Optical Networking With Variable-Code-Rate Transceivers

Abstract

We evaluate the impact of variable-code-rate transceivers on cost, capacity and survivability of wavelengthrouted optical networks. The transmission rate and reach tradeoff is quantified for two hypothetical coded modulation schemes (aggressive and conservative) in a wavelength routing network with 50-GHz-spaced channels. The aggressive scenario assumes the 64-QAM modulation format, a small gap to capacity, and a small excess bandwidth. The conservative scenario considers the 16-QAM modulation format, and a larger capacity gap and excess bandwidth. The performance of the conservative and aggressive technologies is evaluated in three representative networks. Transparent reaches are calculated by means of an existing analytical method which assumes the AWGN hypothesis for the nonlinear noise. It is shown that variable-code-rate transceivers enable the concept of soft protection, in which the protection lightpath operates at a data rate which is lower than the corresponding working lightpath, in a way to avoid regeneration. This is specially attractive in the transport of IP traffic, where capacity reduction (in average up to 25%) may be tolerable during a repair time. It is also shown that variable-code-rate transceivers have the potential to offer significant savings in terms of transceiver usage and wavelength occupation, when compared to current fixed-rate transceivers operating at 100, 200 or 400 Gb/s. Finally, practical variable-code-rate transceivers may achieve a discrete set of N code rates, yielding a quantized capacity-versus-reach curve. The system impact of N is evaluated for several network scenarios.

PAM Performance Analysis in Multicast-Enabled Wavelength-Routing Data Centers

“…Multilevel PAM is being developed for both 850 nm and 1550 nm optical interconnects [21]- [24]. To compensate for the sensitivity of this modulation scheme to physical-layer impairments, short block-length error-correcting codes with rate adaptation [25], [26] can be introduced to help minimize the redundancy overheads and processing latencies.…”

Soft protection in optical networks with variable-code-rate transceivers

“…It is thus possible to envision future optical networks where a connection, upon a failure in its primary path, switches to a longer protection path, experiencing a service degradation which is equivalent to the protection path length. In a recent publication, we called this feature soft protection [3].…”

Redes ópticas de longa distância com transceptores de taxa de código variável

“…GHz seja contornada pela aplicação de grade flexível com menor granularidade (e.g., 12,5 GHz) [17], ainda assim a taxa máxima de símbolos estará restringida ao estado-da-arte dos DACs/ADCs [5].…”

“…Com base na proposta de se variar a taxa líquida de transmissão pela adaptação da taxa de código, definiram-se três cenários de simulação, detalhados na Tabela 5.1 [5]. O cenário conservador admite tecnologia atualmente factível: DACs/ADCs cuja resolução limita o formato de modulação para PM-16QAM; códigos corretores de erro com palavras-código pequenas e com penalidade de codificação razoável; e que eleé o mais afetado por interferência não-linear dentre todos os canais do espectro [57].…”

“…Esse conjunto de taxas será apresentado na forma de diagrama de caixa (Box Plot) [5], que mostra cinco patamares (do mais inferior ao mais transmissão e com o tipo de rota (trabalho ou proteção). Com relação aos VCRTs de taxas contínuas, a Figura 6.8 apresenta quatro diagramas de caixa referentesàs rotas de trabalho (RT) e proteção (RP) da rede alemã, com cenário agressivo (Agr) e conservador (Con).…”