A

A (Amp, Ampere) - A unit of electrical current flow that is equal to one volt applied to one ohm of resistance.The ampere can also be defined as one coulomb of charge flowing past a point in one second. One coulomb of charge is equal to 6,300,000,000,000,000,000 electrons.

A Law - An ITU-T standard companding method used to convert analog voice to compressed digital in the majority of the world for cellular radio networks. In the United States, the mu-Law standard is used. See Companding.

AA (Automated Attendant) - Most voice-mail systems come with an automated attendant built in. An automated attendant is an answering machine that asks the caller to push 1 for sales, 2 for service, etc. They are also capable of routing callers to a dial by name directory. See also Directory Tree.

AAL (ATM Adaptation Layer) - A transfer format, cell header format, and functional section of the ATM transport method. There are five variations of the ATM Adaptation layer. Each is intended to be used with a specific type of data. For a diagram of ATM layers.

AAL1 (ATM Adaptation Layer One) - The part of the ATM protocol that enables the transfer of time-sensitive data, such as voice or video. AAL1 uses an adaptive clock method, where the devices at each end of the link negotiate a clock agreement, then incorporate a small buffer to monitor the rate at which cells are being transferred across the link. AAL1 is used for DS0, DS1 emulation, and other voice and video.

AAL2 (ATM Adaptation Layer Two) - For class-B traffic (see diagram under AAL), packet technologies, and the transport thereof. It is similar to voice over frame, video over frame, etc.

AAL3/4 (ATM Adaptation Layer Three and Four) - For class C and D (see the AAL diagram) layers that are designed to handle nontime- sensitive data transfer. This layer class adds header information that incorporates error-checking functions before and after the original data. Also, a Message ID function allows multiplexed or interleaved transmissions to be sent directly over the single ATM virtual channel. This layer would be used as a backbone to carry many X.25 or Frame-Relay logical links, or could be used in a campus application to carry Ethernet from one building to another.

AAL5 (ATM Adaptation Layer Five) - The layer created for class C and D types of traffic . The cell header re- mains the same except larger buffers are used and a CRC (Cyclic Redundancy Check) is appended to the end of the last cell of the packet's cell stream. No Message ID function is available to directly transfer multiplexed data. Cell payloads are 48 bytes, and a PTI bit is used to indicate the last cell of a packet.

AAR (Automatic Alternate Routing) - A feature of some networks and protocols to reroute traffic on the fly without interrupting or corrupting traffic.

AB Switch - A mechanical/manual switch used to switch a signal between two source or destination devices. For example, if you have two computers and one monitor, you could implement an AB switch to control which computer the monitor is connected to. The monitor would connect to the "C" port on the switch, and the two computers would connect to the "A" and the "B" ports. AB switches suit many applications of connectivity from computer to audio/video.

Abandoned Call - When you make a call, are put on hold, then hang up before someone answers, you have abandoned the call. Customer-service call centers like to know the number of abandoned calls they have so that they know how many people to employ answering calls, etc. Believe it or not, if you hang up when calling a call center, someone that cares eventually finds out!

Ablation - To burn holes into metal film with a laser. The holes represent ones and zeros for optical storage on disks.

ABR (Available Bit Rate) - Quality of Service (QOS) defined by the ATM Forum for ATM networks that is used for connections that are not time or delay sensitive. A connection would be rightfully commissioned as an ABR connection if it carried only spontaneous or bursty data. Other QOSs defined by the ATM forum for ATM connections include CBR (Constant Bit Rate), UBR (Unspecified Bit Rate), and VBR (Variable Bit Rate).

Absorption Loss - The weakening of light intensity as it travels a length of optical fiber. The unit for absorption loss is dB/Km (decibels per kilometer).

AC (Alternating Current) - Alternating current is electricity that changes/ alternates it's direction of flow in a steady cycle or period. The line voltage in most American homes is somewhere between 110-V and 120 V AC RMS, which makes the actual peak to peak voltage about 325 V.

AC-to-DC Converter - This is an electronic device that defines itself. Large-scale AC/DC converters are mostly referred to as rectifiers. They convert alternating current to direct current (or voltage) by incorporating a large capacitor and two or four diode rectifiers for a half wave or full wave, respectively. Almost all rectifiers have regulated output, meaning the output DC voltage is kept at a steady level, regardless of the electronic device it is providing power to. Rectifiers are also available with battery backup and redundant circuits so if a component fails the output voltage won't be disturbed. AC to DC converters are rated by input voltage requirementd output voltage/current ability.

Acceptable Angle - The maximum angle that a fiber optic accepts light and doesn't reflect it away.

Access Charge (Carrier Common-Line Charge) - What local phone companies charge long-distance companies to connect the far-end local portion of a call. A fee that everyone pays for every phone line to make up for subsidies that long-distance services paid to help the less-profitable local services before the divestiture of AT&T and the RBOCs (Regional Bell Operating Companies).

Access Line - A connection provided by a telephone company that runs from a customer's premises to a central office or to a colocation within the central office.

Access Link - The local phone line that connects you to a central office switch and gives you access to a long-distance carrier. It's an access line with all the electronics that give you dial tone or private line communications capability.

Access List - A list kept by routers to control access to or from the router for a number of services. A good example is the prevention of packets within a specific IP address leaving a particular interface on the router.

Access Network - Regarding xDSL, the portion of a public switched network that connects access nodes to individual subscribers. It is also called a local network. Today's access network is predominantly passive twisted-pair copper wiring and fiber optic, and is owned by such telephone companies as SBC, Ameritech, Qwest, and GTE.

Access Node - A connecting point for a data transport or data-packet network. Access nodes usually reside in a central office environment, or are a part of a leased space agreement. Connections to access nodes are provided by local carrier loops. Access devices at the end of the customer loop are generally provided by the data-network service provider or by the customer.

Access Point (AP) - Another name for a cross-box where telephone cables are cross connected. See also Aerial Cross Box.

Access Server - A communications processor that connects asynchronous devices to a LAN or WAN through network-emulation software that resides in its memory. It performs synchronous and asynchronous routing of such supported protocols as Ethernet, token ring, frame relay, and X.25. Access servers are sometimes referred to as network-access servers or communications servers.

Access Service Request - When a special-service provider (frame relay or long distance private line) needs wire facilities from their point of presencein the city to your location, they call the local telephone company and make an access service request to provide a line that runs from your network interface to them. Many special service providers have their equipment located in the local phone company's central office as a part of a co-location agreement. When a CLEC (competitive local exchange carrier) needs to provide service where they don't have facilities, this is how they do it by using the RBOC's (Regional Bell Operating Company) wire facilities.

Access Switch - A point in a network where multiple services/protocols are differentiated and routed for enterprise networking services.

Access Tandem - A telephone company central office or node that contains a switch in which all inter and outer area code traffic is handled. The main LEC (Local Exchange Carrier) central office in an area code where the hand-off for long-distance service happens .

