RE: [rohc] Byte-alignment

[khiem.le@nokia.com]

Hi all,

I don't recall any discussion in Adelaide on byte alignment, even less a
consensus?

Anyway, I think the byte alignment should not be included in the
requirements.
The reason is it would create an unnecessary constraint. If we have such a
byte alignment requirement, we are restricting ourselves to producing
schemes which are byte aligned. Link technologies which do not need the byte
alignment will likely be penalized by that constraint in terms of efficiency
(as was said in Adelaide, 1 byte = some large amount of $).
If we do not have the byte alignment requirement, we have more freedom. If
we end up designing a non byte aligned scheme, it can always be made byte
aligned in a trivial manner by padding bits, if the link technology requires
byte alignment.
The converse is not true.

It was said that a byte aligned header would make processing easier, but
what matters is not whether the overall compressed header is byte aligned,
but whether the individual subfields of the header are byte aligned. What
the CPU processes are the subfields, not the complete header. I don't think
any compression scheme has the property that every subfield is byte aligned.

Khiem Le, PhD
Nokia Research Center

 
-----Original Message-----
From: EXT Mikael Degermark [mailto:micke@cs.arizona.edu]
Sent: Friday, April 07, 2000 4:09 PM
To: Lars-Erik Jonsson
Cc: rohc; Mikael Degermark; Carsten Bormann
Subject: Re: [rohc] Byte-alignment


I was planning to say that, yes. It seemed to be the consensus in Adelaide. 
Objections, anyone?

Micke

At 02:14 PM 4/7/00 +0200, Lars-Erik Jonsson wrote:
>Some days ago, I sent this question to the list. Since there have been no
>arguments against the opinions I raised in this issue, I would like to make
a
>request to put this into the requirements document. Even if it is obvious
to me
>that the scheme should be byte-aligned, I know that it is not clear to all
of
>those involved in this. Therefore the requirements document must state that
only
>byte-aligned solutions should be considered.
>
>Micke, will you include that in some way??
>
>BR
>/Lars-Erik
>
>
>
>
>
>>Hi all ROHC-ers!
>>
>>Discussion of technical issues on this list is of fundamental importance
to get
>>results in the WG. I will therefore start with a discussion about the
>>byte-alignment issue and I hope we can clear this out easily.
>>
>>The question is whether there is any reason to design a robust header
>>compression framework that can support non-byte-aligned versions of the
scheme.
>>I do not think so. All link-layers I have seen are byte-aligned and that
is
>also
>>preferrable from an implementation point of view.
>>
>>This question is important because the answer gives different approaches
to the
>>problem.
>>1) When designing a non-byte-aligned scheme, the objective is to make all
>fields
>>as small as possible on a bit-level.
>>2) For byte-aligned schemes the objective is instead to squeeze as much
>>information as possible into 1, 2 or several bytes. Then the smallest
possible
>>header size must always be used.
>>
>>We MUST always have versions of the scheme that are designed byte-aligned.
A
>>non-byte-aligned scheme may be instantiated to byte-alignment but will not
make
>>use of all bits in an optimal way.
>>
>>I think it is important to clarify that (and if) we are only considering
>>byte-aligned solutions. Some mechanisms for non-byte-aligned solutions
will not
>>be usable at all in a byte-aligned scheme and we could then ignore such
>>mechanisms when discussing solutions.
>>
>>Regards!
>>/Lars-Erik
>>
>>
>>--------------------------------------------------------------
>>Lars-Erik Jonsson, M.Sc. - Ericsson Research
>>AWARE - Advanced Wireless Algorithm Research at Erisoft
>>Box 920, S-971 28 Luleå, Sweden
>>E-mail: lars-erik.jonsson@ericsson.com
>>Phone: +46 920 20 21 07
>>Mobile: +46 70 554 82 71
>>Fax: +46 920 20 20 99
>>Home: +46 920 999 57
>>
>>
>>---
>>Mailing list for Robust Header Compression WG
>>Archive: http://www.cdt.luth.se/rohc/
> 
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