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Bring yourself up to speed with our introductory content.
Get started
Bring yourself up to speed with our introductory content.
fax
A fax (short for facsimile and sometimes called telecopying) is the telephonic transmission of scanned-in printed material (text or images), usually to a telephone number associated with a printer or other output device. Continue Reading
Routing versus routed protocols and the CCNA
Many networking professionals don't really know what a routing protocol is or does. There are those who also couldn't tell you the difference between a routing protocol and a routed protocol. If you are working as a network engineer or preparing to ... Continue Reading
OpenNMS, an introduction: Affordable network management
Open source expert Maria Winslow brings network managers up to speed about the free open source enterprise-grade network-management system OpenNMS. Continue Reading
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Wireless networking (CWNA)
Do you think you know a lot about wireless networking? Are you interested in taking the Certified Wireless Network Administrator (CWNA) exam? Test your knowledge with our 13-question quiz on wireless networking! Continue Reading
firehose effect
A firehose effect occurs in a network when the source (transmitting) computer or terminal sends data too fast for a destination (receiving) computer or terminal to deal with it. The term comes from the analogy between a data stream and the flow of ... Continue Reading
Ethernet point-of-presence (EPOP)
Ethernet point-of-presence (EPOP) is a technology developed by Level 3 Communications that provides widespread access to broadband networks. As a large network increases its bandwidth, it can include large and expanding groups of subscribers. This ...Continue Reading
Content Delivery Networking: an introduction
Doug Downer gives an overview of Content Delivery Network (CDN) technology and its components, which bring together the functionality of file access, caching, multimedia delivery and application processing.Continue Reading
capacity planning
In information technology, capacity planning is the science and art of estimating the space, computer hardware, software and connection infrastructure resources that will be needed over some future period of time.Continue Reading
isochronous
In information technology, isochronous (from the Greek "equal" and "time"; pronounced "eye-SAH-krun-us") pertains to processes that require timing coordination to be successful, such as voice and digital video transmission.Continue Reading
H.323
H.323 is a standard approved by the International Telecommunication Union (ITU) in 1996 to promote compatibility in videoconference transmissions over IP networks.Continue Reading
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multicast
Multicast is communication between a single sender and multiple receivers on a network.Continue Reading
802.11a
802.11a is one of several specifications in the 802.11 family applicable to wireless local area networks (wireless LANs or WLANs).Continue Reading
Clientless VPN: Artful misnomer, useful technology
They may not be completely clientless, but clientless VPNs can provide secure, user-friendly and largely affordable solutions to enable remote access over the Internet.Continue Reading
Securing your Layer 2 network: Don't overlook the basics
Before dropping substantial cash on a fancy surveillance system, most sensible home owners would ensure that their doors and windows were locked. Similarly, there are simple security measures you can take to configure your systems for Layer 2 ...Continue Reading
terminal
In data communications, a terminal is any device that terminates one end (sender or receiver) of a communicated signal.Continue Reading
handshaking
In telephone communication, handshaking is the exchange of information between two modems and the resulting agreement about which protocol to use that precedes each telephone connection.Continue Reading
home server
A home server is a computer that functions as a server in a client-server home network.Continue Reading
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.Continue Reading
802.11 Learning Guide
802.11 is perhaps the fastest-changing network protocol around. We've gathered a wealth of information to get you up-to-speed quickly on the various specifications. Learn about all the 802.11 wireless LAN (WLAN) specifications in this learning guide.Continue Reading
wink
In telecommunications, a wink is a signal in the form of a brief interruption in an otherwise continuous signal.Continue Reading
cloud
In telecommunications, a cloud is the unpredictable part of any network through which data passes between two end points.Continue Reading
OSI model: Crash Course
The OSI model is the conceptual backbone of most enterprise networks, but do you remember all the details? Read our rundown of the OSI model and what all those layers do.Continue Reading
Crash Course: Firewalls
Firewalls aren't as simple as they used to be. Use our Crash Course to learn the latest and make sure your firewall is right for your network.Continue Reading
port
