Telephone Service. 2 PSTN l The Public Switched Telephone Network l Worldwide l A call may cross many telephone company boundaries l Also Known as POTS

TelephoneTelephone

ServiceService

2

PSTPSTNN

The Public Switched Telephone Network Worldwide A call may cross many telephone company

boundaries

Also Known as POTS Plain old telephone service “Old” “Uninteresting”

3

PSTNPSTN

Importance

Corporate telephony spending is very high

Amount of use makes it very important

Deregulation is spurring price and product complexity

Management is exploding in complexity

Datacoms & telephony are managed together

4

The Traditional Telephone The Traditional Telephone SystemSystem

Customer Premises Local Loop Switching Office

End Office Trunk Lines

5

Customer PremisesCustomer Premises

Your home or office You control service on your premises

Beyond your premises, you need a telephone carrier

6

Local LoopLocal Loop Line between your premises and the first

telephone company switching office Limits your transmission speed Usually a single twisted pair of copper wire Businesses may use higher-speed links “The Last Mile,” although often 2-4 miles

Customer Premises Switching Office

Local Loop

7

Switching OfficesSwitching Offices

Connect Telephone Callers Can support many simultaneous connections

Connection

Switching OfficeLocalLoop

CustomerPremises

CustomerPremises

8

Hierarchical Hierarchical Organization of Organization of SwitchesSwitches

Classes (1-5)

Class 5 Class 5

Class 4

Class 3

Class 4

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Trunk LinesTrunk Lines

Connect switching offices All lines except local loop

TrunkLine

LocalLoop

TrunkLines

LocalLoop

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Carriers in the United Carriers in the United StatesStates

Local Access and Transport Area (LATA) Intra-LATA Service

Local Exchange Carrier (LEC) Competitive Access Providers (CAPs)

Inter-LATA Service Inter-exchange Carriers (IXCs)

International Common Carriers (ICCs)

http://www.psc.state.md.us/psc/other/LATA.html

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Carriers in the United Carriers in the United StatesStates

POP

Point of presence

Located on LEC’s premises

Connects all customers of the LEC, CAPs, IXCs, ICCs

Allows new carriers to reach the total installed base, making competitive entry possible

Gives customers access to everyone else

http://tcbworks.cba.uga.edu/~adennis/res.htm#Organizations

12

Carriers in Most Carriers in Most CountriesCountries

PTT Public Telephone and Telegraph (Authority) Traditional telephone monopoly carrier Government-owned Nationwide service

Ministry of Telecommunication Government ministry that oversees, regulates

the PTT

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Regulation in the Regulation in the United StatesUnited States

Nationally Federal Communications Commission (FCC) Sets interstate regulations, standards, prices Can set intrastate policies that affect the nation-

wide system Within States

Public Utilities Commissions (PUCs) Regulate most intrastate matters

http://www.fcc.gov/

http://www.psc.state.md.us/psc/

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Deregulation in the Deregulation in the United StatesUnited States

Deregulation Relaxing rules that protect monopolies Fostering competition Competition should bring new services Competition should bring lower prices

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Ma Bell The Bell System AT&T Had national monopoly on long-distance

service Owned LECs serving more than 80% of the

U.S. Population

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Breaking Up Ma Bell (1983)

Justice Department antitrust suit

Results in agreement and Consent Decree

AT&T keeps long-distance service, equipment manufacturing

LECs divided among 7 Regional Bell Operating Companies (RBOCs)--”Baby Bells”

Court-administered limits on AT&T & RBOCs

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Second Breakup of AT&T (1996)

AT&T given freedom by courts to enter intra-LATA competition for transmission service

AT&T moving increasingly into international competition for transmission services

Problem: also sells equipment (switches, etc.)

