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Mapping Network Device Functions to the OSI Reference Model
Published in James Aweya, Designing Switch/Routers, 2023
A multiport hub works by repeating bits received from one of its ports to all other ports. It can detect Physical Layer “packet” start (preamble), idle line (interpacket gap), and sense access collision which it also propagates to other ports by sending a jam signal. A hub cannot further examine or manage any of the traffic that comes through it – any packet entering any port is rebroadcast on all other ports. Essentially, a repeater provides signal regeneration by detecting a signal on an incoming port, cleaning up and restoring this signal to its original shape and amplitude, and then retransmitting (i.e., repeating) this restored signal on all ports except the port on which the signal was received.
Relay-Assisted FSO Communications
Published in Z. Ghassemlooy, W. Popoola, S. Rajbhandari, Optical Wireless Communications, 2019
Z. Ghassemlooy, W. Popoola, S. Rajbhandari
Although AOAF-based relay systems are an attractive option for practical implementation due to their simplicity, accumulation of the noise at each R ultimately limits the achievable maximum transmission distance. As such, the key component to enable large-scale transparent all-optical networks is the all-optical regenerator at the intermediate node/hop. This process is referred to as the AORF relaying technique, which has witnessed a significant worldwide research activity recently [69]–[72], but with no practical implementation in FSO systems yet. Optical signals propagated through a channel (free space or a fibre) experience signal impairments due to accumulated noise, fading, ASE noise, and nonlinearity of the fibre, which degrade the optical signal-to-noise ratio (OSNR) at the Rx. In order to preserve the signal integrity and ensure that it is transmitted over longer distances while routed via several optical nodes, signal restoration or regeneration can be employed periodically along the transmission path. Signal regeneration includes re-amplification, re-shaping, and re-timing, which are conveniently referred to as 1R, 2R, or 3R. The implementation of signal regeneration depends on the network-case scenario since it is not always beneficial to systematically use the three operations at each optical relay node. Note that the regeneration in 2R and 3R includes re-amplification and re-shaping. For smaller networks, 2R regeneration is more than adequate to maintain a satisfactory signal quality level, which is cost effective. Furthermore, for a long-haul communication link, loss and amplitude fluctuations are usually considered the two major sources of signal impairment compared to timing-jitter, thus there is no need for re-timing on a frequent basis.
3R (Retiming, Reshaping, Regeneration)
Published in Kenichi Iga, Yasuo Kokubun, Encyclopedic Handbook of Integrated Optics, 2018
Through the binary decision process, we can regenerate the signal, removing the waveform distortion and restoring the power level. Such signal regeneration is performed by optical repeaters, which are periodically placed in the fiber link. Since the repeater includes the 3R functions, namely “reshaping,” “retiming,” and “regeneration,” we can maintain the signal quality along the entire length of the link, although certain amounts of decision errors are accompanied with the signal regeneration process.
Effects of two-photon absorption on pseudo-random bit sequence operating at high speed
Published in Journal of Modern Optics, 2019
Sunil Thapa, Xiang Zhang, Niloy K. Dutta
High-speed communication system will play a prominent role in the future of optical networks such as signal regeneration, data encryption and data encoding (1,2). These optical networks may utilize optical logic gates such as AND, OR, XOR, etc. (3-7). These Boolean logic functions have been demonstrated using semiconductor optical amplifier (SOA) based devices such as Mach–Zehnder interferometer (MZI, SOA-MZI) (3,4, 6-9), four-wave mixing in SOA (5) or delayed interferometer and SOA, and using binary phase shifted or on-off keyed signal (10). The use of SOA based MZI is preferred due to its simplicity, stability, and compactness. QDSOA based MZI XOR gate can be cascaded and implemented to form complex circuits which show improved functionality (11). The introduction of quantum-dot based (QD) based SOA allows high data rate operation and an addition of two-photon absorption (TPA) results in a fast phase change in probe signal. The excited state carriers in the QD provides fast gain recovery and two-photon absorption is responsible for carrier generation in the bulk region of QD-SOA. Moreover, TPA induced pumping produces a fast phase change in SOA when a train of optical pulses is injected (12).
Comparison of Cost, Power Consumption, and Spectrum Utilization in Protected Fixed- and Flexi-Grid Optical Networks
Published in IETE Journal of Research, 2018
Sridhar Iyer, Shree Prakash Singh
In view of satisfying demand(s) of the various heterogeneous services having different applications and varied bandwidth requirements, architectures of the optical transport networks (OTNs) have evolved from the fixed-grid wavelength-switched optical networks (WSONs) towards flexi-grid elastic optical networks (EONs) technology [1,2]. In WSONs, a particular transceiver type is assumed, and only a single demand serving method exists, which fixes, bit-rate, transmission reach (TR), and spectrum utilization [3]. However, WSONs are required to admit all the channels within a fixed frequency grid which may not be adequate for high-speed channels, and may also under-utilize the spectrum for low bit-rate requests. Hence, for future OTNs, it is essential to resort to EON technology in which (1) on the basis of requirement(s), wider channels are created by combining spectrum units (or frequency slots), and (2) use of multiple subcarrier(s) ensures that the wavelength capacity can be zoned into finer granularities, hence provisioning an increased flexibility in capacity allocation to heterogeneous demands. The other main features of EONs include the (1) use of different modulation formats (MFs) differing in both, the spectral efficiency (SE) and the TR, (2) signal regeneration execution ability with modulation conversion [4], and (3) transmission of super channel(s) (or multiple carrier(s)) [5].
Success Journey of Coherent PM-QPSK Technique with Its Variants: A Survey
Published in IETE Technical Review, 2020
Divya Sharma, Y. K. Prajapati, R. Tripathi
During the survey of PM-QPSK technique, various issues and challenges came up from time to time had to be tackled successfully to improve the system performance. Few encountered issues during this survey are listed below: for the sake of improving SE on PM-QPSK based MLR system, channel spacing within a sub-band and frequency spacing between sub-bands can be reduced. Moreover, shorter sub-band spacing adversely affects optical reach due to inter-channel crosstalk. This subsequently raises the power consumption of PM-QPSK based MLR systems due to more signal regeneration [37];strategy of interleaving one polarization tributary of PM-QPSK signal is insignificant without an RZ pulse (duty cycle typically 50%) in terms of appreciable transmission reach [51];achieving MDM and demultiplexing in PM-QPSK signal is challenging. M. Salsi et al. designed an integrated spatial mode converter incorporating an LCOS spatial light modulator, where MDM is obtained by reprogramming to the desired mode. This case led to a potential difficulty in achieving the expected mode rejection ratio [57];receivers with ideal photon counting exhibit higher sensitivity than optical amplifiers along with offering insufficient bandwidth, which makes stacking strategy of PPM with PM-QPSK unsuitable for high data rate, i.e. 1 Gb/s and more [72].