Telephone Network
Voice grade leased circuits (also private circuits, private lines, leased circuits or dedicated circuits) are normal telephone circuits that have been taken out of dial-up telephone service by the common carrier (telephone company) and dedicated to one organization
country code precedes the area code when you call another country
Echoes arise in telephone circuits because there is a reflection of the electrical wave from the far end of the circuit
Echo suppressors can be installed to suppress the echo
Propagation time is the time it takes a signal to travel from one end of a pair of wires to the other end (1000 miles: propagation delay 10 milli seconds)
Echo cancellers subtract the echo from the original signal
Time Assignment Speech Interpolation (TASI) allows packing of extra voice conversations into a fixed number of circuits:
hello send how thirty are more you