What is MDF jumpering?

What is an MDF?

An MDF, or main distribution frame, is the point where every phone and internet line enters a building, and the room it sits in is the MDF room. In telecom terms it is the handover: the street cable arrives on one side of the frame, and the building’s own cabling leaves from the other side and runs up to each unit, office or shop.

In practice the MDF room is a basement room, a corner of the car park or a fire cupboard. People also call it the comms room. The side where the provider’s service arrives is the A side and belongs to the network. The side that runs up the risers to each unit or suite is the B side and belongs to the building.

A bigger building adds a smaller frame on each floor, called an IDF, between the basement and your socket. That matters, because a service can be live at the MDF in the basement and never carried up to your floor.

What is jumpering?

Jumpering is joining one pair on the A side of the frame to one pair on the B side with a short wire called a jumper. One pair in, one pair out. That jumper is the whole connection between the service your provider delivered and the cable that runs to your door.

It is a few centimetres of wire, and it takes about a minute to run once the right pair is known. Finding the right pair is the work. A frame can carry hundreds of pairs, and on plenty of them the tags are missing or wrong, which is why our MDF jumpering service starts by tracing the line rather than reading the labels.

The same idea covers a phone line and an internet service. Telephone line jumpering connects a voice line so the phone works when you lift it. NBN MDF jumpering connects the pair that carries your internet. On copper NBN services in a building, such as fibre to the building, the pair from the frame to your unit still does the work, so the jumper still matters.

Watch: MDF Tagging Gone Wrong | When Telstra Doesn't Mark Your Connection

From the streetThe network's side

To the unitsThe building's side

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Why a unit can be dead while the provider says it is connected

Your provider has done everything on their side, and from the street to the frame downstairs the line is fine. The landlord will not touch the frame because nobody knows which pair is yours. You have moved in, signed up, plugged in the modem, and there is nothing at the socket.

That is the usual MDF jumpering call, and it is a gap between three parties rather than a fault in any one of them. Street to the MDF is the network’s. MDF to your door is the building’s or yours, depending on the lease. The jumper sits exactly on the line between the two, so it is easy for each side to say it belongs to the other.

What goes wrong at the frame

Most of what we find at a building frame is a records problem, not a broken cable. We analysed 324 of our own filmed fault jobs, and 67 of them were in apartments and strata buildings. These are the most common faults in those 67 jobs.

Fault in units	Share of unit jobs
Old sockets still connected to the line (a bridge tap)	14.9%
The documented path is not the real path	11.9%
Missing jumper	9.0%
Tagging does not match reality	7.5%
Customer disconnected at the frame	6.0%

The top one, old sockets still connected to the line, is explained in what a bridge tap is. In plain terms, this is what those look like on the day:

• On the wrong pair. Your service was put on someone else’s pair, or a neighbour is live on yours.
• Not tagged. The line is active at the MDF and nobody knows which pair is yours. Nothing is broken except that nothing is labelled.
• Stops at the floor frame. Active in the basement, never carried up to the IDF on your floor or on to the unit.
• The numbers do not match. Where a cable is joined between frames, pair 6 at the floor frame can be a completely different number at the MDF, so the paperwork points at the wrong pair.
• Old changes nobody recorded. Years of alterations by different people, with the building’s records never updated.

The full figures, and how they were counted, are in our study of 324 fault jobs.

The MDF jumpering process, step by step

The order matters more than the tools. Nothing on the frame is moved until the pair has been identified.

1. 1

   Identify the pair

   Start from the cable details your provider gave you, then confirm on the frame which pair actually carries the service.

2. 2

   Trace the path to the unit

   Send a tone from the wall socket back toward the main frame and follow it through every frame in between. The tone shows where the wire really goes. The label only shows where somebody once meant it to go.

3. 3

   Run the jumper

   Join the service pair to the unit's pair, one to one, and remove anything left on the line that should not be there.

4. 4

   Test at the socket

   Check that the modem connects at the socket in the unit, not just that the frame looks right.

5. 5

   Tag and record it

   Label the pair at the frame so the next person does not have to find it again.

When the jumper is on and the line still doesn’t work

A jumper can go on the right pair and the service still not reach your modem. The cable between the frame and your unit can be broken, or badly joined somewhere in the riser. The wall socket can be old, corroded or wired to other sockets. Sometimes it’s the lead or the modem itself. The jumper was right, and the fault is further along. On one new FTTB apartment we were called to, what looked like a missing jumper turned out to be three separate faults on the one line.

