wired and wireless telephony week3

7/30/2019 Wired and Wireless Telephony Week3

1/23

Wired and wireless telephone

networks


2/23

Evolution of the Public Switched

Telephone System (PSTN)

(a) Fully-interconnected network.

(b) Centralized switch.

(c) Two-level hierarchy.


3/23

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)


4/23

Structure of the Telephone

SystemA typical circuit route for a medium-distance

call.


5/23

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.


6/23

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.


7/23

Wireless local loops


8/23

Circuit Switching

(a) Circuit switching.

(b) Packet switching.


9/23

Message Switching

(a) Circuit switching (b) Message switching

(c) Packet switching


10/23

Packet Switching

A comparison of circuit switched and packet-

switched networks.


11/23

The Mobile Telephone System

First-Generation Mobile Phones:

Analog Voice

Second-Generation MobilePhones: Digital Voice

Third-Generation Mobile

Phones: Digital Voice and Data


12/23

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


13/23

Advanced Mobile Phone

System

(a) Frequencies are not reused in adjacent cells.

(b) To add more users, smaller cells can be used.


14/23

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


15/23

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.


16/23


17/23

D-AMPS

Both analog and digital transmission is

supported, channels dynamically

allocated.

4-8kbps rate per user.

Handoff is mobile assisted.

GSM


18/23

GSM

Global System for Mobile

CommunicationsGSM uses 124 pairs of simplex frequency

channels, each of which uses an eight-

slot TDM system


19/23

GSM (2)

A portion of the GSM framing structure.


20/23

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


21/23

CDMA(a) Binary chip

sequences forfour stations(b) Bipolar chip

sequences

(c) Six examplesoftransmissions

(d) Recovery of

station Cssignal


22/23

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


23/23

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

wired and wireless telephony week3

Documents