VBrick Glossary (# - I)

10Base-T -- The IEEE 802.3 specification for ethernet over unshielded twisted pair (UTP).

100Base-T Fast Ethernet -- A 100 Mbps technology based on the Ethernet/CD network access method. Application Program Interface (API) -- Means of communication between programs to give one program transparent access to another.

Asymmetrical Digital Subscriber Line (ADSL) -- A new standard for transmitting at speeds up to seven Mbps over a single copper pair.

Asynchronous -- Referring to two or more signals which, though they have the same nominal rates, actually operate at different rates. Asynchronous Transfer Mode (ATM) -- The CCITT standard for cell relay wherein information for multiple types of services (voice, video, data) is conveyed in small, fixed-size cells. ATM is a connection oriented technology used in both LAN and WAN environments.

AAL 5 -- Accommodates bursty LAN data traffic with less overhead than AAL 3/4.

ATM Layer -- The layer in the ATM protocol stack for routing and processing activities. For example: building the ATM header; payload identification; header validation and cell reception; cell routing using VPIs/VCIs; cell multiplexing/demultiplexing; quality of service specification; prioritization and flow control.

Audioconferencing--Teleconferencing method used mostly by audio communications channels such as telephone lines provided by a telecommunications company interconnecting the various parties.

Bandwidth--(1) A range of frequencies between two defined limits expressed in cycles per second, or hertz (Hz). It is also the information carrying capacity of a circuit. (2) The expression of the carrying capacity of the transmission line. In a digital transmission, the bandwidth is the range of transmission rates at which information can be sent in a particular medium. The bandwidth is expressed in kilobits per seconds or megabits per second (Mbps). (3) The capacity of a transmission channel.

Baud (Bite at Unit Density) -- A unit of transmission speed equal to the number of times the state (or condition) of a line changes per second. The baud rate usually refers to the number of bits transmitted each second.

Bridge--Device for the interconnection of telecon-ferencing systems and communications lines in a multipoint session. A bridge is called an audio bridge in audio-conferencing and a multipoint control unit in videoconferencing. The bridge can be an analog or a digital device. An essential component of an audio-conferencing system, the bridge also balances the signal levels of the audio transmission, reduces noise, and minimizes echo.

Cable Television (CATV) -- The transmission of television signals, including signals that originate at over-the-air television stations, to consumers on a wired network, usually for a fee.

Carrier Sense Multiple Access/Collision Detection (CSMA/CD) -- A channel access mechanism wherein devices wishing to transmit first check the channel for a carrier. If no carrier is sensed for some period of time, devices can transmit. If two devices transmit simultaneously, a collision occurs and is detected by all colliding devices, which subsequently delays their retransmissions for some random length of time. CSMA/CD access is used by Ethernet and IEEE 802.3

Central Processor Unit (CPU) -- Traditionally refers to the core components of a computer that interpret and execute binary instructions.

Circuit -- A physical, metallic path used for two-way communications between two or more points.

Classical IP -- Set of IETF-developed specifications for the operation of LAN-to-LAN IP connectivity over an ATM network.

Client/Server -- A distributed system model of computing that brings computing power to the desktop, where users ("clients") access resources from servers.

Codec - -A videoconferencing system component that processes incoming and outgoing audiovisual signals in terms of coding and compression.

Coding or Compression -- A technique used to reduce the amount of space taken up by data during transmission.

Coder/Decoder (Codec) -- Equipment to convert between analog and digital information format. Also may provide digital compression and switching functions. Primarily used to describe video equipment performing this function.

Compression -- Reducing the size of a data set to lower the bandwidth or space required for transmission or storage.

Constant Bit Rate (CBR) -- Delay intensive applications such as video and voice, that must be digitized and represented by a continuous bit stream. CBR traffic requires guaranteed levels of service and throughput.

Data Compression -- Reducing the size of a data file by reducing unnecessary information, such as blanks and redundant data.

Data Terminal Equipment (DTE) -- That part of a data station that serves as a data source, data sink, or both. It is the part of the terminal that interfaces with the communications circuit.

Datagram -- In TCP/IP, the basic unit of information passed across the internet environment. An IP datagram consists of an IP header, followed by the Transport layer data.

Digital--The transmission of discontinuous signals in which information is encoded in binary form.

