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Glossaries

  • Alarm Cut Off (ACO)
  • Button or similar feature that allows all alarm signals to be manually silenced.
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  • Add Drop Multiplexer (ADM)
  • Equipment in a fiber optic network that combines multiple signals into one single signal for further transmission. The "add drop" means that it can add or extract single signals from the major transmission route similar to on/off-ramps in a highway.
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  • Advanced Encryption Standard (AES)
  • An algorithm for the encryption of electronic data. It has growingly replaced Data Encryption Standard (DES) nowadays. It adopts the symmetric-key algorithm, which indicates that the same key is used for both encrypting and decrypting the data.
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  • Alarm Indication Signal (AIS)
  • In a T1 network, this is the signal is sent to let the receiver know that a fault has happened earlier in the transmission path. The signal is also called "all ones" because a transmission of all 1s is sent to maintain transmission continuity.
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  • Alternate Mark Inversion (AMI)
  • A type of line code used in E1 and T1 networks. With AMI, zeros are represented as 0 volts during each bit cell or clock cycle, while ones are represented as a positive voltage in one clock cycle and a negative voltage in the next one. This prevents a sufficient DC voltage from building up as well as maintaining "ones density" for clock recovery.
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  • American National Standards Institute (ANSI)
  • A private, non-profit, voluntary organization that coordinates standard relating activities, approves US national standards, and represents the United States in international standard organizations. It creates standards in computers, networking, telecommunications, and a variety of other engineering fields.
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  • Automatic Ring Down (ARD)
  • A setup where two telephones are connected such that lifting the handset of one will cause the other to ring immediately. This is used primarily by busy financial market traders and military units.
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  • Available Second (AS)
  • A measure of time during which service is available to the paying customer.
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  • Asynchronous Transfer Mode (ATM)
  • A standard switching technique that can be used to carry many different service types such as voice, video, or data all over one network. It does this by dividing the data stream into fixed length cells of size 53 bytes, which thus can be more easily implemented in hardware. ATM also goes by the connection-oriented model which establishes a "virtual circuit" connection between data points before it transmits data.
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  • American Wire Gauge (AWG)
  • A standardized system to measure the diameter of round, electrical carrying copper wire. The cross-sectional area of the wire is an important factor in determining the amount of current that it can carry. Numbers are integers that vary from 36 (very thin) to 0 (relatively thick).
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  • Bipolar with Eight Zero Substitution (B8ZS)
  • Type of line code used in T1 and E1 systems, in which a special signal is transmitted whenever eight consecutive zeros are sent of the line. The code is then reinterpreted at the end of the connection as all 0s. The technique guarantees ones density and thus clock reconstruction regardless of the data stream.
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  • Bit Error Rate (BER)
  • Ratio of received bits that contain errors either due to noise, interference, or bit synchronization errors.
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  • Bit Error Rate Test (BERT)
  • A test that determines the bit error rate across a given communications network. A predetermined pattern that is known at both the sender and the receiver is sent. The results are compared to the expected pattern to determine the number of bit errors. Alternately, the signal can be instructed to loop back to the sender in which case only one machine is necessary.
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  • Bursty Error Second (BES)
  • A measure of time during which the line is noisy and service is unavailable to the paying customer.
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  • Bit Interleaved Parity (BIP)
  • A method used to monitor errors in ATM. A check bit is sent as part of the link overhead for the previous block or frame. Bit errors can then be detected and reported as maintenance information.
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  • Bayonet Connector (BNC)
  • Type of mechanical connector typically used to connect 10Base coaxial cable to an Ethernet access unit. The design contains two pins on either side of the cord or device that insert and twist into an L-shaped receptor, thus locking it into place.
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  • Bipolar Violation (BPV)
  • An error that can occur in a T1 or E1 network. When Alternate Mark Inversion is used, a 1 signal is a positive pulse in one clock cycle and a negative pulse in the next clock cycle. When two positive or negative pulses are detected consecutively, the BPV error occurs.
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  • Base Station Controller (BSC)
  • Device that provides the control functions and physical links between a Base Transceiver Station (BTS) and the MSC (mobile switching center). The BSC typically controls many BTSs and optimizes the power and signals transmitted by them, thus acting as the "intelligence" behind the BTS.
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  • Base Transceiver Station (BTS)
  • A land-based station in a mobile wireless network that consists of transceivers and antennas. The term BTS is typically used in reference to GSM and CDMA cell phone communications.
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  • Channel Associated Signaling (CAS)
  • Transmitting signaling information over the voice channel. Also called per-trunk signaling (PTS) or "robbed-bit" signaling because it takes up bandwidth that could have otherwise been used by data.
