U
U Interface
n. The electrical interface between an ISDN telephone line and a network terminator (NT1) device.
U Interface, N.
The electrical interface between an ISDN telephone line and a network terminator (NT1) device.
U-Law
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for sampling data by means of Pulse Coded Modulation (PCM). U-Law is most commonly used in North America and Japan.
U-interface
adj. Specifies an ISDN communications device that connects directly to an ISDN telephone line. A U-interface device contains its own network terminator (NT1).
U-interface, Adj.
An ISDN communications device that connects directly to an ISDN telephone line. A U-interface device contains its own network terminator (NT1).
UDP
User Datagram Protocol
UDP Port
A 16-bit number that allows multiple processes to use User Datagram Protocol (UDP) services on the same host. A UDP address is the combination of a 32-bit IP address and a 16-bit port number. Examples of well-known UDP ports are 7 (for Echo packets), 161 (for SNMP packets), and 514 (for Syslog packets).
UDP Queue
A queue containing unprocessed User Datagram Protocol (UDP) requests.
UNI
User-Network Interface. 1) An interface point between Asynchronous Transfer Mode (ATM) end users and a private ATM switch, or between a private ATM switch and the public carrier ATM network; defined by physical and protocol specifications in ATM Forum UNI documents. 2) A similar connection in a Frame Relay network . 3) The interoperability standard adopted by the ATM Forum to define connections between users or end stations and a local switch.
UNIX
A multiuser, multitasking operating system originally developed by AT&T Bell Labs that runs on a wide variety of computer systems.
UNIX To UNIX Copy Program (UUCP)
An application program developed in the mid 1970’s for Version 7 UNIX that allows one UNIX time sharing system to copy files to or from another UNIX time sharing system over a single link.
URL
Uniform resource locator. The address of a file (resource) accessible on the Internet. The type of resource depends on the Internet application protocol. For the World Wide Web's protocol, the Hypertext Transfer Protocol (HTTP), the resource can be an HTML page, a program such as a Java applet, or any other file supported by HTTP. The URL contains the name of the protocol required to access the resource, a domain name that identifies a specific computer on the Internet, and, if necessary, a path to the resource on the computer. The URL for Lucent Technologies, for example, is http://www.lucent.com.
UTP
Unshielded Twisted Pair
UTP cable
Unshielded Twisted Pair cable. Two paired wires with wire twisted two or more times per inch to help cancel out noise.
UUCP
UNIX-to-UNIX Copy Program. Interactive communication system for connecting two UNIX computers to send and receive data.
UUI
User-to-user identification. A field within ISDN protocol which can provide end-to-end information exchange (telephone number, credit card number, login ID, etc.)
Unicast Network
A network in which a router sends packets to one user at a time.
Unified Messaging
A platform that lets users send, receive and manage all email, voice and fax messages from any telephone, PC or information device. By linking to a consumer's e-mail account, for example, one component of unified messaging -- Lucent's Message Notifier solution -- immediately and proactively alerts users via their voice/fax mailbox that they have received e-mail.
Universal Asynchronous Receiver/Transmitter (UART )
A UART is a chip that provides a RS-232C data terminal equipment (DTE) interface to a device, enabling the unit to communicate with its attached serial devices.
Universal Time
The Greenwich Mean Time.
Unshielded Twisted Pair Cable
UTP cable consists of two wires twisted two or more times per inch in order to help cancel out noise. The entire cable has no covering. UTP cable is typically used in telephone lines for voice service, ARCnet networks, 10Base-T Ethernet networks, and particular sections of token ring networks.
Unspecified Bit Rate (UBR)
UBR is an asynchronous transfer mode (ATM) service class that handles bursty LAN traffic, as well as data that is tolerant of delays and cell loss. UBR is a best-effort service that does not specify bit-rate or traffic values, and offers no Quality of Service (QoS) guarantees.
Upstream Path
The path a call takes from the end user’s home to the carrier’s central office (CO).
User Datagram Protocol (UDP)
UDP is a transport-layer protocol that provides connectionless service without packet acknowledgment.
User-Network Interface (UNI)
The point at which users connect to the network.
n. The electrical interface between an ISDN telephone line and a network terminator (NT1) device.
U Interface, N.
The electrical interface between an ISDN telephone line and a network terminator (NT1) device.
U-Law
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for sampling data by means of Pulse Coded Modulation (PCM). U-Law is most commonly used in North America and Japan.
U-interface
adj. Specifies an ISDN communications device that connects directly to an ISDN telephone line. A U-interface device contains its own network terminator (NT1).