Sold equipment to firms with whom it was beginning to compete for transmission services

Competitors would stop buying equipment once competition began

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Second Breakup of AT&T (1996)

Voluntarily divided the company

AT&T keeps transmission services

Lucent manufactures telephone equipment

NCR manufacturers computer equipment

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Telecommunications Act of 1996 Congressional Act

Subjects intra-LATA service to open competition

Before, many PUCs had limited local competition

New competitors for service, including the local loop (dial tone service)

New freedom in pricing

Slowed by legal maneuvering

http://www.fcc.gov/telecom.html

20

Deregulation Trends in Deregulation Trends in the U.S.the U.S.

Customer Premises Most deregulated Once, you could not own modems or even

telephones Deregulated in the 1970s Now fully deregulated: you can do what your

like on your premises

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Deregulation Trends in Deregulation Trends in the U.Sthe U.S.

Data networking services Called value added networks (VANs) Deregulated in 1970s Now wide open

Inter-LATA service Deregulated in 1970s and 1980s Now, equal access: you get to choose your long-distance

carrier Now wide-open

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Deregulation Trends in Deregulation Trends in the U.S.the U.S.

Intra-LATA Service Least deregulated Some prior deregulation Deregulation really began in earnest only with

the Telecommunications Act of 1996

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Deregulation in Other Deregulation in Other CountriesCountries

Varies Considerably

Few countries as deregulated as U.S.

Prices generally higher than U.S.

Services available in U.S. may not be available

Customer premises usually deregulated most

Basic voice telephone service usually deregulated least

24


World Trade Organization (WTO) Agreement in 1997 on Telecommunications

Services Agreement to open domestic (internal)

competition Not total deregulation Not all countries sign Timetable for deregulation may be long Encouraging but not decisive

http://www.wto.org/press/summary.htm

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Europe 1998

European Community

Has been breaking down many national monopolies

As of January 1998, high degree of domestic telecommunication competition is mandated

26

International ServiceInternational Service Provided by international common carriers

(ICCs)

Each pair of countries negotiates which ICCs may provide service

Each pair of countries negotiates settlement charges on calls

This bilateral negotiation often brings uneven pricing when you call nearby countries

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Customer Premises Customer Premises EquipmentEquipment

Private Branch Exchanges (PBXs) Internal telephone network PBX is the switch Wiring to individual telephones Telephones themselves Lines to carriers for incoming, outgoing calls

PBX

CompanyPhones

Carriers

http://www.webopedia.com/PBX.htm

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Building Telephone Building Telephone WiringWiring

In the Basement Line from carrier Termination Equipment protects carrier line PBX Wiring bundle (many pairs) out of PBX

Termination Equipment

PBX

Wiring Bundle

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Between Floors Vertical riser spaces

Vertical Riser Spaces

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Wiring Closets Break up bundle Sub-bundle goes to next floor Other wires are for distribution on floor

Wiring Closet

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Horizontal Distribution on Floors Run wires through false ceilings, conduits Drop down to faceplate phone jacks

Wiring BundleSingle Line

Wallplate

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Telephone Wiring and Telephone Wiring and LAN WiringLAN Wiring

LAN Wiring Based on Building Wiring Cat5 UTP wiring bundles

8-wire bundles 100 meter limitation

Sufficient to get from wiring closet to station Vertical Distribution

Distance limitations sufficient to reach internetting device in basement

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PBX NetworksPBX Networks

PBXs at different sites work together Connected by leased lines You can dial any telephone in the firm

LeasedLine

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PBX User ServicesPBX User Services

Speed Dialing Dial a number using a 1- or 2-digit code

Last Number Redial Easy redial of last number called

Display of Called Number Display shows the number you dialed Allows you to check for dialing errors

35


Camp On You dial another number You get a busy signal You hit the camp on button You hang up When the called party hangs up, your phone

rings You pick it up Called party’s phone rings

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PBX User ServicesPBX User Services Call Waiting

You are on the phone Hold

Place someone on hold ANI

Automatic Number Identification Displays number of calling extension when

your phone rings Conferencing

3-party calling

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Call Transfer You will be away from you desk Calls go automatically to a phone near you