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  • Common Channel Signaling (CCS)
  • Different from CAS, CCS designates a certain channel specifically for signaling. Information on this common channel controls and provides information for all the other data-carrying channels in the system.
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  • Code Division Multiple Access (CDMA)
  • A method in radio communications that divides a shared channel (the radio spectrum) among multiple users through assignment of unique codes. The method is analogous to two users speaking a foreign language in a crowded room.
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  • Compression
  • Data processing that reduces the amount of bandwidth necessary to transmit a signal in a given time or reduce the amount of time for a given bandwidth.
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  • Configuration (CFGN)
  • In terms of computers and telecommunications, configuration is the unique collection of settings that can be tweaked for maximum performance or reliability. It is usually a stored as a file that is executed when the device first boots up.
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  • Cellular Geographic Service Area (CGSA)
  • The physical area over which a cellular provider is licensed to give service.
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  • Competitive Local Exchange Carrier (CLEC)
  • A company that builds and operates communications networks in metropolitan areas (also called a carrier) that are competing with other more established carriers.
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  • Coded Mark Inversion (CMI)
  • A type of line coding used in communications. A zero bit is encoded as half a time period of 1 and the other half as 0, while a one bit is encoded as a full time period at a constant level.
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  • Computerized Management Maintenance System (CMMS)
  • Software system that is meant to assist workers by identifying which devices need maintenance and how. It can also be used to track safety and regulatory compliance.
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  • Co-directional Interface
  • The term co-directional is used to describe an interface across which the information and its associated timing signal are transmitted in the same direction (ITU G.703).
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  • Customer Premises Equipment (CPE)
  • Equipment that resides at the customer's site such as modems, telephones, handsets…etc, that act as terminating equipment or end-point devices for the communications network.
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  • Cyclic Redundancy Check (CRC)
  • Type of error detection method. In the method, the data contents are divided by a large prime number and the remainder is stored with the data as a check-sum value. On retrieval this value is recalculated and compared to the checksum for accuracy. Can be used in both storing and sending data.
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  • Canadian Standards Association (CSA)
  • Standards making organization in Canada, similar to ANSI in the United States, with a focus on safety-related standards.
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  • Control Slip Second (CSS)
  • A one second interval containing one or more "control slips", in which a frame is either repeated or deleted to account for frequency drifting.
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  • Channel Service Unit (CSU)
  • Digital interface device that connects the end-user equipment to the local telephone loop. Also provides maintenance and loopback functionality.
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  • Coarse Wavelength Division Multiplexing (CWDM)
  • A method of multiplexing different signals over a fiber optical network by using different wavelengths (or colors) of light. Coarse WDM is comparable to dense WDM because of a closer spacing of wavelengths and a different type of light amplifiers used.
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  • Digital Access Cross-Connect System (DACS)
  • Also called a digital cross-connect system (DCS). A piece of circuit-switched telephone equipment that can switch any T1 line to any other one line in the system, often automatically in a time of failure.
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  • Data Communication Channel (DCC)
  • A channel in charge of data communication in SONET/SDH networking.
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  • Data Circuit-terminating Equipment (DCE)
  • Devices such as a modem or interface card that connect the user to a communication channel.
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  • Digital Cross-connect System (DCS)
  • Also called a DACS, Digital Access Cross-connect System. A piece of circuit-switched telephone equipment that can switch any T1 line to any other one line in the system, often automatically in a time of failure.
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  • Dual In-line Package Switch (DIP)
  • Small manual electric switch on a device that can used to change a setting. These are used on printed circuit boards to quickly and easily change settings. While not in use much in recent consumer products (due to software and the lower cost of memory), they are still prevalent in industrial electronics. The main advantage is that settings can be easily viewed and quickly changed without powering on the device.
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  • Digital Loop Carrier (DLC)
  • A method that digitizes the voice data over a telephone network and thus allows it to use existing copper infrastructure without worrying about traditional analog problems such as impedance and attenuation.
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  • Degraded Minute (DM)
  • A 60 second long group of time in which the estimated error rate exceeds 1e-6 but not 1e-3.
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  • Digital Signal, Level 0 (DS0)
  • 64 Kbps, corresponding to the capacity required for a single digitized voice call.
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  • Digital Signal, Level One (DS1)
  • Same as T1. DS1 is the time division multiplexing of 24 DS0 signals to create a capacity of 1.544 Mbps.