Account Code - In accounting for communications costs, an account code is used. If you have multiple employees in your office using multiple phone lines to make long-distance calls, figuring out who made those calls can be impossible. Some long-distance companies offer a service where employees enter an account code before their call is completed. When the phone bill comes, it is easy to see who is making long-distance calls, to where, and for how long. Most importantly, it is easy to distribute the costs among a group. Most PBX (Private Branch Exchange) switches have call accounting systems available that allow a telephone extension (or group of extensions) to be attached to an account code that shows how much each phone is utilized, and what calls are made and received.

ACD (Automatic Call Distributor/Distribution System) - A separate footprint or built-in feature of a PBX (Private Branch Exchange) that equally distributes incoming calls to agents. As calls come in, they are placed into a queue (or a waiting line) for the next available agent. ACD systems are very versatile and relatively easy to program as some incorporate their own script programming feature. For incoming calls, the waiting times, pre-recorded announcements and other call treatments can be set up by the users/companies to their discretion. Some well-known ACD systems are made by ACCENT, Lucent, and Northern Telecom. See also ACS.

ACIS (Automatic Customer/Caller Identification Service) - This feature comes with many ACD (Automatic Call Distribution) systems and enables them to make useful the DNIS signal attached to an inbound call. The DNIS (Dialed Number Identification Service) can be used to identify the caller or call type. If you have a call center where more than one business is served, then the Automatic Customer/Caller Identification feature can forward the call to a certain group of agents that are as- sociated with the dialed number. It can even tell them what kind of call they are answering on the display of their phone. If a customer calls from Mexico, then the ACD ACIS feature will relate the dialed number with an ACD group that speaks Spanish. Of course, the ACD system needs to be set up or programmed by an administrator to do this.

ACK - ASCII control code abbreviation for acknowledgement. Binary code is 0110000 Hex is 60.

ACM (Advanced Communications Function) - Also known as an advanced communications function control program. The ACM program resides within a communications controller and interfaces with the SNA (System Network Architecture) access method in the host computer/mainframe to control network communications.

Acoustic - This term refers to the natural sound vibrations of an object or space. In telecommunications, acoustics are a concern when using hands- free or speaker-phone devices. If the acoustics of the electronic hands- free device are poor, it will vibrate or resonate when the volume level is increased. If the acoustics of the room that the device is in are bad, the device will cut in and out as it "hears" its own echo. Cloth cubicles have a good acoustic vibration-dampening effect. Wide open rooms with no ceiling tile and sheet rock walls have a poor acoustic-dampening effect.

Acquisition - The process of a terrestrial-based device locking on a satellite's GPS (Global Positioning System) signal. Included in the process of acquiring the signal is AGC (Automatic Gain Control) for optimum signal level, synchronization, and processing of the data signal.

ACR (Allowed Cell Rate) - A parameter defined by the ATM Forum for ATM Traffic Management. The ACR varies between the Minimum Cell Rate (MCR) and the Peak Cell Rate (PCR). It is managed by the protocol congestion control mechanisms.

ACS (Automatic Call Sequencer) - If you can't afford an ACD system, this could be the answer you have been looking for. An ACS answers the call, plays a recorded announcement, and puts the caller on hold. The calls coming in (all the calls) appear as lights on a telephone (or multiple telephones). The calls that have been on hold the longest blink the fastest (or have other signaling methods). ACS systems are designed primarily for or as a part of key systems.

Activated Return Capacity - The ability of your cable TV box to send information back to the cable-TV office head end and the ability of the head end to receive the data. This information can include the ID number of the cable TV box and what station you are watching.

Active Device - An active device is an electronic component that requires external power to manipulate or react to an electronic input for a desired output. Examples of active devices are: transistors, op amps, diodes, cathode ray tubes, and ICs. If it's not active, it is a passive device. Included in the passive-device category are capacitors (condensers, if you want to use a really old term) resistors, and inductors (or coils), which include transformers.

Active Matrix Display Also called TFT (Thin Film Transistor) displays. A type of laptop computer display technology. In an active matrix display, each picture element has its own control transistor. The display performance of active matrix displays is significantly sharper, faster, and are less stressful on human eyes, yet they consume more battery power than passive matrix displays. See also Passive Matrix Display.

Active Vocabulary - A list of words that a voice-recognition system has been programmed to recognize. Each voice-recognition system has it's own set of words that are selected to fit its application. This is done so that when a voice says "pair," the voice recognizes a word that means two, not a fruit ("pear").

ACU (Automatic Calling Unit) - A device that IBM computers use to access outside dial tone for communications. It does the job of a modem, but uses its own protocols to communicate with the computer.

AD (Analog to Digital Converter, ADC) - A part of a channel bank that encodes analog voice signals into a stream of binary digits. The digital to analog converter or analog to digital converter samples a caller's voice at a rate of 8000 times per second. (The sample rate for a T1 channel is 8000 times per second.) Each sample's voltage level is measured and converted to one of 256 possible sample levels. These levels are from the lowest, 0000000, to the highest, 11111111. The reason for 256 levels is because if you count in binary from 00000000 to 11111111, you end up with 256, the highest number possible with 8 bits. The bits are then transmitted one after another at a high rate of speed to their destination, where the same process happens in reverse. For a diagram, see Analog to Digital Conversion.

Ad Insertion Module - In cable TV or broadcast radio networks, a device that broadcasts commercial advertising during pre-determined time segments. Ad-insertion equipment enables local cable TV companies to sell and insert advertising space to local businesses. The same is applicable for broadcast TV/AM/FM radio stations.

Adaptable Digital Filtering - A method of conditioning twisted-pair telephone lines to carry data more efficiently up to 12,000 feet before regeneration. The adaptive digital filter can be customized to the characteristics of any given pair (that is in good condition). This method of line conditioning is not compatible with XDSL.

Adaptive Differential Pulse Code Modulation (ADPCM) - A family of techniques used to compress audio information for data storage and wireless telephone networks. This is accomplished by using algorithms that code the difference between sound samples and dynamically switching the coding scale to compensate for audio signal amplitude and frequency. This technique requires less disk storage space and less bandwidth to transmit, as opposed to PCM, which encodes absolute quantitative values.

ADCCP (Advanced Data Communications Control Protocol) - A bit- oriented data link protocol developed by ANSI. ADCCP was similar in make-up to that of HDLC and SDLC. See also HDLC.

Add On - A PBX, Centron, or Central Office feature (also known as three- way calling). Some telephone stations have a button that is designated "add on." To add a third caller, you push the add-on key and dial the number of the third party, then push add-on again to bridge the calls together.

Address Mapping - A method of making dissimilar protocols work together. It is done by translating the address of one protocol to another protocol. For example, when routing IP over X.25, the IP address must be routed or forwarded to the X.25 address, and vice versa on the opposite end of the transmission.

Address Mask - A bit combination used to describe which portion of an address refers to the network or subnet, and which part refers to the host. The address mask is usually referred to as the mask. See also Subnet Mask.

Address Resolution - A general term that refers to overcoming the differences between computer addressing schemes. Address resolution is most commonly a method of mapping or transferring layer 3 (network layer) addresses to layer 2 (datalink layer) addresses.

