Telephone switches route calls through the PSTN (Public Switched Telephone Network).

When you pick up the handset on your home telephone, you are initiating a connection with your local telephone switch. When you dial a telephone number, your phone switch interprets the digits you dial and determines where to route your call.

If your call is to another number in the same area, your local end-office switch will make the call itself. If your call is to another area, your local end-office switch will route your call to a toll-switch. That toll switch will then route your call either to another toll switch or to an end-office switch. When your call is finally routed to an end-office switch, the phone line of your called party will ring.

Telephone switches in use include:

SWITCH VENDOR TYPE DESCRIPTION
1AES Lucent Analog No. 1A ESS
1ES Lucent Analog No. 1 ESS
2BES Lucent Analog No. 2B ESS
2ES Lucent Analog No. 2 ESS
3ES Lucent Analog No. 3 ESS
3XB Lucent E/M No. 3 Cross-Bar
4ES Lucent Digital No. 4 ESS
5AXB Lucent E/M No. 5A Cross-Bar
5ES Lucent Digital No. 5 ESS
5ORM Lucent Digital Optical Remote Module
5RSM Lucent Digital Remote Switching Module
5XB Lucent E/M No. 5 Cross-Bar
AXE10 Ericsson Digital Stand Alone or Host
AXRSS Ericsson Digital Remote
DGTL Digital Generic Digital Switch
DMS1/200 Nortel Digital DMS 100/200 Local Switching System
DMS10 Nortel Digital DMS 10 Carrier Class Switching System
DMS100 Nortel Digital DMS 100 Local Switching System
DMS200 Nortel Digital DMS 200 Local Switching System
DMS250 Nortel Digital DMS 250 Long Distance Tandem Switching System
DMS500 Nortel Digital DMS 500 Local and Long Distance Switching System
DPN Nortel Packet DPN Packet Switch
EDX Siemens Packet Packet Switch
NC23 NEC E/M NEC Cross-Bar
NEAX61E NEC Digital NEC switch
RLCM Nortel Digital Rmote Line Conc Module
RLCM-10 Nortel Digital Remote Line Conc Module
RLM Nortel Digital Remote Line Module
RSC Nortel Digital Remote Switching Center
RSCI Nortel Digital ISDN RSC
RSLE Nortel Digital Remote Subscriber Line Equipment
RSM Lucent Digital Remote Switching System
RSS Lucent Analog Remote Switching System
RSU Digital Generic Remote Switching Unit
SXS Lucent E/M Step by Step