Computer Networking Unit 5

crossover cable

A twisted-pair patch cable in which the termination locations of the transmit and receive wires on one end of the cable are reversed as compared with the other end

core

A cable's central component that is designed to carry a signal, such as glass or plastic fibers in fiberoptic cable or strands of copper in twisted-pair cable

open circuit

A circuit in which necessary connections are missing, such as occurs when a wire breaks

BNC connector

A coaxial cable connector type that uses a turn-and-lock (or bayonet) style of coupling

hot-swappable

A component that can be installed or removed without disrupting operations

ST (straight tip)

A connector with a 2.5-mm ferrule that is used with single-mode, fiber-optic cable.

LED (light-emitting diode)

A cool-burning, longlasting technology that creates light by the release of photons as electrons move through a semiconductor material

FDP (fiber distribution panel

A device on a rack where fiber cables converge, connect with each other, and connect with fiber-optic terminal equipment from the ISP

media converter

A device that enables networks or segments running on different media to interconnect and exchange signals

repeater

A device used to regenerate a digital signal in its original form. Repeaters operate at the Physical layer of the OSI model.

CFP (centum form-factor pluggable)

A fiber-optic transceiver intended for 100-Gbps network connections

QSFP (quad small form-factor pluggable)

A fiber-optic transceiver that complies with the 802.3ba standard, squeezing four channels in a single transceiver and supporting data rates up to 40 Gbps (4 x 10 Gbps).

RFI (radio frequency interference

A kind of electromagnetic interference that can be generated by broadcast signals from radio or TV antennas

SFP+

A type of SFP that can send and receive data at rates of up to 16 Gbps.

Twisted-pair

A type of cable similar to telephone wiring that consists of color-coded pairs of insulated copper wires, each with a diameter of 0.4 to 0.8 mm. Every two wires are twisted around each other to form pairs, and all the pairs are encased in a plastic sheath.

DB-25 connectors

A type of connector with 25 pins that's used in serial communication and conforms to the RS-232 standard

FEXT (far end crosstalk)

Crosstalk measured at the far end of the cable from the signal source.

NEXT (near end crosstalk)

Crosstalk that occurs between wire pairs near the source of a signal.

alien crosstalk

Electromagnetic interference induced on one cable by signals traveling over a nearby cable.

Signals are free to travel in both directions over a medium simultaneously. As an analogy, talking on the telephone is a full-duplex transmission because both parties in the conversation can speak at the same time. Modern NICs use full-duplex by default.

Full-duplex or duplex

QSFP+

Generally the same technology as QSFP while supporting data rates over 40 Gbps.

bit rate

In digital transmissions, a measurement of throughput and bandwidth that is expressed as bits transmitted per second

LC (local connector)

The most common 1.25-mm ferrule connector, which is used with single-mode, fiber-optic cable

MTRJ (Mechanical Transfer-Registered Jack)

The most common type of connector used with multimode fiber-optic cable.

twist ratio

The number of twists per meter or foot in a twisted-pair cable

pinouts

The pin numbers and color-coded wire assignments used when terminating a cable or installing a jack, as determined by the TIA/EIA standard

802.3at

The IEEE standard that improves upon the older 802.3af by supplying more power (up to 25.5 watts) over Ethernet connections

-PSE (power sourcing equipment) -PDs (powered devices)

The PoE standard specifies two types of devices:

RTT (round trip time)

The length of time it takes for a packet to go from sender to receiver, then back from receiver to sender. RTT is usually measured in milliseconds.

attenuation

The loss of a signal's strength as it travels away from its source

size and scalability

The maximum segment length for both STP and UTP is 100 m, or 328 feet, on Ethernet networks that support data rates from 1 Mbps to 10 Gbps

RJ-45 (registered jack 45)

The standard connector used with shielded twisted-pair and unshielded twisted-pair cabling

RJ-11 (registered jack 11

The standard connector used with unshielded twisted-pair cabling (usually Cat 3) to connect analog telephones

console port

The type of port on a router used to communicate with the router itself, such as when making configuration changes to the device

Ethernet ports

The type of port that connects devices on a LAN; it uses an RJ-45 connector.

F-connectors

A connector used to terminate coaxial cable that transmits television and cable broadband signals

SC (subscriber connector or standard connector)

A connector with a 2.5-mm ferrule that is used with single-mode, fiber-optic cable

BiDi transceivers

A fiber-optic transceiver that supports bidirectional transmission on both its ports.

multiplexing

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

Modal bandwidth

A measure of the highest frequency of signal a multimode fiber-optic cable can support over a specific distance. Modal bandwidth is measured in MHz-km.

