I am on BT Infinity FTTC 40/10, using a Draytek 2750 router, connected via Ethernet.
I have been trying to understand why Speedtest.net gives me very differing upload speeds between my standard BT router/modem, and my 2750. With the 2750, I get round about 7Mbps, but with the BT setup, I get over 8Mbps. The download speeds are about the same - about 37.4Mbps on both. Using TBB's speedtester, the speeds on both routers are very similar - 36Mbps down and 6Mbps up.
I have captured the Speedtest packets using Microsoft's Network Monitor 3.4.
With the 2750, the payload length on each TCP packet sent by my PC is normally 536, and occasionally 1072. However, with the BT modem/router, the payload length is often 2824, with a frame length of 2878. Occasionally, the payload length can reach 5648, with a frame length of 5702.
This could easily explain the difference in upload results between the two routers, because of the extra overheads involved with the shorter payloads.
However, when I used to work with TCP/IP and Ethernet, many years ago, I thought that Ethernet frames above about 1500 bytes were illegal. Has this changed, now that Ethernet is not usually a shared media any more?
And the other, more important, question is :- how can I make my Draytek connection use the larger payload sizes, thus improving the upload Speedtest results?