Public Switched Telephone Network SPSTN SPSTN n Partial

Public Switched Telephone Network (S-PSTN)

S-PSTN n 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. n 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.

Table of Contents Overview Learning Objectives Network Overview Switching Systems Post-Divestiture Network Signaling Contributors 5 6 7 13 19 28 38

Overview n n n Network setup Switching systems Post-Divestiture network Signaling SS 7 CCS

Learning Objectives After completing this module you will be able to: n Discuss the basic operations of the Public Switched Telephone Network (PSTN) n Define the telephony switching hierarchy n Describe the signaling required to complete a typical telephone call through the PSTN n Describe how the SS 7 network is overlayed onto the PSTN

Network Overview

What Is A Network ? Switching Office CPE Transmission Facilities

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

Switching Offices SWITCHING OFFICE CONTROL NETWORK

Transmission Facilities Switching Line Trunks Office Switching Office Special Service Circuit Line

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: n Single Line Telephone Set n Modems or Data Sets n Private Branch Exchange (PBX)

Switching Systems

Traffic Networks n The Public Switched Telephone Network: q Pre-divestiture q Post-divestiture

Local Network Structure Exchange Area 1 Wire Center A • Exchange Area 4 Exchange Area 2 Wire Center B • Exchange Area 5 Exchange Area 3

Typical Local Network Tandem Office T Wire Center C Tandem Trunk Groups (Final) Wire Center A Direct Trunk Groups (High Usage) Wire Center B

Toll Network Structure Pre-Divestiture FINAL in ct ne FINAL Toll Connecting ll g in C ct on ne To HU 7 Toll Center H on Telephone 1 FINAL HU 1 Primary Center G C Local Office (End Office) Class 5 HU 2 HU 3 Sectional Center F ll g HU 4 To Toll Center A Class 4 HU 5 FINAL Regional Center B Class 3 Regional Center E HU 6 FINAL Regional Center C Class 2 FINAL Regional Center D Class 1 Local Tandem Office Local Office Telephone 2

Toll Network Structure Pre-Divestiture in ct ne FINAL Toll Connecting ll g in C ct on ne To HU 7 Toll Center H on Telephone 1 FINAL HU 1 Primary Center G C Local Office (End Office) Class 5 HU 2 HU 3 Sectional Center F ll g HU 4 To Toll Center A Class 4 HU 5 FINAL Regional Center B Class 3 Regional Center E HU 6 FINAL Regional Center C Class 2 FINAL Regional Center D Class 1 Local Tandem Office Local Office Telephone 2

The Post. Divestiture Network

The Post-1984 Network IEC 1 IEC 2 IEC 3 LATA x Inter. LATA Carriers LATA y

Typical LEC Network Central Office Tandem Office IC POP Switching Systems Distribution Facility/Local Loop Interoffice Facilities/Trunks Distribution Facility/Local Loop LEC Central Office IC

LATA Access Services n Switched Access n Special Access (Nonswitched)

Switched Access Service n n n Feature Group A Feature Group B Feature Group C Feature Group D Equal Access End Office

North American Numbering Plan Area N X X 2 -9 0 -9 Central Office N X X 2 -9 0 -9 Station X X X 0 -9 0 -9 X 0 -9

Number Plan Area (NPA) These special purposes codes include: NXX Reserved Codes: N 11 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

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 -8* = 152 *Excluding codes of N 11 format New format N X X 8 x 10 = 800 -8* = 792* *Excluding codes of N 11 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 Codes Trunk Code Local Code Subscriber Number

Signaling

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

Signaling 1 2 Terminating Switching Office Originating CPE Terminating CPE Idle Off-hook Dial Tone Dialed Digits 3 Off-hook (wink) On-hook (wink) Dialed Digits Audible Ring Answer Disconnect Ringing Off-hook

Signaling 1 2 Terminating Switching Office Originating CPE Terminating CPE Idle Off-hook Dial Tone 3 Dialed Digits 4 5 Off-hook (wink) On-hook (wink) Dialed Digits Audible Ring Answer Disconnect 6 6 Ringing Off-hook

Signaling 1 2 Terminating Switching Office Originating CPE Terminating CPE Idle Off-hook Dial Tone 3 Dialed Digits 4 5 Off-hook (wink) On-hook (wink) 7 Dialed Digits Audible Ring Answer Disconnect 6 6 Ringing Off-hook 8

Signaling 1 2 Terminating Switching Office Originating CPE Terminating CPE Idle Off-hook Dial Tone 3 Dialed Digits 4 5 Off-hook (wink) On-hook (wink) 7 Dialed Digits Audible Ring Answer 10 Disconnect 6 6 Ringing 8 Off-hook 9 10

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 (SS 7) LINKS F CO CO CO A A E STP C B D B STP C A SCP

SS 7 Switching Office B Switching Office A STP Customer “B” Customer “A” IAM ACM ANM REL RLC

Network Administration, Maintenance and Services n n n Network Management Traffic Measurements Billing Maintenance Customer Services