articles for telecom engineers

GENERALIZED SYSTEM OF THE EXCHANGES AND SERVERS

The voltage on the voice information of the telephone lines is on the order of 250 MV. During the conversation, this is about 5-10 V DC. The current on the lines is about 20-100 mA. The voltage on the opened circuits and the voltage on the lines when there is no conversation on it were first 24V. But now these voltages are 48V.

There is a system on the stations like telephone, telegraph and data stations named as switching system. This system connects one telephone exchange to the other exchange. If we look at a general communication network, we can easily see that the exchanges are located in the most important and middle points. Also these exchanges work like a switching system

Switching circuits are designed in different structures looking into the traffic of the concentrative stations.

Signalling Systems

The communication between two or more stations is done in the following steps:

1) Choosing an empty channel

2) Sending the number which shows the address of the channel

3) Holding the channel for sending voice and data

4) Leaving the channel after the conversation

The connection between the communication systems of the stations are done in the way which maximizes the speed of connection. Selection, catching, connection, sending and taking the data of the addresses, transmitting the answer signal and solving operations are done with the help of signalling mechanism. The circuits which enable connections between the stations and become a united whole with the signalling, are named as trunks. The signalling systems from the fastest to the slowest are as follows: NO7, NO6, NO5, R1, R2, CC I TT, NO4 and PP.