Networking Definitions

This glossary explains the meaning of key words and phrases that information technology (IT) and business professionals use when discussing networking and related software products. You can find additional definitions by visiting WhatIs.com or using the search box below.

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  • R

    running disparity (RD)

    Running disparity (RD or rd) is the difference between the number of logic 1 bits and logic 0 bits between the start of a data sequence and a particular instant in time during its transmission.

  • runt

    In networks, a runt is a packet that is too small.

  • S

    network switch

    A network switch is a hardware device that channels incoming data from multiple input ports to a specific output port that will take it toward its intended destination.

  • S interface

    In Integrated Services Digital Network (ISDN) service, an S interface is the electrical interface between a network terminating unit 1 (NT and up to eight addressable devices such as a computer or a telephone.

  • satellite Internet connection

    A satellite Internet connection is an arrangement in which the upstream (outgoing) and the downstream (incoming) data are sent from, and arrive at, a computer through a satellite.

  • satellite news gathering (SNG)

    Satellite news gathering (SNG) is the use of mobile communications equipment for the purpose of worldwide newscasting.

  • satellite return Internet connection

    A satellite return Internet connection is an arrangement in which incoming data arrives at your computer from a satellite downlink and outgoing data (such as your request for the next Web page) is sent over a regular telephone line.

  • SCART connector

    A SCART connector is a physical and electrical interconnection between two pieces of audio-visual equipment, such as a television set and a video cassette recorder (VCR).

  • SCTP (Stream Control Transmission Protocol)

    SCTP (Stream Control Transmission Protocol) is a protocol for transmitting multiple streams of data at the same time between two end points that have established a connection in a network.

  • SD-branch

    SD-branch is a single, automated, centrally managed software-centric platform that replaces or supplements an existing branch network architecture.

  • SD-WAN (Software-defined WAN)

    Software-defined WAN (SD-WAN) is technology that uses software-defined networking (SDN) concepts to distribute network traffic across a wide area network (WAN).

  • SDH (Synchronous Digital Hierarchy)

    SDH (Synchronous Digital Hierarchy) is a standard technology for synchronous data transmission on optical media.

  • SDLC (Synchronous Data Link Control)

    (SDLC is also an abbreviation for systems development life cycle.

  • SDN application (software-defined networking application)

    An SDN application is a software program designed to perform a task in a software-defined networking (SDN) environment. SDN applications can replace and expand upon functions that are implemented through firmware in hardware devices in a conventional networking environment.

  • SDN controller (software-defined networking controller)

    An SDN controller is an application in a software-defined networking (SDN) architecture that manages flow control for improved network management and application performance.

  • SDN overlay (software defined networking overlay)

    An SDN overlay is a deployment method for network virtualization and software-defined networking (SDN) that involves running a logically separate network or network component on top of existing infrastructure.

  • Secure Access Service Edge (SASE)

    Secure Access Service Edge, also known as SASE -- pronounced 'sassy' -- is a cloud architecture that bundles network and security solutions together and delivers them as a unified cloud service.

  • Seebeck effect

    The Seebeck effect describes the generation of electricity following the connection of two dissimilar electrical conductors or semiconductors that illustrates the thermoelectric effect. 

  • segmentation and reassembly (SAR)

    In a packet-switched telecommunication network, segmentation and reassembly (SAR, sometimes just referred to as segmentation) is the process of breaking a packet into smaller units before transmission and reassembling them into the proper order at the receiving end of the communication.

  • Sequenced Packet Exchange (SPX)

    SPX (Sequenced Packet Exchange) is the protocol for handling packet sequencing in a Novell NetWare network.

  • Serial Digital Interface (SDI)

    Serial Digital Interface (SDI) is a standard for digital video transmission over coaxial cable.

  • Server Message Block Protocol (SMB protocol)

    The Server Message Block Protocol (SMB protocol) is a client-server communication protocol used for sharing access to files, printers, serial ports and other resources on a network.

  • Service Location Protocol (SLP)

    The Service Location Protocol (SLP) is a protocol or method of organizing and locating the resources (such as printers, disk drives, databases, e-mail directories, and schedulers) in a network.

