Networking

UTP supplied by a telecommunications carrier that contains 100 wire pairs.

Part of an organization’s cross-connect facilities, a type of punch-down block designed to terminate Cat 5 or better twisted pair wires.

UTP supplied by a telecommunications carrier that contains 25 wire pairs.

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

A modulation technique in which the amplitude of the carrier signal is modified by the application of a data signal.

The IEEE standard for error and flow control in data frames

The IEEE standard for Ethernet networking devices and data handling (using theCSMA/CD access method).

The IEEE standard for token ring networking devices and data handling.

The IEEE standard for wireless networking.

(acknowledgment) A response generated at the Transport layer of the OSI model thatconfirms to a sender that its frame was received. The ACK packet is the third of three in thethree-step process of establishing a connection.

(American National Standards Institute) An organization composed of more than1000 representatives from industry and government who together determine standards forthe electronics industry in addition to other fields, such as chemical and nuclear engineering,health and safety, and construction.

(application programming interface) A set of routines that make up part of a softwareapplication.

A method of error checking that determines if the contents of an arriving dataunit match the contents of the data unit sent by the source.

A type of Transport layer protocol that requires the establishment ofa connection between communicating nodes before it will transmit data.

A type of Transport layer protocol that services a request without requiringa verified session and without guaranteeing delivery of data.

(cyclic redundancy check) An algorithm (or mathematical routine) used to verify theaccuracy of data contained in a data frame.

The second layer in the OSI model. The Data Link layer bridges thenetworking media with the Network layer. Its primary function is to divide the data it receivesfrom the Network layer into frames that can then be transmitted by the Physical layer.

(Electronic Industries Alliance) A trade organization composed of representatives fromelectronics manufacturing firms across the United States that sets standards for electronicequipment and lobbies for legislation favorable to the growth of the computer andelectronics industries.

The process of wrapping one layer’s PDU with protocol information so that itcan be interpreted by a lower layer. For example, Data Link layer protocols encapsulateNetwork layer packets in frames.

A networking technology originally developed at Xerox in the 1970s andimproved by Digital Equipment Corporation, Intel, and Xerox. Ethernet, which is themost common form of network transmission technology, follows the IEEE 802.3standard.

(Extended Unique Identifier-64) The IEEE standard defining 64-bit physicaladdresses. In the EUI-64 scheme, the OUI portion of an address is 24 bits in length.A 40-bit extension identifier makes up the rest of the physical address to total 64 bits.

A unique set of characters assigned to each NIC by its manufacturer.In the traditional, 48-bit physical addressing scheme, the extension identifier is 24 bits long.In EUI-64, the extension identifier is 40 bits long.

(frame check sequence) The field in a frame responsible for ensuring that data carriedby the frame arrives intact. It uses an algorithm, such as CRC, to accomplish thisverification.

A method of gauging the appropriate rate of data transmission based on howfast the recipient can accept data.

A Network layer service that subdivides segments it receives from theTransport layer into smaller packets.

A package for data that includes not only the raw data, or “payload,” but also thesender’s and recipient’s addressing and control information. Frames are generated at theData Link layer of the OSI model and are issued to the network at the Physical layer.

(Hypertext Transfer Protocol) An Application layer protocol that formulates andinterprets requests between Web clients and servers.

(Internet Architecture Board) A technical advisory group of researchers and technicalprofessionals responsible for Internet growth and management strategy, resolution oftechnical disputes, and standards oversight.

(Internet Assigned Numbers Authority) A nonprofit, United States governmentfundedgroup that was established at the University of Southern California and charged withmanaging IP address allocation and the Domain Name System. The oversight for many ofIANA’s functions was given to ICANN in 1998; however, IANA continues to performInternet addressing and Domain Name System administration.

(Internet Corporation for Assigned Names and Numbers) The nonprofitcorporation currently designated by the United States government to maintain and assignIP addresses.

(Institute of Electrical and Electronics Engineers) An international society composedof engineering professionals. Its goals are to promote development and education in theelectrical engineering and computer science fields.

(Internet Engineering Task Force) An organization that sets standards for howsystems communicate over the Internet (for example, how protocols operate andinteract).

(Internet Protocol)A core protocol in the TCP/IP suite that operates in the Networklayer of the OSI model and provides information about how and where data should bedelivered. IP is the subprotocol that enables TCP/IP to internetwork.

