Re: ROHCv2 Packet Formats

Hi Klaus,

Thanks for your response.
Please clarify my queries (inline in the below mail). 

Regards,
Anil Kumar Maguluri





Klaus Warnke <[email protected]> 
11/10/2009 07:43 PM

To
Anil Maguluri <[email protected]>
cc
<[email protected]>
Subject
Re: [rohc] 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.

[ANIL]
How to send IPv6 Extension Headers (Destination Option, Routing
header, Hop-by-Hop options) in ROHCv2? 
The above extension headers are classified in static and dynamic fields.
There is no irregular fields in those headers.
1. Do we need to consider static fields while selecting the flow? 
For example: In case of Destination option, next_header and length are 
static fields. If the length value changes means is that is new flow?
2. How to send (in which packet) if the dynamic field value changes?
For example: In case of Destination option, value is dynamic. If the 
value changes, on which packet do we need to send value information?

> 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

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