By: Hugo Garcia, Market Manager Wireless/Wireline
Fiber consolidation is always attractive, especially in the HD (High-Density) environments where the 24 fibers MPO can be an excellent fit, saving trough space while connecting AE (Active Equipment), to a distribution area (Cross-connect) to another AE. No doubt the most popular jacket size for LC jumpers is 2mm zip cord, because of the robustness and/or cost-effectiveness, but it is a struggle not only for the HD panels but also for cable managers.
HD density bays are designed to provide connectivity for ~5760 fibers with LC connectors in a footprint of 30x24” that is when the fiber infrastructure vendors start talking about % of the effectiveness of cable management in terms of jacket size, fiber counts, CM area, access, etc.
MPO systems are designed for multiple purposes:
Fiber consolidation is one of the biggest applications of the MPO systems, 12 fiber jumpers with 2mm zip cord jackets can be replaced for a single 3mm 24MPO trunk cable.
Like any other system, there are pros and cons. The 3 major complaints from the field are: high IL (insertion loss), maintenance, and polarity. 24MPO connectors and systems have reached certain maturity were the price, performance, and installation knowledge are well balanced.
In term of IL (if we put aside some high-end connector vendor ensuring very minimal IL specs between 2 of its own connectors) it is possible to get IL ≤0.35 dB from a 12MPO or a 24MPO pair (MM or SM) ULL (Ultra-low loss), Amphenol Network Solutions (Amphenol-NS) has determined through the years a typical MPO IL of ~0.17 dB loss for connected pair. The impact of the IL to the system will be determined of the transceiver used and fiber plant (SM or MM), it can be estimated with a Link Budget calculation (topic for a different paper)
Maintaining an MPO fiber system does not require more effort than an LC system anymore, cleaning devices, like “clickers” and scopes, integrated on hand-held optical meter devices make it easy to clean, inspect, and measure the attenuation in a concise period of time. Less time than cleaning and inspecting 24 LC connectors for sure, and not to mention the scalability of an MPO system. The second maintenance problem is when a single fiber of the trunk cable does not have connectivity between AE’s, it could be the end-face damaged or a single strand (less likely) to be stressed or broken. It does not matter if is an LC or MPO fiber plant, cable must be replaced or re-routed via software (SDN).
Polarity 24 fibers MPO
12MPO and 24MPO share most of their characteristics: enclosure size, adapters, color code, etc. but they differ in the ferrule used, fiber positioning, and polarity management.
Connectors and adapters:
A 12MPO connector and 24MPO are mechanically compatible, including the key of the MPO adapter, but the fiber alignment is different, and it is a common mistake trying to connect a 12MPO with a 24MPO. There is not going to be transmission at all, not even in 12 fibers, opposite of the Base-8 and the 12MPO system that can be interconnected.
The picture above shows the fiber layouts, both are aligned horizontally to the center of the ferrule, but there is a different quantity of fibers to accommodate. Alignment pins are the same and the ferrule overall area is the same for both connectors.
There are 2 types of MPO adapters: Type A (Key Up to Key Down) and Type B (Key Down to Key Down). Singlemode fiber connectors can use only Type A adapters because of the end-face 8° Angle Polish (APC) as shown in the picture below:
MPO multimode connectors can use Type A or Type B, because of the flat end-face of the ferrule. Fiber alignment between Side A and Side B of an MPO adapter will depend not only on the polarity but also on the fiber count. For a 12MPO system, adapter Type A the fiber 1 of the side A is going to connect to the fiber 1 of the Side B. In Type B adapter, fiber 1 of the side A will be connected to fiber 12 side B. for the 24MPO systems, in the type A adapter, fiber 1 of the side A will be connected to the fiber 13 of the side B and the fiber 12 to the fiber 24. The Type B adapter fiber 1 will be connected to fiber 12 and 13 to 24, in both types of connectors there will be across, and that needs to be considered when a 24MPO system is designed.
In the table above, it can be seen that type A adapters in the 12MPO will provide 1-1, 12-12 connectivity, but the 24MPO will be across in the path. If this was a 10x10G system, Tx and Rx would be crossing in this component, if this is a 2-cassette system, the transceiver in port 1 on one side would be connected to the transceiver in port 7 (see connectivity examples – next section).
Type B adapters for Multimode fiber, in the 12MPO there is a cross in the path, if this is a 4x10G system, Tx and Rx are crossed, if it is a 2-cassette system, the transceiver in port 1 is connected to the transceiver 6 in the other side. There is also a cross in the 24MPO but the problem is different if this is a 10x10G system, the actual pairs are going to be flipped, pair number 1 will be connected to pair number 12, if this is a 2-cassette system, the transceiver in port number 1 will be connected to port 6 (crossed Tx and Rx) and port 7 will be connected to port 12 (see connectivity examples – next section).
MPO trunk Cables:
At first sight, it is not possible to distinguish a 12MPO cable and a 24MPO. Some cable companies use red boots for the 24MPO, some 12MPO cables have 2mm jacket or 3mm, most of the 24MPO cables are 3mm jacket type. As mention before, 12MPO and 24 MPO are not compatible because of the fiber alignment, although 8MPO and 12MPO are compatible. The fiber path is also different on each configuration as shown below.
Connectivity examples for 24MPO
24MPO transceivers Pinout 10x10G
The top row of the MPO is RX and the bottom row is TX, communication pairs are aligned vertically in the 24MPO 10x10G opposite to the Base8 protocols that pairs are horizontally and outside to inside. Transceivers are pinned (male); therefore, the unpinned side of the MPO trunk cable is required to avoid damage.
Direct connectivity between 24MPO transceivers
The “Cross” between TX and RX of the transceivers is performed in the Type A 24MPO trunk cable. This could be confusing because Type A 12MPO cables do not cross signal.
Connectivity between 24MPO transceivers with a Cross-Connect patch panel
In this example, 3 crosses are made: 2 with cables and 1 with the adapter even though everything is type A. Please note: this configuration does not work for 12MPO or 8MPO.
Two Cassette System
Cable consolidation solution:
This is a great example of cable consolidation, as it was mention at the beginning of this document. 12x 2mm zip cord duplex cables can be consolidated in a single 24MPO 3mm trunk cable to communicate one rack to another, one room to another, or one location to another. Polarity is taken care of this example by combining a type A cassette, type A trunk cable, and an Amphenol-NS custom wiring cassette. The same LC jumper can be used on both sides, crossing RX with TX is already inside the Type D cassette. It is very important that the transceiver in ports 1 and 2 on the left side is connected to the transceiver in ports 1 and 2 on the right side.
Bi-Di transceivers solution:
BiDi infrastructure requires only one fiber for TX and RX per transceiver, information flows both ways in a different wavelength. The two cassette system is very similar to the previous one, but the physical cross between TX with RX is not required; therefore, the Amphenol-NS type E cassette will take care of the polarity management to communicate transceiver in port 1 on the left side to the transceiver in port 1 on the right side of the example.
100G migration to 10x10G:
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