Telecom-history

2 local loop

2.3 ISDN

• 用户端负责D/A转换(之前是电信局端做D/A转换, 用户到电信是模拟信号)
• 2B1Q调制类似QAM

3 trunk

3.1 FDM

12 Channel carrier System

3.2 T-carrier (T-1)

• codec: PCM
• multiplex TDM

T-carrier

4 电话交换

4.2 电磁交换

电磁式电话交换机

CT380:Strowger Step-by-step Demonstration

AT&T Archives: The Step-By-Step Switch

6 网络

6.1 参考资料

Wikipedia Time Line of telophone

history of telecommunication