This enumerated value selects whether the VT/VC mapping is asynchronous (the DS1/E1's internal DS0 channel structure is neither visible nor preserved) or byteSynchronous (individual DS0 channels inside the VT/VC can be located and extracted), defaulting to asynchronous. An admin cares because byte-synchronous mapping is required if downstream equipment needs to cross-connect or drop individual DS0 channels out of a T1/E1 tributary, while asynchronous mapping treats the tributary as an opaque bit stream. For example, a circuit that needs individual voice channels drop-and-inserted at an intermediate SONET node must use byteSynchronous mapping rather than the asynchronous default.