Address Resolution Protocol (ARP) - The ARP function is to match higher-level network IP addresses with the physical hardware address of a piece of hardware, such as a NIC (Network Interface Card), which is the subsequent router, PC, server, or terminal that it belongs to. ARP provides the link of the physical address (NIC) and the appropriate IP address. For example, an IBM mainframe attempting a connection to a server on an IP network would send an ARP broadcast (it contains the IP address of the target server, as well as its own IP address) to the network. If the mainframe receives the ARP, it will recognize its own IP address in the packet, and respond by sending its physical address.

Address Signals - The digits you dial on your phone pad, the phone number is actually an address signal to the local central office that you are connected to.

Address Translation Gateway - A reference to a router software function. This software provides address format conversions as data packets are routed from one network to another. Most address translation gateways enable a router to do specific address format conversions for transmissions between specific nodes of separate networks.

Addressable Programming - For Pay Per View, cable TV companies use an addressable programming system. When you call the phone number to activate the Pay-Per-View movie or event, an IVR system receives your ANI signal or asks for your phone number. Then, it uses your phone number as your customer ID code for billing; in some cases, it identifies which cable-TV converter box to enable. Your cable TV box has an ID code or address code in its memory. When it receives its own address signal from the cable-TV office head end, it enables the horizontal sync or digital channel for the Pay-Per-View program. It's called addressable program- ming because the converter box is programmed after it receives it's address, which acts like a password.

Addressed Call Mode - Another way of saying "dial-up mode." Sometimes the term phone number is substituted with address by some of the standards committees. This happened in the V.25bis standard. Addressed call mode permits DTE and DCE to establish and terminate calls by dialing user-determined phone numbers, based on the V.25bis modem standard.

Adjacency - A relationship formed between selected neighboring routers and end nodes for the purpose of exchanging routing information. Devices using the same media segment are considered to be adjacent.

Administrative Distance - A rating of the trustworthiness of a routing information source. In Cisco routers, administrative distance is expressed as a numerical value between 0 and 255. The higher the value, the lower the trustworthiness of the routing information. For example, if routing data has traveled through 1 router and 1 media segment, the chances that it has been corrupted are low, so the administrative distance is considered to be about 2. If the routing data has traveled through 100 routers and 100 media segments, its administrative distance rating could be about 200.

ADPCM (Adaptive Differential Pulse Code Modulation) - A family of techniques used to compress audio information for data storage and wireless telephone networks. This is accomplished by using algorithms that code the difference between sound samples and dynamically switching the coding scale to compensate for audio signal amplitude and frequency. This technique requires less disk storage space and less bandwidth to transmit, as opposed to PCM, which encodes absolute quantitative values.

ADSL (Asymmetric Digital Subscriber Line) - Also referred to as ADSL Full Rate or G.992.1. ADSL is a physical-layer protocol that supports up to 8 Mbps bandwidth downstream and up to 1 Mbps upstream. The asymmetrical aspect of ADSL technology makes it ideal for Internet browsing, video on demand, and remote Local-Area Network (LAN) access. Users of these applications typically download more information than they send. ADSL also allows simultaneous voice communication by transmitting data signals outside of the voice frequency range. Sometimes a faint hiss can be heard on the line. To eliminate the hiss, a voice/data splitter, commonly called a POTS splitter (Plain Old Telephone Service) is installed at the jack of each phone. The base transmission range for an ADSL line is 18,000 feet. ADSL can be extended to remote communities by using ADSL repeaters (to 48,000 feet) or fiber optic. For more information on the DSL family of protocols, see xDSL.

ADSL Router - The device that interfaces a customer's personal computer with the ADSL telephone line. The ADSL router needs its own NIC (Network Interface Card) installed in the personal computer.

ADSU (ATM DSU, Asynchronous Transmission Mode Digital Service Unit) - A terminal adapter used as a demarcation point or interface point to an ATM network.

Advance Replacement - The process of getting a replacement component (card, phone, power supply, software, etc.) by calling the distributor or manufacturer and obtaining an advance-replacement reference number. When you receive your advance replacement item, you replace it in the box with the bad item, mark the box with the advance- replacement reference number and send it back. Hopefully, the replacement item doesn't go bad so that you don't have to go through all that again.

Advanced Data Communications Control Protocol (ADCCP) - A bit- oriented data link protocol developed by ANSI. ADCCP was similar in make-up to that of HDLC and SDLC. See also HDLC.

Advanced Peer-to-Peer Networking (APPN) - An enhancement to the original IBM SNA (System Network Architecture). APPN handles the following: session establishment between peer nodes, dynamic transparent route calculation, and traffic prioritization for Advanced Program-to- Program Communication.

Advanced Program-to-Program Communication (APPC) - The IBM SNA (System Network Architecture) software that allows high-speed communication between programs on different computers in a distributed/mainframe computing environment. APPC establishes and tears down virtual connections between programs that require communication. It has two software interfaces; the first interface is the programming interface, which replies to programs requiring communications. The second interface is the data-exchange interface, which establishes the sessions or "connections" between the programs.

Advertising (Router) - A process in which routers send routing table updates and/or service updates at specified intervals. This is done so that all routers maintain accurate information about their network surroundings, which assists in the efficient and accurate passing of data packets. See also Router Protocol.

Aerial Cable - Twisted copper pair, coax, or fiberoptic cable that is attached to power or telephone poles strung through the air. Electrical (power), telephone (fiber optic and twisted pair), and cable TV (coax) are frequently aerial. Aerial cable is attached to a steel strand with lashing wire in most cases. It is sometimes attached during manufacturing as a part of the jacket or sheath (this kind is called figure-8 cable). The steel strand is attached to pole with strand clamps and other pole attachments. This is all done with pole-attachment agreements with the owner of the pole, which is the power company, in most cases.

Aerial Cross Box - A cross box that is mounted on a pole away from the ground. Aerial cross boxes (also called tree stands) are installed in areas where easement rights are narrow or in areas where vandalism is a high risk .

Aerial Service Wire Splice - A common device used to splice aerial service wire (also called afootball or potato).

AGC (Automatic Gain Control) - Built-in to every radio is an AGC circuit that compensates for the strength of the signal you are receiving. If your radio had no AGC and was tuned to a distant station, tuning to a local station would cause the volume to blare. The way it works is as follows: After the tuner has selected the frequency to be processed, the signal goes to an AGC circuit, which is very similar to a regular intermediate-frequency amplifier (single transistor), except that the gain (amplification) of the circuit is controlled by a level detector. The level detector samples the output voltage of the first preamp and converts it to a DC voltage that is applied to the base configuration of the AGC transistor. The DC voltage controls the bias (amplification configuration) of the AGC circuit, which directly controls how large of a signal is output to the first preamp. The entire system is designed for an optimum signal into the second preamp. When the signal is optimal, then the level of the AGC control signal is zero in most AGC circuits. AGC is an important part of digital microwave. Some microwave links are often miles apart. When the path of the two dish antennas are aligned, the technician connects a volt meter to the AGC control signal. As the dish is rotated on its axis (azimuth), the technician watches as the AGC control signal changes. When the signal peaks, it is pointed directly at the other antenna. Even though terrestrial microwave links do not move or switch stations, they still need AGC to compensate for weather changes.

