Analyzing the speech signal and introducing the standards!

Hello mates!
As we all know, Voice communication is all about the transmission of speech signals from source to the destination. While designing standards and equipments for voice communication the major concern is the delay factor (the signal should be transmitted at the same frequency of voice).

For maintaining the delay factor, we should do a simple calculation with the frequency of voice. It is a known fact that the frequency of voice is 64kHz. In other words, the speech signals should be sampled at 8000 samples per second for reproducing the signal without any distortion. This in turn means that for every 125 microseconds( 1/8000 seconds) a sample must be taken.

To be short, every phone calls and other voice communication we are doing involves the transfer of signals every 125microseconds.

The speech signals are transmitted using some standards mentioned by ITU(International Telecommunication Union). The standards include E1,DS1, PDH,SDH/SONET and recently OTN is also being used.

The ultimate aim of all the above mentioned standards is to transmit speech signals at the rate of 64kHz ( sampling at every 125microseconds).

If all the standards has the same aim, then what makes the difference? The difference is the capacity (the number of voice channels it supports). SDH has higher capacity than PDH and OTN in turn has higher capacity than OTN.

The main aim is to make you understand that whatever the standard may be, they will transmit voice signals sampled at 64kHz rate and only the number of voice channels they support varies ( the number of speech signals they can transmit at the same time) . 

I am happy to listen your suggestions, doubts and ideas.