  • session border controller (SBC)

    A session border controller (SBC) is a dedicated hardware device or software application that governs the manner in which phone calls are initiated, conducted and terminated on a Voice over Internet Protocol (VoIP) network. Phone calls are referred to as sessions.

  • Session layer

    In the Open Systems Interconnection (OSI) communications model, the session layer resides at Layer 5 and manages the setup and teardown of the association between two communicating endpoints.

  • session-based routing

    Session-based routing is a type of routing architecture that is application-centric and designed to route entire sessions instead of individual packets.

  • set-top box

    A set-top box is a device that enables a television set to become a user interface to the Internet and also enables a television set to receive and decode digital television (DTV) broadcasts.

  • Shannon's Law

    Shannon's Law, formulated by Claude Shannon, a mathematician who helped build the foundations for the modern computer, is a statement in information theory that expresses the maximum possible data speed that can be obtained in a data channel.

  • shielded twisted pair

    This definition closely duplicates the definition for twisted pair.

  • shortest path bridging

    Shortest path bridging, or 802.1aq, is the IEEE’s specification for enabling multi-pathing in the data center. Shortest path bridging is similar conceptually to its IETF counterpart, Transparent Interconnection of Lots of Links (TRILL).

  • signal

    In electronics, a signal is an electric current or electromagnetic field used to convey data from one place to another.

  • signal-to-noise ratio (S/N or SNR)

    In analog and digital communications, signal-to-noise ratio is a measure of signal strength relative to background noise. This ratio is usually measured in decibels.

  • Signaling System 7 (SS7)

    Signaling System 7 (SS7) is an international telecommunications standard that defines how network elements in a public switched telephone network (PSTN) exchange information over a digital signaling network. Nodes in an SS7 network are called signaling points.

  • SIGTRAN (Signaling Transport)

    SIGTRAN (for Signaling Transport) is the standard telephony protocol used to transport Signaling System 7 (SS7) signals over the Internet.

  • Simple Network Management Protocol (SNMP)

    Simple Network Management Protocol (SNMP) is an application-layer protocol used to manage and monitor network devices and their functions.

  • Simputer (simple inexpensive mobile computer)

    The Simputer (short for simple inexpensive mobile computer) is an inexpensive, Web-enabled handheld computer designed for use by people in developing countries.

  • single mode fiber

    In optical fiber technology, single mode fiber is optical fiber that is designed for the transmission of a single ray or mode of light as a carrier and is used for long-distance signal transmission.

  • single-user MIMO

    Single-user MIMO (SU-MIMO) is a multi-transmitter and receiver technology for wireless communication that allocates the bandwidth of a wireless access point to a single device.

  • slamming

    Slamming is the practice by some U.S. long-distance phone carriers of switching users to their service without the user's knowledge or authorization.

  • sliding windows (windowing)

    Sliding windows, a technique also known as windowing, is used by the Internet's Transmission Control Protocol (TCP) as a method of controlling the flow of packets between two computers or network hosts.

  • slot time

    In Ethernet and its Carrier Sense Multiple Access/Collision Detect (CSMA/CD) approach to managing which device can use the communication link next, slot time is the amount of time a device waits after a collision before retransmitting.

  • small cell

    Small cell is an overarching term for wireless network base stations with a low radio frequency power output, footprint and range.

  • small form factor (SFF)

    Small form factor (SFF) refers to any of several physically compact connector designs that have been developed for use in fiber optic systems.

  • small form-factor pluggable (SFP)

    Small form-factor pluggable (SFP) is a specification for a new generation of optical modular transceivers.

  • SMDS (Switched Multimegabit Data Service)

    SMDS (Switched Multimegabit Data Service) is a public, packet-switched service aimed at enterprises that need to exchange large amounts of data with other enterprises over the wide-area network on a nonconstant or "bursty" basis.

  • sniffer

    In common industry usage, a sniffer (with lower case "s") is a program that monitors and analyzes network traffic, detecting bottlenecks and problems.

  • Snort

    Snort is an open source network intrusion detection system (NIDS) created by Martin Roesch.

  • softswitch

    Softswitch (software switch) is a generic term for any open application program interface (API) software used to bridge a public switched telephone network (PSTN) and Voice over Internet Protocol (VOiP) by separating the call control functions of a phone call from the media gateway (transport layer).

