Editing Transponder (section)

==Optical communications==
In [[fiber-optic communication]]s, a transponder is the element that sends and receives the optical signal from a [[optical fiber|fiber]]. A transponder is typically characterized by its data rate and the maximum distance the signal can travel.

The term "transponder" can apply to different items with important functional differences, mentioned across academic and commercial literature:
* according to one description,<ref>[https://books.google.com/books?id=xTIonQZI7TMC&q=%22MSA+transceivers+and+MSA+transponders%22&pg=PA353 Optical Fiber Telecommunications V: Systems and networks, Academic Press, 2008, page 353-354]</ref> a transponder and [[transceiver]] are both functionally similar devices that convert a [[full-duplex]] ''electrical'' signal into a full-duplex optical signal. The difference between the two is that transceivers interface electrically with the host system using a ''serial'' interface, whereas transponders use a ''parallel'' interface to do so. In this view, transponders provide easier-to-handle lower-rate parallel signals, but are bulkier and consume more power than transceivers.
* according to another description,<ref>{{Cite web |url=http://www.compeng.dit.ie/staff/tfreir/optical_2/Unit_4.ppt |title=WDM and DWDM Multiplexing Powerpoint presentation, School of Electronic and Communications Engineering, Dublin (Ireland), slide 61 |access-date=2011-02-16 |archive-date=2011-07-21 |archive-url=https://web.archive.org/web/20110721123432/http://www.compeng.dit.ie/staff/tfreir/optical_2/Unit_4.ppt |url-status=dead }}</ref> transceivers are limited to providing an ''electrical-optical'' function only (not differentiating between serial or parallel electrical interfaces), whereas transponders convert an optical signal at one [[wavelength]] to an optical signal at another wavelength (typically [[Frequency grid|ITU standardized]] for [[DWDM]] communication). As such, transponders can be considered as two transceivers placed back-to-back. This view also seems to be held by, for example, [[Fujitsu]].<ref>[http://www.fujitsu.com/downloads/TEL/fnc/pdfservices/DWDM_Tutorial.pdf Fujitsu DWDM Primer, 2004]</ref>

As a result, differences in transponder functionality also might influence the functional description of related optical modules like transceivers and [[muxponder]]s.