1. Telecommunication II

2. Course Books Understanding Telecommunications, Part II
ISBN
Ericsson, Telia
Wireless Communications and Networks
William Stallings
Introduction to
Telecommunication Networks Engineering
Second Edition
Tarmo Anttalainen

3. Course Orientation

4. 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

5. 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.

6. 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)

7. 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).

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

9. Telephony Fundamentals
The telephone connector
Two wire line

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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