The PSTN is a network that connects customer equipment together through lines, trunks, and switches to allow communication. It has four major elements: customer premises equipment, the access system, transport, and signaling. The access system provides the wiring that connects customer equipment to the central network, including lines and trunks. It terminates at central office equipment. The transport component transmits signals through the core of the network using various transmission speeds and media between switches. A cellular call placed to a landline passes through the radio access network, mobile switching office, and the PSTN using its lines, trunks, and switches to connect the calls.

1. PSTN
By Amin Pathan (M.Tech, CSE)

2. What Is The PSTN?
The Public Switch Telephone Network (PSTN)
Is A Mesh Network Of Lines, Trunks, Switches,
Etc. That Connects Customer Provided
Equipment (CPE) Together To Allow The CPE To
Communicate Together.
The PSTN Was Originally Designed To Optimize
The Transmission Of Voice Services.

3. Major Elements Of The PSTN
CO Class 1
Switch
PSTN
CO Class 2
Switch
Analog Loop
Digital Interoffice
Trunks
CO Class 5
Switch
Residence
CPE
Digital Loop
PBX or KTS
Office Bldg

4. The Four Major Elements Of The PSTN
There Are Four Major Elements Of Today’s Public
Switched Telephone Network (PSTN).
Customer Premises Equipment (CPE)
Access System
Transport
Signaling

5. Access System
The Access Component Of The PSTN Provides Customers
All Of The Wiring And Equipment For The Customer’s
CPE To Be Connected To The Central Core Of The Public
Switched Telephone Network.
The Access System Includes Both Lines And Trunks And The
Termination Equipment In The End Office.
Access Lines And Trunks Along With The Telephone Poles,
Conduits, Connector Boxes, Etc. Are Referred To As The
Local Loop.

6. Central Office Termination Equipment
Some Samples Of End Office Termination Equipment.

7. Access System – Residential Access
Each Customer Circuit Is A Two-Wire Cable From The
Customer Demarc Out To The First Cross Connection Box
Class 5 Switch
A & B – Cross
Connection Pedestal
Or Cross Connection
Box

8. Transport Component Of The PSTN
Transport Means Transmission – Taking Voice, Data, And
Video Signals From One Subscriber’s Access Line And
Delivering Them To Another Customer’s Access Line.
The End-Office, Or Class 5 Central Office Is The Point Where
All Customer Access Lines Connect.
The Trunks Within The Transport Core Include A Wide
Variety Of Transmission Speeds (e.g. T1, T3, OC-1, OC-12)
And Transmission Media (e.g. Copper And Optical Fiber).

9. A Cell Call Placed To A Land-Based Phone
Travels Through The PSTN
CO Class 1
Switch
Cellular User
CO Class 2
Switch
Digital Interoffice
Trunks
CO Class 5
Switch
Radio
Controller
MTSO
Analog Loop
Residence
CPE

10. Telephones, One Type Of CPE.
Example Of Some
Modern Telephones