 and retransmits them when a facility becomes available. Synonymous with store-and-forward. message unit A unit of measure for charging local calls that details the length of call, dis- tance called, and time of day. metric Information that a routing algorithm uses to determine the best path to the destina- tion. Some examples of metrics include path length, destination, next-hop associations, reliabil- ity, delay, bandwidth, load, and communication cost. metro access product A MAN product that brings fiber closer to the customer, to reduce deployment costs. metro core product A MAN product used in building citywide rings. MGCP (Media Gateway Control Protocol) A combination of the SGCP and speci- fications. In this protocol, softswitches provide the external control and management, making MGCP a good way to connect an IAD to a gateway. MHz (megahertz) A unit of frequency equal to 1 million cycles per second. MIB (Management Information Base) The specification for how data is stored, moni- tored, and managed in an SNMP device. MIB I and MIB II are revisions of the database used on TCP/IP networks. micro One-millionth. microbrowser An Internet browser specifically designed for mobile devices. microcell A small cell architecture in the cellular system that covers about 1 mile (1.5km) and uses only about 100 milliwatts of power. Microcells allow greater frequency reuse than cells, increasing the overall network capacity and therefore the number of subscribers that can be served. microsecond One-millionth of a second. microwave (1) The portion of the electromagnetic spectrum between 1GHz and 100GHz. (2) High-frequency transmission signals and equipment that employ microwave frequencies, including line-of-sight open-air microwave transmission and satellite communications. MIDI (Musical Instrument Digital Interface) A standard for defining how to code the elements of musical scores, such as sequences of notes, timing conditions, and the instru- ment that is to play each note. milli One-thousandth. millisecond One-thousa