U-interface, Adj.
An ISDN communications device that connects directly to an ISDN telephone line. A U-interface device contains its own network terminator (NT1).
UDP
User Datagram Protocol
UDP Port
A 16-bit number that allows multiple processes to use User Datagram Protocol (UDP) services on the same host. A UDP address is the combination of a 32-bit IP address and a 16-bit port number. Examples of well-known UDP ports are 7 (for Echo packets), 161 (for SNMP packets), and 514 (for Syslog packets).
UDP Queue
A queue containing unprocessed User Datagram Protocol (UDP) requests.
UNI
User-Network Interface. 1) An interface point between Asynchronous Transfer Mode (ATM) end users and a private ATM switch, or between a private ATM switch and the public carrier ATM network; defined by physical and protocol specifications in ATM Forum UNI documents. 2) A similar connection in a Frame Relay network . 3) The interoperability standard adopted by the ATM Forum to define connections between users or end stations and a local switch.
UNIX
A multiuser, multitasking operating system originally developed by AT&T Bell Labs that runs on a wide variety of computer systems.
UNIX To UNIX Copy Program (UUCP)
An application program developed in the mid 1970’s for Version 7 UNIX that allows one UNIX time sharing system to copy files to or from another UNIX time sharing system over a single link.
URL
Uniform resource locator. The address of a file (resource) accessible on the Internet. The type of resource depends on the Internet application protocol. For the World Wide Web's protocol, the Hypertext Transfer Protocol (HTTP), the resource can be an HTML page, a program such as a Java applet, or any other file supported by HTTP. The URL contains the name of the protocol required to access the resource, a domain name that identifies a specific computer on the Internet, and, if necessary, a path to the resource on the computer. The URL for Lucent Technologies, for example, is http://www.lucent.com.
UTP
Unshielded Twisted Pair
UTP cable
Unshielded Twisted Pair cable. Two paired wires with wire twisted two or more times per inch to help cancel out noise.
UUCP
UNIX-to-UNIX Copy Program. Interactive communication system for connecting two UNIX computers to send and receive data.
UUI
User-to-user identification. A field within ISDN protocol which can provide end-to-end information exchange (telephone number, credit card number, login ID, etc.)
Unicast Network
A network in which a router sends packets to one user at a time.
Unified Messaging
A platform that lets users send, receive and manage all email, voice and fax messages from any telephone, PC or information device. By linking to a consumer's e-mail account, for example, one component of unified messaging -- Lucent's Message Notifier solution -- immediately and proactively alerts users via their voice/fax mailbox that they have received e-mail.
Universal Asynchronous Receiver/Transmitter (UART )
A UART is a chip that provides a RS-232C data terminal equipment (DTE) interface to a device, enabling the unit to communicate with its attached serial devices.
Universal Time
The Greenwich Mean Time.
Unshielded Twisted Pair Cable
UTP cable consists of two wires twisted two or more times per inch in order to help cancel out noise. The entire cable has no covering. UTP cable is typically used in telephone lines for voice service, ARCnet networks, 10Base-T Ethernet networks, and particular sections of token ring networks.
Unspecified Bit Rate (UBR)
UBR is an asynchronous transfer mode (ATM) service class that handles bursty LAN traffic, as well as data that is tolerant of delays and cell loss. UBR is a best-effort service that does not specify bit-rate or traffic values, and offers no Quality of Service (QoS) guarantees.
Upstream Path
The path a call takes from the end user’s home to the carrier’s central office (CO).
User Datagram Protocol (UDP)
UDP is a transport-layer protocol that provides connectionless service without packet acknowledgment.
User-Network Interface (UNI)
The point at which users connect to the network.
V
V.110
A rate-adaption standard, based on fixed frames, that subdivides the ISDN channel so that it can carry one lower-speed data channel.
V.110 Terminal Adapter
A V.110 TA is a device that changes the format of asynchronous data to match the specifications of the V.110 standard for data transmission over an ISDN line.
V.120
A standard for encapsulating asynchronous data communication into synchronous ISDN data. Using standard, asynchronous-only COM ports and a V.120 Terminal Adapter (TA), two computers can communicate over an ISDN connection.
V.120 Terminal Adapter
A V.120 TA is an asynchronous device that changes the format of asynchronous data to match the specifications of the V.120 standard for data transmission over an ISDN line. A V.120 TA is also known as an ISDN modem.
V.21
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for 300-bps full-duplex modems.
V.22
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard that supports a data rate of up to 1200 bps at 600 baud.