  • software-defined networking (SDN)

    Software-defined networking (SDN) is a network architecture that aims to make data center networks agile and flexible.

  • software-defined networking monitoring application (SDN monitoring application)

    An SDN monitoring application is a software program that oversees the traffic in a software-defined network (SDN) as a component of network management.

  • software-defined radio (SDR)

    Software-defined radio (SDR), sometimes shortened to software radio (SR), refers to wireless communication in which the transmitter modulation is generated or defined by a computer, and the receiver uses a computer to recover the signal intelligence.

  • soliton

    A soliton is a special form of light pulse that can be transmitted over a fiber optic channel.

  • source quench

    Using the Internet Control Message Protocol (ICMP), a source quench is a message from one host computer to another telling it to reduce the pace at which it is sending packet to that host.

  • Source Quench Introduced Delay (SQuID)

    Also see SQUID, a UNIX-based program for caching Web pages and other Internet content closer to the user.

  • Source-route transparent (SRT) bridging

    Source-route transparent (SRT) bridging is a bridging scheme developed by IBM that combines source-route bridging (SRB) and transparent bridging in the same network.

  • spanning tree protocol (STP)

    Spanning tree protocol (STP) is a Layer 2 network protocol used to prevent looping within a network topology. The protocol allows two bridges to exchange information for only one bridge to handle a given message sent between two computers within the network. STP prevents the condition known as bridge looping.

  • spatial division multiple access (SDMA)

    Also see frequency division multiple access (FDMA) and time division multiple access (TDMA).

  • spectrum analyzer

    A spectrum analyzer is a device that displays signal amplitude (strength) as it varies by signal frequency.

  • SPID (Service Profile Identifier)

    A SPID (Service Profile Identifier) is a number assigned by a phone company to a terminal on an Integrated Services Digital Network B-channel.

  • split

    Among Internet Relay Chat (IRC) users, a split is a condition where two or more IRC servers are temporarily unable to communicate.

  • split horizon

    Split horizon is a method of preventing a routing loop in a network.

  • splitter

    In telephony, a splitter, sometimes called a "plain old telephone service splitter," is a device that divides a telephone signal into two or more signals, each carrying a selected frequency range, and can also reassemble signals from multiple signal sources into a single signal.

  • splitterless

    Splitterless refers to a type of Digital Subscriber Line (DSL) telephone service that does not require the installation of a plain old telephone service splitter at the customer location.

  • spread spectrum

    Spread spectrum is a form of wireless communications in which the frequency of the transmitted signal is deliberately varied.

  • stackable hub

    A stackable hub is a hub designed to be connected and stacked or positioned on top of another hub, forming an expanding stack.

  • staggered quadrature phase-shift keying

    Staggered quadrature phase-shift keying (SQPSK), also known as offset quadrature phase-shift keying (OQPSK), is a method of phase-shift keying (PSK) in which the signal carrier-wave phase transition is always 90 degrees or 1/4 cycle at a time... (Continued)

  • star network

    A star network is a local area network (LAN) in which all nodes (workstations or other devices) are directly connected to a common central computer.

  • start of authority record

    A start of authority (SOA) record is information stored in a domain name system (DNS) zone about that zone and about other DNS records.

  • stateful inspection

    Stateful inspection is a firewall technology that monitors the state of active connections and uses this information to determine which network packets to allow through the firewall. Stateful inspection is also known as dynamic packet filtering.

  • STDM (statistical time division multiplexing)

    STDM, or statistical time division multiplexing, is one method for transmitting several types of data simultaneously across a single transmission cable or line (such as a T1 or T3 line).

  • STUN (Simple Traversal of UDP through NAT)

    Simple Traversal of UDP through NAT (STUN) is a protocol that governs the exchange of data over a User Datagram Protocol (UDP) connection by communications devices operating behind a Network Address Translator (NAT) or firewall... (Continued)

  • subcarrier

    A subcarrier is one telecommunication signal carrier that is carried on top of another carrier so that effectively two signals are carried at the same time.

  • subnet (subnetwork)

    A subnet, or subnetwork, is a segmented piece of a larger network.

  • subnet mask (subnetting)

    A subnet mask is a 32- or 128-bit number that segments an existing IP address in a TCP/IP network and divides that address into discrete network and host addresses.

