| 单词 | PON (Passive Optical Network) |
| 释义 | PON (Passive Optical Network) an ATM-based Passive Optical Network (APON) scheme, was ratified by the ITU-T within the G.983.1 standard. Elements of a PON comprise an Optical Line Terminal (OLT), an Optical Network Terminal (ONT), an Optical Network Unit (ONU), a passive splitter, and optical fiber. • Optical Line Terminal (OLT) The OLT terminates the optical local loop at the edge of the network. In a telco PON, the OLT is housed in the central office (CO). In a CATV PON, the OLT is housed in the headend.The OLT can either generate downstream optical signals on its own, or can pass optical signals from the optical backbone through a collocated optical crossconnect or multiplexer. The OLT also receives upstream signals from the ONTs and ONUs. • Optical Network Terminal (ONT): The ONT terminates the optical circuit at the customer premises in a fiber-to-the-premises (FTTP) scenario.The ONT serves as a media converter, interfacing the optical fiber to the copper-based inside wire.The ONT is an addressable device that recognizes and accepts downstream data addressed to it specifically, ignoring all other data.The ONT is synchronized with the OLT, and assigned time slots for user-generated upstream data, which it buffers as necessary. • Optical Network Unit (ONU): The ONU terminates the optical circuit in a remote network node in a fiber-to-the-curb (FTTC) or fiber-to-the-neighborhood (FTTN) scenario.The ONU serves as a media converter, interfacing the fiber circuit to embedded copper in the form of unshielded twisted pair (UTP) in a telco network and coaxial cable in a CATV network. • Splitter: The passive optical splitter is positioned between the OLT and the ONUs or ONTs, depending on the scenario.The splitter divides the single downstream signal into multiple, identical signals at reduced power levels. As a passive network, PON has no provision for amplifying the signal. The splitter serves as a passive signal concentrator with respect to upstream transmissions. • Optical Fiber: The ITU-T specifies two types of optical fiber to be employed in a PON. G.652 describes a standard type of single-mode fiber (SMF). G.652c/d describes low-water-peak fiber (LWPF) or zero-water-peak fiber (ZWPF).The fiber link can be organized in either simplex or duplex configuration. Simplex refers to a single-fiber configuration supporting transmission in both directions. Duplex refers to a configuration of two fibers, one supporting downstream transmissions, and another supporting upstream transmissions. See also APON, backbone, buffer, CATV, CO, coaxial cable, coupler, cross-connect, downstream, duplex, FSAN, FTTC, FTTN, FTTP, headend, ITU-T, local loop, LWPF, multiplexer, passive, Physical Layer, repeater, simplex, SMF, splitter, telco, time slot, upstream, UTP, and ZWPF. |
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