Ray Horak, Technology Editor, Telecom Reseller
We live in a complex world that increasingly is defined by information technology, by which I do not mean classical data processing but rather the creation, storage, and distribution of all forms of information, including audio, text, image, and video. In combination, such information becomes multimedia in nature. Computers of one sort or another are used to capture and create much of that information, which is remarkable in itself, but the value of the data is largely dependent on our ability to share it with others. In terms of technology, networks enable the sharing of information—Local Area Networks (LANs) within the premises, Metropolitan Area Networks (MANs) within a metro area, and Wide Area Networks (WANs) for the longer haul.
Since Alexander Graham Bell invented the telephone in 1876, copper wires have given way to glass fibers in the WAN backbone, and fiber optics is now commonplace in the local loop. Coaxial cable has been rendered obsolete in the LAN by twisted pair, glass and plastic optical fiber, and now RF technologies. Wireline technologies have yielded to or are supplemented by wireless in many applications, not only in the LAN, but also in the MAN and WAN. Since its invention in 1877 and for well over 100 years, circuit switching was the sole method by which telephone calls were connected, but is now rapidly being replaced by packet switching. Voice over Internet Protocol (VoIP) technologies undoubtedly are rendering the traditional circuit-switched PSTN obsolete. The Internet has been commercialized and made available to the general public. All of these and many other relevant technologies build in some way on those that came before and each adds to the vocabulary of telecommunications a set of terminology, along with the seemingly requisite abbreviations, acronyms, contractions, initialisms and portmanteaux. Many of these have multiple definitions, sensitive to historical or technological context. Broadband, for example, has one set of definitions in a WAN context, but quite another in the LAN domain. Carrier also has several definitions, as do buffer and ATM, and there are at least four kinds of cells. Some acronyms really aren’t acronyms at all—ISO comes to mind. The origin of some terms is fascinating, with bug and ping being good examples.
All the communications technology in the world will not help us understand each other unless we have a common vocabulary. I love words, their origins, their evolution and their precise meanings. As a kid, I loved to read the Webster’s Dictionary and Brittanica Encyclopedia on a cold or wet afternoon in South Texas. Don’t ask me why—I can’t explain it except to blame it on my mother, who instilled in me a love of books. If you can relate to that at all, you can imagine how happy I was when my editor at Wiley asked me to write Webster’s New World Telecom Dictionary. It is not an open-source dictionary like Wikipedia, written by a community of unknown people of uncertain skill and motivation, and peer reviewed by a community of peers of the same ilk. I wrote every word of Webster’s and I am solely responsible for its content, which is how I know that it is correct and objective. This free glossary is excerpted from Webster’s, with the blessing of the folks at Wiley. I hope you enjoy it, find it useful and hunger for more. If so, please feel free to buy the book, which is much more complete but is not free.
Ray Horak is Technology Editor of Telecom Reseller and a published author. Here is a link to Ray’s popular Webster’s New World Telecom Dictionary.
http://www.digitalguru.com/ProductDetails.asp?ProductCode=9780471774570
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0B+D Referring to a variation of the ITU-T specification for ISDN basic rate interface (BRI), also known as basic rate access (BRA). BRI supports two bearer (B) channels and one data (D) channel. Intended for applications that do not require an information-bearing channel for voice or data transmission, 0B+D supports zero bearer (B) channels and one data (D) channel, which provides a transmission rate of 16 kbps. The D channel is designated for signaling and control purposes, but also can be used for low-speed packet data applications such as transaction processing, credit card verification, and telemetry.
1394 The IEEE specification for a data transport bus between a host computer and peripherals, such as high-density storage devices and high-resolution still and video cameras, and is designed to eliminate the bottleneck at the serial port of a LAN-attached PC. 1394 increases the speed of the Small Computer System Interface (SCSI) to100, 200, and 400 Mbps to support take full advantage of high speed LANs. A single 1394 port can support up to 63 peripherals over a six-conductor cable up to 4.5 meters in length, and as many as 16 cables can be daisy-chained to extend the total length to as much as 72 meters. IEEE 1394 is known as FireWire in Apple Computer terminology.
23B+D Synonymous with primary rate interface (PRI). Referring to the ITU-T specification for an ISDN interface supporting 23 bearer (B) channels and one data (D) channel. 23B+D is compatible with T1 and J-1, and is used in North America and Japan.
2B+D Synonymous with basic rate interface (BRI) and basic rate access (BRA). Referring to the ITU-T specification for an ISDN interface supporting two bearer (B) channels and one data (D) channel.
2B1Q (2 Binary 1 Quaternary) A line coding technique, with echo cancellation, used in North America for ISDN basic rate interface (BRI). 2B1Q is a form of pulse amplitude modulation (PAM) that uses four (i.e., quaternary) levels of amplitude (i.e., voltage), each of which represents two adjacent bits in a bit stream, and is accomplished by varying the voltage at nominal levels of 1 (actually 0.833) and 3 (actually 2.5) volts, as illustrated in Figure 2B1Q. As 2B1Q impresses two bits on each baud, the baud rate is halved, and a baud rate of 80 kilobaud will support a signaling rate of 160 kbps. Because statistics force the line voltage to be positive half the time and negative half the time, on average, the signal power lies at a frequency of 40 kHz, which is half the baud rate. 2B1Q also is the electrical line coding technique used in high-bit-rate digital subscriber line (HDSL). 2B1Q also is known as 4-level pulse amplitude modulation (4 PAM). In European and many other countries, the line coding technique employed is 4 Binary 3 Ternary (4B3T).
30B+D Synonymous with primary rate access (PRA). Referring to the ITU-T specification for an ISDN interface supporting 30 bearer (B) channels and one data (D) channel. 30B+D is compatible with E-1, and is used outside of North America and Japan.
abbreviation A shortened form of a word or phrase. P-phone, for example, is an abbreviation of Proprietary phone. Acronyms, contractions, and initialisms are special forms of abbreviations comprising the initial letters or other parts of several words that constitute a term.
access circuit An access circuit is one used to gain access to, or entry to, a Wide Area Network (WAN) or Metropolitan Area Network (MAN). An access circuit usually is described as a local loop that connects a customer premises to a switch, router, multiplexer, or other device at the edge of the carrier or service provider network.
access rate The maximum data rate of a channel between a user site and a network, as defined by the bandwidth of the access link available for data transmission.
access tandem switch A switch in the public switched telephone network (PSTN) that serves to connect the local exchange carriers (LECs), i.e., local telephone companies, to the interexchange carriers (IXCs), i.e., long distance carriers.
ACK (ACKnowledgement) 1. A transmission control character sent by a station indicating that it is ready to receive a transmission. In ASCII, ACK is represented by the bit pattern 0110000. See also ASCII. 2. A positive acknowledgement that a message, block, or frame has been received without error across a communications circuit, that the data set can be erased from buffer memory, and that the next data set can be sent.
acronym A pronounceable word formed of the initial letters or other parts of several words. An acronym generally comprises all upper case letters. SONET, for example, is the acronym for Synchronous Optical NETwork, a North American standard for fiber optic transmission systems. SONET became internationalized as SDH, an unpronounceable initialism for Synchronous Digital Hierarchy. Acronyms occasionally comprise all lower case letters. For example, bit is the acronym for binary digit, which is the basic unit of information in a binary numbering system. Bit also is a word unto itself, and with multiple meanings, including a small piece of something. Acronyms sometimes comprise both upper case and lower case letters. Sesame, for example, is the acronym for Secure European Systems for Applications in a Multivendor Environment.
aliasing A phenomenon that occurs when different analog continuous signals overlap and become indistinguishable. If the sampling of the analog waveform is too infrequent (less than half the highest frequency present), the digitally encoded signal cannot reliably be decoded faithfully. Rather, it can be reconstructed as an alias of the true signal. Aliasing is a major concern in the digital encoding of analog audio and video signals. Aliasing in video signals results in artifacts in video images that can manifest as jagged blockings or a tiling effect.
