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# Cisco CCNA Sem 1 Chapter 4 Cable Testing, Cabling LAN’s and WAN’s - PowerPoint PPT Presentation

Cisco CCNA Sem 1 Chapter 4 Cable Testing, Cabling LAN’s and WAN’s. Terms to understand Waves – energy traveling form one place to another Period – time between waves Frequency – Number of waves in a given time period (measured in waves per second called hertz

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Cisco CCNA Sem 1 Chapter 4Cable Testing, Cabling LAN’s and WAN’s

• Terms to understand

• Waves – energy traveling form one place to another

• Period – time between waves

• Frequency – Number of waves in a given time period (measured in waves per second called hertz

• Amplitude – Height of wave (for electrical signals, this is volts)

• Deliberate disturbance with fixed, predictable duration is called a pulse

• Pulses determine value of the data being transmitted

• Three types of waves are of interest in networking:

• Voltage waves on copper media

• Light waves in fiber optic

• Alternating electric and magnetic fields in wireless communitcation

• Sine waves are graphs of mathematical functions:

• Y=5 * Sin(x)

• Periodic – repeat at regular intervals

• Continuously variable

• Analog waves

• Like analog waves are periodic

• Do not vary continuously with time

• Represent digital pulses or signals

• Describe by Amplitude, Frequency and period

• Decibels are measures of power

• dB=10log10(Pfinal/Pref)

• dB=20log10(Vfinal/Vref)

• dB measures loss or gain of power of a wave. Usually negative

• Log10 uses base 10 logarithm

• Pfinal is delivered power in watts

• Pref is original power in watts

• Vfinal is delivered voltage in Volts

• Vref is original voltage in Volts

• Data can be represented by voltage patterns

• Voltage patterns can be viewed graphed against time by an oscilloscope

• X-axis (domain) represents time

• Time-domain analysis

• Spectrum analyzer analyzes signals against a frequency as the x-axis.

• Frequency-domain analysis

• Noise – Undesirable signals

• Sources of Noise

• Nearby cables that carry signals

• Electromagnetic Interference (EMI)

• Laser noise at Tx or Rx

• Noise that affects all frequencies equally – white noise

• Noise that affects only small range of frequencies – narrowband interference

• Analog Bandwidth – refers to frequency range of an analogy electronic system

• Range of frequencies transmitted by radio station or electronic amplifier

• Units of analog bandwidth is Hz

• 3 kHz telephony

• 20 kHz for audible signals

• 5 kHz for AM radio

• 200 kHz for FM

• Digital Bandwidth – how much information can flow

• Units of measurement are bps

• Usually expressed as kbps or mbps

• Analog bandwidth is used in cable testing to determine digital bandwidth of copper media

• Analog signal Tx on one end, and Rx on other.

• Attenuation is calculated

• In general, higher analog bandwidth = higher digital bandwidth.

• Noise – any interference on physical media that makes it difficult for receiver to detect signal

• Copper media susceptible to several sources of noise

• Optical fiber considerably less susceptible

• Proper installation of cable and connectors limit noise and attenuation

• After installation of physical medium, must be tested to meet TIA/EIA 568-B standards

• After installation, periodic testing of cables and connectors required in order to insure continued network performance

• Bits are represented by voltage changes

• Voltage changes are measured against a reference ground.

• Voltages are generally at <= 5 volts.

• Signals can’t be amplified or extended duration at receiver

• As much of the original signal as possible is required to reach receiver

• Shielded

• Protect against external noise sources

• Some types of shielding protect against internal noise sources

• Unshielded

• Coaxial cable- solid copper core surrounded by insulating material, then braided conductive shielding.

