A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

1

• 10BaseT - Ethernet connector which implements the IEEE standard on 24-gauge unshielded twisted pair wiring.

A

• AC - Alternating Current. The common form of electricity from power plant to home/office. Its direction is reversed 60 times per second in the U.S. ; 50 times in Europe.
• AMI - Alternate Mark Inversion. A line encoding scheme for transmitting data bits over T1 transmission systems.
• ANI - Automatic Number Identification. A feature in which a series of digits, either analog or digital, are included in the call, thus identifying the telephone number of the caller.
• ANSI - American National Standards Institute. This organization organizes committees, made up of computer users, manufacturers etc., to develop and publish industry standards.
• APS 1+1 - Automatic Protection Switching One-Plus-One Mode - The T1 or E1 Automatic Protection Switching (APS) feature enables traffic on a failed T1 or E1 facility to be automatically moved to an alternate T1 or E1 facility and restores service automatically to the previously failed working facility when it is made good. Traffic is bridged onto both the working and protection links so that both links are carrying the same traffic. Each end independently determines which link is better based on certain link failure criteria. Therefore, there is no requirement for communication paths between the two termination points in order to complete a switchover. All T1 and E1 link types are supported. A connection is only allowed on the working link.
• APS 1:1 - Automatic Protection Switching One-for-One Mode - The T1 or E1 Automatic Protection Switching (APS) feature enables traffic on a failed T1 or E1 facility to be automatically moved to an alternate T1 or E1 facility and restores service automatically to the previously failed working facility when it is made good. Communications between both ends of the link is done via the 4kbps management channel (facility data link) over the protection link. There are line type limitations because of the FDL implications. A connection is allowed on the working link and protection link. Each end independently determines which link is better based upon certain link failure conditions. A decision to switch traffic to the alternate (protection) link is communicated to the far end device via the management channel, so both sides switch and stay in sync. Traffic on the protection channel will either be preempted or merged, depending upon the time slot availability on the protected/working link.
• ASCII - American Standard Code for Information Interchange. An asynchronous signaling code with character framing. An ASCII character consists of a start bit, seven data bits, a parity bit (even if unused) and a stop bit. In some cases, 1-1/2 or 2 stop bits are used. Thus ASCII is at best 70% efficient with seven data bits out of every ten-bit character. Note that 1-1/2 stop bits can not be used if the data will be carried by modern-day modems. The parity bit is used as an eighth data bit with able characters from 128 to 256. ASCII data can also be transported synchronously (aka clocked async).
• Asynchronous Transmission - Digital signals are transmitted without precise clocking. The signals have different frequencies and phase relationships. Individual characters contained in control bits (start and stop bits) designate the beginning and end of each character.
• ATM - Asynchronous Transfer Mode. A component of ISDN. A switching technology that organizes digital data in 53 byte packets and transmits them using digital signal technology.
• AU - Administrative Unit. A managed entity within the SDH structure, it is the top-most level of the STM1 configuration hierarchy. AU3 (Administrative Unit, Level 3) has the payload pointer for each payload envelope consolidated with the respective payload into one unit. Since there are three payload envelopes in an STM-1 frame, there are also three AU3 administrative units. AU4 (Administrative Unit, Level 4) applies to the entire STM-1 payload in a blanket fashion. Instead of having three Administrative Units in an STM-1 frame like AU3, the AU4 structure is the only administrative unit in an STM-1 Frame.
• AUI - Attachment Unit Interface. A 15-pin connector and cable used to connect a network interface card and an Ethernet network.
• Authentication - The process of attempting to ensure that the person using the computer system and performing tasks such as sending or receiving messages is one and the same as the person in whose name the account is registered. Networks require passwords as a means of authentication; however, passwords do not guarantee that the person using the system is the person to whom the password was given.
• AWG - American Wiring Gauge. A U.S. measurement standard of the diameter of non-ferrous wire, which includes copper and aluminum. The smaller the number, the thicker the wire. In general, the thicker the wire, the greater the current-carrying capacity and the longer the distance it can span.

