisted Pair CableCategory 3 (Cat3)Category 3 (Cat3) Early network cablingEarly network cabling 3 to 4 twists per foot3 to 4 twists per foot Up to 16MHzUp to 16MHz Low speed applicationsLow speed applications Still used for structured telephone wiringStill used for structured telephone wiring
Category 5 (Cat5)Category 5 (Cat5) 3 to 4 twists per inch3 to 4 twists per inch Reduces cross-talk noiseReduces cross-talk noise Up to 100 MhzUp to 100 Mhz Widely usedWidely used
Twisted Pair CablingTwisted Pair Cabling
Category 5e (Cat5e)Category 5e (Cat5e) More twists per inchMore twists per inch Can be used for Gigabit Ethernet using all four pairsCan be used for Gigabit Ethernet using all four pairs
Category 6 (Cat6)Category 6 (Cat6) Supports Gigabit Ethernet using four pairsSupports Gigabit Ethernet using four pairs GigE at higher speeds than Cat5eGigE at higher speeds than Cat5e
Category 7 (Cat7) – still in developmentCategory 7 (Cat7) – still in development Different connectorDifferent connector 1.2 GHz bandwidth1.2 GHz bandwidth
Twisted PairTwisted Pair
See See http://www.infocellar.com/networks/cables/twihttp://www.infocellar.com/networks/cables/twi
sted-pair-cables.htmsted-pair-cables.htm
Note TIA-568 BNote TIA-568 B
Coaxial CableCoaxial Cable
Coax – two common typesCoax – two common types 50 ohm coax – intended for digital 50 ohm coax – intended for digital
communicationscommunications 75 ohm coax – intended for analog 75 ohm coax – intended for analog
communications, cable TVcommunications, cable TV With cable Internet service 75 is often used With cable Internet service 75 is often used
for digital communicationsfor digital communications
Coaxial CableCoaxial Cable
Coax – center conductor surrounded by a Coax – center conductor surrounded by a relatively large insulator…relatively large insulator…
Encased in a braided conductor…Encased in a braided conductor…
… … the outside insulation jacketthe outside insulation jacket
From Tanenbaum, 2003
Coaxial CableCoaxial Cable
Very good noise immunityVery good noise immunity
High bandwidth – around 1GHzHigh bandwidth – around 1GHz
Bandwidth sensitive to quality of Bandwidth sensitive to quality of terminationsterminations