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MTP Polarity Management

For 1G to 10G Serial Networks

What is polarity?

Maintaining the correct polarity across a fibre network ensures that a transmit signal (Tx) from any type of active equipment will be directed to the receive port (Rx) of a second piece of active equipment – and vice versa.

TIA/EIA 568-b-1-7 defines 3 standard methods for maintaining polarity within multi fibre links.

Complete Connect standardises its products on Method C and recommends using this method in the majority of installations. However, products are available to enable method A. We do not recommend using method B as this requires the added complexity of having 2 types of cassette and using Key Up – Key Up MTP® adaptors. Method B products are primarily used within 40G networks and can be found here.

Maintaining Polarity when using MTP MPO fibre channels

MTP (male) connectors are mated to MTP (female) connectors using an MTP adaptor. Each MTP connector (both male and female) have an asymmetrical housing (a Key) which only allows insertion into an adaptor one way. There are 2 types of MTP adaptors, Key-Up to Key-Up and Key-Up to Key-Down.

A Key-Up to Key Up adaptor will flip all the fibres when two 12 fibre cables are connected through the adaptor, i.e. fibre no. 1 (of the 12 fibres) in the first cable will connect to fibre no. 12 in the second cable. At every point in a fibre link where a Key-Up to Key-Up adaptor is used the fibres 1 to 12 will be flipped and reverse the polarity of the link.

A Key-Up to Key-Down adaptor mainatins the fibres so that fibre 1 in cable 1 is joined to fibre 1 in cable 2. This means that no matter how many of these adaptors are used in a link the polartiy of the link remains.

Key-Up to Key-Down adaptors are far easier to use when trying to maintain a consistent polartity across an installation both at the time of installation and for subsequent moves, adds and changes.

For this reason Complete Connect standardises its products on this type of adaptor. See Physical considerations below

MTP 12 Fibre Male Connector

Achieving Polarity A or C for 10G Networks

1. Polarity A is achieved through an A-A patch cord at one end of the link (fibre channel)
2. Polarity A can be achieved by flipping fibres within a ruggedised fan-out when directly connecting to equipment instead of using a A-A patch cord
3. Polarity C is achieved through using 1 polarity C trunk cable within the link and maintaining A-B patch cords through out

Note: Polarity Method B is not recommended as it requires different types of cassettes and uses of Key up – Key up MTP® adaptors.

How many connections? What type of connections?
How long are the links?
How much rack space is available?
Anticipated future moves, adds and changes?
Future bandwidth requirements?

The main aspects taken into consideration when looking at a network are outlined below:

  • Traffic across various sections of the data centre or network
  • Quantity and variety of fibre channels, physical space and channel flexibility
  • Expansion and growth plans for the data centre or network
  • Expected volume and frequency of MACs
  • Site Access
  • Physical space and outlet density

These factors will determine the network design and subsequently determine which level of product performance you will require at which points.

Complete Connect gives you flexibilty to chooses products that match the design requirements and so ensure that costs are kept to a minimum without being detrimental to performance.

Polarity Method C

Polarity C

Polarity Method A

MTP Network Polarity Method A

Polarity Method B

MTP networks Polarity Method B

Polarity B

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Considerations on using MTP Based Networks

Some key points to note:

→ M300 products use MTP standard connectors and LC / SC standard connectors and so will be suitable where a combination of either shorter runs or fewer connections are required
→ M310 products use MTP ELITE connectors and LC / SC premium connectors (giving reduced insertion loss at each mating) and so will be suitable when channel lengths are longer or more connections (such as the introduction of Zonal or Horizontal distribution) are required
→ Ruggedised fan-outs allow connectivity without the need for rack space
→ MTP-MTP cross connects can be used as an alternative to LC cassettes in the main distribution area and so reduce both the U space required and the number of connections in the channels
→ M350 HP products give direct cabling to zonal areas or active equipment and can remove U space requirement
→ The MTP 24 fibre connector can be used where rack space is heavily restricted

Physical Considerations

1. All cassettes have MTP® male internal rear connectors and will require an MTP® female connector for a correct mating
2. All M300 and M310 products are manufactured to be used with only MTP® adaptors that are Key Up – Key Down ensuring continuity of fibre (fibre 1 to fibre 1) at each adaptor
3. Refer to product specifications of trunks and ruggedised fan-outs to ensure the connector to connector distances you require are based around our definitions of trunk and ruggedised fan-out lengths (i.e. when breakouts and stub lengths.
4. Only Complete Connect products can be used across a link.
5. MTP-MTP cross connects can be used in the Main Distribution Area (MDA). To do this the LC cassettes in the MDA are replaced with MTP adaptors housed in adaptor plates. This decreases the insertion loss across the channel and enables greater channel distances to be achieved because 2 LC matings have been removed.
6. The 24 fibre MTP® connector can be used to double the density of fibre within MTP® adaptor plates
7. The 24 fibre MTP® connector can be used to half the number of cables to a cassette.

3u panel mtp couplers
fibre patch cord

What Installation Steps are required?

The same principles apply whether you are installing a 24 fibre link either between 2 buildings, connecting an office floor to a comms room or creating hundreds of channels in a data centre.

There are 4 main steps to adhere to: –

Step 1

Ensure that the link being created (distance and number of connector matings) meets the required standard.

Step 2

Ensure that the polarity is managed across the link and in accordance with the network design

Step 3

Ensure physical forces on the cables and connectors are managed by using strain relief on the cables to limit the tension in the cabling and maintain bend radii in both the cabling and patching according to the allowed specifications.

Step 4

Follow the fibre connection procedures that you should use when connecting any type of fibre connectors together.

Before connecting a fibre to a cassette or connecting 2 MTP connectors via an adaptor, you should always clean both fibre ferrules with approved cleaning tools, visually inspect both ferrules using an appropriate scope, repeat until the ferrules are clean, and test with a light source and power meter (that is properly referenced).

Step 5

If the tested link is giving insertion losses greater than expected repeat step 4.

NEVER insert a connector into a cassette without the cleaning and inspection process in step 4 being completed.

 Optical considerations

Maximum channel lengths are calculated using the Complete Connect channel calculator application tool
Channel lengths can be increased by using M310 products instead of M300 products which reduces the insertion loss at each connector mating
Channel lengths can be increased by using M350 direct cabling products to reduce the total number of connectors in the link
Channel lengths can be increased by using MTP–MTP cross connects instead of LC cassettes
Channel lengths can be increased by using direct cabling such as ruggedised fan outs instead of trunks and cassettes

1U and 3U modular cassette housing panels

Tools Required

1. The Complete Connect design application tool with ensure step 1 is passed
2. The Complete Connect Installation Guide will demonstrate how to manage polarity correctly.
3. Cable ties for trunks, transition glands for ruggedised fan-out (supplied with all fan-outs), recessing panels to give extra room for patchcords (standard with all panels) and following the cable specifications when laying cables overhead or underfloor.
4. LC cleaning tool. MTP cleaning tool (approved by US Conec). Appropriate light source and power meter. Appropriate reference patch leads. Visual scope – All tools are available from Complete Connect.

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