I need some help in RxTx and wvdial

We are developing a modem dialer program using RxTx, to connect to some devices.
After establishing a connection with the modem, we pass some commands to retrieve the data.
The problem is that we are getting the data, but it is coming in some chunks/blocks. After some data, it waits for some input. So after pressing enter, the next set of data is got. Wanted to know, if this is some stream related problem or buffering issue related to the stream.

Could this be a problem with the serial port hardware buffer filling after which the data is being read.
Previously we were using wvdial and faced no such problem of data coming in chunks. So is wvdial providing some internal buffering mechanism?

Please let me know if you can provide some help/solution in this issue.