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BUILDING BROADBAND NETWORKS phần 5

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Các sáng kiến dưới ngày nay thường sử dụng công nghệ WDM và DWDM cho phép truyền đại dương ở mức giá multigigabit và multiterabit trên một khoảng cách dài. Sáng kiến đại diện trong lĩnh vực mạng quang học dưới nước được khám phá. | performance reports for network maintenance. In recognition of DMT capabilities operational effectiveness and robustness in noisy local loop environments ANSI American National Standards Institute selected DMT as the basis of the ANSI T1.413 specification developed in 1993. 6.5.2.1 DMT and Discrete Wavelet Multitone Multicarrier DWMT Modulation Based on DMT DWMT Discrete Wavelet Multitone Multicarrier Modulation creates more isolation between subchannels than DMT for performance enhancement. 6.5.2.2 DMT Modulation and Carrierless Amplitude and Phase CAP Modulation DMT Discrete Multitone modulation and CAP Carrierless Amplitude and Phase modulation are sophisticated digital signaling processing DSP techniques that enable point-to-point transmission over voice-grade telephone lines. DMT is the standard line code for DSL technologies. In addition to serving as the basis for the ANSI American National Standards Institute T1.413 specification DMT modulation is also endorsed by the European Telecommunications Standards Institute ETSI and the International Telecommunications Union-Telecommunications Standards Sector ITU-T . DMT manufacturers include Alcatel Amati Motorola Texas Instruments PairGain Motorola Orckit ADI and Aware. CAP Carrierless Amplitude and Phase modulation is also a version of QAM Quadrature Amplitude Modulation . In contrast to DMT CAP is a proprietary technology. As a consequence CAP chipsets are not always interoperable. Nonetheless CAP modems for DSL operations are still in use by vendors such as Nokia. In comparison to CAP DMT transmissions are adaptable to changing bandwidth and line conditions. Moreover DMT-supported DSL transmissions are resistant to crosstalk universal thermal noise impulse noise generated by electrical appliances and RFI Radio Frequency Interference produced by AM radio band signals. 6.6 DSL STANDARDS ORGANIZATIONS AND ACTIVITIES DSL technologies provide an unprecedented amount of affordable bandwidth over ordinary copper .