B

• B8ZS - Binary with 8 Zero Substitution. Line code type, used on T1 and E1 circuits, in which a special code is substituted whenever eight consecutive zeros are sent over the link. Code is then interpreted at the remote end of the connection.
• BER - Bit Error Rate. Ratio of received bits that contain errors.
• BERT - Bit Error Rate Tester. A device that calculates the bit error rate on a communication channel.
• Bipolar Violations - Violations of the electrical characteristic denoting a circuit with both negative and positive polarity.
• Bit Rate - The speed at which bits are transmitted, usually expressed in bits per second (bps). The speed at which a point-to-point transmission line can convey data.
• bps - Bits per second. The speed at which a point-to-point transmission line can convey data.
• Broadband - A communication channel having a bandwidth greater than a voice grade channel and, therefore, capable of higher speed data transmission.
• Broadband Primary Card - This card resides in the N+1 Protection Switch and is used in conjunction with the broadband redundant card to back up a T3, Hybrid DS3, or STS1 Application Module in slots 1-6, 8, 9 or 10.
• Broadband Redundant Card - This card resides in the N+1 Protection Switch and is used in conjunction with the broadband primary cards to back up a T3, Hybrid DS3, or STS1 Application Module; it must reside in slot 7 or 11.

C

• CCITT - Consultative Committee for International Telephony and Telegraphy. A standards organization that devises and proposes recommendations for international communications. Also see ANSI.
• CHAP - Challenge Handshake Authentication Protocol. A type of authentication protocol in which the authentication agent sends the client program a key to be used to encrypt the user name and password. CHAP doesn't only require the client to authenticate itself at startup time, but sends challenges at regular intervals to make sure the client hasn't been replaced by an intruder, for instance by switching phone lines. Also see PAP.
• CLEC - Competitive Local Exchange Carrier. A company that creates and operates communication networks and provides customers with an alternative to the local telephone company.
• Clocking - An oscillator-generated signal that provides a timing reference for a transmission link. A clock provides signals used in a transmission system to control the timing of certain functions. The clock has two functions: (1) to generate periodic signals for synchronization, and (2) to provide a time base.
• CMOS - Complementary Metal Oxide Semiconductor. Technology employing integrated field-effect transistors in a complementary symmetry arrangement, which simulates "Push/Pull" operation because of the placement of opposing polarity devices (p-channel and n-channel FETs).
• CODEC - enCOder/DECoder. Chip used in the voice card to compress or decompress speech or audio signals.
• Controller Card - provides communications between the DNX's System Manager and the N+1 Protection Switch.
• CPE - Customer Premises Equipment. Equipment, such as terminals and modems, supplied by the telephone company, that is installed at customer sites and connected to the telephone company network.
• CRC - Cyclic Redundancy Check. A method of checking for errors in data that has been transmitted on a communications link. The dividend polynomial is initially preset to 0, and the 1s and 0s of the data stream become the coefficients of the dividend polynomial.
• CRV - Call Reference Value. In GR303, the subscriber access ID which is used to determine service and billing status. With path protection set up, up to 2024 CRVs can be provisioned as part of one Interface Group in the DNX.
• CSU - Channel Service Unit. A device used to connect a digital phone line coming in from the phone company to network access equipment located on the customer premises. CSU may also be built into the network interface of the network access equipment.

D

• D4 - Super Frame. A common framing type used on T1 circuits. It consists of twelve frames of 192 bits each, with the 193rd bit providing error checking and other functions. It is superseded by ESF but still widely used.
• DAC - Digital to Analog Converter. A device for converting digital signals into continuous analog signals. The converter usually buffers the input so that the output remains the same until the input changes. A typical converter provides two analog output channels ranging from 0 to +10 volts with eight bits per channel resolution; also provides two logic level outputs for external device control.
• DB Connector - A family of plugs and sockets widely used in communications and computer devices. DB connectors come in 9, 15, 25, 37 and 50-pin sizes. The DB connector defines the physical structure of the connector, not the purpose of each line.
• DC - Direct Current. An electrical current that travels in one direction and used within the computer's electronic circuits.
• DCE - Data Circuit-Terminating Equipment. Device and connections of a communications network that comprise the network end of the user-to-network interface. It provides physical connection to the network, forwards traffic and provides clocking signals used to synchronize data transmission between DTE devices and itself.
• DCS - Digital Cross-Connect System. A network element providing automatic cross-connection of a digital signal or its constituent.
• DDS - Dataphone Digital Service (previously Digital Data Service). A digital network service available from AT&T, the Bell Operating Companies and independent telephone companies. Non-switched synchronous data rates of 2400, 4800, 9600 and 56,000 bps and switched synchronous 56,000 bps are available.
• DHCP - Dynamic Host Configuration Protocol. A protocol that allocates dynamic IP addresses to client stations logging onto a TCP/IP network, so that addresses can be reused when hosts no longer need them. Eliminates having to manually assign permanent IP addresses.
• DNS - Domain Name System. The manner in which the Internet locates and translates domain names into IP addresses.
• DS0 - Digital Signal Level 0. The base for the digital signal X series; transmits digital signals over a single channel at 64 Kbps.
• DS1 - Digital Signal Level 1. Framing specification used in transmitting digital signals at 1.544-Mbps on a T1 facility (United States) or at 2.108-Mbps on an E1 facility (Europe).
• DS3 - Digital Signal Level 3. Framing specification used in transmitting digital signals at 44.736 Mbps on a T3 facility (United States) or at 34.368-Mbps on an E3 facility (Europe).
• DSL - Digital Subscriber Line. Technology that brings high-bandwidth information to homes and small business over copper telephone lines. It can carry both data and voice signals.
• DSU - Data Service Unit. A device used in digital transmission that adapts a physical interface on a DTE device to a transmission facility such as T1 or E1. It is also responsible for functions such as timing.
• DTE - Data Terminal Equipment. A device at the user end of a user-network interface that serves as a data source, destination, or both. It connects to a data network through a DCE device (such as a modem) and typically uses clocking signals generated by the DCE. It includes devices such as computers, protocol translators and multiplexers.
• DTMF - Dual Tone Multi Frequency. The signal a telephone company receives when a telephone's touch keys are pressed. Also known as Touch tone.

