al signal never needs to be converted to an electronic signal. enterprise network A network that connects the computer resources throughout a com- pany and supports a wide variety of the company's applications. enterprise wiring hub A hub that connects the PCs on a LAN and also provides the flexi- bility to perform a number of network functions that can benefit network administrators and network users in general. ENUM (Electronic Number Mapping Standard) A protocol that is the result of work the IETF's Telephone Number Mapping working group, whose charter was to define a DNS- based architecture and protocols for mapping a telephone number to a uniform resource identi- fier (URI), which can be used to contact a resource associated with that number. ephemeral port A TCP or UDP port number that is automatically allocated from a pre- defined range by the TCP/IP stack software, typically to provide the port for the client end of client/server communication. equalization The introduction of components to an analog circuit by a modem to compen- sate for signal attenuation and delay distortion. Generally, the higher the transmission rate, the greater the need for equalization. ERL (echo return loss) Attenuation of echo currents in one direction caused by telephone circuits operating in the other direction. error In data communications, any unwanted change in the original contents of a transmission. error burst error burst A concentration of errors within a short period of time as compared with the average incidence of errors. Retransmission is the normal correction procedure in the event of an error burst. error control A process of handling errors that includes the detection and correction of errors. error correction code A code that incorporates sufficient additional signal elements to enable the nature of some or all of the errors to be indicated and corrected entirely at the receiving end. error rate The ratio of the amount of data incorrectly received to the total amount of data transmitted. ESCON (Enterprise System