ove. It ranges from extremely low-frequency radio waves of 30Hz-with a wavelength of nearly the earth's diameter-to high-frequency cosmic rays of more than 10 million trillion Hz-with wavelengths smaller than the nucleus of an atom. The electromagnetic spectrum is depicted as a logarithmic progression: The scale increases by multiples of 10, so that the higher regions encompass a greater span of frequen- cies than the lower regions. The greater the span of frequencies, the greater the bandwidth of the media operating over that portion of the electromagnetic spectrum. Glossary electronic tandem networking electronic tandem networking The operation of two or more switching systems in parallel. e-mail (electronic mail) An application that enables users to send and receive messages and files over their computer networks. EMI (electromagnetic interference) Noise on data transmission lines that reduces integrity. Motors, machines, and other generators of electromagnetic radiation cause EMI, but shielding can reduce EMI. EMS (Enhanced Messaging Service) An extension of SMS that enables the sending combination of simple melodies, images, sounds, animations, and formatted text as a message to another EMS-compatible phone. emulate To imitate one system with another SO that the imitating system accepts the same data, executes the same computer programs, and achieves the same result as the imitated system. encapsulation The process of encasing one protocol in another protocol's format. Also called tunneling. encryption The process of coding data so that a specific code or key is required to restore the original data. Encryption is typically applied for secure data transmission or to prevent unautho- rized reception of broadcast material. Sometimes referred to as scrambling. end office The first point of access to the PSTN, or the point at which the subscriber loop ter- minates. Also referred to as a Class 5 office, local exchange, central office, or serving office. end-to-end optical architecture A network in which the optic