The difference in expectations must be dealt with. One of the suggested solutions is for the instructor to state his or her availability upfront so that students know when they can expect a response to a question. I announce at the beginning of the course that I will be available for one hour each day. New roles need to be very well defined. Instructors don't have to try to do online everything they do in class.
Discussion forums are there to support participative modes of learning.
For instance, task assignment and task rotation are found most appropriate in order for a community of learners to move from asymmetric to more symmetric learning processes. Instructors are finding that a web-based learning environment is quite similar to a classroom discussion, in the sense that it seems most successful when they are able to get students sending messages to each other rather than always back and forth to them. Instructors spend less time helping students - they help one another. They're quick to respond to questions in the HELP section. Those who are not familiar with online conferences learn by doing.