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What is the difference between optical fiber main distribution frame (MODF) and traditional ODF

MODF has been used at the scale of operators for nearly 10 years, but why is it so little in demand? After communicating with colleagues in the field of transmission, I found out that not many transmission designers in design institutes know that there is such a product as MODF.

1. Problems in the use of traditional ODF

Designers who specialize in transmission should not be familiar with ODF, so they must be familiar with the scene in Figure 1.

Figure 1 Current situation of ODF fiber jumper

Are the pigtails of the ODF messed up in this picture? chaos! But just a general mess. Because the terminal utilization rate of these ODFs is very low, if the terminal utilization rate of ODF is higher than 50%, then the situation is unbearable.

2. Causes of ODF fiber jumping confusion

There are two main reasons for the confusion of ODF fiber jumper layout: product design defects and engineering design deviations.

2.1 Defects in product design

The current mainstream ODF size is 2200×840×300 (height×width×depth, mm), with a capacity of 648 cores, as shown in Figure 2. The space on the left side of the rack is the fiber coil unit, where the remaining length of the fiber jumper is coiled; this space is also the only channel for the fiber jumper to be laid out, whether it is inside the rack or between racks (from other equipment or ODF to this ODF) ) jumpers must be routed through this channel.

Figure 2 Internal layout of traditional ODF

If 2/3 of the capacity of the ODF rack is used for intra-rack connections (one jumper fiber is connected to every two ports), and 1/3 of the capacity is used for inter-rack connections, then a maximum of 432 jumper fibers will be deployed. Let’s imagine what it would be like if all 432 jumpers were laid out from the space on the left side of the ODF!

2.2 Engineering Design Deviations

According to the size of ODF, the maximum length of the fiber jumper in the frame should not exceed 3m, the length of 70% of the fiber jumper should not exceed 2.5m, the length of 40% of the fiber jumper should not exceed 2.0m, and even a small amount of fiber jumper length only needs 1.5m m is enough. However, the fiber jumper lengths listed in our design documents are basically 3.0m in length, and the average excess length of each jumper fiber exceeds 0.5m.

The diameter of the fiber jumper is 2.0mm or 1.2mm, and the performance indicators meet the requirements of use, but almost all the designed and configured jumpers are 2.0mm in diameter.

Such a phenomenon occurs when there are too many long and thick fiber jumpers, as shown in Figure 3.

Figure 3 ODF disordered fiber jumper

3. The design concept of MODF

The design of MODF adopts the design concept of cable main distribution frame (MDF), and the frame is divided into line side and equipment side, as shown in Figure 4. The fiber core of the external optical cable is terminated on the line side, and the end of the optical fiber connected to the port of the equipment is on the equipment side. The jumper jumps from the corresponding equipment port on the equipment side to the corresponding external optical fiber core on the line side.

Figure 4 Line side and device side of MODF

The MODF disk fiber unit is set on both sides of the frame body, which is also the channel for the fiber jumper to be routed from the equipment side to the line side. Of course, no matter how large the capacity of the fiber coil unit is, it cannot meet the extra length requirement of several meters for each fiber jumper in the design. Therefore, in order to deal with those sloppy designers, MODF has designed a matching fiber storage rack. See Figure 5 for the fiber jumpers and fiber storage racks on the MODF equipment side and line side.

Figure 5 The fiber jumpers and fiber storage racks on the equipment side and line side of MODF

When the MODF contains multiple racks, in order to facilitate the placement of fiber jumpers between the racks, one side (device side) or both sides of the MODF is provided with a horizontal fiber jumper channel, as shown in Figure 6.

Figure 6 Arrangement of MODF multiple racks

4. Main types of MODF

In terms of the welding position of the external optical cable, MODF is mainly divided into: final fusion separation type and final fusion integration type.

4.1 Final melting separation type

The MODF frame of the final fusion separation type is composed of two types of frames: the fusion frame and the terminal frame. The external optical cables are spliced at the splicing frame and terminated at the line side of the terminal frame, as shown in Figure 7.

Figure 7 final melting separation MODF

The size of the splicing frame is: 2200×900×300 (unit: mm), and the capacity is 1728 cores. Generally, 2 splicing frames are installed back to back. The size of the terminal rack is: 2200×900×600 (unit: mm), and the capacity is 1152 cores (576 cores on the line side and equipment side); the number of terminal racks is generally 2 to 3 for the first time, and then increase according to the demand. 2 back-to-back fusion splice racks correspond to a maximum of 6 terminal racks.

The final melting separation type MODF is mainly used for the station with a large final capacity, such as the core node. However, there is a certain proportional relationship between the setting of the welding frame and the terminal frame, and the expansion is limited to a certain extent. The advantage is that the terminal frame does not need to be equipped with lightning protection ground wires.

4.2 Final fusion type

The final fusion integrated MODF is the same as the ODF. Each rack contains an optical cable termination fusion unit, which is divided into A type, B type and C type. The structure of each model is similar, see Figure 4 and Figure 6, and the rack capacity of 2200×900×600 (unit: mm) is shown in the table below.

Model Line side Device side

Number of cores Number of units Capacity (core) Number of cores Number of units Capacity (core)

Type A 72 10 720 72 10 720

Type B 72 9 648 96 6 576

Type C 72 10 720 96 6 576

5. Conclusion

The design concept of MODF is not to increase the capacity density of ODF, but to facilitate the management of fiber jumpers. But we still need to pay attention to 2 points in the design:

(1) Try to configure fiber jumpers of appropriate length according to the needs, and do not leave too much excess length.

(2) Try to use φ1.2mm fiber jumper instead of φ2.0mm jumper fiber.