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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  • P

    What are port numbers and how do they work?

    A port number is a way to identify a specific process to which an internet or other network message is to be forwarded when it arrives at a server.

  • What are predictive networks and how do they work?

    Predictive networks are intelligent IT network systems that use artificial intelligence (AI), machine learning (ML) and real-time analytics to anticipate and proactively address network issues before they occur.

  • What is a point of presence (PoP)?

    A point of presence (PoP) is a point or physical location where two or more networks or communication devices build a connection from one place to the rest of the internet.

  • What is a programmable network (network programmability)?

    A programmable network is one in which software that operates independently of network hardware handles the behavior of network devices and flow control.

  • What is a protocol data unit (PDU)?

    A protocol data unit (PDU) is the basic unit of exchange between entities that communicate with a specified networking protocol.

  • What is packet loss in networking?

    Packet loss is when one or more transmitted data packets fail to arrive at their destination.

  • What is ping and how does it work?

    Ping (Packet Internet Groper) is a basic internet program that enables a user to test and verify if a particular destination Internet Protocol (IP) address is reachable and can respond to network requests.

  • What is Point-to-Point Protocol over Ethernet (PPPoE)?

    Point-to-Point Protocol over Ethernet (PPPoE) is a network protocol that facilitates communication between network endpoints.

  • What is port address translation (PAT)?

    Port address translation (PAT) is a type of network address translation (NAT) that maps a network's private internal IPv4 addresses to a single public Internet Protocol address by using network ports.

  • What is PSTN (public switched telephone network)?

    PSTN (public switched telephone network) is the world's collection of interconnected voice-oriented public telephone networks via traditional circuit-switched networks.

  • Q

    What is QAM (quadrature amplitude modulation) and how does it work?

    QAM (quadrature amplitude modulation) is a method of combining two amplitude modulation (AM) signals into a single channel.

  • R

    radio access network (RAN)

    A radio access network (RAN) is a major component of a wireless telecommunications system that connects individual devices to other parts of a network through a radio link.

  • radio frequency (RF, rf)

    Radio frequency (RF) is a measurement representing the oscillation rate of electromagnetic radiation spectrum, or electromagnetic radio waves, from frequencies ranging from 300 GHz to as low as 9 kHz.

  • Real-time Transport Protocol (RTP)

    Real-time Transport Protocol (RTP) is a network standard designed for transmitting audio or video data that is optimized for consistent delivery of live data.

  • remote infrastructure management

    Remote infrastructure management, or RIM, is a comprehensive approach to handling and overseeing an organization's IT infrastructure, systems and services from a remote location.

  • Reverse Address Resolution Protocol (RARP)

    Reverse Address Resolution Protocol (RARP) is a protocol a physical machine in a local area network (LAN) can use to request its IP address.

  • routing table

    A routing table is a set of rules, often viewed in table format, that's used to determine where data packets traveling over an Internet Protocol (IP) network will be directed.

  • RS-232C

    RS-232C is one of the earlier versions of the long-established standard RS-232, which defines a physical interface for relatively low-speed serial data communication between computers and related devices.

  • runbook

    Runbooks are a set of standardized written procedures for completing repetitive IT processes within a company.

  • What is Routing Information Protocol (RIP)?

    Routing Information Protocol (RIP) is a distance vector protocol that uses hop count as its primary metric.

  • S

    Seebeck effect

    The Seebeck effect is a phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances.

  • serial digital interface (SDI)

    Serial digital interface (SDI) is a standard for digital video and audio transmission over coaxial or fiber optic cabling.

  • Service Profile Identifier (SPID)

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

  • 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.

  • session layer

    The session layer is Layer 5 of the OSI communications model. It is the long-lived logical connection that persists between endpoints over time.

  • Signaling System 7 (SS7)

    Signaling System 7 (SS7) is an international telecommunication protocol standard that defines how the network elements in a public switched telephone network (PSTN) exchange information and control signals.

  • single-user multiple input, multiple output (SU-MIMO)

    Single-user multiple input, multiple output (SU-MIMO) is a multitransmitter and receiver technology that lets a wireless access point send multiple, simultaneous data streams to one compatible endpoint at a time.