• Conductive shielding must be properly grounded

• Prevents external noise from disrupting signal

• Helps keep signal loss down by confining signal to cable

• Less noisy than Twisted pair

• Bulky, more expensive, must be grounded

• 2 types

• Shielded Twisted Pair (STP)

• Screened Twisted Pair (ScTP)

• Foil Twisted Pair (FTP)

• Outer conductive shield that is grounded

• Inner foil shields around each wire pair

• More expensive and difficult to install than UTP. Less frequently used

• Unshielded Twisted Pair (UTP)

• Inexpensive and easy to install

• Tx data by increasing and decreasing light intensity to represent binary 1’s and 0’s

• Strength of signal doesn’t diminish over same distance as copper

• Not affected by electrical noise

• Doesn’t require grounding

• Often used between buildings and floors.

• Attenuation – decrease in signal amplitude over length of link

• Long cable lengths and high frequencies lead to greater attenuation

• Attenuation measured by cable tester using highest frequencies that cable is rated to support

• Attenuation expressed in dB using negative numbers

• Smaller negative dB values indicate better link performance

• Resistance of copper cable converts energy of signal to heat

• Signal lost when leaks through insulation of cable

• Impedance caused by defective connectors

• Measurement of resistance of cable to AC current in ohms (Ω)

• CAT 5 normal is 100 Ω

• Improper connector installation creates a different impedance than cable

• Impedance discontinuity or Impedance mismatch

• Causes attenuation because part of signal is reflected back to Tx (similar to an echo).

• Multiple discontinuities compound problem. As echo reverberates through cable, Rx can’t accurately detect signal values.

• Effect is called Jitter

• Combination of Attenuation and Impedance discontinuities called Insertion Loss

• Noise – any electrical energy on Tx cable that makes it hard for Rx to interpret data

• TIA/EIA-568-B requires testing for variety of noise.

• Crosstalk – Tx of signals from one wire pair to nearby pairs

• Wires act like radio antennas generating similar signals

• Cause interference with data on adjacent wires

• Can come from separate nearby cables

• Comes from other cables called alien crosstalk

• More destructive at higher Tx frequencies

• Cable testing applies signal to one pair of wires and measures amplitude of unwanted signals induced in other pair of wires

• Occurs when wire pairs untwisted

• Near-end crosstalk (NEXT)

• Far-end crosstalk (FEXT)

• Power sum near-end crosstalk (PSNEXT)

• Computed as ratio in voltage amplitude between test signal and crosstalk signal when measured from same end of the link

• Expressed in negative dB values

• Low negative values indicate more noise

• Cable testers don’t show negative sign

• 30 (really -30) dB is better than 10 (-10) dB

• Needs to be measured every pair to every pair

• Far-end crosstalk

• Less noise than NEXT because of attenuation

• Noise is still sent back to Tx, but is significantly less because of attenuation

• Not as significant as NEXT

• Measures cumulative effect of NEXT from all wire pairs

• Combined affect from multiple simultaneous transmission can degrade signal

• TIA/EIA-568-B now requires PSNEXT test

• 1000BASE-T receive data simultaneously from multiple pairs in same direction. PSNEXT is important test

• Primary tests to meet TIA/EIA-568-B

• Wire map

• Insertion loss

• Near-end cross talk – NEXT

• Power sum near-end crosstalk – PSNEXT

• Equal-level far-end crosstalk – ELFEXT

• Power sum equal-level far-end crosstalk – PSELFEXT

• Return loss

• Propagation delay

• Cable length

• Delay skew

• Assures no Open or Short circuits in cable

• Open circuit – wire not attached correctly at a connection

• Short circuit – two wires connected to each other

• Also assures wires attached to correct pins on both sides

• Reversed pair fault: Correct on one side, reversed on other

• Split-pair: 2 wires from different wire-pairs are connected to wrong pins on both ends of the cable

• Transposed pair: wire pair is connected to completely different pins at both ends or two different color codes used on punch-down blocks (T568A and T568B)

• Crosstalk

• NEXT

• ELFEXT: Equal-level far-end crosstalk

• Measure FEXT

• Pair-to-pair ELFEXT expressed in dB as difference between measured FEXT and insertion loss

• Important test in 1000BASE-T networks

• PSELFEXT

• Combined effect of ELFEXT from all wire pairs

• Return loss

• Measured in dB from return signals due to impedance. Not loss in signal, but in signal jitter.

