RE: Re: [rohc] ROHC context reuse & mode

[zhigang.c.liu at nokia.com]

To be accurate, we should say context ID is reused, not the context
(e.g. header field values, parameters, etc).

In addition, we can also make a clarification related to this: an IR 
packet will flush out the decompressor context that exists before 
receipt of the IR packet. (Note: mode is treated differently than
the "normal" context which can be in different states.)

BR,
Zhigang

> -----Original Message-----
> From: ext Lars-Erik Jonsson [mailto:larsman@home.se]
> Sent: 18 February, 2004 07:32 AM
> To: kristofer.sandlund@effnet.com
> Cc: rohc@ietf.org; Liu Zhigang.C (Nokia-NRC/Dallas)
> Subject: Re: Re: [rohc] ROHC context reuse & mode
> 
> 
> 
> OK,
> 
> I can buy that argumentation. So, what we should clarify then is that:
> 1) This is what happens when a context is re-used 
>    for a new flow, compressed with the same profile.
> 2) If a context is re-used for compression of a new
>    flow using a different profile, compression is
>    obviously restarted in U-mode, independent of 
>    previous mode
> 
> Would that be it?
> /L-E
> 
> 
> 
> Zhigang/L-E,
> 
> I think that Zhigang's scheme of letting mode be inherited 
> when we have the same 
> profile seems like the best choice to me. I think this 
> approach will be more 
> consistent with the mode transition logic.
> If we choose the "always U-mode when new flow" approach, and 
> a new flow appears 
> in the middle of a pending mode transition, we would probably 
> have to specify 
> that the decompressor must detect that it is a new flow (for example 
> static-def-diffing as I suggested earlier) and also it should 
> set D_TRANS=done & 
> D_MODE=U-mode when we have a new flow (i.e. mode trans must 
> be restarted). The 
> inheritance scheme will just complete the mode transition 
> without having to 
> understand that it is a new flow.
> 
> I can agree that this is slightly inconsistent with the spec, 
> but I don't think 
> it "clearly says new contexts must start in U-mode". All it 
> says is "Compression 
> with ROHC MUST start in the Unidirectional mode" (sec. 
> 4.4.1), which _could_ be 
> interpreted as being on a per-channel basis. If so, mode 
> inheritance is 
> completely ok.
> 
> Rgds,
> 	Kristofer Sandlund, Effnet AB
> 
> 
> 

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