 One of the simplest devices we have in our house.  very simple because the telephone connection to our house has not changed in nearly a century. Introduction - The Telephone Telephone

 A switch - to connect and disconnect the phone from the network - generally called the hook switch - It connects when you lift the handset.  A speaker - generally in a small size, 8-ohm speaker.  A microphone - as simple as carbon granules compressed between two thin metal plates. - Sound waves from our voice compress and decompress the granules, changing the resistance of the granules and modulating the current flowing through the microphone. microphone The Telephone  contains 3 parts :-

 human’s voice frequency  human’s voice frequency – 3400 Hz  In order to allow more long-distance calls to be transmitted, the frequencies transmitted are limited to a bandwidth of about 3000 hertz.  All of the frequencies in our voice below 400 hertz and above 3,400 hertz are eliminated.  That's why someone's voice on a phone has a distinctive sound. Telephone Bandwidth

- The various types of tones generated by the exchange to guide the users are :- 1. Dial Tone (DT).  A 33 c/s continuous note and is applied to the line after the subscriber has lifted his handset and the switching equipment has allocated him an available outlet for this call to proceed.  There would have been a physical limit on the number of calls an exchange could handle so if all equipment was already in use, the subscriber would not get a dial tone. PROGRESS TONES 2. Busy Tone (BT).  A higher pitched note of 400 c/s interrupts to give a cadence of 0.75 seconds on, 0.75 seconds off.  Busy tone indicates either that the called subscriber is already off-hook (busy) or that the route to the called subscriber is congested.  In later systems, a slightly different cadence was introduced in order to distinguish between these two scenarios.  A busy tone is made up of a 480-hertz and a 620-hertz tone, with a cycle of one and a half second on and one and a half second off.

3. Number Unobtainable Tone (NUT).  Identical pitch to the busy tone but continuous.  This tone is used to indicate that a number is out of service, faulty or that a spare line has been dialed. PROGRESS TONES 4. Ring Tone (RT).  A tone of 133c/s which interrupts in the same cadence as the ring current which rings the telephone bell at the called party's end : 0.4 seconds on, 0.2 seconds off.

***The telephone exchange is the place where all the telephone lines are connected so that the communication using the human’s voice could be achieved. The device in the exchange will act as a switch which contacts whenever it is directed.*** The Telephone Exchange SUBSCRIBER A SUBSCRIBER A SUBSCRIBER B SUBSCRIBER B LOCAL EXCHANGELOCAL EXCHANGE Figure 1: Telephone communication between subscribers

1.When Subscriber A picks up the telephone set, Local Exchange will detect a call request signal from Subscriber A. THE TELEPHONE CONNECTION BETWEEN 2 SUBSCRIBERS 2. Local Exchange will send a dial tone to Subscriber A. 3.Subscriber A starts to dial the numbers. The numbers received will be tested by the Local Exchange. 4. If the numbers are valid, Local Exchange will test whether the line is available or not. 5.If the line is available, Local Exchange will do the connection. Local Exchange will send a ringing tone to Subscriber A and the signal to ring the Subscriber B’s telephone. Subscriber B will pick up the telephone set, thus making the dialing tone stop. 6.If either one of the subscribers hangs up the phone, communication will be disconnected and the Local Exchange will clear the line.

Telephone Network For Local Exchange Exchange Man - hole Cabinet Upper Cable DP Box Underground Cable Connection IB CableHouse Figure 2 : The Connection from the Exchange to the Customer House Main Distribution Frame (MDF)  The Main Distribution Frame is situated at the telephone exchange.  It is used to connect the customer (phone user) with the main switching system after passing through the cabinet.  It comprises of all the customers and data which are situated in one area or district.  The duties of MDF :- 1.To test the phone line. 2.To execute the jumper process. 3.To check the problem phone line. 4.To cut the phone line manually. 5.To connect the phone line manually. MDF

Cabinet ►The cabinet is a place to distribute lines to the DP Box before reaching a customer’s house as portrayed in figure 3. ►Generally, the cabinet is the end for the main cable where it starts at the Main Distribution Frame (MDF) and passes through the cabinet. ►Connection from the cabinet to the MDF normally uses the ‘lead’ cable of different sizes where each of it has 200 pairs and to be distributed to about 20 DP Box. ► From the cabinet to the DP Box, it uses the plastic cable. ►In the cabinet, there are 1800 pairs of terminals. The Cabinet’s functions are as follows :- ►To save the usage of cable and replacing cable would be easier. ►To avoid the joint to be opened and this would save cost and time. ►To act as a place to perform maintenance checking. ►To upgrade the arrangement of lines. Figure 3 : Cabinet

Distribution Point Box (DP) ►The DP Box’s function is to make maintenance work and underground cabling easier. ► The DP Box has 10 pairs but only 8 pairs are used and the others kept for testing work from DP Box to the MDF. Upper Cable ►The upper cable is used to make connection with the subscribers using the DP Box. ► The two wire cable is used. Underground Cable ►The underground cable is connected to the cabinet from the DP through man-holes. ► The underground cable will end at the telephone exchange. Man-hole ►The place where the underground cable is connected to the cabinet.

MSC ZSC DSC LE S S S S S S S S S S S S S S SS The National Telephone Network Hierarchy MSC – Main Switching Center ( for international call ) ZSC – Zone Switching Center ( for call between states in Malaysia ) DSC – District Switching Center ( for call between different districts ) LE – Local Exchange S – Phone User / Subscriber NOTES :-  the network that links all the exchanges in one country.

Do you wonder how the telephone exchange works?