Oracle Database Discussions

We have a little problem with the connection to the Oracle database we have in production. It turns out that in any transactions through the default Oracle port (1521) and over the internet (I mean, the server and the client are always in two different networks) gives a performance well below the expected connection (about 1Mb, symmetrical), but there is no problem if we transact from within the same network. Query seems to be ok, proccessing time is normal and the problem happens when any transaction is done: querying, compiling, retrieving, uploading code, etc.
For example, a query on a heavy records table that retrieves about 700 KB of information in 500 records takes us 3:31 minutes, which gives an average speed of downloading about 3-4 KB/s, though we have upload bandwidth in abundance to the server and more than enough download bandwith in the customer's network. With this query specifically happens that the reception / transmission of data takes place at regular intervals, receiving a chunk of around 20 KB and waiting about 5 seconds to receive new data. It does not seem to happen in other queries but we continue to detect average speeds of 4-5 KB/s. We could not verify whether the traffic managed through the graphical application developed in Oracle Forms has the same problem, I have been told that the protocol is not the same (http in this case, I guess) so it can not be compared. Does this matter? We use Toad and SQL developer as clients, both get the same results and the same performance, the query time is nailed to the second in both. For ODBC connections seems to take even longer, but that I do understand, It is an obsolete way.

We do not know if this might be due to an incorrectly configured parameter in client or server, or is a limitation of software, hardware or line, but in the housing where the server we insist that they do not limit any traffic or anything, and our DBA insists that this is normal, we can not ask more to the system. I think it should go faster, I know for sure that there is a lot of idle bandwith. Any help or idea will be appreciated.

Oracle Database 10g Release 10.2.0.3.0 - 64bit Production, installed on a Windows Server 2003 R2

Thank you very much in advance!