RE: [rohc] SigComp state creation request, requested feedback, a nd SMS = 0

["Price, Richard" <richard.price@roke.co.uk>]

Hi Zacco,

It's an implementation decision at the receiver whether to
announce that SMS > 0 or not. Note however that if the
receiver chooses not to do this, then the sender MUST
assume that SMS = 0 (in other words it has to assume that
the receiver can't save state).

Regards,

Richard

> -----Original Message-----
> From: Lajos Zaccomer (ETH) [mailto:Lajos.Zaccomer@eth.ericsson.se]
> Sent: Friday, February 07, 2003 10:18 AM
> To: Price, Richard; 'zhigang.c.liu@nokia.com'; rohc@ietf.org
> Subject: RE: [rohc] SigComp state creation request, requested 
> feedback,
> a nd SMS = 0
> 
> 
> Hi,
> 
> This may help, but sending the returned parameters is not 
> mandatory, moreover not recommended!
> 
> BR/Zacco
> 
> -----Original Message-----
> From: Price, Richard [mailto:richard.price@roke.co.uk]
> Sent: Friday, February 07, 2003 10:59 AM
> To: 'zhigang.c.liu@nokia.com'; rohc@ietf.org
> Subject: RE: [rohc] SigComp state creation request, requested 
> feedback, a nd SMS = 0
> 
> 
> > Hi,
> > 
> > (This is not specified on RFC 3320, so I want to double check.)
> > 
> > If a message carries state creation request but the receiving 
> > endpoint has SMS = 0, I understand that the message can still be
> > accepted but the state creation request will be rejected.
> 
> Hi Zhigang,
> 
> That's right - state creation requests can be rejected due to lack
> of memory, even if the decompressed message is accepted.
> 
> > Now, what about the requested feedback carried in the message?
> > Will it be returned?
> 
> The requested feedback can still be returned even if SMS = 0.
> 
> > If yes, that means the sender must not rely on feedback to determine
> > if the state has been successfully created. Then, is the answer no?
> 
> The sender can still rely on the feedback to determine if the state
> has been successfully created, but only if it takes into account the
> returned SigComp parameters as well. In particular it needs to check
> that the receiver has advertised SMS > 0.
> 
> SigComp-Extended has the following to say on the subject:
> 
>    Note: There is a possibility that state(S) is discarded due to lack
>    of state memory even though the announcement information is
>    successfully forwarded.  This possibility must be taken into account
>    (otherwise a decompression failure may occur); this can be done by
>    using the SigComp parameter state_memory_size which is announced by
>    the SigComp feedback mechanism.  The endpoint can use this parameter
>    to infer if a state creation request has failed due to lack of
>    memory.
> 
> Hope this helps!
> 
> Regards,
> 
> Richard
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