Aloha From the Hawaiian aloha, meaning hello and goodbye. Also known as pure Aloha. A protocol developed at the University of Hawaii in the early 1970s as a contention management mechanism for use in inter-island wireless networks. Aloha is a very simple protocol that in which the source just sends a frame of data whenever it desires. A target receiver confirms a frame whenever it receives one, and the source sends another whenever it desires. If the target receiver does not confirm the receipt of the frame within a specified time, the source resends it until it receives a confirmation. Pure Aloha is simple and inexpensive, but not useful in managing contention in large, complex networks.
AlohaNet A packet radio system technology developed at the University of Hawaii in 1970. AlohaNet packet technology subsequently was incorporated into the first local area network (LAN) technology, which became known as Ethernet.
amplitude noise A type of noise that occurs when the amplitude of the signal output by an amplifier or other device is not a linear function of the input amplitude.
analog 1. A continuously present and continuously variable signal. In their native, or original, forms, audio and visual signals are analog. 2. Pertaining to the representation of data in the form of a continuous signal.
artifact Unintended and unwanted distortions or other aberrations in reproduced audio or video due to transmission errors or signal processing operations. Artifacts often result from the use of lossy compression algorithms at high compression ratios. Artifacts in video images can manifest as jagged blockings or a tiling effect known as aliasing, banding of colors, white spots, and even dropped frames.
ATM (Asynchronous Transfer Mode) A fast-packet, connection-oriented, cell-switching technology for broadband signals. ATM was an outgrowth of the ITU-T development efforts towards broadband integrated services digital network (B-ISDN). Although B-ISDN faltered, ATM became the switching technology of choice in the broadband backbone of the public telephone network. ATM is designed to accommodate any form of data, including voice, facsimile, computer data, video, image, and multimedia, whether compressed or uncompressed, whether real-time or non-real-time in nature, and with guaranteed quality of service (QoS). ATM generally operates at minimum access speeds of DS-1 (e.g., T1 at 1.544 Mbps and E-1 at 2.048 Mbps) and DS-3 (e.g., E-3 at 34.368 Mbps and T1 at 44.736 Mbps). Designed to operate at very high speeds, ATM benefits from fiber optic transmission systems (FOTS) and commonly is provisioned over SDH/SONET networks. Access circuits operating at OC-3 (155 Mbps) are not unusual and backbone transmission rates generally are OC-3, at a minimum. ATM traffic consists of three basic types.
- Constant Bit Rate (CBR) traffic requires access to time slots at regular and precise intervals. Real-time, uncompressed voice and video are examples of CBR traffic.
- Variable Bit Rate (VBR) traffic, such as compressed voice and video and bursty data traffic, requires access to time slots at a rate that can vary dramatically from time to time.
- Available Bit Rate (ABR) traffic, also known as best-effort ATM, supports bursty LAN traffic and other traffic that can deal with time slot access on an as-available basis
ATM organizes data into cells, as illustrated in the following Figure. Each cell comprises a header of 5 octets and payload of 48 octets, with the payload including some amount of overhead attributable to Convergence Sublayer and Data Link Layer and Network Layer headers. Although the total overhead is in the range of 10 percent, the small cell size offers the advantage of effectively supporting any type of data. The fixed cell size offers the advantage of predictability, very much unlike the variable-length frames associated with services such as X.25, frame relay, and Ethernet, or the variable-length packets associated with the Internet Protocol (IP). This level of predictability yields much improved access control and congestion control. ATM multiplexes the cells, which contend for access to a broadband facility that ideally is SDH or SONET in nature.
The ATM cell header provides limited Data Link Layer functionality, managing the allocation of the resources of the underlying Physical Layer of the transmission facility. The ATM cell switches also perform Layer 1 functions such as clocking, bit encoding, and physical-medium connection. The header also is used for channel identification, thereby ensuring that all cells travel the same physical path and, therefore, arrive in sequence. The header is structured as follows:
- Generic Flow Control (GFC): 4 bits that provide local flow control.
- Virtual Path Identifier (VPI): 8 bits identifying the Virtual Path (VP).
- Virtual Channel Identifier (VCI): 16 bits identifying the Virtual Channel (VC).
- Payload Type Indicator (PTI): 3 bits distinguishing between cells carrying user information and cells carrying service information.
- Cell Loss Priority (CLP): 1 bit identifying the priority level of the cell to determine the eligibility of that cell for discard in the event of network congestion.
- Header Error Control (HEC): 8 bits providing error checking of the header, but not the payload. There is no provision for error correction.
ATM standards largely are outgrowths of B-ISDN standards set by the ITU-T. The ATM Forum, now merged into the MFA Forum, developed interoperability specifications. The Frame Relay Forum (FRF), also now merged into the MFA Forum, worked with the ATM Forum in the development and publishing of joint Implementation Agreements (IAs) that specify the protocol interworking functions between frame relay and ATM networks. The Internet Engineering Task Force (IETF) also got involved in standards development as ATM has significant implications relative to the Internet backbone.
AWG (American Wire Gauge) The standard measurement of gauge in United States for all metals other than iron and steel. The gauge numbers are retrogressive; in other words, the larger the number, the thinner the conductor. The AWG number indicates the approximate number of wires that, laid side-by-side, span one inch. Historically, the AWG number indicated the number of times during the manufacturing process that the copper wire was cold drawn through the wire machine, with each draw involving a die of slightly smaller diameter in order to reduce the diameter of the wire a bit more. The contemporary process involves many fewer draws. Twisted-pairs commonly employed in telco networks vary from 19 to 28 gauge, with the most common being 24 gauge.
B&S (Brown and Sharp Wire Gauge) The original name for American Wire Gauge (AWG).
bonding 1. The process or method of permanently joining the metallic shields, screens, or armor of multiple wire and cable segments in order to establish electrical continuity between them, to a ground strap or wire that connects to a ground rod, and eventually to ground. Bonding serves to ensure that electrical noise will be conducted to ground, rather than coupling with and, therefore, interfering with the desired signal. 2. Synonymous with channel aggregation, dynamic bandwidth allocation, multirate ISDN, and Nx64. A feature of ISDN-compatible terminal adapters (TAs), PBXs, and routers that enables the system to dynamically allocate, or bond, multiple contiguous 64-kbps bearer (B) channels to serve an application that requires more than a narrowband channel. From the transmitter, through the network, and to the receiver, the narrowband channels are bonded and treated as a single superrate channel known as a high-speed (H) channel. As an example, a videoconference might require 128 kbps (2 channels) or 384 kbps (6 channels). Dial-up Internet access typically benefits from bonding two channels for a connection at 128 kbps. Also, multiple IP, ATM, or frame relay links can be joined to emulate a faster channel.
