rohc team mailing list archive

[Didier Barvaux <didier@xxxxxxxxxxx>]

Hello,

My answers below.


>     We have an implementation in the Linux kernel using the ROHC-lib.
> We've found a problem on the decomp side where the dynamic fields of
> a packet are changed, but the option list is not updated.   This
> occurs only when we push large-size packets (> 1024) as quickly as
> possible, thus causing packet drops and retransmits.

Do the drops/retransmits happen before or after the ROHC compression?


> So, it seems like a retransmitted packet's options do not match the
> option list on the decomp side.  My idea of a fix is on the comp side
> - when I detect a change in the dynamic parts, I should send an
> IR_DYN to update the option list.

The compressor should indeed send more information about the changing
options. Not necessarily in an IR-DYN packet however.


>  When I was looking at the d_tcp.c
> code,  I saw several places ifdef'd out with "TODO's"  that seem to
> do similar things.  For example, the following snippet from the code:
> [...]
> Is the purpose of the above code to refresh the decomp side when
> changes in the dynamic fields are detected? Have these TODO's been
> completed?  What needs to be done to make it work?

The TCP profile is work in progress. The transitions between
compression states is not fully written. Hence the commented code.

The compressor shall be able to handle your TCP stream fine even
without the state transitions. It probably didn't detect one or more
changes correctly and failed to use the required packet type.

If you're able to capture the faulty TCP stream, please send it to
this mailing list*. We'll be able to improve the ROHC library.

Regards,
Didier

* if the PCAP capture is big (> 500KB), don't send it on the mailing
  list, upload it somewhere then post the link on the ML.

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