How does call tracing work? (Part 1)
23:18
Explaining Call Tracing (Part 2): The No. 5 Crossbar
11:06
DMS-10: The first phone call!
10:39
The Last Towns to Use Operators to Connect Calls - AT&T Archives
12:34
How does telephone ringing work?
10:14
The Pye Mk6 broadcast television camera - as used by the crew of MCR21
16:34
Booting up the 3ESS
22:13
Strowger Step By Step Telephone exchange A close Look
17:28