A Survey on OFDM-Based Elastic Core Optical Networking <s> A. Elastic Optical Network Concept <s> Reach estimations for several variable-bitrate OFDM schemes are presented and discussed in the framework of a transparent EU core network scenario. 44% reduction on OE interfaces is found compared to a fixed-bitrate 40Gb/s network. <s> BIB001 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> A. Elastic Optical Network Concept <s> With the growth of traffic volume and the emergence of various new applications, future telecom networks are expected to be increasingly heterogeneous with respect to applications supported and underlying technologies employed. To address this heterogeneity, it may be most cost effective to set up different lightpaths at different bit rates in such a backbone telecom mesh network employing optical wavelength-division multiplexing. This approach can be cost effective because low-bit-rate services will need less grooming (i.e., less multiplexing with other low-bit-rate services onto high-capacity wavelengths), while a high-bit-rate service can be accommodated directly on a wavelength itself. Optical networks with mixed line rates (MLRs), e.g., 10/40/100 Gb/s over different wavelength channels, are a new networking paradigm. The unregenerated reach of a lightpath depends on its line rate. So, the assignment of a line rate to a lightpath is a tradeoff between its capacity and transparent reach. Thus, based on their signal-quality constraints (threshold bit error rate), intelligent assignment of line rates to lightpaths can minimize the need for signal regeneration. This constraint on the transparent reach based on threshold signal quality can be relaxed by employing more advanced modulation formats, but with more investment. We propose a design method for MLR optical networks with transceivers employing different modulation formats. Our results demonstrate the tradeoff between a transceiver's cost and its optical reach in overall network design. <s> BIB002 </s> A Survey on OFDM-Based Elastic Core Optical Networking <s> A. Elastic Optical Network Concept <s> We introduce the network defragmentation problem for FWDM networks, formulate it, and propose heuristics. The network defragmentation process consolidates the available spectrum significantly while minimizing the number of interrupted connections. <s> BIB003
Due to the rapid growth of broadband Internet services and applications such as IPTV, video on demand, and cloud computing, it is expected that diverse bandwidth demands will emerge in future optical networks, with speeds ranging from Gb/s up to Tb/s. Moreover, the temporal as well as the geographical patterns of future Internet traffic will change dynamically. Although current WDM-based optical network architectures offer advantages of high capacity transmission and reconfigurable wavelength switching, they also present drawbacks of rigid bandwidth and coarse granularity. These may lead to inefficient spectrum utilization and inflexible accommodation of various types of traffic, as each WDM channel occupies the same spectrum width without regard of the transmitted data rate, and each data rate needs a separate transponder which cannot be reconfigured once deployed (although some high-speed (e.g., BIB003 Gb/s) data-rate-adaptive transponders are currently emerging BIB001 ). Sub-wavelength services could be supported with optical transport network grooming switches; however these electrical switches have high cost and energy consumption. These problems are expected to become even more significant when higher-speed transmission systems (e.g., BIB003 Gb/s and beyond) are deployed. On the other hand, as transmission speed increases to beyond 100 Gb/s, e.g., 400 Gb/s and 1 Tb/s, it is not likely for WDM systems to adopt traditional 50 GHz channel spacing for long-haul transmission, because of the increased SNR requirement for higher order-modulation formats, meaning higher rate data will need more spectrum BIB002 . For example, the bandwidth of a 400 Gb/s channel (using PDM 16-QAM with 56-64 Gbaud) is likely to require a 75 GHz channel spacing, while a 1 Tb/s channel (using PDM 32-QAM with 112-128Gbaud) would require a 150 GHz channel spacing BIB002 . Therefore, the optical network needs to support flexible spectrum bandwidth provisioning in order to accommodate future high-speed traffic. To meet future Internet traffic requirements, a novel elastic optical network architecture with flexible data rate and spectrum allocation, high resource efficiency, low cost, and low power consumption is desirable. Recently, several such network architectures have been proposed, and have drawn increasing attention.