Lesson 1 Topics

PSTN Overview The Role of The PSTN CPE An Example, How A Telephone Works Public Switch Telephone NetworkThought For The Week Building on Lessons Learned In TCM 134The

Study This Set Of PowerPoint Slides Complete Assignment 1 And Post All Answers In The Lesson 1 Drop Box By The Due Date.

In This Lesson, You Will Learn How The Public Switch Telephone Network (PSTN) Was Originally Designed To Carry Voice Services. Next, We Will Learn That The Original Design Of The PSTN Has Evolved To Carry Most Of Todays Advanced Voice, Data And Video Services. You Will Study A Brief Overview Of The PSTN A Building Block For Our Course. Finally, You Will Learn How One Piece Of CPE Works In Conjunction With The PSTN. Objectives

Section 1.1 PSTN Overview

The Public Switch Telephone Network (PSTN) Is A Mesh Network Of Lines, Trunks, Switches, Etc. That Connects Customer Provided Equipment (CPE) Together To Allow The CPE To Communicate Together. The PSTN Was Originally Designed To Optimize The Transmission Of Voice Services. What Is The PSTN?

Major Elements Of The PSTNCO Class 5 SwitchCO Class 2 SwitchResidence CPECO Class 1 SwitchPBX or KTSDigital LoopAnalog LoopDigital Interoffice TrunksOffice BldgPSTN

There Are Four Major Elements Of Todays Public Switched Telephone Network (PSTN).

Customer Premises Equipment (CPE) Access System Transport Signaling The Four Major Elements Of The PSTN

Prior To 1984 And The Breakup Of The AT&T Monopoly, All Parts Of The Public Switched Telephone Network Was Owned And Operated By The Telephone Company.After 1984, The Ownership And Maintenance Of All Telecommunications Equipment And Wiring On The Customers Site Became The Responsibility Of The Customer. Customer Premises Equipment

Customer Premises Equipment Includes: Telephones Fax Machines Wiring & Jacks Multiplexers Cross Connect Systems Computers PBXs Key Systems CSUs DSUs Video Codecs Etc.

Customer Premises Equipment - Continued: Each Of These Pieces Of CPE Are Different. They Each Work Differently Electronically, And Many Have Different Ways In Which They Connect To The PSTN. Later In This Lesson We Will Study In More Detail, As One CPE Example, How Telephones Work Electronically And How They Connect To The PSTN. Later In This Course, We Will Study How Several Other CPEs Work Electronically And How They Connect To The PSTN.

The FCC Defined A Point, The Demarcation Point, In The Telecommunications Network That Separates CPE From Telephone Company-Provided Equipment And Wiring. The Demarcation Point Is Often Referred To As The Demarc. Demarcation Point

The Access Component Of The PSTN Provides Customers All Of The Wiring And Equipment For The Customers CPE To Be Connected To The Central Core Of The Public Switched Telephone Network. The Access System Includes Both Lines And Trunks And The Termination Equipment In The End Office.

Access Lines And Trunks Along With The Telephone Poles, Conduits, Connector Boxes, Etc. Are Referred To As The Local Loop. Access System

Some Samples Of End Office Termination Equipment. Central Office Termination Equipment

Most Access Circuits Run From The Carriers Central Office And A Residence Are Analog Circuits (Ref. Slide 6). Most Access Circuits Run Between The Carriers Central Central Office And Businesses With Private Branch Exchanges Are Digital Circuits (Ref. Slide 6). Since Most Circuits That Connect Central Offices To Customer Premises Are Connected To Residences, Then, Most Circuits In The Local Loop Are Analog. Access System

Access System Residential AccessClass 5 Switch Each Customer Circuit Is A Two-Wire Cable From The Customer Demarc Out To The First Cross Connection Box A & B Cross Connection Pedestal Or Cross Connection Box

Access System Residential AccessClass 5 Switch Even Though Customer Circuits Are Two-Wire Cable, Carriers Will Install Either 2-Pair, Or 4-Pair Cable. Customer Circuits Are Combined With Other Circuits At The Cross Connection Box 2-Pair Cable100-Pair Cable

Access System Residential AccessClass 5 Switch Each Customer Circuit Is A Two-Wire Cable From The Customer Demarc Out To The First Cross Connection Box. From The Cross Connection Box To The Central Office The Customer Two-Wire Circuit Is Carried Inside Of A Much Thicker Cable That Carries 100 Pairs Of Cable Or More. Each Customers Two-Wire Circuits Remain Separate From Other Customers Circuits Which Are Carried On Separate Sets Of Wires.

