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telephony Slide 1

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Bell Telephone acquired them. and interconnected them for long distance. Local. Exchange ... FXS is like exchange - provides voltage, ringing, dialtone ... – PowerPoint PPT presentation

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Title: telephony Slide 1


1
Basic Telephone
CO (Local Exchange)
SubscriberLine
Telephone
dial switch
tip ()
T
cradle switch
off-hook
on-hook
mouth
C
ear
SLIC
ringer
ring (-)
R
2
Subscriber Line Interface
Subscriber Line Interface Circuit
ring switch
Telephone
T
tip ()
crossconnect switch
SubscriberLine
hybrid
current detector
ring (-)
control channel
ring generator (100Vrms 25 Hz)
Processor

-48 VDC
Call States idle on hook dialing
dialing in progress calling after
dialing ringing incoming call called call in
progress
3
The PSTN circa 1900
PSTN Review
pair of copper wires local loop
manual routing at local exchange office (CO)
  • Analog voltage travels over copper wire
    end-to-end
  • Voice signal arrives at destination severely
    attenuated and distorted
  • Routing performed manually at exchanges
    office(s)
  • Routing is expensive and lengthy operation
  • Route is maintained for duration of call

4
Multiplexing
PSTN Review
  • 1900 25 of telephony revenues went to copper
    mines
  • standard was 18 gauge, long distance even heavier
  • two wires per loop to combat cross-talk
  • needed method to place multiple conversations on
    a single trunk
  • 1918 Carrier system (FDM)
  • 5 conversations on single trunk
  • later extended to 12 (group)
  • still later supergroups, master groups,
    supermaster groups
  • 1963 T-carrier system (TDM)
  • T1 24 conversations per trunk
  • later T3 28 T1s
  • still later SDH rates with 1000s of conversations
    per trunk

5
Cross-connect switch
Analog Crossbar switch
Digital Cross-connect (DXC)
processor
  • Complexity increases rapidly with size

6
Basic TDM CO
DXC
SubscriberLines
Tone Ann

PCM MUX
4w
2w
E1/T1
E1/T1

DTMF decode
Processor
7
PSTN Topology
PSTN Review
Local Exchange
local loop
Local Exchange
Long distance network
trunk circuit
subscriber line
  • Many local telephone exchanges had sprung up
  • Bell Telephone acquired them
  • and interconnected them for long distance

8
Old US PSTN
PSTN Review
Class 1
Regional centers
Class 2
Class 2
Sectional centers
Class 3
Class 3
Class 3
Primary centers
Toll (tandem) offices
Class 4
Class 4
Class 4
Class 4
circuits,trunks
Central (end) offices
Class 5
Class 5
Class 5
Class 5
Class 5
last mile
subscriber lines
local loop
Class 5 switch is the sole interface to the
subscriber lines
9
Numbering Plans
  • An E.164 International Number has the format
  • Country-Code Area-Code Exchange-Code Line-Number
  • EX 972 2 588
    9159
  • Country-Codes
  • 1 N America (US, CA, Caribbean) 1 digit
  • 2 Africa 2 or 3 digits 20
    Egypt 27 South Africa 235 Chad
  • 3 Europe 2 or 3 digits 31
    Netherlands 354 Iceland
  • 4 Europe 2 or 3 digits 44 UK
    49 Germany 420 Czech Republic
  • 5 S America 2 or 3 digits 54
    Argentina 595 Paraguay
  • 6 Australia S Pacific 2 or 3 digits 61
    Australia 675 Papua
  • 7 Russia 1 digit
  • 8 China N Pacific 2 or 3 digits 86 PR
    China 855 Cambodia
  • 9 Middle East 2 or 3 digits 90
    Turkey 972 Israel

10
Signaling
PSTN Review
  • PSTN with automatic switching requires signaling
  • The present PSTN has thousands of features
  • and all require signaling support
  • Examples
  • On-hook / off-hook
  • Pulse / Tone dialing
  • Receiver off-hook
  • Call waiting
  • Caller number identification
  • Call forwarding
  • Hook-flash

Fax transmission detect Inter-CO messaging Echo
cancellation Voice mail Conference
calls Coin-drop Billing
11
Signaling Methods
PSTN Review
  • Signaling can be performed in many ways
  • Analog voltage signaling loop-start,
    ground-start, EM
  • In-band signaling DTMF, MFR1, MFR2
  • Channel associated signaling (CAS) AB bits, ABCD
    bits
  • Common channel signaling (CCS) SS7, QSIG
  • Trunk Associated CCS
  • Separate signaling network CCS

