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Jaws | 2 Jun 2012 18:11
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Missing Ack and TCP retransmission

Hi,
my embedded application send to Cosm some sensor data every 15 secs. 
Everything works fine for about 20 connections.
At some point there is a TCP retransmission due to, I am supposing, a 
missing ACK. After that no data is received from the Cosm Server and the 
connection doesn't complete properly.

In attach the pcap captured for the connections. Any suggestions is welcome.

I am using lwip 1.3.2.

Thanks
Jaws
Attachment (connection_issue.pcap): application/cap, 32 KiB
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Jaws | 2 Jun 2012 18:23
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Missing Ack and TCP retransmission


Hi,
my embedded application send to Cosm some sensor data every 15 secs.
Everything works fine for about 20 connections.
At some point there is a TCP retransmission due to, I am supposing, a
missing ACK. After that no data is received from the Cosm Server and the
connection doesn't complete properly.

In attach the pcap captured for the connections, the issue is present starting form packet n.201.

Any suggestion is welcome.

I am using lwip 1.3.2.

Thanks
Jaws
Attachment (connection_issue.pcap): application/cap, 32 KiB
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Jaws | 3 Jun 2012 23:31
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Re: Missing Ack and TCP retransmission

Hi,
I want to add that the issue is caused to a no memory available for pbuf allocation.
Enabling PBUF_DEBUG we have seen continuosly this message after about 20 connection to a server: pbuf_alloc(length=1536).
After that, the connection to wifi router through HD wifi driver went down.
It seems some memory leak on lwip stack. Attached the log with pbuf alloc-free.
Let me know if you have any suggestion how to find where is the issue.

Thanks in advance.
Jaws




On 06/02/2012 06:23 PM, Jaws wrote:

Hi,
my embedded application send to Cosm some sensor data every 15 secs.
Everything works fine for about 20 connections.
At some point there is a TCP retransmission due to, I am supposing, a
missing ACK. After that no data is received from the Cosm Server and the
connection doesn't complete properly.

In attach the pcap captured for the connections, the issue is present starting form packet n.201.

Any suggestion is welcome.

I am using lwip 1.3.2.

Thanks
Jaws




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Kieran Mansley | 6 Jun 2012 17:13

Re: Missing Ack and TCP retransmission


On 3 Jun 2012, at 22:31, Jaws wrote:

> Hi,
> I want to add that the issue is caused to a no memory available for pbuf allocation.
> Enabling PBUF_DEBUG we have seen continuosly this message after about 20 connection to a server: pbuf_alloc(length=1536).
> After that, the connection to wifi router through HD wifi driver went down.
> It seems some memory leak on lwip stack. Attached the log with pbuf alloc-free.
> Let me know if you have any suggestion how to find where is the issue.

Given that others aren't seeing this sort of memory leak, the leak is most likely in your port of lwIP, your
driver, or your application.

Kieran
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