In my lab, my shdsl line is 2.3Mbps speed. When I connect a PC to the CPE, and download from server in uplink network, the download speed is about 2Mbps. But, when I upload and download in the same time, upload speed is 2Mbps, but the download speed decrease to 0.8Mbps!!
I don't know why, the download speed should be 2Mbps