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  • Data Service Unit (DSU)
  • Adapts the physical interface on a DTE to a transmission channel such as E1 or T1. Responsible for signal timing and synchronization.
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  • Digital Signal Cross connect (DSX-1)
  • A place where DS-1 signals are connected, typically at a central location.
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  • Data Terminal Equipment (DTE)
  • End user device such as a PC or workstation at the end of a communications network. Often communicates over a DCE such as a modem. Serves as a data source, destination, or both.
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  • Error Free Second (EFS)
  • In T1 and E1 systems, a second where no error blocks are received.
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  • Electro-Magnetic Compatibility (EMC)
  • The field of electrical sciences that addresses a device's unintended electro-magnetic radiation or its vulnerability to spare radiation in order to prevent interference.
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  • Electro-Magnetic Interference (EMI)
  • Interference from an external source that disturbs an electrical circuit and prevents it from operating normally.
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  • Embedded Operational Channel (EOC)
  • A channel in a telecommunications facility provided specifically for administration, operations, and maintenance.
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  • Errored Second (ES)
  • An interval of a second during which any possible error has occurred.
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  • Extended Super Frame (ESF)
  • In T1 circuits this consists of 24 frames of 192 bits each, with the 193rd bit for timing and CRC check.
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  • Errored Second Ratio (ESR)
  • The ratio of errored seconds (ES) to total number of seconds during any given measurement interval.
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  • European Telecommunication (ETSI)
  • Standards making organization in Europe. Similar to ANSI and CSA, but specifically for the telecom industry.
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  • External Clock (EXT CLK)
  • A timing signal external to the operating unit, to which the unit is synchronized.
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  • Frame Alignment Signal (FAS)
  • A distinctive set of bits that demarcate the beginning of a frame. May also contain other bits for control.
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  • Fault, Configuration, Accounting, Performance, and Security (FCAPS)
  • Term used to define the major functions of a network management system (NMS). Accounting can also mean Administration in non-billed networks.
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  • Federal Communications Commission - USA (FCC)
  • United States government agency that supervises, controls, and licenses companies related to the telecommunications, networks, electromagnetic field, broadband, and media.
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  • Facility Data Link (FDL)
  • A 4Kbps channel provided by the Extended Super Frame (ESF). It is not part of the payload capacity. It allows a service provider to check error statistics on customer equipment without intruding on the channel.
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  • Frequency Division Multiplexing (FDM)
  • Technique where information from multiple channels can be sent over one channels by using different frequencies. Comparable to time division multiplexing (TDM) and code division multiplexing (CDM).
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  • Frequency Division Multiple Access (FDMA)
  • In the protocol layer, allocates different frequencies to different channels. Similar to FDM but not exactly the same. Term often used in the context of wireless communications such as mobile and satellites.
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  • Full Duplex
  • A mobile wireless transmission type that allows communication in both ways at the same time. Can use adjacent channels (frequency division duplex) or adjacent timeslots (time division duplex).
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  • Fast Ethernet (FE)
  • Ethernet that transmits at 100 Mbits per second. Fast in comparison to original Ethernet at 10 Mbits/second. Also called 100BASE-T when transmitted over copper.
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  • First In, First Out (FIFO)
  • Also called "first come, first served" or a queue/line. The first data packet recieved is the first packet sent out.
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  • Foreign Exchange Office (FXO)
  • Any device that can interact with the plain-old telephone system (POTS) and generate the appropriate ring signals. Examples include analog telephones, fax machines, and modems.
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  • Foreign Exchange Station (FXS)
  • A telephone exchange that provides the ring, voltage, and dial tone to an foreign exchange office (FXO). Can be a public network or a private branch exchange (PBX).
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  • General Attribute Registration Protocol (GARP)
  • Protocol defined by IEEE 802.1ak that allows bridges, switches, or other devices to register/deregister attribute values such as VLAN identification.
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  • Gigabit Ethernet (GbE)
  • Transmission of Ethernet frames in up to 1 Gigabit per second speed. Called 1000BASE-T when referred to copper wiring, 1000BASE-X in reference to fiber.
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  • Generic Framing Procedure (GFP)
  • Multiplexing technique defined by G.7041. Maps data over SDH/SONET or PDH.
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  • Gateway GPRS Support Node (GGSN)
  • Key node in a GRPS (General Radio Packet Service). It exists between mobile networks such as 2G, 3G, and CDMA and an Ethernet packet-switched network such as the Internet.
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  • Ground (GND)
  • Voltage reference point for measurement, usually a direct connection to the earth. Can also refer to a large conductor or any other device that acts as a "current sink."
