Skype for Business Online and Skype for Business on-prem communication (Business to business) questi

[Deleted]

Please correct me if I'm wrong, but a federated connection is not needed to have business to business communication between S4B Online and S4B 2015, correct?

This would be for two separate companies. The S4B Online settings are set up for open communication with any outside company. So the 2015 version should only have to do something similar (or whitelist the Online domain), right?

[#2]

Pretty much yes... if the 365 tenant is set up for open comms, and 2015 has that one domain whitelisted, you're OK.  But that is a federated connection, it's just somewhat controlled.

[#3 · Accepted solution]

Just make sure federation is enabled for you on prem Edge Server(s)

Set-CsAccessEdgeConfiguration -AllowFederatedUsers $True

If you want to talk with Skype Online/Skype consumer you need to set Hosting Providers (https://erwinbierens.com/setting-up-federation-in-skype-for-business/)

[#4]

Just make sure federation is enabled for you on prem Edge Server(s)

Set-CsAccessEdgeConfiguration -AllowFederatedUsers $True

If you want to talk with Skype Online/Skype consumer you need to set Hosting Providers (https://erwinbierens.com/setting-up-federation-in-skype-for-business/)

You can also test federation from powershell:
Test-CsFederatedPartner -TargetFqdn access.yourdomain.com -Domain externaldomain.com