Cisco CCNA Sem 1 Chapter 4 Cable Testing, Cabling LANs and WANs Terms to understand Waves – energy traveling form one place to another Period – time between.

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

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:

1. Voltage waves on copper media2. Light waves in fiber optic3. 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

-6

-4

-2

0

2

4

6

1 3 5 7 9 11 13 15 17 19

Series1

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 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 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

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

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)

Data Link Layer

Physical Layer

IEEE 802.2

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

Ethernet Media Connector Requirements

Media Max. Segment Length

Topology Connector

10BASE2 50-ohm Coax (Thinnet)

185 m Bus British Naval Connector (BNC)

10BASE5 50 Ω 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 μ3 -10 km on single mode fiber

Star SC

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.

Pinouts – Straight Through cable

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

Pinouts – Crossover cable

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

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 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

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

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

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

Pin Signal

1 Unused

2 Unused

3 Tx+

4 Rx+

5 Rx-

6 Tx-

7 Unused

8 Unused

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

Routers and cable connections

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

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