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  • General Packet Radio Service (GPRS)
  • Service defined by ETSI, European Telecommunications Standards Institute. Defines a packet-based IP network and interfacing with the Internet for mobile communications. See GGSN.
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  • Global System for Mobile Communications (GSM)
  • A second generation (2G) standard for mobile communications, defined by ETSI. Uses TDMA technology and operates in the 900 MHz radio band. A digital technology, it is an improvement over the original analog (1G) mobile cell phone network.
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  • GARP VLAN Registration Protocol (GVRP)
  • Replaced by MVRP (Multiple VLAN Registration Protocol). Specific use of GARP to set up VLAN information automatically between switches and other devices. Replaced by the more specialized MVRP because it did not scale well to large VLANs.
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  • High Density Bipolar Three Substitution (HDB3)
  • Type of line code used in E1 type systems. Replaces four consecutive zero bits with one of two patterns. The two patterns ensure that consecutive violations/replacements are of different polarity. Similar to B3ZS in T1.
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  • High-level Data Link Control (HDLC)
  • A bit-oriented synchronous data link layer protocol, providing both connection-oriented and connectionless service. It is used to connect one device to another with Asynchronous Balanced Mode (ABM).
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  • High bit rate Digital Subscriber Line (HDSL)
  • 1.544 Mbps over two copper twisted pair wires. One of four types of DSL technologies used to interconnect local telephone exchanges or high speed data across large enterprises. Operates at T1 speed so as to reuse existing infrastructure.
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  • Half Duplex
  • A mobile wireless transmission type that allows communication in both directions but in only one way at a time, for example "push to talk."
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  • Internet Group Management Protocol (IGMP)
  • Protocol used by IP hosts to report their multicast group memberships to a multicasting router.
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  • International Mobile Subscriber Identity (IMSI)
  • A unique 64-bit identifier stored in the SIM card of a cell phone. The phone sends this device to the base station which forwards it on to the Home Location Register for identification and tracking.
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  • Internet Protocol (IP)
  • The network layer protocol in the TCP/IP stack that offers connection-less networking through the use of packets that are forwarded based on address. IPv4 is defined in RFC 791 (1981).
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  • Integrated Services Digital Network (ISDN)
  • ISDN is a communications protocol that allows voice, data, video, and other source traffic to be carried over the existing publicly switched telephone network. It's usage for internet access has dropped down in favor of ADSL, Asymmetric Digital Subscriber Line.
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  • Jitter
  • The undesirable delay or deviance in frequency from a truly periodic signal. In voice and video applications, it can cause data loss, flickering, and audio-blips. It can also refer to the variance in the inter-packet arrival time for a packet-switched network.
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  • Kilo bits per second (Kbps)
  • 1000 bits per second. Can also mean 1 Time Slot, as Kbps is a measure of bandwidth.
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  • Local Area Network (LAN)
  • High speed local area network for a small geographic area such as a school, business, or office. Ethernet is a widely used technology with LANs. Compare with WAN, wide area network.
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  • Link Access Procedure (LAP)
  • Data link layer protocols for framing and transmitting data from point-to-point links.
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  • Line Build Out (LBO)
  • A compact network that simulates a length of transmission line.
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  • Liquid Crystal Display (LCD)
  • A display technology that uses liquid crystals sealed between two plates of glass. Common nowadays in computer monitors, fax machines, calculators, TVs, clocks, and many other electronic displays.
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  • Link Control Protocol (LCP)
  • Part of PPP, Point to Point Protocol. Establishes, tests, and configures data-link connections for further use by PPP.
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  • Light Emitting Diode (LED)
  • Semiconductor device that emits light from electrical energy. Considerably more efficient than incandescent light-bulbs, LEDs are often used as indicator lights in computer hardware.
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  • Load Number (LN)
  • A measure of how much work a computer is performing. An idle computer has a load number of 0 and each process that is running or waiting to run increments the load number by 1. It is typically measures the performance in the last one, five, and fifteen minute periods.
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  • Loss of Frame (LOF)
  • A generic term to designate an error in a packet-switched network. Typically indicates the device is over capacity or misconfigured.
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  • Loss of Frame Count (LOFC)
  • The number of seconds during which a Loss of Frame alarm condition was detected.
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  • Loss of Frame Sync (LOFS)
  • Occurs when errors in the Digital Signal Level 3 (DS3) framing pattern are detected by the UXM backcard receiver. This error represents consecutive errors in the terminal framing bits.
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  • Loss of Multi-frame (LOM)
  • Occurs when two consecutive multi-frame alignment signals have generated an error in a T1/E1 system.
