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

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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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Presentation Transcript
• 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
• 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 are graphs of mathematical functions:
• Y=5 * Sin(x)
• Periodic – repeat at regular intervals
• Continuously variable
• Analog 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 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
• 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 – 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 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 – how much information can flow
• Units of measurement are bps
• Usually expressed as kbps or mbps
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
• 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)
• 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
• 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
• Shielded
• Protect against external noise sources
• Some types of shielding protect against internal noise sources
• Unshielded
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
• 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
• 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 – 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
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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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)

Ethernet

1000BASE-CX

100BASE-T4

1000BASE-T

100BASE-FX

100BASE-TX

10BASE-F

10BASE-T

10BASE2

10BASE5

LAN Physical Layer Symbols
• Token Ring
• FDDI Ring
• Ethernet Line
• Serial Line

Token Ring

FDDI

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
• 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
• 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
• 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
• 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)
• 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
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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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 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
• 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
• DSL – modem technology inexpensive high speed transmission over existing phone lines
• Uses RJ-11 connectors
Routers and cable connections
• Coaxial cable carries signal (same as television)