this a document about planing and dimensioning a PSTN network , actually its an advanced document ,and its very interesting-this is a document about planing and dimensioning a PSTN network , actually its an advanced document ,and its very interesting

Overview Physical Layer Interface Standards (PSTN) EIA RS-232-C/D, V.24, V.28, RS-423-A, RS-422-A, RS-449, EIA-530, V.35, USB, Hierarchy ITU - T V series.