In this particular case, packet 9 (from Linux) acknowledged the data your LWIP
device sent in packet 8, so packet 10 does seem odd. The Linux system must have
had some reason it wanted to send data at that point. Perhaps the application
wrote the data in two or more separate write calls, and Linux decided to
transmit some of it just before the last block was available.
Another possibile explanation: I note that your LWIP device is advertising a
window size of 1500, and the Linux system sent 750 bytes. The fact that this is
half the window size seems to be too much of a coincidence. Perhaps the Linux
TCP/IP stack has a rule that it will never send a block of data which is
greater than half the window size. You could test this by increasing your
advertised window, e.g. to 3K instead of 1.5K.
IP reassembly won't make any difference - you aren't getting IP fragmentation.
This is a simple case of TCP sending a block of data which is less than MSS.
In general, your application should able to cope with receiving arbitrarily
sized blocks of data via TCP, and reassembling received data as required if you
need logical blocks of data of a certain size. There are many reasons why TCP
might deliver data in blocks smaller than MSS.
----- Original Message -----
From: B B
To: [email protected]
Sent: Friday, August 07, 2009 9:04 PM
Subject: [lwip-users] TCP transmission issue, with linux server.
Hi all,
I am using 1.3.0 stable, and I am experiencing a problem, when my unit is
communicating with a linux server.
I am using the netconn api and using the TCP protocol.
So far we have been running test up against a windows server, which have been
trouble free.
The problem is that the windows server is sending MSS size frames to the
unit, but the linux server is splitting the frames.
I have tried to enable ip reass. But this didn't help.
I have attached the packet capture. The problem is frame no. 10. This is an
ack packet with 750 bytes data.
I would have expected it to be a PSH, ACK packet with 1436 bytes of data.
Has anyone encountered an simillar issue, or can anyone explain to me, why
the linux and windows behave that differently and what a solution might be to
this ?
best regards,
Martin
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