NT1210 Introduction to Networking

Unit 4:

Chapter 4, Transmitting Bits

1

Objectives

Differentiate among major types of LAN and WAN technologies 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 necessary configurations to enable desired connectivity and controls.

 Explain the fundamentals of electrical circuits.

Identify different types of physical cabling.

2

Transmitting Bits: Communication Analogy

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

3

Sending Bits with Electricity and Copper Wires: Electrical Circuits

Electrical 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; must be good electrical conductor (e.g., copper wire).

Figure 4-2Simple Direct Current Circuit Using a Battery4

Sending Bits with Electricity and Copper Wires: Electrical Circuits

Direct Current (DC) electrical circuits

Electrical current: Amount of electricity that flows past single 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 Circuit5

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

DC 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 -1

volt (1 volt, but in opposite direction), repeating over time. Resulting AC wave: Sine wave

Figure 4-4Graphs of 1 Volt (Y-Axis) over time: DC (Left) vs AC (Right)6

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

To send data, networking Physical layer standards can change amplitude, frequency, phase, period of AC electrical signal.

Figure 4-5Graphs of AC Circuit: Amplitude, Period, Frequency7

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

Figure 4-6Encoding Options: Frequency, Amplitude, and Phase Shifts8

• Frequency is the rate of change with respect to time.

• Change in a short span of time

means high frequency.

• Change over a long span of time means low frequency.

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

Table 4-1Common Features Used by Encoding Schemes9

Wave Feature

Definition of the GraphElectrical Feature it Represents

AmplitudeMaximum height of the curve over the centerline.

Voltage

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

Speed with which current alternates directions.

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 again.

Frequency and period in Time

• Frequency and period are the inverse of each other.

Comparison of analog and digital signals

Sending Bits with Electricity and Copper Wires: Circuit Bit Rates

Bit rate (link speed): Defines number of bits sent over link per second (bps).

Impacts how nodes send data over circuit.

Figure 4-10Example where Encoder Changes Signal Every Bit Time12

Sending Bits with Electricity and Copper Wires: Using Multiple Circuits

Simplex 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/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 Direction13

Sending Bits with Electricity and Copper Wires: Problems with Electricity

Noise: Electro-Magnetic Interference (EMI)

Cables help prevent effects of EMI in many ways, including 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

Ethernet standards limit copper links to 100 meters.

Very important when designing network.

14

Sending Bits with Electricity and Copper Wires: LAN Standards Progression

Ethernet has long history (developed in 1970s and is still used today).

IEEE 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 Standards15

Transmission medium and physical layer

Classes of transmission media

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

10Base-T, 100Base-T & 1000Base-T uses Unshielded Twisted Pair (UTP).

Cable 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 install.

Supports full-duplex.

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

18

Twisted-pair cable

UTP and STP cables

UTP connector

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

Ethernet standards allow use of RJ-45 connectors on twisted pair cable and matching RJ-45 ports (sockets) on NICs, switch ports, and other devices.

Again, RJ-45 connectors and ports accommodate 8 wires (pins) in single row.

Figure 4-15Example RJ-45 Connectors and Sockets22

Sending Bits with Electricity and Copper Wires: Cable Pinouts

Pinouts: 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 Numbers23

Sending Bits with Electricity and Copper Wires: Cable Pinouts

Straight-through: Each wire connects to the same pin number on both ends of the cable.

Figure 4-17Conceptual Drawing of Straight-Through Cable24

Sending Bits with Electricity and Copper Wires: Cable Pinout Standards

Ethernet 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 Cable25

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

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

NOTE: 568B switches green and orange wires.

2.27

Figure 7.7 Coaxial cable

Break

28

Take 15

Sending Bits with Light and Fiber Optic Cables

Fiber optics transmission like turning light switch on and off: ON = 1, OFF = 0.

Endpoints agree to use same speed and same basic encoding scheme.

Figure 4-20Encoding Bits Using Light On/Off29

Fiber construction

Sending Bits with Light and Fiber Optic Cables

Fiber cables contain several parts that wrap around glass or plastic fiber core.

