NT1210 Introduction to NetworkingNT1210 Introduction to ...€¦ · NT1210 Introduction to...

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NT1210 Introduction to Networking NT1210 Introduction to Networking Unit 4: Chapter 4, Transmitting Bits Chapter 4, Transmitting Bits 1

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NT1210 Introduction to NetworkingNT1210 Introduction to Networking

Unit 4:Chapter 4, Transmitting BitsChapter 4, Transmitting Bits

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ObjectivesObjectives

Differentiate among major types of LAN and WAN g j yptechnologies and specifications and determine how each is used in a data network.

Explain basic security requirements for networks.

Install a network (wired or wireless), applying all fi ti t bl d i d ti itnecessary configurations to enable desired connectivity

and controls.

Explain the fundamentals of electrical circuitsExplain the fundamentals of electrical circuits.

Identify different types of physical cabling.

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ObjectivesObjectives

Identify wireless network communication needs.y

Distinguish among the different needs for wired and wireless networks.

Classify Layer 2 networking components used in a typical LAN.

Compare and contrast advantages and disadvantages of network media.

Use basic troubleshooting techniques to ensure network connectivity at Layers 1 and 2.

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Transmitting Bits: Communication Analogy

Wh t f i d t lk t lk hil th li t dWhen two friends talk, one talks while other listens and understands (we hope!).

Speaker makes sounds that travel through air toSpeaker makes sounds that travel through air to listener’s ears.

Sounds have no meaning unless each person’s brainSounds have no meaning unless each person s brain works to interpret those sounds.

In networks, nodes send data to each other over link: Sending node acts like person talking; receiving node acts like person listening.

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Transmitting Bits: Communication Analogy

G l id f h TCP/IP t k f d IP k t fGeneral idea of how a TCP/IP network forwards IP packets from one host to another: Nodes (routers in this example) each make a choice of where to send the packet next so the data arrives at the correct destination Always keep the big goal of the network in mind: Deliveringdestination. Always keep the big goal of the network in mind: Delivering data from the source to the destination.

Figure 4-1Sending Data Through a Network of Nodes and Links5

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Electrical Circuits

El t i l i it t i t l t l fElectrical circuit must exist as complete loop of material (medium) over which electricity can flow.

Material used to create circuit can’t be just any material;Material used to create circuit can t be just any material; must be good electrical conductor (e.g., copper wire).

Figure 4-2Simple Direct Current Circuit Using a Battery6

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Electrical Circuits

Di t C t (DC) l t i l i itDirect Current (DC) electrical circuitsElectrical current: Amount of electricity that flows past single point on circuit (amount of electron flow in circuit).point on circuit (amount of electron flow in circuit).

Current always flows away from negative (-) lead in circuit and towards positive (+) lead.

Figure 4-3Powering a Light Bulb with a DC Circuit7

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Frequency, Amplitude, Phase

DC i it ( l ft) d AC i it ( i ht) b th 1 ltDC circuit (on left) and AC circuit (on right) both use 1 volt.DC shows constant +1 volt signal.AC circuit slowly rises to +1 volt falls to 0 then falls to 1AC circuit slowly rises to +1 volt, falls to 0 then falls to -1 volt (1 volt, but in opposite direction), repeating over time.Resulting AC wave: Sine waveg

Figure 4-4Graphs of 1 Volt (Y-Axis) over time: DC (Left) vs AC (Right)8

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: AC Frequency, Amplitude, Phase

T d d t t ki Ph i l l t d dTo send data, networking Physical layer standards can change amplitude, frequency, phase, period of AC electrical signalg.

Figure 4-5Graphs of AC Circuit: Amplitude, Period, Frequency9

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: AC Frequency, Amplitude, Phase

M t l d i t ki di hMost commonly used in networking encoding schemes.

One signal used by encoding scheme means binary 0, other means binary 1other means binary 1.

Figure 4-6Encoding Options: Frequency, Amplitude, and Phase Shifts10

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Sending Bits with Electricity and Copper Wires:Sending Bits with Electricity and Copper Wires: AC Frequency, Amplitude, Phase, PeriodWave Electrical Feature itWave Feature

Definition of the GraphElectrical Feature it Represents

AmplitudeMaximum height of the curve over the centerline

Voltage over the centerline.

