Why 63 E1 is equal to STM1?

Answer 1

It's not.

-- The E1 line rate is 2.048 Mb/s.

-- The data rate of 63 E1s, simply time multiplexed, would be 63 x 2.048 = 129.024 Mb/s

-- 64 E1s may be multiplexed into a single E4 stream, at a rate of 139.264 Mb/s.

-- The STM1 data rate is 155.52 Mb/s. Any combination of data streams totaling

roughly that rate, including as many as perhaps 75 E1s, could be packaged for

transport on an STM1 facility.

Answer 2

In mapping of PDH Signals into SDH is true.

SDH supports only 63 E1 ports for STM-1.