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Glossary
1 8 A B C D E F G H I J L M N O P Q R S T U V W
A
  • AAA

Short for authentication, authorization, and accounting, a system in IP-based networking to control what computer resources users have access to and to keep track of the activity of users over a network.

Authentication is the process of identifying an individual, usually based on a username and password. Authentication is based on the idea that each individual user will have unique information that sets him or her apart from other users.

Authorization is the process of granting or denying a user access to network resources once the user has been authenticated through the username and password. The amount of information and the amount of services the user has access to depend on the user's authorization level.

Accounting is the process of keeping track of a user's activity while accessing the network resources, including the amount of time spent in the network, the services accessed while there and the amount of data transferred during the session. Accounting data is used for trend analysis, capacity planning, billing, auditing and cost allocation.

  • absolute address

A fixed address in memory. The term absolute distinguishes it from a relative address, which indicates a location by specifying a distance from another location. Absolute addresses are also called real addresses and machine addresses.

  • AC

Alternating Current. An electrical power transmission system in which the direction of current flow alternates on a periodic basis.

  • access control

Refers to mechanisms and policies that restrict access to computer resources. Also see ACL.

  • access control entry

Abbreviated as ACE, access control entry is an entry in an access control list (ACL) that will grant or deny a user or group access to a resource. See also access control list (ACL).

  • Access List

List kept by routers to control access to or from the router for a number of services. For example, the list can prevent packets with a certain IP address from leaving a particular interface on the router.

  • accounting

In information technology, accounting is the process of keeping track of a user's activity while accessing a network's resources, including the amount of time spent in the network, the services accessed while there and the amount of data transferred during the session. Accounting data is used for trend analysis, capacity planning, billing, auditing and cost allocation. Also see AAA

  • Acknowledgment

Notification sent from one network device to another to acknowledge that some event (for example, receipt of a message) has occurred. Sometimes abbreviated ACK.

  • ACL

Short for access control list, a set of data that informs a computer's operating system which permissions, or access rights, that each user or group has to a specific system object, such as a directory or file. Each object has a unique security attribute that identifies which users have access to it, and the ACL is a list of each object and user access privileges such as read, write or execute.

  • Active Hub

Multiported device that amplifies LAN transmission signals.

 

  • ad-hoc mode

An 802.11 networking framework in which devices or stations communicate directly with each other, without the use of an access point (AP). Ad-hoc mode is also referred to as peer-to-peer mode or an Independent Basic Service Set (IBSS). Ad-hoc mode is useful for establishing a network where wireless infrastructure does not exist or where services are not required.

  • ADPCM

Short for Adaptive Differential Pulse Code Modulation, a form of pulse code modulation (PCM) that produces a digital signal with a lower bit rate than standard PCM. ADPCM produces a lower bit rate by recording only the difference between samples and adjusting the coding scale dynamically to accommodate large and small differences. Some applications use ADPCM to digitize a voice signal so voice and data can be transmitted simultaneously over a digital facility normally used only for one or the other

  • ADSL

Short for asymmetric digital subscriber line, ADSL is a type of DSL broadband communications technology used for connecting to the Internet. ADSL allows more data to be sent over existing copper telephone lines (POTS), when compared to traditional modem lines. A special filter, called a microfilter, is installed on a subscriber's telephone line to allow both ADSL and regular voice (telephone) services to be used at the same time. ADSL requires a special ADSL modem and subscribers must be in close geographical locations to the provider's central office to receive ADSL service. Typically this distance is within a radius of 2 to 2.5 miles. ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).

  • ADSL2+

ADSL+2 is an extension to ADSL broadband technology that provides subscribers with significantly faster download speeds when compared to traditional ADSL connections. ADSL+2 works in the same fashion as ADSL a special filter is installed on a subscriber's telephone line to split existing copper telephone lines (POTS) between regular telephone (voice) and ADSL+2. ADSL2+ service is most commonly offered in highly-populated metropolitan areas and subscribers must be in close geographical locations to the provider's central office to receive ADSL2+ service.

  • AES

Short for Advanced Encryption Standard, a symmetric 128-bit block data encryption technique developed by Belgian cryptographers Joan Daemen and Vincent Rijmen. The U.S government adopted the algorithm as its encryption technique in October 2000, replacing the DES encryption it used. AES works at multiple network layers simultaneously. The National Institute of Standards and Technology (NIST) of the U.S. Department of Commerce selected the algorithm, called Rijndael (pronounced Rhine Dahl or Rain Doll), out of a group of five algorithms under consideration, including one called MARS from a large research team at IBM. While the terms AES and Rijndael are used interchangeably, there are some differences between the two. AES has a fixed block size of 128-bits and a key size of 128, 192, or 256-bits, whereas Rijndael can be specified with any key and block sizes in a multiple of 32-bits, with a minimum of 128-bits and a maximum of 256-bits.

  • Alpha Ring (α-Ring)

Alpha Ring is a redundant protocol created by EtherWAN. In the event of a failed switch or switch port, an alternative route is created. The biggest advantage of Alpha Ring over STP, RSTP and MSTP is the time it takes to switch to a new path. Alpha Ring (α-Ring) switches to a new path in >15ms.

