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PSTN Basics | US PSTN hierarchy | UK PSTN hierarchy

This page covers PSTN basics. PSTN stands for Public Switched Telephone Network. It mentions US PSTN hierarchy and UK PSTN hierarchy. Other than PSTN basics it mentions difference between PSTN,ISDN and PSDN is also provided.

PSTN is the short form of Public Switched Telephone Network. The telephone lines are connected to local exchanges. local exchanges are connected with toll offices which are interconected using transmission lines. The transmission mediums can be fiber optic, microwave links or satellite.

The figure-1 depicts typical PSTN components. As shown the PSTN is divided into access network and core network. The connectivity between telephone lines and exchange is known as access network while connectivity between exchanges is known as core network.


The figure-2 depicts PSTN network components. As shown individual telephones are connected with telephone poles using twisted pair cable. The poles are getting terminated on DP (Distribution Panel) in the area. Likewise all the DPs are connected together at cabinet which is interfaced with MDF (Main Distribution Frame). Telephone handset side equipments are known as customer premises equipments while exchange side equipments are known as operator or service provider equipments.

PSTN network

Voice uses 300 Hz to 3300 Hz bandwidth on telephone line. For voice communication dedicated circuit switched connection is established between calling and called party before the conversation. Refer Telephone signal call flow.

Data uses 600 Hz to 3000 Hz bandwidth on telephone line. For data communication modem is needed as PSTN lines are analog in nature. Transmitting side modem converts digital data to analog data and receiving side modem converts analog data to digital data.
Refer Telephone System tutorial➤    EPABX basics➤

US PSTN Hierarchy

US PSTN hierarchy

The figure-2 depicts US PSTN hierarchy.
EO-End Office
IXC- Inter-exchange Carrier

UK PSTN Hierarchy

UK PSTN hierarchy

The figure-3 depicts UK PSTN hierarchy.
DLE-Digital Local exchanges
DMSU-Digital Main Switching Units
DISC-Digital International Switching Centers.

This PSTN basics guide is very useful for beginners and experienced switching professionals. One can also refer basic concepts of Circuit Switching and Packet switching which are used in PSTN and PSDN respectively.

What is Difference between PSTN, ISDN, PSDN, CS, PS

PSTN vs PSDN vs ISDN  Circuit Switching vs Packet switching
Packet Switching vs Message switching
hub Vs. switch  TCP vs UDP 

RF and Wireless Terminologies

SATELLITE  RF  Antenna  Avionics  Wireless  LiFi vs WiFi  MiFi vs WiFi  BPSK vs QPSK  BJT vs FET  PDH vs SDH 

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