if u use direct plug in , just use Dial up / RAS ( dont use Window Mobile Broadband Connection or the Dashboard Connection

as Dial up / RAS original MTU is 576 as well,..
Packet size, often referred to as MTU (Maximum Transmission Unit) is the greatest amount of data that can be transferred in one physical frame on the network. For Ethernet, the MTU is 1500 bytes, for PPPoE 1492, dial-up connections often use 576.

Each transmission unit consists of header and actual data. The actual data is referred to as MSS (Maximum Segment Size), which defines the largest segment of TCP data that can be transmitted. Essentially,
MTU=MSS + TCP & IP headers.
It is obvious then that smaller packets will be transmitted faster, simply because of the throughput limitation of the line. It's however somewhat moot point in large transfers, all that's illustrated above is the fact that transferring more data takes more time

source -> Here

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