Author: Hayden
Main Distribution Frame (MDF): Deploying These Things Can Seem Scary
Main Distribution Frame (MDF): Deploying these things can seem scary, but getting your head around Main Distribution Frame MDF is vital for new optical networks. Many operators, including CMCC, stick to blazing FTTX paths without Main Distribution Frame MDF, but talking to a few transmission professionals, it appears that Main Distribution Frame MDF have been deployed by other operators (also in China) in significant numbers for nearly a decade. This article explains an Main Distribution Frame MDF, its advantages and how it differs from traditional ODF.
1. Why Are Traditional ODF a Problem?
Transmission design engineers as a whole are fairly familiar with ODFs, but the stitching and weaving process needed to wrangle patch cords right now is all too apparent. Figure 1 shows what I mean:figure1-odf-patchcord-now
OK, not pretty, but totally manageable. The 72 patch cords here are just a bit messy, but this floor-full of patch cords is all right as long as the ports aren't filled 100% of the time. Get it up over 50% and the order in the ODF gets havoc-struck and brute maintenance and troubleshooting force goes out the window. So what's causing the patch cord to be disorganized, and what are the practical limits?
2. Reasons an ODF Patch Cord is Disorganized, Limits
The crazy patch cord in an ODF is usually caused by either product design, engineering design errors. We take a look.
2.1 Product Limitations in Today's ODF
Most ODF are 2200(millimeters) by 840 by 300(typ.)(H by W by D) and are capable of holding 648 fibers. (Here's an example from ADVA/Finisar as an example, but most are similar):
If you look on the left side of the unit, there is a fiber management unit which stores excess patch polynomial cord patch cord--one of the places essential for routing patch cords to make room for equipment to slide in or out of racks with cords neatly in their crampons. This is also the only place where ODF patch cords route back and forth from rack to rack.
Figure 2: Internal Configuration of a Typical ODF
When a third of the ODF capacity is used internally for connections between fiber ports and 2/3 for connections outside the ODF to other racks, 432 patch cords may run through one channel, causing severe congestion.
2.2 Implementation Design Stray
Design specifications call for a patch cord the same or less than size given by the ODF physical dimensions specification but such design specifies a 3.0 meter patch cord and the ODF size means a maximum of 3 meters (70% ≤ 2.5 m, 40% ≤ 2.0 m, a few that are 1.5 m long). Also design patch cord size is 2.0 mm otherwise should be φ1.2 mm so must use messy larger diameter cords (Figure 3).
Figure 3: Messy ODF Patch Cord Loop
3. MDF Design Philosophy
The Main Distribution Frames (MDF) are designed like copper MDFs, clearly on line side equipment side separation (Figure 4).
Line Side: External cable is terminated here on the fiber core.
Equipment Side: Termination of ports on devices and other equipment. Patch Cords connect to the line side fiber from ports on the equipment side as efficiently as possible.
Figure 4: Line Side and Equipment Side of an Main Distribution Frame MDF
Fiber patchcord management units go on both sides of the Main Distribution Frame MDF to segregate patchcords in designated channels. To accommodate the excess patchcord length a bib there are fiber storage racks in the Main Distribution Frame MDF (Figure 5).
Figure 5: Patch Cord Layout with Equipment Side, Line Side, and Fiber Storage Rack
For deployments with multiple racks, horizontal patch cord channels are added on one or both sides of the equipment side for routing between racks (Figure 6).
Figure 6: Arrangement of Multiple MDF Racks
4. Main Types of Distribution Frame (MDF)
MDF is categorized based on the location of fiber splicing as follows: separate splice type and integrated splice type.
4.1 Separate Splice
Separate splice type includes a splice rack and termination racks. External cables are spliced onto the rack and are terminated on the line side of the termination rack (Figure 7).
Figure 7: Separate Splice Main Distribution Frame MDF
Splice Rack: HDD type 2200 × 900 × 300; capacity: 1728 fibers; installed back to back in pairs.
Termination Rack: HDD type 2200 × 900 × 600; capacity: 1152 fibers (minimum 576 each side); expandable.
Two rear to rear splice racks can accommodate up to 6 termination racks.
They are suitable for stations with large end-of-life capabilities (core nodes) as termination racks do not require lightning ground. The type of racks chosen limits the future expansion ratios of splice to termination racks.
4.2 Integrated Splice
Each rack has its own fiber termination and fiber splicing unit (similar to ODFs), and is available in type A, B, and C form. Floor area for each rack in mm is 2200 × 900 × 600.
Capacities:
| Type | Line Side Unit Fiber Count | Line Side Unit Quantity | Line Side Capacity (fibers) | Equipment Side Unit Fiber Count | Equipment Side Unit Quantity | Equipment Side Capacity (fibers) |
|---|---|---|---|---|---|---|
| A | 72 | 10 | 720 | 72 | 10 | 720 |
| B | 72 | 9 | 648 | 96 | 6 | 576 |
| C | 72 | 10 | 720 | 96 | 6 | 576 |
5. Benefits of Using a Main Distribution Frame (MDF) Over Traditional ODF
Efficient Management of Patch Cords
Reduced Congestion of Patch Cords on Equipment Side or Line Side
Easy Expansion: More racks and fiber storage units can be added without affecting the overall layout
Clean Wiring: Reduced chances of accidental fiber damage
Compliance: Meets structured cabling standards for high-density fiber networks
6. Conclusion
Main Distribution Frame (MDF) is designed to result in better management of patch cords, not to provide more space than traditional ODFs. Design rules:
Position patch cords to suitable length and avoid excessive slack; use φ1.2 mm patch cords instead of φ2.0 mm.
Correct deployment improves maintainability, operational efficiency, and compliance with international standards of fiber management.
