The advantages of optical transparency are still confined to the boundaries of a domain, since the optical signals are subject to O/E/O conversions at the border nodes that separate two optical domains. The extension of transparent connections across domains requires advances both in the modeling of the impairments suffered by the optical signals as well as in devising strategies to exploit such models in practice. In this latter regard, one of the main challenges is to design information exchange models and protocols enabling optical bypass without disclosing detailed physical-layer information among domains. In this paper, we focus on the modeling and the exchange of impairmentrelated information between optical domains. We propose a model that conveniently captures the degradation experienced by an optical signal along a lightpath, and describe it use in the frontier between two neighbor domains. Our approach respects the privacy and administrative limits of carrier networks, while enabling the provision of transparent connections beyond domain boundaries. The model and strategies proposed in this paper generalize the contributions made by some of the most relevant works in the field, providing in this way a first attempt toward a unifying view and theory for quantifying the transmission impairments in DWDM optical networks.

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