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[Didier Barvaux <didier@xxxxxxxxxxx>]

Hello,

>         Incoming ROHC packet (supposed to be a SACK):
> 
> 	0xfa 0x8f 0xf4 0x00 0xb2 0x6f 0x83 0x56
> 	0x4a 0x27 0xd8 0x29 0x1d 0x19 0xed 0x85
> 	0x28 0x49 0xc5 0xba 0x4a 0xc5 0xba 0x4a
> 	0x01 0x0b 0x50 0x05 0xa8

Let's analyze the packet:
 * byte 0xfa:
    * the ROHC packet is in CO common format
    * ttl_flag = 0
 * byte 0x8f:
    * ack_flag = 1
    * psh_flag = 0
    * rsf_flag = 0
    * MSN = 15
 * byte 0xf4:
    * seq_indicator = 3
    * ack_indicator = 3
    * ack_stride_indicator = 0
    * window_indicator = 1
    * ip_id_indicator = 0
    * urg_ptr_present = 0
 * byte 0x00:
    * reserved = 0
    * ecn_used = 0
    * dscp_present = 0
    * ttl_hopl_present = 0
    * list_present = 0
    * ip_id_behavior = 0
    * urg_flag = 0
 * byte 0xb2:
    * df = 1
    * CRC = 0x32
 * bytes 0x6f 0x83 0x56 0x4a
    * 32-bit sequence number = 0x6f83564a
 * bytes 0x27 0xd8 0x29 0x1d
    * 32-bit ACK number = 0x27d8291d
 * bytes 0x19 0xed
    * 16-bit window = 0x19ed
 * bytes 0x85
    * 8-bit IP-ID LSB = 0x85
This is the end of the CO common base header. Now, let's analyze the
irregular chain:
 * ipv4_irregular is empty
 * tcp_irregular
    * bytes 0x28 0x49
       * TCP checksum = 0x2849 (tcp_irregular)
 * nop_irregular is empty
 * nop_irregular is empty
 * tsopt_irregular
    * bytes 0xc5 0xba 0x4a
       * discriminator = '110'
       * tsval = 0x5ba4a
    * bytes 0xc5 0xba 0x4a
       * discriminator = '110'
       * tsecho = 0x5ba4a
 * sack1_irregular
    * byte 0x01
       * discriminator = '00000001'
    * block_1
       * block_start = 0x0b 0x50
          * discriminator = '0'
          * sack_field = 0x0b50
       * block_end = 0x05 0xa8
          * discriminator = '0'
          * sack_field = 0x05a8

I made some hypothesis about the structure of the list of TCP options:
  NOP + NOP + Timestamp + SACK + NOP + NOP
Is my hypothesis right?

The above analysis seems to show that indeed the tcp_irregular decoding
is wrong, more especially the sack1_irregular decoding. The following
bytes are malformed:
  0x02 0x1c 0x48 0x05 0xa8 0x0b 0x50 0x05 0xa8
They should probably be something like:
  0x05 0x0a 0x27 0xd8 0x34 0x6d 0x27 0xD8 0x3A 0x15 0x01 0x01
If you got the original uncompressed packet, please check against it.

The CO common format doesn't contain all the information about the
uncompressed packet, so the ROHC library cannot decompress it without
the previous IR packets. If you can provide them to me, I could test it
further. See the thread [1] where the person provided me the full flow
and I was able to reproduce his/her problem quickly.

[1] https://answers.launchpad.net/rohc/+question/245791
  


>      The option list:
> 
> 	0x01 0x01 0x08 0xff 0xff 0xff 0xff 0xff
> 	0xff 0xff 0xff  0xff 0xff  0xff  0xff  0xff

Hmm, I think that I finally discovered what your "option list" is. It
looks like the content of the tcp_context->tcp_options_list or
tcp_context->tcp_opts_list_struct buffers, not the content of the
uncompressed or compressed packet. That's why I said that the list was
malformed. Am I right?


Regards,
Didier