wired and wireless telephony week3
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Wired and wireless telephone
networks
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Evolution of the Public Switched
Telephone System (PSTN)
(a) Fully-interconnected network.
(b) Centralized switch.
(c) Two-level hierarchy.
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Three Major Components of
the Telephone System
Local loops
Analog twisted pairs (category 3) going
to houses and businesses (1-10km)
Trunks
Fiber optics connecting the switching
offices carrying multiplexed digital signals
Switching offices
Where calls are moved from one trunk to
another (digital)
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Structure of the Telephone
SystemA typical circuit route for a medium-distance
call.
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The Politics of Telephones
The relationship of LATAs(Local Access and Transport Area),
LECs(Local Exchange Carrier), and IXCs(Inter Exchange
Carrier). All the circles are LEC switching offices. Each
hexagon belongs to the IXC whose number is on it.
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The Local Loop: Modems,
ADSL, and Wireless
The use of both analog and digital transmissionsfor a computer to computer call. Conversion is
done by the modems and codecs.
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Wireless local loops
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Circuit Switching
(a) Circuit switching.
(b) Packet switching.
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Message Switching
(a) Circuit switching (b) Message switching
(c) Packet switching
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Packet Switching
A comparison of circuit switched and packet-
switched networks.
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The Mobile Telephone System
First-Generation Mobile Phones:
Analog Voice
Second-Generation MobilePhones: Digital Voice
Third-Generation Mobile
Phones: Digital Voice and Data
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First generation Mobile Phones
Push-to-talk: Wireless radiophones. One
transmitter. Single channel. Half duplex.
IMTS (Improved Mobile Telephone System):
One transmitter on hilltop. 23 channels. Duplex. AMPS (Advanced Mobile Phone System):
Cells, microcells=>Frequency reuse=>Increased
capacity
Base station at each cell
MTSO(Mobile Telephone Switching Office)
Changing base stations: Soft Handoff, Hard Handoff
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Advanced Mobile Phone
System
(a) Frequencies are not reused in adjacent cells.
(b) To add more users, smaller cells can be used.
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Channel Categories
832 full-duplex channels (824-849Mhz) upstream
(869-894Mhz) downstream.
Four categories: Control (base to mobile) to manage thesystem (Location registration)
Paging (base to mobile) to alert users to
calls for themAccess (bidirectional) for call setup and
channel assignment
Data (bidirectional) for voice, fax, or data
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AMPS Communication
Mobile phone broadcasts serial and tel. No.
Base station tells its MTSO, which records and
informs home MTSO of location
Call: Caller transmits its id and callee phone no.
Base station informs callers MTSO which allocates
channel, caller switches to this channel.
Callee is found via its home MTSO
Callees current MTSO allocates channel and callee
switches to this channel.
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D-AMPS
Both analog and digital transmission is
supported, channels dynamically
allocated.
4-8kbps rate per user.
Handoff is mobile assisted.
GSM
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GSM
Global System for Mobile
CommunicationsGSM uses 124 pairs of simplex frequency
channels, each of which uses an eight-
slot TDM system
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GSM (2)
A portion of the GSM framing structure.
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CDMA Code Division Multiple
Access Quallcomm
2. and 3. generation
125 Mhz band
Transmission uses entire frequency spectrum,all the time
Algorithm: Everyone transmits his own message using his
unique symbol
Sum is received Decoding of a particular users message by using his
symbol
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CDMA(a) Binary chip
sequences forfour stations(b) Bipolar chip
sequences
(c) Six examplesoftransmissions
(d) Recovery of
station Cssignal
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Third-Generation Mobile Phones:
Digital Voice and Data
Basic services an IMT-2000 network should
provide
High-quality voice transmission Messaging (replace e-mail, fax, SMS, chat,
etc.)
Multimedia (music, videos, films, TV, etc.) Internet access (web surfing, w/multimedia.)
Videoconferencing, group game playing
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Third-Generation Mobile Phones UMTS (W-CDMA):
Ericsson Direct sequence spread spectrum
UMTS to GSM handoff possible
CDMA2000: Qualcomm
Direct sequence spread spectrum Backward compatible with 2. generation CDMA system (IS-95)
GPRS (General Packet Radio Service) Overlay packet network on top of GSM.
Send and receive IP packets.
Pay per packet transfer EDGE/EGPRS Enhanced Data rates for GSM Evolution-
2.5G) 48 kbps for each timeslot and upto 8 timeslots
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