(Internet Protocol address) The Network layer address assigned to nodes touniquely identify them on a TCP/IP network. IPv4 addresses consist of 32 bits dividedinto four octets, or bytes. IPv6 addresses are composed of eight 16-bit fields, for a totalof 128 bits.

(International Organization for Standardization) A collection of standardsorganizations representing 162 countries with headquarters located in Geneva, Switzerland.Its goal is to establish international technological standards to facilitate the global exchangeof information and barrier-free trade.

(Internet Society) A professional organization with members from 90 chaptersaround the world that helps to establish technical standards for the Internet.

(Internet service provider) A business that provides organizations and individuals withInternet access and often, other services, such as e-mail and Web hosting.

(International Telecommunication Union) A United Nations agency that regulatesinternational telecommunications and provides developing countries with technical expertiseand equipment to advance their technological bases.

(Logical Link Control) sublayer The upper sublayer in the Data Link layer. The LLCprovides a common interface and supplies reliability and flow control services.

(maximum transmission unit) The largest data unit a network (for example, Ethernetor token ring) will accept for transmission.

A unique identifying number for a network node that follows ahierarchical addressing scheme and can be assigned through operating system software.Network addresses are added to data packets and interpreted by protocols at the Networklayer of the OSI model.

The third layer in the OSI model. Protocols in the Network layer translatenetwork addresses into their physical counterparts and decide how to route data from thesender to the receiver.

(Open Systems Interconnection) model A model for understanding and developingcomputer-to-computer communication developed in the 1980s by ISO. It divides networkingfunctions among seven layers: Physical, Data Link, Network, Transport, Session,Presentation, and Application.

(Organizationally Unique Identifier) A 24-bit character sequence assigned by IEEEthat appears at the beginning of a network interface’s physical address and identifies theNIC’s manufacturer.

(protocol data unit) A unit of data at any layer of the OSI model.

A 48- or 64-bit network interface identifier that includes two parts: theOUI, assigned by IEEE to the manufacturer, and the extension identifier, a unique numberassigned to each NIC by the manufacturer.

The lowest, or first, layer of the OSI model. Protocols in the Physical layergenerate and detect signals so as to transmit and receive data over a network medium. Theseprotocols also set the data transmission rate and monitor data error rates, but do notprovide error correction.

The sixth layer of the OSI model. Protocols in the Presentation layertranslate between the application and the network. Here, data are formatted in a schemathat the network can understand, with the format varying according to the type of networkused. The Presentation layer also manages data encryption and decryption, such as thescrambling of system passwords.

The process of reconstructing data units that have been segmented.

(Regional Internet Registry) A not-for-profit agency that manages the distribution ofIP addresses to private and public entities. ARIN is the RIR for North, Central, and SouthAmerica and sub-Saharan Africa. APNIC is the RIR for Asia and the Pacific region. RIPE isthe RIR for Europe and North Africa.

To intelligently direct data between networks based on addressing, patterns of usage,and availability of network segments.

A device that connects network segments and directs data based on informationcontained in the data packet.

A unit of data that results from subdividing a larger protocol data unit.

The process of decreasing the size of data units when moving data from anetwork that can handle larger data units to a network that can handle only smallerdata units.

The process of assigning a placeholder to each piece of a data blockto allow the receiving node’s Transport layer to reassemble the data in the correctorder.

A connection for data exchange between two parties. The term session may beused in the context of Web, remote access, or terminal and mainframe communications, forexample.

The fifth layer in the OSI model. The Session layer establishes and maintainscommunication between two nodes on the network. It can be considered the “traffic cop”for communications, such as videoconferencing, that require precisely coordinated dataexchange.

A documented agreement containing technical specifications or other precisecriteria that are used as guidelines to ensure that materials, products, processes, and servicessuit their intended purpose.

(synchronization) The packet one node sends to request a connection with anothernode on the network. The SYN packet is the first of three in the three-step process ofestablishing a connection.

(synchronization-acknowledgment) The packet a node sends to acknowledge toanother node that it has received a SYN request for connection. The SYN-ACK packet is thesecond of three in the three-step process of establishing a connection.

A device with little (if any) of its own processing or disk capacity that depends ona host to supply it with applications and data-processing services.

