MDF & DF in PABX Telephone Exchange

Hello Asitha,

The MDF is the connection point system inside the building, where the cables or lines to/from the district telephone exchange terminate on the line side, and cross-connections (jumpers) run to the opposite (exchange) side of the MDF, and from those terminals a multi-core cable runs from a second set of terminals to the actual PABX exchange in the particular building.

A multi-core cable runs from the PABX to each DF which are commonly located in areas, for example in 2-floor business premises, there would normally be a DF on each floor.

From the DF, the smaller cables run to each individual extension telephone outlet socket.

The reason for using these frames, with Numbered/lettered cable terminals on both sides, interlinked by removable or alterable wiring connections called "jumpers", is that if a particular telephone extension needs to be moved, for a change of desk or office, it is easy to just remove and alter the cross connections (jumpers) at the DF or MDF.

Thus the system is far more efficient.

Line and connection records are taken, and kept up-to-date, of course, so that it is easy for any technician to alter the cross-connections to suit the owner/occupier's requirements.

Hope that explains it for you.

Kind Regards....

Thank you very much for your detail explanation.

Thank you, Sparky, excellent explanation. I hadn't known the English names of that components. so your description was really useful for me too.

Indeed for PABX's with more than six extensions it is good practice to terminate PABX cables (champ connector cables) on the MDF.

On the MDF, the extension lines are cross connected to service the DFs in other floors (for buildings) and open fields via the ELP (External Line Plant) cables.

The MDF in its simple form, is a special metallic frame designed and constructed with columns of receptacles (2-in-1 partial blunt leads) to firmly hold LS disconnect modules (popularly called Krone modules in this clime)

The the cable terminations and cross connections take place in the array of LS disconnect modules in the MDF.

Simply put, the MDF and DF have similar constituents but in application, the MDF is normally bigger than the DF and as the name implies, it is the central or core distribution frame.

Cheers,

Ethobil

hi,

'Sparstation has given a fine explanation which should cover all your requirement. I only want to add that MDF has two sides the one cable termination from telephone exchange and other cable termination from external distribution to telephone lines. At MDF over voltage arrestors ( which forms a part of MDF) are installed to protect the exchange equipment from accidental high voltage signals from line side.In old electro mechanical exchanges the MDF used to be very large with fuses mounted on one side and carbon arrestors on other side. Now with technology improvement the size of MDF and the arrestors have become very small with Krone Style MDF and can be installed occupying little space. The MDF has provision to insert tools to carry out line fault tests after separating outside line from exchange side.