Digital Modem -- A system component which allows modem users to communicate over digital access facilities. They work by converting the PCM-encoded digital data streams sent by analogue modem users into their original analogue waveform.

Digitize -- To convert an analog signal to a digital signal.

Direct Broadcast Satellite (DBS) -- High-powered satellites that can transmit or retransmit signals which are intended for direct reception by the public. The signal is transmitted to small and inexpensive earth stations or "dishes" mounted on homes or other buildings.

Document Conferencing--A conferencing technology that enables customers to review a document and collaborate with others, right from their computer using either analog and modem dial-up or existing Internet accesses (LAN, dial-up, etc.)

Ethernet -- A baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation. Ethernet networks operate at 10Mbps using CSMA/CD to run over coaxial cable. Ethernet is similar to a series of standards produced by IEEE referred to as IEEE 802.3.

Fiber Distributed Data Interface (FDDI) -- An ANSI-defined standard specifying a 100Mbps token-passing network using fiber-optic cable. Uses a dual-ring architecture to provide redundancy.

File Transfer Protocol (FTP) -- An Internet protocol that allows a user on one host to transfer files to and from another host over a network.

Fragmentation -- The process of breaking a packet into smaller units when transmitting over a network medium that cannot support the original size of the packet.

Full Duplex -- LAN Technique for transmitting full duplex between a LAN station and the wiring hub. Supports 10Mbps in each direction (20Mbps) for Ethernet and 16Mbps in each direction (32Mbps for Token Ring). Only supports single stations, not LAN segments.

GLOP -- The "GLOP" address space (not an acronym) is a way to assign addresses based on an autonomous system number, as described in RFC 2770. Basically, a /24 is assigned to each Autonomous System based on the 16 bit Autonomous System Number (ASN). For a given ASN number, converted into two octets (say X and Y) in the usual fashion of Internet addresses, the GLOP space is therefore 233.X.Y/24. This address range is assumed to be assigned by default and does not have to be explicitly requested. Note, however, that a GLOP allocation only provides 256 separate addresses, which is widely viewed as not enough for large scale broadcasters. There are no restrictions on your GLOP space.

Gigabit -- One billion bits. H H.263 -- A standard algorithm for video coding approved by the ITU-T.

Half-Duplex Transmission -- Data transmitted in either direction, one direction at a time.

Hz--Hertz.

High-bit-rate Digital Subscriber Line (HDSL) -- A standard defined by the TlE1.4 standards committee, designed to be a cost-effective method of delivering T1/E1 line speeds over unconditioned copper cable.

High Performance Parallel Interface (HIPPI) -- An emerging ANSI standard which extends the computer bus over fairly short distances at speeds of 800 and 1600Mb/s. HIPPI is often used in a computer room to connect a supercomputer to routers, frame buffers, mass-storage peripherals, and other computers.

Hyper Text Markup Language (HTML) -- The language used in the World Wide Web to create web pages with links to other documents, rich text enhancements (bold, italic, etc.) and so on. The "source" file for what you see on a web page is written in HTML.

Hyper Text Transfer Protocol (HTTP) -- The protocol most commonly used in the World Wide Web to transfer information from Web servers to Web browsers.

Integrated Services Digital Network (ISDN) -- The recommendation published by CCITT for private or public digital telephone networks where binary data, such as graphics and digitized voice and data transmission, pass over the same digital network that carries most telephone transmissions today.

Interface -- A connection between two systems or devices. In routing terminology, a network connection. Also, the boundary between adjacent layers of the OSI model. In telephony, a shared boundary defined by common physical interconnection characteristics, signal characteristics, and meanings of interchanged signals.

Internet -- A collection of networks interconnected by a set of routers which allow them to function as a single, large virtual network.

Internet Address -- Also called an IP address. It is a 32-bit address assigned to hosts using TCP/IP. The address is written as four octets separated with periods (dotted decimal format) that are made up of a network section, an optional subnet section, and a host section.

Internet Engineering Task Force (IETF) -- An organization that provides coordination of standards and specifications development for TCP/IP networking.

Internet Protocol (IP) -- A Layer three (network layer) protocol that contains addressing information and some control information that allows packets to be routed. Documented in RFC 791.

