The second model that the industry is currently focusing on is the deployment of coherent pluggables directly into routers, commonly referred to as IP over Dense Wavelength Division Multiplexing (IPoDWDM). This model has the advantages of low capital expenditure (CAPEX), low power consumption, and reduced footprint by eliminating the need for an optical transport platform. Moreover, coherent pluggables benefit from a complete ecosystem of Multi-source Agreements (MSA) and interoperability forums for a seamless line interworking and service provisioning. 

However, IPoDWDM presents operational challenges related to management and compatibility across different host devices and operating systems. Furthermore, this model does not come to par with fully-fledged transponder-based platforms due to the lack of complete traffic aggregation capabilities and operational functionality. 

Additionally, the IPoDWDM model has a direct one-to-one mapping between the router port speed and the pluggable speed – for example, where 400G pluggables are deployed in 400G router ports and 800G pluggables in 800G router ports. Nonetheless, sometimes the coherent pluggables must be dialed down to operate at a lower bit rate, such as 600 Gb/s or 400 Gb/s, to close a specific link, which results in a wasted router port capacity. Moreover, pluggables cannot fully replicate the optical functionality of embedded transponders.

Figure 1: Expanding deployment models with thin transponders
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Expanding deployment modules with thin transponders

Figure 2: Typical Thin Transponder Application
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