FrequencyNumber of complete waves (cycles) per second (in Hertz).

Speed with which current alternates directions.V l j hi h k

Phase Single location in repeating wave. Voltage jumps, which makes signal graph jump to new phase.

PeriodTime (width on x-axis) for one complete wave to complete.

Time for voltage to change from maximum positive voltage back to same point

Table 4-1Common Features Used by Encoding Schemes11

p p g pagain.

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Network Cabling

B f d d d t it d t t i itBefore a node can send data, it needs to create a circuit between itself and the destination node.Copper cable has outer plastic cover (jacket) that holdsCopper cable has outer plastic cover (jacket) that holds wires (conductors).Sending/receiving nodes use a pair of wires connected at their ends to create circuit.

Figure 4-7Photo of Wires Inside a Networking Cable12

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Network Cabling Example

C bl h 4 i f i 2 d 2 dCable has 4 pairs of wires: 2 used, 2 unused.Hardware of each node must agree which wires to use and which to ignoreand which to ignore.For wires chosen to use, nodes loop ends together to create a circuit.

Figure 4-8Physical Components to Create an Electrical Circuit Between Two Nodes13

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Network Cabling

L ( i it) ’t t i it b it lf thi hLoop (circuit) can’t create circuit by itself: something has to create electrical current.Transmitting node creates electrical signal changingTransmitting node creates electrical signal, changing signal over time to encode different bit values.Transmitter: Part of node that sends data.Receiver: Part that listens for signal of incoming bits.

Figure 4-9Transmitter Generating a Current to Send; Receiver Sensing Current to Receive14

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Circuit Bit Rates

Bit t (li k d) D fi b f bit t li kBit rate (link speed): Defines number of bits sent over link per second (bps).

Impacts how nodes send data over circuitImpacts how nodes send data over circuit.

Example of how bit rate and encoding scheme work together: Bit rate = 10 bps; encoding scheme states thattogether: Bit rate 10 bps; encoding scheme states that binary 1 should be +2 volts and binary 0 as +1 volts.

Figure 4-10Example where Encoder Changes Signal Every Bit Time15

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Encoding Scheme

W k lik l D fi l t i l i l t f 1’Works like language: Defines electrical equivalent of 1’s and 0’s.

Different frequencies represent binary 1’s and 0’sDifferent frequencies represent binary 1 s and 0 s.

Example sending 1010: Lower frequency represents binary 1, higher frequency represents binary 0.binary 1, higher frequency represents binary 0.

Figure 4-11Frequency Shift Keying: Low Frequency = 1, High Frequency = 016

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Manchester Encoding Scheme

U d l Eth t t kUsed on some early Ethernet networks.Does not choose one electrical signal at beginning of bit time instead changes signal in middle of bit timetime, instead changes signal in middle of bit time.Follows this logic:

To encode 0: Start high, and transition low in the middle of bit time.To encode 1: Start low, and transition high in the middle of bit time.

Figure 4-12Manchester Encoding: 0 = High-to-Low, 1 = Low-to-High17

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Using Multiple CircuitsSimplex transmissions are one way: If encoding schemeSimplex transmissions are one way: If encoding scheme works in only one direction (on single circuit):

Devices must take turns using that circuit or …

Devices must use different circuits for each direction.

Half-duplex transmissions take turns: Node1 sends while Node2 listens; when Node1 finishes, Node2 sends while Node1 listens.

Full duplex transmissions can send/receiveFull duplex transmissions can send/receive simultaneously: Both endpoints can send at same time because they use multiple wire pairs.

Figure 4-13Full Duplex Using Two Pair, One for Each Direction18

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Using Multiple Circuits

Figure 4-13Full Duplex Using Two Pair, One for Each Direction19

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Problems with Electricity

N i El t M ti I t f (EMI)Noise: Electro-Magnetic Interference (EMI)Cables help prevent effects of EMI in many ways, including shielding.shielding.

Twisting of wire pairs creates “cancellation” effect to help stop EMI effect.

Attenuation: Signals fade away over distance to point where devices can’t interpret individual bits

Eth t t d d li it li k t 100 tEthernet standards limit copper links to 100 meters.

Very important when designing network.