Agent - 1. In data administration, software that processes queries then returns replies on behalf of an application program. 2. In network-management systems, such as Novell RIP or Cisco IGRP, an agent is a subprocess that resides in all managed devices (such as routers and servers) and reports the values of specified network variables to management stations.

AGP (Accelerated Graphics Port) - A newer bus/interface architecture developed by Intel Corporation to be used as an interface for computer monitors. AGP is based on the PCI bus architecture, except that AGP provides a dedicated connection to main memory for a video card. This enables throughput that exceeds 1 Gbps. The push for a faster monitor interface has come from the demands of 3-D graphics. AGP slots/sockets can easily be distinguished by their offset pin configuration.

Aggregate Bandwidth - The total bandwidth of a broadband circuit and all of its tributaries, including the payload and overhead. A T1 has an aggregate bandwidth of 1.544 Mb/s.

Aggregation Device - An ISDN terminal adapter that can combine two B channels (64 Kb/s each) together for a single channel that has twice the bandwidth (128 Kb/s). These adapters can switch back and forth from aggregated to non-aggregated while the circuit is in use.

Aggregator - A long-distance reseller. They sign up with a long-distance company as a reseller and all their customers are "aggregated" together for a bulk discount. The long-distance company provides the service and does the billing. The advantage to the long-distance company is that they have more people selling their long distance. The advantage to the customer is the value-added service (consultation/expertise) that the aggregator offers.

AH (Amp Hour) - A battery rating for UPS system and other batteries. The amp-hour rating is derived by multiplying the amount of current that a battery can supply by the time it can supply it. It works out to be a ratio so that you can calculate how long your battery back-up system will last if the power goes out. For example: If a battery has an amp-hour rating of 100, then it can supply 100 amps for 1 hour. Or it can supply 50 amps for 2 hours, 25 amps for 4 hours, 1 amp for 100 hours, etc.

AIN (Advanced Intelligent Network) - The ability of a communications network to determine the routing or handling of a call based on the way the caller desires. AIN is used by local and long-distance companies to give customers a choice as to how they would like their calls routed. A particular trunk can be specifically programmed to route a specific path through switching centers across a geographical area. AIN is ultimately an upgrade to SS7. Some AIN trunks can be made to route to an IVR (Interactive Voice Response) system that gives the customer options for their call handling.

AIOD (Automatic Identification of Outward Dialing) - This is a call- accounting system feature of PBX and some key systems that captures every number dialed by a specific telephone extension and prints it out on a report for accounting and cost-tracking purposes.

AIR (Allowed Information Rate) - The maximum data transfer rate that a frame-relay DLC (Data Link Connection) will allow. The AIR is equal to the CIR (Committed Information Rate) plus the EIR (Excess Information Rate) of the particular DLC.

Air-Pressure Cable - Telephone cable that is equipped with air-pressure equipment. In many cables nitrogen is used instead of air because it is noncorrosive (air contains humidity and oxygen that corrodes copper pairs). Nitrogen is pumped into the cable and the pressure is monitored. If the cable is cut, the pressure drop notifies the telephone company of a cable problem and the nitrogen rushing out of the cable helps prevent any water from entering the cable.

Airline Mileage - The mileage between two cities that long-distance private- line pricing is based on. AT&T developed a grid coordinate system (coordinates shown in V&H table) that gives every telephone central office in the United States a vertical and horizontal grid number. To calculate the mileage between two cities, the Pythagorean theorem is used.

To calculate mileage between two cities, follow these steps:

1. Take the difference of the V coordinates and square it.
2. Take the difference of the H coordinates and square it.
3. Add the two squared numbers together.
4. Divide by 10
5. Take the square root of that number. This is the mileage.

Example: What is the airline mileage from Los Angeles, CA to New York, NY?

• The V coordinate of Los Angeles is 9213. The V coordinate of New York is 4977. The difference is 4236
• H coordinate of Los Angeles is 7878. The H coordinate of New York is 1406. The difference is 6472
• Next, square both numbers: 4 236² = 17,940,000. 64 72² = 41,890,000
• Now, add these numbers: 17,940,000 + 41,890,000 = 59,830,000
• Now, divide these numbers: 59,830,000 -10 = 5,983,000.
• Take the square root: V5,983,000 = 2446.
• 2446 miles is the airline mileage between Los Angeles and New York.

Algorithm - A well-defined rule or process for arriving at a solution to a problem. In networking, they are commonly used to determine the best route for traffic from particular source to a particular destination, and used to create error detection and correction processes.

Alignment Error - In most Ethernet networks, an error that occurs when the total number of bits of a received frame is not divisible (a factor of) by eight. Alignment errors are usually caused by collisions.

All-Routes Explorer Packet - In a source route bridging network, a signal sent by a user device that hunts for another end device across an entire network.

All Trunks Busy - You might try to make a call and get a fast busy signal or an intercept message that says "I'm sorry, all circuits are busy now. Please try your call again later." This situation can happen for a number of reasons. If you are dialing long distance, you get this message because all of the trunks that your long-distance company has between their in- terlata central office POPs (Points of Presence) are busy. If you are making a local call that terminates to a different local CO and you get this message, it is because all the inter-office trunks are busy. If you are calling your neighbor and you get this message, then the inter-grouping trunks within the local CO switch are all busy. Inter-grouping trunks are used in large switches to interconnect "smaller CO switch groups" within the CO switch.

Alligator Clips - Most analog test equipment comes equipped with alligator clips. For a photo, see Bed of Nails Clips.

Allowed Cell Rate (ACR) - A parameter defined by the ATM Forum for ATM Traffic Management. The ACR varies between the Minimum Cell Rate (MCR) and the Peak Cell Rate (PCR). It is managed by the protocol congestion control mechanisms.

Allowed Information Rate (AIR) - The maximum data transfer rate that a frame-relay DLC (Data Link Connection) will allow. The AIR isequal to the CIR (Committed Information Rate) plus the EIR (Excess Information Rate) of the particular DLC.

ALPETH (Aluminum/Polyethylene) - The sheath or jacket of an outside plant telephone cable that is used mostly for aerial applications. It is basically an aluminum wrap around the conductors, which resembles a serrated tin can, coated with of black plastic.

Alternate Answering Position - A second attendant console where the first console can forward calls if the first console attendant is absent. An alternate answering position can also be used for overflow of calls that the first attendant can't keep up with.

Alternate Routing - A switch feature that enables all trunks to have alternate outgoing assignments. If the primary routing or least-cost routing is all busy or out of service, then the switch will route the call to an alternate trunk to connect the call. It is a good idea to use multiple longdistance and local services in conjunction with alternate routing in case of a service outage.

AM (Amplitude Modulation) - AM is a technique of making a voice or other signal ride on (or modulate with) another frequency (the carrier frequency). For a diagram, see Amplitude Modulation.

AMA (Automatic Message Accounting) - What RBOCS call their call tracking system for billing.

Ambient Current - The result of the voltages created by random movement of electrons in a circuit when the power is off. There is always ambient voltage, which is why oscillator circuits start oscillating when the power is turned on. The natural oscillations of the electrons become filtered and amplified when the power is applied to the circuit.