On computer and telecommunication devices, a port (noun) is generally a specific place for being physically connected to some other device, usually with a socket and plug of some kind.Continue Reading
acceleration hardware
Acceleration hardware is a general term that refers to devices that speed up data communications, storage and retrieval, encryption and decryption, mathematical operations, graphics, and Web page viewing. Acceleration hardware can consist of an ...Continue Reading
encoding and decoding
Encoding is the process of putting a sequence of characters (letters, numbers, punctuation, and certain symbols) into a specialized digital format for efficient transmission or transfer. Decoding is the opposite process -- the conversion of a ...Continue Reading
Turtle Firewall
Turtle Firewall is an open source firewall program written in Perl that supports Linux Kernels 2.4.x and iptables. Turtle Firewall was written by Andrea Frigido of Frisoft, and is available under the GNU Public License (GPL) .Continue Reading
Wireless LAN quiz answers
Wireless LANs quiz answer key.Continue Reading
Wireless LAN quiz
Take our wireless LAN quiz to find out how much you know about WLAN technologies.Continue Reading
Link Quality Source Routing (LQSR)
LQSR (Link Quality Source Routing) is a routing protocol for wireless mesh networks. The protocol was developed by Microsoft for use with their MCL (Mesh Connectivity Layer) technology, which facilitates the interconnection of computers into a mesh ...Continue Reading
E.164
E.164 is an international numbering plan for public telephone systems in which each assigned number contains a country code (CC), a national destination code (NDC), and a subscriber number (SN).Continue Reading
packet mangling
Packet mangling is the modification of packets at a packet-based network interface before and/or after routing.Continue Reading
Media Access Control layer (MAC layer)
In the Open Systems Interconnection (OSI) model of communication, the Media Access Control layer is one of two sublayers of the Data Link Control layer and is concerned with sharing the physical connection to the network among several computers.Continue Reading
Morse code
Morse code is a method of sending text messages by keying in a series of electronic pulses, usually represented as a short pulse (called a "dot") and a long pulse (a "dash").Continue Reading
Resilient Packet Ring (RPR)
Resilient Packet Ring (RPR) is a network topology being developed as a new standard for fiber optic rings.Continue Reading
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.Continue Reading
open relay (insecure relay or a third-party relay)
An open relay (sometimes called an insecure relay or a third-party relay) is an SMTP e-mail server that allows third-party relay of e-mail messages.Continue Reading
Snort
Snort is an open source network intrusion detection system (NIDS) created by Martin Roesch.Continue Reading
packet filtering
On the Internet, packet filtering is the process of passing or blocking packets at a network interface based on source and destination addresses, ports, or protocols.Continue Reading
Serial Digital Interface (SDI)
Serial Digital Interface (SDI) is a standard for digital video transmission over coaxial cable.Continue Reading
varicode
Varicode is a method of binary character encoding in which the number of bits for each character is not fixed, but varies for each character depending on how often that character occurs in general usage.Continue Reading
MFSK (multiple frequency shift keying)
MFSK (multiple frequency shift keying), also called multi-frequency shift keying, is a method of signal modulation in which discrete audio tone bursts of various frequencies convey digital data.Continue Reading
keystone jack
A keystone jack is a female connector used in data communications, particularly local area networks (LANs).Continue Reading
chiral fiber
Chiral fiber is a specialized optical fiber medium with its core twisted into a helical shape.Continue Reading
network perimeter
A network perimeter is the boundary between the private and locally managed-and-owned side of a network and the public and usually provider-managed side of a network.Continue Reading
Infranet Initiative
The Infranet Initiative is a collaborative effort to develop a high-performance universal public network that would serve as a supplement to the Internet for businesses and other high-demand users.Continue Reading
zone
In general, a zone is an area of administration.Continue Reading
B8ZS (bipolar 8-zero substitution, binary 8-zero substitution, clear channel, clear 64)
B8ZS (bipolar 8-zero substitution, also called binary 8-zero substitution, clear channel, and clear 64) is an encoding method used on T1 circuits that inserts two successive ones of the same voltage - referred to as a bipolar violation - into a ...Continue Reading
distributive numerical control (DNC)
Distributive numerical control (DNC) is a technology that allows a single computer to be networked with one or more machines that use computer numerical control (CNC).Continue Reading
terahertz (THz)
The terahertz, abbreviated THz, is a unit of electromagnetic (EM) wave frequency equal to one trillion hertz (1012 Hz).Continue Reading
multimode fiber
