This document describes how circuit-switched digital networks work. A dial-up router recognizes external data and initiates a call to a destination using a preprogrammed table. A switching matrix then temporarily connects local and long distance lines for the call. The central office switch accepts the incoming call and digitally connects to the destination using high-speed fiber-optic trunks between switches, after which the receiving router packages the data into Ethernet frames.

1. How Circuit-Switched Digital
Networks Work

2. The dial-up router
●It recognizes data with a destination
outside the LAN and initiates a call to a
destination selected from a
preprogrammed table.

3. A switching matrix
● It connects local access lines and long
distance services on a temporary per-
call basis.

4. The central office switch
● It accepts the incoming call and
makes a digital connection to the
destination.

5. A high-speed intraswitch truck
● It is a fiber-optic link operating at a
minimum of 45 megabits per second.

6. The receiving router
● It packaged The TCP/IP packets into
Ethernet.