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)

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 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 Unshielded 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 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.

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 Ethernet 1000BASE-CX 10BASE2 10BASE5 10BASE-T 10BASE-F 100BASE-TX 100BASE-FX 100BASE-T4 1000BASE-T

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 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

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 1 RD+ TD+ 2 RD- TD- 3 4 NC 5 6 7 8

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

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

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

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

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