In optical fiber technology, multimode fiber is optical fiber that is designed to carry multiple light rays or modes concurrently, each at a slightly different reflection angle within the optical fiber core.Continue Reading
discrete multitone (DMT)
Discrete multitone (DMT) is a method of separating a Digital Subscriber Line (DSL) signal so that the usable frequency range is separated into 256 frequency bands (or channels) of 4.3125 KHz each.Continue Reading
queries-per-second (QPS)
Queries-per-second (QPS) (or the query-per-second rate) is a measure of how much traffic a particular query server is handling at a given time.Continue Reading
RCA connector
An RCA connector is a plug and a jack designed for use with coaxial cable for frequencies ranging from the very lowest up to several megahertz.Continue Reading
coarse wavelength division multiplexing (CWDM)
Coarse wavelength division multiplexing (CWDM) is a method of combining multiple signals on laser beams at various wavelengths for transmission along fiber optic cables, such that the number of channels is fewer than in dense wavelength division ...Continue Reading
long-haul optics
Long-haul optics refers to the transmission of visible light signals over optical fiber cable for great distances, especially without or with minimal use of repeaters.Continue Reading
triangulation
Triangulation is a process by which the location of a radio transmitter can be determined by measuring either the radial distance, or the direction, of the received signal from two or three different points.Continue Reading
integrated T1 (channelized T1)
Integrated T1 (also called channelized T is a digital carrier modulation method in which a T1 line is divided into 24 channels, each having a maximum data speed of 64 thousand bits per second (Kbps), and each capable of supporting a unique ...Continue Reading
CDSL (Consumer Digital Subscriber Line)
Also see our Fast guide to DSL. CDSL (Consumer Digital Subscriber Line) is a version of Digital Subscriber Line (DSL) service, trademarked by Rockwell Corp.Continue Reading
A-Law
A-Law is the standard codec (compression/decompression) algorithm for pulse code modulation (PCM) from the ITU-T (the Telecommunication Standardization Sector of the International Telecommunications Union).Continue Reading
ping sweep (ICMP sweep)
A ping sweep (also known as an ICMP sweep) is a basic network scanning technique used to determine which of a range of IP addresses map to live hosts (computers).Continue Reading
gigapop (gigabit point-of-presence)
Gigapop is short for gigabit point-of-presence, an access point to Internet2, the network collaboration between universities and partners in industry and government to develop advanced Internet technologies and applications such as telemedicine and ...Continue Reading
whiteboard
A whiteboard is a non-electronic variation of the traditional "rewriteable" schoolroom blackboard, but is white instead of black and of a material that can be written on with colored markers (known as dry erase markers).Continue Reading
NSFNET
NSFNET was a network for research computing deployed in the mid-1980s that in time also became the first backbone infrastructure for the commercial public Internet.Continue Reading
mu-Law
Mu-Law is the standard codec (compression/decompression) algorithm for pulse code modulation (PCM) from the CCITT (Consultative Committee for International Telephone and Telegraph).Continue Reading
E-ZPass
E-ZPass is a toll collection system in the northeastern U.S. that uses RFID technology to allow a driver to pass through a tollbooth and pay the toll without stopping the vehicle.Continue Reading
information theory
Information theory is a branch of mathematics that overlaps into communications engineering, biology, medical science, sociology, and psychology.Continue Reading
HELLO packet
In the Open Shortest Path First (OSPF) communications protocol - which enables network routers to share information with each other, a HELLO packet is a special packet (message) that is sent out periodically from a router to establish and confirm ...Continue Reading
hoot-n-holler
In telecommunications, a hoot-n-holler is a dedicated "always on" connection used for two-way business-to-business voice communication.Continue Reading
Freephone
In the U.K., Freephone is a type of Number Translation Service (NTS) that allows a phone user to call a non-geographic number beginning with 0800 or 0500 without incurring a charge.Continue Reading
multi-tapping
Multi-tapping is an older procedure used to enter text using a telephone keypad.Continue Reading
Home Location Register (HLR)
The Home Location Register (HLR) is the main database of permanent subscriber information for a mobile network.Continue Reading
line doubler
A line doubler is an electronic device that converts analog or digital television (TV) video signals into a format suitable for display on a computer monitor.Continue Reading
circular mil
The circular mil is a unit of area used especially when denoting the cross-sectional size of a wire or cable.Continue Reading
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.Continue Reading
DTTV (digital terrestrial television)