12
Subscriber - Exchange Signaling
  • On/off hook DC current flow
  • Dial-tone 350440 continuous
  • Pulse Dialing
  • DTMF
  • L1 697 L2 770 L3 852 L4 941
  • H1 1209 H2 1336 H3 1477 H4 1633
  • Ring AC with cadence
  • Ring-back 440480 with 24 cadence
  • Busy 480620 with 1/21/2 cadence
  • Trunk busy 480620 but 0.20.3 cadence
  • Receiver off-hook 1400206024502600 with
    ).10.1 cadence
  • Invalid (nonworking, unobtainable) number
    announcement, SIT-tone
  • US cadences - national differences

13
Subscriber - Subscriber Subscriber - Exchange
Signaling
  • Hook-flash on-hook for 0.1 - 1 sec
  • Echo suppressor disabler 2100 continuous
  • FAX CED 2100 2.6 - 4 sec
  • Modem ANS 2100 with phase reversals every 450 ms
    for 3.3 s
  • ANSAM 2100 with phase reversals and 15 Hz AM
    modulation
  • CNG
  • FAX 1100 with 0.53 cadence
  • Modem 1300 with 0.52 cadence
  • Caller Line Identification (CLI/CND)
  • 1200 bps FSK (V.23) data signal 1300 1 2100
    0
  • Between 1st and 2nd rings

14
Supervision procedures
  • FXO/FXS Foreign Exchange Office / Foreign
    Exchange Subscriber
  • FXS is like exchange - provides voltage,
    ringing, dialtone
  • FXO is like a phone - requires voltage,
    detect ring, etc.
  • When connecting PBX to CO, PBX is FXO, CO is FXS
  • Analog loop start
  • Digital loop start
  • Analog ground start
  • Digital ground start
  • EM (wink)

15
Interexchange Signaling
  • CAS - R2
  • CAS - R1
  • CCS - SS7

16
Optimized Telephony Routing
PSTN Review
Circuit switching (route is maintained for
duration of call) Route set-up is an expensive
operation, just as it was for manual
switching Today, complex least cost routing
algorithms are used Call duration consists of
set-up, voice and tear-down phases
17
The PSTN circa 1960
PSTN Review
trunks circuits
local loop subscriber line
automatic routing through universal telephone
network
  • Analog voltages used throughout, but extensive
    Frequency Division Multiplexing
  • Voice signal arrives at destination after
    amplification and filtering to 4 KHz
  • Automatic routing
  • Universal dial-tone
  • Voltage and tone signaling
  • Circuit switching (route is maintained for
    duration of call)

18
The Digitalization of the PSTN
PSTN Review
  • Shannon (Bell Labs) proved
  • is better than
  • and the PSTN became digital
  • Better means
  • More efficient use of resources (e.g. more
    channels on trunks)
  • Higher voice quality (less noise, less
    distortion)
  • Added features
  • Analog
  • Communications
  • Digital
  • Communications

19
Timing
PSTN Review
  • In addition to voice, the digital PSTN transports
    timing
  • This timing information is essential because of
  • the universal use of TDM
  • the requirement of accurate playback (especially
    for fax/modem)
  • Receiving switches can recover the clock of the
    transmitting switch
  • Every telephony network has an accurate clock
    called stratum 1
  • Clocks synchronized to it are called stratum 2
  • Clocks synchronized to them are called stratum
    3
  • and so on

20
The Present PSTN
PSTN Review
core backbone
PSTN Network
subscriber line
  • Analog voltages and copper wire used only in
    last mile,
  • but core designed to mimic original situation
  • Voice signal filtered to 4 KHz at input to
    digital network
  • Time Division Multiplexing of digital signals in
    the network
  • Extensive use of fiber optic and wireless
    physical links
  • T1/E1, PDH and SONET/SDH synchronous protocols
  • Signaling can be channel/trunk associated or via
    separate network (SS7)
  • Automatic routing
  • Circuit switching (route is maintained for
    duration of call)
  • Complex routing optimization algorithms (LP,
    Karmarkar, etc)

21
Nonvoice services
PSTN Review
  • The PSTN can even be used to transport non-voice
    signals
  • such as FAX
    or DATA
  • These services disguise themselves as voice by
    using a modem
  • Proper timing is essential
  • Special signaling is required
  • turn off LEC
  • turn off call waiting
  • service recognition

PSTN
  • capabilities negotiation
  • mutual identification
  • end of page/document
  • modem recognition
  • modem training
  • data compression

22
Digital Loop Carrier
PSTN Review
  • Pushes the digital PSTN closer to customer
  • ATT SLC-40, SLC-96, Nortel DMS P-phone,
    pair-gain

TR-08 Mode 1 pair-gain Replace 96 pairs with 5
T1s (one spare for span protection)
96 10 86 TR-08 Mode 2 pair-gain Replace 96
pairs with 2 T1s (without span protection)
96 4 92
Access Network
CLASS 5
Street cabinet
UTP/coax/fiber
CPE
FTTB/FTTC
pedestal
UTP
TR-08 multiplex 96 lines on
Mode 1 4 T1s Mode 2 2 T1s (21
concentration) GR303/V5.1/V5.2 multiplex up to
2048 lines
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