This document summarizes how a fixed landline call is setup and routed through the telecommunications network. It first goes to the nearest switching center (PSTN). If the caller and receiver are in the same base switching center (BSC), the call is completed. Otherwise, it is transferred to the main switching center (MSC) and then to the receiver's prior BSC. For mobile calls, the call transfer is handled by the mobile telephone switching office (MTSO) and base transceiver stations (BTSs). The telephone exchange checks if numbers are valid and sends busy tones if lines are engaged. Calls are connected between telephones via remote exchanges.

1. FIXED LANDLINE NETWORK

2. CALL SETUP
• When a subscriber calls to another subscriber first
its request goes to the nearest switching centre that is
PSTN (Public Switching Telecommunication Network). Then
it processes the caller and subscriber’s number if it exists in
the same BSC then call setup is completed.
• If subscriber is not in the same BSC (Base Switching
Centre) then call transfer to MSC (Main Switching Centre)
then it transfers the call to prior BSC then call setup is
completed.
• If Caller calls to a mobile subscriber then call
transfer is done by MTSO now call transfer is done on BTSs
(Base Transceiver Station) and call setup is completed.

3. Fig:- HOW LINE REACHES FROM SUBSCRIBER
TO EXCHANGE

4. TELEPHONE EXCHANGE
• Whenever the user dials a no it checks whether it is valid user
or not
• If receiver is busy then it sends a busy tone
• Whenever telephone dials a number then it is received by the
telephone & it connect to the relevant telephone via remote
exchange

5. MDF(MAIN DISTRIBUTION FRAME)
• All the telephone channel are terminated at the MDF
• It is a cable rack where all the telephone channels are terminated
• If a new connection is given at the exchange side &cable side relevant
point are connected by using another small cable these cables are called
Jumper
• MDF is a passive device (no need of electrical power)

6. CABINET
• 50 pair 100 pair 200 pair etc. multipair cables are drawn from MDF to
cabinet
• From cabinet 10 pair 5 pair cables are drawn up to distribution
Primary Cable:- MDF to Cabinet
secondary cable:- Cabinet to DP

7. DP(Distribution point)
• 5 pair or 10 pair cable is laid from cabinet to
DP that means there are 10 loops , 5 loops in a
dp
• When a new connection is provided a pair of
cable is drawn from DP to home this means
that 10 to 5 telephone new connection can be
provided from a dp

8. HOW A TELECOM EXCHANGE
WORKS:-
• It require -48 Vdc.
• A telephone exchange or telephone switch is a system of electronic componen
ts that
connects telephone calls. A central office is the physical building used to house
inside plant equipment including telephone switches, which make telephone
calls “work” in the sense of making connections and relaying the speech
information.
• The basic block diagram for a telecom exchange is as follows-

9. POWER PLANT:-
• It provides -48V to the switch rooms and 48V to the connections.
• Batteries are artificially discharged once in a year for their maintenance.
• Cooling is provided through fans & AC.
• There is earth region too for protection.
OMC (Operation and Maintenance Control)
It contains input-output processor terminals, visual display units,
printers, cartridges, etc. It controls the entire operation of
exchange data and billing data. The new connections, adding and
removing of facilities to the subscriber is done in the OMC room.

10. Switch
• It provides the switching facility and
connection to the outside of the exchange.
The switch room contains actual telephone
switching hardware such as cabinets, racks,
slots and cards. Switching is the most
important part of the exchange process.