and reconfigura- tion. DCSs add, drop, and/or switch payload as necessary across multiple links. DDS (digital data service) A digital transmission service that supports speeds up to 56Kbps/64Kbps. DECnet A proprietary suite of network protocols created by Digital Equipment Corporation to connect two minicomputers. It evolved into one of the first peer-to-peer network architectures. dedicated line An end-to-end communications line used exclusively by an organization. Also called a dedicated circuit. delay distortion The change in a signal from the transmitting end to the receiving end that results from the tendency of some frequency components within a channel to take longer to be propagated than others. delta modulation A method of representing a speech waveform (or another analog signal) in which successive bits represent increments of the waveform. The increment size is not neces- sarily constant. It produces digitized voice at 56Kbps. demodulation The process of recovering data from a modulated carrier wave. It is the reverse of modulation. DEN (Directory Enabled Networking) DEN (Directory Enabled Networking) An industry group formed by Microsoft and Cisco to create a common data format for storing information about users, devices, servers, and applica- tions in a common repository. DEN describes mechanisms that enable equipment, such as switches and routers, to access and use directory information to implement policy-based networking. DES (Data Encryption Standard) A cryptographic algorithm that enciphers and deci- phers data using a 56-bit key. As a secret-key, symmetric system, it requires the exchange of secret encryption keys between users. diagnostics Software routines or microcode used to check equipment malfunctions or to pin- point faulty components. dial tone A signal, generated by a service circuit within the local exchange or PBX, that is sent to an operator or a user as an audible indication that the switch is ready to receive dialing digits. dialup The process of, or the equipment or facilities i