PoE+

A method of delivering more current (up to 25.5 watts) than PoE does to devices using Ethernet connection cables.

PoE (Power over Ethernet

A method of delivering up to 15.4 watts to devices using Ethernet connection

TDM (time division multiplexing)

A method of multiplexing that assigns a time slot in the flow of communications to every node on the network and, in that time slot, carries data from that node.

transceivers

A modular interface that can be inserted in a switch to connect its motherboard with an external, fiber-optic cable.

WDM (wavelength division multiplexing

A multiplexing technique in which each signal on a fiber-optic cable is assigned a different wavelength, which equates to its own subchannel

DWDM (dense wavelength division multiplexing or dense WDM)

A multiplexing technique used over single-mode or multimode fiber-optic cable in which each signal is assigned a different wavelength for its carrier wave

CWDM (coarse wavelength division multiplexing or coarse WDM

A multiplexing technique used over single-mode or multimode fiber-optic cable in which each signal is assigned a different wavelength for its carrier wave.

TIA/EIA 568A

A standard pinout for RJ-45 plugs required by the federal government on all federal contracts

GBIC (Gigabit interface converter)

A standard type of modular interface that may contain RJ-45 or fiber-optic cable ports (such as LC, SC, or ST). They are inserted into a socket on a connectivity device's backplane. Pronounced jee-bick

crimper

A tool used to attach a connector onto the end of a cable, causing the internal RJ-45 pins to pierce the insulation of the wires, thus creating contact between the conductors at each wire

jitter

A transmission flaw caused by packets experiencing varying amounts of delay and arriving out of order. Also called PDV (packet delay variation).

bidirectional

A transmission method that allows each fiber cable to carry data in both directions

loopback adapter

A troubleshooting tool that plugs into a port (for example, an RJ-45 or fiber-optic port) and crosses the transmit line with the receive line, allowing outgoing signals to be redirected back into the computer for testing. Also called a loopback plug

straight-through cable

A twisted-pair patch cable in which the wire terminations in both connectors follow the same scheme

toner and probe kit

A two-piece tool that includes both a tone generator and a tone locator. Used together, they can help locate the termination of a wire pair.

Fast Ethernet

A type of Ethernet network that is capable of 100-Mbps throughput

Gigabit Ethernet

A type of Ethernet network that is capable of 1000-Mbps, or 1-Gbps, throughput. Requires Cat 5e or higher cabling

XFP (10 Gigabit small form-factor pluggable)

A type of SFP that can send and receive data at rates of up to 10 Gbps

coaxial cable

A type of cable that consists of a central metal conducting core, surrounded by an insulator, shielding, and an outer cover. Today coaxial cable, called "coax" for short, is used to connect cable Internet and cable TV systems

DB-9 connectors

A type of connector with nine pins that's used in serial communication and conforms to the RS-232 standard

UPC (Ultra Polished Connector)

A type of ferrule in which the tip has been highly polished, thereby increasing the efficiency of the connection

MMF (multimode fiber)

A type of fiber-optic cable containing a core that is usually 50 or 62.5 microns in diameter, over which many pulses of light generated by a laser or LED (light-emitting diode) travel at different angles

SMF (single mode fiber)

A type of fiber-optic cable with a narrow core of 8 to 10 microns in diameter that carries light pulses along a single path from one end of the cable to the other end

-fiber stripper -fiber cleaver

A typical fiber termination kit might include the following tools:

short circuit

An unwanted connection, such as when exposed wires touch each other

Dirty connectors

If fiber connectors get dirty or just a little dusty, signal loss and other errors can start to cause problems. Always keep protectors on fiber connectors and dust covers over fiber jacks when they're not in use

A Physical layer standard for networks that specifies baseband transmission, twisted-pair cabling

100 Base-T

TX/RX reverse

A problem caused by mismatched pinout standards, resulting in near end crosstalk

speed and duplex mismatch

A problem that occurs when neighboring devices are using different speed or duplex configurations and results in failed transmissions

patch cable

A relatively short section (usually between 3 and 25 feet) of cabling with connectors on both ends

multimeter

A simple instrument that can measure multiple characteristics of an electric circuit, including its resistance, voltage, and impedance

tone locator (or probe

A small electronic device that emits a tone when it detects electrical activity on a wire pair. When used in conjunction with a tone generator, it can help locate the termination of a wire pair. Also called a probe

tone generator (or toner)