Ambient Noise - Noise caused by the random movement of electrons in an electronic circuit when the power is off or by the random movement of air.

Ambient Voltage - Electromotive force created by the random movement/vibration of electrons in a circuit when the power is off. There is always ambient voltage, which is why oscillator circuits start oscillating when the power is turned on. The natural oscillations of the electrons become filtered and amplified when the power is applied to the circuit.

American National Standards Institute (ANSI) - A nongovernmental nonprofit standards setting institute that publishes standards that industries voluntarily follow. ANSI works very hard to bring together the interests of the private and public sector. ANSI is the official U.S. member body to the world's leading standards bodies.

Some examples of ANSI communications standards are:

ANSI T1.110-1987 SS7 General information

ANSI T1.111-1988 SS7 Message Transfer Part (MTP)

ANSI T1.112-1988 SS7 Signaling Connection Control Part (SCCP)

ANSI T1.113-1988 SS7 ISDN user part

ANSI T1.114-1988 SS7 Transaction Capability Application Part (TCAP)

ANSI T1.206 Digital Exchanges and PBX loop-back test lines

ANSI T1.301 ANSI ADPCM standard

ANSI T1.401-1988 Interface between carriers and customer installations for voice-grade switched analog lines Loop Start and Ground Start.

ANSI T1.501-1988 Network performance/network encoding limits for 32Kb/s ADPCM

ANSI T1.601-1988 Basic access interface/electrical loops for the network side

AMI (Alternate Mark Inversion) - AMI is a line format that serves two advantages to sending a digital signal directly over a twisted pair. The feature of AMI that makes it unique is that each bit is inverted. This makes the first bit +5 V, the second -5 V, the third =5 V, etc. Alternating the bit polarity also makes the signal look like it is half the frequency to the twisted pair Reference voltage for T1 carrier is typically +135 Volts over the public network, so AMI actually switches from + 140V to + 130V .

Amp - Abbreviation for Ampere, see Ampere.

Amp Hour (AH) - A battery rating for UPS system and other batteries, the Amp Hour rating is derived by multiplying the amount of current that a battery can supply by the time it can supply it. It works out to be a ratio so that you can calculate how long your battery back-up system will last if the power goes out.

For example: If a battery has an amp hour rating of 100, then it can supply 100 amps for 1 hour, 50 Amps for 2 hours, 25 Amps for 4 hours, 1 amp for 100 hours, etc.

Ampere - 6,300,000,000,000,000,000 electrons moving past a point in one second (a coulomb) is equal to one ampere (also known as an amp) of electrical current. The shortcut/alternative to counting all the electrons as they run by is to use the Ohm's law formula and calculate the amperage instead. If you know two of the following about your circuit, voltage, resistance, or watts you can perform the calculation. </font>

Amplified Handset - A handset with a built-in amplifier for the hearing impaired. Amplified handsets can be purchased for virtually every kind of PBX telephone. Walker Electronics is a well-known manufacturer of these devices.

Amplifier - An electronic circuit designed to increase an input level characteristic to a desired output level characteristic. Some amplifiers are designed to amplify the voltage level of a signal and others are designed to amplify the current of a signal flowing through a load. A typical stereo system has both of these types of amplifiers. If you are listening to a CD player, the signal (after digital to analog processing) is fed to a voltage amplifier to increase its ability to drive a current amplifier, which amplifies the current that is driven through the loudspeaker. Both of these amplifiers (voltage and current) combined make a power amplifier, hence power (in watts) is a function of voltage and current. Amplifiers are usually rated by the amount of power that they are capable of producing in a loudspeaker. Peak power is calculated by using the peak value of a sinusoidal waveform. RMS (root mean square) power is calculated by using the RMS value of the sinusoid waveform, which mathematically works out to be 70.7% of the peak value. Many amplifier manufacturers use the peak-power rating because it looks better. If you compare a JVC amplifier that is rated at 71 watts RMS output, it is the same output as the 100-watt peak-power "other brand" amplifier. High-quality audio amplifiers are usually rated in RMS power.

Amplitude - The peak or peak-to-peak amplitude of a signal measured in volts. The AC signal below has a peak amplitude of 10 volts or a peak-to- peak amplitude of 20 volts.

Amplitude Modulation - AM is a technique of making a voice or other signal ride on (or modulate with) another frequency (the carrier frequency).

AMPS (Advanced Mobile Phone System) - This is the cellular/PCS network as we know it today. The first mobile phone system was called MTS (Mobile Telephone System) and was developed during World War II. To make a call on an MTS system, a human operator was needed to hand- off/connect the call. In the early 60's IMTS (Improved Mobile Telephone System) evolved. IMTS did not require a human operator to connect a call from one mobile phone to another, but calls could only be made within one cell. In 1983, the implementation of the AMPS (Advanced Mobile Phone System) began. AMPS allows callers to call from one mobile phone to another, from one cell to another, and connect calls between the land-based network and the mobile network without the need for an operator.

Analog - A signal having an infinite number of levels per cycle, in contrast to digital, which has only two possible levels per cycle (i.e., on or off).

Analog-to-Digital Conversion (Digital-to-Analog Converter/Analog- to-Digital Converter) - A part of a channel bank that performs the function of encoding analog voice signals into a stream of binary digits. The analog-to-digital converter samples a caller's voice at a rate of 8000 times per second. (The sample rate for a T1 channel is 8000 times per second) Each sample's voltage level is measured and converted to one of 256 possible sample levels. These levels are from the lowest, 0000000, to the highest 11111111. It has 256 levels because if you count in binary from 00000000 to 11111111, you end up with 256, that is the highest number possible with 8 bits. The bits are then transmitted one after another at a high rate of speed to their destination, where the same process happens in reverse.

ANI (Automatic Number Identification) - ANI is also called Caller Identification or Caller ID. This feature, offered by local phone companies, sends the phone number (and often the name of the caller) down the phone line in a digital data packet between the first and second ring. To receive the data, a subscriber that has signed up for the service needs to have a caller ID unit (also called a caller-ID box) plugged into the phone line. The caller-ID unit displays the name and the number of the calling party for each incoming call. Caller ID only works if the caller and the called party's phone service is fed out of a central office that has caller-ID capability. If the central office does not have caller-ID capability, then the display will read "out of area" to the called party. If the called party does not have caller service they will get a display that says "no data sent."

Annex A - A frame relay standard extension that outlines the provisioning of a Local Management Interface (LMI) that goes between the customer's equipment and the frame relay network. The LMI will provide network monitoring and status through the transmission overhead.

Annex D - The second frame relay standard extension that outlines the provisioning of a Local Management Interface (LMI) that goes between the customer's equipment and the frame relay network. The LMI will provide network monitoring and status through the transmission overhead.

Annular Ring - A marking around a cable to show length—some are in meters and some are in feet.

Anonymous Call Rejection - A feature that can be provided by the local phone company that will not complete anonymous calls to your line. You can also reject anonymous calls by installing a caller-ID unit that has anonymous call rejection built-in to it.

ANSI (American National Standards Institute) - A nongovernmental nonprofit standards-setting institute that publishes standards that industries voluntarily follow. ANSI works very hard to bring together the interests of the private and public sector. ANSI is the official U.S. member body to the world's leading standards bodies.