Internet Protocol Version 6 (IPng, IPv6) -- IPv6 (version five is a stream protocol used for special applications) is a new version of the Internet Protocol which is designed to be an evolutionary step from its predecessor, version four. There are many RFCs defining various portions of the protocol, its auxiliary protocols, and the transition plan from IPv4. The core RFCs are 1883 through 1886.

Internet Service Provider (ISP) -- Any of a number of companies that sell Internet access to individuals or organizations at speeds ranging from 300bps to OC-3.

ISDN (Integrated Services Digital Network) --An international standard developed for transmitting voice, data, and video simultaneously over digital lines. These lines run at 64 kilobits per second.

Isochronous -- All devices in the network derive their timing signal directly or indirectly from the same primary reference clock. ITU --International Telecommunication Union (telecommunications standards division).

VBrick Glossary (J - Z)

Java -- A programming language developed by Sun Microsystems™. Applets written in Java include their own software players, so you can download and run them on any computer.

Jitter -- Analogue communication line distortion caused by a variation of signals from its reference timing positions. Jitter can also cause data loss, particularly at high speeds.

Joint Photographic Experts Group (JPEG) -- Industry organization developing standards and specifications for the encoding and transmission of photographic images over various media and network technologies.

JPEG--Joint Photographic Experts Group.

Kilobits per second (Kbps) -- Thousand bits per second. A measure of transmission speed.

LAN --Local area network. LAN Emulation -- A technique for legacy LAN MAC-layer protocols like Ethernet and token ring, to work transparently across an ATM network.

Latency -- The delay between the time a device receives a frame and the frame is forwarded out of the destination port.

Load Balancing -- In routing, the ability of the router to distribute traffic over all its network ports that are the same distance from the destination address. It increases the use of network segments, which increase the effective network bandwidth.

Local Area Network (LAN) -- A network covering a relatively small geographic area (usually not larger than a floor or small building). Compared to WANs, LANs are usually characterized by relatively high data rates.

Management Information Base (MIB) -- A database of information on managed objects that can be accessed via network management protocols such as SNMP and CMIP.

Megabits Per Second (Mbps) -- A digital transmission speed of millions of bits per second.

MCU --Multipoint control unit.

Moving Pictures Experts Group (MPEG) -- Industry organization developing standards and specifications for the encoding and transmission of video information over various media and network technologies.

Multicast -- Single packets copied to a specific subset of network addresses. These addresses are specified in the destination-address field. In contrast, in a broadcast, packets are sent to all devices in a network.

Multicast Address -- A class D address that refers to multi-network devices. Synonymous with group address.

Multicast Backbone (MBONE) -- A collection of Internet routers that support IP multicasting. The MBONE is used as a "broadcast (actually multicast) channel" on which various public and private audio and video programs are sent. Examples include audio/ video transmissions from the IETF meetings. At a recent IETF meeting there were as many participants "listening in" on the MBONE as there were people present at the meeting itself.

Multipoint --The connection of more than two locations to affect a teleconference, as opposed to only point-to-point connections.

National Television System Committee (NTSC) -- In the United States, a television industry group that develops standards for television broadcasting and receiving equipment.

Network -- A collection of computers and other devices that are able to communicate with each other over some network medium.

Network File System (NFS®) -- A distributed file system developed by Sun Microsystems which allows a set of computers to cooperatively access each other's files in a transparent manner.

Network Interface Card (NIC) -- The circuit board or other hardware that provides the interface between a communicating DTE and the network.

Packet -- Continuous sequence of binary digits of information is switched through the network and an integral unit. Consists of up to 1024 bits (128 octets) of customer data plus additional transmission and error control information.

Packet Switch -- The vehicle of the Local Public Data Network which performs the switching function. For Local Public Data Network service, this is a Telephone Company facility Hub.

Packet Switched Network -- A network in which data is transmitted in units called packets. The packets can be routed individually over the best available network connection and reassembled to form a complete message at the destination.

Packet Switching -- Type of data transfer that occupies a communication link only during the time of actual data transmission. Messages are split into packets and reassembled at the receiving end of the communication link.

PBX (Private Branch Exchange) --A private phone system existing within an organization that allows communication within the organization by dialing an extension and outside the organization by dialing "9" and then the number.

