Have a confusion that one STM1 has 63 E1. Size of E1 is 2.048Mbps. then size of one STM1 should be equals 63x2.048 equals 129.024Mbps. but in real STM1 is 155Mbps?

Answer 1

E1 is carried inside C-12 container in SDH enviroment. Size of container is bigger than payload requirment of E1 in order to have clock alignment, justification opportunity bits, justification control bits, & overhead bits.

C-12 container is 272 bits which multplies with 8000 (frames per second) to get data rate for one C-12 per second. Multiplying it with 63 will give you 137.088 Mbps.