[lwip-devel] [patch #7858] Patch for window scaling support for lwip-1.4.0

[christian]

Follow-up Comment #3, patch #7858 (project lwip):

Hi all:

After submitting the patch we discovered some problems when large windows are
supported with high bandwidth.  In tcp_receive, the pcb->acked was updated and
truncated to 16 bits, limiting the effective window (and bandwidth). The
original code was:

/* Update the send buffer space. Diff between the two can never exceed 64K?
*/
pcb->acked = (u16_t)(ackno - pcb->lastack);

To achieve high bandwidths we needed to use 32 bits because this diff can
indeed be more than 64KB, and ended up with:

/* Update the send buffer space. Diff between the two can never exceed 64K?
*/
/* Yes, this might happen with high BW and Jumbo frames. We change the size of
the acked to 32bit. Otherwise, ACKs maybe lost*/
      
pcb->acked = (u32_t)(ackno - pcb->lastack);

with acked field of 32 bits.

Cheers.

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