Yes, this is supposed to happen, although I would think that you should be able to get 33.6 out of them. The reason for this is that 56k doesn't work like slower modem protocols. 56k has different speeds for sending and receiving (56k receiving, 28.8 sending). So, to connect two modems at 56k, you would have to have one "normal" modem (56k receive, 28.8 send) and one "special" modem (28.8 receive, 56k send). If you call a "normal" modem with another "normal" modem, you won't be able to get 56k, but instead, a slower protocol with synchronous send and receive speeds will be used.