Optical Networks - _6_1 SONET_SDH_74

Path status g1 the g1 byte is used to convey the

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Path Status (G1). The G1 byte is used to convey the performance of the path from the destination back to the source node. The destination inserts the current error count in the received signal into this byte, which is then monitored by the source node. Part of this byte is also used to carry a defect indicator signal back to the source. We will study the use of defect indicator signals in Section 8.5.4.
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384 Client Layers of the Optical Layer 6.1.5 SONET/SDH Physical Layer A variety of physical layer interfaces are defined for SONET/SDH, depending on the bit rates and distances involved, as shown in Table 6.3. We have used the SDH version standardized by the ITU, as it is more current. The interfaces defined for SONET systems generally align with the SDH versions. Generally, we can classify the different applications based on the target distance and loss on the link between the transmitter and receiver. With this in mind, the applications defined fit into one of the following categories: Intraoffice connections (I) corresponding to distances of less than approximately 2 km (the SONET term for this is short reach ) Short-haul interoffice connections (S) corresponding to distances of approxi- mately 15 km at 1310 nm operating wavelength and 40 km at 1550 nm operat- ing wavelength (the SONET term for this is intermediate reach ) Long-haul interoffice connections (L) corresponding to distances of approxi- mately 40 km at 1310 nm operating wavelength and 80 km at 1550 nm operat- ing wavelength (the SONET term for this is long reach ) Very-long-haul interoffice connections (V) corresponding to distances of approx- imately 60 km at 1310 nm operating wavelength and 120 km at 1550 nm oper- ating wavelength Ultra-long-haul interoffice connections (U) corresponding to distances of approx- imately 160 km The other variables include the type of fiber and the type of transmitter used. The fiber types are the ones we covered in Section 2.5.9 and include standard single-mode fiber (G.652), dispersion-shifted fiber (G.653), and nonzero dispersion-shifted fiber (G.655). The transmitter types include LEDs or multilongitudinal mode (MLM) Fabry-Perot lasers at 1310 nm for short distances at the lower bit rates to 1550 nm single-longitudinal mode (SLM) DFB lasers for the higher bit rates and longer distances. The physical layer uses scrambling to prevent long runs of 1s or 0s in the data (see Section 4.1.1). The applications specify many transmission-related parameters, of which the main ones are the allowed loss range and the maximum chromatic dispersion on the link. The loss includes connectors and splices along the path. The relative contribu- tion of the latter to the overall loss is particularly high in intraoffice connections, where a number of patch panels and connectors can be present in the interconnect. We can translate the loss numbers into target distances by assuming a loss of ap- proximately 3.5 dB/km for intraoffice connections, 0.8 dB/km for short-haul, and
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6.1 SONET/SDH 385 Table 6.3 Different physical interfaces for SDH. Adapted from ITU recommendations G.957 and G.691. No optical amplifiers are used in the spans. The first letter in the application code specifies the target reach and the following number indicates the bit rate. The number after the
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