Socket send problem (ucLinux)

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Hi

I have a problem with sockets:(Coldfire DilnetPC DNP5280)

I have a listen socket that can send data to  a remote client.
If a client connects, the server socket opens a file and sent its bytes to
the socket so the remote client can process the bytes.

I noted that when i disrupt (eg 0.2sec ) the network connection the transfer
does not
resume.  The same happens when using a slow connection.(e.g. with a gateway
through internet)

The program seems to block on the send() function.
The full sendbuffer seems to block the send() becorse the data can't be
delivered but it should resume as ethernet communication proceeds.

I would expect get a return value of  -1 when the network disruption takes
too long (causing a sent timeout)  but this is not the case.

When i do this experiment between two windows machines i don't get this
problem. (transfer resumes a few moments i reconnect the network ) neither
does it occur between 2 linux desktop machines.

Is there a problem with the TCPIP stack in ucLinux ? or with the low level
network driver ?

any help much appreciated.

Johan.



Re: Socket send problem (ucLinux)
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If the Network connection is broken, neither of the sockets is informed
that the connection is lost. Both think it's still working.

The one that some time later sends a packet does not receive an
acknowledge packet from the addressees stack, so, after some 90 seconds
it declares the connection broken and the application is informed. Still
the other end thinks the connection is still working (though idle).

If (e.g.) the client application knows that the connection is broken, it
might try a reconnect. If the cable is restored, the server will decline
the connect, as it thinks there is still a working connection.

To improve this situation you need to implement a life check protocol
lin the application or use the stack's "keep alive" feature.

-Michael

Re: Socket send problem (ucLinux)
Discovered  that after a disruption (or network congestion ) the board
retries to sent the packet but it has checksum errors on the data part !!

This seems to be a serious bug in the uclinux.....
see below for a snippet made with etherreal

The boards repeats the bad packet several times until the conection times
out after severla minutes .

Frame 3484 (254 on wire, 254 captured)
    Arrival Time: Dec 30, 2006 23:55:43.758822000
    Time delta from previous packet: 0.811065000 seconds
    Time relative to first packet: 47.427310000 seconds
    Frame Number: 3484
    Packet Length: 254 bytes
    Capture Length: 254 bytes
Ethernet II
    Destination: 00:09:f3:0f:22:dc (WELL_0f:22:dc)
    Source: 02:80:ad:20:b8:b2 (02:80:ad:20:b8:b2)
    Type: IP (0x0800)
Internet Protocol, Src Addr: 192.168.1.61 (192.168.1.61), Dst Addr:
dD577BF9E.access.telenet.be (213.119.191.158)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 240
    Identification: 0x030f
    Flags: 0x04
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: TCP (0x06)
    Header checksum: 0xdffd (correct)
    Source: 192.168.1.61 (192.168.1.61)
    Destination: dD577BF9E.access.telenet.be (213.119.191.158)
Transmission Control Protocol, Src Port: 2050 (2050), Dst Port: 2126 (2126),
Seq: 1948016716, Ack: 471731837, Len: 200
    Source port: 2050 (2050)
    Destination port: 2126 (2126)
    Sequence number: 1948016716
    Next sequence number: 1948016916
    Acknowledgement number: 471731837
    Header length: 20 bytes
    Flags: 0x0018 (PSH, ACK)
        0... .... = Congestion Window Reduced (CWR): Not set
        .0.. .... = ECN-Echo: Not set
        ..0. .... = Urgent: Not set
        ...1 .... = Acknowledgment: Set
        .... 1... = Push: Set
        .... .0.. = Reset: Not set
        .... ..0. = Syn: Not set
        .... ...0 = Fin: Not set
    Window size: 5840
    Checksum: 0x69cc (correct)
Data (200 bytes)

0000  00 09 f3 0f 22 dc 02 80 ad 20 b8 b2 08 00 45 00   ....".... ....E.
0010  00 f0 03 0f 40 00 40 06 df fd c0 a8 01 3d d5 77   ....@.@......=.w
0020  bf 9e 08 02 08 4e 74 1c 60 4c 1c 1e 0e 7d 50 18   .....Nt.`L...}P.
0030  16 d0 69 cc 00 00 68 65 6c 6c 6f 20 77 6f 72 6c   ..i...hello worl
0040  64 31 31 37 20 20 20 20 20 20 20 20 20 20 20 20   d117
0050  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
0060  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
0070  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
0080  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
0090  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
00a0  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
00b0  20 20 20 0a 0d 00 23 23 23 23 23 23 23 23 23 23      ...##########
00c0  23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23   ################
00d0  23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23   ################
00e0  23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23   ################
00f0  23 23 23 23 23 23 23 23 23 23 23 23 23 23         ##############