• Propagation delay – time it takes for signal to travel along cable being tested.

• Depends on length, twist rate, electrical properties

• Delays measured in hundreths of nanoseconds.

• Basis of cable length measurements based on Time Domain Reflectometry (TDR)

• Can also identify distance to wiring faults

• Delay difference between pairs of wires is called Delay Skew

• Critical in 1000BASE-T networks

• Subject to optical equivalent of impedance discontinuities

• Portion of light reflected back along path resulting in less light at receiver

• Improperly installed connectors main cause of impedance discontinuities

• Amount of acceptable light loss is called optical link loss budget

• Fiber test instrument measure light loss, and can indicate where optical discontinuities exsist.

• After faults are corrected, cable must be retested

• June 20, 2002 ANSI/TIA/EIA-568-B.2.1 – CAT 6 standard

• Standard sets tests for certification

• CAT 6 same as CAT 5 but higher standards

• Lower levels of crosstalk and return loss

• Capable of supporting frequencies of 250 MHz

Ethernet

1000BASE-CX

100BASE-T4

1000BASE-T

100BASE-FX

100BASE-TX

10BASE-F

10BASE-T

10BASE2

10BASE5

• Token Ring

• FDDI Ring

• Ethernet Line

• Serial Line

Token Ring

FDDI

• Fast Ethernet and Gigabit Ethernet

• User level for good performance

• Clients or servers with high bandwidth

• Link between user-level and network devices

• Connecting to Enterprise level servers

• Switches and Backbone

• RJ-45 – A connector used for finishing twisted-pair wire

• AUI – Attachment Unit Interface

• An interface for connecting NIC that may not match media connecting to it

• GBIC – Gigabit Interface Converter

• Used at interface between Ethernet and fiber-optic systems

• GBIC transceiver converts electrical currents to optical signals

• Short wavelength (1000BASE-SX)

• Long wavelength (1000BASE-LX/LH)

• Extended distance (1000BASE-ZX)

• Wires in the cable must be connected to correct pins in terminator

• Straight-through cable: maintains pin connection all the way through cable (i.e. pin 1 to pin 1, pin 2 to pin 2, etc)

• Crossover cable: critical pair of wires is crossed over in order to make sure Rx-Tx pairing.

• Straight through

• Switch to router

• Switch to PC or server

• Hub to PC or server

• Crossover

• Switch to switch

• Switch to Hub

• Hub to Hub

• Router to router

• PC to PC

• Router to PC

• Repeaters

• Regenerate and retime signals at bit level to allow greater distances

• Four repeater rule (5-4-3 rule)

• 5 network segments connected end-to-end by 4 repeaters with only 3 segments with hosts on them

• Primarily used in Bus topology networks, not with switches and extended star topologies

• Hubs – Repeaters on steroids

• Active – Requires power to regenerate and amplify signal

• Changes Bus topology to Star topology

• All devices attached to Hub hear all traffic – single collision domain

• Bridges – used to break up large LAN to smaller segments

• Decreases traffic on a single LAN and extends geographical area

• Makes intelligent decisions about how to pass on a frames

• Frame is examined for destination MAC address

• Address on same segment as source MAC, blocks frame from going to other segment – filtering

• Address on different segment, Bridge forwards to correct segment

• Address unknown, Bridge sends frame to all segments - flooding

• Multiport Bridge (Layer 2)

• Like Bridges, Switches build forwarding tables based on MAC address for decision making

• More sophisticated than Bridge

• Improve network performance

• Often replace shared Hubs

• Two basic functions

• Switching data frames

• Maintenance of switching operations

• Operate at higher speeds than bridges

• Support other functionality (VLAN’s)

• Provide collision free environment

• Utilize radio frequency (RF), laser, infrared (IR) or satellite/microwave to carry signals.

