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Lecture#03
Plain Old Telephone Service (part I)
The Bonch-Bruevich Saint-Petersburg State University of Telecommunications
Series of lectures “Telecommunication networks”
Instructor: Prof. Nikolay Sokolov, e-mail: [email protected]
Forecast (XV century)
“The time will come when people from the most distant countries will speak to one another and answer one another”.
Leonardo da Vinci
History of microphones
liquid-based microphone
carbon microphone
modern microphone
Dialing equipmentOne of the most important elements of a telephone set is dialer. On the initial stage of the telephone communications development there was no dialer. Automatisation of the telephone communications created the demand for such an element as part of the terminal equipment. First dialers were mechanical. They are known as “disc dialers”. Then the key pulsers emerged. Both type of the dialers send into the subscriber’s line signals with standardized parameters of pulse durations and pauses between pulses. After that a new type of dialers was invented, which send multifrequency signals, known by acronym DTMF. Two types of the
telephone dialer
Speech transmission
Microphone TelephoneLine
Battery
Transformer
MultiplexingS1(t)
Time
Time
S2(t)
f1 f1 f2f2
f1 f1 f2f2
Frequency
Time
S1(t) S2(t)
F1
F1 F2 F3 F4
S1(t) S2(t)
FDM
TDM
Digital telephonyF0(t)
Time
Time
Time
TD
F1(t)
F2(t)
1
2Dmax
Tf
Telephone communications system
"Telephone communications system" term is usually refers to base principles of telephone network’s construction, operation and development. These principles usually include the following positions:•purpose of the system;•supported services;•network structure;•quality of service ratings;•numbering plan;•maintenance; •equipment requirements;•main directions of system development.
Main abbreviations PSTN – public switched telephone network,UTN – urban telephone network,RTN – rural telephone network, ISC – international switching centre, (U/T)LDE – (universal/transit) long-distance exchange, TE – transit exchange,ITN – incoming traffic nodes [TE(I) – transit exchange used as ITN],OTN – outgoing traffic nodes [TE(O) – transit exchange used as OTN],OITN – outgoing and incoming traffic node (equivalent to TE),CO – central office,PBX – private branch exchange, C – concentrator, CE – central exchange, LE – local exchange, SN – service node,SL – subscriber line,TL – trunk lines, TS – telephone set.
Model of hypothetic PSTN
CO15
C154
PBX157
TS1501
TS1542
TS1573
TE(O)1
TE(I)1
CO26
C263
PBX268
TS2604
TS2635
TS2686
TE(I)2
TE(O)2
SN
First nodal area Second nodal area
LDETE2
Call Centers
. . .CE9
LE903
TE91 LE911
LE912
SL
SLSL
SL SL
SL
SL
TS9037
TLTL
TLTL
TLTL
TL
TL
TL
TL
TL
TL
TLTL
TL
TL
TL
TL
TL
Rural Network
Urban Network
TL
TL
TL
Hierarchical levels in PSTN
Tra
nspo
rt n
etw
ork
Sw
itch
ed n
etw
ork
Additional taxons
Customer premises network
Access network
International telephone network
Long-distance telephone network
Domestictelephone network
Regional telephone network
Network between Central Offices
Network between Transit Exchanges
Classif
icatio
n by
func
tions
Classification by hierarchy
Urban telephone network with one CO
CCP1
CO
CCP2
CCP4CCP3
Main cable
Link cable
CCP – cross-connection points
Three types of the cross-connection points
Central Office
Old crossbar exchange
Modern digital exchange
Perspective PSTN structure with one CO
NN1
NN0
NN2
NN4NN3
NN5NN6
C1
CO
C2
C4C3
C5C6
a) Transport network structure b) Switched network structure
Ring III
Ring I Ring II
NN – network node
Cost of port per user Cost per port
Total cost
Cost of subscriber line
Cost of trunk line
N
Cost of switch
Urban telephone network with several exchanges
CO1
CO2
CO3
CO4CO5
UTN with incoming traffic nodes
CO15
C154
PBX157
TS1501
TS1542
TS1573
CO11
CO17
First nodal area Second nodal area
SL
SL
SL
TL
TL
ITN1ITN2
CO23
CO29
UTN with outgoing and incoming traffic nodes
CO15
C154
PBX157
TS1501
TS1542
TS1573
OTN1
ITN1
CO22
ITN2
OTN2
SL
SL
SL
TLTL
TL
TL
TL
TL TL
TL
TL
TLTL
CO21
CO23
TL
TL
TL
TL
First nodal area Second nodal area
Typical structure of the RTN
LDE
CE9
LE903
TE91 LE911
LE912
TL
TL
TL
TL
LE902TL
TL
TL
Main components of the area telephone network
. . . . . .
Urban network in the administrative center
Urban networks in the large cities of the administrative region
Rural networks and small urban networks
1 K 1 L
TL
TL
TL
TL
TL
Connection types in the intraareal telephone communications network
LDE
CE
LE
CO
TL
LE
TE
TL
TE
TS1
TS3
TS2
TL
TL
Modern principles of the long-distance communication organization
.
.
.
1
2
M
Urban network “А”
Urban network “В”
Long-distance Operators
Manual switchboard
Structure of the existing long-distance telephone network
TLDE1 TLDE2
TLDE3TLDE4
LDE1 LDE2
Alternative route
Direct trunk group
(city “A”) (city “B”)
Long-distance exchanges
Beginning
Present
Structure of the perspective long-distance telephone network
1 2
34
5ULDE
Direct trunk group
LDE
ULDE
ULDE
ULDE
ULDE
Connection of the international switching centers
GW
GW
GW
PSTN of country “A” PSTN of country “B”
PSTN of country “C”
GW – gateway (for international communications)
Important feature of telephony
Form of communication
Com
mun
icat
ion
effe
ctiv
enes
s
2 people at whiteboard
2 people on phone
2 people on mail
Videotape
Audiotape
Paper
Source: http://www.maxkir.com
