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[lwip-devel] [bug #18782] the default PBUF_POOL_BUFSIZE value should be


From: dupengbo
Subject: [lwip-devel] [bug #18782] the default PBUF_POOL_BUFSIZE value should be changed
Date: Mon, 15 Jan 2007 03:37:42 +0000
User-agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; Maxthon)

URL:
  <http://savannah.nongnu.org/bugs/?18782>

                 Summary: the default PBUF_POOL_BUFSIZE value should be
changed
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: dupengbo
            Submitted on: Monday 01/15/07 at 03:37
                Category: IPv4
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

for example:
A is LWIP system , B is other TCPIP system.

A: the default TCP_WND is 2048, PBUF_POOL_SIZE is 16, PBUF_POOL_BUFSIZE  is
128. TCP_MSS is 128.
static u8_t pbuf_pool_memory[MEM_ALIGNMENT - 1 + PBUF_POOL_SIZE *
MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE + sizeof(struct pbuf))];
the size of pbuf_pool_memory is 2048.

B: has known A has 2048 bytes available buffer.

So, B will send 2048 bytes to A (do not wait the ACK from A).

But B will send 128 + TCP header + IP header = 168 bytes to A.
LWIP will need two POOLs to save the data, because the PBUF_POOL_BUFSIZE  is
128, it could not save the 168 bytes data.

the result: B know the A has 2048 bytes available buffer, but actually A only
has 1024 bytes buffer available, because every segment need two POOLs.

suggestion: PBUF_POOL_BUFSIZE is 128 + TCP header + IP header






    _______________________________________________________

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  <http://savannah.nongnu.org/bugs/?18782>

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