Re: IP-ID encoding

Hello carl,

Correct me if my understanding is wrong.

Does this means Compressor can send the negative values ( offset ( -10) =
ID( 20) - SN(30)) and W-LSB Decoder must reconstruct the value back.

I understand nowhere in RFC, they mention about negative offset value.

Thanks
Gurushant

-----Original Message-----
From: Carl Knutsson [mailto:[email protected]]
Sent: Monday, March 09, 2009 3:28 PM
To: [email protected]; Gurushant G Kotagi; rohc
Subject: Re: [rohc] IP-ID encoding


Gurushant,

A new IP-ID offset can be established in the decompressor context
either by using irregular encoding or W-LSB encoding. 16 bits irregular
encoding covers the whole space of possible IP-ID offset values. A 16
bit LSB (W-LSB encoded IP-ID offset) also covers the whole space of
possible IP-ID offset values. The decompressor will only fail if the
compressor sends to few lsb bits, ie if the "new" IP-ID offset is
outside the interpretation interval of the decompressor.

The details of the ip-id encoding can be found in RFC0395 section 4.5.5
for 0x0002 and in the formal notation part of RFC5225 for 0x0102.


Best Regards,

Carl Knutsson

On Fri, 6 Mar 2009, Biplab Sarkar wrote:

> Hi Gurushant,
>
> The linear property of both IP-ID and the generated SN is what is
> exploited during IP-ID encoding. Its encoded using Offset-IP-ID. As it
> is using a sliding window with p=0, it can send across both a positive
> or a negative offset.
>
> Thanks
> Biplab
>
> Gurushant wrote:
> > Hi all,
> > Could you please tell me How the IP-ID encoding work in case of profile
> > 0x0002 or 0x0102, where SN is generated inside the Compressor. And IP-ID
> > jumps sequentially in the input packet and SN generated is greater than
the
> > IP-ID value.
> >
> > In this case if offset for the current packet is less than previous
offset.
> > I believe Decompressor will not be successful.
> >
> > Thanks
> > Gurushant
> >
> >
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>


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