Plastic InsulatorMetal Conductor Sample 4-Pair Cable The Photo Below Shows A 4-Pair Copper Wire Cable Similar To The Type Of Cable That Might Be Run To A Residence. Each Pair Of Cable Supports A Separate Circuit. Because Of The Cost Of Installing Outside Cable, Carriers Usually Install More Than 1 Pair Of Wires.

Access System Business AccessClass 5 Switch Access For Small Business Customer Circuits Are Similar To Residential Access Circuits. Business Trunks From PBXs Are Digital, Usually T1s Or T3s. If The Trunks Are T1s, 24 Separate End-User Applications Are Carried On One Set Of Wires At A Time. Well Study More About Data Rates Of Trunks In The Lessons In Module 3 Of Our Text.TrunksBusiness W/ PBX

Transport Component Of The PSTN Transport Means Transmission Taking Voice, Data, And Video Signals From One Subscribers Access Line And Delivering Them To Another Customers Access Line. The End-Office, Or Class 5 Central Office Is The Point Where All Customer Access Lines Connect. The Trunks Within The Transport Core Include A Wide Variety Of Transmission Speeds (e.g. T1, T3, OC-1, OC-12) And Transmission Media (e.g. Copper And Optical Fiber). Well Study More About The Transport System Later In This Course.

Signaling Component Of The PSTN Signaling Means The Controlling Of Calling Including: Setting Up A Path For A Conversation Through The Transport Core. Maintaining And Terminating The Conversation Path. Collecting Billing Information. Handling Other Supervisory Functions. Well Study More About The Signaling System Later In This Course.

Section 1.2 The Role Of The PSTN

Many People View Voice Services, And The PSTN Used To Deliver Those Services, As Old, Ho- Hum Topics. Those People Reason That The Most Lucrative, Future Growth Areas In Telecommunications Will Be In Data Services As Opposed To Voice Services. Many Of Those People Believe That Telecommunications Students Should Not Study Topics Related To Voice Communications Services And The PSTN. The Role Of The PSTN

Those Same People Believe That Data Communications Will Underpin The New Emerging Technologies And Will Be The Wave Of The Future.Why Then Study Plain Old Telephony? The Role Of The PSTN - Continued

Throughout This Course We Will Learn How POTS And The PSTN Play Vital Roles In Providing Many Services Such As: Voice-over-IP (VoIP) Third Generation Cellular Internet Applications E-Mail E-Commerce WANs & MANs Etc., Etc., Etc.Todays Emerging TechnologiesDo These Services Seem Like POTS!

Cellular Many Major Cellular Features Depend On The PSTN Two Examples Follow Several Examples Of The Role Of The PSTN

A Cell Call Placed To A Land-Based Phone Travels Through The PSTNCO Class 5 SwitchCO Class 2 SwitchCO Class 1 SwitchAnalog LoopDigital Interoffice TrunksRadioControllerMTSOCellular User Residence CPE

SS7/ PSTNCellular Roaming Depends On The PSTN SS7 NetworkRoamingMTSOHome MTSOVLRHLRSSPSSPSTPSTPRoaming Cellular User Cellular Roaming Would Not Be Possible Without SS7 Network In PSTN

Private Line Data Networks Rely On Several Elements Of The PSTN Another Example Of The Role Of The PSTN

Site ASite B56 KbpsPrivate LineSite E56 KbpsPrivate LineT3Private LineSite DOC3 Private LineSite C56 KbpsPrivate LineT1Private LinePSTN Backbone Circuits Are Provisioned To Create Corporate Private-Line Data Networks RouterRouterRouterRouterRouter

Router

ASN Router

Router

ASN Router

Router

ASN Router

Router

ASN Router

Router

ASN Router

Internet Access Relies On The PSTN Another Example

ISP Access Use PSTN CircuitsCO Class 5 SwitchCO Class 2 SwitchCO Class 1 SwitchMultiplexed/Channelized Digital LoopAnalog LoopDigital Interoffice TrunksResidential End-UserISPMCDLCorporate End-UserPSTNRouter

Router

ASN Router

Section 1.3 Customer Premises Equipment

CPE Includes All Telecommunications-Related Equipment That Is Located On The Consumers Side of the Demarcation Point.Customer Premises Equipment Customer Premises Equipment

Lets Study How Telephones, One Type Of CPE, WorksExample Of Some Modern Telephones

Direct Current (DC)

- An Electrical Charge Flows Steadily In One Direction Over the Conductor.Voltage Over Time In A DC CircuitTimeVoltage+- Do You Remember From TCM 134 How DC Current Flows?