ANSI Standards - See American National Standards Institute Communications Standards for some examples of their communications standards.

Answer Back - A command that a local data terminal sends to a computer or device across a network asking it to send its address so that the local terminal can verify that it has connected to the correct computer.

Answer Supervision - The ability of a central office to know when a longdistance call has been answered so that the call can be billed. This feature is a combination of the SS7 network and CO switch software that integrates with the telephone company's call accounting and billing system. Anyone who bills people for phone calls should have this system, but some do not. Hotels are famous for not having answer supervision. If you make a call from your hotel room and the end you are calling rings for more than 30 seconds (eight rings) you will probably be billed for the call. The hotel's PBX has no way to know if anyone picked up the phone on the other end, so it starts billing for the call after a certain time. The hotel's PBX is supervising and billing according to you being off-hook and the digits you dialed, not according to when the "answerer" picked up the line. To this day, some long-distance companies don't have answer-supervision capability.

Antenna - A device for receiving and transmitting electromagnetic signals. The optimal antenna for a given transmission or reception of a frequency has a length equal to the wavelength (or a usable fraction) of that frequency. CB radio antennas are very long in comparison to the antenna on your PCS cellular phone. CB radio is transmitted at frequencies that are low, which have a long wavelength and PCS cellular is transmitted at high frequencies, which have shorter wavelengths. See also Yagi Antenna, Parabolic Dish Antenna, and Monopole Antenna. Antennas are available in many varieties that are designed to manipulate the incoming or outgoing signal.

• Single 'pole, full wavelength For picking up weak signals or transmitting over long distances.
• Single-pole half or quarter wavelength Smaller size and for receiving nearby stations.
• Dipole For directional applications. Rabbit ears, for example, are directional.
• Phased array For picking very distant signals.
• Parabolic dish For focusing a signal from or to one direction.
• Vertical Loop For low-noise, directional reception. Common for UHF TV.
• Horizontal Loop For low-noise, directional reception.
• Multielement For low-noise, directional reception or transmission.
• Monopole Used in cellular and PCS applications.

Antenna Farm - A collection of satellite dish antennas located at a cable- TV head end or satellite telecommunications center.

Antenna Gain - The two types of antenna gain are field gain, which is expressed in volts, and power gain, which can be expressed in decibels. The important thing to remember about antennas and their characteristics is that they are built to be an integral part of the transmitter. An antenna's ratings determine what type of transmitter it should be matched with and vice-versa.

Anti-Static - Materials coated or manufactured with semiconductive materials makes them anti-static, which is good for CMOS (Complementary Metal-Oxide Semiconductor) components. CMOS components are highly sensitive to static discharges and static fields (ESD). Your body can easily hold a static charge of 40,000 V on a dry day. About 25,000 V is required to get a static shock from a door knob. Exposure to static electricity can ruin a CMOS component instantly or just weaken it, which would cause it to fail unpredictably. CMOS components include microprocessor chips, transistors, RAM and ROM chips, and many others. If a CMOS device must be used in an ESD hazard area, TTL components are used as an alternative. TTL components are not as static sensitive, but, they are not as fast, not as small, use more electricity, and produce more heat.

AOSP (Alternate Operator Service Provider) - A long-distance company that works like the old days, when a live operator would assist you with your call. Some calling-card companies incorporate this in their service. AOSP service is great, and it's a good thing because we pay for each use.

AP (Access Point) - Another name for a cross-box where telephone cables are cross connected.

APD (Avalanche Photo Diode) - A device used as a light-to-electricity converter and signal amplifier at the same time. They are incorporated in optoelectronic circuits used in fiber-optic terminating applications.

Application Layer - The seventh and highest layer of the OSI communications model. The applications layer is the function of connecting an application file or program to a communications protocol. The latest model or guideline for communications protocols is the OSI (open systems interconnect). It is the best model so far because all of the layers or functions work independently of each other. Older proprietary communications models are shown below along side the OSI. For a diagram of the OSI, SNA, and DNA layers, see Open Systems Interconnection.

API (Application Program Interface) - A set of routines, protocols and other tools that are used by software programmers to create applications. Microsoft Windows has an API that enables programmers to create applications that are consistent with the Windows user environment.

APON (ATM Passive Optical Network) - A passive network consists of devices that do not require external power. The physical characteristics of the carrier (light, in this case) are used to route and distribute signals. In xDSL networks, it is possible to extend and route the xDSL signal using fiber optic. Passive optical networks are less expensive to implement and operate. An APON is a passive optical network that is carrying ATM. ATM is a practical and frequently used method to transport xDSL. For more details on the physical characteristics of light transmissions, see Fiber Optic, WDM, and Refraction.

APPC (Advanced Program-to-Program Communication) - The IBM SNA (System Network Architecture) software that allows high-speed communication between programs on different computers in a distributed/mainframe computing environment. APPC establishes and tears down virtual connections between programs that require communication. It has two software interfaces; the first interface is the programming interface, which replies to programs requiring communications. The second interface is the data-exchange interface, which establishes the sessions or "connections" between the programs.

Applications Processor - An add-on to a PBX (Private Branch Exchange) system or CO (Central Office) switch that expands its ability to provide extended services or process additional protocols. An example of an applications processor is a voice-mail system, ACD, frame relay or ISDN interface. Physically, the applications processor is often an additional shelf, module, or card that interfaces into the PBX system's bus architecture.

APPN (Advanced Peer-to-Peer Networking) - An enhancement to the original IBM SNA (System Network Architecture). APPN handles the following: session establishment between peer nodes, dynamic transparent route calculation, and traffic prioritization for Advanced Program-to- Program Communication.

ARCnet (Attached Resource Computer Network) - A token-bus local-area network protocol/package developed by Datapoint Corporation. ARCnet was a popular coax media network solution after its initial inception in the late 1970s. Newer versions have evolved for use on other physical media.

Area Code - An area code is a three-digit code that designates a toll center in the North American Numbering Plan. To call outside of your toll center, you first dial 1, then the area code for the toll center or "area" you wish to call. See Appendix C for a listing of area codes by area. See Appendix D for a listing of area codes by number.

ARP (Address Resolution Protocol) - A set of communications rules and instructions used by computers and communications interface equipment to map or forward IP (.Internet Protocol) addressed data packets to a hardware address. A hardware address is also known as a MAC (Media Access Control) address. ARP can only be used in networks that have broadcast capabilities

ASCU (Agent Set Control Unit) - An address identifier for a set of terminals that handle type-A messages in an IBM network environment. An ASCU identifies a workstation to a concentrator and can use P1024B or P1024C protocol.

ASIC (Application Specific Integrated Circuit) - A proprietary integrated circuit created to do a specific job. An example is Motorola manufacturing a chip to do multiplexing specifically for a MUX that is made by Nortel. Motorola manufactures the chips for Nortel and stamps Nortel's name on them. Then, only Nortel uses the technology and no one else.