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Unshielded Twisted Pair (UTP)

10B T 100B T & 1000B T U hi ld d10Base-T, 100Base-T & 1000Base-T uses Unshielded Twisted Pair (UTP).Cable contains twisted pairs of wires and no addedCable contains twisted pairs of wires and no added shielding materials.Twisting reduces EMI effects between pairs in same jacket and in nearby cables.Lack of shielding makes cables less expensive, lighter, easier to installeasier to install.Supports full-duplex.

Note: Twisted pair cables with shielding are called p gShielded Twisted Pair (STP).

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: LAN Standards Progression

Eth t h l hi t (d l d i 1970 d iEthernet has long history (developed in 1970s and is still used today).IEEE standardized Ethernet in 802 3 standard in earlyIEEE standardized Ethernet in 802.3 standard in early 1980s.Has added many more Ethernet standards since then.Each standard took years to grow in marketplace and eventually drive prices down.

Figure 4-14Timeline of the Introduction of Ethernet Standards22

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: RJ-45 Connectors, Ports

Eth t t d d ll f RJ 45 tEthernet standards allow use of RJ-45 connectors on twisted pair cable and matching RJ-45 ports (sockets) on NICs, switch ports, and other devices., p ,Again, RJ-45 connectors and ports accommodate 8 wires (pins) in single row8 wires (pins) in single row.

Figure 4-15Example RJ-45 Connectors and Sockets23

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Cable Pinouts

Pi t H h i i bl h ld b t dPinouts: How each wire in cable should be connected to each pin in connector according to Ethernet standards.Wires must be in correct order so correct wires in twisted pair send to correct direction.

Figure 4-16Wires, Connector Pin numbers, and Socket Pin Numbers24

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Cable PinoutsSt i ht th h E h i t t th iStraight-through: Each wire connects to the same pin number on both ends of the cable.

Figure 4-17Conceptual Drawing of Straight-Through Cable25

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Cable Pinout Standards

Eth t TIA (T l i ti I d tEthernet uses TIA (Telecommunications Industry Association) standards to define specific wires to use for pinouts.

UTP cables have four pairs of wires, each using a different color: green, blue, orange, brown.

Each pair has 1 wire with solid color and other one with white stripe.

Figure 4-18TIA Cable Pinouts – T568A On Each End Creates a Straight-Through Cable26

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Cable Pinout Standards—568A/568B

NOTE: 568B switches green and orange wires.

Figure 4-18TIA Cable Pinouts – T568A On Each End Creates a Straight-Through Cable27

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Sending Bits with Electricity and CopperSending Bits with Electricity and Copper Wires: Cable Pinout Standards

UTP bl ith f i (8 i ) t f i itUTP cable with four pairs (8 wires) can support four circuits.10Base-T and 100Base-T only use two pairs.

NOTE: 1000BaseT uses all 4 wire pairsNOTE: 1000BaseT uses all 4 wire pairs.Ethernet uses following rules for creating circuits:

One pair at pins 1 and 2One pair at pins 3 and 6

Figure 4-19PC NIC Transmitting on Pair at 1,2, Receiving on Pair 3,628

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Break

Take 15

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables

Fib ti t i i lik t i li ht it h dFiber optics transmission like turning light switch on and off: ON = 1, OFF = 0.Endpoints agree to use same speed and same basicEndpoints agree to use same speed and same basic encoding scheme.

Figure 4-20Encoding Bits Using Light On/Off30

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables

Fib bl t i l t th t dFiber cables contain several parts that wrap around glass or plastic fiber core.

Core is about as thin asCore is about as thin as human hair.

Fiber breaks easily withoutFiber breaks easily without some type of support.

Core and cladding have direct effect on how light travels down cable.

Optical transmitter (laser or LED) shines light into core t t it d tto transmit data.

Figure 4-21Components of a Fiber Optic Cable31

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables

Cladding surrounds core for entire length of cableCladding surrounds core for entire length of cable.Reflects light back into coreLight waves reflect off cladding back into core until light waves reach other end of cablereach other end of cable

Fiber optic cables work well to send light in one direction at time, but not two.Cable acts like dark tunnel so nodes can easily see light coming through cablenodes can easily see light coming through cable.

If both ends try to shine light and look for light at same time, couldn’t tell whether light is coming from local or remote node.