E

• E&M - Receive and Transmit. A trunking arrangement used for two-way switch-to-switch or switch-to-network connections. It is used with E1 and T1 interfaces.
• E1 - A digital transmission link with a capacity of 2.048 Mbps, used predominantly in Europe . E1 is channelized into 32 DSOs, each capable of carrying a single voice conversation or data stream.
• EIA - Electronic Industries Association. A membership organization that sets standards for consumer products and electronic components.
• EOC - Embedded Operations Channel (GR303). The EOC occupies a single DS0 of bandwidth in timeslot 12, and is used to control inbound and outbound GR303 call operations.
• ESF - Extended Superframe. A framing format for T1 applications that consists of twenty four frames of 192 bits each with the 193rd bit providing timing and other functions. It includes provisions for continuous monitoring by both the user and the telephone company central office. ESF provides a 4 Kbps link control channel (transparent to user data) which allows the telephone company to monitor the local loop, transmit and receive test messages and retrieve performance data, all without interrupting normal operations.
• Ethernet - The most widely-used standard for local area networks (LANs).

F

• FAD - Facility Access Digroup. The DS1 path(s) between the Digital Test Access Unit and the test system.
• FCC - Federal Communications Commission. United States government agency that supervises, licenses and controls electronic and electromagnetic transmission standards.
• FPGA - Field Programmable Gate Array. A programmable logic chip in a high density of gates. There are a variety of FPGA architectures including programmable logic blocks, programmable interconnects and switches between the blocks.
• Frame - At the data link layer in a point-to-point transmission line, the technique used to demarcate the data so that it can be received in an orderly and meaningful way.
• Frame Relay - At the data link layer in a wide area network (WAN), a protocol for transferring packets at speeds up to 1.544 Mbps, depending on the physical medium being used. Frame Relay is designed for noise-free digital lines, and therefore omits the error correction facilities. The result is increased bandwidth.
• FTP - File Transfer Protocol. Application protocol used for transferring files between network nodes.
• Full Duplex - The process of operating a circuit so that each end can transmit and receive simultaneously.
• FXO - Foreign Exchange Office. An interface that connects to the Public Switched Telephone Network's (PSTN) central office and is the interface offered on a standard telephone. Example: RJ-11 connector that allows analog connection to the central office.
• FXS - Foreign Exchange Subscriber. An interface that connects directly to a standard telephone and supplies ring, voltage, and dial tone. Example: RJ-11 connector allows connections to basic telephone equipment.

G

• GR303 - GR303 refers to a Telcordia-defined interface between the Class 5 local digital switch (LDS) and an Integrated Digital Terminal (IDT). It is used to groom and concentrate multiple local loop telephone subscriber lines into fewer DS1 lines; the concentration ratio is determined by the number of subscriber lines configured versus the number of available DS1 timeslots.

H

• Half Duplex - A channel or device which can communicate in both directions, but not simultaneously.
• HDLC - High-Level Data Link Control. An ISO communications protocol used in X.25 packet switching networks. It provides error correction at the data link layer.
• HDSL - High-bit rate Digital Subscriber Line. The earliest variation of DSL. It is used for wideband digital transmission within a business and between the telephone company and a customer. HDSL is symmetrical meaning an equal amount of bandwidth is available in both directions.

