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What are transponders and what is their role in DWDM and OTN networks?

In optical fiber communications, transponders extend network distance by converting short-range optical interfaces of LAN and SAN switches and routers into wavelengths. The transponder converts the optical client signal to an electrical signal by preforming the 3R (retiming reshaping and re-amplifying) or by mapping it into the optical transport network (OTN), and converts it back to an optical signal toward the line side, and into the user-selected wavelength. Performing the 3Rs enables a reliable error-free optical communication link, and mapping the signals into standard OTN which supports forward error correction (FEC) in long haul and metro amplified links, enables transmission without the need for regenerators. Transponders transport data, storage, video, and voice services and rates over metro, long haul, and data center interconnect applications. The transponders create full demarcation between local Layer-2/3 switches and routers and the optical network layer, and are agnostic to the equipment used. Carriers, dark-fiber providers, ISPs and other industries often deploy transponders for building their carrier-grade backbone and DCI network, or for providing managed services to enterprises.