My company just recently implemented a full DS3 from our office in New Jersey to the headquarters in China. Needless to say the RTT is about 250ms which to my understanding is typical for LFNs. Here is where I am puzzled,
If I FTP a 29MB file TO China, time start to end is about 2 minutes, which is "ok", but if I try to pull the same file from China, it takes more like 16 minutes.
I asked the provider to adjust the TCP window size on both routers plus suggested to Windows Engineers in China to make sure Windows 2000 box has latest patches to support TCP Window scaling,,
Yes, the end hosts TCP receive window size and the queue sizes on the routers. Both should be sized to support the LFN's BDP.
The TCP window size on the router only is significant if the router itself is a TCP receiving host.
BTW: Many Windows host TCP stacks earlier than Vista's can support Windows scaling, but I recall they don't use it by default and you still also need for those to configure the receive window size. Windows XP hosts also sizes its TCP receive window size differently depending on the speed of the host's LAN connection. (Unsure what w2k does.)
Another thing you could check is the bandwidth utilization of the link in both directions, i.e. New Jersey to China and China to New Jersey. It is common for links not to have the same utilization in both directions. If the direction from China to New Jersey already has somewhat high utilization, you could be running into some degree of congestion. (You implemented the DS3 recently, so either you now have plenty bandwidth or you absolutely needed the upgrade). You could be reaching high utilization on the link instantaneously (instant bursts might not be easily noticeable in management graphs) during the file transfer in only one direction, which can lower the performance of TCP in that direction only.
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