Figure 4-22Cladding Reflecting the Light Back into the Fiber Optic Cable’s Core32

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables

Instead of using one fiber cable for half-duplexInstead of using one fiber cable for half-duplex communication, most fiber links use pair of cables so can use full-duplex.

Each fiber NIC, port, interface, etc., has interface with two sockets: One for send cable, one for receive cable.

Each node’s transmit socket must connect to same cable as other node’s receive socket.same cable as other node s receive socket.

NOTE: In addition to sending data using light over cables, fiber technology also includes free space optics (e.g., TV remote) which sends light through air; requires line of sightwhich sends light through air; requires line-of-sight.

Figure 4-23Two Fiber Optic Cables, with Connectors33

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables: Transmitters

Key technical difference between LEDs and lasers: LEDs shine light in multiple directions; lasers shine in one directiondirection.Fiber cables come in two major categories: Multimode(MM), single mode (SM).( ) g ( )Multimode have larger cores and work best with LED transmitters.Si l d h llSingle mode have smaller diameter cores and work best with laser transmitters.

Figure 4-24LEDs with Multiple Modes (Angles), and Lasers, with a Single Mode (Angle)34

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables: Ethernet LANs

Fib bl d t t EMIFiber cables do not create EMI.Fiber links more secure.Example: Typical campusExample: Typical campus LAN has employees in two buildings in office park that sit 150 meters apart, which exceeds Ethernet standards for copper ppcabling. However, multimode links can run past 200 meters.

Figure 4-25Typical Use of Fiber Optics in a LAN: Links Between Neighboring Buildings35

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables: WAN LinksTelcos and ISPs that support WAN services use fiber optics becauseTelcos and ISPs that support WAN services use fiber optics because they service businesses that sit far apart. To do this, Telco/ISP must have a link from the customer to the Telco central office (CO) or ISP Point of Presence (POP)Point of Presence (POP).

Figure 4-26Two Perspectives on a Leased Line36

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables: WAN Links

E l Fib th t t i t i CO t thExample: Fiber that connects equipment in CO to other Telco sites (called core sites).

COs sit at edge sites of Telco network and have links to core gsites.Physical locations include office buildings withoffice buildings with server rooms.In this figure, all links use fiber except links fromfiber except links from CO to customer routerwhich use copper.

Figure 4-27Fiber Links Used to Help Create a Telco Network37

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Sending Bits with Light and Fiber OpticSending Bits with Light and Fiber Optic Cables: WAN Links

S h O ti l N t k (SONET) O f lSynchronous Optical Network (SONET): One of longer-established standards for WAN links.SONET defines series of Physical layer standards forSONET defines series of Physical layer standards for data transmission over optical links.

Name (Rounded) Line Speed OC-1 52 Mbps

Uses hierarchy of speeds that are multiples of base speed (51.84 Mbps) plus

pOC-3 155 Mbps OC-12 622 Mbps OC-24 1244 Mbpsp ( p ) p

some overhead.OC-24 1244 Mbps OC-48 2488 Mbps OC-96 4976 Mbps OC 192 9952 Mb

SONET Optical Carrier (OC) Names and (Rounded) Line Speeds Table 4-238

OC-192 9952 Mbps

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: Radio Basics

Radio stations broadcast signals so anyone near enough toRadio stations broadcast signals so anyone near enough to station’s large antenna (radio tower) can hear broadcast.Radio tower sends electricity through antenna to create radio waves.More electrical power creates stronger radio waves that can travel longer distancescan travel longer distances.Radio tower sends signals upward because radio waves bounce off ionosphere (one of layers of Earth’s atmosphere).Bouncing radio waves off ionosphere lets radio waves reach wider areareach wider area.

A Radio Station Broadcasting a Radio Signal to a Car Radio Figure 4-2839

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: Radio Basics

A Radio Station Broadcasting a Radio Signal to a Car Radio Figure 4-2840

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: Radio Basics

El t ti di ti (ER) D ib d iElectromagnetic radiation (ER): Described using electromagnetic spectrum conceptual modelThese types of energy travel as waves so have specificThese types of energy travel as waves, so have specific wavelength.Spectrum categorizes energy based on wavelength.

Radio waves make up one category in EM spectrum.Other parts include visible light, X-rays, microwaves.