• Requires Transmitters (Tx) and Receivers (Rx)

• Most common techonologies RF and IR

• IR – Must be line of sight and signal easily obstructed

• RF – limited range and single frequency easily monitored by others

• Must protect waveform from eavesdropping

• Waveform of wireless bridges concentrate in single beam. Must be in the path of the beam in order to intercept data stream

• Encryption is required to assure security

• Main Goals

• Prevent decoding of captured WLAN traffic

• Same key needs to be used by encrypting and decrypting endpoints

• Not extremely robust security – should be supplemented with firewalls or VPN

• Centralized authentication and dynamic key distribution

• Standard for port-based network access control

• Allows client adapters that support different authentication types to communicate with back-end servers

• Cisco’s LEAP uses mutual authentication: Both user and access point must be authenticated before allowed on to network

• Centralized authentication and key distribution

• Large-scale WLAN deployment

• PC board that fits into expansion slot on motherboard

• Provides connectivity for host to network medium

• Operates at Layer 1 and Layer 2 of OSI model

• Considered Layer 2 because every NIC has a Media Access Control (MAC) address.

• Layer 1 because only looks at bit and not higher level protocols

• Transceiver built-in

• Computer issuing a request is Client

• Computer responding is Server

• Peer-to-Peer network

• Computers act as equal partners (peers)

• Referred to as workgroups

• Each computer acts as both client and server at different times

• Individual users control own resources

• Easy to install

• Works well with small number of hosts <=10

• Do not scale well

• Security can be a problem

• Specialized computers respond to Client requests

• Easy to Scale

• Better security

• Introduces single point of failure to system

• Require additional hardware and specialized software = increased cost

• WAN cabling standards are different than LAN

• WAN Services provide different services and connection methods

• Serial connections

• Integrated Services Digital Network Basic Rate Interface (ISDN BRI)

• Digital Subscriber Line (DSL)

• Cable

• Console connections

• Physical layer requirements depend on speed, distance, and actual service utilized

• Serial connections support dedicated leased lines that use Point-to-Point Protocol (PPP) or Frame Relay.

• Speed 2400 bps to T1(1.544Mbps)

• ISDN – utilizes dial-on-demand services or dial backup

• ISDN BRI – 2 64-kbps bearer channels (B channels) for data and 1 16-kbps delta channel for control (D channel)

• Typically uses PPP protocol for B Channels

• DSL/Cable services to businesses and homes

• DSL can achieve T1/E1 speeds

• Physical connections depend on equipment, and services

• Serial connectors used to connect end-user devices and service providers

• V.35 is most common

• Ports on Cisco routers use Cisco’s proprietary 60 pin “Smart serial” Connector.

• After determining cable type, need to determine if Date Terminal Equipment (DTE) or Data Communications Equipment (DCE) is required.

• DTE is endpoint of users device on WAN

• DCE used to convert data from DTE to form that can be used on WAN link

• If connecting to service provider or device that performs signal clocking (CSU/DSU) the router is a DTE and requires DTE Serial cable. Most typical case

• Sometimes routers will be DCE

• Routers can have either fixed or modular ports. Type of port affects syntax used to configure port

• Fixed ports use the syntax: port type and port number

• Serial 0

• Modular ports use the syntax: port type slot number/port number

• Serial 1/0

• 2 type of interfaces

• BRI S/T

• If service provider uses an NT1 device then an S/T connection is required

• BRI U

• If customer needs to provide NT1 device, then U connection is used

• DSL – modem technology inexpensive high speed transmission over existing phone lines

• Uses RJ-11 connectors

• Coaxial cable carries signal (same as television)

• RG-6 – recommended

• F connector

• Initial configurations of routers typically utilizes a console connection

• Connect to console port

• Console ports in Cisco switches, hubs and routers

• Rollover cable (console cable) with RJ-45 connector

• Terminal Emulation Config:

• 9600 bps

• 8 data bits

• No parity

• 1 stop bit

• No flow control