I

• IC - Integrated Circuit. An integrated circuit (IC), sometimes called a chip or microchip, is a semiconductor wafer on which thousands or millions of tiny resistors, capacitors, and transistors are fabricated. An IC can function as an amplifier, oscillator, timer, counter, computer memory, or microprocessor. A particular IC is categorized as either linear (analog) or digital, depending on its intended application.
• IDT - Integrated Digital Terminal. An intelligent interface provided by the Local Digital Switch (LDS) that is typically used in a local telephone end office.
• IG - Interface Group. A collection of subscriber lines configured as one entity for use in a GR303 environment. Control of the Interface Group is supported by EOC and TMC links.
• Interface Card (Module) - A computer circuit board, card or module that is installed in a computer so that it can be connected to a network.
• IP - Internet Protocol. The method by which data is sent from one computer to another on the Internet. It is a connectionless protocol, meaning there is no established connection between the two computers. Data is sent as independent packets, also known as data units or data grams, which are contained in the IP address, a 32-bit number that identifies each sender or receiver of information. When the packets are received, they are put into the correct order by the Transmission Control Protocol (TCP).
• IPX - Internetwork Packet Exchange. A NetWare communications protocol used to route messages from one node to another. IPX packets include network addresses and can be routed from one network to another.
• ISDN - Integrated Service Digital Network. A system that provides simultaneous voice and high-speed data transmission through a single channel to the user's premises. ISDN is an international standard for end-to-end digital transmission of voice, data and signaling.
• ITU-T - International Telecommunication Union - Telecom. International body that develops worldwide standards for telecommunications technologies.
• IXC - Inter-exchange Carrier. A common carrier providing long distance connectivity between local telephone areas. Includes AT&T, MCI and Sprint.

K

• Kbps - Kilobits per second or one thousand bits per second.

L

• LAN - Local Area Network. A computer network that links personal computers and workstations within a limited geographic area, such as a building or several contiguous buildings. Linked by cables such as coaxial cables or twisted pair, the computers connected to
• LDS - Local Digital Switch. The type of telecommunications switching device used in a local telephone end office. All local digital switches may use the same type of hardware, however, the services they can provide are differentiated by the software that runs i
• LED - Light Emitting Diode. A display technology that uses a semiconductor diode that emits light when charged.
• Loopback - A method of checking the accuracy of data transmission in which the transmitted data stream is returned, or looped back, to its source for comparison with the original data. Loopbacks can be performed on data in an analog or digital state.

M

• Mbps - Megabits per second or one million bits per second.
• MIB - Management Information Base. A directory listing information that is used and maintained by a network's management protocol, such as SNMP.

N

• N+1 Device Redundancy (NDR) - A spare or redundant device is provided to replace a failed primary device in a group.
• N+1 Device Redundancy Group (NDRG) - A collection of configured primary devices and a redundant device that will be used for redundancy.
• Narrowband - Any analog signal or analog representation of a digital signal whose essential spectral content is limited to that which can be contained within a voice channel of nominal 4-kHz bandwidth.
• Narrowband Primary Card - This card resides in the N+1 Protection Switch and is used in conjunction with the narrowband redundant card to back up an Octal T1/E1 Application Module in slots 2-11.
• Narrowband Redundant Card - This card resides in the N+1 Protection Switch and is used in conjunction with the narrowband primary cards to back up an Octal T1/E1 Application Module; it must reside in slot 1.
• NAT - Network Address Translation. A method for translating internal IP addresses or network addresses into a single globally unique IP address. It permits a nearly unlimited number of users of one class C Network address because global addresses are required only when a user is connected to the Internet. It also serves as a fire wall by keeping individual IP addresses hid den from the outside world. NAT is configured by defining address pools and specifying whether a port is "Inside" or "Outside". Also see IP.
• NC - Normally Closed. Relay switch contacts that remain closed when inactive.
• NEBS - Network Equipment Building Systems. Adhering to standards from Bellcore for equipment used in Telco central offices (COs). It provides stringent specifications for durability, grounding, cables and hardware interfaces.
• NO - Normally Open. Relay switch contacts that remain open when inactive.