A three-step process in which Transport layer protocols establish aconnection between nodes. The three steps are: Node A issues a SYN packet to node B,node B responds with SYN-ACK, and node A responds with ACK.

(Telecommunications Industry Association) A subgroup of the EIA that focuses onstandards for information technology, wireless, satellite, fiber optics, and telephoneequipment. Probably the best known standards to come from the TIA/EIA alliance are itsguidelines for how network cable should be installed in commercial buildings, known as the“TIA/EIA 568-B Series.”

A special control frame that indicates to the rest of the network that a particularnode has the right to transmit data.

A networking technology developed by IBM in the 1980s. It relies upondirect links between nodes and a ring topology, using tokens to allow nodes totransmit data.

The fourth layer of the OSI model. In the Transport layer, protocolsensure that data are transferred from point A to point B reliably and without errors.Transport layer services include flow control, acknowledgment, error correction,segmentation, reassembly, and sequencing.

A device that boosts, or strengthens, an analog signal.

A measure of a signal’s strength.

A signal that uses variable voltage to create continuous waves, resulting in an inexact transmission.

The extent to which a signal has weakened after traveling a given distance.

(American Wire Gauge) A standard rating that indicates the diameter of a wire, such as the conducting core of a coaxial cable.

A measure of the difference between the highest and lowest frequencies that a medium can transmit.

A form of transmission in which digital signals are sent through direct current pulses applied to a wire. This direct current requires exclusive use of the wire’s capacity, so baseband systems can transmit only one signal, or one channel, at a time. Every device on a baseband system shares a single channel.

The radius of the maximum arc into which you can loop a cable before you will cause data transmission errors. Generally, a twisted pair cable’s bend radius is equal to or greater than four times the diameter of the cable.

A system founded on using 1s and 0s to encode information.

(binary digit) A bit equals a single pulse in the digital encoding system. It may have only one of two values: 0 or 1.

(Bayonet Neill-Concelman, or British Naval Connector) A standard for coaxial cable connectors named after its coupling method and its inventors.

A coaxial cable connector type that uses a twist-and-lock (or bayonet) style of coupling. It may be used with several coaxial cable types, including RG-6 and RG-59.

A braided metal shielding used to insulate some types of coaxial cable.

A form of transmission in which signals are modulated as radio frequency analog pulses with different frequency ranges. Unlike baseband, broadband technology does not involve binary encoding. The use of multiple frequencies enables a broadband system to operate over several channels and, therefore, carry much more data than a baseband system.

A transmission that involves one transmitter and multiple, undefined receivers.

Eight bits of information. In a digital signaling system, broadly speaking, 1 byte carries one piece of information.

The hardware that constitutes the enterprise-wide cabling system.

Abbreviation for the word category when describing a type of twisted pair cable. For example, Category 5 unshielded twisted pair cable may also be called Cat 5.

(Category 3) A form of UTP that contains four wire pairs and can carry up to 10 Mbps, with a possible bandwidth of 16 MHz. Cat 3 was used for 10-Mbps Ethernet or 4-Mbps token ring networks.

(Category 5) A form of UTP that contains four wire pairs and supports up to 100-Mbps throughput and a 100-MHz signal rate.

(Enhanced Category 5) A higher-grade version of Cat 5 wiring that contains highquality copper, offers a high twist ratio, and uses advanced methods for reducing cross talk. Enhanced Cat 5 can support a signaling rate of up to 350 MHz, more than triple the capability of regular Cat 5.

(Category 6) A twisted pair cable that contains four wire pairs, each wrapped in foil insulation. Additional foil insulation covers the bundle of wire pairs, and a fire-resistant plastic sheath covers the second foil layer. The foil insulation provides excellent resistance to cross talk and enables Cat 6 to support a signaling rate of 250 MHz and at least six times the throughput supported by regular Cat 5.

(Augmented Category 6) A higher-grade version of Cat 6 wiring that further reduces attenuation and cross talk and allows for potentially exceeding traditional network segment length limits. Cat 6a is capable of a 500-MHz signaling rate and can reliably transmit data at multi-gigabit per second rates.

(Category 7) A twisted pair cable that contains multiple wire pairs, each separately shielded then surrounded by another layer of shielding within the jacket. Cat 7 can support up to a 1-GHz signal rate. But because of its extra layers, it is less flexible than other forms of twisted pair wiring.

