Upload
vanessa-lane
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
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
9
Trunk LinesTrunk Lines
Connect switching offices All lines except local loop
TrunkLine
LocalLoop
TrunkLines
LocalLoop
10
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)
11
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
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
13
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
14
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
15
Deregulation in the Deregulation in the United StatesUnited 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
16
Deregulation in the Deregulation in the United StatesUnited 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
17
Deregulation in the Deregulation in the United StatesUnited 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
18
Deregulation in the Deregulation in the United StatesUnited States
Second Breakup of AT&T (1996)
Voluntarily divided the company
AT&T keeps transmission services
Lucent manufactures telephone equipment
NCR manufacturers computer equipment
19
Deregulation in the Deregulation in the United StatesUnited 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
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
21
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
22
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
23
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
24
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
25
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
26
Building Telephone Building Telephone WiringWiring
Between Floors Vertical riser spaces
Vertical Riser Spaces
27
Building Telephone Building Telephone WiringWiring
Wiring Closets Break up bundle Sub-bundle goes to next floor Other wires are for distribution on floor
Wiring Closet
28
Building Telephone Building Telephone WiringWiring
Horizontal Distribution on Floors Run wires through false ceilings, conduits Drop down to faceplate phone jacks
Wiring BundleSingle Line
Wallplate
29
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
30
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
31
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
32
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
33
HandoffsHandoffs
When you move to another cell You are transferred automatically to that cell’s
cellsite
34
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
35
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
36
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
37
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
38
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
39
First Generation First Generation CellularCellular
United States AMPS standard
Elsewhere Many incompatible standards Use different radio bands Limits multinational roaming
40
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)
41
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
42
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
43
Wide Area Wireless NetworksWide Area Wireless Networks(next class meeting)(next class meeting)
Review of multiplexing spread spectrum cellular generations
Comparison of Wi-Fi and cellular New generation: 4G WiMAX and LTE
Wi-Fi and cellular convergence mobile computing growth
44
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
45
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
46
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