1. 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
Amplitude – Height of wave (for electrical signals, this is volts)

2. 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

3. 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

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

5. 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

6. 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

7. 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

8. 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

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

10. 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.

11. 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

12. 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

13. 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

14. 2 types of copper cable Shielded Unshielded
Protect against external noise sources
Some types of shielding protect against internal noise sources
Unshielded

15. 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

16. 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

17. 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.

18. 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

19. 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

20. 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

21. 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.

22. 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

23. Three types of Crosstalk
Near-end crosstalk (NEXT)
Far-end crosstalk (FEXT)
Power sum near-end crosstalk (PSNEXT)

24. 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

25. 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

26. 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

27. 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

28. 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)

29. Other Test Parameters Crosstalk Return loss 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.

30. 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

31. 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

32. 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

33. LAN Physical Layer (Layer 1 OSI)
Data Link Layer
Physical Layer
IEEE 802.2
Ethernet
1000BASE-CX
10BASE2
10BASE5
10BASE-T
10BASE-F
100BASE-TX
100BASE-FX
100BASE-T4
1000BASE-T

34. LAN Physical Layer Symbols
Token Ring
FDDI Ring
Ethernet Line
Serial Line
Token Ring
FDDI

35. 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

36. Ethernet Media Connector Requirements
Max. Segment Length
Topology
Connector
10BASE2
50-ohm Coax (Thinnet)
185 m
Bus
British Naval Connector (BNC)
10BASE5
50 Ω Coax (Thicknet)
500 m
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
100BASE-FX
62.5/125 multimode fiber
400 m
Duplex media interface connector MIC, ST, SC
1000BASE-CX
STP
25 m
1000BASE-T
CAT 5 UTP, 4 pair
1000BASE-SX
62.5/50 micro multimode fiber
275 m for 62.5 μ; 550 m for 50μ 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

37. 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)

38. 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.

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

40. Pinouts – Crossover cable
RJ-45 Pin Label 1
RD+
TD+ 2
RD-
TD- 3 4 NC 5 6 7 8

41. Using cables Straight through Crossover 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

42. 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

43. 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

44. 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

45. 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

46. 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

47. 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

48. 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

49. 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

50. 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

51. 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

52. 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

53. 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

54. 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.

55. 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

56. 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

57. 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 3
Tx+ 4
Rx+ 5
Rx- 6
Tx- 7 8

58. Routers and DSL Connections
DSL – modem technology inexpensive high speed transmission over existing phone lines
Uses RJ-11 connectors
Pin
Signal 1
Unused 2 3 Tx 4 Rx 5 6

59. Routers and cable connections
Coaxial cable carries signal (same as television)
Radio grade (RG-59)
RG-6 – recommended
F connector

60. 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