  • sliding window (windowing)

    The sliding window (windowing) technique is used by Transmission Control Protocol (TCP) to manage the flow of packets between two computers or network hosts.

  • Snort

    Snort is an open source network intrusion detection system (NIDS) created by Sourcefire founder and former CTO Martin Roesch.

  • spectrum analyzer

    A spectrum analyzer is a device that measures and displays signal amplitude (strength) as it varies by frequency within its frequency range (spectrum).

  • split horizon

    Split horizon is a method used by distance vector protocols to prevent network routing loops.

  • star network

    A star network is a local area network (LAN) topology in which all nodes -- personal computers (PCs), workstations or other devices -- are directly connected to a common central computer that is often referred to as a hub.

  • stateful inspection

    Stateful inspection, also known as dynamic packet filtering, 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.

  • Stream Control Transmission Protocol (SCTP)

    Stream Control Transmission Protocol (SCTP) is a connection-oriented network protocol for transmitting multiple streams of data simultaneously between two endpoints that have established a connection in a network.

  • subcarrier

    A subcarrier is a secondary modulated signal frequency modulated into the main frequency (the carrier) to provide an additional channel of transmission.

  • Switched Multimegabit Data Service (SMDS)

    Switched Multimegabit Data Service (SMDS) 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.

  • SYN scanning

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

  • Synchronous Data Link Control (SDLC)

    Synchronous Data Link Control (SDLC) is a transmission protocol used to synchronously transfer code-transparent, serial-by-bit data over a communications channel.

  • Synchronous Digital Hierarchy (SDH)

    Synchronous Digital Hierarchy (SDH) is a group of fiber optic transmission rates that transport digital signals with different capacities.

  • system administrator (sysadmin)

    A system administrator (sysadmin) is an information technolog professional who supports a multiuser computing environment and ensures continuous, optimal performance of IT services and support systems.

  • What is a self-organizing network (SON) and do you need one?

    A self-organizing network (SON) is an intelligent infrastructure designed to simplify and accelerate the planning, configuration, management, optimization and healing of mobile radio access networks (RANs).

  • What is an SD-branch?

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

  • What is an SDN controller (software-defined networking controller)?

    A software-defined networking controller is an application in SDN architecture that manages Flow control for improved network management and application performance.

  • What is shielded twisted pair (STP) and how does it work?

    Shielded twisted pair (STP) is a kind of cable made up of smaller wires where each small pair of wires is twisted together and has an outer coating to electrically shield it.

  • What is signal-to-noise ratio and how is it measured?

    A signal-to-noise ratio compares the strength of a desired signal with any undesired signals created by background noise.

  • What is streaming network telemetry?

    Streaming network telemetry is a real-time data collection service in which network devices, such as routers, switches and firewalls, continuously push data related to the network's health to a centralized location.

  • What is Synchronous Optical Network (SONET)?

    Synchronous Optical Network (SONET) is a North American standardized digital communication protocol for synchronous data transmission over optical fibers.

  • What is the Server Message Block (SMB) protocol? How does it work?

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

  • T

    ternary content-addressable memory (TCAM)

    Ternary content-addressable memory (TCAM) is a specialized type of high-speed memory that searches its entire contents in a single clock cycle.

  • Time Division Multiple Access (TDMA)

    Time Division Multiple Access (TDMA) is a digital modulation technique used in digital cellular telephone and mobile radio communication.

  • token ring

    A token ring is a data link for a local area network (LAN) in which all devices are connected in a ring or star topology and pass one or more tokens from host to host.

  • top-of-rack switching

    Top-of-rack switching is a data center architecture design in which computing equipment like servers, appliances and other switches located within the same or adjacent rack connect to an in-rack network switch.

  • transceiver

    A transceiver is a combination transmitter/receiver in a single package.

  • Transmission Control Protocol (TCP)

    Transmission Control Protocol (TCP) is a standard protocol on the internet that ensures the reliable transmission of data between devices on a network.