Core is about as thin as human hair.

Fiber 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 to transmit data.

Figure 4-21Components of a Fiber Optic Cable31

Optical fiber

2.33

Figure 7.12 Propagation modes

Sending 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 direction.

Fiber cables come in two major categories: Multimode (MM), single mode (SM).

Multimode have larger cores and work best with LED transmitters.

Single 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

Sending Bits with Light and Fiber Optic Cables: Ethernet LANs

Fiber cables do not create EMI. Fiber links more secure. Example: Typical campus

LAN has employees in two buildings in office park that sit 150 meters apart, which exceeds Ethernet standards for copper cabling. However, multimode links can run past 200 meters.

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

Sending Bits with Light and Fiber Optic Cables: WAN Links

Synchronous Optical Network (SONET): One of longer-established standards for WAN links.

SONET defines series of Physical layer standards for data transmission over optical links.

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

SONET Optical Carrier (OC) Names and (Rounded) Line Speeds Table 4-236

Name (Rounded) Line Speed

OC-1 52 Mbps

OC-3 155 Mbps

OC-12 622 Mbps

OC-24 1244 Mbps

OC-48 2488 Mbps

OC-96 4976 Mbps

OC-192 9952 Mbps

7-2 UNGUIDED MEDIA: WIRELESS7-2 UNGUIDED MEDIA: WIRELESS

Unguided media transport electromagnetic waves Unguided media transport electromagnetic waves without using a physical conductor. This type of without using a physical conductor. This type of communication is often referred to as wireless communication is often referred to as wireless communication.communication.

Wireless transmission waves

Sending Bits with Radio Waves and No Cables: Radio Basics

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

Sending Bits with Radio Waves and No Cables: Radio Basics

Three 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

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, period, wavelength.

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

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

9.41

CELLULAR TELEPHONYCELLULAR TELEPHONY

Cellular telephonyCellular telephony is designed to provide is designed to provide communications between two moving units, communications between two moving units, called mobile stations (MSs), or between called mobile stations (MSs), or between one mobile unit and one stationary unit, one mobile unit and one stationary unit, often called a land unit. often called a land unit.

9.42

Figure 16.1 Cellular system

Typical Radius = 1-12 miles

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

Steps 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).

3. Phone sends (encodes) bits as 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).

43

Sending Bits with Radio Waves and No Cables: WAN Standards

Mobile Wireless Standards and Terms Table 4-3

Gen Umbrella StandardOther Terms Related to Generation

Standards Body

2GGSM (Global System for Mobile Communications)

TDMA, CDMA ETSI

3GIMT-2000 (International Mobile Telecommunications-2000)

UTMS ITU

4G

IMT-Advanced (International Mobile Telecommunications - Advanced)

LTE, Wi-MaxITU, ETSI, IEEE

44

Mobile phone Standard

• GSM: Global System for Mobiles

• CDMA: Code Division Multiple Access

• UMTS: Universal Mobile Telephone System

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

Wireless 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 tower.

All wireless user devices communicate through AP.

A Small Wireless LAN with One Access Point (AP) Figure 4-3346

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

Wireless 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 4-3747

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

WLAN Standards and Speeds Table 4-4

IEEE WLAN Standard

Maximum Stream Rate (Mbps)

Frequency Range

Number of Non-overlapping Channels

802.11b 11 2.4 GHz 3

802.11a 54 5 GHz 23

802.11g 54 2.4 GHz 3

802.11n 72 5 GHz 21

802.11n* 150 5 GHz 9

802.11ac** 1000 Plus 5 GHz 12

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

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

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Unit 4 Assignment

• Complete the following tasks using the Chapter Review Activities at the end of Chapter 4 in the Odom textbook (answers can be found in the textbook):

• Respond to the multiple-choice questions.

• Complete the Define Key Terms table.

Unit 4 Lab

• Complete all Labs in Chapter 4 of the lab book.