CCNA – Semester1

Module 3Networking Media

Objectives

• Copper media and electronic signal

• Optical media and light signal

• Wireless media and wave

Copper Media

Electricity Basics

The basic unit of all matter is an atom.– Protons – particles that

have positive charge

– Neutrons – particles that have no charge (neutral)

– Electrons – particles that have negative charge and orbit the nucleus

Static electricity

• Electrons have been loosened from the atom and stay in one place, without moving.

• Electrostatic discharge (ESD).– ESD, though usually

harmless to people, can create serious problems for sensitive electronic equipment.

free electron

Measuring electricity: Current

• The flow of charges that is created when electrons move.

• Symbol: I.

• Ampere (A).

Electrical definitions: AC and DC

• Alternating Current (AC): – Electrical current flows in both directions; positive and

negative terminals continuously trade places (polarity).

• Direct Current (DC): – Electrical current flows in one direction; negative to

positive.

Measuring electricity: Resistance

• Resistance: property of a material that opposes the electrical flow.

• Resistance consume electrical energy and cause attenuation.

• Symbol: R.

• Ohm (Ω).

• Impedance: total opposition to the current.

• Symbol: Z.

• Ohm (Ω).

Measuring electricity: Voltage

• Force or pressure caused by the separation of electrons and protons.

• Symbol: U.

• Volt (V).

Basic Circuit

• Source

• Complete path

• Load

Oscilloscope

• Graphs voltage over time

• X-axis represents T, Y-axis represents V

Electrical definitions: Ground

• Ground can refer to the place on the earth.

• Ground can also mean the reference point, or the 0 volts level, when making electrical measurements.

Cable Specifications

• What speeds for data transmission can be achieved using a particular type of cable?

• What type of transmission is being considered? Will the transmissions be digital or will they be analog-based?

• How far can a signal travel through a particular type of cable before attenuation of that signal becomes a concern?

Ethernet Specifications

• 10BASE-T

• 10BASE5

• 10Base2

Coaxial Cable

• If not properly grounded, shielding is very poor.• Speed of transmission:10-100Mpbs• Longer cable runs than UTP & STP.• Maximum cable length :

– Thin cable : 185 m.– Thick cable : 500 m.

• Impedance: 50Ω.

Shielded Twisted-Pair Cable

• Protection from all types of external interference, include EMI and RFI.– Cancellation: twisting of wires.– Shielding.

• Moderately expensive, quite difficult to install.• Speed of transmission:10Mpbs-1Gbps• Maximum cable length 100m.

Screened Twisted-Pair Cable

Cancellation

Unshielded Twisted-Pair Cable

• More prone to EMI/RFI interference than any other cable types.

• Least expensive of all media

– small diameter of cable (~ .43cm),

– easy to install.

• Speed of transmission:10Mpbs-1Gbps

• Maximum cable length 100m.

Straight-through cable

• Station to hub/switch

• Router to hub/switch

Crossover cable

• Switch/hub to switch/hub

• Router/station to Router/station

Connecting devices

• Connecting devices of the same group: cross-over

• Connecting devices of different group: straight-through

1 2 3

4 5 6

7 8 9

* 8 #

iMac

PWR

OK

WIC0ACT/CH0

ACT/CH1

WIC0ACT/CH0

ACT/CH1

ETHACT

COL

100Base-TX

1: Transmit

2: Transmit

3: Receive

4: Not used

5: Not used

6: Receive

7: Not used

8: Not used

1: Transmit

2: Transmit

3: Receive

4: Not used

5: Not used

6: Receive

7: Not used

8: Not used

Rollover cable

• PC requires an RJ45-to-DB9 or RJ45-to-DB25 adapter• This provide out-of-band console access

Note: only straigh-through and cross-over cable are used in making network while rollover cable is used in making control connection

Optical Media

Electromagnetic Spectrum

• Electromagnetic Energy– Radio– Microwaves– Radar– Visible light– X-rays– Gamma rays

• If all the types of electromagnetic waves are arranged in order from the longest wavelength down to the shortest wavelength, a continuum called the electromagnetic spectrum is created.

Reflection and refraction of light

Total Internal Reflection

• A light ray that is being turned on and off to send data (1s and 0s) into an optical fiber must stay inside the fiber until it reaches the far end.

Laws of Total Reflection

• The following two conditions must be met for the light rays in a fiber to be reflected back into the fiber with out any loss due to refraction: – The core of the optical fiber has to have a larger index of refraction

than the material that surrounds it (the cladding).

– The angle of incidence of the light ray is greater than the critical angle for the core and its cladding.

Single-Mode Fiber and Multimode Fiber

Other Optical Components

• A transmitter is needed to convert the electricity to light and at the receiver convert the pulse of light at the proper wavelength back to electricity.

Optical Connector

• The type of connector most commonly used with multimode fiber is the Subscriber Connector (SC connector). On single-mode fiber, the Straight Tip (ST) connector is frequently used.

Advantages of optical signal

• Fiber-optic cable is not affected by the sources of external noise like EMI

• Transmission of light on one fiber in a cable does not generate interference that disturbs transmission on any other fiber

• High speed, high security and long cable length

Signals and Noise in Optical Fibers

• The farther a light signal travels through a fiber, the more the signal loses strength. This attenuation is due to several factors involving the nature of fiber itself.– Scattering of light in a fiber is caused by microscopic non-uniformity

(distortions) in the fiber that reflects and scatters some of the light energy.

