TDC 461: Basic Telecommunications DePaul University 9 April, 2001 LoriLee M. Sadler

TDC 461: Basic Telecommunications

DePaul University

9 April, 2001

LoriLee M. Sadler

Agenda

• Telephone Network

• Telephone Numbering

Format

• Signaling on Subscriber

Loop

• Analog vs. Digital

Information

• Central Office Switch

Technologies

• How is a Voice Call

Made?

• Carrier Services

Public Switched Telephone Network:

AmeritechCentral Office


PBX

Subscriber LinesCentrex Lines

IXCPOP

AmeritechTandem Office

IXCPOP

Inter-Office Trunks

Dir

ect

IXC

Tru

nkPOP = Point of PresencePBX = Private Branch Exchange

The PSTN:

• Topology of Connections

• Network=>– Demarcation point (Demarc)=>also called

station drop.

Network Configuration

• Star configuration from the Central Office (CO) to the demarc

• Star or ring configuration from the Central Office to other COs or higher-level offices

• Wire Center or FrameSwitch

• Physical vs. logical connections• Facilities

The Subscriber (Local) Loop

Outside Plant

• Demarcation Point (Demarc)

• Feeders:

• Lateral distribution:

• Branch feeders:

Subscriber Loop Signaling

• Carrier Sense=>

Battery

CentralOffice

-48 v.

The Subscriber Loop

• The Subscriber Line or Subscriber Loop is made up of 2 copper wires twisted together (wires called “tip” and “ring”)

Battery

CentralOffice

-48 v.

The Subscriber LoopIdle Line

• Central Office provides battery power (48 volts DC) to subscriber loop.

• When telephone is ON-HOOK, it keeps loop open (wires are not connected) and there is no current flow.

Battery

CentralOffice

-48 v.

The Subscriber LoopService Request

• Off-Hook signals request

• Request fulfilled by CO

Battery

CentralOffice

-48 v.

North American Numbering Plan (NANP)

• Determines format for dialed numbers.• Administered by BellCore• Format before 1995:

Prefix + 0/1 + N(0/1)X - NNX - XXXX (N digits are 2-9, X digits are 0-9)

• Format as of January, 1995:Prefix + 0/1 + NXX - NXX - XXXX

(N digits are 2-9, X digits are 0-9)

Address Signaling Rotary Pulse Dial

– After pulling dial for digit ‘N’, telephone opens and closes subscriber loop ‘N’ times as dial returns to its original position.

• Dual Tone Multifrequency (DTMF) or Touch Tone– One frequency assigned to each

row and each column.

– Pressing any key sends a 2-frequency signal tone.

ABC

2DEF

31

Oper

0 #*

TUV

8WXY

9PRS

7

JKL

5MNO

6GHI

4

1447 Hz

852 Hz

770 Hz

697 Hz

1209 Hz 1336 Hz

941 Hz

Business Station Set Features

• Access to multiple lines:– Multiple Directory Numbers– Multiple Access to single Directory Number (MADN)– Call Pickup privileges to other lines– Call status indicator lamps and display– Intercom dialing

• Speakerphone• Voice Mail Access

– Message Waiting lamp

Business Station Set Features

• Calling Features:– Hold– Drop– Conference– Transfer– Speed Dial– Call Forward– Call Waiting

TrunksAmeritech

Central OfficeAmeritech

Central OfficeInter-Office Trunks

Repeaters Repeaters

• • •

Analog TrunksAmeritech



Repeaters Repeaters

• Trunk types:– 2-wire analog trunk– 4-wire analog trunk

Digital TrunksAmeritech



Repeaters Repeaters

• 1962 (T-1 carrier)

Digital TrunksAmeritech



Repeaters Repeaters

• Advantages of Using Digital Trunks:

Voice Digitization1 Voice Channel = 64,000 bits/second

Sample Quantize 100111011

8000 samples/sec 8 bits/sample

Call over Digital TrunkAmeritech



Regenerators Regenerators

• Codec (Coder/decoder) circuits in COs do analog-digital conversion.

• Analog Central Office Switch:– Analog signal is switched internally.

• Digital Central Office Switch:– Digital signal is switched internally.

Channel BanksAnalogSwitch

AnalogSwitch

T-1 TrunkRepeater Repeater

T-1Channel

Bank

T-1Channel

Bank

......

24 AnalogVoice Channels

• T-1 Channel Bank converts between 24 analog voice channels and a single T-1 trunk.– Digitizes 24 voices (codec function)– Combines 24 DS0 signals into a DS1 signal

(multiplexing function)

Central Office Switch Technologies


Wire Center Components

• Central Office Switches

• Main Distribution

Frame (MDF)

• Cable Vault

Main Distribution Frame (MDF)

C.O. Switch

Central Office / Wire Center

Switch Side

Cable Side (Protected)

Switch Matrix

ServiceCircuits

CommonControl

DataStore

Trunk Cards

Cable Vault

OutsidePlant

Line Cards


• Central Office Switch Components– Common Control

– Data Store

– Service Circuits


C.O. Switch


Switch Side


Switch Matrix

ServiceCircuits

CommonControl

DataStore

Trunk Cards

Cable Vault

OutsidePlant

Line Cards


• Central Office Switch Components– Switch Matrix

– Line Cards

– Trunk Cards


C.O. Switch


Switch Side


Switch Matrix

ServiceCircuits

CommonControl

DataStore

Trunk Cards

Cable Vault

OutsidePlant

Line Cards


• Distribution Frame– –

• Cable Vault• Outside Plant

– –


C.O. Switch


Switch Side


Switch Matrix

ServiceCircuits

CommonControl

DataStore

Trunk Cards

Cable Vault

OutsidePlant

Line Cards

How is a Voice Call Made?

