Alice                      Bob
                  |                         |
                  |     INVITE (Offer)      |
                  |------------------------>|
                  |      183 (Answer)       |
                  |<------------------------|
                  |                         |
                  |               +----------------------+
                  |               |Bob:  I don't know if |
                  |               |Alice got my 183 or if|
                  |               |her dialog is already |
                  |               |in the early state.   |
                  |               |  Can I send INFO???  |
                  |               +----------------------+
                  |                         |