V.22bis
An extension of the V.22 standard, providing a data rate of up to 2400 bps at 600 baud.
V.23
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for 600-bps and 1200-bps full-duplex modems.
V.24
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard that specifies a physical-layer interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE). V.24 is nearly identical to RS-232.
V.25
An automatic calling and answering command set for use between DTE and DCE that includes both in-band and out-of-band signaling.
V.25 bis
An automatic calling and answering command set for use between DTE and DCE which includes both in-band and out-of-band signaling.
V.25bis
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for automatic calling and answering equipment on (PSTN).
V.32
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for full-duplex modem transmission of data across phone lines at rates of up to 9600 bps, with a fallback rate of 4800 bps. A V.32 modem automatically adjusts its transmission speed based on the quality of the line.
V.32bis
An extension of the V.32 standard, providing a data rate of up to 14,400 bps or fallback to 12,000, 9600, 7200, and 4800 bps.
V.34
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for full-duplex modem transmission of data across phone lines at rates of up to 28,800 bps. A V.34 modem automatically adjusts its transmission speed based on the quality of the line.
V.34bis
An extension of the V.34 standard, providing a data rate of up to 33,600 bps. Compare with V.34.
V.35
Commonly used to describe electrical characteristics and connector characteristics for a high-speed synchronous interface between DTE and DCE. Originally V.35 described a 48 Kbps group band modem interface with electrical characteristics defined in an appendix. Although V.35 is considered obsolete and no longer published by the CCITT, its legacy lives on in the data communications world in the form of the electrical characteristics originally described in the appendix.
V.42
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) error-detection standard for high-speed modems over digital telephone lines. The V.42 standard makes use of the link access procedure, modem (LAPM).
V.42bis
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) data-compression standard for use with V.42 technology. The V.42bis data-compression standard provides a maximum of a four-to-one data-compression ratio. Because compression algorithms are software based, overhead can cause problems in real-time environments. Most of the time, V.42bis can sense when compression is unnecessary, and so can avoid slowing the transfer of precompressed files.
V.90
A standard for data transmission over a modem at 56 kilobits per second. The V.90 standard resolves the difference between two modem technologies - x2 and K56flex. Both technologies now conform to V.90, and most previously manufactured 56Kbps modems can support V.90 via a software upgrade. See also K56flex.
VDC
Volts DC
VLAN
Virtual LAN. A group of devices on one or more LANs that communicate as if they were connected to the same wire even though they are physically located on different local area network segments. Because VLANs are configured through software rather than hardware, they are extremely flexible.
VPN
Virtual private network. A restricted network that uses public wires to connect nodes. A VPN provides a way to encapsulate, or "tunnel," private data cheaply, reliably, and securely through a public network, usually the Internet.
VSAT
Very small aperture terminal. Relatively small satellite antenna used for satellite-based point-to-mulit-point data communications applications.
VSU
Video Service Unit. See Multiband VSU.
VT-100
An ASCII character data terminal, consisting of screen and keyboard. Manufactured by Digital Equipment Corporation (DEC), the VT-100 has become an industry standard data terminal. VT-100 emulation software allows a standard PC to act as a VT-100 terminal. Videoconferencing
VTP
Virtual Terminal Protocol. An application for establishing a virtual terminal connection across a network.
Variable Bit Rate-Real Time (VBR-RT )
VBR-RT is an asynchronous transfer mode (ATM) service class that handles the packaging of special delay-sensitive applications, such as packet video, that require low cell-delay variation between endpoints.
Very High Bit Rate Digital Subscriber Line (VDSL)
VDSL is an asymmetric DSL technology that offers about eight times the performance of ADSL. The downside is that it requires a fiber-optic line from the central office (CO) to the subscriber’s neighborhood. Because infrastructure changes are required in the local loop, VDSL is considered a specialized and long-term technology.
Video Dial Tone
A network concept in which common carriers deliver video services in response to customers' dial-up commands, the same way users access the public network by dialing their phones.
Video Headend
Node on a video network where incoming program signals are converted to distribution signals and moved out onto the video distribution network for transmission to subscribers.
Video on Demand
The ability for a subscriber to an interactive TV service to select and view a specific program provided by a device such as an interactive video server.
Videoconferencing
The use of digital video transmission systems to communicate between sites using video and voice. Digital video transmission systems typically consist of camera, codec (coder-decoder), network access equipment, network, and audio system.
Virtual Bandwidth
Channel capacity calculated to allow for the over subscription of channel usage.
