A method of transmitting/receiving a frame between a portable terminal and a base station in a wireless broadband Internet network are provided. More particularly, a method of transmitting/receiving frames can include activating a session between the portable terminal and the base station, removing at least one header information field included in an Internet protocol (IP) datagram after activating the session, adding a network header which sets a predetermined transport connection identifier (TCID) to the IP datagram, generating the frame, and transmitting the generated frame via the activated session. Preferably, the frame is generated in any one of the portable terminal and the base station, and transmitted to the other one of the portable terminal and the base station.