Radio waves work well for networking because can beRadio waves work well for networking because can be changed (modulated) over time to send data.

A Radio Station Broadcasting a Radio Signal to a Car Radio Figure 4-2841

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: Radio Basics

Th f t i k i t b t h diThree facts summarize key points about why radio can be used to wirelessly send data.1. Radio waves have energy level that moves up and down over gy p

time, so when graphed, waves look like sine wave.2. Radio waves can be changed and sensed by networking

devices, including changes to frequency, amplitude, phase, , g g q y, p , p ,period, wavelength.

3. EM energy does not need physical medium to move.

A Radio Station Broadcasting a Radio Signal to a Car Radio Figure 4-2842

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WANs—Mobile Phones & Voice

M bil t k id tMobile network provider creates its own network.

But most phone users want toBut most phone users want to communicate with more phones than just those on same mobile company’s network, as well as landline phones.

Enter the Public SwitchedEnter the Public Switched Telephone Network (PSTN)

Major Components in the Mobile Phone Network Model Figure 4-2943

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WANs—Mobile Phones & Voice

M t bil h t di it l hMost mobile phones act as digital phones.Send and receive digits (bits) that represent voice traffic.

To transmit bits phones use wireless radio technologyTo transmit bits, phones use wireless radio technology.Phone sends bits encoded as radio waves to nearby radio antenna on tower owned by mobile phone company.

Connecting a Mobile Phone Call through a Radio Tower to the Telco Network Figure 4-3044

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WANs—Mobile Phones & VoiceSt t l ll bil hSteps to place call on mobile phone:1. Person speaks creating sound waves (as usual).2. Phone converts sound waves into bits (as with all digital phones).2. Phone converts sound waves into bits (as with all digital phones).3. Phone sends

(encodes) bits as radio wavesas radio waves through air towards cell tower.

4. Radio equipment at tower receives (decodes) radio waves back into original bits.

5 Rest of trip uses various technology (details not included here)5. Rest of trip uses various technology (details not included here).

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WANs—Mobile Phones & Data

R di li k h t d t i j t itRadio link on phone supports data service just as it does for voice.When sending or receiving data phone passes bitsWhen sending or receiving data, phone passes bits using radio waves between itself and radio tower.Phone encapsulates data.To support data applications, mobile network connects to Internet and any other networks that support data apps requested by userapps requested by user.

Mobile network forwards data to correct destination in Internet, not through PSTN.

Smart Phone: Using Radio to Forward Bits to the Tower, and then to the Internet Figure 4-3146

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WANs—Mobile Phones & DataSt i i I t t i bil hSteps in accessing Internet via mobile phone:1. Person types URL or taps hyperlink.2. Phone encapsulates HTTP request into IP packet, then Data Link2. Phone encapsulates HTTP request into IP packet, then Data Link

layer frame.3. Phone sends (encodes) frame’s bits as radio waves towards cell

tower.tower.4. Radio equipment at

tower receives (decodes) radio(decodes) radio waves back into original bits.

5 Equipment near cell tower forwards bits into Internet as for any IP5. Equipment near cell tower forwards bits into Internet as for any IP packet.

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WANs—Other Mobile Devices

L t t bl t t t t kLaptops, tablets can connect to same network as mobile phone.Laptops typically need wireless NIC that supplies radioLaptops typically need wireless NIC that supplies radio to connect to network radio towers.Also need contract with mobile provider for connectivity to wireless network.

Using the Wireless WAN (Mobile Network) from Computers Instead of Phones Figure 4-3248

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WAN Standards

Gen Umbrella StandardOther Terms Related to Generation

Standards BodyGeneration

2G GSM (Global System for Mobile Communications) TDMA, CDMA ETSI

IMT-2000 (International3G

IMT-2000 (International Mobile Telecommunications-2000)

UTMS ITU

IMT-Advanced

4G (International Mobile Telecommunications -Advanced)

LTE, Wi-Max ITU, ETSI, IEEE

Mobile Wireless Standards and Terms Table 4-349

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WLANs—Devices & Topology

Wi l LAN d i dWireless LAN devices need WLAN Network Interface Card (NIC).( )

Gives PC ability to connect WLAN

Uses radio antenna that allows NIC to send and receive data

Most WLANs use Access Points (AP) which are small devices that acts like small radio towerdevices that acts like small radio tower.