DC VoltageResistor RIDC VoltageResistor RI Flows When Switch ClosedDC Series Circuits With & W/O A Switch Ohms Law: V = I x R

DC VoltageResistor R Do You Remember From TCM 134 How A Capacitor Affects Current Flow In A Circuit?Does I Flow?Does Current Flow In Circuits A Or B?CapacitorAC VoltageResistor RCapacitorDoes I Flow? Ohms Law: V = I x R

A View Of A Telephone Set

RingerLine From CORTSwitch HookHybrid CoilBalancing NetworkReceiverTransmitter123456789*0# Examine The Diagram Below To See If You Can Apply Any Of The Lessons Learned From The Previous Two Slides. Under What Conditions Will Current Flow (1) Through The Ringer, (2) Through The Keypad, and (3) Into The Hybrid Coil.Closed Functional Diagram Telephone Set

RingerLine From CORTSwitch HookHybrid CoilBalancing NetworkReceiverTransmitter123456789*0# What Should The CO Switch Do First? What Should The CO Switch Do Next?Closed What Does The Central Office Do To Allow You To Dial Your Telephone?

A Touch Tone Phone Operates By Transmitting A Combination Of Two Frequencies Each Time A Button Is Pressed.Pressing Each Button Sends Out A Different Combination Of Frequencies. How Does DTMF Dialing Work?

Rotary Dialing - A User Chooses A Number And Turns A Wheel From That Number To The Finger Stop Then Releases The Wheel.Finger Stop How Does Rotary Dialing Work?

The Phones Internal Electronics Repeatedly Breaks The Electric Current To Signal The Number Dialed. The Interrupts In The Current Causes Pulses Of Specific Lengths, These Pulses Of Interrupted Current Flow Are Used In Pulse Dialing Rather Than Frequencies To Represent Each Digit. How Does Rotary Dialing Work? - Continued

To Dial The Number 2 The Phones Electronics Breaks The Current 2 Times. To Dial The Number 9 The Phones Electronics Breaks The Current 9 Times. Question: How Is The Number 0 Dialed? How Does Rotary Dialing Work? - Continued

RingerLine From CORTSwitch HookHybrid CoilBalancing NetworkReceiverTransmitter123456789*0# How Is Current Transitioned From The Two-Wire CO Circuit To The Four Wires Required To Operate The Receiver And Transmitter? What Is An Impedance Mismatch & How Does It Apply Here?Closed Operation Of The Receiver And Transmitter

Carbon Filled Receiver/Transmitter Carbon Particles Used To Create Current. Transmitter - The Input Voice Alternately Compresses The Carbon Particles Which Create A Matching Oscillating Current. Receiver The AC Current From The Telephone Wires Moves A Membrane Which In Turn Alternately Compresses The Carbon Particles Which Produces Sound.

RingerLine From CORTSwitch HookHybrid CoilBalancing NetworkReceiverTransmitter123456789*0# What Is The Role Of The Hybrid Coil Or Hybrid Network? What Is The Role Of The Balancing Network?Closed Hybrid Coil And The Balancing Network

RingerLine From CORTSwitch HookHybrid CoilBalancing NetworkReceiverTransmitter123456789*0# What Should The CO Switch Do First? What Should The CO Switch Do Next?Open How Does The Central Office Ring Your Telephone?

RingerLine From CORTSwitch HookHybrid CoilBalancing NetworkReceiverTransmitter123456789*0# When The Switch Hook Is Closed, Current Flows.ClosedCurrentCurrent Functional Diagram Telephone Set: Switch Hook Closed

The Electronics Within Each CPE Listed Earlier Works Differently. All CPE Are Similar, However, Since They All Eventually Create Electrical Signals Which Are Transmitted Over Telecommunications Wiring And Those Signals Are Received By A Compatible Piece Of CPE. Later In This Course, We Will Have The Opportunity To Study How Additional CPE Works. Summary Of CPE