Cisco CCNA Sem 1 Chapter 4 Cable Testing, Cabling LAN

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Cisco CCNA Sem 1 Chapter 4Cable Testing, Cabling
LANs and WANs

• 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)

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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

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Sine Waves and Square Waves

• Sine waves are graphs of mathematical functions
• Y5 Sin(x)
• Periodic repeat at regular intervals
• Continuously variable
• Analog waves

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Square Waves

• Like analog waves are periodic
• Do not vary continuously with time
• Represent digital pulses or signals
• Describe by Amplitude, Frequency and period

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Decibels

• Decibels are measures of power
• dB10log10(Pfinal/Pref)
• dB20log10(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

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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

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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

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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

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Digital Bandwidth

• Digital Bandwidth how much information can flow
• Units of measurement are bps
• Usually expressed as kbps or mbps

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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.

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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

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Signals and Noise on Networking Media (Contd)

• 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

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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 lt 5 volts.
• Signals cant be amplified or extended duration
  at receiver
• As much of the original signal as possible is
  required to reach receiver

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2 types of copper cable

• Shielded
• Protect against external noise sources
• Some types of shielding protect against internal
  noise sources
• Unshielded

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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

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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

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Fiber Optic Cable

• Tx data by increasing and decreasing light
  intensity to represent binary 1s and 0s
• Strength of signal doesnt diminish over same
  distance as copper
• Not affected by electrical noise
• Doesnt require grounding
• Often used between buildings and floors.

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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

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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

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Impedance

• Measurement of resistance of cable to AC current
  in ohms (O)
• CAT 5 normal is 100 O
• 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 cant
  accurately detect signal values.
• Effect is called Jitter
• Combination of Attenuation and Impedance
  discontinuities called Insertion Loss

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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.

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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

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Three types of Crosstalk

• Near-end crosstalk (NEXT)
• Far-end crosstalk (FEXT)
• Power sum near-end crosstalk (PSNEXT)

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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 dont show negative sign
• 30 (really -30) dB is better than 10 (-10) dB
• Needs to be measured every pair to every pair

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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

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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

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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

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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)

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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.

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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

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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

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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

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LAN Physical Layer (Layer 1 OSI)
Data Link Layer
Physical Layer
IEEE 802.2 IEEE 802.2 IEEE 802.2 IEEE 802.2 IEEE 802.2 IEEE 802.2 IEEE 802.2 IEEE 802.2 IEEE 802.2

Ethernet
1000BASE-CX
100BASE-T4
1000BASE-T
100BASE-TX
100BASE-FX
10BASE-T
10BASE-F
10BASE2
10BASE5
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LAN Physical Layer Symbols

• Token Ring
• FDDI Ring
• Ethernet Line
• Serial Line

Token Ring
FDDI
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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

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Ethernet Media Connector Requirements
Media Max. Segment Length Topology Connector
10BASE2 50-ohm Coax (Thinnet) 185 m Bus British Naval Connector (BNC)
10BASE5 50 O Coax (Thicknet) 500 m Bus Attachment unit interface (AUI)
10BASE-T CAT 3,4,5 UTP, 2 pair 100 m Star RJ-45
100BASE-TX CAT 5 UTP, 2 pair 100 m Star RJ-45
100BASE-FX 62.5/125 multimode fiber 400 m Star Duplex media interface connector MIC, ST, SC
1000BASE-CX STP 25 m Star RJ-45
1000BASE-T CAT 5 UTP, 4 pair 100 m Star RJ-45
1000BASE-SX 62.5/50 micro multimode fiber 275 m for 62.5 µ 550 m for 50µ Star SC
1000BASE-LX 62.5/50 micro multimode fiber 9 µ single mode fiber 440 m for 62.5 µ 550 m for 50 µ 3 -10 km on single mode fiber Star SC
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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)

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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.

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Pinouts Straight Through cable
RJ-45 Pin Label RJ-45 Pin Label RJ-45 Pin Label RJ-45 Pin Label
1 RD 1 TD
2 RD- 2 TD-
3 TD 3 RD-
4 NC 4 NC
5 NC 5 NC
6 TD- 6 RD-
7 NC 7 NC
8 NC 8 NC
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Pinouts Crossover cable
RJ-45 Pin Label RJ-45 Pin Label RJ-45 Pin Label RJ-45 Pin Label
1 RD 1 TD
2 RD- 2 TD-
3 TD 3 RD-
4 NC 4 NC
5 NC 5 NC
6 TD- 6 RD-
7 NC 7 NC
8 NC 8 NC
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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

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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

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LAN Connection Devices (Contd)

• 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

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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 (VLANs)
• Provide collision free environment

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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

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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

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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

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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
• Ciscos 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

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NICs 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

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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 lt10
• Do not scale well
• Security can be a problem

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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

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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

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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

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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 Ciscos proprietary 60
  pin Smart serial Connector.

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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

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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

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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

Pin Signal
1 Unused
2 Unused
3 Tx
4 Rx
5 Rx-
6 Tx-
7 Unused
8 Unused
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Routers and DSL Connections

• DSL modem technology inexpensive high speed
  transmission over existing phone lines
• Uses RJ-11 connectors

Pin Signal
1 Unused
2 Unused
3 Tx
4 Rx
5 Unused
6 Unused
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Routers and cable connections

• Coaxial cable carries signal (same as television)
• Radio grade (RG-59)
• RG-6 recommended
• F connector

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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