Optical Network Design and Implementation

SONET Multiplexing

Various TDM PDH services can be natively accepted by SONET systems. These signals are mapped into the SONET payload envelope through service adapters. All inputs are eventually converted to a base format of a synchronous STS-1 signal, with the exception of concatenated signals. As shown in Figure 5-20, DS1 inputs are mapped into VT1.5 SPEs and consequently into VT1.5s. Other low-speed signals, such as E1, DS1C, and DS2, are also mapped into their respective VTs. The VTs combine to form a virtual group (VG). Seven VGs are then mapped into an STS-1 SPE. The STS-SPE is then provided with its appropriate overhead and converted into an electrical STS-1. Several synchronous STS-1s are then multiplexed together in either a single- ...