1d. telephone basicspdf
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COMMUNICATION SYSTEM
REVIEW
TELEPHONE BASICS
PBX Block Diagram
2
Internal
Switching
Matrix or
Network
Internal
Switching
Matrix or
Network
Line/Loop
Interface
Trunk
Interface
Control
Processor
(CPU, RAM
etc.)
Line/Loop
Interface
Line/Loop
Interface
TrunkInterface
Trunk
Interface
More
not shownMore
not shown
Multiple station loopsMultiple T-1 trunk groups
optional
remote
line
concen-
trator
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Simple PBX
3
Extension to Extension Call
(Internal Call)
4
1. Station comes off hook
2. Line circuit notes origination
3. Control detects origination, check
line class-mark
4. Control finds free signaling
receiver5. Control finds and sets up a path
from line to receiver
6. User hears dial tone, starts
dialing/signaling
7. Dial tone is removed, digits are
accumulated
8. Control examines dialed number:
Find called line
Check for busy, hunt group,
call forwarding, pick-up group
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Extension to Extension Call
(Internal Call)
5
9. Control finds and sets up path,
caller to ring-back tone
10.Finds and sets up path, called
phone to ringing
11.Monitors for answer or abandon
12.Called party answers; control
detects answer at line circuit
13.Control finds and sets up calling-
to-called talk path
14.Monitor for flash and/or hang-up
Basic Telephone
6
ear
T
R
mouthDTMF
ringer
C
dial switch
SLIC
Telephone
Subscriber
Line
CO
(Local Exchange)
cradle switch
off-hookon-hook
tip (+)
ring (-)
Thisimage cannot currently bedisplayed.
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Basic Telephone
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Basic Telephone
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Subscriber Line Interface
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hybrid
TTelephone
current
detector
~
ring switch
ring
generator
(100Vrms 25 Hz)-48 VDC
Subscriber
Line
crossconnect
switch
Subscriber Line Interface Circuit
Processor
control channel
Call Statesidle on hook
dialing dialing in progress
calling after dialing
ringing incoming call
called call in progress
tip (+)
ring (-)
Battery Supply Feeding of subscriber handset
Over-voltage Protection for electronic components
Ringing Ringing current to subscriber
Signaling Recognizing dial digits
Coding Analog/digital conversion
Hybrid 2-wire/4-wire conversion
Test Access testing of subscriber lines
Subscriber Line Interface
10
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Subscriber Line Interface
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Subscriber Line Interface
MT91600
12
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Tones
13
DTMF Receiver MT8870
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DTMF Receiver MT8870
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Switching Matrix CD22100
16
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Control
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Outgoing Call
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1. Station comes off hook
2. Line circuit notes origination
3. Control detects origination, check
line class-mark
4. Control finds free signaling
receiver5. Control finds and sets up a path
from line to receiver
6. User hears dial tone, dials trunk
access code
7. Dial tone is removed, access
code is received
8. Control examines access code:
Check against line class mark
for restriction
Looks for free trunk group
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Outgoing Call
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9. Control finds and sets up path,
from the line to the selected trunk
10.Control causes trunk to send
seizure toward CO
11.CO responds with dial tone to the
caller; caller dial called number
12.Dialed number goes to the CO to
set up the call, and the digit
receiver to check restriction
13.Control examine access code, if
any, and office code, if necessary.
Compare them with the list in
memory
14.Call is permitted. Drop path to
signaling receiver
15.Monitor line for flash and/or hang-
up, monitor trunk for hang-up
Incoming Call to Attendant
20
1. CO seizes trunk, rings; trunk
detects ringing
2. Control detects seizure at trunk;
checks trunk class marks
3. Control activates lamp, sounder
at console4. Attendant accepts call, signals
control
5. Control finds, sets up a trunk
switched-loop path
6. Ringing from CO is tripped,
answer supervision returned
7. Attendant greets caller; obtains
called extension identity
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Incoming Call to Attendant
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8. Attendant keys in called
extension
9. Control examines dialed number:
Finds called line
Check for busy, hunt group,
call forwarding, pick-up group
10. Finds and sets up path to ring-
back tone, ringing, drops
switched loop
11.Monitor for abandon or answer
12.Called party answers
13.Answer is detected, ringing is
tripped
14.Control finds and sets up a talk
path
15.Control monitor for flash and/or
hang-up
Trunk Interface
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Analog Trunk Interface
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Analog Trunk Interface
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Analog Trunk Interface
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Analog Trunk Interface
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E&M Trunk Interface
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Basic Digital PBX
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SLIC
PCM
MUX
Hybrid
SLIC
TDM
port
TDM
port
TDM
port
TDM
port
Tone
&Ann
DTMF
decode
Processor
Subscriber
Lines
Hybrid
2w4w
DXC
E1/T1E1/T1
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Digital Trunk Interface
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Digital Trunk Interface
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Digital Trunk Interface
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Digital Trunk Interface
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Digital Trunk Interface
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Time Slot Interchange
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