Telephone
Service
PSTN

The Public Switched Telephone Network



Worldwide
A call may cross many telephone company
boundaries
Also Known as POTS


Plain old telephone service
“Old” “Uninteresting”
2
PSTN

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
3
The Traditional Telephone
System



Customer Premises
Local Loop
Switching Office


End Office
Trunk Lines
4
Customer Premises


Your home or office
You control service on your premises

Beyond your premises, you need a telephone
carrier
5
Local 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
Local Loop
Customer Premises
Switching Office
6
Switching Offices

Connect Telephone Callers

Can support many simultaneous connections
Local
Loop
Switching Office
Connection
Customer
Premises
Customer
Premises
7
Hierarchical Organization
of Switches

Class 3
Classes (1-5)
Class 4
Class 5
Class 4
Class 5
8
Trunk Lines


Connect switching offices
All lines except local loop
Trunk
Line
Local
Loop
Trunk
Lines
Local
Loop
9
Carriers in the United
States


Local Access and Transport Area (LATA)
Intra-LATA Service



Inter-LATA Service


Local Exchange Carrier (LEC)
Competitive Access Providers (CAPs)
Inter-exchange Carriers (IXCs)
International Common Carriers (ICCs)
10
States

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
11
Carriers in Most Countries

PTT





Public Telephone and Telegraph (Authority)
Traditional telephone monopoly carrier
Government-owned
Nationwide service
Ministry of Telecommunication

Government ministry that oversees, regulates
the PTT
12
Regulation in the United
States

Nationally




Federal Communications Commission (FCC)
Sets interstate regulations, standards, prices
Can set intrastate policies that affect the nationwide system
Within States


Public Utilities Commissions (PUCs)
Regulate most intrastate matters
13
Deregulation in the United
States

Deregulation




Relaxing rules that protect monopolies
Fostering competition
Competition should bring new services
Competition should bring lower prices
14
Deregulation in the United
States
 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
15
Deregulation in the United
States

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 16
Deregulation in the United
States

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
17
Deregulation in the United
States

Second Breakup of AT&T (1996)

Voluntarily divided the company

AT&T keeps transmission services

Lucent manufactures telephone equipment

NCR manufacturers computer equipment
18
Deregulation in the United
States

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
19
Deregulation Trends in 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
20
Deregulation Trends in the
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
21
Deregulation Trends in the
U.S.

Intra-LATA Service



Least deregulated
Some prior deregulation
Deregulation really began in earnest only with
the Telecommunications Act of 1996
22
Deregulation in Other
Countries

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
23
Deregulation in Other
Countries

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
24
Deregulation in Other
Countries

Europe 1998

European Community

Has been breaking down many national
monopolies

As of January 1998, high degree of domestic
telecommunication competition is mandated
25
International 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
26
Customer Premises
Equipment

Private Branch Exchanges (PBXs)





Internal telephone network
PBX is the switch
Wiring to individual telephones
Telephones themselves
Lines to carriers for incoming, outgoing calls
Carriers
PBX
Company
Phones
27
Building Telephone Wiring

In the Basement




Line from carrier
Termination Equipment protects carrier line
PBX
Wiring bundle (many pairs) out of PBX
PBX
Wiring Bundle
Termination Equipment
28
Building Telephone Wiring

Between Floors

Vertical riser spaces
Vertical Riser Spaces
29
Building Telephone Wiring

Wiring Closets



Break up bundle
Sub-bundle goes to next floor
Other wires are for distribution on floor
Wiring Closet
30
Building Telephone Wiring

Horizontal Distribution on Floors

Run wires through false ceilings, conduits

Drop down to faceplate phone jacks
Single Line
Wiring Bundle
Wallplate
31
Telephone Wiring and LAN
Wiring


LAN Wiring Based on Building Wiring
Cat5 UTP wiring bundles


100 meter limitation


8-wire bundles
Sufficient to get from wiring closet to station
Vertical Distribution

Distance limitations sufficient to reach
internetting device in basement
32
PBX Networks

PBXs at different sites work together


Connected by leased lines
You can dial any telephone in the firm
Leased
Line
33
PBX User Services

Speed Dialing


Last Number Redial


Dial a number using a 1- or 2-digit code
Easy redial of last number called
Display of Called Number


Display shows the number you dialed
Allows you to check for dialing errors
34
PBX User Services

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
35
PBX User Services

Call Waiting


Hold


Place someone on hold
ANI



You are on the phone
Automatic Number Identification
Displays number of calling extension when
your phone rings
Conferencing

3-party calling
36
PBX User Services

Call Transfer



Call Forwarding


You will be away from you desk
Calls go automatically to a phone near you
Someone calls you
Voice Mail

Can leave messages
37
PBX Attendant Services

Operator Assistance


Automatic Call Distribution



In-house operators to handle problems
Call comes in from outside
Automatically goes to correct extension
Message Center

Leave message with operator for anyone in the
building
38
PBX Attendant Services

Paging


Nighttime Call Handling



Broadcasts call for person over loudspeakers
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
39
PBX Management Services

Automatic Route Selection



Call Restriction


For outgoing calls
Automatically selects the lowest-cost line
Prevent certain numbers from calling out,
making long-distance calls, etc.
Call Detail Reporting

Reports with detailed charges go to departments
40
Voice 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
41
Carrier Services and
Pricing

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
42
Local 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
43
Toll 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
44
Toll Calls


Direct Distance Dialing
 Most common method
Collect Calls



800/888 Numbers



Called party pays if accepts calls
Pays more than direct dial rate
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
45
Toll 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?
46
Electronic Switching
Services

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)
47
Electronic Switching
Services

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
48
Cellular Telephones

Original Mobile Telephones



One transmitter/receiver
Limited number of channels
For good service can support about 20
subscribers per channel
Mobile
Phone
Transmitter/
Receiver
49
Cellular Telephones

Divide Region into Cells


One cellsite per cell
Channels can be reused in non-adjacent cells
Uses
Channel
232
Yes
No
No
No
Yes
Channel 232
Used in 4 cells
Can Reuse
Ch. 232?
Yes
No
No
No
50
Cellular 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
51
Handoffs

When you move to another cell

You are transferred automatically to that cell’s
cellsite
52
Roaming

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
53
Control

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
POP at
LEC
MTSO
54
Placing 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
55
Receiving 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
56
First Generation Cellular

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
57
First Generation Cellular

United States


AMPS standard
Elsewhere



Many incompatible standards
Use different radio bands
Limits multinational roaming
58
Second Generation Cellular

What it is




In the United States




Digital instead of analog for better service
Still uses large cells
Still has about the same number of channels
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)
59
Third-Generation Cellular

Personal Communication Service (PCS)


Smaller cells


More frequency reuse
More channels


Or Personal Communication Network (PCN)
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
60
Third-Generation Cellular

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
61
Potential System Capacity
Category
Cells/City
Channel reuse
Channels
Effective channels
Subscribers
1st Gen 3nd Gen
30
100?
~4
~14
800
2,500
3,200
35,000
60,000 700,000
This analysis is inexact but illustrative
62
U.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
63
Personal Service
Telephones

On the road


At home



Personal cellphone acts like 3d generation
cellphone
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
64
Traditional Communications
Satellites

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
65
LEO 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
Omnidirectional
Antenna
66
LEO 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
67