I've D-Link DSL-2500U/BRU/D, ADSL mode is "ADSL2+ AnnexM EU-56", configured as bridge and connected to linux (Gentoo) workstation. Line is good enough, I've stable speed 2.09MiB/sec (i.e. about 18-20Mbps)... but I can see this speed only while downloading torrents or when downloading something using multiple connections (like running several wget processes in parallel).
Single wget process download at only 200KiB/sec in average from anywhere (like kernel.org or other servers I've tried). When wget started it may begin downloading at up to 400-500Kib, but quickly lower speed to about 100Kib, and then slowly increase it to 150-200Kib. Of course, this issue apply to any single tcp connection, not only to wget.
I've tried same wget to kernel.org in WinXP SP3, and LiveCDs of OpenSUSE-11.3, Ubuntu-9.04 and Ubuntu-6.10 - just to exclude possibility of wrong configuration of my Gentoo workstation. In all these OS I see same issue - single wget unable to download faster than 200KiB/sec, but I can run several wget's at that speed simultaneously, so it's not limitation of ADSL line.
Initially I think this issue is because of some ISP's shaper, but later I discover WinSeven able to wget from kernel.org at 1-2MiB/sec! Also, I've tried to switch modem from bridge to router mode, and got 1-2MiB/sec in single wget in my Gentoo, so this issue probably has nothing with ISP.
The MTU is set to 1500 on eth0 and 1492 on ppp0. I notice WinSeven use MTU 1480 on pppoe interface, and tried same value on linux - that doesn't helps. Also I've tried to play with different tcp optimizations using sysctl (rmem/wmem/etc.) - also without any success.
Any ideas how to fix this without switching modem from bridge to router?