Question

I wrote a program using tcpip sockets to send commands to a device and receive the data from the device. The data size would be around 200kB to 600KB. The computer is directly connected to the device using a 100MB network. I found that the sending packets always arrive at the computer at 100MB/s speed (I have debugging information on the unit and I also verified this using some network monitoring software), but the receiving time differs a lot from 40ms to 250ms, even if the size is the same (I have a receiving buffer about 700K and the receiving window of 8092 bytes and changing the window size does not change anything). The phenomena differs also on different computers, but on the same computer the problem is very stable. For example, receiving 300k bytes on computer a would be 40ms, but it may cost 200ms on another computer.
I have disabled firewall, antivirus, all other network protocol except the TCP/IP. Any experts on this can give me some hints?

Answer 1

I’ve found the answer to this question. The problem is due to the even/odd number of packets before the last fragment packet caused by the Nagle’s algorithm.

see the link which is very informative:
http://www.stuartcheshire.org/papers/NagleDelayedAck/