Virtual Channel (VC)
A communications link that carries asynchronous transfer mode (ATM) cells between two points over a shared facility. The link can be established on-demand (as a switched service), or pre-provisioned (as frame relay PVCs). The two communicating ATM entities are associated by a Virtual Path Identifier (VPI) and the Virtual Channel Identifier (VCI). All communications proceed along the same VC, preserving cell sequence and Quality of Service.
Virtual Circuit (VC)
On a frame relay, X.25 or Open Shortest Path First (OSPF) network, a VC is a bi-directional data path between two endpoints.
Virtual Circuit Manager
In each asynchronous transfer mode (ATM) node, the VC manager is the switching intelligence that builds the input port-to-output port VC mappings required for the switching device’s basic operation. The VC manager also compares the bandwidth resources required by an additional connection against the actual available resources on a link, thereby helping to prevent circuits from being created in congested areas of the network.
Virtual Paths
A bundle of virtual channels that have the same endpoint, enabling them to be manipulated as if they were a single channel.
Visitor Location Register
In cellular communications, a database that stores the information to handle calls while mobile subscribers roam outside their home areas.
VoIP
A category of hardware and software that allows people to use the Internet to make telephone calls. Currently, VoIP does not offer the same quality of telephone service as direct telephone connections. VoIP is also known as Internet telephony and Voice over the Internet.
Vocoder (Voice encoder)
Converts the analog sounds of the human voice into the zeroes and ones of digital code for computer processing.
Voice-over-IP (VoIP)
A term applied to a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). Voice information is sent in digital form in discrete packets over the Internet instead of in analog form over the public switched telephone network (PSTN). A major advantage of VoIP is that it avoids the tolls charged by ordinary telephone service.
Voice-over-frame Relay (VoFR)
A term applied to a set of facilities for managing the delivery of voice information using frame relay.
Volt
The force required to produce a current of one ampere through a resistance or impedance of one ohm.
A rate-adaption standard, based on fixed frames, that subdivides the ISDN channel so that it can carry one lower-speed data channel.
V.110 Terminal Adapter
A V.110 TA is a device that changes the format of asynchronous data to match the specifications of the V.110 standard for data transmission over an ISDN line.
V.120
A standard for encapsulating asynchronous data communication into synchronous ISDN data. Using standard, asynchronous-only COM ports and a V.120 Terminal Adapter (TA), two computers can communicate over an ISDN connection.
V.120 Terminal Adapter
A V.120 TA is an asynchronous device that changes the format of asynchronous data to match the specifications of the V.120 standard for data transmission over an ISDN line. A V.120 TA is also known as an ISDN modem.
V.21
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for 300-bps full-duplex modems.
V.22
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard that supports a data rate of up to 1200 bps at 600 baud.
V.22bis
An extension of the V.22 standard, providing a data rate of up to 2400 bps at 600 baud.
V.23
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for 600-bps and 1200-bps full-duplex modems.
V.24
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard that specifies a physical-layer interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE). V.24 is nearly identical to RS-232.
V.25
An automatic calling and answering command set for use between DTE and DCE that includes both in-band and out-of-band signaling.
V.25 bis
An automatic calling and answering command set for use between DTE and DCE which includes both in-band and out-of-band signaling.
V.25bis
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for automatic calling and answering equipment on (PSTN).
V.32
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for full-duplex modem transmission of data across phone lines at rates of up to 9600 bps, with a fallback rate of 4800 bps. A V.32 modem automatically adjusts its transmission speed based on the quality of the line.
V.32bis
An extension of the V.32 standard, providing a data rate of up to 14,400 bps or fallback to 12,000, 9600, 7200, and 4800 bps.
V.34
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) standard for full-duplex modem transmission of data across phone lines at rates of up to 28,800 bps. A V.34 modem automatically adjusts its transmission speed based on the quality of the line.
V.34bis
An extension of the V.34 standard, providing a data rate of up to 33,600 bps. Compare with V.34.
V.35
Commonly used to describe electrical characteristics and connector characteristics for a high-speed synchronous interface between DTE and DCE. Originally V.35 described a 48 Kbps group band modem interface with electrical characteristics defined in an appendix. Although V.35 is considered obsolete and no longer published by the CCITT, its legacy lives on in the data communications world in the form of the electrical characteristics originally described in the appendix.
V.42
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) error-detection standard for high-speed modems over digital telephone lines. The V.42 standard makes use of the link access procedure, modem (LAPM).
V.42bis
An International Telecommunication Union–Telecommunication Standardization Sector (ITU-T) data-compression standard for use with V.42 technology. The V.42bis data-compression standard provides a maximum of a four-to-one data-compression ratio. Because compression algorithms are software based, overhead can cause problems in real-time environments. Most of the time, V.42bis can sense when compression is unnecessary, and so can avoid slowing the transfer of precompressed files.