broadband 1. In the Wide Area Network (WAN) domain, broadband is an imprecise term referring to a circuit or channel providing a relatively large amount of bandwidth. The ITU-T defines broadband in Recommendation I.113 as a transmission rate faster than the primary rate (referring to ISDN), which translates into 1.544 Mbps in North America and 2.048 Mbps in most of the rest of the world. The U.S. Federal Communications Commission (FCC) does not define broadband, but defines high-speed services as supporting a data rate of at least 200 kbps in at least one direction and advanced telecommunications capability as at least 200 kbps in both directions. Asymmetric digital subscriber line (ADSL) generally is described as a broadband access technology, even though many ADSL services operate at less than T1 and E-1 rates. In this context, ADSL certainly operates at much higher rates than the predecessor modem technology, which operates at narrowband rates of less than 64 kbps. Relatively speaking, ADSL is broadband in nature, even at very low operating rates. See also bandwidth, FCC, ISDN, ITU-T, narrowband, and wideband. 2. In the Local Area Network (LAN) domain, broadband refers to a multichannel RF-based (Radio Frequency-based) LAN, with the channels derived through frequency division multiplexing (FDM).The workstations and other attached digital devices access analog channels through radio frequency (RF) modems that accomplish the digital-to-analog conversion process. Broadband LANs commonly use 75-ohm CATV-type coax, and use CATV-style connectors, taps, filters, and amplifiers in a tree and branch topology, which essentially is a variation of the bus with multiple branches off of a main root bus, much as there are branches off of the main trunk of a tree. The only broadband LAN to gain any significant following was 10Broad36, which has long been considered obsolete. All other LANs are baseband in nature.
buffer 1. A region of memory that temporarily stores data in a networking device, commonly to compensate for congestion at an incoming or outgoing port on a concentrator, multiplexer, switch, or router. If, for example, the level of incoming traffic exceeds the resources of a switch, a buffer at the incoming switch port can temporarily store the excess traffic until the switch has sufficient resources to process the traffic. If the level of outgoing traffic exceeds the capacity of the circuit, a buffer at the outgoing switch port can temporarily store the excess traffic until the circuit can accommodate it. A buffer also can serve to store packet data temporarily to allow retransmission in the event that a downstream device does not receive the packet without error within an acceptable period of time. 2. A standalone storage device specifically designed to store data until such time as it is downloaded by another device for processing. A PBX system, for example, commonly outputs call detail records to a buffer, which stores them in temporary memory until a centralized poller accesses the buffer and downloads the data for subsequent processing into various call detail Reports for purposes of cost allocation and management, traffic analysis, and security analysis. 3. Electrically powered mechanical device that rotates abrasive pads for cleaning floors. Buffers are known to cause network problems when plugged into shared outlets by injecting electrical noise or blowing fuses. Note: It is always a good idea to make sure that a computer system has access to clean power, i.e., a dedicated circuit that, by definition, will be free of power dips caused by buffers and other devices. See also CDR and register.
bug 1. An error in coding or logic that causes a computer software program to malfunction (i.e., perform erratically, suffer catastrophic failure (crash), or produce invalid results. Although the origin of the term bug is somewhat in dispute, folklore dates it the mid-to-late 1940s, when a moth attracted to the light given off by the vacuum tubes of one of the first digital computers, either the Mark I or the ENIAC, died and shorted one of the circuits, causing a system failure. Others attribute the term to Thomas Edison (1878). So much for the etymology of bug. As for entomology, a moth is not a bug, strictly speaking. A true bug has thickened forewings and mouth parts adapted for piercing and sucking, and is of the insect order Hemiptera, which includes aphids, cicadas, and squash bugs. Moths suck, but do not pierce, and belong to the order Lepidoptera, as do butterflies. (Note: There are two kinds of people in this world—those who just love this arcane trivia, and those who hate it. I love it, in moderation. Arcane trivia is somewhat tautological, which is a pedantic word for redundant. There are two types of people in this world—those who love pedants and those who hate them. I hate them.) By the way, a bug fix is in the form of a patch, update, upgrade, or instecticide, depending on the type of bug involved. See also bug fix, Edison, Thomas Alva; etymology, entomology, and pedant 2. An undocumented feature. (Thats a joke.)
carrier 1. A continuous signal, or waveform, at a certain frequency on a circuit, or within a certain frequency range, and that can be modulated to support an information-bearing signal. In other words, the carrier carries the information signal, which the transmitter impresses on the carrier by varying the signal in some fashion. The carrier also can support signaling and control information used to coordinate and manage various aspects of network operations, although signaling and control can also occur over a sub-carrier frequency. A carrier also is known as a carrier wave. 2. A company that provides information transport services. As examples, a Local Exchange Carrier (LEC) provides local information transport services, and an Interexchange Carrier (IEC or IXC) provides transport services between LECs. A heavy carrier is facilities-based, i.e., owns the switching and transmission systems that comprise the network it uses to provide services to its customers. A light carrier is not facilities-based, i.e., leases rather than owns the network it uses to provide services.
CCS 1. Centum Call Seconds In traffic engineering, hundred (centum) call seconds. One hour contains 3600 call seconds (60 seconds times 60 minutes), or 36 CCS. 2. Common Channel Signaling A technique that uses a highly robust subnetwork, or separate network, to support the signaling and control and the network management requirements of the primary communications network. A CCS link is digital in nature, based on packet switching, and often in the form of a dedicated T1 or E-1 channel over a broadband optical fiber. A CCS subnetwork connects the various network switches and routers to centralized computer systems and databases in order to monitor and control the operations of an entire communications network, from end to end. Signaling System 7 (SS7), also known as Common Channel Signaling System 7 (CCS7) is a CCS network.
channel A means of supporting a connection between two devices, such as a transmitter and a receiver, in support of a single communication. More specifically, a channel is a logical connection over a physical circuit in support of a single conversation.
circuit An end-to-end communications path between a transmitter and a receiver. Circuit generally implies a logical connection, or session, over a physical medium. Circuit often is used interchangeably with path, link, line, and channel, although the usage can be specific to the underlying technology, the overall context, and other factors.
circuit An end-to-end communications path between a transmitter and a receiver. Circuit generally implies a logical connection, or session, over a physical medium. Circuit often is used interchangeably with path, link, line, and channel, although the usage can be specific to the underlying technology, the overall context, and other factors.
client In a client/server architecture, a complete, standalone computer that optimizes the user interface, relying on servers to handle the more mundane tasks associated with application and file storage, network administration, security, and other critical functions.
client/server A network architecture that distributes intelligence and responsibilities at several levels, with some machines designated as servers to serve the needs of client machines.
clocking pulse Periodic signals generated by a timing source for purposes of synchronizing the flow of data within a computer or between computers across a circuit.
cloud A wide area network (WAN) commonly is depicted as a cloud, which serves to obscure its complex inner workings from view. Data just pops in on one side of the cloud and pops out on the other side, so to speak.
