Coming back to Transmission if we talk about SDH Technology SDH full form is “Synchronous Digital Hierarchy”. If we divide SDH into parts the lowest part is E1. The E1 carries Data in the speed (or rather say Data Rate) as 2048 Kbps. This 2 Mbps data rate is acheived by a small calculation. We know that Human Voice frequency range is 4 KHZ and as per the Shanon’s Sampling Theorem Sampling Voice Signal is twice the frequency means 8 KHZ. Now as per A-Law minimum 8 Bits are required to make 1 Byte hence 8 KHZ*8 bits= 64 Kbps. Number of channels or bytes in an E1 is 32 hence the calculation would be 64 Kbps* 32 TS = 2048 Kbps or 2 Mbps.
Next level after E1 in SDH is single SDH frame means STM-1 “Synchronous Transfer Mode” which is equals to 63 E1s.
Hence to conclude SDH is the most efficient and famous in transmission network.