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• ACD (Automatic Call Distribution/Distributor) A specialized phone system, or the service it provides, for handling many incoming calls. Typically used by airlines and hotels, it recognizes and answers incoming calls according to instructions in a database, before sending the call to an operator or agent. It also offers management information on the type and volume of calls and efficiency of the agents.
  
• ACF/NCP (Advanced Communication Function/Network Control Program) In host based IBM SNA networks, it is the control software running on a communications controller that supports the operation of the SNA backbone network.
  
• ACF/VTAM (Advanced Communication Function/Virtual Terminal Access Method) In host-based IBM SNA networks, it is the control software running or a host computer that allows the host to communicate with networked terminals.
  
• Actius (Association of Computer Telephone Integration Users and Suppliers) A UK forum for users and suppliers to increase awareness of the business benefits of CTI. Act us develops education programs and information campaigns on CTI.
  
• Address One or a group of characters specifying the recipient or originator of transmitted data. An address car also denote the position of data in computer memory or the data packet itself while in transit through a network. IEEE 802.3 and 802.5 recommend having a unique address for each device worldwide.
  
• ADPCM (Adaptive Differential Pulse Code Modulation) A ITU-TS standard technique for voice encoding and compression. It allows an analog to be carried within a 32Kbit/s digital channel.
  
• Adjusted Ring Length When a segment of Token Ring (in practice a dual ring) trunk cable fails, a function known as the Wrap connects the main path to the backup path. In the worst case - the longest path - would occur if the shortest trunk cable segment tailed, so ARL is calculated during network design to ensure the system will always work.
  
• Agent A software-driven process running on a communications or networking device that allows that device to participate in a network management system. For example, an SNMP agent running on a router provides the ability for the router to exchange information with an SNMP network management system through the use of the SNMP protocol.
  
• ADSP (Apple Datastream Protocol) A transport mechanism for interprocess communications between Apple Macintosh and Dec Vax minicomputers.
  
• AFP (Apple Filing Protocol) A standard means of presenting the filing system of a server to the user with a consistent Apple Macintosh interface.
  
• Aggregate bandwidth The total bandwidth of channel carrying a multiplexed bit stream.
  
• Alerts Messages that Microsoft's LAN Manager network operating system sends under certain conditions. The three classes of alerts are admin alerts, error alerts and printer alerts.
  
• Algorithm A process or set of rules necessary for a computer or intelligent device to perform a task, such as voice compression.
  
• Alternate buffer Two buffers are sometimes used to handle data I/0. These are a alternated to achieve continuous throughput.
  
• Alternate routing - Safety technique enabling communication to continue iii the event of node failure or congestion. The network design allows for alternate paths through the network to arrive at the same destination.
  
• Analog An analog (US analog) signal is electrical and varies constantly in voltage, unlike a digital signal which varies between two constant values, usually denoted as 0 and 1. The value of the analog signal varies all the time during transmission, whereas a digital signal changes on y between two set values without intermediate variations.
  
• Ansi (American National Standards Institute) A group that defines US standards for the information processing industry. Ansi participates in defining network protocol standards and represents the US on other international standards-setting bodies like ISO.
  
• Applications Programming Interface (API) Software designed to make computer functions available to an application program PC and network operating systems have them. APIs in a network must be compatible to ensure programs are accessible to machines other than those they reside in. Some APIs, such as NetBios, are de facto standards.
  
• APPC (Advanced Program-to-Program Communications) A set of IBM protocols also known as LU 6.2 and Type 2.1 architectures. It functions within SNA's APPN to support peer to-peer communications between workstations attached to SNA LANs and the applications running on those workstations. It was added to SNA as part of the "new" SNA to support peer to-peer networking, unlike the traditional hierarchical SNA approach in which the mainframe acts as host or master and treats the other computer as a terminal or slave.
  
• APPC/PC A version of APPC developed by IBM to run on PC based Token Ring networks.
  
