Public Switched
Telephone
Network
(S-PSTN)
July, 2001
Copyright 2001 Global Wireless Education Consortium
S-PSTN 1
S-PSTN
© Copyright 2001 Global Wireless Education Consortium
All rights reserved. This module, comprising presentation slides with notes,
exercises, projects and Instructor Guide, may not be duplicated in any way
without the express written permission of the Global Wireless Education
Consortium. The information contained herein is for the personal use of the
reader and may not be incorporated in any commercial training materials or
for-profit education programs, books, databases, or any kind of software
without the written permission of the Global Wireless Education Consortium.
Making copies of this module, or any portion, for any purpose other than your
own, is a violation of United States copyright laws.
Trademarked names appear throughout this module. All trademarked names
have been used with the permission of their owners.
July, 2001
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S-PSTN 2
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.
GWEC EDUCATION PARTNERS: This material is
subject to the legal License Agreement signed by your
institution. Please refer to this License Agreement for
restrictions of use.
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S-PSTN 3
Table of Contents
Overview
Learning Objectives
Network Overview
Switching Systems
Post-Divestiture Network
Signaling
Contributors
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5
6
7
13
19
28
38
S-PSTN 4
Overview
July, 2001
Network setup
Switching systems
Post-Divestiture network
Signaling
SS7
CCS
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S-PSTN 5
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
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S-PSTN 6
Network Overview
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S-PSTN 7
What Is A Network ?
Switching
Switching
Office
Office
CPE
CPE
Transmission Facilities
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S-PSTN 8
Public Switched
Telephone Network
(PSTN)
Major Components of the Public Switched
Telephone Network (PSTN):
Switching Offices
Transmission facilities
Customer Premise Equipment (CPE)
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S-PSTN 9
Switching Offices
SWITCHING
OFFICE
CONTROL
NETWORK
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S-PSTN 10
Transmission Facilities
Switching
Line
Trunks
Switching
Office
Office
Line
Special
Service
Circuit
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S-PSTN 11
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)
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S-PSTN 12
Switching Systems
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S-PSTN 13
Traffic Networks
The Public Switched Telephone Network:
Pre-divestiture
Post-divestiture
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S-PSTN 14
Local Network Structure
Exchange
Area 1
Wire
Center
A
Exchange
Area 2
Wire
Center
B
•
Exchange
Area 5
•
Exchange
Area 3
Exchange
Area 4
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Typical Local Network
Tandem Office T
Wire
Center
C
Tandem Trunk
Groups (Final)
Wire
Center
A
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Direct Trunk Groups
(High Usage)
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Wire
Center
B
S-PSTN 16
Toll Network Structure
Pre-Divestiture
FINAL
Regional Center D
Class 1
Regional Center E
HU6
Regional Center C
Class 2
Sectional Center F
HU5
Primary
Center HU7
G
HU4
Regional Center B
Class 3
HU2
HU3
HU1
Toll Center A
Class 4
Toll Center H
Toll Connecting
Local Office
(End Office)
Class 5
Local
Tandem
Office
Local Office
Telephone 1
July, 2001
Telephone 2
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S-PSTN 17
Toll Network Structure
Pre-Divestiture
FINAL
Regional Center D
Class 1
Regional Center E
HU6
Regional Center C
Class 2
Sectional Center F
HU5
Primary
Center HU7
G
HU4
Regional Center B
Class 3
HU2
HU3
HU1
Toll Center A
Class 4
Toll Center H
Toll Connecting
Local Office
(End Office)
Class 5
Local
Tandem
Office
Local Office
Telephone 1
July, 2001
Telephone 2
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S-PSTN 18
The PostDivestiture
Network
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The Post-1984 Network
IEC1
IEC2
IEC3
LATA x
InterLATA
Carriers
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LATA y
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Typical LEC Network
Central Office
Tandem Office
IC POP
Switching
Systems
Distribution
Facility/Local Loop
Interoffice
