Type-B Polarity MTP Cable User Guide

August 9, 2016

Type-B Polarity MTP Cable User Guide

As demand grows for higher speed, large data centers being built today have begun to make preparations for 40G/100G transmission. MTP cables, with great performance and high speed, have become the main component in data centers.

In today's data centers, MTP cables, like 8-fiber or 12-fiber MTP cable, are frequently used to establish an optical path between switch tiers. Different from common fiber patch cords, one MTP cable has multiple fibers that can be of different positions inside, and an MTP connector terminates these fibers in a single high-density interface, which will be more complicated to handle in the polarity management. To match these fiber positions, TIA standards define three types of polarity MTP cables: type-A, type-B and type-C. Different types of MTP polarity cables may have different applications. In this tutorial, we will mainly introduce the type-B polarity MTP cables and its applications. For a complete polarity guide of FS products, you can refer to our white paper Understanding Fiber Polarity.

Overview: Get Close to Type-B Polarity MTP Cable

The type-B polarity MTP fiber uses a key-up connector on both ends of the cable. Often referred to as a 40G MTP cable, the type-B MTP cable is the second standard for polarity, and extremely versatile. This cable assembly can be used to plug directly between your 40G QSFP+ optic transceivers, so it is commonly referred to as a QSFP/QSFP+ cable or direct attach 40GBASE-SR4, 40GBASE-PLR4 or 40GBASE-PLRL4. As you can see in the diagram, this cable has a "flipped" polarity and will result in a Pin 1 to Pin 12 relationship. This is extremely useful because 40G optics utilize parallel optics, meaning instead of alternating Tx and Rx in a duplex pattern, the port will look like the following diagram.

mtp type-b cable Figure 1: Type-B polarity MTP cable

Categories: Diverse Types to Meet Different Challenges

In today's fiber optic networks, especially in data centers, MTP trunk cable and MTP-LC harness cable are the two most common types used. Besides, the MTP connector is pin and socket connectors, which require a male side and a female side. Therefore, in terms of MTP trunk cable, there are female-female, female-male and male-male three types. In addition, when connecting two parallel optics 40G SR4 QSFP+ transceivers, only a female to female type-B MTP cable should be used. For MTP-LC harness cable, female MTP-LC harness cable and male MTP-LC harness cable are available.

mtp type-b cable Figure 2: Type-B polarity MTP cable types

Applications: One Cable, More Possibilities

MTP cables are designed for higher bandwidth applications such as 40GbE and 100GbE. Due to the special structure, a female MTP cable is often required to mate a male MTP cable. Male guide pins fit into the female holes to ensure precise fiber alignment. Attempting to mate two female connectors or male connectors will cause light loss or damage the fiber connectors. The following examples mainly explore applications of female type-B polarity MTP cables.

Direct Connection: Female to Female Type-B Polarity Trunk Cable

Except for the parallel 40G optical transmission mentioned above, female to female type-B trunk cable also can be used for direct switch to switch connectivity with no patch panels. The following figure shows two Cisco 40G transceivers connected by a 12-fiber MTP female cable directly.

mtp type-b trunk cable Figure 3: Female to female 12-fiber type-B MTP cable in 40G connection

With an MTP adapter, a type-B MTP polarity trunk cable can be used for connecting a patch panel and a QSFP+ SR4 transceiver.

Direct Connection: Female MTP to LC Type-B Polarity MTP Harness Cable

How to breakout 40G link into four 10G links for a different purpose? A female MTP-4LC type-B harness cable can solve this problem easily. The following figure shows the four 10GBASE-SR transceivers interconnect with one 40GBASE-SR4 transceiver by one female MTP-4LC harness cable directly.

type-b mtp-lc harness cable Figure 4: 8-fiber type-B MTP-LC breakout cable in 40G connection

Interconnections: Type-B MTP Trunk Cable and Type-B MTP Harness Cable

Type-B MTP trunk cable and harness cable can be used together to achieve high performance fiber networking. Figure 5 shows the interconnect of 10GBASE-LR SFP+ transceivers connected by type-B MTP trunk cable and harness cable. It is an ideal solution to link two Cisco switches in the data center for high-speed fiber optic transmission.

mtp type-b trunk cable and harness cableFigure 5: type-B MTP trunk cable and harness cable in 10G interconnection


The biggest market for 40GbE and 100GbE is in data centers for interconnection links with servers and storage area networks. Optimal for 40G and 100G applications, MTP cables become more and more popular in data centers. To simplify the complex networking cabling, FS.COM polarity management solution for base-8, base-12, and base-24 MTP/MPO cabling allow data center managers to effectively migrate to 40/100G or higher speeds.


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