Polarity A and Polarity B MTP Cassettes Deployment

With the widespread deployment of 40G and 100G network, high density modular system has gained much popularity. MTP modular cassette is loaded with factory-installed and tested optical fiber assembly inside to connect the front LC or SC adapter to the back MTP connector adapter, which is often used to interconnect MTP backbones with LC or SC patching. This post aims to introduce how to deploy polarity A and polarity B MTP cassettes correctly.

Polarity A and Polarity B MTP Cassettes Overview

As mentioned, MTP cassette features simplex or duplex port adapters across the front and one or two MTP connector adapters across the back as shown below. The MTP adapter mounted at the rear of a cassette defines it as either a polarity A or polarity B cassette. The only differences between polarity A and polarity B MTP cassette is the orientation of the internal MPO/MTP connector with respect to the mating MPO/MTP array cable connector.

MPO MTP cassette structure

The polarity A MTP cassette makes a key-up to key down connection between the internal MPO/MTP connector and the MPO/MTP array cable connector, while the polarity B MTP cassette makes a key-up to key up connection. But we have to pay attention that a polarity B MTP cassette will not allow single-mode angle polish mated pair connections, because the angles of the mating connectors are not complementary.

How to Deploy Polarity A and Polarity B MTP Cassettes in Different Connectivity Methods´╝č

To ensure the proper polarity of array connections using multifiber MPO/MTP components from end-to-end, the TIA 568 standard has defined three methods, known as Method A, Method B, and Method C. In different method, the deployments of polarity A and polarity B are different.

Connectivity Method A: In this connectivity method, a type-A trunk cable is used to connect a polarity A MTP cassette with key-up to key-down MTP adapters on each side of the link, then there is a A-to-B type duplex patch cable on the left and a A-to-A type duplex patch cable on the right as shown below.

method-a

Note: 1. Type-A trunk cable is a straight through cable with a key-up MTP connector on one end and a key-down MTP connector on the other end, which makes the fibers at each end of the cable have the same fiber position. For example, the fiber located at position 1 of the connector on one side will arrive at position 1 at the other connector. 2. A-to-A and A-to-B type patch cables are defined by TIA standard, which are terminated with LC or SC connectors to complete an end-to-end fiber duplex connection. Generally, A-to-A type patch cable is a cross version and A-to-B type is a straight version.

Connectivity Method B: In method B, a type-B trunk cable is used to connect a polarity B MTP cassette with key-up to key-up MTP adapters on each side of the link, and there are A-to-B type duplex patch cable used on both ends to achieve the connection between MTP cassettes and other equipment as shown below.

method-b

Note: Type-B trunk cable is with two key-up MTP connectors terminated at both ends. So the position 1 of one connector is corresponding to the position 12 of the other connector.

Connectivity Method C: In this method, a type-C trunk cable is used to connector a polarity A MTP cassettes on each side of the link, and then use two standard A-to-B type duplex cables at both ends of the link as shown below.

method-c

Note: Type-C trunk cable is similar to type-A trunk cable with one key-up connector and one key-down connector at each end, but in type-C cable, each adjacent pair of fibers at one end is flipped at the other end. For example, the fiber at position 1 on one connector is shifted to position 2 at the other connector, and the fiber at position 2 at one connector is shifted to the position 1 at the other connector, etc.

Conclusion

MTP cassette allows for rapid deployment of high density data center infrastructure as well as improved troubleshooting and reconfiguration during MACs(moves, adds and changes). The text above have introduced connectivity of polarity A and polarity B cassettes in three different connectivity method. We have to figure it out that its deployment is closely related to the other components used in the same method, when deploy it, you should pay much attention to the trunk cable and patch cable type used in different method.

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