Telecommunication II

Course Books Understanding Telecommunications, Part II ISBN 91-44-00214-9 Ericsson, Telia Wireless Communications and Networks William Stallings Introduction to Telecommunication Networks Engineering Second Edition Tarmo Anttalainen

Course Orientation

Understanding Telecommunications, Part II “The global telecommunications network is the largest and most complex technical system that man has created” Understanding Telecommunications, Part II ISBN 91-44-00214-9

Telecommunication Networks Basic purpose of a telecommunications network: transmit user information in any form to another user of the network. Many forms of networks, such as voice or data; subscribers may use different access network technologies to access the network, for example, fixed or cellular telephones. Three technologies needed for communication through the telephone. 1) Transmission (2) Switching (3) Signaling.

Transmission Transmission is the process of transporting information between end points of a system or a network. Transmission systems use four basic media for information transfer from one point to another: 1. Wire-pair (copper) cables, such as those used in telephone subscriber lines (access network) 2.Optical fiber cables, such as those used in high data rate transmission in telecommunications networks (especially in transport networks)

Transmission 3. Radio waves, such as microwave radio links, cellular telephones and satellite transmission. 4.Free-space optics, and infrared communications (limited application, e.g. PC-to-PC short range links).

Telephony Fundamentals Basic Telecommunication Network Users of public networks, for example, a telephone network, are called subscribers

Telephony Fundamentals The telephone connector Two wire line

Telephony Fundamentals Signaling is the mechanism that allows network entities (user terminal or network switches) to establish, maintain, and terminate sessions in a network Off-hook position The exchange notices that the subscriber has raised the telephone hook and gives a dial tone to the subscriber On-hook position The exchange notices that the subscriber has finished the call (subscriber loop is disconnected), clears the connection, and stops billing Dial Pad/Dial-plate The subscriber dials digits and they are received by the exchange

Telephony Fundamentals Signaling is naturally needed between exchanges as well because most calls have to be connected via more than just one exchange The ordinary home telephone receives the electrical power that it needs for operation from the local exchange via two copper wires The subscriber line, which carries speech signals as well, is a twisted pair called a local loop The principle of the power supply coming from the exchange site makes basic telephone service independent of the local electric power network

Telephony Fundamentals Telephone exchanges supply dc voltage to subscriber loops, and telephone sets use this supplied voltage for operation On/Off hook switch Each telephone has a switch that indicates an on- or off-hook condition When the hook is raised, the switch is closed and an approximately 50 mA of current starts flowing The control unit Rotary or Pulse dialing In rotary dialing a local loop is closed and opened according to the dialed digits, and the number of current pulses is detected by the exchange

Telephony Fundamentals Slow Does not support supplementary services such as call forwarding etc. The local-loop interfaces in telephone exchanges have to support this old technology though it has been gradually replaced by tone dialing Currently telephones include electronic circuits that make possible the implementation of better means for signaling electronic circuitry, which is needed for number repetition, abbreviated dialing, and other additional features of modern telephone sets

Telephony Fundamentals DTMF Signaling Each push button generates a tone with two frequencies All frequencies are inside the voice frequency band (300–3,400 Hz) and can thus be transmitted through the network from end to end, when the speech connection is established The subscriber is able to select with a switch on his telephone which type of dialing is to be used. Tone dialing should always be selected if the local exchange is a modern digital one

Telephony Fundamentals Rotary or Pulse dialing Tone dialing It is quicker and dialing of all digits takes the same time Additional push buttons are available (*, #, A, B, C, D) for activation of supplementary services

Telephony Fundamentals 2W/4W Hybrid Separates the transmitted and received signal Matches the impedance of 2W local loop to 4W network circuit Cancels the echo