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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)
  • 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 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
  • 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)
  • 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
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
      • 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)











lan physical layer symbols
LAN Physical Layer Symbols
  • Token Ring
  • FDDI Ring
  • Ethernet Line
  • Serial Line

Token Ring


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
  • 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
  • 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