Unable to download/Upload files

Hello,

I have a peculiar problem. There is a G.703 line and at either ends i am using a G.703 to Ethernet Converter(Telindus). One end ethernet is connected to ISP. The other end ethernet is connected to My PC. I am able to ping continously without any drops even with a load of 4096bytes. The browsing is also very fast and goes up to 2Mbps(the speed of the G.703 Line). However when I start to up load or down load, either it gets struck up at the beginning or gets struck up after nearly completing the upload/download. At the ISP end the G.703 to ethernet converter is connected to a Cisco Catalyst switch. Kindly let me know if there is any changes to be made either in switch or my converter.

Thank you.