– Absorption makes the light signal a little dimmer. – Another factor that causes attenuation of the light signal is

manufacturing irregularities or roughness in the core-to-cladding boundary.

Installation of Optical Fiber

• If the fiber is stretched or curved too tightly, it can cause tiny cracks in the core that will scatter the light rays.

• Bending the fiber in too tight a curve can change the incident angle of light rays striking the core-to-cladding boundary.

• When the fiber has been pulled, the ends of the fiber must be cleaved (cut) and properly polished to ensure that the ends are smooth.

Testing of Optical Fiber

• When a fiber-optic link is being planned, the amount of signal power loss that can be tolerated must be calculated. This is referred to as the optical link loss budget.

• Two of the most important testing instruments are Optical Loss Meters and Optical Time Domain Reflectometers (OTDRs).

Wireless Media

IEEE 802 Committees

802.0 SEC

802.1 High Level Interface (HILI)

802.2 Logical Link Control (LLC)

802.3 CSMA/CD Working Group

802.4 Token Bus

802.5 Token Ring

802.6 Metropolitan Area Network (MAN)

802.7 BroadBand Technical Adv. Group (BBTAG)

802.8 Fiber Optics Technical Adv. Group (FOTAG)

802.9 Integrated Services LAN (ISLAN)

802.10 Standard for Interoperable LAN Security (SILS)

801.11 Wireless LAN (WLAN)

802.12 Demand Priority

802.14 Cable-TV Based Broadband Communication Network

802.15 Wireless Personal Area Network (WPAN)

802.16 Broadband Wireless Access (BBWA)

RPRSG Resilient Packet Ring Study Group (RPRSG)

IEEE 802.11IEEE 802.11aIEEE 802.11b WiFiIEEE 802.11gIEEE 802.15.1 BluetoothIEEE 802.11eIEEE 802.11fIEEE 802.11hIEEE 802.11i Security 2004IEEE 802.15 TG2IEEE 802.15 TG3IEEE 802.15 TG4

WLAN Organizations and Standards

Standard Data RateModulation

SchemePros/Cons

802.11 ≤ 2Mbps 2.4GHz

FHSS or DSSS

This specification has been extended into 802.11b.

802.11a ≤ 54Mbps 5GHz

OFDM

"Wi-Fi Certified." 8 available channels. Less potential for RF interference than 802.11b and 802.11g. Better than 802.11b at supporting multimedia voice, video and large-image applications in densely populated user environments. Relatively shorter range than 802.11b. Not interoperable with 802.11b.

802.11b ≤ 11Mbps 2.4GHz

DSSS with CCK

"Wi-Fi Certified." 14 channels available. Not interoperable with 802.11a. Requires fewer access points than 802.11a for coverage of large areas. High-speed access to data at up to 300 feet from base station.

802.11g ≤ 54Mbps 2.4GHz

OFDM > 20Mbps DSSS + CCK <

20Mbps

"Wi-Fi Certified." 14 channels available. May replace 802.11b. Improved security enhancements over 802.11. Compatible with 802.11b.

Bluetooth Up to 2Mbps

2.45GHzFHSS

No native support for IP, so it does not support TCP/IP and wireless LAN applications well. Best suited for connecting PDAs, cell phones and PCs in short intervals.

Wireless Devices and Topologies

• A wireless network may consist of as few as two devices.

• Devices in WLAN are peers

• An access point (AP) is commonly installed to act as a central hub for the WLAN

How WLANs Communicate

• After establishing connectivity to the WLAN, a node will pass frames similarly to any other 802 network.

• WLANs use CSMA/CA • The receiving node returns a

positive ACK, causing a consumption of 50% of the available bandwidth, actual throughput may reduce to 5 –5.5 Mbps

• Adaptive Rate Selection (ARS) is used to set proper speed for network nodes.

Adaptive Rate Selection

• Performance of the network will also be affected by signal strength and degradation in signal quality due to distance or interference.

• As the signal becomes weaker, Adaptive Rate Selection (ARS) may be invoked.

• IEEE 802.11 lists two types of authentication processes. – Open system – only the SSID must match

– Shared key – requires Wireless Equivalency Protocol (WEP)

• Association permits a client to use the services of the AP to transfer data.

Authentication and Association

Carrier Signal and Modulation

• In a transmitter, the electrical (data) signals from a computer or a LAN are not sent directly into the antenna of the transmitter. Rather, these data signals are used to alter a second, strong signal called the carrier signal.

Signals and Noise on a WLAN

• The most obvious source of a signal problem is the transmitting station and antenna type.

• Leakage from a microwave of as little as one watt into the RF spectrum can cause major network disruption. Wireless phones operating in the 2.4GHZ spectrum can also cause network disorder.

• Fog or high moisture conditions can affect wireless networks.

• Lightning can also charge the atmosphere and alter the path of a transmitted signal.

Wireless Security

• VPN

• EAP-MD5 Challenge

• LEAP (Cisco)

• User authentication

• Encryption

• Data authentication

Summary

• Electronic parameters

• Ethernet cable type

• Light and optical fiber

• Optical fiber installation

• WLAN communication and authentication

• Signal modulation and WLAN security