Add-drop multiplexer Add-drop multiplexer An add-drop multiplexer (ADM) is an important element of an optical fiber network. A multiplexer combines, or multiplexes, several lower-bandwidth streams of data into a single beam of light. An "add-drop" multiplexer also has the capability to "add" one or more lower-bandwidth signals to an existing high-bandwidth data stream, and at the same time can extract or "drop" other low-bandwidth signals, removing them from the stream and redirecting them to some other network path. This is used as a local "on-ramp" and "off-ramp" to the high-speed network. ADMs can be used both in long-haul core networks and in
What Child Is This? What Child Is This? "What Child Is This?" is a Christmas carol whose lyrics were written by William Chatterton Dix, in 1865. At the time of composing the carol, Dix worked as an insurance company manager and had been struck by a severe illness. While recovering, he underwent a spiritual renewal that led him to write several hymns, including lyrics to this carol that was subsequently set to the tune of "Greensleeves", a traditional English folk song. Although it was written in Great Britain, the carol is more popular in the United States than in its country of origin today.