CO (Central Office) 1. A local telephone company office that provides a central point for the termination of lines and trunks, and where they can be interconnected, i.e., connections can be exchanged. 2. The CO switch, rather than the building that houses it.
compression A means of reducing the amount of data to be transmitted or stored. Compression is possible since there always is some amount of data redundancy or there may be a predictable flow to the data. These characteristics of a set of data or a stream of data allow the use of a sort of mathematical algorithm to represent or describe the original data in fewer bits. A matching decompression process reverses the compression process and restores the data to its original form, or an approximation thereof. Compression serves to improve the efficiency of data transmission and storage, and is especially valuable if bandwidth and memory resources are limited.
contraction The shortening of a word or phrase by omitting letters or syllables. In the English language, a contraction generally, but not always, marks the omitted letters or syllables with an apostrophe or a period. Telco, for example, is a contraction of telephone company. Doesnt is a contraction of does not. Mr. is a contraction of mister, a title of courtesy for a man. Mrs. is a contraction of mistress, a title of courtesy for a married or widowed woman. Once upon a civilized time, we used the title of courtesy Miss to denote a girl or unmarried woman. The feminist movement of the 1970s forced a change to Ms., which makes no distinction in a womans marital status. Now we frequently delete such titles, altogether, leaving those who dont (do not) know the person to guess at both their (his/her) gender and marital status, which is all quite silly, even if it is PC (politically correct). (Note: PC is an initialism.)
dielectric A substance that is not a conductor of direct electric current, a dielectric is an insulator, rather than a conductor. A dielectric permits the passage of the lines of force associated with an electromagnetic field, but does not conduct the current. As dielectrics, however, can sustain an electromagnetic field, they are commonly used in capacitors and between wires in a cable. Dielectrics include rubber, gutta percha, wood pulp, polyethylene, polyvinyl chloride, flouropolymer resin, and Teflon, all of which have been used at various times as insulation in telecommunications cable and wire applications. The dielectric properties of plastic and glass make them ideal optical conductors in fiber optic cables, which are immune from electromagnetic interference (EMI). The dielectric nature of aramid fiber and fiberglass make them excellent strength members for improving the tensile strength of fiber optic and copper cables, respectively.
digital Pertaining to the representation of data by means of digits, or discrete quantities such as numbers or signals that can be interpreted as numbers. By contrast, analog signals have meaning at all intermediate levels. In telecommunications, digital transmission systems make use of pulses or varying levels of electromagnetic energy, such as electricity, radio waves, or light.
edge switch An edge switch is positioned at the physical edge of a public network. The user organization gains access to an edge switch via an access link, or local loop. A Central Office (CO) is an example of an edge switch in the context of the circuit-switched Public Switched Telephone Network (PSTN). In the context of asynchronous transfer mode (ATM) an edge switch may be referred to as an access node or service node.
empty suit A derisive term for an anonymous business executive or bureaucrat lacking in both individuality and substance, i.e., a phony. Such a person is little more than a suit of clothes. As we used to say when I was a young man in Texas, such a person is all hat and no horse, i.e., a drugstore cowboy. A suit, especially an empty suit, is in sharp contrast to a techie.
encode The process of coding data into symbolic form.
encrypt The process of coding or ciphering data into symbolic form.
end office A local central office (CO), which is at the end, or edge, of the public switched telephone network (PSTN).
entropy (S) 1. In physics, and particularly in the area of thermodynamics, a measure of the amount of energy unavailable to do work in a closed system. 2. The degradation of the matter and energy in the universe to the point of inert uniformity. The dispersal of energy. 3. In information theory, a measure of the content of a message evaluated with respect to its probability of occurrence, or uncertainty of occurrence, depending on your perspective. 4. In communications, a measure of the randomness of signal noise occurring in transmission
facsimile (fax) From the Latin facere simile, which translates to make similar. Technology that enables the transmission of images between paired transmitters and receivers. The transmitting fax scans the image document from top to bottom and from left to right, looking for dots of color—most machines support only black and white, some systems will also support 256 levels of grayscale, and some will support a large color palette—at various levels of resolution, as measured in lines per inch (lpi) and dots per inch (dpi). The fax machine translates the dots into data bits, which it compresses in order to reduce transmission time, and transmits through a network to the receiving machine. If the local loop is analog in nature, as is usually the case, an embedded modem transmits the digital data by modulating the analog waveforms.
fair use policy A policy of some Internet service providers (ISPs) that imposes bandwidth restrictions on users who exhibit patterns of system usage that exceed certain thresholds for extended periods of time. Direct broadcast satellite (DBS) providers offering two-way Internet access have fair use policies in place as bandwidth is so highly limited and a small number of highly active users can consume large amounts of bandwidth, leaving little for consumption by others. More traditional terrestrial ISPs in various countries (e.g., Australia and South Africa) have similar policies with respect to international usage such as web surfing and file transfers.
firewall Security software that can actively block unauthorized entities from gaining access to internal resources such as systems, servers, databases, and networks.
footprint 1. The physical space something occupies, as in the footprint of a computer or a PBX. 2. The coverage area of a satellite or other radio transmitter system,
forked ringing An IPBX feature that allows a call processor to ring multiple phones at once, rather than in turn, and serve the call to the first phone that answers. Forked ringing is enabled by the Session Initiation Protocol (SIP) signaling and control protocol.
forklift upgrade Referring to a complete system replacement. The term originated in days of yore, when mainframe computers and PBXs were so big and heavy that it literally took a forklift to remove an obsolete system from the computer room or switch room and replace it with another, usually of at least equal size and weight.
gateway 1. A node that interconnects two or more disparate networks, both physically and logically, serving as a protocol converter (e.g., PSTN to IP) and media converter. 2. The collection of hardware and software required to interconnect two or more disparate networks, including performing protocol conversion.
ground A conducting connection, whether intentional or accidental, by which an electric circuit is connected at some point to the Earth, or to some other large conducting body that can serve in place of the earth. The point can be a single point common to a great many circuits, such as an equipment frame, chassis, or cabinet. Ground variously serves as a reference point, a return path for an electrical signal, and to carry current safely away from a circuit in the event of a fault. In the event that earth is not available as a ground, the conducting frame of an aircraft, spacecraft, or land vehicle not conductively connected to the earth can serve as ground.
ground start A signaling technique typically used between PBXs and central office switches. Ground start signaling momentarily grounds one side (usually the tip rather than the ring side) of the circuit, sending an immediate signal to the central office switch in order to start, i.e., seize the trunk and get dial tone. Ground start is superior to loop start as it avoids glare, or collisions between incoming and outgoing calls. Loop start is used in POTS applications between central offices and telephone sets or key telephone systems.
GSTN (Global Switched Telephone Network) The generic ITU-T term for the international public telephone network that comprises the national PSTNs (Public Switched Telephone Networks) and the facilities that interconnect them.
H.323 The ITU-T Recommendation for multimedia communications over packet networks, H.323 addresses service over local area networks (LANs), but extends to the Internet and other IP-based networks. H.323 is not linked to any specific hardware device or operating system (OS) and, therefore, can be deployed in a wide variety of devices, including PCs, telephone sets, cable modems, and set-top boxes. H.323 supports multicast communications, thereby avoiding the requirement for specialized multipoint control units (MCUs) in a network where routers assume the responsibility for packet replicating. Version 2 1998) provides a means for encryption, includes mechanisms for call transfer and call forward, supports URL-style addresses, and provides the ability for endpoints to set quality of service (QoS) levels through Resource Reservation Protocol (RSVP).
hardphone A conventional telephone set, which is single function terminal, hardwired to support voice communications. A hardphone is in sharp contrast to a softphone, which is a software-based telephone comprising a desktop, laptop, or tablet computer equipped with a microphone, a speaker, and software that allows it to emulate a hardphone.
hardware The physical components, peripherals, and equipment that comprise a computer system, as compared to the logical system software programs and routines that run the computer and the application programs that support the tasks of end users. If you can break it with a hammer, its hardware. Otherwise, its software.
harmonic A sinusoidal component of waveform that is an integral multiple of a fundamental frequency. The signal waveform is known as the first harmonic. A waveform that has a component that is twice the frequency of the fundamental frequency, or signal waveform, is known as the second harmonic. An unwanted harmonic causes harmonic distortion.