  • subnetwork

    A subnetwork is a separately identifiable part of a larger network that typically represents a certain limited number of host computers, the hosts in a building or geographic area, or the hosts on an individual local area network.

  • switched virtual circuit (SVC)

    In a network, a switched virtual circuit (SVC) is a temporary virtual circuit that is established and maintained only for the duration of a data transfer session.

  • symmetric communications

    Compare asymmetric communications.

  • SYN scanning

    SYN scanning is a tactic that a malicious hacker (or cracker) can use to determine the state of a communications port without establishing a full connection.

  • Synchronous Optical Network (SONET)

    Synchronous Optical Network (SONET) is a standard for synchronous data transmission on optical fibers.

  • system administrator (sysadmin)

    In information technology (IT), a system administrator (sysadmin) is a person who supports a multi-user computing environment and ensures continuous, optimal performance of IT services and support systems.

  • T

    T-carrier system

    To see the relationship between T-carrier, E-carrier, and DS0 multiples, see digital signal X. The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission.

  • T1 (T-1)

    Also see the T-carrier system, of which the T1 is a part.

  • TCP (Transmission Control Protocol)

    TCP (Transmission Control Protocol) is a standard that defines how to establish and maintain a network conversation through which application programs can exchange data.

  • TCP/IP (Transmission Control Protocol/Internet Protocol)

    TCP/IP, or the Transmission Control Protocol/Internet Protocol, is a suite of communication protocols used to interconnect network devices on the internet.

  • TCP/IP offload engine (TOE)

    The TCP/IP offload engine (TOE for short) is a technology that is gaining popularity in high-speed Ethernet systems for the purpose of optimizing throughput.

  • TDMA (time division multiple access)

    TDMA (time division multiple access) is a technology used in digital cellular telephone communication that divides each cellular channel into three time slots in order to increase the amount of data that can be carried. (Continued...)

  • Technical Office Protocol (TOP)

    Technical Office Protocol (TOP), also called Technical and Office Protocol, is a set of protocols intended for networks that perform distributed information processing in business offices... (Continued)

  • telco (telephone company)

    In the United States and possibly other countries, "telco" is a short form for telephone company.

  • telecenter

    A telecenter (US spelling) or telecentre (UK spelling) is a work location usually in a different place than the organization's main office that provides convenient occasional access for telecommuting to work equipment that they don't have at home or on the road.

  • telecom carrier

    A telecom carrier is a company that is authorized by regulatory agencies to operate a telecommunications system.

  • telecom cloud provider

    A telecom cloud provider is a telecommunications company that has shifted a significant part of its business from landline service to devote resources to providing cloud services.

  • telecommunications (telecom)

    Telecommunications is the transmission of data, voice and video over significant distances by electronic means that use a wide variety of networks and media.

  • Telecommunications Act of 1996

    The Telecommunications Act of 1996, enacted by the U.S. Congress on February 1, 1996, and signed into law by President Bill Clinton on February 8, 1996, provided major changes in laws affecting cable TV, telecommunications, and the Internet.

  • Telecommunications Display Device (TDD)

    A Telecommunications Display Device (TDD), also known as a text telephone, is a telephone equipped with a keyboard and a display for people who are hearing- or speech-impaired.

  • telematics

    Telematics uses GPS and mobile devices to send and receive information that helps control remote objects, primarily in the automotive industry.

  • telephone jacks

    In the U. S., telephone jacks are also known as registered jacks, sometimes described as RJ-XX, and are a series of telephone connection interfaces (receptacle and plug) that are registered with the U.S. Federal Communications Commission (FCC).

  • teleportation

    Teleportation is the duplication or re-creation of physical objects or their properties using light beams, according to researchers at the California Institute of Technology.

  • Telnet

    Telnet is a network protocol used to virtually access a computer and to provide a two-way, collaborative and text-based communication channel between two machines.

  • terahertz (THz)

    The terahertz, abbreviated THz, is a unit of electromagnetic (EM) wave frequency equal to one trillion hertz (1012 Hz).

  • terbo

    The suffix terbo appears in the V.32terbo modem protocol and indicates the third version of the V.32 protocol.

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