 to selectively identify three- digit area codes and to either permit or deny passage of long-distance calls to those specific area codes. (Address Resolution Protocol) A protocol that determines the physical address of node, given that node's IP address. ARP is the mapping link between IP addresses and the MAC address. ARQ (automatic repeat request) ARQ (automatic repeat request) An error control technique that requires retransmission of a data block that contains detected errors. A special form, called "go-back-n," allows multiple blocks to be acknowledged with a single response. "Stop and wait" requires an acknowledgment after each block. artificial intelligence The capability of a computer to perform functions associated with human logic such as reasoning, learning, and self-improvement. ASCII (American Standard Code for Information Interchange) The code developed by ANSI for information interchange among data-processing systems, data communications sys- items, and associated equipment. The ASCII character set consists of 7-bit coded characters (8 bits, including the parity bit), providing 128 possible characters. The ASCII character set consists of 34 control codes and 94 text characters, including the letters of the alphabet in both upper- and lowercase, the 10 digits, and a number of special characters. ASIC (application-specific integrated circuit) An integrated circuit that is customized for a particular use (e.g., to run a mobile phone), rather than intended for general-purpose use. ASON (Automatic Switched Optical Network) ANSI specification ITU G.8080, which describes a network based on a technology that enables the automatic delivery of transport ser- vices. ASON describes the set of control-plane components used to manipulate transport net- work resources in order to provide the functionality of setting up, maintaining, and releasing connections. ASP (application service provider) A supplier that makes applications available on a sub- scription basis. aspect ratio The horizontal:vertical size ratio 