Call Forwarding Someone calls you

Voice Mail Can leave messages

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PBX Attendant ServicesPBX Attendant Services

Operator Assistance In-house operators to handle problems

Automatic Call Distribution Call comes in from outside Automatically goes to correct extension

Message Center Leave message with operator for anyone in the

building

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PBX Attendant ServicesPBX Attendant Services

Paging Broadcasts call for person over loudspeakers

Nighttime Call Handling Special functions for nighttime calls E.g., transfer control to guard station

Change Requests Automated adding, dropping, changing of

numbers once information is typed in

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PBX Management PBX Management ServicesServices

Automatic Route Selection For outgoing calls Automatically selects the lowest-cost line

Call Restriction Prevent certain numbers from calling out, making

long-distance calls, etc. Call Detail Reporting

Reports with detailed charges go to departments

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Voice ResponseVoice Response Customer calls in Gets a recording that gives them a

menu of choices Caller hits button on phone to select a

menu choice Not voice recognition!

Reduces operator time Can upset customers Can also be used in product support

42

Carrier Services and Carrier Services and PricingPricing

Tariffs Filed by carriers, approved by authority Lets customer know the details of the service to

be provided Lets customer know exactly what price they

should pay Provides recourse in disputes Deregulation is generating many untariffed

services for faster response to competition

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Local CallingLocal Calling Within local area Flat rate pricing

Fixed payment per month No charge per call

Message unit pricing Charged message units for each call in local

area Depends on distance and duration Penalizes Internet access, other resource hogs

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Toll CallsToll Calls Long-distance calls

Inter-LATA or Intra-LATA Priced per minute Price based on distance

International calls Prices depend primarily on country called Prices depend less on distance than on country

called Price may be lower calling from one country

than from the other in the pair

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Toll CallsToll Calls Direct Distance Dialing

Most common method Collect Calls

Called party pays if accepts calls Pays more than direct dial rate

800/888 Numbers Area codes are with 800 or 888 Pays less than direct dial rates to support customers

900 Numbers Caller pays Pays more than direct dial rate Called company can charge for user service

46

Toll CallsToll Calls WATS

Wide Area Telephone Service Company can call out from site, to phones

throughout the WATS service area Pay less than direct dial rates

Universal Availability Personal telephone number for person Will reach you wherever you are physically Some day given at birth?

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Electronic Switching Electronic Switching ServicesServices

Switches are Computers

Can provide services beyond switching through software

Can provide PBX-like user services to carrier customers

ISDN standardizes these services and allow them to work worldwide. (Integrated Services Digital Network)

48

Electronic Switching Electronic Switching ServicesServices Automatic Number Identification (ANI)

You see the number of the person calling you

Lets you screen calls

Lets companies route caller to personal service representative automatically

Concerns about privacy

Can be blocked, so that receiver will not see your number

Receiver can refuse calls from blocked ANI

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Cellular TelephonesCellular Telephones Original Mobile Telephones

One transmitter/receiver Limited number of channels For good service can support about 20

subscribers per channel

Transmitter/Receiver

MobilePhone

50

Cellular TelephonesCellular Telephones

Divide Region into Cells One cellsite per cell Channels can be reused in non-adjacent cells

No

No

YesNo

Yes

No

No

Yes

No

UsesChannel

232

Can ReuseCh. 232?