Frame 3497 (60 on wire, 60 captured)
    Arrival Time: Dec 30, 2006 23:55:43.953376000
    Time delta from previous packet: 0.194554000 seconds
    Time relative to first packet: 47.621864000 seconds
    Frame Number: 3497
    Packet Length: 60 bytes
    Capture Length: 60 bytes
Ethernet II
    Destination: 02:80:ad:20:b8:b2 (02:80:ad:20:b8:b2)
    Source: 00:09:f3:0f:22:dc (WELL_0f:22:dc)
    Type: IP (0x0800)
    Trailer: 2A51DBC67616
Internet Protocol, Src Addr: dD577BF9E.access.telenet.be (213.119.191.158),
Dst Addr: 192.168.1.61 (192.168.1.61)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 40
    Identification: 0xf35a
    Flags: 0x04
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 120
    Protocol: TCP (0x06)
    Header checksum: 0xb879 (correct)
    Source: dD577BF9E.access.telenet.be (213.119.191.158)
    Destination: 192.168.1.61 (192.168.1.61)
Transmission Control Protocol, Src Port: 2126 (2126), Dst Port: 2050 (2050),
Seq: 471731837, Ack: 1948016916, Len: 0
    Source port: 2126 (2126)
    Destination port: 2050 (2050)
    Sequence number: 471731837
    Acknowledgement number: 1948016916
    Header length: 20 bytes
    Flags: 0x0010 (ACK)
        0... .... = Congestion Window Reduced (CWR): Not set
        .0.. .... = ECN-Echo: Not set
        ..0. .... = Urgent: Not set
        ...1 .... = Acknowledgment: Set
        .... 0... = Push: Not set
        .... .0.. = Reset: Not set
        .... ..0. = Syn: Not set
        .... ...0 = Fin: Not set
    Window size: 16520
    Checksum: 0x0835 (correct)

0000  02 80 ad 20 b8 b2 00 09 f3 0f 22 dc 08 00 45 00   ... ......"...E.
0010  00 28 f3 5a 40 00 78 06 b8 79 d5 77 bf 9e c0 a8   .(. snipped-for-privacy@.x..y.w....
0020  01 3d 08 4e 08 02 1c 1e 0e 7d 74 1c 61 14 50 10   .=.N.....}t.a.P.
0030  40 88 08 35 00 00 2a 51 db c6 76 16               @..5..*Q..v.

Frame 3667 (254 on wire, 254 captured)
    Arrival Time: Dec 30, 2006 23:55:46.028327000
    Time delta from previous packet: 2.074951000 seconds
    Time relative to first packet: 49.696815000 seconds
    Frame Number: 3667
    Packet Length: 254 bytes
    Capture Length: 254 bytes
Ethernet II
    Destination: 00:09:f3:0f:22:dc (WELL_0f:22:dc)
    Source: 02:80:ad:20:b8:b2 (02:80:ad:20:b8:b2)
    Type: IP (0x0800)
Internet Protocol, Src Addr: 192.168.1.61 (192.168.1.61), Dst Addr:
dD577BF9E.access.telenet.be (213.119.191.158)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 240
    Identification: 0x0312
    Flags: 0x04
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: TCP (0x06)
    Header checksum: 0xdffa (correct)
    Source: 192.168.1.61 (192.168.1.61)
    Destination: dD577BF9E.access.telenet.be (213.119.191.158)
Transmission Control Protocol, Src Port: 2050 (2050), Dst Port: 2126 (2126),
Seq: 1948016916, Ack: 471731837, Len: 200
    Source port: 2050 (2050)
    Destination port: 2126 (2126)
    Sequence number: 1948016916
    Next sequence number: 1948017116
    Acknowledgement number: 471731837
    Header length: 20 bytes
    Flags: 0x0018 (PSH, ACK)
        0... .... = Congestion Window Reduced (CWR): Not set
        .0.. .... = ECN-Echo: Not set
        ..0. .... = Urgent: Not set
        ...1 .... = Acknowledgment: Set
        .... 1... = Push: Set
        .... .0.. = Reset: Not set
        .... ..0. = Syn: Not set
        .... ...0 = Fin: Not set
    Window size: 5840
    Checksum: 0x6903 (incorrect, should be 0xaf49)
Data (200 bytes)

0000  00 09 f3 0f 22 dc 02 80 ad 20 b8 b2 08 00 45 00   ....".... ....E.
0010  00 f0 03 12 40 00 40 06 df fa c0 a8 01 3d d5 77   ....@.@......=.w
0020  bf 9e 08 02 08 4e 74 1c 61 14 1c 1e 0e 7d 50 18   .....Nt.a....}P.
0030  16 d0 69 03 00 00 00 00 00 00 68 65 6c 6c 6f 20   ..i.......hello
0040  77 6f 72 6c 64 31 31 38 20 20 20 20 20 20 20 20   world118
0050  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
0060  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
0070  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
0080  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
0090  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
00a0  20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20
00b0  20 20 20 20 20 20 20 0a 0d 00 23 23 23 23 23 23          ...######
00c0  23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23   ################
00d0  23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23   ################
00e0  23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23   ################
00f0  23 23 23 23 23 23 23 23 23 23 23 23 23 23         ##############




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