O

• OSPF - Open Shortest Path First. OSPF is a routing protocol that determines the best path for routing IP traffic over a TCP/IP network. It uses less router-to-router update traffic than the RIP protocol that it has been designed to replace.

P

• Packet - Also known as a data unit or a datagram. A unit of data that has been broken down into a small enough size so that the Internet Protocol can handle it and the Internet transport it.
• PAP - Password Authentication Protocol. PAP is the most basic form of authentication for logging into a network. A user's name and password are transmitted over a network and compared to a table of name-password pairs. Typically, the passwords stored in the table are encrypted. Also see CHAP.
• Parity - A character-level error-control mechanism used with asynchronous signaling codes. A parity bit is set to either a "one" (mark) or a "zero" (space) to ensure that the total quantity of "ones" within a character are either odd (odd parity) or even (even parity). Start and stop bits are excluded from the parity calculation. Character-level error-control has not been successful, and today, parity is rarely used. Asynchronous hardware, however, requires that the parity bit be present (usually forced to "one") even if unused.
• PCM - Pulse Coded Modulation. Transmission of analog information in digital form through sampling and encoding the samples with a fixed number of bits.
• PCS - Personal Communications Service. A network that provides personal, terminal and service mobility. Includes broadband and narrowband in the United States.
• PLAR - Private Line Auto Ring. A leased voice circuit that connects two single endpoints together. When the telephone handset is removed from the hook, the remote telephone automatically rings.
• PPS - Path Protection Switch. The PPS is used to provide backup switching (redundancy) for the GR303 control links (EOC and TMC).
• Primary Device - A device in an NDRG that would normally carry traffic.
• Primary Slots (DNX) - Cards plugged into these slots are considered active and online under normal operation.
• Primary Slots (N+1 Protection Switch) - Holds Interface Cards for the cards plugged into the DNX's primary slots.
• Protected Device - This is a primary device that will be replaced by a redundant device should it fail within its NDRG.
• Protocol - A set of rules controlling the orderly exchange of information between stations in data communications networks or systems.
• PSTN - Public Switched Telephone Network. General term referring to the world's collection of interconnected voice-oriented public telephone networks, both commercial and government-owned. Sometimes called POTS (plain old telephone service).

R

• RDT - Remote Digital Terminal. An intelligent network element that provides the interface between customer lines and DS1 facilities. The RDT is generally a concentration device that is deployed closer to the actual subscriber plant interfaces.
• Redundant Device - One device in an NDRG that has been configured to replace or substitute for a failed primary device in the NDRG.
• Restore - An action that occurs when traffic is returned to the primary device that was being protected in the NDRG by a redundant device.
• RFC - Request for Comments. The document series maintained by the Internet community that records the protocols within the Internet and gives other information.
• RIP - Routing Information Protocol. A simple routing protocol that is part of the TCP/IP protocol suite. It determines a route based on the smallest hop count between source and destination. RIP is a distance vector protocol that routinely broadcasts routing information to its neighboring routers and is known to waste bandwidth.
• Router - An electronic device that connects a local area network (LAN) to a wide area network (WAN) and handles the task of routing messages between the two networks.
• RS232 - RS232 is an electrical signaling specification published by the Electronic Industries Association (EIA). Although not identified in the specification, the 25-pin (DB25) connector, with specific pin assignments, is commonly accepted as "the RS232 connector." The DNX supports RS232 on the Quad High Speed Module's DB25 connector via industry-standard pin assignments.

S

• SDH - Synchronous Digital Hierarchy. A standard technology for synchronous data transmission using optical media as the physical transport for high speed long-haul networks. It is the international equivalent of Synchronous Optical Network (SONET). SDH uses the following Synchronous Transport Modules (STM) and rates: STM-1 (155 megabits per second), STM-4 (622 Mbps), STM-16 (2.5 gigabits per second), and STM-64 (10 Gbps).
• SDSL - Single-line Digital Subscriber Line. One of four DSL technologies. SDSL delivers 1.544 Mbps both downstream and upstream over a single copper twisted pair. The use of a single twisted pair limits the operating range of SDSL to 10,000 feet (3048.8 meters).
• Service - The provision of telecommunications to customers by a common carrier, administration, or private operating agency, using voice, data, and/or video technologies.
• Signaling - Communications between switches to set up and terminate calls.
• SNMP - Simple Network Management Protocol - Network management protocol used in TCP/IP networks. SNMP monitors and controls network devices, and manages configurations, statistics collection, performance and security.
• SONET - Synchronous Optical NETwork. A high speed (up to 2.5 Gbps), fiber-optic transmission system for digital traffic. SONET uses time division multiplexing (TDM) to send multiple data streams simultaneously. STS-1 is the basic building block of SONET.
• Standby Slots (DNX) - Cards plugged into these slots are considered inactive and off-line under normal operation. They become active and go online when a card plugged into the primary slot becomes non-operational.
• Standby Slots (N+1 Protection Switch) - Holds Interface Cards for the cards plugged into the DNX's standby slots.
• STS-1 - Synchronous Transport Signal level 1. Basic building block signal of SONET, operating at 51.84 Mbps. Faster SONET rates are defined as STSn, where n is a multiple of 51.84 Mbps.
• Switchover - an action that occurs when a redundant device replaces a primary device that failed.
• Synchronous Transmission - Communications in which the timing is achieved by sharing a single clock. Each end of the transmission synchronizes itself with the use of the clocks and information sent along with the transmitted data.
• System Manager Controller Card - All of the application modules in the DNX chassis are under the control of the DNX on-line System Manager Card (also referred to as SMC card).

