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c++qttcpwindows-xpnetwork-programming

Using Tcp, why do large blocks of data get transmitted with a lower bandwidth then small blocks of data?

Using 2 PC's with Windows XP, 64kB Tcp Window size, connected with a crossover cable
Using Qt 4.5.3, QTcpServer and QTcpSocket

Sending 2000 messages of 40kB takes 2 seconds (40MB/s)
Sending 1 message of 80MB takes 80 seconds (1MB/s)

Anyone has an explanation for this? I would expect the larger message to go faster, since the lower layers can then fill the Tcp packets more efficiently.

Solution

  • Bug in Qt 4.5.3

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