3.1.5.3 Processing an addConference Response
A protocol client application SHOULD use the following when processing an addConference response:
If the response indicated failure, obtain the cause by reading the reason attribute from the addConference element, stop further processing, and indicate failure and return the reason to the higher layer.
If the response indicated success, read the conference-URI from the entity attribute of the addConference element, return it to the higher layer, and indicate that the corresponding request succeeded.