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  • Line of Sight (LOS)
  • The fact that there must be an clear, unobstructed path between transmitters and receivers in a wireless communications system.
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  • Loss of Signal (LOS)
  • Occurs when N consecutive zeros are detected on an incoming signal, where N is defined by the device or user.
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  • Loss of Synchronization Word Second (LOSWS)
  • Whether an alarm was sent due to a Loss of Synchronization Word failure during the last second.
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  • Line Power
  • General purpose alternating current electric power from the wall. Can also refer to any general source of power.
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  • Low Voltage Differential Signal (LVDS)
  • An electrical digital signaling standard that can run at very high speeds over inexpensive twisted pair copper cables. Specifies the interoperability between the input and output connection points on integrated circuits. Is differential in that it transmits data as the voltage difference between two electrical wires.
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  • Media Access Control Address (MAC Address)
  • Also known as a hardware address or physical address. It is a unique identifier required for every physical port or device that connects to a LAN network. Other devices use the MAC address to create routing tables and data structures. It operates at the physical, data-link layer in contrast to IP addresses at the network layer.
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  • Mega bits per second (Mbps)
  • Number of megabits per second. Equal to 1,000,000 bits per second or 1,000 kilobits per second.
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  • Multiple rate Digital Subscriber Line (MDSL)
  • Also called Multiple Rate Symmetrical Digital Subscriber Line. A type of DSL technology with multiple transfer rates that can be set by the Internet Service Provider. The maximum transfer rate is 2 Mbit/s.
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  • Management Information Base (MIB)
  • A collection of information about devices on a network that can be managed with a protocol such as SNMP. The database is tree-based and hierarchical. Important documents that describe MIBs include RFC 1155 and 1213.
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  • Mobile Switching Center (MSC)
  • The device that provides telephone switching and data routing for GSM/CDMA mobile phones.
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  • Mobile Telephone Switching Office (MTSO)
  • Also called a land station, it is the equivalent of a Central Office for a publicly switched telephone network, PSTN. Routes mobile calls, tracks and bills information, assigns and reassigns frequencies, and interacts with the land-based telephone network.
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  • Maintenance Termination Unit (MTU)
  • Installed at the demarcation between the carrier's network and the customer premises equipment (CPE), it conducts tests on the CPE or the connected network to see if maintenance is necessary.
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  • Multiplexing
  • Sharing the same channel with multiple users. Designed to use an under-utilized channel more effectively. Multiplexing can be done over time, frequency, or in code.
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  • Network Element (NE)
  • A generalized term for a manageable logical entity, usually a combination of hardware and software, designed for a single telecommunications function. Usually means any one single element in a management system.
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  • Network Interface (NI)
  • The boundary between a carrier network and the customer's privately owned network.
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  • Network Management System (NMS)
  • System responsible for managing a network. Usually a computer in an engineering workstation running specialized software to track FCAPS (fault, configuration, accounting, performance, and security) on the system. Manages a collection of network elements.
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  • Nodule for Base Transceiver Station (BTS NODE B)
  • The antenna and associated electrical circuitry which directly communicate and receive transmissions from mobile phones. The term "Node B" is commonly used in reference to CDMA technology, while "BTS" is used with GSM.
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  • Operations, Administration and Maintenance (OAM)
  • A general term used to describe the facilities, personnel, and processes used to successfully maintain a telecommunications network.
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  • Office Channel Unit Data Port (OCUDP)
  • A legacy interface for data transmission up to 64 kbps.
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  • Out of Frame (OOF)
  • Occurs when errors in the framing pattern are detected by the backcard receiver. This happens when consecutive errors in the terminal framing bits are encountered.
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  • Off Premises Extension (OPX)
  • In a private telephone system (private branch exchange or PBX), the OPX is a telephone that terminates in a location far from the main PBX but is still part of the system.
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  • Operation Support System (OSS)
  • Computer systems used by telecommunications service providers (carriers) to automate and integrate common business tasks such as signing up a new customer, provisioning service, tracking faults, and sending bills all in one central software system.
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  • Pulse Amplitude Modulation (PAM)
  • A form of signal modulation where the pulse stream samples an incoming data stream at fixed points, sending only the amplitude. The amplitude can be analog (one of many numbers) or digital (one number out of a fixed collection).
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  • Private Branch Exchange (PBX)
  • Private telephone network that serves a certain company or office. Can be connected to the wider publicly switched telephone network (PSTN).
