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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 4 cable testing cabling lan s and wan s
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)


Waves
Waves

  • 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 and square waves
Sine Waves and Square Waves

  • Sine waves are graphs of mathematical functions:

    • Y=5 * Sin(x)

    • Periodic – repeat at regular intervals

    • Continuously variable

    • Analog waves


Square waves
Square Waves

  • Like analog waves are periodic

  • Do not vary continuously with time

  • Represent digital pulses or signals

  • Describe by Amplitude, Frequency and period


Decibels
Decibels

  • 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


Signals in time and frequency
Signals in Time and Frequency

  • 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 in time and frequency
Noise in Time and Frequency

  • Noise – Undesirable signals

  • Sources of Noise

    • Nearby cables that carry signals

    • Radio Frequency Interference (RFI)

    • 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 and digital bandwidth
Analog and Digital Bandwidth

  • 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
Digital Bandwidth

  • Digital Bandwidth – how much information can flow

    • Units of measurement are bps

      • Usually expressed as kbps or mbps


Use of analog bandwidth in cable testing
Use of analog bandwidth in cable testing

  • 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.


Signals and noise on networking media
Signals and Noise on Networking Media

  • 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


Signals and noise on networking media cont d
Signals and Noise on Networking Media (Cont’d)

  • 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


Signaling over copper and fiber optic cabling
Signaling over Copper and Fiber-Optic Cabling

  • 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


2 types of copper cable
2 types of copper cable

  • Shielded

    • Protect against external noise sources

    • Some types of shielding protect against internal noise sources

  • Unshielded


Coaxial cable
Coaxial Cable

  • 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


Twisted pair cable
Twisted pair cable

  • 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


  • Fiber optic cable
    Fiber Optic Cable

    • 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 and insertion loss on copper media
    Attenuation and Insertion Loss on Copper Media

    • 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


    Factors leading to attenuation
    Factors leading to attenuation

    • Resistance of copper cable converts energy of signal to heat

    • Signal lost when leaks through insulation of cable

    • Impedance caused by defective connectors


    Impedance
    Impedance

    • 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


    Source of noise on copper media
    Source of Noise on Copper Media

    • 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.


    Types of noise
    Types 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


    Three types of crosstalk
    Three types of Crosstalk

    • Near-end crosstalk (NEXT)

    • Far-end crosstalk (FEXT)

    • Power sum near-end crosstalk (PSNEXT)


    NEXT

    • 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


    FEXT

    • 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


    Psnext power sum near end crosstalk
    PSNEXT – Power sum near-end crosstalk

    • 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


    Cable testing standards
    Cable Testing Standards

    • 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


    Wire map
    Wire map

    • 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)


    Other test parameters
    Other Test Parameters

    • 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.


    Time based parameters
    Time-Based parameters

    • 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


    Testing fiber optic cables
    Testing Fiber-Optic Cables

    • 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


    New cable standard
    New Cable Standard

    • 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


    Lan physical layer layer 1 osi
    LAN Physical Layer (Layer 1 OSI)

    Ethernet

    1000BASE-CX

    100BASE-T4

    1000BASE-T

    100BASE-FX

    100BASE-TX

    10BASE-F

    10BASE-T

    10BASE2

    10BASE5


    Lan physical layer symbols
    LAN Physical Layer Symbols

    • Token Ring

    • FDDI Ring

    • Ethernet Line

    • Serial Line

    Token Ring

    FDDI


    Ethernet technologies in campus lan
    Ethernet technologies in campus LAN

    • 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



    Connection media
    Connection Media

    • 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)


    Utp implementation
    UTP Implementation

    • 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.




    Using cables
    Using cables

    • 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


    Lan connection devices
    LAN Connection Devices

    • 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


    Lan connection devices cont d
    LAN Connection Devices (Cont’d)

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

      • Decreases traffic on a single LAN and extends geographical area

      • Layer 2 (Datalink)

      • 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


    Switches
    Switches

    • 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


    Wireless networking media
    Wireless Networking Media

    • 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


    Security in wireless environment
    Security in Wireless Environment

    • Radio waves radiate in all directions

      • 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


    WEP

    • Main Goals

      • Deny access to unauthorized users

      • 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


    802 1x eap extensible authentication protocol
    802.1X/EAP – Extensible Authentication Protocol

    • 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


    Nic s and interfaces
    NIC’s and Interfaces

    • 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


    Workstation and server relationships
    Workstation and Server Relationships

    • 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


    Client server networks
    Client/Server Networks

    • 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


    Cabling the wan
    Cabling the WAN

    • 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


    Wan physical layer
    WAN Physical Layer

    • 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


    Wan serial connections
    WAN Serial Connections

    • 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.


    Routers and serial connections
    Routers and Serial Connections

    • 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 and ports
    Routers and Ports

    • 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


    Routers and isdn bri connections
    Routers and ISDN BRI connections

    • 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


    Routers and dsl connections
    Routers and DSL Connections

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

    • Uses RJ-11 connectors


    Routers and cable connections
    Routers and cable connections

    • Coaxial cable carries signal (same as television)

      • Radio grade (RG-59)

      • RG-6 – recommended

      • F connector


    Console connectors
    Console connectors

    • 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


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