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