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Unformatted text preview: 436 WDM Network Elements O/E/O IP router SONET SONET O/E/O ITU l 1 l OSC l OSC ITU l 2 ITU l 3 l 1 l 2 l 3 Non ITU l Non ITU l Mux/demux Optical line terminal Transponder Receiver Laser Figure 7.2 Block diagram of an optical line terminal. The OLT has wavelength multi- plexers and demultiplexers and adaptation devices called transponders. The transponders convert the incoming signal from the client to a signal suitable for transmission over the WDM link and an incoming signal from the WDM link to a suitable signal toward the client. Transponders are not needed if the client equipment can directly send and re- ceive signals compatible with the WDM link. The OLT also terminates a separate optical supervisory channel (OSC) used on the fiber link. optical layer. To an IP network residing above the optical layer, the lightpaths look like links between IP routers. The set of lightpaths can be tailored to meet the traffic requirements of the higher layers. This topic will be explored further in Chapter 10. 7.1 Optical Line Terminals OLTs are relatively simple network elements from an architectural perspective. They are used at either end of a point-to-point link to multiplex and demultiplex wave- lengths. Figure 7.2 shows the three functional elements inside an OLT:lengths....
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- Spring '09
- Multiplexing, Optical Network, Optical Line Terminals, optical line, optical line terminal