V.90
A standard for data transmission over a modem at 56 kilobits per second. The V.90 standard resolves the difference between two modem technologies - x2 and K56flex. Both technologies now conform to V.90, and most previously manufactured 56Kbps modems can support V.90 via a software upgrade. See also K56flex.
VDC
Volts DC
VLAN
Virtual LAN. A group of devices on one or more LANs that communicate as if they were connected to the same wire even though they are physically located on different local area network segments. Because VLANs are configured through software rather than hardware, they are extremely flexible.
VPN
Virtual private network. A restricted network that uses public wires to connect nodes. A VPN provides a way to encapsulate, or "tunnel," private data cheaply, reliably, and securely through a public network, usually the Internet.
VSAT
Very small aperture terminal. Relatively small satellite antenna used for satellite-based point-to-mulit-point data communications applications.
VSU
Video Service Unit. See Multiband VSU.
VT-100
An ASCII character data terminal, consisting of screen and keyboard. Manufactured by Digital Equipment Corporation (DEC), the VT-100 has become an industry standard data terminal. VT-100 emulation software allows a standard PC to act as a VT-100 terminal. Videoconferencing
VTP
Virtual Terminal Protocol. An application for establishing a virtual terminal connection across a network.
Variable Bit Rate-Real Time (VBR-RT )
VBR-RT is an asynchronous transfer mode (ATM) service class that handles the packaging of special delay-sensitive applications, such as packet video, that require low cell-delay variation between endpoints.
Very High Bit Rate Digital Subscriber Line (VDSL)
VDSL is an asymmetric DSL technology that offers about eight times the performance of ADSL. The downside is that it requires a fiber-optic line from the central office (CO) to the subscriber’s neighborhood. Because infrastructure changes are required in the local loop, VDSL is considered a specialized and long-term technology.
Video Dial Tone
A network concept in which common carriers deliver video services in response to customers' dial-up commands, the same way users access the public network by dialing their phones.
Video Headend
Node on a video network where incoming program signals are converted to distribution signals and moved out onto the video distribution network for transmission to subscribers.
Video on Demand
The ability for a subscriber to an interactive TV service to select and view a specific program provided by a device such as an interactive video server.
Videoconferencing
The use of digital video transmission systems to communicate between sites using video and voice. Digital video transmission systems typically consist of camera, codec (coder-decoder), network access equipment, network, and audio system.
Virtual Bandwidth
Channel capacity calculated to allow for the over subscription of channel usage.
Virtual Channel (VC)
A communications link that carries asynchronous transfer mode (ATM) cells between two points over a shared facility. The link can be established on-demand (as a switched service), or pre-provisioned (as frame relay PVCs). The two communicating ATM entities are associated by a Virtual Path Identifier (VPI) and the Virtual Channel Identifier (VCI). All communications proceed along the same VC, preserving cell sequence and Quality of Service.
Virtual Circuit (VC)
On a frame relay, X.25 or Open Shortest Path First (OSPF) network, a VC is a bi-directional data path between two endpoints.
Virtual Circuit Manager
In each asynchronous transfer mode (ATM) node, the VC manager is the switching intelligence that builds the input port-to-output port VC mappings required for the switching device’s basic operation. The VC manager also compares the bandwidth resources required by an additional connection against the actual available resources on a link, thereby helping to prevent circuits from being created in congested areas of the network.
Virtual Paths
A bundle of virtual channels that have the same endpoint, enabling them to be manipulated as if they were a single channel.
Visitor Location Register
In cellular communications, a database that stores the information to handle calls while mobile subscribers roam outside their home areas.
VoIP
A category of hardware and software that allows people to use the Internet to make telephone calls. Currently, VoIP does not offer the same quality of telephone service as direct telephone connections. VoIP is also known as Internet telephony and Voice over the Internet.
Vocoder (Voice encoder)
Converts the analog sounds of the human voice into the zeroes and ones of digital code for computer processing.
Voice-over-IP (VoIP)
A term applied to a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). Voice information is sent in digital form in discrete packets over the Internet instead of in analog form over the public switched telephone network (PSTN). A major advantage of VoIP is that it avoids the tolls charged by ordinary telephone service.
Voice-over-frame Relay (VoFR)
A term applied to a set of facilities for managing the delivery of voice information using frame relay.
Volt
The force required to produce a current of one ampere through a resistance or impedance of one ohm.
