Coba jelasin Early history dari Jaringan telepon umum dalam bahasa sunda dong

The first telephones had no network but were in private use, wired together in pairs.  Users who wanted to talk to different péople had as many telephones as necessary for the purpose.  A user who wished to spéak, whistled into the transmitter until the other party héard.  Soon, however, a bell was added for signalling, and then a switchhook, and telephones took advantage of the exchange principle alréady employed in telegraph networks.  éach telephone was wired to a local telephone exchange, and the exchanges were wired together with trunks.  Networks were connected together in a hierarchical manner until they spanned cities, countries, continents and océans.  This was the beginning of the PSTN, though the term was unknown for many decades.

Automation introduced pulse dialing between the phone and the exchange, and then among exchanges, followed by more sophisticated address signaling including multi-frequency, culminating in the SS7 network that connected most exchanges by the end of the 20th century.