Holmes, E.T. The inventor of the first exchange for telephone service. Holmess father had invented and installed the centralized burglar alarm system in 1858 in Boston, Massachusetts. In 1877, Holmes obtained telephone numbers 6 and 7, and attached them to a wire in his office. He then placed six box telephones on a new shelf in his office. During the daylight hours, the telephone exchange operator could switch any of these telephones could be switched into connection with the burglar alarm wires and any two of the six wires could be joined by a wire cord. At night, when the telephone operator was off duty, the telephone network reverted to a burglar alarm network.
home run An inside cable and wire star configuration in which each telephone or data jack connects directly back to a common point, such as a demarcation point (demarc), wiring closet, or key service unit (KSU). The alternative is a shared loop that connects multiple jacks to one or two pairs that connect to the demarc or KSU.
horizontal cable A type of inside cable used for horizontal use in non-plenum areas. While horizontal cable must be fire retardant, the National Electrical Code (NEC) specifications are not as demanding as those governing the use of plenum cable or riser cable.
host 1. In a mainframe or midrange computer environment, the host is the central computer to which the networks and terminals connect. 2. In telecommunications, local area networks (LANs), and networks, in general, a server that functions to provide programs or data files to client computers. 3. In the Internet, any computer that can serve as a the source or destination for data transfers. An Internet host has a unique Internet Protocol (IP) address and unique domain name.
hot standby Referring to a redundant system or processor that is not only turned on and warmed up, but is active and prepared to immediately assume the responsibilities of the primary system in the event it suffers a catastrophic failure.
Huh? An informal human-to-human error correction protocol used in voice over frame relay (VoFR), voice over Internet Protocol (VoIP), and voice over Wi-Fi (VoWiFi). When quality is less than acceptable and the meaning is lost, the Huh? protocol, as in Huh? What did you say?, must be invoked. If that fails, next level is the hang up and call back protocol. Both protocols have been used extensively in cellular networks for many years.
hunt group A group of lines or trunks through which a switch or other device is programmed to search in a predetermined order until it finds one available to complete a connection.
hunt The process by which a switch or other device searches for a circuit within a group of lines or trunks in order to complete a connection.
hybrid A circuit, device, or component that comprises multiple elements or performs multiple functions not normally associated with one another. A hybrid KTS, for example, can function as either a KTS or a PBX, or both, depending on the software load. A hybrid communications system might support both digital and analog signals or perhaps both circuit switching and packet switching.
initialism An unpronounceable abbreviation comprising the initial letters of a term and commonly used in place of that term. Each letter of an initialism is pronounced independently. Fox example, SDH is the initialism for Synchronous Digital Hierarchy. An acronym is a pronounceable word formed from the initials or other parts of several words that comprise a term. SONET, for example, is the acronym for Synchronous Optical NETwork, the North American standard for fiber optic transmission systems that later became internationalized as SDH. Acronyms and initialisms generally comprise all upper case letters, although they sometimes are all lower case, or a mixture of upper and lower case. Examples include SONET, SDH, bit (binary digit), bps (bits per second), QoS (Quality of Service), and Sesame (Secure European Systems for Applications in a Multivendor Environment).
in the clear Referring to radio frequency (RF) transmission with no encryption or scrambling mechanism for security purposes.
in the wild Referring to an application in the real world, rather than a laboratory experiment or demonstration or an unproven concept.
interframe compression A step in video compression that considers and eliminates redundant information in successive video frames. The background of a movie scene, for example, might not change, even though the actors move around the set.
Internet A massive, global network of packet data networks based on the Internet Protocol (IP) suite. The Internet is grounded in the U.S. Department of Defense ARPANET (Advanced Research Projects Agency NETwork), which began in 1969 as a means of linking personnel and systems involved in various computer science and military research projects. The Internet since has grown to comprise more than 400 million hosts connected to more than 60,000 academic, business, and governmental networks in more than 150 countries.
internet Abbreviation of internetwork. An interconnection of networks that is so seamless as to appear to the user as one network. The networks can include local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs).
Internet2 A private Internet for the benefit of its member organizations, which include the U.S. National Science Foundation (NSF), the U.S. Department of Energy, more than 200 U.S. research universities, and over 60 private companies formed into a not-for-profit consortium. Internet2 is not a separate physical network, and it does connect to the present Internet, as required. Internet2 is a project of the University Corporation for Advanced Internet Development (UCAID), a not-for-profit entity created specifically to develop and manage the network. The Internet2 and its members are in the process of developing and testing technologies such as IPv6, multicasting, and quality of service (QoS) mechanisms in support of what they characterize as revolutionary Internet applications such as digital libraries, virtual laboratories, distance-independent learning, and tele-immersion.
ISO (International Organization for Standardization) ISO is not an acronym. Rather, it is derived from the Greek isos, meaning equal, suggesting that all members of the organization have an equal voice. ISO is a network of the standards institutes of 157 countries. ISO is a non-governmental organization intended to serve as a bridge not only between countries, but between the governmental and private sectors. In the context of telecommunications, ISO is perhaps best known for the development of the OSI Reference Model. See Appendix A for contact information.
isochronous From the Greek isos, meaning equal or uniform, and chronos, meaning time. 1. Equal in frequency, or periodicity, i.e., uniform in time, having equal duration, or occurring at precise intervals. Isochronous communications, such as realtime audio and video, is stream-oriented, i.e., flows at a constant and regular pace, with each audio and video element being of equal importance. Therefore, each element (e.g., instant of audio or pixel of color) must be delivered to the receiver in exactly the sequence in which it was presented to the transmitter, and with no significant level of either latency (i.e., delay), or jitter (i.e., variation in delay). 2. A type of digital circuit in which the device on one end sets the bit rate for its own transmission and the receiving device copies that bit rate when responding, but there is no clock signal on the circuit interface.
JBOD (Just a Bunch Of Disks) A derogatory term for spanning, which is the use of a number of external physical hard drives organized into a single logical drive. JBOD is a simple storage technology that allows a computer to write to a large storage medium comprising multiple smaller drives. Unlike a redundant array of independent disks (RAID), JBOD does not provide any advantages in terms of redundancy or performance.
joule (J) The work done when a force of one newton applied to a point moves that application point one meter in the direction of application. Joule is named for James Prescott Joule (1818-1889), a British physicist.