All wireless user devices communicate through AP.

A Small Wireless LAN with One Access Point (AP) Figure 4-3350

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WLANs—Devices & TopologyWLAN ith AP t WLAN B i S i S t (BSS) I BSSWLAN with AP creates a WLAN Basic Service Set (BSS). In a BSS, all communications happen with the AP, much like it does in the wireless WAN model.

A WLAN AP Bridges Between the WLAN and an Ethernet LAN Figure 4-3451

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WLANs—Sending DataF t WLAN t d d th di h f fFor most WLAN standards, the encoding scheme uses some form of amplitude shift keying or phase shift keying, which changes the amplitude or phase (respectively) to represent a 0 or 1.

Amplitude and Phase Shift Basic Examples Figure 4-3552

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WLANs—Typical Problems

AP it d t l d k ( di d tAP sits under metal desk (radio waves do not pass through metal very well).AP sits next to other equipment and cables thatAP sits next to other equipment and cables that interfere (EMI).AP sits on wrong side of interior wall away from end user devices.

A WLAN with Possible Sources of Interference Figure 4-3653

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WLANs—TransmissionWi l LAN t k t b i l ll d C i S M lti lWireless LANs take turns by using rules called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). This technology is similar to wired Ethernet’s CSMA/CD.

CSMA/CA Process Figure 4-3754

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WLANs—Transmission

St 1 All d i i d d t d it ti ifStep 1: All devices use independent random wait time if they have data to send.

Step 2: When particular device completes its wait timer itStep 2: When particular device completes its wait timer, it sends data.

Sender lists time it estimates is needed to send data (in (milliseconds) so other devices know how long WLAN will be in use.

Step 3: Receiving device shows required ACKStep 3: Receiving device shows required ACK (acknowledgement) to confirm data received.

Step 4: ACK triggers silence on WLAN.Step 4: ACK triggers silence on WLAN.

CSMA/CA Process Figure 4-3755

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: WLAN IEEE Standards

Maximum Number of Non-IEEE WLAN Standard

Maximum Stream Rate (Mbps)

Frequency Range

Number of Non-overlapping Channels

802.11b 11 2.4 GHz 3802.11a 54 5 GHz 23802.11g 54 2.4 GHz 3802.11g 54 2.4 GHz 3802.11n 72 5 GHz 21802.11n* 150 5 GHz 9802.11ac** 1000 Plus 5 GHz 12

• * When using bonded 40 MHz channel, instead of 20 MHz channel (as used by other standards outlined in table).

WLAN Standards and Speeds Table 4-4

)• ** http://www.radio-electronics.com/info/wireless/wi-fi/ieee-802-11ac-gigabit.php

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Sending Bits with Radio Waves and NoSending Bits with Radio Waves and No Cables: Example EnterpriseMany corporate campus LANs have both wired and wireless LAN supportMany corporate campus LANs have both wired and wireless LAN support on each floor. The WLAN connects to the same Ethernet network as the wired network does so all devices in the two building can communicate.

Campus LAN: Wireless Devices, Wired Desktops, and Fiber Trunks Figure 4-3857

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Summary, This Chapter…Looked at the details of how to move bits from one nodeLooked at the details of how to move bits from one node to the next node in a network.Focused on moving bits over a single link.Looked at how to move bits using copper wires and electricity.E plained the f ndamentals of ho electricit can beExplained the fundamentals of how electricity can be graphed.Discussed fiber optics.pCompared and contrasted the two common types of fiber optic transmitters and two general categories of fiber

ti bloptic cables.

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Summary, This Chapter…Listed common reasons for using fiber optic cablesListed common reasons for using fiber optic cables instead of copper cables in networks.Drew a diagram of the relationships between mobile phones, mobile phone radio towers, the mobile network, the worldwide telephone network, the Internet, home telephones, and web servers in the Internet.telephones, and web servers in the Internet.Concluded by introducing the basics of Wireless LANs. Compared and contrasted mobile phones, mobile

di t i l LAN NIC d i lcompany radio towers, wireless LAN NICs, and wireless LAN Access Points.Created an example demonstrating how devices share a p gwireless LAN using CSMA/CA.

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Questions? Comments?

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