A distinct communication path between two or more nodes, much like a lane is a distinct transportation path on a freeway. Channels may be separated either logically (as in multiplexing) or physically (as when they are carried by separate wires).

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. This reflection allows fiber to bend around corners without impairing the light-based signal.

A type of cable that consists of a central metal conducting core, which might be solid or stranded and is often made of copper, surrounded by an insulator, a braided metal shielding, called braiding, and an outer cover, called the sheath or jacket. Coaxial cable, called “coax” for short, was the foundation for Ethernet networks in the 1980s. Today it’s used to connect cable Internet and cable TV systems.

The pipeline used to contain and protect cabling. Conduit is usually made from metal.

The pieces of hardware that connect the wire to the network device, be it a file server, workstation, switch, or printer.

The central component of a cable designed to carry a signal. The core of a fiber-optic cable, for example, consists of one or several glass or plastic fibers. The core of a coaxial copper cable consists of one large or several small strands of copper.

A twisted pair patch cable in which the termination locations of the transmit and receive wires on one end of the cable are reversed.

A type of interference caused by signals traveling on nearby wire pairs infringing on another pair’s signal.

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

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

(demarc) The point of division between a telecommunications service carrier’s network and a building’s internal network.

(demux) A device that separates multiplexed signals once they are received and regenerates them in their original form.

As opposed to analog signals, digital signals are composed of pulses that can have a value of only 1 or 0.

(dense wavelength division multiplexing) 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. In DWDM, little space exists between carrier waves in order to achieve extraordinary high capacity.

(electromagnetic interference) A type of interference that may be caused by motors, power lines, televisions, copiers, fluorescent lights, or other sources of electrical activity.

The facilities necessary for a service provider (whether it is a local phone company, Internet service provider, or long-distance carrier) to connect with another organization’s LAN or WAN.

(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.

A short tube within a fiber-optic cable connector that encircles the fiber strand and keeps it properly aligned.

A form of cable that contains one or several glass or plastic fibers in its core. Data is transmitted via pulsing light sent from a laser or light-emitting diode (LED) through the central fiber (or fibers). Fiber-optic cables offer significantly higher throughput than copper-based cables. They may be single-mode or multimode and typically use wavedivision multiplexing to carry multiple signals.

(frequency modulation) A method of data modulation in which the frequency of the carrier signal is modified by the application of the data signal.

The number of times that a signal’s amplitude changes over a fixed period of time, expressed in cycles per second, or hertz (Hz).

A connector used to terminate coaxial cable used for transmitting television and broadband cable signals.

A type of transmission in which signals may travel in both directions over a medium simultaneously. May also be called, simply, “duplex.”

A type of transmission in which signals may travel in both directions over a medium, but in only one direction at a time.

(Hz) A measure of frequency equivalent to the number of amplitude cycles per second.

(intermediate distribution frame) A junction point between the MDF and concentrations of fewer connections—for example, those that terminate in a telecommunications closet.

The resistance that contributes to controlling an electrical signal. Impedance is measured in ohms.

The delay between the transmission of a signal and its receipt.

(local connector) A connector used with single-mode or multimode fiber-optic cable.

(main distribution frame) Also known as the main cross-connect, the first point of interconnection between an organization’s LAN or WAN and a service provider’s facility.

A device that enables networks or segments using different media to interconnect and exchange signals.

(multimode fiber) A type of fiber-optic cable that contains a core with a diameter between 50 and 100 microns, through which many pulses of light generated by a lightemitting diode (LED) travel at different angles.

A device that modulates analog signals into digital signals at the transmitting end for transmission over telephone lines, and demodulates digital signals into analog signals at the receiving end.

A technique for formatting signals in which one property of a simple carrier wave is modified by the addition of a data signal during transmission.

(mechanical transfer registered jack) A connector used with single-mode or multimode fiber-optic cable.

A device that separates a medium into multiple channels and issues signals to each of those subchannels.

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

(near end cross talk) Cross talk, or the impingement of the signal carried by one wire onto a nearby wire, that occurs between wire pairs near the source of a signal.

The unwanted signals, or interference, from sources near network cabling, such as electrical motors, power lines, and radar.