Chapter 5 Concepts

Cable continuity tester

AKA cable testers. Tests whether cable carries signal to destination. Copper based cable tester consists of two parts: 1. base unit generates voltage 2. remote unit detects voltage Series of lights and/or audible ton used to signal pass or fail. Some continuity testers verify UTP and/or STP wires paired correctly - that they're not shorted, exposed, or crossed.

Rollover cable

AKA console cable. All wires are reversed; terminations are a mirror image of each other. Used to connect a computer to the console port of a router - when making configuration changes to the device.

Full-duplex

AKA duplex. Signals travel in both directions over medium simultaneously.

Cable performance tester

AKA line tester, or certifier. Performs similarly to continuity testers, but can be used to: 1. Measure distance to a connectivity device, termination point, or cable fault 2. Measure attenuation 3. Measure NEXT (near end cross-talk) 4. Measure termination resistance and impedance 5. Issue pass/fail ratings for Cat 3-7 standards 6. Store and print results or save to a computer database 7. Graphically depict attenuation and cross-talk

Straight-through cable

AKA patch cable. Terminate RJ-45 plugs at both ends identically.

BiDi transceivers

Allows bidirectional transmission on both ports. Means fiber cable carries data in both directions.

Noise

Any undesirable influence degrading or distorting signal. Measured in db (decibels)

Twisted-Pair Cable

Color-coded insulated copper wire pairs: 1. 0.4 - 0.8 mm diameter 2. Encased in a plastic sheath 3. Every two wires are twisted together 4. Contains four wire pairs: -- fast ethernet uses one pair to send data and one pair to receive data -- networks using Gigabit ethernet use all four pairs for both sending and receiving 5. Wiring standard specification -- TIA/EIA 568 6. Most common twisted pair types -- Category (cat) 3, 5, 5e, 6, 6a, and 7 -- CAT 5e or higher used in modern LANs 7. Two categories -- Shielded twisted pair (STP) -- Unshielded twisted pair (UTP)

Multiplexer (mux)

Combines many channel signals. Required at the transmitting end of the channel.

Fiber-optic cable (fiber)

Contains one or more glass or plastic fibers at its center (core). Data tranmission is made by pulsing light sent from laser or light-emitting diode (LED) through central fibers.

To avoid transceiver mismatch:

Devices must be paired based on supported speeds and protocols

Ethernet standards for twisted-pair cable

1. A cable's category (Cat 5e or Cat 6) determines the fastest network speed it can support -- A layer 1 characteristic 2. A device's NIC is also rated for max network speeds 3. Most LAN's today use devices and NICs that can support Fast Ethernet and Gigabit Ethernet -- devices can auto-negotiate for the fastest standard they have in common

Benefits of fiber-optic over copper cabling:

1. Extremely high throughput 2. Very high noise resistance 3. Excellent security 4. Able to carry signals for longer distances Drawbacks: 1. More expensive than twisted pair cable 2. Requires special equipment to splice

Ethernet standards using fiber-optic cable

1. Gigabit Ethernet: - 1000Base-LX - 1,000 Mbps - 550m for MMF, 5000m for SMF - MMF or SMF - 1000Base-SX - 1,000 Mbps - Up to 550, depending on modal bandwidth and fiber core diameter - MMF 2. 10-Gigabit Ethernet - 10GBase-SR and 10GBase-LW - 10,000 Mbps - Up to 300m, depending on modal bandwidth and fiber core diameter - MMF - 10GBase-LR and 10GBase-LW - 10,000 Mbps - 10,000m - SMF - 10GBase-ER and 10GBase-EW - 10,000 Mbps - 40,000m - SMF

Fiber connectors

1. MMF connectors - classified by the number of fibers 2. SMF connectors - classified by the size and shape of the ferrule 3. Ferrule - the extended tip of a connector that makes contact with the receptacle in the jack

Newer transceivers that have made the GBIC obsolete:

1. SFP (small form-factor pluggable) 2. XFP (10 Gigabit small form-factor pluggable) 3. SFP+ 4. QSFP (quad small form-factor pluggable) 5. QSFP+ 6. CFP (centum form-factor pluggable)

Installing a transceiver:

1. Slide the transceiver into a socket on the back of the connectivity device 2. Most SFPs come with a tab or latch system and keyed so that they will slide into the socket when aligned proplerly

Shapes to reduce back reflection

1. UPC - Ultra Polished Connector (rounded) 2. APC - Angle Polished Connector

GBIC

Gigabit Interface Converter. A standard type of modular interface designed fro Gigabit Ethernet connections. -- May contain RJ-45 or fiber-optic cable ports.

