A telecommunication method based on transmission control protocol (TCP) includes setting an initial value of a congestion window according to a communication situation of a communication network to more efficiently use uncongested bandwidth of the communication network. An IP network access unit in a telecommunication network determines a congestion window value based on a predetermined reference, and transmits the determined congestion window value to the mobile telecommunication terminal. The mobile communication terminal receives the congestion window value, and performs a TCP access for data telecommunication using the initial congestion window value in a slow start algorithm of TCP in a mobile telecommunication environment. The bandwidth of telecommunication network may be more efficiently used by setting an initial value of the congestion window according to the telecommunication situation or available bandwidth.