Re: [rohc] ROHC context reuse & mode

[Kristofer Sandlund <kristofer.sandlund at effnet.com>]

Hi Carsten,

Are you saying that every IR packet (regardless of it being for a new flow or 
not) should flush the ENTIRE decompressor context?

One case where some state probably should be kept is for the list compression. 
Just because an extension header (or CSRC identifier) is not present in the 
current IR packet does not mean that it's not present in the context and could 
reappear in a later packet. If I flush the list compression tables every time I 
get an IR packet, I will have to re-establish every item once again. This does 
not seem to be very efficient, especially in U-mode where I should periodically 
refresh the context with IRs.

Also, if every IR would mean the same as establishing a new context, wouldn't 
that mean that all IR:s would need to carry U-mode? (since all compression 
should start in U-mode). Why then a mode parameter in the profile 1 IR packet?

Rgds,
	Kristofer Sandlund, Effnet AB

Carsten Bormann wrote:
> > > RFC3095 Section 4.4.1.  "Unidirectional mode -- U-mode" says:
> > >     Compression with ROHC MUST start in the Unidirectional mode.
> > >
> > > Does this mean that the compressor starts in U-mode "when the
> > > channel is set-up" or "whenever the compressor re-initializes
> > > a context"?
>
> I believe the intention has been all the time that initializing a 
> context using an IR packet would start with a clean slate, as if the 
> channel was just created.  I.e., this is a new context, even when a CID 
> is being reused.
>
> I'm too busy to do the analysis (read: dusting off brain cells) right now:
> Do we have any case where we need to maintain previous state beyond an 
> IR packet?
>
> Gruesse, Carsten


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