HUT Comms Lab., Timo O. Korhonen
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 purely physical connection (physical switch contacts)
nNowadays by time slots ~ ISDN is integrated to PSDN
nPCM is the TDMA standard for the digital transmission
nPCM time slots consist of 8 bit samples
nFor voice digital exchange sets up 64 kbit/s connections
nData connections by (1) modems, (2) ISDN interface
(3) leased lines via X.25 / Frame relay, or (4) ADSL
PCM: pulse coded modulation
*What are semi-duplex and simplex?