LAN (Local Area Network) A packet network designed to interconnect host computers, peripherals, storage devices, and other computing resources within a local area, i.e., limited distance. LANs conform to the client/server architecture, a distributed computing architecture that runs applications on client microcomputers against one or more centralized servers, which are high-performance multiport computers with substantial processing power and large amounts of memory. A LAN might serve an office, a floor of a building, and entire building, or a campus area, but generally does not cross a public right-of-way such as a street. The distance limitation generally is in the range of a few kilometers, at most, although that is sensitive to the transmission media employed, which include coaxial cable, twisted pair, optical fiber, infrared (IR) light, and radio frequency (RF) systems. Raw bandwidth ranges up to 10 Gbps, although actual throughput generally is much less. LANs generally are private networks, although public wireless hotspots offering wireless Internet access currently are popular. Most LAN standards are set by the 802 Working Group of the Institute of Electrical and Electronic Engineers (IEEE), with examples being 802.3 (Ethernet) and 802.11a/b/g (Wi-Fi). A personal area network (PAN) such as Bluetooth, is much more limited in geographic scope than a LAN. LANs and LAN segments can be interconnected over a metropolitan area network (MAN) or wide area network (WAN). LANs operate at Layer 1, the Physical Layer, and Layer 2, the Data Link Layer, of the OSI Reference Model.
line 1. A station line refers to the circuit between a private branch exchange (PBX) switch and a station users terminal equipment. 2. In rate and tariff terminology, a local loop connection from the telephone company central office (CO) switch to the user premises in support of customer premises equipment (CPE) other than a switch.
line 1. A station line refers to the circuit between a private branch exchange (PBX) switch and a station users terminal equipment. 2. In rate and tariff terminology, a local loop connection from the telephone company central office (CO) switch to the user premises in support of customer premises equipment (CPE) other than a switch.
line powered In reference to equipment that is electrically powered by the telecommunications circuit to which it connects, thereby eliminating the need for local power.
link 1. A two-point segment of an end-to-end physical circuit. 2. A conceptual two-point segment of an end-to-end circuit that connects two end users and enables them to communicate, even when two separate physical paths are used.
logical Based on facts, rational thought, and clear reasoning. In the context of telecommunications, a logical circuit, for example, does not have a physical presence in the sense that it is not tangible.
loop 1. An electrical loop. The two conductors of an electrical loop comprise one wire carrying the go signal and the other carrying the electrical return signal. The circuit is closed and the loop is completed when the conductors are connected. 2. A local loop. In the broader contemporary sense, any access circuit between the customer premises and the edge of the telco network, or that of any other service provider, is termed a local loop, whether it is electrically-based or employs optical or radio energy. 3. A physical configuration used in residential or small business inside wire installations. Such a configuration connects multiple voice telephone jacks to one or two pairs of wires in a continuous, shared electrical loop, rather than connecting each via a home run.
loop 1. An electrical loop. The two conductors of an electrical loop comprise one wire carrying the go signal and the other carrying the electrical return signal. The circuit is closed and the loop is completed when the conductors are connected. 2. A local loop. In the broader contemporary sense, any access circuit between the customer premises and the edge of the telco network, or that of any other service provider, is termed a local loop, whether it is electrically-based or employs optical or radio energy. 3. A physical configuration used in residential or small business inside wire installations. Such a configuration connects multiple voice telephone jacks to one or two pairs of wires in a continuous, shared electrical loop.
loop start A signaling technique used in single line, multi-line telephones, and key telephone systems (KTSs) to start, or seize the line between the terminal and the central office switch. With loop start signaling, the telco central office switch provides battery. When the handset of the telephone is lifted, the electrical loop is completed and dc current flows across the circuit. The central office switch detects that fact, bridges the line, assigns a register, and returns dial tone for an outgoing call, or connects an incoming call, as appropriate. Loop start also is used in some PBXs, although it is unusual due to issues of glare, or collision between incoming and outgoing calls.
lossless compression Referring to compression techniques that enable faithful reproduction of the signal, with no data loss, although compression rates tend to be relatively low.
lossy compression Referring to compression techniques that tend to produce artifacts, which are unintended and unwanted distortions or aberrations that result in a degraded signal, but supports very high compression rates. In video systems and communications, the artifacts often show up as jagged blockings or tiling effect known as aliasing, banding of colors, white spots, and even dropped frames. Although the picture is degraded as a result, the compression ratios can be as high as 200:1. The MPEG standards, for example, specify lossy compression in the form of discrete cosine transform (DCT).
MAN (Metropolitan Area Network) A public data network that serves an entire metropolitan area, or perhaps a portion of a metropolitan area such as a city or a suburb, commonly serving to interconnect Local Area Networks (LANs). A number of carriers offer Metropolitan Ethernet services, for example. MANs can be interconnected across a Wide Area Network (WAN).
metadata From the Greek meta, meaning beside or after, and the Latin datum, meaning what is given. Data about data, that is, data that describes other data. For example, the title, subject, publisher, and author comprise metadata about its contents.
metric gauge The measure of the diameter, or thickness, of a conductor, metric gauge is used outside of the United States and England, where American Wire Gauge (AWG) and British Standard Gauge (BSG) are used, respectively. In the metric gauge scale, the gauge is 10 times the diameter of the wire in millimeters (mm), so a 50 gauge metric wire would be 5 mm in diameter. Note that AWG is retrogressive, i.e., the larger the number, the thinner the conductor, but metric gauge is progressive. In order to avoid confusion, metric sized wire generally is specified in millimeters rather than metric gauge.
network (net) A fabric of elements that work together much as the fabric of a net to support the transfer of information. A network includes all links, amplifiers and repeaters, multiplexers, switches, routers, and other intermediate devices involved in establishing, maintaining, and terminating a session between a transmitter and a receiver.
noise Unwanted disturbances superimposed on a signal and interfering with its integrity, noise can be introduced by equipment or can be the result of natural phenomena. Noise can take a number of forms, including amplitude noise, cross-talk, echo, intermodulation noise, harmonic distortion, impulse noise, random noise, and white noise.
path The physical route of a circuit.
PBX (Private Branch eXchange) A voice-optimized switching system physically located on the customer premises, serving the internal station-to-station communications requirements of one or more user organizations and with trunk circuits connecting to the public switched telephone network (PSTN) via one or more central office (CO) switches, and perhaps one or more other PBXs comprising a private network.
PCM (Pulse Code Modulation) A modulation technique in which an analog signal is encoded, i.e., converted from analog to digital format. The term generally is applied to the conversion of voice from a continuous analog waveform to digital pulses as specified in ITU-T Recommendation G.711,which specifies two companding techniques that define the assignment of 14-bit values to 8-bit values. μ-law (mu-law) is used in the North American T-carrier systems. A-law is used in the European E-carrier systems and the Japanese J-carrier systems.
physical 1. Something that exists in the reality of the material world, rather than in logic, as an idea or notion. Something physical is tangible, and can be seen and touched. A physical circuit, for example, might consist of metal, glass, or plastic. 2. Associated with the sciences such as chemistry and physics that deal with nonliving things such as energy and matter, rather than the sciences such as biology and physiology that deal with living organisms. So, a radio circuit is physical, even though it is not tangible.
plug n play (plug and play) A reference to the ability of a computer system to automatically recognize the presence of a new peripheral hardware device, locate the necessary support software (e.g., driver), and configure the device interface.
ping 1. A utility used to test a path from one host computer to another across an IP-based network in what is essentially a command to echo the packet from the remote host back to the originating host. Ping is an application of the Internet Control Message Protocol (ICMP). Ping was invented by Mike Muus of the Army Research Laboratory in 1983 to diagnose an IP network problem. Muus had done a considerable amount of work in college on sonar and radar modeling and was inspired by the principle of echo location. He named the utility after the sound that sonar makes when a signal returns. A lot of people think that ping is an acronym for Packet INternet Groper. According to Muus, packet internet groper is a backronym reverse-engineered by Dr. David L. Mills. Note: Mills warns people that the clock on his wall runs backwards. I guess that explains it. See also acronym, backronym, host, ICMP, IP, radar, sonar, and utility. 2. Slang for bouncing something off of someone, i.e., asking someone a question, as in Hold on just a minute while I ping Margaret and see if shed like to join us.
