Telephone Service

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Telephone Service
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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

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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

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The Traditional Telephone System

• Customer Premises
• Local Loop
• Switching Office
• End Office
• Trunk Lines

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Customer Premises

• Your home or office
• You control service on your premises
• Beyond your premises, you need a telephone carrier

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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
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Switching Offices

• Connect Telephone Callers
• Can support many simultaneous connections

Switching Office
Local Loop
Connection
Customer Premises
Customer Premises
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Hierarchical Organization of Switches

• Classes (1-5)

Class 3
Class 4
Class 4
Class 5
Class 5
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Trunk Lines

• Connect switching offices
• All lines except local loop

Trunk Lines
Trunk Line
Local Loop
Local Loop
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Carriers in the United States

• 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)

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Carriers in the United States

• POP
• Point of presence
• Located on LECs 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

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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

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Regulation in the United 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

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Deregulation in the United States

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

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Deregulation in the United States

• Ma Bell
• The Bell System
• ATT
• Had national monopoly on long-distance service
• Owned LECs serving more than 80 of the U.S.
  Population

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Deregulation in the United States

• Breaking Up Ma Bell (1983)
• Justice Department antitrust suit
• Results in agreement and Consent Decree
• ATT keeps long-distance service, equipment
  manufacturing
• LECs divided among 7 Regional Bell Operating
  Companies (RBOCs)--Baby Bells
• Court-administered limits on ATT RBOCs

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Deregulation in the United States

• Second Breakup of ATT (1996)
• ATT given freedom by courts to enter intra-LATA
  competition for transmission service
• ATT 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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Deregulation in the United States

• Second Breakup of ATT (1996)
• Voluntarily divided the company
• ATT keeps transmission services
• Lucent manufactures telephone equipment
• NCR manufacturers computer equipment

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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

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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

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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

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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

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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

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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

Company Phones
Carriers
PBX
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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
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Building Telephone Wiring

• Between Floors
• Vertical riser spaces

Vertical Riser Spaces
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Building Telephone Wiring

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

Wiring Closet
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Building Telephone Wiring

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

Wiring Bundle
Single Line
Wallplate
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Telephone Wiring and LAN 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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Cellular Telephones

• Original Mobile Telephones
• One transmitter/receiver
• Limited number of channels
• For good service can support about 20 subscribers
  per channel

Transmitter/ Receiver
Mobile Phone
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Cellular Telephones

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

Yes
No
Can Reuse Ch. 232?
Uses Channel 232
No
No
Yes
Yes
No
No
Channel 232 Used in 4 cells
No
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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

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Handoffs

• When you move to another cell
• You are transferred automatically to that cells
  cellsite

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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
• Dont confuse this with handoff, which takes
  place within a cellular system between cells

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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
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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

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Receiving a Call

• MTSO has each cellsite broadcast cellphones 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

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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

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First Generation Cellular

• United States
• AMPS standard
• Elsewhere
• Many incompatible standards
• Use different radio bands
• Limits multinational roaming

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Second Generation Cellular

• 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)

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Third-Generation Cellular

• 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

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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

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Potential System Capacity

• 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

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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

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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
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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