Re: ROHCv2 Packet Formats

Hi Anil,

comments inline...

At Tue, 10 Nov 2009 17:08:50 +0530,
Anil Maguluri wrote:
> 
> Hi All,
> 
> Please can anyone explain me how to compress IPv6 extension headers
> in ROHCv2?
> 
> Please clarify me whether my understanding is right or not. Also
> clarify me the below queries.
> 
> My understanding as per RFC 5225,
>
> 1. we have to consider the IPv6 extension header as a normal header
>    and use irregular chain to build in the compressed packet (Refer
>    6.6.1.  baseheader_extension_headers)
> 
> 2. should consider while selecting the CID. If the adding or
>    removing of the extension header considered as a new flow and
>    proceed.
>
> " RFC 5225: 4.2  Improvements of ROHCv2 over RFC 3095 Profiles
> IP extension header
> 
>       Profiles in RFC 3095 compress IP Extension headers using list
>       compression.  ROHCv2 profiles instead treat extension headers
>       in the same manner as other protocol headers, i.e., using the
>       chaining mechanism; it thus assumes that extension headers are
>       not added or removed during the lifetime of a context (CID),
>       otherwise compression has to be restarted for this flow.  "
> 
> Queries
>
> 1. In case of sending IPv6 extension header in IRREGULAR chain,
>    which format do we need to use to build?

With the ah_irregular and gre_irregular formats. Or did I
missunderstood something?  In the irregular format are data sent,
which can not be compressed otherwise. For gre, for example, it is
"optional_checksum", if present, and the (optional) sequence_number,
if present.

> 2. In case of change in the data field in extension header, do we
>    need to send complete extension header? if yes, on which format?

Yes, with an IR packet, because a new flow was detected.

If a field, which is STATIC/STATIC-DEF declared, contains data that
does not match of any defined contexts/flows, a new flow starts. That
is, you can not transmit changes of data in extension headers, because
a flow with different data in extension headers defines a different
flow. Excepted the as IRREGULAR/PATTERN defined fields in AH and GRE
extension headers. See A.8. for GRE and A.10. for AH. These field data
are sent in the irregualr chain.

> Thanks for your support.
> 
> Regards,
> Anil Kumar Maguluri

br
Klaus