history of pstn (aqsa)

Mr. Zulfiqar Sb.

AQSA JAMEEL #19SADIA SHAHID #33AYESHA ABID #34

PSTN PUBLIC SWITCH TELEPHONE

NETWORK

HISTORY OF PSTN

Introduction by Alexander Graham Bell in 1876.

“Ring Down” concept contain a physical wires.

“RING DOWN” concept is a UNI directional communication

UNI directional transmission transform into bi directional transmission.

History of PSTN

Both uni directional and bi directional transmission was un reliable and difficult to implement also very costly.

Now the concept of switches was emerged.

In this mechanism only one cable will be connected with the central switch.

History of PSTN

In the beginning telephone operator acted as a switch.

Human switches is replaced by electronic switches.

the concept of the modern Public Switched Telephone Network is built.

PSTN was developed to transmit analog electrical signals from one place to another.In PSTN phone converted analog sound waves into analog electrical signals.

History of PSTN

In fact we can say that any thing to be transmitted over the PSTN had to be in an analog signal form

Originally PSTN was designed to handle analog voice signals which was based on the circuit switching network .But gradually PSTN was evolved into digital circuit network.

History of PSTN

In this sense CODEC means encoder/decoder is required. The function of the CODEC is to convert analog voice signals into digital voice signals and vice versa.

All the transmission which is converted with CODEC is handled with the help of “DIGITAL PSTN”

History of PSTN

• Switching system of LECs and ICEs.

• LEC is a local exchange carrier.

• IEC is an inter exchange carrier.

Defining PSTN with the help of pictures

Analog working

LAN Cards

Digital cards

Digital cards

New technology of fiber

PIC of PSTN

Advantages of PSTN

• Well established technology.

• Easy maintenance.

• Hassle free set-up process.

• Simplicity in usage procedures.

Disadvantage of PSTN

• Dedicated line required to complete a call.

• Limited scalability.

• Monthly fees applicable for maintenance.

• Higher call charges.