Media converter

Hardware that enables networks or segments running on different media to interconnect and exchange signals. Completes the physical connection and converts electrical signals from copper cable to light wave signals. -- Can also be used to convert networks using MMF with networks using SMF.

Demultiplexer (demux)

Separates the combined signals

TDR

Time domain reflectometer: issue signal, measures signal bounce back; indicates distance between nodes; indicates whether terminators properly installed and/or functional.

Crossover cable

Transmit and receive wires on one end reversed.

1000Base-SX segment lengths

Multimode fiber diameter - Max segment length 1. 50 microns - 550m 2. 52.5 microns - 275m

Types of noise

*1. EMI* (electromagnetic interference) -- Caused by motors power lines, TVs, copiers, fluorescent lights, etc. -- One type of EMI is RFI (radio frequency interference) *2. Cross-talk* -- Signal on one wire infringes on adjacent wire signal -- Alien cross-talk occurs between two cables -- Near end cross-talk (NEXT) occurs near source -- Far end cross-talk (FEXT) occurs at the far end *3. Attenuation* -- Loss of signal's strength as it travels away from source *4. Signals can be boosted* -- Repeater - regenerates a digital signal in its original form (without noise previously accumulated). *5. Latency* -- Delay between signal transmission and receipt -- May cause network transmission errors *6. Latency causes* -- Cable length -- Intervening connectivity device *7. Round trip time* (RTT) -- Time for a packet to go from sender to receiver, then back from receiver to sender *8. If packets experience varying amounts of delay* -- They can arrive out of order -- A problem commonly called jitter or PDV (packet delay variation)

Three types of multiplexing on copper lines:

*1. TDM* (time division multiplexing) -- Divides channel into multiple time intervals *2. STDM* (statistical time division multiplexing) -- Transmitter assigns slots to nodes - according to priority and need *3. FDM* (frequency division multiplexing) -- Assigns different frequency band for each communications subchannel

Fiber-optic cable specs

*1. Throughput* -- Proven reliable in transmitting data at rates that can reach 100 Gbps per channel. *2. Cost* -- Most expensive transmission medium *3. Noise immunity* -- Unaffected by EMI *4. Size and scalability* -- Segment lengths vary from 2 to 40,000 meters -- Depends on the light's wavelength and type of cable

STP vs UTP

*1. Throughput* -- STP and UTP can transmit the same rates *2. Cost* -- STP and UTP can vary in cost -- STP is more expensive than UTP *3. Connector* -- STP and UTP use Registered Jack 45 (RJ-45) *4. Noise immunity* -- STP is more noise resistant *5. Size and scalability* -- Max segment length for both: 100 meters on ethernet networks that support data rates from 1 Mbps and 10 Gbps

Toner and probe kit

*1. Tone generator* (toner) -- small electronic device -- issues signal on wire pair *2. Tone locator (probe) -- emits tone when electrical activity detected *3. Probe kit or toner probe* -- generator and locator combination Testing requires trial and error. Used to determine where wired pair terminates. Not used to determine cable characteristics.

Three types of multiplexing on fiber-optic cable:

*1. WDM* (wavelength division multiplexing) -- Carries multiple light signals simultaneously by dividing a light beam into different wavelengths or colors *2. DWDM* (dense wavelength division multiplexing) -- Extraordinary capacity -- Typically used on high-bandwidth or long-distance WAN links *3. CWDM* (coarse wavelength division multiplexing) -- Channels are spaced more widely apart across entire frequency band -- Effective distance is more limited because the signal is not amplified

Common fiber cable problems

*1.* Fiber type mismatch -- more of a fiber core mismatch -- even same-mode cables can be mismatched if the cores have different widths *2.* Wavelength mismatch -- SMF,MMF, and POF (plastic optical fiber) use different wavelengths *3.* Dirty connectors -- signal loss and other errors can start to cause problems

Multiplexing

A form of transmission that allows multiple signals to travel simultaneously over one medium.

NIC settings

NIC settings include the direction in which signals travel over the media and the number of signals that can traverse the media at any given time

Bit rate

A measurement in bits per second (bps), used to measure bandwidth and throughput

Fiber optic continuity tester

Issues light pulses on fiber. Determines whether pulses reach other end. Offer convenience: protable, lightweight, and low cost.

Fiber-optic cladding

Layer of glass or plastic surrounding fibers. Different density from glass or plastic in strands. Reflects light back to the core. Allows fiber to bend.

Fiber-optic plastic buffer outside cladding

Protects cladding and core. Opaque to absorb escaping light. Surrounded by Kevlar (polymeric fiber) strands. Plastic sheath covers kevlar strands.

