Optical fiber provides huge bandwidth compare to any other communication medium. Bandwidth of one strand of an optical fiber in 25000 GHz compared to air medium, which may provide maximum 25 GHz (approximately). Optical fiber is a very significant advantage for long distance communication.
Optical network can be formed using point-to-point star ring connections. But no matter what type of connection converted to an optical signal (EO) at the transmission end and optical signal is converted to electrical signals (OE) at receiving end.
Synchronous Optical Network (SONET) and synchronous Digital Hierarchy(SDH) are two point-to-point optical network standards. SONET was developed by ANSI (T.1.105) to resolve the problem of internetworking between different communication companies after breakup of AT&T. SDH was defined by ETSI and standardized by ITU as standards G.707, G.783, G.784, G.803.
In SONET Time Division Multiplexing (TDM) is used. Since TDM woks in electrical mode, we need to convert optical signal to electrical for TDM, which causes “celector-optical” bottleneck. A TDM signal carries the aggregate traffic of different clients and each TDM node must be able to operate at the aggregate line rate of speed. The aggregate line rate is limited by the fastest available electronic processing device. Therefore, although fiber optic offer very high line rate the maximum line rate is limited by electronics.