In a hybrid PON xDSL access network, multiple customer premise equipment (CPE) nodes connect over individual digital subscriber lines (DSLs) to a drop-point device. The drop-point device, which is typically reverse powered from the customer, is co-located with an optical network unit (ONU) of the passive optical network (PON). We demonstrate that the drop-point experiences very high buffer occupancies when no flow control or standard Ethernet PAUSE frame flow control is employed. In order to reduce the buffer occupancies in the drop-point, we introduce two gated flow control protocols that extend the polling-based PON medium access control to the DSL segments between the CPEs and the ONUs. We analyze the timing of the gated flow control mechanisms to specify the latest possible time instant when CPEs can start the DSL upstream transmissions so that the ONU can forward the upstream transmissions at the full PON upstream transmission bit rate. Through extensive simulations for a wide range of bursty traffic models, we find that the gated flow control mechanisms, specifically, the ONU and CPE grant sizing policies, enable effective control of the maximum drop-point buffer occupancies.
Two physical-layer systems to bridge VDSL signals over a fiber access network were proposed in @cite_22 . Individual VDSL signals are converted to be spectrally stacked into a composite signal that modulates an optical carrier. In the first system the optical carrier is supplied by a laser at the ONU and in the second system the optical carrier is supplied by a laser in the OLT that is reflected and modulated by a Reflective Semiconductor Optical Amplifier (RSOA) at the ONU. The optical carrier provides 1 GHz of spectral width accommodating 40 VDSL lines without guard bands and 25 VDSL lines with guard bands. Although, this approach to a hybrid PON xDSL allows the drop-point device to avoid buffering as well as contain simple logic by pulling the DSLAM functionality into the OLT, the design requires the PON to carry the full bandwidth of each VDSL line even when idle. Designs that operate at the link layer rather than physical layer can avoid transmission of idle data on the PON thereby increasing the number of subscribers that can be supported by capitalizing on statistical multiplexing gains.
@cite_22
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Feature Issue on Optical Access Networks (OAN) We describe two schemes developed to carry very-high-data-rate DSL (VDSL) signals over a fiber to the cabinet architecture for the upgrade of legacy copper networks. The first technique exploits the subcarrier bandwidth of uncooled semiconductor lasers for the transmission of multiple VDSL signals by using inexpensive interfacing hardware in the optical network unit (ONU). With a hybrid fiber-copper link comprising 100 m of twisted-pair copper cable and as much as 45 km of single-mode fiber, data transmission comparable with that for fiber to the home is achieved. In an extension to this design we demonstrate a system using a reflective semiconductor optical amplifier in a carrierless remote ONU configuration. Such a design might provide wavelength agility in the fiber access network for signal routing or active bandwidth allocation. Preface to the Second Edition. Preface to the First Edition. 1 Ray Optics. 2 Wave Optics. 3 Beam Optics. 4 Fourier Optics. 5 Electromagnetic Optics. 6 Ploarization Optics. 7 Photonic-Crystal Optics. 8 Guided-Wave Optics. 9 Fiber Optics. 10 Resonator Optics. 11 Statistical Optics. 12 Photon Optics. 13 Photon and Atoms. 14 Laser Amplifiers. 15 Lasers. 16 Semiconductor Optics. 17 Semiconductor Photon Sources. 18 Semiconductor Photon Detectors. 19 Acousto-Optics. 20 Electro-Optics. 21 Nonlinear Optics. 22 Ultrafast Optics. 23 Optical Interconnects and Switches. 24 Optical Fiber Communications. A Fourier Transform. B Linear Systems. C Modes of Linear Systems. Symbols and Units. Authors. Index. We present different mechanisms for downstream transmissions in the coax segment of Ethernet Passive Optical Network (EPON) Protocol over Coax (EPoC). EPoC is the transparent extension of EPON over a cable operator's Hybrid Fiber-Coax network. For managing and controlling such a hybrid network, a network operator prefers to have a unified scheduling, management, and quality of service environment that includes both the optical and coax portions of the network. In EPoC, this is achieved by extending the EPON Medium Access Control to run over the coax physical layer, to have a centralized end-to-end network control from the cable head-end to the end users premises. In this paper, we focus on the downstream transmissions in EPoC. We study three different framing approaches for downstream coax frames based on how sub-carriers in an orthogonal frequency division multiplexed symbol are modulated. We discuss the merits and demerits of each approach and then compare them based on their control overheads and the maximum average data transmission rates each of them can achieve. We analyze how different parameters such as modulation profile, symbol duration, number of sub-carriers and length of resource blocks affect the data rates and the performance of downstream transmissions. We present simulation results to examine the implications of these factors on packet-level performance, such as delay. The results indicate that dynamic and hybrid framing approaches tend to perform better than static approaches, when traffic and usage pattern are identical to those in real-world scenarios. Finally, we outline the important engineering and research problems in this area which can be topics of future research. As optical networks evolve towards more dynamicity and an ever more efficient and elastic spectrum utilization, a more integrated, fault tolerant and system efficient design is becoming critical. To increase efficiency of spectral resource in bit rate per Hz (bit s Hz), high-level modulation formats are used, challenged by the accompanying optical impairments and the resulting limitation of optical reach. Previous work has addressed the issue of optical reach and transmission fault tolerance in the physical layer by deploying various FEC schemes and by a careful design of optical transceivers and links. This paper uses a different approach, applicable to link and networking layers. We propose a novel theoretical framework, whereby a randomized linear network coding (LNC) is applied to the main optical path, and in parallel, an auxiliary optical path is used at much lower transmission speeds, i.e., in addition to the main path. With the reception of the auxiliary path, as we analytically show, the system is highly tolerant to bit errors and packet loss caused by optical impairments in the main path, whereby alleviating the constraints on optical transmission quality and indirectly achieving better optical reach and spectral efficiency. The results are shown for a case study of high-speed Ethernet end-system transmitted over optical OFDM networks, which due to the inherent system-level parallelism in both networks, present one of the most interesting candidate technologies for the proposed method to yield best performance.