Subchannels

Logical multiple smaller channels

Throughput

Measure of how much data is actually transmitted during given time period

Multimeter

Measures electric circuit characteristics - resistance, voltage, and impedance. Use a multimeter to do the following: 1. Measure voltage to verify cable is conducting electricity. 2. Check for the presence of noise. 3. Test for short or open circuits in the wire: -- short circuit is an unwanted connection -- open circuit is one where needed connections are missing

MMF connector

Most common is the MTRJ. Existing fiber networks might use ST or SC connectors - LC and MT-RJ are used on the very latest fiber-optic tech.

MMF

Multimode Fiber. *1.* Contains a core with a larger diameter than single mode fiber. -- common sizes: 50 or 62.5 microns *2.* Laser or LED generated light pulses travel at different angles *3.* Greater attenuation than single-mode fiber *4.* Common uses: -- cables connecting routers, switches, and servers on the backbone of a network -- Cables to connect a desktop workstation to the network *5.* Transition between SMF and MMF might occur at an FDP (fiber distribution panel)

OPM

Optical power meter (AKA light meter): measures the amount of light power transmitted on a fiber-optic line; must be calibrated precisely, following highly accurate optical power standards. Surrounding room temp, connection type, and the skill of the technician all affect the final test results.

OTDRs

Optical time domain reflectometers: measure fiber length; determine faulty splice locations, breaks, connectors, bends, and measure attenuation over cable; can be expensive.

PoE

Power over Ethernet. IEEE 802.3af standard, which specifies a method for supplying electrical power over twisted-pair ethernet connections. 1. amount of power provided: -- 15.4 watts for standard PoE devices -- 25.5 watts for newer PoE+ devices (802.3at standard) 2. PoE standard specifies two types of devices -- PSE (power sourcing equipment) -- PD (powered devices) 3. PoE requires Cat 5 or better copper cable 4. The IEEE standard requires that a PSE device first determin whether a node is PoE-capable before attempting to supply it with power. 5. On networks that demand PoE but don't have PoE-capable equipment, you can add PoE adapters

Cable pinouts

Proper cable termination is a requirement for two nodes on a network to communicate. Poor terminations can lead to loss or noise in a signal. TIA/EIA specifies two methods of inserting wires into RJ-45 plugs: 1. TIA/EIA 586A 2. TIA/EIA 586B No functional difference between the two standards - just make sure you use the same standard on every RJ-45 plug and jack.

STP

Shielded Twisted Pair. Individually insulated. Surrounded by metallic substance shielding (foil): -- Barrier to external electromagnetic forces -- Contains electrical energy of signals inside -- Must be grounded

Half-duplex

Signals may travel in both directions, but only in one direction at a time

Simplex

Signals may travel in only one direction and is sometimes called one-way or unidirectional communication

SMF

Single Mode Fiber. *1.* Consists of narrow core (8 - 10 microns in diameter): -- Laser-generated light travels over one path - little reflection *2.* Can carry signals over many miles: -- before repeating is required *3.* Rarely used for shorter connections -- Due to cost -- The internet backbone depens on SMF

Fiber Transceivers

Some switches allow you to change and upgrade its interfaces. They contain sockets where one of many types of modular interfaces, called transceivers, can be plugged in.

Ethernet standards used with twisted-pair cabling

Standard - max transmission speed (Mbps) - max distance per segment (m) - physical media - pairs of wires used for transmittion 1. 100Base-T Fast Ethernet - 100 Mbps - 100 m - Cat 5 or better - 2 pair 2. 1000Base-T Gigabit Ethernet - 1000 Mbps - 100 m - Cat 5 or better (Cat 5e is preferred) - 4 pair 3. 10GBase-T 10-Gigabit Ethernet - 10,000 Mbps - 100 m - Cat 6a or Cat 7 (Cat 7 is preferred) - 4 pair

Troubleshooting tools

Start troubleshooting a network connection problem by checking the network connection LED status indicator lights: 1. Steady light indicates connectivity 2. Blinking light indicates activity 3. Red or amber light might indicate a problem If a cabling issue is suspected, know which tools are designed to analyze and isolate problems.

Bandwidth

The amount of data that could be theoretically transmitted during a given period of time

SMF Connectors

Typically available with a 1.25-mm ferrule or a 2.5-mm ferrule: - Most common 1.25-mm connector is the LC (local connector) - Two 2.5-mm connectors are the sc (standard connector) and ST (straight tip)

UTP

Unshielded Twisted Pair. One or more insulated wire pairs in plastic sheath: -- No additional shielding -- Less expensive, less noise resistance