quipment (STE). Wavelength Regenerators Figure 2-42 Wavelength Performs "3R" signal processing (retime, reshape, regenerate) through optical-to-electrical-to-optical (O-E-O) conversions regenerators. Removes accumulated signal noise Optical Regen- erator Arriving Signal Departing Signal Chapter 2 SONET Line-terminating equipment (LTE) a) Includes the functions of a SONET regenerator. b) Terminates a Line and the associated Section. c) Operates on Stratum clock. d) Multiplexes Paths onto a Line and demultiplexes a Line into Paths. e) It is a dual-simplex Path mux. f) Supports maintenance/protection switching for muxed Paths between LTEs. SONET Path-terminating equipment (PTE) a) Terminates a Path and the associated Line and Section. b) Operates on local clock. c) Equipment is where the SONET path overhead is processed. SONET transponder a) Couples differing optical physical-medium-dependent functions back to back (for example, wavelength 1 to wavelength 2, multimode to single-mode, 850 nm to 1,300 nm). b) Dual simplex. Passive transponder. c) Transparently passes all bits (items a and b). Active transponder. d) A special case of SONET regenerator supporting item a. e) Terminates Section (see regenerator) and Line (see LTE). Preferably, the amplification function in an optical domain can be han- dled without resorting to the optical-electrical-optical (O-E-O) conversions used by devices in the previous list. The functionality of a general optical amplifier is shown in Figure 2-43. An optical amplifier, such as simple EDFAs in Figures 2-44 and 2-45, is used to boost an attenuated input signal. The amplifier is the repeater tech- nology that is used in long-haul applications, oceanic cables, and some metro core applications. A basic EDFA consists of isolators, a pump laser, an erbium-doped fiber, and a coupler. The isolators reside at the front and back ends of the amplifier to prevent pump-laser emission or suppress light reflection coming from the erbium-doped fiber. The pump laser supplies power to the fiber carry