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  • Plesiochronous Digital Hierarchy (PDH)
  • A way of transmitting data over fiber optic and microwave transmission. Plesio- being a Greek word for almost, it describes a timing system where the two clocks are nearly but not exactly synchronized. PDH is being replaced by SDH (synchronous digital hierachy) and SONET (synchronous optical networking).
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  • Private Line, Automatic Ringdown Plug-in Card (PLAR card)
  • An Electronic Order Wire (EOW) device. It allows two dual private line automatic ringdown interfaces to be multiplexed to 64 kbps DSO signals. PLAR refers to a private telephone line that is not serviced by a carrier. When one handset is taken off the hook, it applies a voltage across the line that causes the other end to ring.
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  • Payload Loopback (PLB)
  • Loopback of the "payload" portion of the signal, used for testing.
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  • Power over Ethernet (PoE)
  • Power over Ethernet (PoE), as described in the IEEE 802.3af protocol, is a technology that allows power to be carried over existing Ethernet cables, especially Cat-5e cables. The power to run the device and the user data can be carried over the same physical wire. Thus with PoE, the number of wires can be kept to a minimum. In addition, when operating with a UPS (Uninterruptable Power Supply), PoE ensures devices still function during a power failure.

    Two major components of the PoE system are the Power Sourcing Equipment (PSE) and the Powered Device (PD). A PSE is a device that supplies power on the Ethernet cable while a PD accepts power from a PSE. When a PSE device is a switch or similar device, it is called an endspan. When a PSE device is intermediate between non-PoE and PoE devices, then it is called a midspan.
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  • Parts Per Million (PPM)
  • Equivalent to 1 part out of 1,000,000 units. A engineering measure used to identify small quantities. Dimension-less.
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  • Point to Point Protocol (PPP)
  • A data link protocol that is used to establish a direct connection between two networking nodes. Works over synchronous and asynchronous circuits. It has superseded SLIP (serial line internet protocol), an earlier protocol. It works with many other higher level protocols such as IP and AppleTalk.
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  • Pseudo Random Binary Sequence (PRBS)
  • A sequence of N bits that appears to be random but is the result of a fixed deterministic process. N can be chosen to be a sufficiently large number.
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  • Public Switched Telephone Network (PSTN)
  • Also called POTS or plain old telephone system, it refers to the variety of telephone services and systems throughout the world. It is a circuit switched, not a packet switched, network. Traditionally mechanical/analog, the system is now entirely digital except for devices at the customer's premises.
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  • Quad E&M Plug-in Card
  • A voice card that allows four E&M interfaces to be multiplexed to four 64 kbps DS0 (digital signal 0) signals. There are two usage modes for this card, either 1) phone to phone or phone to switch 2) switch to switch.
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  • QFXS Plug-in Card
  • A voice card that provides four foreign exchange service connections. When CAS (channel associated signaling) is off, it can be used to transmit data. This card goes at the telephone end.
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  • QFXO Plug-in Card
  • A voice card that provides connections for the PBX (private branch exchange) end. When CAS (channel associated signaling) is off, it can be used to transmit data. This card goes at the PBX end.
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  • Quality of Service (QoS)
  • A set of performance measures for a communications network that ensures transmission quality and service availability for different types of network traffic.
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  • Quasi-Random Signal Sequence (QRSS)
  • A test pattern used in BERT (bit error rate testing) to simulate voice signals. Containing many different test patterns, it is the standard test to measure jitter.
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  • Remote Alarm Indication (RAI)
  • Also called a yellow alarm. This happens when the received stream of bits is in a data/framing pattern that indicates the far end is in “red alarm.” Red alarm means a corruption or loss of signal that the equipment is unable to recover from.
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  • Random Access Memory (RAM)
  • Volatile memory in a computer. It has fast access time but it does not preserve its value if the unit is restarted or turned off.
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  • Ringer Equivalence Number (REN)
  • A number that describes the electrical load that a telephone ringer puts on the electrical line. This is important for traditional telephone lines that are powered entirely by the telephone network and not the electrical power grid.
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  • Routing Information Protocol Version 1 (RIP1)
  • A routing protocol using the arrays of distance to other nodes in the network with hop count. To prevent routing loops, RIP has a limit number of hops in a path from the source to a destination, and the maximum number is 15.

    RIPv1 adopts classful routing. The subnet information is not shown in periodic routing updates and lacks Variable Length Subnet Masks (VLSM). In other words, all subnets in a network class must have the same size. In addition, there is no authentication mechanism, causing RIP1 easy to be attacked.
