Do I need to createSession to use VoiceInterface in OnlineSubsystem?

hello.I am making a voice chat with OSS Steam.
I have some questions

  1. Do I need to createSession to use VoiceInterface in OnlineSubsystem?
  2. I think, when using Voice Interface, VOIP is delivered to other players through Dedicated Server, right?
  3. What is the difference between OSS Null and OSS Steam VoiceInterface?

The sentence is not smooth because I am not an English-speaking person.
sorry…

These are the exact questions I’ve had, if anyone knows?