PC --Personal computer. PSTN --Public Switched Telephone Network

Quality of Service (QoS) -- Term for the set of parameters and their values which determine the performance of a given virtual circuit.

QuickTime -- Video file format developed by Apple computer.

Remote Procedure Call (RPC) -- A TCP/IP mechanism that provides a standard for initiating and controlling processes on remote or distributed computer systems.

Router -- A dedicated computer hardware and/or software package which manages the connection between two or more networks.

Shared Ethernet -- Conventional CSMA/CD Ethernet configuration to which all stations are attached by a hub and share 10 or 100 Mbps of bandwidth. Only one session can transmit at a time. This is the most popular network type today.

Simple Network Management Protocol (SNMP) -- The Internet network management protocol. SNMP provides a means to monitor and set network configuration and runtime parameters.

Small Computer Serial Interface (SCSI) -- Physical interface standard between high speed external devices, such as disks and CD-ROMs, and desktop systems.

Solaris -- Operating system for Sun Microsystems SPARC workstation.

Store and Forward -- Switching technique where frames, packets or messages are temporarily received and buffered at intermediate points between the source and destination. Bridges, Routers, X.25 switches and ATM switches are all based on store and forward technology.

Structured Query Language (SQL) -- The international standard language for defining and accessing relational databases.

Switched Ethernet -- An ethernet arrangement in which the end devices are connected to a centralized switch rather than a shared bus. Each connection is its own collision domain. All communication occurs through the switch.

Synchronous -- Operating at the same speed, all circuits in a synchronous network are constrained to operate at their nominal rates with no significant variation.

T1 -- Digital transmission facility operating with a nominal bandwidth of 1.544Mbps. Also known as Digital Signal Level 1 (D1). Composed of 24 DS-0 channels in many cases. The T1 digital transmission system is the primary digital communication system in North America.

T3 -- Digital transmission facility operating at 45Mbps bandwidth. Composed of 28 DS-1 channels in many cases. Also known as DS-3.

Televisioning -- Two-way interactive video conference conducted with true broadcast quality.

Token Ring -- As defined in IEEE 802.5, a communications method that uses a token to control access to the LAN. The difference between a token bus and a token ring is that with a token ring the LAN does not use a master controller to control the token. Instead, each computer knows the address of the computer that should receive the token next. When a computer with the token has nothing to transmit, it passes the token to the next computer in line.

Transmission Control Protocol (TCP) -- A reliable, full duplex, connection-oriented end to end transport protocol running on top of IP.

Transmission Control Protocol/Internet Protocol (TCP/IP) -- The common name for the suite of protocols developed by the U.S. Department of Defense in the 1970s to support the construction of world-wide internetworks. TCP and IP are the two best-known protocols in the suite. TCP corresponds to Layer four (the transport layer) of the OSI reference model. It provides reliable transmission of data. IP corresponds to layer three (the network layer) of the OSI reference model and provides connectionless datagram service.

Uniform Resource Locator (URL) -- An identifier which describes the location of a particular piece of information ("document") including the protocol used to retrieve that information. For example, http://www. interop.com/publications/connexions.html says: Use the HTTP protocol to retrieve the file "connexions.html" from host "www.interop.com" in directory "publications."

User Datagram Protocol (UDP) -- A connectionless transport-layer protocol belonging to the Internet protocol family.

Variable Bit Rate (VBR) -- Applications that produce traffic of varying bit rates, like common LAN applications, which produce varying throughput rates.

Virtual LAN -- Membership to a Virtual LAN is defined administratively independent of the physical network topology. A virtual LAN segment is a unique broadcast domain.

Virtual Private Network (VPN) -- A network service offered by public carriers in which the customer is provided a network that in many ways appears as if it is a private network (customer-unique addressing, network management capabilities, dynamic reconfiguration, etc.) but which, in fact, is provided over the carrier's public network facilities.

Web -- Web, used as a noun, is shorthand for the World Wide Web.

Web Server -- A server that stores and retrieves HTML documents and other Internet or intranet resources using HTTP. Also called an HTTP server.

Wide Area Network (WAN) -- A network that encompasses interconnectivity between devices over a wide geographic area. Such networks would require public rights-of-way and operate over long distances.

World Wide Web (WWW) -- The Internet's worldwide, HTML-based, hypertext-linked information system.