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  • Routing Information Protocol Version 2 (RIP2)
  • The Routing Information Protocol (RIP) is a routing protocol using the arrays of distance to other nodes in the network with hop count. To prevent routing loops, RIP has a limit number of hops in a path from the source to a destination, and the maximum number is 15.

    RIPv2 evolves with the ability to carry subnet information, thus supporting Classless Inter-Domain Routing (CIDR). Unlike RIPv1 using broadcast, RIPv2 uses multicast. This can avoid unnecessary load on hosts that do not participate in routing. Yet unicast is still allowed for special applications. It supports authentication.
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  • Remote Loopback (RLB)
  • Loopback activated at the remote location of a circuit.
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  • Remote Line Loopback (RLLB)
  • Remote loopback of the entire line.
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  • Remote Monitoring (RMON)
  • A type of MIB (management information base) used to monitor and profile LANs. RMON is typically used for flow-based and traffic management while SNMP is used for device-based management.
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  • Radio Network Controller (RNC)
  • Controls Node Bs in a radio network communications system. Typically performs encryption and resource management.
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  • Remote Payload Loopback (RPLB)
  • Remote loopback of the payload portion of the line.
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  • Rapid Spanning Tree Protocol (RSTP)
  • An improvement upon the original STP algorithm. It provides faster convergence after a topology change. Defined by IEEE 802.1w.
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  • Real Time Clock (RTC)
  • A piece of hardware inside a computer or any other electronic device that keeps track of the time.
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  • Request to Send (RTS)
  • A flow control hand-shaking method used in RS-232 or wireless systems. The sending device sends out an RTS frame or signal, and the receiving device send back a CTS or Clear To Send frame.
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  • Supervisory Auditory Tone (SAT)
  • A high pitched, inaudible tone used between mobile phones and the tower to setup calls or navigate the geolocation of cell phones.
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  • Station Class Mark (SCM)
  • A 4 or 8 bit number transmitted by a mobile phone to the tower which contains information about the type of transmission you are sending.
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  • Serial Communications Port (SCP)
  • A form of communication where bits are transferred one at a time over a channel. As compared to parallel transmission, where bits are sent at the same time. The term also typically refers to RS-232 type hardware connectors as opposed to newer USB, Firewire, or Ethernet interfaces.
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  • Synchronous Digital Hierarchy (SDH)
  • International standard that defines a set of rate and format standards used to transmit optical signals over fiber. Almost exactly the same as SONET in the United States. Compare with PDH, plesiochronus digital hierarchy.
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  • Sealing Current
  • A low level current, typically 1 to 20 milliamps, that burns off any oxidation film that may have built up on the switch contacts. This prevents line noise or transmission irregularities that may be caused by the oxidation.
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  • Severely Errored Second (SES)
  • Similar to an Errored Second, except that it contains much more path code violations or alarm indication signals.
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  • Severely Errored Second Ratio (SESR)
  • The ratio of severely errored seconds (SES) to the total number of seconds during any given measurement interval.
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  • Server GPRS Support Node (SGSN)
  • Works with the Gateway GRPS Support Node. The SGSN delivers packets to cell phones within its given geographical access area.
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  • Subscriber Identity Module (SIM)
  • The component inside a mobile phone or mobile device that contains all the subscriber information. It is commonly called a SIM card because it is a small, transferable card.
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  • Simplex
  • Communication in only direction only. Examples include a pager and mouse-to-CPU connection.
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  • Simple Network Management Protocol (SNMP)
  • A protocol used in TCP/IP systems to manage devices inside the network. It is often used to collect performance statistics and monitor for alarm conditions. It can also be used to control the device and set configurations.
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  • Signal to Noise Ratio (SNR)
  • Ratio of signal power to noise power, it is a measure of transmission quality. Often expressed in decibels (dB).
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  • Synchronous Optical Network (SONET)
  • A set of protocols and methods used to multiplex signals over optical fibers. SONET is used in the United States and Canada, and is practically the same as SDH used elsewhere around the world.
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  • Strict Priority (SP)
  • Method of forwarding packets from a router. Packets with a higher priority are always sent out first, regardless of how many there are. If there are a lot of high priority packets, it is possible that lower priority packets will be excessively delayed or dropped. Compare to Weighted Round Robin.
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  • Signaling Tone (ST)
  • In telephone communications, a periodic tone that is sent in-band (along with the data) to indicate a condition. Common signaling tones include a dial tone, ringing tone, and a busy tone.
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  • Synchronous Transport Module, level 1 (STM-1)
  • A type of SDH format that specifies a frame structure for a SDH cell. It has a bit rate of 155.52 Mbps.
