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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:

> The difference between the example and this real application is
> the definition of compressor and decompressor. Here is how
> decompressor is defined on the receiver(RX) side:
>           decompressor = rohc_alloc_decompressor(compressor);
> It depends on the compressor. However, this compressor should
> be the one that is defined on the transmitter(TX) side. Looks like
> the RX needs the compressor data from TX. I think some info like
> profile should be synced up between two sides. Am I right?

Sorry, you're totally wrong. The parameter of the
rohc_alloc_decompressor() function is a related compressor on the same
side as the decompressor. That compressor is used by the decompressor
for its feedback channel (see RFC 3095 for the definition of feedback

                         host A
host B

----IP----->  comp #1       -----ROHC----->  decomp #1  ----IP---->
                             ^                                                         |
                              | feedback                                       | feedbacks
                              |                                                         V
                    decomp #2  <-----feedback-----  comp #2

On host A:
  comp1 = rohc_alloc_compressor()
  decomp2 = rohc_alloc_decompressor(comp1)

On host B:
  comp2 = rohc_alloc_compressor()
  decomp1 = rohc_alloc_decompressor(comp2)


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