  • amplifier repeater

A repeater that cannot distinguish between a data signal and transmission noise along a network. An amplifier repeater will receive the signal and amplify it regardless of the integrity of the signal.

  • Analog

A continuous wave or signal (such as human voice).

  • Analog Loopback

A testing technique that isolates faults in transmission equipment by performing a loopback on the data at the analog (line) side of the modem.

  • Analog Transmission

The transmission of a continuously variable signal, as opposed to a discrete (digital) one.

  • AP

Short for Access Point, a hardware device or a computer's software that acts as a communication hub for users of a wireless device to connect to a wired LAN. APs are important for providing heightened wireless security and for extending the physical range of service a wireless user has access to.

  • arbitrated loop

A Fibre Channel standard defining a loop topology where up to 126 devices can communicate with one another using an arbitrated access protocol.

  • ARP

Short for Address Resolution Protocol, a network layer protocol used to convert an IP address into a physical address (called a DLC address), such as an Ethernet address. A host wishing to obtain a physical address broadcasts an ARP request onto the TCP/IP network. The host on the network that has the IP address in the request then replies with its physical hardware address. There is also Reverse ARP (RARP) which can be used by a host to discover its IP address. In this case, the host broadcasts its physical address and a RARP server replies with the host's IP address.

  • ARP spoofing

A method of attacking an Ethernet LAN by updating the target computers ARP cache with both a forged ARP request and reply packets in an effort to change the Layer 2 Ethernet MAC address (i.e., the address of the network card) to one that the attacker can monitor. Because the ARP replies have been forged, the target computer sends frames that were meant for the original destination to the attackers computer first so the frames can be read. A successful APR attempt is invisible to the user.

  • ARQ

Automatic Request for Repeat or Retransmission
A communications feature where the receiver asks the transmitter to resend a block or frame because errors were detected by the receiver.

  • ASCII

American Standard Code for Information Interchange
A seven-level code (128 possible characters) used for data transfer.

  • Asynchronous Transmission

A transmission method that sends units of data one character at a time. Characters are preceded by start bits and followed by stop bits, which provide synchronization at the receive terminal. Also called start-stop transmission.

  • attenuation

Reduction of signal strength during transmission. Attenuation is the opposite of amplification, and is normal when a signal is sent from one point to another. If the signal attenuates too much, it becomes unintelligible, which is why most networks require repeaters at regular intervals. Attenuation is measured in decibels.

  • attenuation crosstalk ratio

Also known as headroom, attenuation crosstalk ratio (ACR) is the difference between attenuation and crosstalk at a given frequency along a cable. Measured in decibels, ACR is a calculation used in networking transmission to assure that a signal transmitted across a twisted-pair cable is stronger at the receiving end than any interference signals imposed on that same pair by crosstalk from adjacent pairs.

  • AUI

Short for Attachment Unit Interface, the portion of the Ethernet standard that specifies how a cable is to be connected to an Ethernet card. AUI specifies a coaxial cable connected to a transceiver that plugs into a 15-pin socket on the network interface card (NIC).

  • auto partitioning

An Ethernet technology that isolates malfunctioning ports, devices and/or network lines from the rest of the network, stopping the transmission of data from flowing through the faulty network element. Auto partitioning is one method networks use to ensure that no data is lost during transmission. When a network detects a malfunction, such as collisions along the network, a disconnected port, a jamming signal or even the wrong type of or degraded wiring, the faulty element is automatically partitioned (i.e., further data is stopped from traveling the suspicious path) so that the integrity of the entire network is not compromised.

  • Auto-Negotiation

Auto-Negotiation is a technology that was introduced by National Semiconductor to the IEEE 802.3u 100BASE-T working group in the Spring of 1994 as a result of the need for a mechanism to accommodate multi-speed network devices. It's a mechanism that takes control of the cable when a connection is established to a network device. Auto-Negotiation detects the various modes that exist in the device on the other end of the wire and advertises it own abilities to automatically configure the highest performance mode of interoperation. As a standard technology, this allows simple, automatic connection of devices that support a variety of modes from a variety of manufacturers.

  • autodiscovery

1.     Term used to describe a set of tools that collects data on a network and records any changes made to the network assets. This could be changes made to memory, software versions, storage, new or deleted files and so on.

2.     In RSS terminology, autodiscovery is the process used by spiders to look for RSS content. When audodiscovery is enabled for your RSS feed, browsers and aggregators can then automatically detect the RSS feed, making it easier for users to subscribe to it.

  • Automatic Rate Fallback

Ensures that the logical channel remains open even if individual links fail, by automatically dropping to the next lower rate. When failed links are recovered, the original rate is restored.

  • Autonegotiation

Auto-Negotiation is a technology that was introduced by National Semiconductor to the IEEE 802.3u 100BASE-T working group in the Spring of 1994 as a result of the need for a mechanism to accommodate multi-speed network devices. It's a mechanism that takes control of the cable when a connection is established to a network device. Auto-Negotiation detects the various modes that exist in the device on the other end of the wire and advertises it own abilities to automatically configure the highest performance mode of interoperation. As a standard technology, this allows simple, automatic connection of devices that support a variety of modes from a variety of manufacturers.

  • AWG

The American Wire Gauge System, which specifies wire width.