ASR (Access Service Request) - If a special service provider (frame relay or long-distance private line) needs wire facilities from their point of presence in the city to customer's location, they call the local telephone company and make an access service request to provide a line that runs from your network interface to them. Many special service providers have their equipment located in the local phone company's central office as a part of a co-location agreement. When a CLEC needs to provide service where they don't have facilities, they do it by using the RBOCS wire facilities.

Asymmetric - Communications transmission that is full or half duplex, where one direction is very fast, compared to the other. Cable TV is an example of asymmetrical communication. The cable TV head end sends massive amounts of video and audio information down a coax one way, and the cable TV set-top decoder boxes send small amounts of ID and status information the other way back to the head end over the same coaxial connection. Sometimes asymmetrical channels are referred to as "upstream" for slow and "downstream" for fast. ADSL is another example of asymmetric communications.

Asymmetric Digital Subscriber Line (ADSL) - Also referred to as ADSL Full Rate or G.992.1. ADSL is a physical-layer protocol that supports up to 8 Mbps bandwidth downstream and up to 1 Mbps upstream. The asymmetrical aspect of ADSL technology makes it ideal for Internet browsing, video on demand, and remote Local-Area Network (LAN) access. Users of these applications typically download more information than they send. ADSL also allows simultaneous voice communication by transmitting data signals outside of the voice frequency range. Sometimes a faint hiss can be heard on the line. To eliminate the hiss, a voice/ data splitter, commonly called a POTS splitter (Plain Old Telephone Service) is installed at the jack of each phone. The base transmission range for an ADSL line is 18,000 feet. ADSL can be extended to remote communities by using ADSL repeaters (to 48,000 feet) or fiber optic. For more information on the DSL family of protocols, see xDSL. For a diagram see, ADSL.

Asynchronous - To communicate without external timing and to have each communicating device work at its own speed. People talk asynchronously. Even though one person talks very fast and another very slowly, their brains still receive the conveyed messages and respond. Modems, FAX machines, and TCP/IP communications are asynchronous.

Asynchronous Transfer Mode (ATM) - An ANSI and CCITT standard communications protocol. ATM is a frame-format communications protocol whereby data is transmitted and received 53 bytes or octets at a time. There are 48 customer bytes (Payload) and 5 bytes for control and addressing. Three things make ATM special.

1. It is capable of carrying delay-sensitive transmissions without delay (such as speech, music, or video).
2. Many ATM channels can be concatenated to provide more bandwidth (carrying capacity).
3. It has the ability to carry many different types of data at the same time: LAN, WAN, video, voice, and anything else that is capable of being digitized. Another good thing about ATM is that the overhead is a bit more than 10%, which is an improvement over other transport methods. To put ATM into a simple picture, imagine that you have a computer network LAN signal and a video signal. You want to send the signals that your computer and video are generating to other computers and TVs. Now, take the scenario a step further. Imagine that your computer LAN signals are motorcycles and the video signals are cars. ATM would then be large trucks that carry the motorcycles and cars to their destination and back, linking your communications gap with two great things in mind. Your cost is lower in contrast to many small circuits and you only buy one piece of gear to connect everything (in contrast to many different terminal adapters, CSU/DSU, etc.). See also ATM.

AT (Access Tandem) - A telephone company central office or node that contains a switch in which all inter and outer area-code traffic is handled. The main LEC central office in an area code, where the hand-off for longdistance service happens. For a diagram, see Access Tandem.

AT (Advanced Technology) - A reference to the IBM clone motherboard standard baby AT form factor. A generation of personal computers that was introduced by IBM in 1984. The first AT computers had an Intel 80286 microprocessor and hard disk drives that ranged from 10 MB to 30 MB. AT computer architecture is able to be upgraded easily by replacing RAM, hard disk drives, plug-in CPUs, and even the motherboard. AT architecture has enabled PCs to evolve with new technologies, spawning machines that incorporate CPUs with speeds in excess of 300MHz and hard disk drives that exceed 8 GB in memory. Illustrated is an AT socket-7 motherboard. The newer version of AT architecture is ATX. See also ATX.

ATA (AT Attachment) - Also referred to as IDE (Intelligent Drive Electronics and Integrated Drive Electronics). ATA is a refers to a drive-interface standard for CD-ROM drives and hard disk drives. It was called ATA because of the popularity of the AT (Advanced Technology) motherboard at the time of its development by the Small Form Factor

Committee. It is a relatively less-expensive alternative to SCSI (Small Computer System Interface) and has retained popularity in the PC industry because it manages to continuously improve while remaining price competitive. Newer versions of this interface standard are called Fast ATA, ATA-66, and EIDE (Enhanced IDE). See also IDE, SCSI, and Hard Disk Drive.

ATM (Asynchronous Transfer Mode) - An ANSI and CCITT standard communications protocol. ATM is a frame-format communications protocol whereby data is transmitted and received 53 bytes or octets at a time. There are 48 customer bytes (Payload) and 5 bytes for control and addressing. For more information, see Asynchronous Transfer Mode.

ATM25 - The ATM Forum-defined 25.6-Mbps cell-based user interface that is based on the IBM token-ring network.

ATM Adaptation Layer (AAL) - A transfer format, cell header format, and functional section of the ATM transport method. There are five variations of the ATM Adaptation layer. Each is intended to be used with a specific type of data. For a diagram of ATM layers, see ATM. For a diagram of AAL classifications, see AAL.

ATM Adaptation Layer One (AAL1) - The part of the ATM protocol that enables the transfer of time-sensitive data, such as voice or video. AAL1 uses an adaptive clock method, where the devices at each end of the link negotiate a clock agreement, then incorporate a small buffer to monitor the rate at which cells are being transferred across the link. AAL1 is used for DS0, DS1 emulation, and other voice and video. For a diagram, see AAL.

ATM Adaptation Layer Two (AAL2) - For class-B traffic , packet technologies, and the transport thereof. It is similar to voice over frame, video over frame, etc.

ATM Adaptation Layer Three and Four (AAL3/4) - For class-C and -D layers that are designed to handle nontime- sensitive data transfer. This layer class adds header information that incorporates error-checking functions before and after the original data. Also, a Message ID function allows multiplexed or interleaved transmissions to be sent directly over the single ATM virtual channel. This layer would be used as a backbone to carry many X.25 or frame-relay logical links, or could be used in a campus application to carry Ethernet from one building to another.

ATM Adaptation Layer Five (AAL5) - The layer created for class-C and -D types of traffic . The cell header remains the same except larger buffers are used and a CRC (Cyclic Redundancy Check) is appended to the end of the last cell of the packet's cell stream. No Message ID function is available to directly transfer multiplexed data. Cell payloads are 48 bytes, and a PTI bit is used to indicate the last cell of a packet.

ATM DXI (ATM Data Exchange Interface) - A connectivity and conversion method that allows an existing LAN network element (i.e., router) to access an ATM network via a private line that is equipped with a CSU/DSU (V.35 or HSSI).

ATM DSU (Asynchronous Transmission Mode Digital Service Unit) - A terminal adapter used as a demarcation point or interface point to an ATM network.

ATM DXI (ATM Data Exchange Interface) - A connectivity and conversion method that allows an existing LAN network element (i.e., router) to access an ATM network via a private line that is equipped with a CSU/DSU (V.35 or HSSI).