Some services do MDF jumpering and nothing else. If the line still doesn’t work once their jumper is on, the job ends there, and you have to book someone else to come out and find the fault.

We’re internet technicians, so finding that fault is part of the same visit. If the line won’t work once the jumper is on, we trace it through to your socket and fix the fault, and if that’s done within the first hour on site it’s covered by the same service call.

When the frame is too old to work on

Building frames come in a few types: older blocks where every wire is soldered on, the disconnection modules most buildings have used for decades, and a few rare older types you only find in some buildings. Plenty of them have been neglected for years. Terminals are loose, labels are gone and some blocks are falling apart.

On a frame in that state, adding another jumper can make things worse. Sometimes we bypass the old frame for your pair. Sometimes the right fix is to upgrade the blocks so the whole frame is sound again. This job shows an MDF upgrade from start to finish.

Watch: MDF Upgrade Redfern | Fixing Messy Main Distribution Frame for NBN

If your building’s frame looks like this, we upgrade MDFs as well as jumper them.

Clean up and maintenance of MDFs

Plenty of MDF rooms haven’t been touched in years. The frame is greasy and dusty, old jumpers hang off it, and dead cables are still connected. Grime on the terminals makes for poor connections, and a poor connection is how a line ends up slow or dropping out.

We clean frames as well as work on them. We clear out the dead wiring and clean the terminals so each connection is solid. This job shows an IDF and MDF clean-up.

Watch: IDF & MDF Clean Up & Maintenance + MDF Jumpering for FTTB in Sydney | Network Setup & WiFi

Building and strata managers can ask us about a clean-up and maintenance visit.

For committees, a comms room checklist to walk through once a year.

Connecting a building’s MDF to the NBN

How much of this applies to you depends on where the fibre stops.

On fibre to the building, NBN’s equipment sits at the frame and the copper pair from there to your door carries the service. A jumper connects the two, and the building’s cabling is part of your connection whether anyone has looked at it in years or not. There is more on that in what fibre to the building is, and where the trouble is between the frame and the units, our fibre to the building work covers it.

On fibre to the node or fibre to the curb, the copper comes in from the street, lands on the frame, and is jumpered across to your unit’s pair in the same way.

On fibre to the premises in a newer building, the last step is often a patch lead from the floor frame to your socket rather than a copper jumper at all.

Phone systems and the MDF

Offices and shops often have a phone system, sometimes called a PABX, wired through the frame. A PABX to MDF connection is the same job in a different direction: the system’s lines are jumpered to the pairs that leave the building.

It also cuts the other way. An old phone system that nobody uses can still be wired across the frame and sit in the path of a new service. When a suite has changed hands a few times, checking for that is part of tracing the line.

How to get ready for an MDF jumpering visit

A little preparation keeps the visit short. Every item here is something we ask about on the phone before we come out.

1. 1

   Get your cable details from your provider

   Ask for the channel pair or the vertical and pair for your MDF, and have the reference number ready. Without it, the technician is toning a frame with hundreds of pairs on it.

2. 2

   Arrange access to the MDF room

   Frames are usually locked. Ask the building manager or security who holds the key and make sure the room can be opened on the day.

3. 3

   Find out where the frames are

   Ask the building manager where the MDF is and whether there are IDFs on the floors. In a tower, that decides where the tracing starts.

4. 4

   Sort out parking

   In a busy area, a visitor space or loading zone saves time on site.

5. 5

   Check the building's rules

   Some buildings need an induction, a sign-in with security or a safe work method statement before anyone can work in the comms room. Ask ahead.

6. 6

   Gather what is already known

   Earlier reports, fault reference numbers and anything a previous technician said. If someone told you the fault is inside the building, try to get that in writing.

With those sorted, book an MDF jumpering visit online, with the price shown before you confirm.

Who is allowed to work on an MDF?

Jumpering is cabling work, and work on a building’s frame is done by a registered cabler. That is not red tape for its own sake. One wrong move on a shared frame can take a neighbour’s service down, and a jumper on the wrong pair can leave two units fighting over one line.

If you are a tenant, ask the building manager before you book anyone. Strata may already have someone who looks after the frame, and depending on the lease, the building may be the one who pays.