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[lwip-users] Problems receiving data from camera using lwip to QTcpSocke

From: jarno . tuovinen
Subject: [lwip-users] Problems receiving data from camera using lwip to QTcpSocket under Ubuntu 9.04
Date: Thu, 20 Aug 2009 13:15:42 +0300
User-agent: Internet Messaging Program (IMP) 3.2.3

Some more details:

Here is pcap-file. is camera and is Ubuntu. When
connection has been made successfully, Ubuntu writes 0x22 to camera which send
same data back. This tells that both are ready to communicate. At packet number
8 Ubuntu sends 0x01 to camera. This requests last data again. This is done twice
in this capture-file, at packet 8 and 36. Again camera answers with same data.
Then camera should send packets which have 512 bytes data. Whole data structure
is 87316 bytes. First camera sends single 512 byte packet and waits for ACK. At
some point it begin to send 2x512 bytes packets and wait for ACK. There is loop
in the camera that sends those packets and after that loop rest 87316 mod 512 is
sent (there comes single packet few seconds after flow stops which have 788
bytes payload, but I can't tell where this 788 comes from. It's somehow cameras
buffer(3*256) + 87316mod256). If single packet times out (250ms) whole loop
"crashes". Third and last attempt starts from packet number 50. There camera
sends fresh data instead of Ubuntu asking old datas retransmission. I begin to
suspect cameras code more and more instead of lwip, but I'm happy to hear your
opinion. Unfortunately I wasn't able to cap successful transmission this time.

- Jarno Tuovinen -

Attachment: pcap_ubuntu_lwip
Description: Binary data

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