The Phone Network

Telephone System

Uses switched circuits (virtuals...).

Access via low bandwidth circuits.

“out-of-band” call establishment using signaling system based in packets (SS7).

Channels between switching exchanges carry multiple calls

• Multiplexing (analogue or digital)

Public telephony (PSTN): history

• 1876 invention of the phone

• 1915 first transcontinental connection (NY–SF)

• 1920’s first automatic switching exchanges

• 1956 transatlantic cable TAT-1 (35 linhas)

• 1962 digital transmission (T1)

• 1974 Internet: voice over packets

• 1977 digital switching exchange

• 1980s Signaling System #7 (out-of-band)

• 1988 RDIS (ISDN Blue Book)

• 1990s Intelligent Networks

• (1990s ATM)

• 2000 local bundle liberalization (Europe)

Phone service in US | AT&T Divestitude

Evolution: Voice vs Data

Deutsche Telekom % change in call volume (min) 98/99

Number of int’l circuits in use, worldwide, and by region 1998 (in thousands)