A small electronic device that issues a signal on a wire pair. When used in conjunction with a tone locator, it can help locate the termination of a wire pair. Also called a toner

SFP (small form-factor pluggable)

A standard hot-swappable network interface used to link a connectivity device's backplane with fiber-optic or copper cabling

TIA/EIA 568B

A standard pinout for RJ-45 plugs commonly used in homes and businesses

FDM (frequency division multiplexing

A type of multiplexing that assigns a unique frequency band to each communications subchannel. Signals are modulated with different carrier frequencies, then multiplexed to simultaneously travel over a single channel

STDM (statistical time division multiplexing)

A type of multiplexing that assigns time slots to nodes (similar to TDM), but then adjusts these slots according to priority and need

duplex

A type of transmission in which signals may travel in both directions over a medium simultaneously

full-duplex

A type of transmission in which signals may travel in both directions over a medium simultaneously; also called, simply, duplex

-fiber type mismatch -wavelength mismatch -dirty connectors

Problems that are unique to fiber cable include:

wavelength mismatch

SMF, MMF, and POF (Plastic Optical Fiber) each use different wavelengths for transmissions. A wavelength mismatch occurs when transmissions are optimized for one type of cable but sent over a different type of cable

throughput

STP and UTP can both transmit data at 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps, depending on the grade of cabling and the transmission method in use.

connector

STP and UTP use RJ-45 (registered jack 45) modular connectors and data jacks, which look similar to analog telephone connectors and jacks. However, telephone connections follow the RJ-11 (registered jack 11) standard. For comparison, this figure also shows a traditional RJ-11 phone line connector. Most types of Ethernet that rely on twisted-pair cabling use RJ-45 connectors.

cost

STP and UTP vary in cost, depending on the grade of copper used, the category rating, and any enhancements. Typically, STP is more expensive than UTP because it contains more materials and it has a lower demand. It also requires grounding, which can lead to more expensive installation. High-grade UTP can be expensive, too, however

continuity

The ability of a cable to carry a signal to its destination

throughput

The amount of data that a medium transmits during a given period of time. Throughput is usually measured in megabits (1,000,000 bits) per second, or Mbps.

bandwidth

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

ferrule

The extended tip of a fiber-optic cable connector that encircles the fiber strand to keep it properly aligned and ensure that it makes contact with the receptacle in a jack or other connector

cladding

The glass or plastic shield around the core of a fiber-optic cable. Cladding reflects light back to the core in patterns that vary depending on the transmission mode

APC (Angle Polished Connector)

The latest advancement in ferrule technology that uses the principles of reflection to its advantage by placing the end faces of the highly polished ferrules at an angle to each other, thus reducing the effect of back reflection

EMI (electromagnetic interference) Crosstalk

Two common sources of noise

fiber cleaver

cuts a clean slice through the fiber strands

Signals may travel in both directions over a medium but in only one direction at a time. For example, an apartment building's intercom system might be half-duplex if only one person can speak at a time.

half-duplex

Signals may travel in only one direction, and is sometimes called one-way, or unidirectional, communication. Broadcast radio and garage door openers are examples of simplex transmissions.

simplex

fiber stripper

strips off the outer layers of a fiber-optic cable

noise immunity

Because of its shielding, STP is more noise resistant than UTP. On the other hand, noise on UTP cable can be reduced with filtering and balancing techniques

Fiber type mismatch

This term is misleading because a fiber type mismatch is actually more of a fiber core mismatch. Connecting an SMF cable to an MMF cable will prevent the transmission from traversing the connection successfully, though some of the signal can get through. However, even same-mode cables can be mismatched, if the cores have different widths. A cable with a 50-micron core, for example, should not be connected to a cable with a 62.5-micron core, even though they're both MMF.

-alien crosstalk -NEXT (near end crosstalk) -FEXT (far end crosstalk)

Three common types of crosstalk?

-TDM (time division multiplexing) -STDM (statistical time division multiplexing) -FDM frequency division multiplexing)

Three common types of multiplexing used with copper lines

-WDM (wavelength division multiplexing -DWDM (dense wavelength division multiplexing or dense WDM) -CWDM (coarse wavelength division multiplexing or coarse WDM)

Three types of multiplexing technologies used with fiber-optic cable