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  • Transmission Control Protocol (TCP)
  • Transport layer protocol used for reliable full-duplex transmission across the web. It is commonly used together with IP and referred to as the TCP/IP suite or TCP/IP stack of protocols.
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  • Time Division Multiplexing (TDM)
  • Type of digital transmission method where multiple signals appear to be using the same channel simultaneously but are actually taking turns using pre-assigned time slots. The channel often contains synchronization and error-correction slots as well.
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  • Time Division Multiple Access (TDMA)
  • Similar to TDM, multiple signals occupy the same channel by using pre-assigned time slots. TDMA is used in wireless communications and refer to the possibility of having multiple senders (such as multiple radio devices) over and one receiver, as opposed to one sender and one receiver in a wired TDM scheme.
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  • Trivial File Transfer Protocol (TFTP)
  • Extremely simple file transfer protocol. Provides no authenticity or security. Is commonly used on private networks to transmit updates and configuration files.
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  • Trace Identifier Mismatch (TIM)
  • A communication alarm in STM where the trace identifier of this network element does not match the trace identifier of the connected SDH element.
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  • Terms of Service (ToS)
  • Rules one must follow when using a service. Generally refers to behavioral rules as compared to distribution and back up rules in software licensing agreements (EULA).
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  • Time Slot (TS)
  • A measure of bandwidth. 1 time slot = 1 TS = 1 kilobit per second = 1 kbps
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  • Time Slot Interchange (TSI)
  • A device in a switching system that allows any incoming byte on a tributary (input) to be mapped to any other byte on the output. Devices that do not have TSI are said to be "hard wired."
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  • Terminal Timing Mode (TTM)
  • The condition when the unit uses its own clock, as compared to external timing mode where an external clock source is used.
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  • Tributary Unit (TU)
  • In SONET, a virtual tributary (VT) along with a pointer that identifies the location of the VT used for switching and cross-connecting.
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  • Unavailable Second (UAS)
  • A second in which the E1/T1 link is unavailable, as defined by a second after which 10 contiguous SES (severely errored seconds) have occurred. The DS1 interface only becomes available after 10 contiguous seconds without any SESs.
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  • User Datagram Protocol (UDP)
  • A protocol used for computers to send messages. With UDP, In IP network, there is no need to set up special channels before data communication.
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  • Underwriters Laboratories (UL)
  • Independent product safety laboratory near Chicago, Illinois in the United States. Issues product certifications that assure safety.
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  • Virtual Connection (VC)
  • Emulates a physically circuit switched network connection over a packet switched network. Presents data as a "virtual circuit" so higher protocols do not have to deal with the overhead of handling frames.
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  • Virtual Local Area Network (VLAN)
  • A group of devices on one or more LANs that are configured through software to act as if they were attached together physically. Because it is a logical, software association rather than through physical hardware, VLAN membership is easier to manage.
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  • Virtual Path Identifier (VPI)
  • Eight bit field in the header of an ATM cell. Together with the VCI (virtual channel identifier), it identifies the next destination of a cell as it passes through an ATM switch.
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  • Virtual Private Network (VPN)
  • Allows users to access a private, secured network over public TCP/IP infrastructure. Useful for traveling businessmen or salespeople to access an enterprise's intranet (internal network). Encrypts data at the IP level.
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  • Video Terminal (VT-100)
  • VT-100 is a type of terminal first built by DEC (Digital Electronics Corporation) in the 1970s. It's style and it's attributes were so popular that it became a de facto standard for terminal emulators. New monitors and computers since the 2000s have made the concept of a traditional video terminal obsolete. However, a new computer can run VT-100 emulator software to interface with legacy equipment. Many Loop products can connect to a computer's DB9 port. Then the user can open a VT-100 emulator software to access the device.
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  • Voice Quality Enhancement (VQE)
  • Noise reduction, echo cancellation, and other techniques used to improve the quality of a telephone call.
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  • Wide Area Network (WAN)
  • A telecommunications network that covers a broad geographic area. Compare to a LAN (local area network).
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  • Weighted Round Robin (WRR)
  • A scheduling algorithm in which the highest priority packets take up the largest percentage of time of the router as opposed to always being delivered first. Assures that high priority packets will not crowd out low priority packets. Generally implemented by sampling a packet queue for each priority. Compare to Strict Priority.
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  • Zero Code Suppression (ZCS)
  • A very simplified type of modified AMI (alternate mark inversion) in which the least significant bit every 8 bit byte is transmitted as a 1. Largely replaced by B8ZS (bipolar eight zero substitution).
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