ATM Forum - An international organization jointly founded in 1991 by Northern Telecom, Cisco Systems, Net/Adaptive, and Sprint. The organization develops and promotes standards based implementation agreements for ATM technology. The ATM Forum expands on official standards developed by ANSI and ITU-T. The organization also develops implementation agreements in advance of official standards.

Attached Resource Computer Network (ARCnet) - A token-bus local- area network protocol/package developed by Datapoint Corporation.

Attendant - Another name for a PBX operator. The person who connects outgoing calls and/or answers, screens and directs incoming calls in a polite mannerly way. If they don't, they would soon be replaced by an auto- attendant.

Attenuation - Reduction of a signal's voltage level as it travels down a line, measured in decibels. Attenuation is also called loss, because some signal is always lost through resistance and reactance. Optical light-wave signals are also attenuated when they traverse through a fiber-optic because of impurities in the fiber optic, and the fact that light intensity decreases with distance.

Attenuator - An attenuator is also called a pad, T pad, or H pad. It is a device that reduces the voltage level of a signal without changing it's impedance. Attenuators are frequently used on telephone lines that terminate to customers close to the central office so that the volume in the handset does not hurt their ears. Attenuators are also made for fiberoptic applications. A fiber-optic attenuator works like your sunglasses, it reduces the level of light entering your eyes so that you can see more effectively. For a photo, see Fiber optic Attenuator.

ATX - A trademark of Intel that is not an abbreviation, but a model number. Many refer to it as Advanced Technology Expanded because it is an improvement of the AT (Advanced Technology) generation of computer hardware architecture. The ATX generation of PC architecture is based on an improved motherboard design, which is rotated 90 degrees within the cabinet. This places devices within the PC closer to their respective plug-in connectors and places the CPU closer to the power-supply cooling fan. ATX motherboards also have on-board I/O interfaces. The most noticeable esthetic difference between an AT and ATX architecture is that the interface connectors are laid out differently. On the AT, the connectors are set along the edge of the motherboard, on the ATX the connectors are blocked together on a metal mounting plate. Illustrated is an ATX slot 1 motherboard. For a visual comparison of AT and ATX..

Audio - Sound. Signal frequencies that if amplified and applied to a loudspeaker can be heard. These frequencies range from 20 Hz to 17 kHz.

Audio Frequency - Signal frequencies that, if amplified and applied to a loudspeaker, can be heard. These frequencies range from 20 Hz to 17 kHz.

Auger - A device that looks like a giant drill bit, which is used for boring holes into the ground for telephone or power poles. Some utility construction vehicles are equipped with augers.

AUI (Autonomous Unit Interface) - A 15-pin connector used in CTI (Computer Telephony Integration) applications. For a picture, see DB15.

Auto Baud - A term that refers to a modem or other communicating device's ability to match or adapt to the bit transmission rate of the device at the far end.

Auto Dialer - A device that automatically dials preprogrammed digits when the line it is attached to breaks a dial tone. Auto dialers are used to program long-distance carrier access codes so that people don't have to deal with the confusion of which long-distance company to access and when. The person making a call pushes a key on their phone that accesses a long-distance trunk equipped with an autodialer that dials the access code, then the person making the call dials in the number they want to call. Auto dialers are also used to make a phone dedicated to one phone number or directory extension. In the city where I live there is a restaurant with no waiters or waitresses. When the patrons to the restaurant are seated, they find a phone at their table. The phone has no dial pad. When the phone is picked up, an autodialer instantly dials the order- taker's extension and the patrons place their order.

Automated Attendant - The machine that answers the line and plays a message that says: "Thank you for calling company X. To speak to a person in sales press one, to speak to a repair person press two." Advantages of auto attendants are that you can have one number advertised for multiple departments and not have to have a full-time person directing calls.

Automated Voice Response - Not to be confused with integrated voice response, an automated voice-response system or network is a way of guiding callers to a department, agent or pre-recorded information. Automated-attendant/voice-mail systems that have directory trees programmed into them are becoming the most popular ways of accomplishing this. Directory trees are set-up by the voice-mail administrator. Directory trees are capable of being as long and complicated as the caller can tolerate. For example, the caller hears a pre-recorded message that prompts them to dial "1" for information about skin ailments, dial "2" for flu-like symptoms or dial "3" for head pain. Options 1, 2, and 3 then branch out into a tree .

Automatic Call Distributor (ACD system) - A separate system or built-in feature of a PBX that equally distributes incoming calls to agents. As calls come in, they are placed into a queue (or a waiting line) for the next available agent. ACD systems are very versatile and relatively easy to program because some incorporate their own script programming language. For incoming calls, the waiting times, pre-recorded announcements and other call treatments can be set up by the users/companies to their discretion. Some well-known ACD systems are made by ACCENT and Nortel Networks.

Automatic Number Identification (ANI) - A service provided by local and long-distance telephone companies that sends the name and number of the calling telephone to a display attached to the called phone line. In an in-band signaled phone line or residential telephone line, the ANI signal packet comes as a miniature data burst between the first and the second ring.

Available Bit Rate (ABR) - Quality of Service (QOS) defined by the ATM Forum for ATM Networks that is used for connections that are not time or delay sensitive. A connection would be rightfully commissioned as an ABR connection if it carried only spontaneous or bursty data. Other QOSs defined by the ATM Forum for ATM Networks include CBR (Constant Bit Rate), UBR (Unspecified Bit Rate), and VBR (Variable Bit Rate).

Avalanche Photodiode - A device used as a light-to-electricity converter and signal amplifier at the same time. They are incorporated in optoelectronic circuits used in fiber-optic terminating applications.

Avalanching - Avalanching occurs when a PN diode or transistor junction is reverse biased (reverse positive and negative) with enough voltage to force it to conduct in the wrong direction. Diodes and transistors have an avalanche voltage rating. When this voltage is exceeded, the device avalanches. The avalanche is actually a sudden steady rush of current that causes lots of heat. This usually damages the device (severely). Some devices (avalanche photodiode, SCR, etc.) are designed to use the avalanche effect in a useful way. They switch "on" or conduct when the reverse or gate voltage applied to them reaches a certain level.

AWG (American Wire Gauge) - A measurement standard for copper wire. The gauge rating is the thickness of a solid copper wire. The larger the gauge, the smaller the wire. Most telephone wire is 19 AWG at the largest and 26 AWG at the smallest. Cat 3 is commonly 24 AWG. The electrical wire in your home is probably 12 AWG.

AX.25 - A protocol that is based on X.25 recommendations. AX.25 is a connection-oriented version of X.25. Rather than sending separate individual packets, as is done in X.25, the AX.25 protocol sets up a layer-3 Permanent Virtual Circuit (PVC) before the transmission begins. When the transmission is complete, the PVC is disconnected. AX.25 is generally useful in older mainframe WAN applications.

Azimuth - In directional radio transmission, the azimuth is the direction in degrees (bearing) that an antenna is transmitting to its far-end counterpart. If a directional radio signal seems weak after a strong windstorm, the azimuth might need to be realigned.