Dear all,

I know that what i'm going to ask isn't related to microcontrollers.But please if anyone can help me just place me on the start of the road.

I want to know the difference between the following:

1-SONET (synchronus optical network).
2-SDH,PDH (synchronus digital heararchy).
3-SS7 (signaling system 7).
4-OSI reference model (open system interconnect).

i just want a hint about the applications of each one,data rates.....etc
And the main differences between them in networks.

Thanks all,
Hatem Zakaria