Facilities/Trunks
Distribution
Facility/Local Loop
Central Office
LEC
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IC
S-PSTN 21
LATA Access Services
Switched Access
Special Access (Nonswitched)
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S-PSTN 22
Switched Access
Service
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Feature Group A
Feature Group B
Feature Group C
Feature Group D
Equal Access End Office
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S-PSTN 23
North American
Numbering Plan
Numbering Plan Area
N
X
X
2-9 0-9 0-9
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Central Office
N
X
X
2-9 0-9 0-9
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Station
X
X
X
X
0-9 0-9 0-9 0-9
S-PSTN 24
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 ICs
800, 888, 877, and 866 Service (INWATS)
900 Service (DIAL-IT Service)
311 Non-Emergency Police and Fire
411 Local Directory Assistance
611 Repair Service*
811 Business Office*
911 Emergency Number
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S-PSTN 25
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
N 0/1 X
8 x 2 x 10 = 160
160-8* = 152
*Excluding codes of N11 format
New format
N X X
8 x 10 x 10 = 800
800-8* = 792*
*Excluding codes of N11 format
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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
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Country Codes
Trunk Code
Local Code
Subscriber Number
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S-PSTN 27
Signaling
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S-PSTN 28
Signaling
Signaling is the generation, transmission,
and reception of information needed to
direct and control the setup and
disconnect of a call.
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Signaling
1
Terminating
Switching
Office
Originating
Switching
Office
Originating
CPE
Terminating
CPE
Idle
Off-hook
2
Dial Tone
3
Dialed Digits
Off-hook
Off-hook (wink)
On-hook (wink)
Dialed Digits
Audible Ring
Answer
Ringing
Off-hook
Disconnect
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S-PSTN 30
Signaling
1
Terminating
Switching
Office
Originating
Switching
Office
Originating
CPE
Terminating
CPE
Idle
Off-hook
2
Dial Tone
3
Dialed Digits
4
5
Off-hook
Off-hook (wink)
6
On-hook (wink)
6
Dialed Digits
Audible Ring
Answer
Ringing
Off-hook
Disconnect
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S-PSTN 31
Signaling
1
Terminating
Switching
Office
Originating
Switching
Office
Originating
CPE
Terminating
CPE
Idle
Off-hook
2
Dial Tone
3
Dialed Digits
4
5
Off-hook
Off-hook (wink)
6
On-hook (wink)
6
7
Dialed Digits
Audible Ring
Answer
Ringing
8
Off-hook
Disconnect
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S-PSTN 32
Signaling
1
Terminating
Switching
Office
Originating
Switching
Office
Originating
CPE
Terminating
CPE
Idle
Off-hook
2
Dial Tone
3
Dialed Digits
4
5
Off-hook
Off-hook (wink)
6
On-hook (wink)
6
7
Dialed Digits
Audible Ring
Answer
10
July, 2001
Disconnect
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Ringing
8
Off-hook
9
10
S-PSTN 33
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.
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Signaling System 7
(SS7) LINKS
F
CO
CO
CO
A
A
E
STP
STP
C
B
B
D
STP
STP
C
A
SCP
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A
SCP
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SS7
Switching
Office B
Switching
Office A
STP
Customer “B”
Customer “A”
IAM
IAM
ACM
ACM
ANM
ANM
REL
RLC
July, 2001
REL
RLC
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Network Administration,
Maintenance and
Services
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Network Management
Traffic Measurements
Billing
Maintenance
Customer Services
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S-PSTN 37
Industry Contributors
The following organizations provided materials and
resource support for this module:
AT&T Wireless (http://www.attwireless.com)
Lucent Technologies (http://www.lucent.com)
Motorola (http://www.motorola.com)
RF Globalnet (http://www.rfglobablnet.com)
Telcordia Technologies, Inc. (http://www.telcordia.com)
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Individual Contributors
The following individuals and their organization or
institution provided materials, resources, and development
input for this module:
Dr. Philip DiPiazza
Florida Institute of Technology
http://www.fit.edu/
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S-PSTN 39
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S-PSTN 40