port 1. A point of physical access or physical interface between a circuit and a device or system at which signals are injected or extracted. 2. A logical connection, identified by a protocol address in a packet header, associated with a Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) service. 3. To modify or translate a software program so that it will run on a different computer operating system (OS). 4. To move files from one computer to another.
portmanteau 1. An old type of leather suitcase that usually opened into two compartments. The word originates from the French portemanteau, from porter (to carry) and manteau (cloak), and inspired Lewis Carrolls use of the word with a new meaning. 2. A combination word, or blend, that combines the sounds and meanings of two words. Modem, for example, is a portmanteau that combines the words modulate and demodulate, describing a device that performs both functions. Similarly, a codec both codes and decodes data, and a transceiver is both a transmitter and receiver. Lewis Carroll coined this usage of the word in his famous book, Through the Looking Glass, and What Alice Found There (1871), which is more commonly known as Alice in Wonderland. In the book, Humpty Dumpty explains to Alice the construct and meaning of words from Jabberwocky, telling her that Well, slithy means lithe and slimy. You see, its like a portmanteau—there are two meanings packed up into one word.
premise An assumption, proposition or presupposition that serves as the basis for an argument. The word is often confused with premises. For example, CPE is the initialism for Customer Premises Equipment, which is equipment physically located on the customer premises, at least that is the premise.
premises A building, or part of a building, including its grounds.
presence technology An application that enables a user to post or advertise his availability status. Through presence technology as user can indicate his availability as online and available for e-mail or IM but unavailable for telephone calls, unavailable for IM or telephone calls, out to lunch, out of the office on business or vacation but returning on a certain date, and so on.
program A sequence of instructions written to be executed by a computer.
propagation The movement of waves, such as electromagnetic waves, through a medium or through free space.
protocol converter A collection of software and firmware that converts the protocols used in one network, sub-network, or network element (NE) into those used by another. Protocol conversion is the responsibility of a gateway.
protocol The rules and conventions for exchanging information between computers or across computer networks.
proxy firewall A firewall in the form of security software installed on a proxy server to act as a barrier between internal and external networks and, thereby, to both prevent unauthorized entities from gaining access to internal company resources and block internal users from gaining access to unauthorized external resources.
proxy In telecommunications, a device or program empowered to act for another
proxy server A hardware device that acts on behalf of other devices for purposes such as data storage and security.
PSTN (Public Switched Telephone Network) Synonymous with PSTS (Public Switched Telephone System). The generic term for the domestic public telephone network, which traditionally is a public utility providing a circuit-switched network optimized for voice communications. The PSTN comprises all of the telecom infrastructure, including inside plant (ISP) and outside plant (OSP) owned by the carrier or carriers. Customer premises equipment (CPE) and other equipment and facilities owned by end users are considered private and, therefore, not part of the PSTN. As voice increasingly shifts to IP-based networks employing packet switching, and to alternative competitive carriers, such as cable television (CATV) providers, the term PSTN becomes somewhat vague.
PTT (Push-To-Talk or Press-To-Talk) Also known as over-over. In reference to the process used to key a microphone or transmitter to send a message over a half-duplex radio system, such as citizens band (CB). The full cycle is push-to-talk and release-to-listen.
ring The electrically negative (-) wire of a cable pair. The central office (CO) feeds talking battery to the customer premises equipment (CPE) over the ring side.
riser cable A type of inside cable intended for use in non-plenum vertical applications such as between floors of a building. In consideration of the longitudinal stress placed on a riser cable, load-bearing strength members are incorporated to increase the tensile strength, as well as to relieve the conductors of the load. Although riser cables must be fire retardant, the National Electrical Code (NEC) specifications for riser cable are not as demanding as those for plenum cable.
Robustness Principle Also known as Postels Law. A principle stated by Jon Postel in RFC 793 (1981) and again in RFC 1122 (1989), Requirements for Internet Hosts – Communications Layers. The Robustness Principle states “Be liberal in what you accept, and conservative in what you send,” which essentially advises the Internet community to design host software in such a way as to 1) be prepared for malevolent incoming packets and 2) be prepared for deficiencies on other hosts that can make it unwise to exploit legal but obscure protocol features that can cause disruption if the other hosts misbehaves.
router An intelligent switch capable of deciding where to forward packets based on a view of the network as a whole.
server In a client/server network architecture, a machine designated as to serve the needs of client machines. A server can be a mainframe, minicomputer, or personal computer that operates in a time-sharing mode to provide for the needs of many clients for application and file storage, network administration, security, and other critical functions.
session Referring to a period of time during which there is a logical association, i.e., communication, between two or more stations, terminals, or systems.
SIP (Session Initiation Protocol) An Application Layer signaling protocol for establishing, modifying, and terminating multimedia sessions or calls over an IP network The IETF defined SIP in RFC 2543 (1999), which was replaced by RFC 3261 (2002). SIP is a modular component of IP telephony, although it can function over any network. SIP offers considerable advantages over H.323, which is criticized for being overly complex and highly centralized. SIP was built specifically for an IP environment in which intelligence is highly decentralized.
social engineering The use of deceptive or fraudulent means that rely on expected human behavior, often used to gain access to information such as a computer access number, password, or user ID.
softphone A software-based telephone comprising a desktop, laptop, or tablet computer equipped with a microphone, a speaker, and software that allows it to emulate a hardphone, i.e., conventional telephone set.
software The programs and routines for a computer system. System software includes programs and routines required to run the computer. Application software comprises programs that enable users to perform tasks that use computer resources.
spike A voltage fluctuation of very short duration, but very high voltage.
splice A permanent or semi-permanent connection between two conductors or cables.
standard A rule, principle, or measure established as a model or example by authority, custom, or general consent.
station A terminal or endpoint on a network, such as a telephone set or data terminal.
subnet (subnetwork) A network, either physical or logical, that operates as part of a larger network. In a local area network (LAN), for example, there may be many virtual LANs (VLANs), each of which may comprise many users on separate physical segments. The users are grouped in VLAN domains by physical port number, Transmission Control Protocol (TCP) port address, medium access control (MAC) address, or Internet Protocol (IP) address. Each VLAN operates as a subnet.
subnet mask In Internet Protocol version 4 (IPv4), an address mask, i.e., address filter, that selectively includes or excludes certain values to distinguish between the subnetwork address and the host address in order to enable a router to forward packets correctly in a network that has been subnetted.
switch 1. A mechanical, electromechanical, or electronic device that opens, closes, or changes the connections in an electrical circuit. 2. A device that establishes, maintains, and changes logical connections over physical circuits.
tele-immersion A developing application of Internet2 intended to allow multiple, geographically distributed users to collaborate in real time in a shared, simulated hybrid environment through a synthesis of media technologies such as three-dimensional (3D) environment scanning, projection and display, tracking, audio, video, robotics, and haptics (i.e., touch) technologies. In other words, tele-immersion creates a multimedia virtual meeting space in cyberspace.
telecommunications From the Greek tele, meaning far off, and Latin communicare, meaning to share or impart, literally to make common. The science and technology of transmitting voice, audio, facsimile, image, video, computer data, and multimedia information over significant distances by the use of electromagnetic energy in the form of electricity, radio, or optics
telecommuter A businessperson who works and communicates largely from home through the use of information and communications technologies, rather than traveling to a company office.
