The MDF (main distribution frame) is the main network room in a building, where carrier services arrive and the core equipment lives. IDFs (intermediate distribution frames) are the smaller telecom rooms, usually one or more per floor, that connect to the MDF by backbone cabling and serve the outlets and access points nearby. Both need enough space, dedicated power, cooling, bonding and security, and they are much easier to get right on drawings than after construction.
Where telecom rooms go
Room location is driven by cable length. Horizontal copper cabling is limited to 90 metres from the patch panel to the outlet, measured along the actual cable route. On large or long floors, that may mean more than one IDF. Good locations are:
- Central to the area served, to keep runs short
- Stacked vertically on each floor, so backbone cables run straight up through sleeves
- Close to accessible ceiling space and cable pathways
- Away from sources of water, such as washrooms, mechanical rooms and roof drains
- Away from large electrical equipment and sources of interference
The MDF is usually near where carrier services enter the building, often on a lower floor, but avoid basements that are prone to flooding.
What the room needs
Space
Size the room for the racks, clearance in front of and behind them, wall-mounted equipment and future growth. ANSI/TIA-569 gives guidance on telecom room sizing based on the area served. A closet that barely fits today's equipment leaves no room for the next technology. Plan for doors that open outward or have clearance, and enough ceiling height for overhead ladder rack.
Power
- Dedicated circuits for network equipment, not shared with cleaning equipment or lighting
- Capacity for PoE switches running at full load, which can be considerable
- A UPS sized for the equipment and the runtime you need, and connection to emergency power if the building has it
- Convenience outlets on separate circuits for tools and test equipment
Cooling
Switches, especially PoE switches, give off heat continuously. A small room with no cooling can overheat, shortening equipment life or causing shutdowns. Telecom rooms need ventilation or cooling that runs around the clock, not just during building occupied hours. Many building HVAC systems set back at night and on weekends, which is when closets overheat. See data centre cooling for the principles at larger scale.
Bonding and grounding
Racks, cable trays and equipment should be bonded to a telecommunications bonding busbar connected back to the building's electrical grounding system, as described in ANSI/TIA-607 and required by the electrical code. This work must be done by a qualified electrician.
Other details
- Fire-retardant plywood backboard on walls for wall-mounted equipment
- Lighting good enough to read labels
- No water, drain or steam pipes running through or over the room
- Sleeves and firestopping for every penetration
- Sealed concrete or anti-static floor finish to reduce dust
Telecom rooms are not storage rooms. Shared janitor closets, electrical rooms and storage rooms are a common compromise that leads to water damage, blocked access and equipment that gets unplugged. Give network equipment its own room or a properly secured enclosure.
Security and access
Anyone with physical access to a network room can disconnect, tap or damage the network. Telecom rooms should be locked, with access limited to the people who need it and ideally logged through access control. Physical security of network spaces is one of the items we check on every WiFi survey, because it is so often overlooked in shared buildings.
Inside the room
A tidy room is easier to maintain and troubleshoot. Plan:
- Rack layout with patch panels and switches arranged to keep patch cords short
- Horizontal and vertical cable managers
- Overhead ladder rack for cable entering the room
- Separate areas for carrier equipment and building systems
- Labelling on every rack, panel and port
- Room for a second rack
Labelling and records are covered in cable labelling and documentation.
A typical case: the closet that overheats on weekends
A common call: the network on one floor drops every few weekends, and the switches in that IDF show high temperature alarms. During the week, everything is fine. The cause is usually found this way:
- Log the temperature. Put a temperature logger, or use the switches' own sensors, to record the room over a full week. The pattern typically shows the room heating up after the building HVAC sets back on Friday evening.
- Check the load. Compare the room's heat output, which is roughly the electrical load of the switches, UPS and other equipment, with what the room was designed for. Rooms often get more PoE switches over the years with no change to cooling.
- Look at the airflow. A door kept shut with no transfer grille, a ceiling return that was blocked during a renovation, or switches mounted so that their exhaust blows straight into another device's intake all make things worse.
- Fix the cooling, not just the symptom. Options include a dedicated cooling unit for the room, a separate zone in the building automation system that runs 24/7, or exhaust ventilation where the space around the room stays cool. Leaving the door propped open is not a fix, since it defeats security.
- Add monitoring. Set a temperature alert so the next problem is caught before equipment shuts down.
Questions to ask at design review
Telecom rooms are easy to shrink or move on drawings when space is tight. At each design review, check:
- Is every outlet and access point within the cable length limit of a telecom room, measured along real routes?
- Do the IDFs stack vertically, with sleeves sized for backbone cable and future growth?
- Is the room big enough for the racks, front and rear clearance and a future rack?
- Are dedicated circuits, UPS capacity and connection to emergency power shown?
- Does cooling run around the clock, separately from occupied-hours HVAC?
- Is a telecommunications bonding busbar shown and connected to the building ground?
- Are there any water, drain or sprinkler branch lines that do not need to be in the room?
- Is access control or a keyed lock specified, and who will hold access?
Building automation can help with the cooling question; see building automation systems for how schedules and zones are set up.
How ehZee can help
IDF and MDF space is part of the installation section of our survey checklist. Through our structured cabling design and build service we plan room locations, layouts and pathways, coordinate the power, cooling and bonding with the other trades, and verify the result.
Common questions
Can a small office use a wall cabinet instead of a room?
Yes. A lockable, ventilated wall-mounted cabinet in a clean, dry location is fine for a small office. It still needs dedicated power, ventilation and labelling.
What temperature should a telecom room stay at?
Check the equipment manufacturer's operating range. In general, keep the room cool and stable all year, and monitor temperature so you find out before equipment overheats.