Main Distribution Frame MDF
Basics of Telephone Exchange:
Telephone Exchange is a place where switching between two subscribers is done through
either manually or electronically.
In addition to switching, signaling and controlling are also done at the exchange.
It consists of the following functional blocks:
a) Main Distribution Frame with protective devices.
b) Card Frame.
c) Motherboard.
d) Power supply panel with protective devices.
Read Also : MDF and IDF with protection Devices
a) Main Distribution Frame (MDF):
In a Telephone exchange different subscribers from
different places are terminated on a frame called “Main Distribution Frame” (MDF) in the
exchange and from there they are extended to subscriber’s line cards/Trunk cards kept in the
exchange rack.
Protective devices are located in the MDF.
1 Rear of Media Gateway |
Purpose of MDF:
There are three purposes of MDF:
1) It is the place where both outdoor and indoor cables are terminated
2) The cross-connection between the two cables conductors is done on the MDF and this
is done by means of jumper wires (Red & White).
3) It carries all the protective devices used in the exchange.
They are Fuses, Heat coils & Lightning protectors.
4) The MDF is the most suitable place for testing purposes.
b) Card Frame: It contains different slots in which the nominated cards are to be inserted. It is different in different types of exchanges.
c) Motherboard: It provides connectivity between different cards. It is a multilayer PCB.
d) Power supply panel:
It provides a power supply to different cards in the exchange at different low D.C. voltages. It also includes protective devices like fuses etc.
Main functional areas in Telephone Exchange:
a) Switching Function: The switching functions are carried out through the switching
network, which provides a temporary path for simultaneous, bi-directional speech between
the following:-
Two subscribers connected to the same exchange. This is called as “Local switching”
Two subscribers connected to different exchanges. This is known as “Trunk
switching”.
Pairs of trunks towards different exchanges. This is known as “Transit switching”
b) Signalling function: The signaling function enables various equipment in a network to
communicate with each other in order to establish and supervise the call.
It is of two types,
i) Subscriber line signaling: It enables the exchange to identify calling subscriber’s line,
extend dial tone, receive the dialed digits, extend the ringing voltage to the called
subscriber, extend the ring back tone to the calling subscriber to indicate the called
subscriber is being connected. In the event the called subscriber is busy, an engaged tone is
sent to the calling subscriber.
ii) Interexchange signaling: It enables a call to be set up, supervised, and cleared between
exchanges.
c) Controlling function: The controlling function performs the task of processing the
signaling information and controlling the operation of the switching network.
The control functions may be,
i) Wired logic control: In this pre-wiring is done between different speech path devices and
common control.
If any changes are required in facilities of subscribers or introduction of
new services require wiring changes.
ii) Stored Program Control (SPC): After the introduction of the microprocessor, a stored program control system came into use.
In this system, the establishment and supervision of the connections in the exchange is under the control of the “Microprocessor”, which is suitably programmed.
0 Comments
You can give your Suggestions and feedback here