I am comparing Wireshark traces of a 10MB file download file from:
- the FileZilla FTP server and
- IIS (using HTTP) on the same Windows 2003 server.
The FTP download performs faster and the trace shows the server behaving as expected, sending more data to the client with every ACK received:
The HTTP server trace shows a more bursty pattern. The timing of the send bursts are sometimes unrelated to any ACKs received from the client (circled in red):
Anyone have a suggestion as to why IIS traffic is having like this?
Update:
We have tried modifying the http.sys registry settings (setting MaxBytesPerSend to 256k and MaxBufferedSendBytes to 64k as recommended). Changing MaxBytesPerSend does seem to improve performance by increasing the amount of in-flight data , but we still see the same bursty pattern.
Best Answer
I suspect it might be to do with the internal QoS admission control that happens within Windows. IIS might be honouring the QoS, FileZilla might be talking straight to the network.