DTTV (digital terrestrial television, sometimes also abbreviated DTT) is digital television (DTV) broadcast entirely over earthbound circuits.Continue Reading
Bel
In electronics and communications, the Bel expresses the logarithmic ratio between two levels of signal power, voltage, or current.Continue Reading
Direct Access File System (DAFS)
Direct Access File System (DAFS) is a network file system, similar to Network File System (NFS) and Common Internet File System (CIFS), that allows applications to transfer data while bypassing operating system control, buffering, and network ...Continue Reading
autofax
Autofax is the automatic (computer-initiated) sending of a facsimile (fax) message over a network in one of two ways: ( to a receiving computer or fax machine that is always ready to receive and store or immediately print such transmissions or (2), ...Continue Reading
G.703
G.703 is a CCITT standard for transmitting voice over digital carriers such as T1 and E1. G.703 provides the specifications for pulse code modulation (PCM) at data rates from 64 Kbps to 2.048 Mbps.Continue Reading
GNSS (Global Navigation Satellite System)
GNSS (Global Navigation Satellite System) is a satellite system that is used to pinpoint the geographic location of a user's receiver anywhere in the world.Continue Reading
IPLC (international private leased circuit)
An IPLC (international private leased circuit) is a point-to-point private line used by an organization to communicate between offices that are geographically dispersed throughout the world.Continue Reading
EtherLoop
EtherLoop, sometimes called next generation DSL or second generation DSL, combines features of Digital Subscriber Line (DSL) with features of Ethernet to provide both voice and data transmission (including Internet connection) over any ordinary ...Continue Reading
wrap plug
A wrap plug, also known as a loopback plug, is a special plug that can be inserted into a port on a communications device to perform a diagnostic test called a loopback test.Continue Reading
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.Continue Reading
electronic program guide (EPG)
An electronic program guide (EPG) is an application used with digital set-top boxes and newer television sets to list current and scheduled programs that are or will be available on each channel and a short summary or commentary for each program.Continue Reading
tree network
In telecommunication networks, a tree network is a combination of two or more star networks connected together.Continue Reading
satellite news gathering (SNG)
Satellite news gathering (SNG) is the use of mobile communications equipment for the purpose of worldwide newscasting.Continue Reading
care-of address
In Internet routing, a care-of address is a temporary IP address for a mobile node (mobile device) that enables message delivery when the device is connecting from somewhere other than its home network.Continue Reading
home address
In the Mobile Internet Protocol (Mobile IP), a home address is the relatively permanent IP address given to a mobile node.Continue Reading
NIC handle (Network Information Center handle)
A NIC (Network Information Center) handle is an alphanumeric character sequence that is unique for each entry in the database of all Internet domain name registrants.Continue Reading
Parlay
Parlay (pronounced PAHR-LAY as in the French verb "parler" - to speak) is an evolving set of specifications for industry-standard application programming interfaces (APIs) for managing network "edge" services such as call control, messaging, and ...Continue Reading
Number Translation Service (NTS)
In the U.K., Number Translation Service (NTS) is the service of routing a telephone call with a non-geographic number beginning with 07, 08, or 09 to a hidden geographic or mobile number.Continue Reading
Transport Services Access Point (TSAP)
A Transport Services Access Point (TSAP) is an end-point for communication between the Transport layer (layer 4) and the Session layer in the OSI (Open Systems Interconnection) reference model.Continue Reading
file server
In the client/server model, a file server is a computer responsible for the central storage and management of data files so that other computers on the same network can access the files.Continue Reading
LAN party
A LAN party is a gathering in which gamers (devotees of computer games) gather to share a local area network (LAN) and participate in extended gaming sessions of popular games such as Quake, Doom, or Wolfenstein.Continue Reading
catchment area
In the context of communication networks, a catchment area describes the geographical boundries of a network's components, including its connecting lines.Continue Reading
bus network
A bus network is an arrangement in a local area network (LAN) in which each node (workstation or other device) is connected to a main cable or link called the bus.Continue Reading
Kazaa Media Desktop (KMD)
Kazaa (its full name is Kazaa Media Desktop or KMD) is a decentralized Internet peer-to-peer (P2P) file-sharing program owned by Sharman Networks.Continue Reading
DoPa (DoCoMo Packet Transmission)
DoPa (DoCoMo Packet Transmission) is a packet-switched network service developed by NTT DoCoMo in Japan for Internet connection from mobile devices.Continue Reading