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Re: [Question #229419]: What protocol number should be for RTP header compression


Question #229419 on rohc changed:

Wei Wang gave more information on the question:
Hi Didier,

It seems the problem is the UDP checksum bytes. I just copied the values
from the IP headers. After I changed them to 0, I can see many
compressed packet sizes are 19, which means, 40 header bytes are
compressed to 3 bytes, great!! Still need your confirm this result is

However, another problem rises. The decompressed packet size is negative. There is an error line in log.
[ERROR] [d_generic.c:3508 d_generic_decode()] non-IR packet (2) received in No Context state

Here is a part of log:
[rohc_comp.c:564 rohc_compress()] ROHC size = 19 (feedback = 0, header = 3, payload = 16), output buffer size = 2048

ROHC packet resulting from the ROHC compression:
0x54 0x00 0x00 0x0c 0x3e 0x8e 0x4a 0x69
0x52 0x1b 0xfa 0x02 0xe0 0xb0 0x37 0x9f
0xd8 0x74 0x10
[rohc_decomp.c:420 rohc_decompress()] decompress the 19-byte packet #26
[rohc_decomp.c:1636 d_decode_feedback_first()] skip 0 byte(s) of padding
[rohc_decomp.c:1568 rohc_decomp_decode_cid()] no add-CID found, CID defaults to 0
[rohc_decomp.c:727 d_decode_header()] ROHC packet is not an IR packet
[rohc_decomp.c:742 d_decode_header()] context with CID 0 found
[d_generic.c:3501 d_generic_decode()] decode packet as 'UO-0'
[ERROR] [d_generic.c:3508 d_generic_decode()] non-IR packet (2) received in No Context state
[rohc_decomp.c:434 rohc_decompress()] state in decompressor = 1
[rohc_decomp.c:923 d_optimistic_feedback()] send a STATIC NACK feedback
[feedback.c:76 f_feedback2()] FEEDBACK-2: first 4 bits = 0xa0 (ACK type = 2, mode = 2)
[feedback.c:92 f_feedback2()] FEEDBACK-2: transmit SN = 0x0000b951 on 20 bits (12 bits in base header, 8 bits in SN option)
[feedback.c:96 f_feedback2()] FEEDBACK-2: 4 bits of SN = 0x0
[feedback.c:98 f_feedback2()] FEEDBACK-2: 8 bits of SN = 0xb9
[feedback.c:107 f_feedback2()] FEEDBACK-2: 8 bits of SN option = 0x51
[feedback.c:387 f_wrap_feedback()] add CRC option to feedback
[rohc_comp.c:1149 c_piggyback_feedback()] try to add 6 byte(s) of feedback to the next outgoing ROHC packet
[rohc_comp.c:1181 c_piggyback_feedback()] 6 byte(s) of feedback added to the next outgoing ROHC packet

decompression of fake IP packet failed. decompressed size = -5

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