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


Question #229419 on rohc changed:

    Status: Open => Answered

Didier Barvaux proposed the following answer:

> I have got the good results from the IP and UDP compressors. However,
> after RTP is determined to be the profile from c_get_profile_from_packet(),
> the result looks incorrect. I understand the first packet size may be even
> larger than the uncompressed one. But the size of the packet I showed you
> in the log is a very later packet, like about the 20th packet. That's why I think
> RTP compressor didn't work well.

Okay. Is that packet the 20th RTP packet of the same stream (same IP
addresses, same UDP ports, same RTP SSRC) or the 20th RTP packet of
different RTP streams?

> Could you give me some hint where I can debug what happened in RTP compressor? If you need more log, please let me know.

Yes, print more logs. Watch whether the compressor uses the same
compression context (CID) [1] for all 20 packets. Watch the type of ROHC
packets [2] that the compressor decides to create and the reason of its
decision. Maybe the RTP stream is not regular at all: the more the IP,
UDP, RTP headers changes from one packet to another in the same stream,
the less the compression is efficient [3].


[1] http://rohc-lib.org/wiki/doku.php?id=rohc-protocol#definitions
[2] http://rohc-lib.org/wiki/doku.php?id=rohc-protocol#packet_types
[3] http://rohc-lib.org/wiki/doku.php?id=rohc-protocol#main_principles

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