T

• T1 - A high-bandwidth telephone trunk line with a capacity of 1.544 Mbps, used in North America . T1 is channelized into 24 DSOs, each capable of carrying a single voice conversation or data stream.
• T3 - The digital signal carried on a North American high-speed facility (DS3) operating an approximately 45 Mbps.
• TAD - Test Access Digroup. A path that connects the Digital Test Access Unit to the test system. The TAD does not carry service traffic; it only carries testing traffic.
• TAP - Test Access Path. A test access link between the Remote Test Unit and the Network Element.
• TCP - Transmission Control Protocol. The method used with the Internet Protocol (IP) to send data in the form of packets between computers over the Internet. TCP is responsible for dividing a message into packets that the IP can use, and for reassembling packets into complete message.
• TDM - Time Division Multiplexing. A technology that transmits multiple signals simultaneously over a single transmission path. Each lower-speed signal is time sliced into one high-speed transmission.
• Telnet - A user command and an underlying TCP/IP protocol for accessing remote computers.
• TFTP - Trivial File Transfer Protocol. Network application that is simpler than the File Transfer Protocol (FTP) but less capable. Uses the User Datagram Protocol (UDP).
• TMC - Timeslot Management Channel (GR303). The TMC occupies a single DS0 of bandwidth in timeslot 24, and is used to provide timeslot management for inbound and outbound GR303 call operations.
• Transmission - The signaling of data over telecommunications channels.
• TU - Tributary Unit. The basic unit of SDH payload together with its management overheads and synchronization data. The tributary unit consists of a Virtual Container plus a Tributary Unit Pointer. It provides a unit of bandwidth necessary to convey a T1 or E1 framed carrier.
• TUG - Tributary Unit Group. A multiplexing scheme of assembling individual Tributary Units into a higher unit of bandwidth, it is made up of a group of identical TUs.

U

• UDP - User Datagram Protocol. A connection less, communication transport method that offers a limited amount of service when messages are exchanged over the Internet Protocol. It is an alternative to TCP. Unlike TCP, UDP does not acknowledge or guarantee delivery, nor does it provide sequencing of packets.

V

• V.35 - V.35 is an electrical signaling specification published by CCITT. Although not identified in the specification, the M-series, 34-pin (Winchestertype) connector, with specific pin assignments, is commonly accepted as "the V.35 connector." V.35 signaling is also legitimately supported on DB25 connectors but the pin assignments have not been standardized within the industry. The DNX Test Access Module supports V.35 per industry standards.
• V.54 - V.54 is an ITU standard for various loopback tests that can be incorporated into modems for testing the telephone circuit and isolating transmission problems. Operating modes include local and remote digital loopback and remote analog loopback.
• VC - Virtual Container. A basic unit of SDH payload together with its management overheads.
• VT - Virtual Tributary. A signal designed for transport and switching of payloads smaller than the STS-1 rate. All services below DS-3 rate are transported in the VT structure. T1 payloads are equivalent to a VT-1.5, while E1 payloads are equivalent to a VT-2.
• VT-100 - A non-intelligent terminal or terminal emulation mode used for asynchronous communications.

W

• WAN - Wide Area Network. A communications network that is capable of spanning a geographic area larger than a metropolitan area.

X

• X.21 - X.21 is an electrical standard published by the CCITT that includes a 15-pin (DB15) mechanical connector identification with specific pin assignments.