need help about PCM TDM and modulation

[fayyaz0346]

pls help me in understanding pulse code modulation, TDM,in most simple word and pics if possible.

 

[Gary B]

PCM (pulse code modulation) and TDM (Time Division Multiplexing) is the standards used for short to medium haul traffic over the telephone network. In PCM, the instantaneous voltage of speech is encoded into an 8 bit word. There are 8,000 words per second for each conversation. Depending upon the carrier system being used, there will be a variable number of conversations.
BRI= 2
US T1= 24
US PRI= 23
Euro E1= 32
Euro PRI= 32
There are others. TDM means one word for one conversation is placed on the link then one word for the next conversation and so on. The alternative is FDM (Frequency Division Multiplexing) which assigns a different carrier to each conversation and they all go at once. This is the older system and is used on long haul circuits.

Most places teach this in a one week course that is petal to the metal for the whole time. PRI is usually given in an additional week but, I have had both dropped on me in the same week by at least two organizations. Point being, don’t expect a quick answer to be anything but confusing.

 

[crutschow]

PCM and TDM are used in other applications besides telephony, of course, but that was one of the first places they were used commercially.