telemedicine A videoconferencing or multimedia conferencing application that supports remote medical consultation and even remote diagnosis and treatment.
telemetry From the Greek tele, meaning far off, and meter, meaning measure, and translating literally as measure far off. The branch of science or process of remote measurement and collection of variable data, such as pressure, temperature, flow, or radiation, and transmission of the data to a distant location for analysis and interpretation.
teleworker A businessperson who works and communicates largely through the use of information and communications technologies, rather than traveling and conducting business face-to-face at various physical company offices and client sites.
tensile strength The maximum lengthwise stretching force that a cable can withstand without breaking. Tensile strength must be considered during the installation process, as a pulling load is placed on an optical fiber, in particular. Riser cables must be manufactured and installed with tensile strength in mind, as they hang vertically in place for long periods of time. Aerial cables run horizontally, attached to and suspended from poles places at intervals along a cable route. Aerial and riser cables commonly are manufactured with strength members, not only to increase the overall tensile strength of the cable, but also to relieve the wires and fibers, themselves, from bearing the load.
terminal 1. A device that constitutes a point of termination of a communications circuit or channel, i.e., a transmitter or receiver, also known respectively as a source or sink. 2. In telecommunications, a voice terminal is a telephone set, which can take many forms, including a simple analog rotary dial set, a digital smartphone, a digital softphone, and a cellular telephone. 3. In data communications, a device comprising a keyboard, video adapter, and monitor.
transparent Something easily seen through and even invisible, in some cases. A DSL modem and the functions it performs, for example, are transparent to an end user.
triple play A marketing term used by broadband service providers to describe the combination of voice, high speed data, and television services over a single local loop. The term is a baseball analogy, referring to the very rare act in which the defense makes three outs on the same play. Some service providers use the term quadruple play to describe a triple play plus wireless services, although the baseball analogy breaks down at that point. Actually, the analogy broke down with the marketer who invented the term, as a triple play is a defensive play. A more appropriate term would be triple, which is a rare offensive play. Also, that would make the non-existent defensive quadruple play a home run.
trunk A communications circuit that interconnects switches. As such, multiple users and multiple transmissions can share a trunk on a pooled basis, with contention for trunk access managed by an intelligent switching device.
trunk A communications circuit that interconnects switches. As such, multiple users and multiple transmissions can share a trunk on a pooled basis, with contention for trunk access managed by an intelligent switching device.
unicast Referring to the transmission of a signal or packet from a single device to another single device over a circuit or network.
UNIX A powerful multi-tasking, multi-user computer operating system (OS). UNIX was developed at AT&T Bell Telephone Laboratories during the period 1969 to 1973 by Ken Thompson and Dennis Ritchie for minicomputer application. As UNIX is written in the highly portable C programming language, it is used on a wide variety of computers, from mainframes to PDAs. A number of UNIX variations have been developed, some of which are available as freeware.
user 1. End user. The living, breathing human being who actually uses a computer or application to perform processes that yield end results. 2. The person, organization, process, device, program, system, or other entity that exploits another person, organization, process, device, program, system, or other entity.
utility A company that performs or provides an essential public service, such as electric power, natural gas, sewer, telephone, or water.
utilize A frilly word that means to make use of something. People who want to sound smarter than they really are utilize utilize. I just use use.
Utopia From the Greek ou, meaning not, and topos, meaning place, and translating literally as no place. The word was first used by Sir Thomas More (1516) in his book, Utopia, as the name of an imaginary island that was the home of a perfect political and social system. In contemporary usage, utopia refers to an ideal place, state of being, or situation. (Note: Utopia sounds like no place Ive ever been. If there were such a place, someone surely would foul it up. If not, it would get so crowded that nobody would go there any more.)
vector 1. A mathematical expression of a quantity, such as velocity, that possesses both magnitude (i.e., amplitude) and direction, and that may or may not be a function of time. See also amplitude. 2. A directed line segment of such an expression. See also HCV and VQC. 3. A set of numbers in an order that has meaning when each position is mapped to a corresponding dimension. 4. In video, a frequency or series of frequencies associated with a video signal.
vector quantization. A lossy video compression technique that analyzes blocks of video pixels to determine their vectors, or frequencies. Prior to transmission, the video codec consults a codebook that contains a number of standard abbreviated vector descriptions in the form of codewords. The codec selects the codeword that produces the lowest level of distortion and outputs that to the channel. A matching codec associated with the receiver reverses the process.
voice mail The intervention of a voice processor in order that a caller can leave a voice message in the event that the incoming call encounters a busy signal or a no answer condition. In such an event, the telephone system (KTS, PBX, Centrex, or CO) directs the call to the voice processor, which answers the call with a default or customized greeting and directs the incoming call to a voice mailbox associated with a particular user or application. The voice processor digitizes, compresses, and stores the voice incoming message in the mailbox, and then advises the user of the fact that a message is waiting, most commonly through message-waiting lamp indication or stuttered dial tone. When the user accesses the system and enters the proper command and password, the message is restored to analog form and played back. Features may include annotation, archiving, attendant access, broadcasting, certification, class of service (CoS), find-me, forwarding, off-site notification, personalized greeting, prioritization, privacy and purge.
VoIP (Voice over Internet Protocol) Referring to voice communications over the public Internet or any packet network employing the TCP/IP protocol suite. Specifically, VoIP operates in datagram mode, employing the Internet Protocol (IP) for addressing and routing, the User Datagram Protocol (UDP) for host-to-host data transfer between application programs, and the Real Time Transport Protocol (RTP) for end-to-end delivery services. VoIP also typically employs sophisticated predictive compression algorithms, such as low delay code excited linear prediction (LD-CELP), to mitigate issues of latency and jitter over a packet-switched network.
WAN (Wide Area Network) A network that covers a wide geographic area such as a state, province, region, or country. The Public Switched Telephone Network (PSTN) is a voice-oriented WAN. The Internet is a data-oriented public WAN. WANs can serve to interconnect LANs and MANs.
waveform The geometric shape of a wave. A waveform is used to graphically represent some recurring characteristic of a wave over time. Electromagnetic energy is commonly plotted in two dimensions as a sinusoidal waveform that varies in amplitude (A), or signal strength, on the vertical (V) axis at a periodic rate, or frequency (f), over time (t) on the horizontal (H) axis.
well-known port A port reserved for the use of system (root) processes or of programs executed by privileged users for specific applications or services. Well-known ports are numbered 0 through 1023, and include 25 for SMTP (Simple Mail Transfer Protocol), 80 for HTTP (HyperText Transport Protocol), and 107 for Remot
wiki 1. Quick or fast, in the Hawaiian language. 2. A type of authoring software that allows users to easily and quickly create and edit Web server content using any browser.
wireline Referring to a service that connects to the public switched telephone network (PSTN) through a local loop of copper wire or glass fiber that terminates in a fixed location at a customer premises. A wireline service is in contrast to a wireless local loop (WLL) and a wireless service such as cellular.
Δ The Greek letter delta, Δ is the symbol for change or difference, as in delta modulation.
λ The Greek letter lambda, λ is used to denote wavelength.
μ The Greek letter mu, μ is used to denote one-millionth, as in μm, a micrometer, or micron.
μ-law (mu-law) A voice companding technique specified in the ITU-T G.711 Recommendation for pulse code modulation (PCM). This technique is used in North America and areas under North American influence.
