1⟩ Tell me Why the STMs in multiple of 1,4,16,64?
I think you have to study SDH network to understand the answer of this question.I am giving the formulae by which the STM-N is generated.
STM-64: 64 VC-4 or 16 VC-4-4c or 4 VC-4-16c or 1 VC-4-64c
STM-16: 16 VC-4 or 4 VC-4-4c or 1 VC-4-16c
STM-4: 4 VC-4 or 1 VC-4-4c
STM-1: 1 VC-4
Higher-level STM-N frames can be simplistically perceived as *4 multiples of a basic STM-1. An STM-4 is constructed by byte-interleaved multiplexing of 4 STM-1s into a frame that is 9 rows by 1080 columns wide. The STM-4 signal has a line rate of 622.080 Mbps (4 * 155.520 Mbps). The four STM-1s (STM-1(1), STM-1(2), STM-1(3), and STM-1(4)) are frame aligned before multiplexing. Frame alignment is achieved by ensuring that the first 12 bytes of the STM-4 signal are A1 framing bytes drawn from STM-1(1), the next 3 from STM-1(2), then 3 from STM-1(3), and finally 3 from STM-1(4). The 12 A1 framing bytes are followed by 12 A2 framing bytes that are obtained from the 4 STM-1s in a process, similar to the way that the A1 bytes were obtained.
