[lwip-devel] Re: [patch #6537] wnd_scale TCP option addition

[Rishi Khan]

You need to implement SACK. That will fix it.
On Apr 8, 2009, at 5:39 AM, Wim Dumon wrote:

> Follow-up Comment #6, patch #6537 (project lwip):
>
> I encountered an issue with this patch. I observed data loss and  
> performance
> degradation when receiving data over TCP connections with large  
> window sizes
> (e.g. TCP_WND=120KBytes). My shift is set at 7 (but it could be  
> anything
> else).
> This is the problem: suppose window is usually filled for about  
> 70K, caused
> by the bandwidth*delay principle. Imagine that the link works well,  
> and at a
> certain moment a single packet is dropped. The OOSEQ code queues  
> packets, but
> there is a little gap in the sequence number for the first ooseq  
> packet. When
> that gap is filled by a retransmit of the missing data, all the
> out-of-sequence queued packets, amounting to 70K of data in our  
> example, is
> concatenated in one pbuf (it is called recv_data). But the tot_len  
> field of a
> pbuf is only 16bit.... The result I observe is that there is a 64K  
> gap in the
> received data stream.
>
> Isn't the intention of this patch to allow TCP_WND to be > 64K? Any  
> hints on
> how to solve this? I have the feeling that simply changing tot_len  
> to a u32_t
> will not be sufficient. Using multiple pbufs is probably easier?
>
>
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