• APPN (Advanced Peer to Peer Networking) An extension to SNA which routes information around the IBM network without help from the host, allowing systems to adjust dynamically to the topology of the network (dynamic routing). APPN keeps track of network topology, making it easier to connect and reconfigure. It also creates a directory of network nodes and other resources. APPN also allows for dynamic SNA networks, where nodes can join and leave the network as required, and session routes can be selected as needed.
  
• AppleShare Apple system software that allows sharing of files and network services via a file server in the Apple Macintosh environment.
  
• AppleTalk A seven- layer protocol stack developed by Apple for communications between its Apple Macintosh product range. Apple defines it in similar terms to the functionality of the seven-layer OSI model.
  
• Application Layer The top layer in the OSI Reference Model comprising the interface between the OSI environment and a user's application. It does not contain applications, but provides a link from application software on one system to applications an another computer through the OSI environment. Several applications layers support different user tasks such as e mail and file transfer and transaction processing.
  
• ARP (Address Resolution Protocol) The lnternet and TCP/IP protocol used to bind dynamically a high-level IP address, such as an lnternet address, to a low-level physical hardware address. ARP operates only across a single physical network and is limited to networks supporting hardware broadcast.
  
• Arpanet The Advanced Research Projects Agency Network developed by the eponymous research agency in the 1960s as the first, large scale, packet switched network. It is still I in use today, connecting a large number of universities in the US and Europe, as well as commercial users.
  
• ASCII The American Standard Code for Information Interchange developed by ANS I to encode characters in seven bit units. These are normally padded out with an eighth bit that can represent parity to make up an eight-bit byte. This eighth bit can also be used to make ASCII support international character sets, extending the 128 possible seven-bit combinations to 256.
  
• Asic (Application-Specific Integrated Circuit) Pronounced A sick, it is a Very Large Scale Integrated circuit, custom-designed to perform one or more particular functions. Advantages include fewer discrete components, lower power consumption and increased reliability.
  
• ASN-1 (Abstract Syntax Notation-1) A formal language used for describing and implementing ISO OSI protocols used in the automated implementation of protocol software. The protocol data units of most Application Layer standards like ACSE, FTAM, MMS, are defined using ASN-1.
  
• Asynchronous communications A method of transmitting data in which each transmitted character is sent separately. The character has integral start and finish start and stop bits so that the character can be sent at an arbitrary time, and separate from any other character. It is the most rudimentary type of communication as the originating and receiving machines do not have to be synchronized. Cheap, reliable and common among PCs and minicomputers, its disadvantage is the large number of extra bits needed for the data to be interpreted.
  
• AT Modem control language for asynchronous dial-up modems designed by Hayes Micro- computer Products.
  
• ATM (Asynchronous Transfer Mode) A cell- based data transfer technique in which channel demand determines packet allocation. ATM offers fast packet technology, real time, demand led switching for efficient use of network resources. It is also the generic term adopted by ANSI and the ITU-TS to classify cell relay technology within the realm of broadband WANs, specifically B-ISDN. In ATM, units of data are not time related to each other and, as part of the B-ISDN standard, is specified for digital transmission speeds from 34Mbit/s to 622Mbit/s. IBM currently offers ATM at a non standard 25Mbit/s format. ATM will be the high band width networking standard of the decade.
  
• Attenuation The weakening of transmitted signals as they travel away from their point of origin. Amplifiers can recharge the signal up to a point.
  
• AUI (Attachment Unit Interface) The IEEE 802.3 specified cable and connector used to attach devices to a MAU. Defined in Section 7 of the 802.3 standard.
  
• Auto partition A feature of 10 BaseT. When 32 consecutive collisions are sensed by a port in a hub or concentrator from its attached work station or network segment, or when a packet that far exceeds the maximum allowable length is received, the port stops forwarding packets. The port continues to monitor traffic and will automatically begin normal packet forwarding when the first correct packet is received.