cannot connect SPF module from FritzBox Fiber router directly to the Fiber wall-outlet


I have a Fiber router with SFP adapter and I cannot connect it (via SFP module) directly to the Fiber white box on the wall,

but it only works with WAN port and Ethernet cable via the black Tango box installed and connected to the Post white fiber outlet.

Why ?

How can I bypass the black box ?




Meilleure réponse par Alin 16 June 2022, 16:53

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Niveau d'utilisateur 1
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Hi @adyendre!


Thank you for your participation in the forum!


In that case, you cannot bypass the black box as it is essential for the Ethernet cable to pass through it and be connected over the fiber optics cable to the Post box.


Best regards,





Thanks, @Aris ,  but why ?

Does this mean that by default Tango prevents the usage of Fiber routers ?

Was ever any measurement of potential bandwidth loss due to this additional network hop ?

I cannot find any documentation on why this black box would be mandatory.

Thank you.

Niveau d'utilisateur 2
Badge +6

Hi @adyendre ,


Thank you for your reply .


The fiber that goes to 1GB is a type of fiber that cannot be directely connected to a fiber router and therefore needs a converter ( black box ) .


However the 2GB connection is the type of fiber you’re looking for . This type of fiber can be directely connected to a fiber router and doesn’t require the converter ( black box ).


This procedures doesn’t apply only to Tango but to all internet providers.


Best Regards,

Thanks, @Alin .

Just to comment that even with a 2Gb subscription Tango did not homologate FritzBox 5590 router made for fiber with SFP module included.

So I presume each ISP has a fixed list of compatible router models.

Niveau d'utilisateur 2
Badge +6

Hi @adyendre ,


Thank you for your reply.


indeed we use the FritzBox 5530 that takes basically the same modules of the FritzBox 5590 ( which has some stronger modules for the internet connection ). 


We , Tango , only propose the FritzBox routers but it is up to our customers to use it or use another router.


Best Regards,


Hi @adyendre

I have the same problem like you. Tango installed me 2020 a white ONT. The technical man from Tango came to me at home and said that is not possible to fix my new 5590 direct to the fiberbox 5590. I must keep my ONT?? He said that Tango users have a black ONT and not a white. This is the reason that i must keep my ONT?? Now i saw that you have a black ONT. They told everybody a reason for pass through her ONT. They don’t want that the client put his 5590 direct on the fiberbox (Post). On the AVM site they say that all 5590/ 5530 can be connected direct on fibre box. AVM tell that you earn euro on the electricity bill when you connect the 5590/5530 direct in the fiberbox. The technical man was 2,5 hours at my home to connect the 5590 via WAN to the ONT for Internet. Result, he coudn’t register the VOIP in the new 5590. Now i have no VOIP!!! My 2 Fritz fon’s are unusable.

I had to change my old Fritzbox 7590 (5 years old) because the wlan signal is broken.

This evening a wrote to AVM Germany and explained the case.

Best regards,



Niveau d'utilisateur 1

Bonjour @jerfis


Je vous ai envoyé un message privé, merci d’y répondre en me communiquant les informations demandées