A

ACK

The acknowledgment message sent between two hosts during a TCP session.

ACL (access control list)

The list of trustees assigned to a file or directory. A trustee can be any object that is available to the security subsystem.

Active Directory

An X.500-compliant directory services system created by Microsoft for use on Windows 2000 networks.

active hub

A hub that has power supplied to it for the purposes of regenerating the signals that pass through it.

active termination

A termination system used on a SCSI bus. Unlike passive termination, which uses voltage resistors, active termination uses voltage regulators to create the termination voltage.

address

A set of numbers, usually expressed in binary format, used to identify and locate a resource or device on a network.

administrator

A person who is responsible for the control and security of the user accounts, resources, and data on a network.

Administrator account

In a Windows NT system, the default account that has rights to access everything and to assign rights to other users on the network. Unlike other user accounts, the Administrator account cannot be deleted.

ADSL (Asymmetric Digital Subscriber Line)

A service that transmits digital voice and data over existing (analog) phone lines.

ANSI (American National Standards Institute)

An organization that publishes standards for communications, programming languages, and networking.

antivirus software

A type of software that detects and removes virus programs.

anycast address

An address that is used in ATM for shared multiple-end systems. An anycast address allows a frame to be sent to specific groups of hosts (rather than to all hosts, as with simple broadcasting).

application layer

Layer 7 of the OSI model, which provides support for end users and for application programs that are using network resources.

Application log

A log that is located in Windows NT/2000 Event Viewer and provides information on events that occur within an application.

archive bit

A flag that is set on a file after it has been created or altered. Some backup methods reset the flag to indicate that it has been backed up.

ARCnet (Attached Resource Computer Network)

A token-bus LAN technology used in the 1970s and 1980s.

ARP (Address Resolution Protocol)

A protocol in the TCP/IP protocol suite that is used to resolve IP addresses to MAC addresses.

ARP table

A table of entries used by ARP to store resolved ARP requests. Entries can also be stored manually.

array

A group of devices arranged in a fault-tolerant configuration.

See also [Redundant Arrays of Inexpensive Disks]

ATM (Asynchronous Transfer Mode)

A high-speed WAN technology that uses fixed cells of 53 bytes each.

attenuation

The loss of signal that is experienced as data is transmitted across network media.

AUI (attachment unit interface)

An IEEE 802.3-specified interface that is used between a MAU and an NIC.

AUI connector

A 15-pin D-type connector that is sometimes used with Ethernet connections.

authentication

The process by which a user's identity is validated on a network. The most common authentication method is a username and password combination.