Public Switched Telephone Network

(S-PSTN)

S-PSTN

Partial support for this curriculum material was provided by the National Science Foundation's Course, Curriculum, and Laboratory Improvement Program under grant DUE-9972380 and Advanced Technological Education Program under grant DUE‑9950039.

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Table of Contents

Overview 5

Learning Objectives 6

Network Overview 7

Switching Systems 13

Post-Divestiture Network 19

Signaling 28

Contributors 38

Overview

Network setup Switching systems Post-Divestiture network Signaling SS7 CCS

Learning Objectives

After completing this module you will be able to: Discuss the basic operations of the Public Switched

Telephone Network (PSTN) Define the telephony switching hierarchy Describe the signaling required to complete a typical

telephone call through the PSTN Describe how the SS7 network is overlayed onto the PSTN

Network Overview

What Is A Network ?

Switching

Office

CPE CPE

Transmission Facilities

Switching

Office

Public Switched Telephone Network (PSTN)

Major Components of the Public Switched Telephone Network (PSTN): Switching Offices Transmission facilities Customer Premise Equipment (CPE)

Switching Offices

CONTROL

NETWORK

SWITCHING

OFFICE

Transmission Facilities

Switching

Office

Switching

Office

Trunks

Line Line

Special Service Circuit

Customer Premise Equipment (CPE)

Customer Premise Equipment (CPE) is the term used to identify any piece of equipment supplied by the customer to interface with the PSTN. Examples include: Single Line Telephone Set Modems or Data Sets Private Branch Exchange (PBX)

Switching Systems

Traffic Networks

The Public Switched Telephone Network:

Pre-divestiture

Post-divestiture

Local Network Structure

ExchangeArea 5

ExchangeArea 4

ExchangeArea 3

ExchangeArea 2Exchange

Area 1

WireCenterA

WireCenterB

•

•

Typical Local Network

Tandem Office T

WireCenter

A

WireCenter

B

WireCenter

C

Tandem TrunkGroups (Final)

Direct Trunk Groups

(High Usage)

Toll Network StructurePre-Divestiture

Telephone 1 Telephone 2

Regional Center DClass 1

Regional Center CClass 2

Regional Center BClass 3

Toll Center AClass 4

FINALRegional Center E

Sectional Center F

PrimaryCenter

G

HU6

HU5

HU4HU3 HU2

HU1

FIN

AL

FIN

AL

FIN

AL

FIN

AL

FIN

AL

FIN

AL

Toll Center H

Toll Connecting

Local Office

Local Office(End Office)

Class 5Local

TandemOffice

HU7

Toll Connec

ting

Toll Connecting

Toll Network StructurePre-Divestiture

Regional Center DClass 1

Regional Center CClass 2

Regional Center BClass 3

Toll Center AClass 4

FINALRegional Center E

Sectional Center F

PrimaryCenter

G

HU6

HU5

HU4HU3 HU2

HU1

FIN

AL

FIN

AL

FIN

AL

FIN

AL

FIN

AL

FIN

AL

Toll Center H

Toll Connecting

Local Office

Local Office(End Office)

Class 5Local

TandemOffice

Telephone 1 Telephone 2

HU7

Toll Connec

ting

Toll Connecting

The Post-Divestiture Network

The Post-1984 Network

IEC1

IEC2

IEC3

LATA xInterLATACarriers LATA y

Typical LEC Network

Tandem OfficeCentral Office

Central Office

SwitchingSystems

InterofficeFacilities/Trunks

DistributionFacility/Local Loop

DistributionFacility/Local Loop

LEC IC

IC POP

LATA Access Services

Switched Access

Special Access (Nonswitched)

Switched Access Service

Feature Group A Feature Group B Feature Group C Feature Group D Equal Access End Office

North American Numbering Plan

Numbering Plan Area Central Office Station

N X X N X X X X X X

2-9 0-9 0-9 2-9 0-9 0-9 0-9 0-9 0-9 0-9

Number Plan Area (NPA)

These special purposes codes include:

NXX Reserved Codes: N11 Reserved Codes:

600 Used in Canada for TWX (teletype service)700 Assigned to ICs800, 888, 877, and 866 Service (INWATS)900 Service (DIAL-IT Service)

311 Non-Emergency Police and Fire411 Local Directory Assistance611 Repair Service*811 Business Office*911 Emergency Number

Number Plan Area (NPA)

Interchangeable area (or NPA) codes are NPA codes of the format NXX.

By changing from the former N-0/1-X format to the NXX format, the maximum number of assignable NPA codes increased by 640 codes as shown:

Old Format

New format

N 0/1 X8 x 2 x 10 = 160

N X X8 x 10 x 10 = 800

160-8* = 152*Excluding codes of N11 format

800-8* = 792**Excluding codes of N11 format

International Numbering

If you have made international calls, you know that the familiar NANP is a subset of the ITU international plan.

Until recently, international numbers were limited to 12 digits.

1, 2 or 3 digits

Varies by location

Country CodesTrunk CodeLocal CodeSubscriber Number

Signaling

Signaling

Signaling is the generation, transmission, and reception of information needed to direct and control the setup and disconnect of a call.

SignalingOriginating

CPE

Terminating Switching

OfficeTerminating

CPE

Originating Switching

Office

Off-hook

Dial Tone

Dialed Digits

Off-hook

Off-hook (wink)

On-hook (wink)

Dialed Digits

Audible Ring Ringing

Answer Off-hook

Disconnect

Idle1

2

3

SignalingTerminating Switching

Office

Originating CPE

Terminating Switching

OfficeTerminating

CPE

Originating Switching

Office

Off-hook

Dial Tone

Dialed Digits

Off-hook

Off-hook (wink)

On-hook (wink)

Dialed Digits

Audible Ring Ringing

Answer Off-hook

Disconnect

Idle1

2

4

3

5

6

6

SignalingTerminating Switching

Office

Originating CPE

Terminating Switching

OfficeTerminating

CPE

Originating Switching

Office

Off-hook

Dial Tone

Dialed Digits

Off-hook

Off-hook (wink)

On-hook (wink)

Dialed Digits

Audible Ring Ringing

Answer Off-hook

Disconnect

Idle1

2

4

3

5

7

6

6

8

SignalingOriginating

CPE

Terminating Switching

OfficeTerminating

CPE

Originating Switching

Office

Off-hook

Dial Tone

Dialed Digits

Off-hook

Off-hook (wink)

On-hook (wink)

Dialed Digits

Audible Ring Ringing

Answer Off-hook

Disconnect

Idle1

2

4

3

5

7

6

6

8

9

10 10

Common Channel Signaling (CCS)Common Channel Signaling (CCS) is a signaling method that uses a separate dedicated channel to send and receive signaling information for a group of trunks or facilities by means of labeled messages.

Signaling System 7 (SS7) LINKS

AAAA

AA AA

EEEE

FF

COCO

COCOCOCO

DDDDBBBBBBBB

CC

CC

STPSTPSTPSTP

STSTPPSTSTPP

STSTPPSTSTPP

STPSTPSTPSTP

SCP SCP

SS7Switching Office A

Switching Office B

Customer “A”

STPSTP

Customer “B”

IAM IAM

ACM ACM

ANM ANM

RELREL

RLC RLC

Network Administration, Maintenance and Services

Network Management Traffic Measurements Billing Maintenance Customer Services