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Community Member

Do I use 1000BASE-BX-D or 1000BASE-BX-U?


I am working with my service providers to provision 2 new 1GB circuits. The circuits are with 2 different providers, COLT and EUNetworks.

They both tell me they will be delivering managed dark fiber, COLT say this will be a 1310 circuit (i am assuming they mean wave length). EU say they can deliver as 1310 or 1490. I would assume if I am getting a 1310 circuit I would use transciever 1000BASE-BX-U based on document however this document confused me with the following line:

1000BASE-BX10-D transmits a 1490-nm channel and receives a 1310-nm signal, whereas 1000BASE-BX10-U transmits at a 1310-nm wavelength and receives a 1490-nm signal.

Can anyone advise me which I should use? If I don't have enough information here can you tell me what question I should ask the service providers to find out (other than asking them which transceiver to actually use).

Help rated



Hall of Fame Super Silver

Re: Do I use 1000BASE-BX-D or 1000BASE-BX-U?

Hello Gavin,

but the two providers are providing you a single fiber cable each or a pair of fibers each ?

the tranceivers you have linked are to be used for single fiber link.

the two are complementary and need to be deployed in pair one at each end and the other at the other end.

from your link:

A 1000BASE-BX10-D device is always connected to a 1000BASE-BX10-U device with a single strand of standard SMF with an operating transmission range up to 10 km.

So if you manage both ends of each fiber strand you can need two 1000BASE-BX10-D and two 1000BASE-BX10-D deployed in pairs D-U.

I think so dark fiber should mean they give you just the fiber and you need to put tx/rx devices at the two ends.

if one side is managed by the provider you need to ask them what to use (but I wouldn't call this a dark fiber service)

But if every provider is going to give a pair of fibers you need to use more standard transceivers like 1000BASE-LX/LH SFP.

Hope to help


Community Member

Hi sir,

Hi sir,

you said above, "So if you manage both ends of each fiber strand you can need two 1000BASE-BX10-D and two 1000BASE-BX10-D deployed in pairs D-U."

Why would need two 1000BASE-BX10-D and two 1000BASE-BX10-U if one strand is bidirectional (means transmit or receive in one strand)? why not one for D and for U?

correct me if i misinterpret.


Community Member

Re: Hi sir,

I think he meant one..

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