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{{Short description|Manipulates DWDM channel contents}}
{{Distinguish|optical add-drop multiplexer}}
{{Refimprove|date=July 2007}}
[[Image:Add-drop-multiplexer-SONET-SDH.jpg|thumb|300px|An add-drop multiplexer.]]
An '''add-drop multiplexer''' ('''ADM''') is an important element of an [[optical fiber]] network. A [[multiplexer]] combines, or [[Multiplexing|multiplexes]], several lower-[[Bandwidth (computing)|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.<ref>{{cite web
A recent shift in ADM technology has introduced so called '''multi-service [[SONET]]/[[SDH]]''' (also known as a multi-service provisioning platform, or [[MSPP]]) equipment which has all the capabilities of legacy ADMs, but can also include cross-connect functionality to manage multiple fiber rings in a single chassis. These new devices can replace multiple legacy ADMs and also allow connections directly from [[Ethernet]] [[LAN]]s to a service provider's optical backbone. ▼
| title = Electrical Engineering Glossary Definition for ADM
| url = http://www.maxim-ic.com/glossary/index.cfm/Ac/V/ID/8/Tm/ADM
| archive-url = https://web.archive.org/web/20080304030505/http://www.maxim-ic.com/glossary/index.cfm/Ac/V/ID/8/Tm/ADM
| archive-date = 2008-03-04}}</ref>
ADMs can be used both in long-haul core networks and in shorter-distance [[Metropolitan area network|metro networks]], although the former are much more expensive due to the difficulty of scaling the technology to the high data rates and [[wavelength division multiplexing|dense wavelength division multiplexing]] (DWDM) used for long-haul communications. The main optical filtering technology used in add-drop multiplexers is the [[Fabry–Pérot etalon]].
▲
An emerging variety of ADMs that is becoming popular as the carriers continue to invest in metro optical networks are [[ROADM]]s, or [[Reconfigurable Add Drop Multiplexers]].▼
▲An emerging variety of ADMs that is becoming popular as the carriers continue to invest in metro optical networks are [[
== See also ==
* [[Optical add-drop multiplexer]]
* [[Drop and insert]]
== References ==
<references/>
[[Category:Telecommunications equipment]]
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