A Voice Call

• Originating phone goes off-hook.

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

LineCards

TrunkCards

A Voice Call• Customer dials number.

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

LineCards

TrunkCards

A Voice Call

Phones go on-hook.

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

LineCards

TrunkCards

Inter-Office Calls

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

LineCards

TrunkCards

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

TrunkCards

LineCards

Inter-Office Trunk

Network Structure



PBX


IXCPOP


IXCPOP

Inter-Office Trunks

Dir

ect

IXC

Tru


Residential Services

• Direct Distance Dialing or DDD service

• Party Line Service

Business Services

• Line vs. Trunk Service

• Private vs. Switched Service

Private Line Services• Private Line Service provides a dedicated

circuit between two locations

Private Line ServicesCentral Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

LineCards

TrunkCards

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

TrunkCards

LineCards

Inter-Office Trunk

• Private Line / Leased Line / Dedicated Line

Private Line Services• Foreign Exchange (FX) Line

• Off Premises Extension (OPX)


Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

LineCards

TrunkCards

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

TrunkCards

LineCards

Inter-Office Trunk

• Foreign Exchange (FX) Line

Private Line Services

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

LineCards

TrunkCards

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

TrunkCards

LineCards

Inter-Office Trunk PBX

• Off Premises Extension (OPX)

FX Line Example• LhasaLabs Corporation in Chicago has many

customers in New York

– DDD Chgo-NY costs 15 cents per minute

– FX line Chgo-NY costs $800 per month

– LhasaLabs makes about 25 calls to NY each day, each

call lasting about 10 minutes

– SHOULD LhasaLabs GET AN FX LINE?

Private Line Services• Tie Line

• Dedicated Access Line to IXC POP


Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

LineCards

TrunkCards

Central Office

Switch Matrix

ServiceCircuits

CommonControl

DataStore

MDF

TrunkCards

LineCards

Inter-Office Trunk PBXPBX

• Tie Line

Private Line Services

• Dedicated access to IXC POP

LEC Sw itch

Switch M atrix

ServiceCircuits

CommonControl

DataStore

M DF

LineCards

TrunkCards

IXC Sw itch

Switch M atrix

ServiceCircuits

CommonControl

DataStore

M DF

TrunkCards

LineCards

IXC T runkPBX

Switched Line Services• Direct Distance Dialing (DDD)

• Wide Area Telecommunications Service (WATS)

• IN-WATS (800, 888 services)

WATS, IN-WATS

• WATS=>Wide-area telecommunications services; Refers to outbound calls only, not inbound.

• old style with banded service rates

• Full-time WATS=>

• Measured WATS=>

WATS Example

• Lhasa Labs is located in Chicago and many customers in New York. Lhasa Labs wants to offer a toll free number to its New York customers. Lhasa Labs anticipates using 200 hours per month.– $37.50 per line per month; additional usage at $.15 a

minute –

– Compare to DDD?– Compared to a T1?

Switched Line Services• 900 Services

–

• International WATS–

• Remote Call Forwarding– –

Switched Line Services• Directory Services

–

• Wide Area Telecommunications Service (WATS)–

• IN-WATS (800, 888 services)–

RCF Example• LhasaLabs Corporation in Chicago has many

customers in New York. LhasaLabs wants to offer a local New York number.– DDD Chgo-NY costs 15 cents per minute

– RCF service costs $50 per month

– FX line Chgo-NY costs $800 per month

– Customers in NY make about 10 calls to LhasaLabs each day, each call lasting about 10 minutes

– SHOULD LhasaLabs GET AN FX LINE?

Residential and/or Business Features

• Call Forwarding• Call Waiting• Three-Way Calling• Call Transfer• Calling Card• Speed Calling• Automatic CallBack• etc. etc.

Network Structure



PBX


IXCPOP


IXCPOP

Inter-Office Trunks

Dir

ect

IXC

Tru


Business Services

• Line vs. Trunk Service – Is access to network directly through telephone

sets or through customer switch (Private Branch Exchange or PBX)?

• Private vs. Switched Service – Does network just provide connection (private)

or dial tone (switched)?

Line vs. Trunk Addressing• Each line has a telephone number

associated with it.– –

• A trunk does not have any telephone number associated with it. –

Documents

TDC 461: Basic Telecommunications DePaul University 9 April, 2001 LoriLee M. Sadler