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,

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 equipment One 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

Multiplexing

Digital telephony

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

Hierarchical levels in PSTN

Urban telephone network with one CO 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 NN – network node

Cost of port per user

Urban telephone network with several exchanges

UTN with incoming traffic nodes

UTN with outgoing and incoming traffic nodes

Typical structure of the RTN

Main components of the area telephone network

Connection types in the intraareal telephone communications network

Modern principles of the long- distance communication organization

Manual switchboard

Structure of the existing long-distance telephone network

Long-distance exchanges Beginning Present

Structure of the perspective long- distance telephone network

Connection of the international switching centers GW – gateway (for international communications)

Important feature of telephony Source:

Instructor: Prof. Nikolay Sokolov, Questions? Plain Old Telephone Service