Channel 232Used in 4 cells

51

Cellular TelephonesCellular Telephones

Reuse Without reuse, only 20 users per channel for

good service If reused 4 times, 80 subscribers per channel

Reuse Rule (Rough) Reuse factor = Number of cells / 7 If 20 cells, reuse factor is about 3

52

HandoffsHandoffs

When you move to another cell You are transferred automatically to that cell’s

cellsite

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RoamingRoaming

Take your cellphone to another city

Use it there to send and receive

Not always possible technically

May be limited procedurally because of high rates of cellular fraud in some areas

Don’t confuse this with handoff, which takes place within a cellular system between cells

54

ControlControl

Mobile Telephone Switching Office Controls cellsites, handoffs, etc. Calls go to/from MTSO Connects to POP at LEC to link to traditional

telephone (wireline) carriers

MTSO

POP atLEC

55

Placing a CallPlacing a Call

Enter number, hit send Cellphone broadcasts request Several cellsites receive, send to MTSO MTSO assigns cellphone to cellsite with

loudest signal MTSO sends message to cellphone, telling

it what incoming, outgoing channels to use

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Receiving a CallReceiving a Call

MTSO has each cellsite broadcast cellphone’s ID number

Cellphone transmits a response Responses from cellsites go to MTSO MTSO selects loudest cellsite MTSO sends message to cellphone, giving

channels and telling the cellphone to ring

57

First Generation First Generation CellularCellular

Analog Operation Limits services and signal quality

How Many Subscribers can it support? Large Cells (20-40 per city) 20 cells, and frequency reuse is about 3 (20/7) 832 channels, and with frequency reuse, 2,496

available channels 20 users per available channel, then only about

50,000 subscribers per system Engineering tricks can extend, but only

somewhat

58

First Generation First Generation CellularCellular

United States AMPS standard

Elsewhere Many incompatible standards Use different radio bands Limits multinational roaming

59

Second Generation Second Generation CellularCellular

What it is Digital instead of analog for better service Still uses large cells Still has about the same number of channels

In the United States Retrofitting existing analog systems with some digital

channels CDPD (Cellular Digital Packet Data) is the most common

technology Not widely used

Elsewhere in the World

Standardizing almost completely on GSM - General System for Mobile (communication)

60

Third-Generation Third-Generation CellularCellular

Personal Communication Service (PCS) Or Personal Communication Network (PCN)

Smaller cells More frequency reuse

More channels About 2,500

Digital, like 2nd generation 3rd generation companies usually offer more

services at a price similar to that of 1st generation instead of dropping prices

61

Third-Generation Third-Generation CellularCellular

Most of World Standardized on DCS Technology Based on GSM

U.S. FCC did not specify a standard! Different carriers use different technologies Many have standardized on DCS Your cellphone may not work with another

carrier Limits roaming

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Potential System Potential System CapacityCapacity

Category 1st Gen 3nd Gen

Cells/City 30 100?

Channel reuse ~4 ~14

Channels 800 2,500

Effective channels 3,200 35,000

Subscribers 60,000 700,000

This analysis is inexact but illustrative

63

U.S. PCS StandardsU.S. PCS Standards Coordinated by the TIA TR-45 Committee

3 standards selected DCS (Digital Communications Service)

Based on GSM

Time division multiplexing

2-3 times as many simultaneous calls as first generation in the same bandwidth

64

Personal Service Personal Service TelephonesTelephones

On the road Personal cellphone acts like 3d generation

cellphone At home

Cellphone acts like cordless telephone No cellular charges when you use it

At work Wireless PBXs treat it like a business phone No cellular charges

65

Traditional Traditional Communications Communications SatellitesSatellites

In geosynchronous orbit Appear to be stationary Far from the ground (22,300 miles) Need much power to send/receive Need dish antennas to concentrate signals Must point dish at the satellite Impractical for portable telephony

66

LEO SatellitesLEO Satellites

Low Earth Orbit Satellites Only 100 to 200 miles above the earth Need far less power to reach than 22,300 mile

geosynchronous satellites Can get by with omnidirectional antenna Can use phone of reasonable size, cost Access anywhere

OmnidirectionalAntenna

67

LEO SatellitesLEO Satellites

Satellites circle the earth every 90 minutes Handoffs between satellites serving you Like cellular, except you are (relatively)

stationary and the transmitter/receiver moves

Documents

Telephone Service. 2 PSTN l The Public Switched Telephone Network l Worldwide l A call may cross many telephone company boundaries l Also Known as POTS