Introduction
nPSTN switching is based on circuit
switching by duplex connections
nTemporary
bidirectional connections
nOriginally
for speech (voice) only at 300-3400 Hz
nEarlier
two subscribers connected by a purely physical connection
nNowadays
by time slots~ISDN integrated to PSDN
nPCM
is the TDMA standard for the A/D conversion
nPCM
time slots consist of 8 bit samples
nFor
voice digital exchange sets up 64 kbit/s connections
nData
connections by (1) modems in old PSTN, by (2) ISDN interface (3)
leased lines as X.25 or (4) ADSLPCM: pulse coded modulation