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Connection using GLC-BX

Matthew Loggan
Level 1
Level 1


I would like to know if the following connection is correct for communicate two site using a SMF (Single Strand):

Catalyst 3850 -> GLC-BX-D ----> Single Strand of SMF <---- GLC-BX-U-> Catalyst 3850

One GLC-BX-D in one side of the link and one GLC-BX-U in the other side? that is correct?

I already have checked the compatibility of both transceivers with the C3850-NM-4-1G

Best Regards.

7 Replies 7

Level 1
Level 1

To tell the truth, GLC-BX-D and GLC-BX-U transceivers both work with single-mode fiber but they operate at different wavelength, so it might cause error. The above links are  for your reference ! 

Tom Randstrom
VIP Alumni
VIP Alumni

Below is taken from the Cisco SFP Modules for Gigabit Ethernet Applications Data Sheet:

1000BASE-BX10-D and 1000BASE-BX10-U SFP for Single-Fiber Bidirectional Applications

The 1000BASE-BX-D and 1000BASE-BX-U SFPs, compatible with the IEEE 802.3ah 1000BASE-BX10-D and 1000BASE-BX10-U standards, operate on a single strand of standard SMF.

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.

The communication over a single strand of fiber is achieved by separating the transmission wavelength of the two devices as depicted in Figure 2: 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. As shown, the presence of a wavelength-division multiplexing (WDM) splitter integrated into the SFP to split the 1310-nm and 1490-nm light paths.

Figure 4.      Bidirectional Transmission of a Single Strand of SMF


Level 1
Level 1

Your connection is absolutely correct!


You required the different tx/rx transmissions provided by your "D" and "U" SPFs in order to properly communicate across a single fiber.  A very common mistake is to use the same type of SFP on a single (BiDi - BiDirectional) fiber.

Level 1
Level 1


I want to established a connection between GLC-BX-D= to GLC-BX-D= SFP module. Will it work??

As both of the transceiver have same wavelength 1490NM. Please help me for this.

No, that will not work due to the internal filter in the SFP. You need to
have a BX-U on one end and a BX-D on the other end of the fiber for this to

Level 1
Level 1


If I want to established a connection between SFP-10G-BXD-I= to SFP-10G-BXD-I=SFP module. Will it work??

Please help me for this.

No, this won't work.

A Bidirectional (BiDi) SFP uses a single strand (simplex) fiber. The SFP
uses two different channels (wavelengths) in order to transmit (Tx) and
receive (Rx) data. An SFP-10G-BXD-I must be used with a SFP-10G-BXU-I. Pay
special attention to the naming convention. Notice the "D" (Downstream) and
"U" (Upstream). Every BiDi SFP must be used with it's appropriate pair. If
you were to look at a spec sheet; you'd see that the SFP-10G-BXD is using
1330nm-TX/1270nm-RX and the SFP-10G-BXU is using 1270nm-TX/1330nm-RX. Since
one SFP's Tx speaks to the other's Rx I hope you can see why you are
required to use D /U in pairs across a fiber.