R&M Data Center Handbook

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Duplex patch cables
Classic duplex cables are involved here, not MPO cables. They are available in a cross-over version (A-to-A) or a
straight-through version (A-to-B) and are terminated with LC or SC connectors.
Modules and adapter plates
Modules and adapter plates are what connect the permanent link to the patch cable. The MPO module enables
the user to take the fibers brought by a trunk cable and distribute them to a duplex cable. As already assembled
units, the MPO modules are fitted with 12 or 24 fibers and have LC, SC or E2000 ∗ adapters on the front side
and MPO at the rear.
The adapter plate connects the MPO trunk cable with an MPO patch cord or harness cable. MPO adapter plates
are available with 6 or 12 MTP adapters, type A or type B.
MPO module with LC duplex adapters MPO adapter plate (6 x MPO/MTP ® )
The polarity methods
The connectors and adapters are coded throughout to ensure the correct orientation of the plug connection. The
three polarity methods A, B and C as defined in TIA-568-C, for their part, are used to guarantee the right bidirectional
allocation. This chapter describes these methods briefly.
Method A
Method A uses straight-through type A backbones (pin1 to pin1) and type A (key-up to key-down) MPO adapters.
On one end of the link is a straight-through patch cord (A-to-B), on the other end is a cross-over patch cord (A-to-
A). A pair-wise flip is done on the patch side. Note that only one A-to-A patch cord may be used for each link.
MPO components from R&M have been available for Method A since 2007. It can be implemented quite easily,
because e.g. just one cassette type is needed, and it is probably the most widespread method.
Method B
Method B uses cross-over type B backbones (pin1 to pin12) and type B (key-up to key-up) MPO adapters. However,
the type B adapters are used differently on the two ends (key-up to key-up versus key-down to key-down),
which requires more planning effort and expense. A straight-through patch cord (A-to-B) is used on both ends of
the link.
Method B does not enjoy wide use because of the greater planning effort and expense involved and because
singlemode MPO connectors cannot be used. R&M does not support this method either or does so only on request.
Method C
Method C uses pair-wise flipped type C backbones and type A (key-up to key-down) MPO adapters. A straightthrough
patch cord (A-to-B) is used on both ends of the link. In other words, the pair-wise flip of polarity occurs in
the backbone, which increases the planning effort and expense for linked backbones. In even-numbered linked
backbones, an A-to-A patch cord is needed.
Method C is not very widespread either because of the greater planning effort and expense involved and because
it does not offer a way of migrating to 40/100GbE. R&M does not support Method C or does so only on request.
∗ E-2000, manufactured under license from Diamond SA, Losone
R&M Data Center Handbook V2.0 © 08/2011 Reichle & De-Massari AG Page 131 of 156