  • transport layer

    The transport layer is Layer 4 of the Open Systems Interconnection (OSI) communications model. It is responsible for ensuring that the data packets arrive accurately and reliably between sender and receiver.

  • trunk (trunking)

    A network trunk is a communications line or link designed to carry multiple signals simultaneously to provide network access between two points.

  • tunneling or port forwarding

    Tunneling or port forwarding is the transmission of data intended for use only within a private -- usually corporate -- network through a public network in such a way that the public network's routing nodes are unaware that the transmission is part of a private network.

  • What is a thin client (lean client)?

    A thin client (lean client) is a virtual desktop computing model that runs on the resources stored on a central server instead of a computer's resources.

  • What is TCP/IP?

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

  • What is telecommunications (telecom)?

    Telecommunications, also known as telecom, is the exchange of information over significant distances by electronic means and refers to all types of voice, data and video transmission.

  • What is telematics?

    Telematics is a term that combines the words 'telecommunications' and 'informatics' to describe the use of communications and IT to transmit, store and receive information from devices to remote objects over a network.

  • What is Telnet?

    Telnet is a network protocol used to remotely access a computer for a text-based communication channel between two machines.

  • What is throughput?

    Throughput is a measure of how many units of information a system can process in a given amount of time.

  • What is traffic shaping (packet shaping)?

    Traffic shaping, also known as packet shaping, is a congestion management method that regulates network data transfer by delaying the flow of less important or less desired packets.

  • U

    Uuencode (Uuencode/Uudecode)

    Uuencode (also called Uuencode/Uudecode) is a popular utility for encoding and decoding files exchanged between users or systems in a network.

  • What is a URL (Uniform Resource Locator)?

    A URL (Uniform Resource Locator) is a unique identifier used to locate a resource on the internet.

  • What is an unshielded twisted pair (UTP)?

    Unshielded twisted pair (UTP) is a ubiquitous type of copper cabling used in networking technologies, such as telephone wiring and local area networks (LANs).

  • What is the Universal Service Fund (USF)?

    The Universal Service Fund (USF) is a United States government program that supports telecommunications access and affordability in rural and low-income communities.

  • What is USSD (Unstructured Supplementary Service Data)?

    USSD (Unstructured Supplementary Service Data) is a GSM (Global System for Mobile) communications protocol that is used to send text messages.

  • V

    Variable Length Subnet Mask (VLSM)

    Variable Length Subnet Mask (VLSM) is a subnet -- a segmented piece of a larger network -- design strategy where all subnet masks can have varying sizes.

  • virtual network adapter

    A virtual network adapter is software that operates like a physical network adapter within the host operating system (OS) or through an application installed on the endpoint or server.

  • virtual routing and forwarding (VRF)

    Virtual routing and forwarding (VRF) is a technology included in Internet Protocol (IP) network routers that enables multiple instances of a routing table to exist in a virtual router and work simultaneously.

  • virtual server

    A virtual server, also known as a virtual machine (VM), is a partitioned space inside a real server and is transparent to users, replicating the functionality of a dedicated physical server.

  • visitor-based networking (visitor-based network)

    Visitor-based networking (VBN) is a computer network with high-speed internet access provided by an organization for temporary use by visitors, guests or other users in a public area.

  • What is voice over LTE (VoLTE)?

    Voice over LTE (VoLTE) is a digital packet technology that uses 4G Long-Term Evolution networks to route voice traffic and transmit data.

  • W

    well-known port numbers

    The well-known port numbers are the port numbers that are reserved for assignment by the Internet Corporation for Assigned Names and Numbers (ICANN) for use by the application end points that communicate using the Internet's Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP).

  • What is a wireless sensor network (WSN)?

    A wireless sensor network (WSN) is a distributed network of spatially distributed sensors that communicate wirelessly to collect, monitor, and transmit environmental or physical condition data to a central system or cloud platform for analysis.

  • What is wavelength?

    Wavelength is the distance between identical points, or adjacent crests, in the adjacent cycles of a waveform signal propagated in space or along a wire.